MicroRNA-34a: A Novel Therapeutic
Target in Fibrosis
, Qin Qi
, Shimin Liu
, Rong Huang
, Jiacheng Shen
, Yi Zhu
, Jing Chai
, Huangan Wu
* and Huirong Liu
Department of Acupuncture-Moxibustion, LongHua Hospital Shanghai University of Traditional Chinese Medicine, Shanghai
University of Traditional Chinese Medicine, Shanghai, China,
Key Laboratory of Acupuncture and Immunological Effects,
Shanghai University of Traditional Chinese Medicine, Shanghai, China,
Shanghai Research Institute of Acupuncture and
Meridian, Shanghai, China
Fibrosis can occur in many organs, and severe cases leading to organ failure and death. No
speciﬁc treatment for ﬁbrosis so far. In recent years, microRNA-34a (miR-34a) has been
found to play a role in ﬁbrotic diseases. MiR-34a is involved in the apoptosis, autophagy
and cellular senescence, also regulates TGF-β1/Smad signal pathway, and negatively
regulates the expression of multiple target genes to affect the deposition of extracellular
matrix and regulate the process of ﬁbrosis. Some studies have explored the efﬁcacy of
miR-34a-targeted therapies for ﬁbrotic diseases. Therefore, miR-34a has speciﬁc potential
for the treatment of ﬁbrosis. This article reviews the important roles of miR-34a in ﬁbrosis
and provides the possibility for miR-34a as a novel therapeutic target in ﬁbrosis.
Keywords: microRNA-34a, ﬁbrosis, apoptosis, autophagy, senescence, TGF-β1/Smad signal pathway, target genes
Fibrosis (FB) is an excessive repair reaction of the body to external injury, resulting in
structural damage and dysfunction of normal tissues and organs, which affects the patients’
physical and mental health and quality of life seriously (Jun and Lau, 2018;Henderson et al.,
2020). It is a high-burden diseases, and the annualized incidence of major ﬁbrosis-related
conditions is nearly 1/20 (Tsou et al., 2014;Zhao et al., 2020). At present, the treatment
methods are limited. In the early stage, drug therapy merely alleviate inﬂammation and
symptoms; in the late stage, only surgery or organ transplantation can be selected. However,
the cure rate is still low and the recurrence rate is high (Rieder et al., 2012;Villac Adde et al.,
2018;Ramos et al., 2019;Cai et al., 2020). Some researches has investigated a variety of
regulator (such as microRNA, TGF-β,interleukins,IFN-γ) for the treatment of FB, which only
acertainefﬁcacy (Ghosh et al., 2013;Richeldi et al., 2017;Gieseck et al., 2018;Weiskirchen
et al., 2019). As the signal transduction network of FB is complex, the current researches on
therapeutic targets is not sufﬁcient to support the clinical practice of FB. We need to further
clarify the speciﬁc function of various signal molecules in ﬁbrosis to guide the clinical therapy.
Recently, many studies have found that microRNA-34a (miR-34a) plays a role in a variety of
ﬁbrotic diseases by regulating cell proliferation, differentiation, apoptosis and other processes (Chen
and Hu, 2012;Alivernini et al., 2014;Zhou et al., 2017;Li et al., 2018)(Table 1). It has been found that
miR-34a can regulate the extracellular matrix (ECM) deposition by acting on the processes of
apoptosis, senescence and autophagy in epithelial/endothelial cells and ﬁbroblasts (Tian et al., 2016;
Cui et al., 2017a;Zhu et al., 2019), and also promote transforming growth factor-β1 (TGF-β1)-
induced ﬁbroblasts activation by targeting Smad4 (Huang et al., 2014;Qi et al., 2020); while the miR-
34a inhibitor can improve collagen deposition and attenuate ﬁbrosis by regulating cell apoptosis and
Université de Fribourg, Switzerland
Paul J. Higgins,
Albany Medical College, United States
Amr M. Abdelhamid,
October University for Modern
Sciences and Arts (MSA), Egypt
This article was submitted to
a section of the journal
Frontiers in Physiology
Received: 13 March 2022
Accepted: 30 May 2022
Published: 20 June 2022
Zhao M, Qi Q, Liu S, Huang R, Shen J,
Zhu Y, Chai J, Zheng H, Wu H and
Liu H (2022) MicroRNA-34a: A Novel
Therapeutic Target in Fibrosis.
Front. Physiol. 13:895242.
Frontiers in Physiology | www.frontiersin.org June 2022 | Volume 13 | Article 8952421
published: 20 June 2022
differentiation through Bcl-2, TGF-β1, and PPAR—γ(Zhou et al.,
2014;Li et al., 2015;Song et al., 2019).
According to current researches, miR-34a may be exploited as
a potential target for anti-ﬁbrosis therapy in the future. In this
paper, we review studies on the involvement of miR-34a in
ﬁbrotic diseases in order to reveal the possible mechanism of
miR-34a as a therapeutic target for FB.
Role of MicroRNA-34a in Various Molecular
Pathways of Fibrosis
MicroRNA are a class of small non-coding RNA containing about
18–22 nucleotides that regulate gene expression at the post-
transcriptional level through completely or partially
complementary base binding to their target mRNAs (Tang
et al., 2015). MiR-34a is a member of miRNA family, which is
widely expressed in mammals (Hermeking, 2010). It has been
found that miR-34a affects the occurrence and development of
ﬁbrotic diseases by regulating cell activities, including apoptosis,
autophagy, cellular senescence, the expression of related target
genes and TGF-β1/Smad signaling pathway (Figure 1).
Role of MicroRNA-34a in Apoptosis
Apoptosis is a process of programmed cell death in multicellular
organisms, which plays an important role in the development of
ﬁbrosis (Zhang et al., 2001;Docherty et al., 2006). After injury,
cell apoptosis induce the recruitment of immune cells with
ampliﬁcation of inﬂammatory response and proﬁbrogenic
factors, enhance ﬁbroblast proliferation, and then promotes
the regeneration of granulation tissue, which eventually leads
to the development of ﬁbrotic lesions (Uhal, 2002;Bhandary
et al., 2012;Jun and Lau, 2018). MiR-34a has been found to play
an important role in the process of ﬁbrosis by regulating
MiR-34a is the direct transcription target of p53, and can
negatively regulate sirtuin 1(SIRT1), resulting in increased p53
acetylation. P53 and SIRT1 are typical genes involved in apoptosis
regulation (Yamakuchi et al., 2008;Li et al., 2011), and p53 is a
major contributor to the onset and progression of ﬁbrotic diseases
(Yang et al., 2010;Sutton et al., 2013;Overstreet et al., 2014;
Valentijn et al., 2021;Fu et al., 2022;Li et al., 2022). Therefore, the
miR-34a SIRT1/p53 signaling pathway forms a positive feedback
loop that has a vital role in cell proliferation and apoptosis
(Tarasov et al., 2007;Kumamoto et al., 2008;Kim et al., 2015).
It was found that the expression level of miR-34a was positively
correlated with the severity of liver injury (Castro et al., 2013). In
liver tissue of rats with hepatic ﬁbrosis, it has been observed that
miR-34a and acetyl-p53 were up-regulated and SIRT1 was down-
regulated; nevertheless, SIRT1 activator signiﬁcantly reduced the
levels of miR-34a and acetyl-p53, and inhibited ﬁbrosis, which
suggested that miR-34a/SIRT1/p53 signaling pathway was
activated in ﬁbrosis; in vitro, it was further conﬁrmed that
miR-34a/SIRT1/p53 signaling pathway was activated in
epithelial cells to induce apoptosis, which activate hepatic
stellate cells (HSCs) and accelerate the process of liver ﬁbrosis
(Tian et al., 2016). In addition, in the lung tissues of patients and
mice with pulmonary ﬁbrosis, the apoptosis levels of alveolar
epithelial cells (AECs) were increased, the expression of acetyl-
p53, PAI-1, and miR-34a was increased, and the expression of
SIRT1 was decreased; however, the above process could be
reversed by knockout of the miR-34a gene (Shetty et al.,
2017). It can be seen that miR-34a/SIRT1/p53 is also involved
in the apoptosis of pulmonary epithelial cells and the induction of
Bcl-2 is an important antiapoptosis gene and one of the target
genes of miR-34a. MiR-34a can promote apoptosis by inhibiting
bcl-2 expression (Bommer et al., 2007). Tubular epithelial cells
apoptosis is one of the mechanisms of tubular atrophy and
TABLE 1 | MiR-34a acts on various organ ﬁbrosis.
Tissue Species Target Mechanism References
Liver Rat, hepatocyte, mice, intrahepatic biliary epithelial cells,
SIRT1, p53; caspase2 apoptosis Tian et al. (2016),Meng et al. (2012)
target genes Yan et al. (2015);Yan. (2016),Oda et al. (2014);Li
et al. (2015)
Smad4, Smad3 TGF-β1/Smad
Feili et al. (2018),Song et al. (2019)
Cellular senescence Wan et al. (2017)
Kidney Mice, rat, renal tubular epithelial cells, renal interstitial
Bcl-2 apoptosis Zhou et al. (2014);Li et al. (2019)
Klotho; Notch1 target genes Liu et al. (2019),Du et al. (2012)
SIRT1 autophagy Xue et al. (2018),Zhu et al. (2019)
Heart Rat, myocardial ﬁbroblasts, mice C-Ski; PNUTS target genes Zhang et al. (2018),Boon et al. (2013)
Huang et al. (2014)
PI3K/AKT autophagy Liu et al. (2018)
Lung Human, mice, type II alveolar epithelial cells SIRT1, p53 apoptosis Shetty et al. (2017)
nectin-1、Abca3 target genes Takano et al. (2017)
Celluar senescence Disayabutr et al. (2016);Cui et al. (2017b)
Skin mice c-Met target genes Simone et al. (2014)
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Zhao et al. MicroRNA-34a: Therapeutic Target in Fibrosis
tubulointerstitial ﬁbrosis (Docherty et al., 2006). In the study of
rats and mice with renal interstitial ﬁbrosis, miR-34a was released
from mesenchymal ﬁbroblasts and transferred to proximal
tubular epithelial cells, where it promoted apoptosis of renal
tubular epithelial cells by inhibiting the transcription and
translation of Bcl-2, further aggravating renal interstitial
ﬁbrosis (Zhou et al., 2014;Li et al., 2019).
Furthermore, caspase-2 is also the target gene of miR-34a,
which helps to enhance apoptosis and plays a role in cell
remodeling and tissue repair (Madesh et al., 2009). In the
study of alcoholic liver disease, miR-34a was found to regulate
apoptosis of hepatocytes and intrahepatic biliary epithelial cells
by targeting caspase 2, affecting cell survival and migration, and
regulating the release of matrix metalloproteinases (MMPs).
Therefore, miR-34a plays a role in the repair of liver injury
and liver ﬁbrosis (Meng et al., 2012). The above results
indicate that miR-34a participates in organ ﬁbrosis by
regulating apoptosis-related signal molecules.
Role of MicroRNA-34a in Autophagy
Autophagy is a conserved lysosomal degradation process in
eukaryotic cells that plays an important role in maintaining
homeostasis in cells and tissues. Autophagy disorders
participate in the development of organ ﬁbrosis. It has
been conﬁrmed that autophagy promote the clearance of
damaged proteins and organelles, and accelerate the
degradation of extracellular matrix proteins (Ding and
Choi, 2014;Lv et al., 2017;Jesus et al., 2019); in addition,
intracellular autophagy ﬂux can increases the energy needed
for extracellular matrix protein formation (Kota et al., 2017).
Some studies have found that autophagy mediates ﬁbrotic
diseases regulated by miR-34a.
A study of epidural scar hyperplasia after laminectomy has
found that the expression of miR-34a and autophagy-related
molecules (beclin-1, ATG5, LC3B-2/1, p53) were changed,
which suggests that the disorder of miR-34a and autophagy
level may be involved in the formation of ﬁbrosis (Wang B. B.
et al., 2017). The PI3K/Akt signaling pathway is a classical
autophagy regulatory pathway involved in the regulation of
cell proliferation, migration and differentiation (Zundler et al.,
2016;Aoki and Fujishita, 2017;Shi et al., 2017). This signaling
pathway is concerned in the study of myocardial ﬁbrosis. In the
rat model of myocardial ﬁbrosis induced by thyroid hormone,
miR-34a expression and PI3K and Akt proteins were found to be
upregulated, while autophagy related proteins (ATG5, Atg7,
Atg16L1, Beclin1, LC3A) were signiﬁcantly downregulated,
and MMPs/TIMPs ratios appeared imbalance. This study
suggested that myocardial ﬁbrosis might be related to miR-
34a-mediated regulation of the PI3K/Akt signaling pathway
and inhibition of autophagy (Liu et al., 2018).
In addition, miR-34a indirectly interferes with the extension of
autolysosomes by inhibiting SIRT1(Yang et al., 2013). SIRT1 is
not only a molecule involved in autophagy activation, but also an
important component of the EMT, which plays an important role
in the process of organ ﬁbrosis (Salminen and Kaarniranta, 2009;
Simic et al., 2013). It has been found that miR-34a-5p is up-
regulated accompanied by the corresponding down-regulation of
SIRT1 in the renal tissue of mice with diabetic nephropathy. MiR-
34a-5p was positively correlated with the expression of
ﬁbronectin (FN), type I collagen (COL 1), and TGF-β1; then
the cell experiments further identiﬁed that miR-34a-5p directly
suppressed SIRT1 to increase the proﬁbrogenic effects of TGF-β1
by targeting the 3′-UTR of SIRT1; it has also been found that
miR-34a-5p inhibitor increases the expression of SIRT1 and
FIGURE 1 | Schematic diagram of miR-34a involved in ﬁbrosis process. MiR-34a is involved in the apoptosis, autophagy and senescence, regulates TGF-β1/Smad
signal pathway, and negatively regulates the expression of multiple target genes to affect the process of organ ﬁbrosis.
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Zhao et al. MicroRNA-34a: Therapeutic Target in Fibrosis
decreases the level of TGF-β1, FN, and COL 1, then a small
interfering RNA (siRNA) targeting SIRT1 enhanced the
expression of TGF-β1 and FB-related genes, indicating that
miR-34a-5p could promote renal ﬁbrosis by inhibiting SIRT1
(Xue et al., 2018). In diabetic cardiomyopathy, miR-34a was also
found to aggravate myocardial injury related to inhibition of
SIRT1 transcription (Zhu et al., 2019). According to the current
research, we found that miR-34a is involved in the ﬁbrosis process
by inhibiting autophagy-related molecules. Unfortunately, there
is insufﬁcient evidence to explore the role of miR-34a in ﬁbrosis
by regulating autophagy at present, further research is needed to
ﬁll in this theory in the future.
Role of MicroRNA-34a in Cellular
Cellular senescence is a process in which cells undergo irreversible
cell cycle arrest and is considered to play a key role in damage repair.
Fibroblast senescence is one of the important factors of ﬁbrosis
pathology (Waters et al., 2018). It has been found that ﬁbroblasts
derived from ﬁbrotic tissue have a variety of senescence-related
characteristics. Myoﬁbroblasts senescence stop synthesizing collagen
and other ECM proteins, and secrete ECM protein-degrading
enzymes to improve matrix deposition and limit the
accumulation of ﬁbrotic tissue (Harding et al., 2005;
Krizhanovsky et al., 2008;Jun and Lau, 2010;Álvarez et al.,
2017). Besides, epithelial cells senescence indirectly promotes the
differentiation of ﬁbroblasts into myoﬁbroblasts, resulting in the
excessive deposition of collage (Lehmann et al., 2017).
As a downstream transcription target of p53, a cell cycle regulator,
miR-34a is closely related to cell senescence (Kyle et al., 2009;Harries,
2014). It has been proved that miR-34a can regulate cell cycle and
senescence by targeting multiple genes, such as SIRT1, cyclin E2,
cyclin D1, and E2F3 (Cui et al., 2017a). AECs are the main senescent
cells of pulmonary ﬁbrosis. In the lung tissues and puriﬁed AECs of
patients with idiopathic pulmonary FB (IPF), the relative levels of
miR-34a, miR-34b and miR-34c were signiﬁcantly increased, the
activity of p16, p21, p53, and SA-β-gal was increased, and the
expression of miR-34 targets (E2F1, c-myc, and CCNE2) was
downregulated, these changes stimulated the senescence of AECs,
promoted myoﬁbroblast transdifferentiation and induced IPF
(Disayabutr et al., 2016;Cui et al., 2017b). In the study of hepatic
ﬁbrosis, the same results were obtained. MiR-34a was up-regulated in
the patients with hepatic ﬁbrosis, which promoting the senescence of
hepatocytes and inducing hepatic ﬁbrosis by reducing the senescence
of HSCs; however, miR-34a inhibitor (morpholino) obstructed this
process and improved hepatic ﬁbrosis, which indicating that miR-34a
plays a role in promoting hepatocytes senescence and reducing HSCs
senescence (Wan et al., 2017). Not only can miR-34a regulates
epithelial cell senescence and induce ﬁbroblast to differentiate into
myoﬁbroblast, but also inhibits ﬁbroblast senescence, promotes
ﬁbroblast proliferation, and aggravates the ﬁbrosis process.
Therefore, cell senescence plays an important role in the process of
miR-34a participating in ﬁbrosis.
Regulation MicroRNA-34a on Typical
MiRNA-34a regulates growth, differentiation and metabolism by
negatively regulating typical target genes. Previous studies have
revealed that miR-34a can combined with multiple target genes to
regulate ﬁbrosis in many ways.
ACSL1 is a member of Acyl-CoA synthetase long-chain
(ACSL) family. ACSL1 is an important gene in liver lipid
metabolism. The luciferase reporter assay conﬁrmed that
ACSL1 was the target gene of miR-34a (Li et al., 2011). In the
research of hepatic ﬁbrosis, miR-34a speciﬁcally bound to the 3′-
UTR of ACSL1, which negatively regulated the expression of
ACSL1 mRNA and protein, promoted the activation and
proliferation of HSCs, and lead to upregulation of ECM-
related indicators (COL 1, a-SMA); in contrast, silencing of
the miR-34a gene increased the expression of ACSL1,
decreased the expression of ECM-related proteins, and affected
HSCs activation (Yan et al., 2015;Yan, 2016). Thus, ACSL1 is one
of the factors by which miR-34a promotes hepatic ﬁbrosis.
Protooncogene c-ski, a transcriptional corepressor, is a
negative regulator of TGF-β/Smad signaling (Cunnington
et al., 2009), and can inhibit TGF-β1-induced activation of
cardiac ﬁbroblasts and ECM deposition (Wang J. et al., 2017).
In vitro and in vivo studies on myocardial ﬁbrosis in rats, it was
found that miR-34a could target and inhibit the expression of
c-ski, and the levels of collagen I and a—SMA were signiﬁcantly
increased; Inhibition of miR-34a signiﬁcantly increased the
expression of c-ski protein and decreased the levels of COL
one and a-SMA protein (Zhang et al., 2018). It can be seen
c-ski mediates miR-34a to promote the proliferation and ECM
deposition of TGF-β1-induced primary cultured rat cardiac
ﬁbroblasts, which contribute to myocardial ﬁbrosis.
Klotho, a speciﬁc antiaging protein of kidney, is mainly
expressed in renal tubular epithelial cells and has a signiﬁcant
anti-ﬁbrosis effect (Guan et al., 2014;Ding et al., 2019). The
luciferase reporter assay showed that miR-34a directly down-
regulated the expression of Klotho. In renal ﬁbrosis, the increased
expression of miR-34a is accompanied by the sharp
downregulation of Klotho, the increase of a—SMA and
ﬁbronectin, and the decrease of E-cadherin, which promote
the process of epithelial mesenchymal transformation (EMT);
however, the expression of Klotho was signiﬁcantly increased and
EMT was inhibited in miR-34a−/−mice, so miR-34a negatively
regulates Klotho to promote EMT and induce renal ﬁbrosis (Liu
et al., 2019).
In addition, there were other miR-34a target genes, including
PPAR-γ, PNUTS, RXRa, Notch1, c-Met, nectin-1, and Abca3,
have been found to affect the ﬁbrosis process by regulating cell
proliferation, the EMT process and collagen synthesis (Du et al.,
2012;Boon et al., 2013;Oda et al., 2014;Simone et al., 2014;Li
et al., 2015;Takano et al., 2017). In various organ ﬁbrosis, miR-
34a affects the process of ﬁbrosis by targeting different protein-
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Zhao et al. MicroRNA-34a: Therapeutic Target in Fibrosis
Role of MicroRNA-34a in Transforming
Growth Factor-β1/Smad Signaling Pathway
Transforming growth factor-β1 (TGF-β1) is a key cytokine
involved in the formation of ﬁbrosis (Ghosh et al., 2013) that
not only plays an important role in the transdifferentiation of
ﬁbroblasts into myoﬁbroblasts but also triggers the EMT,
mesothelial-to-mesenchymal transition (MMT) and
endothelial-to-mesenchymal-transition (EndoMT) processes,
controls the extracellular matrix (ECM) synthesis, and
participates in the pathogenesis of ﬁbrosis (Wu et al., 2013;
Weiskirchen et al., 2019). There is a certain correlation
between miR-34a disorders and TGF-βpathway in ﬁbrotic
diseases (Xie et al., 2011;Zhang et al., 2014;Zhang J. et al., 2021).
Firstly, Bin Zhou found that eight miRNAs and seven mRNA
were involved in TGF-βsignal pathway, including miR-34a, in
systemic sclerosis (SSc) by Gene Expression Omnibus (GEO)
analysis (Zhou et al., 2017), this was a direct evidence that miR-
34a targets ﬁbrosis through TGF-βsignaling pathway. Smad
transcription factors are the core of TGF-βpathway
(Massague et al., 2005). TGF-β1/Smad signaling pathway has
been widely recognized as a typical pathway in ﬁbrosis (Zhang
et al., 2019;Lv et al., 2020). The expression of miR-34a was
increased in mice with cardiac ﬁbrosis, and the degree of ﬁbrosis
was inhibited by miR-34a antagonist; miR-34a directly targets
Smad4 mRNA according to luciferase reporter assay; when the
ﬁbroblasts are transfected with Smad4 siRNA, the expression of
type I collagen, TGF-β1 and a-SMA was suppressed. The study
indicated that TGF-β1 induces the expression of miR-34a, which
in turn promotes the activation of TGF-β1-induced myocardial
ﬁbroblasts and the formation of cardiac ﬁbrosis by targeting
Smad4 (Huang et al., 2014). In carbon tetrachloride (CCl4)-
induced hepatic ﬁbrosis mice, miR-34a imbalance was also found
to promote liver ﬁbrosis via targeting Smad4 and activation TGF-
β1/Smad3 pathway (Feili et al., 2018).
Besides, miR-34a/SIRT1/p53 loop is also involved in the EMT
mediated by TGF-β1/Smad signaling pathway. Activated p53 (ac-
p53 and p-p53) combines with Smad3 to form a multiprotein
complex to promote TGF-β1-induced EMT process (Piccolo,
2008;Termén et al., 2013). In rat model of hepatic ﬁbrosis, it
was found that miR-34a was overexpressed, SIRT1 was down-
regulated, p53 and ac-p53 were increased, with activated TGF-β1/
Smad signal pathway; miR-34a inhibitor and p53 siRNA
signiﬁcantly prevented TGF-β1-induced EMT in hepatocytes,
and alleviated the degree of hepatic ﬁbrosis (Song et al., 2019).
Therefore, these results suggest that TGF-β1/Smad signaling
pathway mediates the process of miR-34a-induced ﬁbrosis.
MIRNA-34A AS THERAPEUTIC TARGETS
As described, miR-34a is a key regulator of FB-related molecules.
In recent years, miR-34a or miR-34a-targeted gene have been
used as new intervention targets in the treatment of FB, which
have better effectiveness. Therefore, the regulation of miR-34a
and related molecules are expected to be new therapeutic targets
for FB (Table 2).
In most studies, miR-34a inhibitors were used to improve the
degree of ﬁbrosis. At the cellular level, miR-34a inhibitor was
transfected into renal tubular cells incubated with TGF-β1to
induce the upregulation of Bcl-2, inhibit the apoptosis of
renal tubular cells and improve the degree of renal ﬁbrosis
(Zhou et al., 2014). Transfection of miR-34a silencing vector
using Lipofectamine2000 into activated HSCs increased the
expression of ACSL1 and promoted lipogenesis, thereby
inhibiting HSCs activation and hepatic ﬁbrosis (Yan et al.,
2015). MiR-34a inhibitor was also found to increase PPAR γ,
decrease a-SMA, and improve the process of liver ﬁbrosis (Li
et al., 2015). Transfection of miR-34a inhibitor in primary
hepatocytes increased SIRT1 and p65/p53 deacetylation
levels, decreased the expression of proinﬂammatory
cytokines and improved liver inﬂammatory response (Kim
et al., 2015). MiR-34a inhibitor could reduce the EMT process
and ﬁbrosis activity of human intrahepatic biliary epithelial
cells, and improved liver ﬁbrosis (Pan et al., 2021). In cardiac
ﬁbroblasts, a miR-34a antagonist improved cardiac ﬁbrosis
by inhibiting TGF-β1 signaling (Huang et al., 2014). In vivo
study, Subcutaneous injection of locked nucleic acid (LNA)-
antimiR-34a (initial dose 25 mg/kg, maintenance dose
10 mg/kg every other day, 3 times a week for 6 weeks) can
improved the cardiac function of female mice with dilated
cardiomyopathy, characterized by attenuated heart
enlargement and lung congestion, inhibit the expression of
cardiac stress genes, and alleviate myocardial ﬁbrosis
(Bernardo et al., 2016). Besides, miR-34a inhibitors can
improve myocardial ﬁbrosis and reduce scar area in
myocardial infarction rats (ZhangF.etal.,2021). In the
mice of CCl4-induced liver ﬁbrosis, miR-34a siRNA
signiﬁcantly reduced the express of TGF-β,a-SMA, and
MCP-1, further inhibited the ﬁbrosis of HSCs (Zhang
J. et al., 2021). It has also been found that ablation of miR-
34a protected aged animals from developing experimental
lung ﬁbrosis (Cui et al., 2017b).
In addition, there are some compounds acting on miR-34a to
intervene in FB. Hydrogen sulﬁde and astragaloside IV(AS-IV)
were found to reverse myocardial ﬁbrosis, which may be related
to the down-regulation of miR-34a to activate autophagy (Liu
et al., 2018;Zhu et al., 2019). Prunella vulgaris aqueous extract
(PVAE) can downregulate miR-34a level, inhibit the activation of
HSCs, and regulate the expression of TIMP-1, MMP-2, and
MMP-13, promoting the degradation of collagen, and
alleviating hepatic ﬁbrosis (Hu et al., 2016); Paclitaxel has
been applied to treat ﬁbrosis by downregulating miR-34a,
upregulating SIRT1, and inhibiting p53 activation and TGF-
β1/Smads signal pathway (Song et al., 2019). Atorvastatin also
inhibited miR-34a and upregulated SIRT1 to improve myocardial
ﬁbrosis (Tabuchi et al., 2012). Therefore, the above study shows
that the downregulation of miR-34a has therapeutic effect on FB.
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Zhao et al. MicroRNA-34a: Therapeutic Target in Fibrosis
The Biological Agents of
The target gene of miR-34a has been used as the therapeutic
target for ﬁbrosis in some researches. SRT1720, the
SIRT1activator, inhibited hepatocyte apoptosis and improved
liver ﬁbrosis by reducing the expression of miR-34a and the
acylation of p53 (Tian et al., 2016). Resveratrol, another SIRT1
activator, was often used as an inhibitor in ﬁbrosis researches
(Chávez et al., 2008;Hong et al., 2010;Li et al., 2010). P53
inhibitor, piﬁthrin—a(PFT), decreased the level of miR-34a and
played a protective role in hepatic ischemia/reperfusion mice
(Kim et al., 2015). In addition, PPAR γactivators blocked the
activation of HSCs in hepatic ﬁbrosis (Attia et al., 2013;Sharvit
et al., 2013). Smad4 siRNA downregulated the mRNA and
protein expression of Col I, a-SMA, and TGF-β1, and
inhibited myocardial ﬁbrosis (Huang et al., 2014). Jagged1
siRNA and Notch 1 siRNAs effectively inhibited EMT in renal
tubular epithelial cells (Du et al., 2012). LGR4 is the direct target
of miR-34a, LGR4 siRNA signiﬁcantly inhibited the proliferation
and migration of retinal pigmented epithelial cell line ARPE-19
(Hou et al., 2016). As a novel direct miR-34a target, PNUTS
improved the functional recovery after acute myocardial
infarction by reducing telomere shortening, DNA damage
response and cardiomyocyte apoptosis (Boon et al., 2013).
These results suggest that miR-34a-related molecules also plays
an important role in the treatment of FB, which may provide
guiding signiﬁcance for clinical research.
LIMITATION OF MICRORNA-34A AS
THERAPEUTIC TARGETS OF FIBROSIS
Currently there are no FDA-approved miRNAs, but many
miRNA therapies have achieved substantial preclinical efﬁcacy,
even entered in clinical trials (Wang et al., 2021;Smith et al., 2022;
Zogg et al., 2022). For example, miravirsen (miR-122 inhibitor)
has completed Phase II clinical trials for the treatment of
Hepatitis C (Janssen et al., 2013;Panigrahi et al., 2022). The
Phase I clinical trials of MRG-110 (miR-92a inhibitor) to improve
wound healing has been completed (Gallant-Behm et al., 2018;
Abplanalp et al., 2020). A Phase I/IIa clinical trial has
demonstrated the potential of RG-125 (AZD4076) (miR-103/
107 inhibitor) for the treatment of type 2 diabetes and non-
alcoholic fatty liver disease (Rottiers and Naar, 2012). A Phase 1b
clinical trial of RGLS4326 (miR-17 inhibitor) in patients with
autosomal dominant polycystic kidney disease is under way (Kim
and Park, 2016). A Phase I clinical trials have shown that
CDR132L inhibits miR-132 in patients with heart failure (Ucar
et al., 2012). Moreover, TargomiRs, a miR-16 mimic, has been
considered as a second- or third-line treatment for recurrent
malignant pleural mesothelioma and non-small cell lung cancer
(van Zandwijk et al., 2017). Therefore, the therapeutic potential of
miRNAs is limitless.
Based on the existing research, miR-34a plays a complex and
important role in ﬁbrotic diseases. It will be a new target for the
treatment of FB, but there are still many practical problems for
miR-34a as a therapeutic target. At present, the anti-ﬁbrosis effect
of miR-34a and its target molecules have been explored mainly at
the cellular level in vitro, perhaps because of the functional
complexity of miR-34a and the non-target effect in vivo. There
are still some problems in the preparation of miR-34a inhibitors.
Although liposome transfection has been used in some
experiments, it has the disadvantage of immunogenicity
(Simone et al., 2014;Yan et al., 2015). Viral delivery enables
long-term, persistent, and high expression of miRNAs, but it also
has the disadvantage of nonspeciﬁc binding, so it cannot
transport miRNAs to the designated site. Microvesicles, a new
cell signaling vector for short- or long-range delivery, contains
TABLE 2 | the biological agents of miR-34a and related molecules for ﬁbrosis.
Type Biologics Target Tissue/Cell References
miR-34a inhibitor MiR-34a inhibitor miR-34a renal tubular epithelial cells, intrahepatic biliary
epithelial cells, HSCs, hepatocyte, Cardiac
ﬁbroblasts, heart, liver, lung
Zhou et al. (2014),Yan et al. (2015),Li et al. (2015),
Kim et al. (2015),Huang et al. (2014),Bernardo
et al. (2016),Pan et al. (2021),Zhang et al. (2021a),
Zhang et al. (2021b),Cui et al. (2017b)
Hydrogen sulﬁde (H
S) heart Liu et al. (2018)
Astragaloside-IV(AS-IVA) cardiomyocytes Zhu et al. (2019)
Aqueous extract from
Prunella Vulgaris (PVAE)
HSCs Hu et al. (2016)
Pterostilbene hepatocyte Song et al. (2019)
Atorvastatin endothelial cell Tabuchi et al. (2012)
Preparation of miR-
SRT1720 SIRT1 hepatocyte Tian et al. (2016)
Resveratrol SIRT1 liver, kidney Chávez et al. (2008);Hong et al. (2010);Li et al.
piﬁthrin -αp53 hepatocyte Kim et al. (2015)
PPARγagonist PPARγHSCs Attia et al. (2013);Sharvit et al. (2013)
Smad4 siRNA Smad4 cardiac ﬁbroblast Huang et al. (2014)
Jagged1 siRNAs Jagged1 renal tubular epithelial cells Du et al. (2012)
Notch1siRNAs Notch1 renal tubular epithelial cells Du et al. (2012)
LGR4 siRNA LGR4 retinal pigment epithelial cells Hou et al. (2016)
PNUTS PNUTS heart Boon et al. (2013)
Frontiers in Physiology | www.frontiersin.org June 2022 | Volume 13 | Article 8952426
Zhao et al. MicroRNA-34a: Therapeutic Target in Fibrosis
protein, mRNA and miRNA (Martins et al., 2013;Recep et al.,
2017). In a study of renal ﬁbrosis, it has been found that (Zhou
et al., 2014;Li et al., 2019) renal interstitial ﬁbroblasts can secrete
microvesicles containing miR-34a to transport to renal tubular
epithelial cells and promote their apoptosis; then the
microbubbles in ﬁbroblasts can be extracted and injected into
cells or mice to imitate the mechanism of miR-34a in renal
ﬁbrosis. With the development of science and technology, other
better biological agents will likely be found in the future, further
improving the treatment of FB.
In summary, although there have been many studies on the
pathogenesis of ﬁbrosis, there are still many deﬁciencies in the
treatment of ﬁbrosis. Various types of ﬁbrosis, such as pulmonary
ﬁbrosis, cardiac ﬁbrosis, liver ﬁbrosis, renal ﬁbrosis, etc., involve
the same or different internal signal network. Therefore, it is very
difﬁcult to ﬁnd the common target of ﬁbrosis. Although there
were two drugs (pirfenidone and nintedanib) have been approved
for the treatment of idiopathic pulmonary ﬁbrosis, they can only
improve lung capacity and survival rate, and do not show
beneﬁcial histological changes in pulmonary ﬁbrosis (Martinez
et al., 2017). Therefore, it is urgent to develop new anti-ﬁbrosis
therapy for other ﬁbrotic diseases. MiR-34a can regulate the
expression of many genes and proteins, and participate in
complex signal mechanism. Compared with traditional
cytokines and signal molecules, miR-34a is more suitable as a
common target for the regulation of organ FB. MiR-34a is a key
regulator of ﬁbrosis, which is involved in the regulation of
apoptosis, senescence, autophagy, and TGF-β1 signaling
pathway in epithelial cells and ﬁbroblasts to affect the
excessive repair; moreover, target genes of miR-34a also
regulate the process of ﬁbrosis in many ways; the application
of miR-34a inhibitor has also been found to signiﬁcantly improve
the degree of ﬁbrosis. So miR-34a is expected to become a new
target for the treatment of ﬁbrosis. However, those vivo or clinical
studies on the treatment of ﬁbrosis with miR-34a are still little and
incomplete, so the speciﬁc mechanism and efﬁcacy need to be
MZ wrote the manuscript. QQ, SL, and RH collect related
literature; JS, YZ, JC, and HZ revised the manuscript; HW and
HL contributed to conception and design of the article. All the
authors reviewed the manuscript and agreed for submission.
This study supported by the National Natural Sciences
Foundation of China (81873374); the Science and Technology
Commission of Shanghai (21ZR1460000); Shanghai Sailing
Program (20YF1445400), and Shanghai Clinical Research
Center for Acupuncture and Moxibustion (No. 20MC1920500).
Abplanalp, W. T., Fischer, A., John, D., Zeiher, A. M., Gosgnach, W., and Darville,
H. (2020). Efﬁciency and Target Derepression of Anti-miR-92a: Results of a
First in Human Study. Nucleic Acid. Ther. 30(6), 335–345. doi:10.1089/nat.
Alivernini, S., Bosello, S. L., Luca, G. D., Canestri, S., Mario, C. D., Gigante, M. R.,
et al. (2014). A3.21 MicroRNA-34a and microRNA-155 in Systemic Sclerosis:
Possible Epigenetic Biomarkers of Endothelial Dysfunction in VEDOSS and
Long-Standing Disease. 73 (Suppl. 1),A50. doi:10.1136/annrheumdis-2013-
Álvarez, D., Cárdenes, N., Sellarés, J., Bueno, M., Corey, C., Hanumanthu, V. S.,
et al. (2017). IPF Lung Fibroblasts Have a Senescent Phenotype. Am.
J. physiology. Lung Cell. Mol. physiology 313 (6), L1164–L1173. doi:10.1152/
Aoki, M., and Fujishita, T. (2017). Oncogenic Roles of the PI3K/AKT/mTOR Axis.
Curr. Top. Microbiol. Immunol. 407, 153–189. doi:10.1007/82_2017_6
Attia, Y. M., Elalkamy, E. F., Hammam, O. A., Mahmoud, S. S., and El-Khatib, A. S.
(2013). Telmisartan, an AT1 Receptor Blocker and a PPAR Gamma Activator,
Alleviates Liver Fibrosis Induced Experimentally by Schistosoma Mansoni
Infection. Parasites vectors 6, 199. doi:10.1186/1756-3305-6-199
Bernardo, B. C., Ooi, J. Y. Y., Matsumoto, A., Tham, Y. K., Singla, S., Kiriazis, H.,
et al. (2016). Sex Differences in Response to miRNA-34a Therapy in Mouse
Models of Cardiac Disease: Identiﬁcation of Sex-, Disease- and Treatment-
Regulated miRNAs. J. physiology 594 (20), 5959–5974. doi:10.1113/JP272512
Bhandary, Y. P., Shetty, S. K., Marudamuthu, A. S., Gyetko, M. R., Idell, S.,
Gharaee-Kermani, M., et al. (2012). Regulation of Alveolar Epithelial Cell
Apoptosis and Pulmonary Fibrosis by Coordinate Expression of Components
of the Fibrinolytic System. Am. J. physiology. Lung Cell. Mol. physiology 302 (5),
Bommer, G. T., Gerin, I., Feng, Y., Kaczorowski, A. J., Kuick, R., Love, R. E., et al.
(2007). p53-mediated Activation of miRNA34 Candidate Tumor-Suppressor
Genes. Curr. Biol. 17 (15), 1298–1307. doi:10.1016/j.cub.2007.06.068
Boon, R. A., Iekushi, K., Lechner, S., Seeger, T., Fischer, A., Heydt, S., et al. (2013).
MicroRNA-34a Regulates Cardiac Ageing and Function. Nature 495 (7439),
Cai, X., Wang, J., Wang, J., Zhou, Q., Yang, B., He, Q., et al. (2020). Intercellular
Crosstalk of Hepatic Stellate Cells in Liver Fibrosis: New Insights into Therapy.
Pharmacol. Res. 155, 104720. doi:10.1016/j.phrs.2020.104720
Castro, R. E., Ferreira, D. M., Afonso, M. B., Borralho, P. M., Machado, M. V.,
Cortez-Pinto, H., et al. (2013). miR-34a/SIRT1/p53 Is Suppressed by
Ursodeoxycholic Acid in the Rat Liver and Activated by Disease Severity in
Human Non-alcoholic Fatty Liver Disease. J. Hepatol. 58 (1), 119–125. doi:10.
Chávez, E., Reyes-Gordillo, K., Segovia, J., Shibayama, M., Tsutsumi, V., Vergara,
P., et al. (2008). Resveratrol Prevents Fibrosis, NF-kappaB Activation and TGF-
Beta Increases Induced by Chronic CCl4 Treatment in Rats. J. Appl. Toxicol.
JAT 28 (1), 35–43. doi:10.1002/jat.1249
Chen, F., and Hu, S. (2012). Effect of microRNA-34a in Cell Cycle, Differentiation,
and Apoptosis: a Review. J. Biochem. Mol. Toxicol. 26 (2), 79–86. doi:10.1002/
miR-34a Inhibits Lung Fibrosis by Inducing Lung Fibroblast Senescence.
Am. J. Respir. Cell Mol. Biol. 56 (2), 168–178. doi:10.1165/rcmb.2016-
Cui, H., Ge, J., Xie, N., Banerjee, S., Zhou, Y., Liu, R.-M., et al. (2017b). miR-34a
Promotes Fibrosis in Aged Lungs by Inducing Alveolarepithelial Dysfunctions.
Am. J. physiology. Lung Cell. Mol. physiology 312 (3), L415–L424. doi:10.1152/
Cunnington, R. H., Nazari, M., and Dixon, I. M. C. (2009). c-Ski, Smurf2, and
Arkadia as Regulators of TGF-Beta Signaling: New Targets for Managing
Frontiers in Physiology | www.frontiersin.org June 2022 | Volume 13 | Article 8952427
Zhao et al. MicroRNA-34a: Therapeutic Target in Fibrosis
Myoﬁbroblast Function and Cardiac Fibrosis. Can. J. physiology Pharmacol. 87
(10), 764–772. doi:10.1139/Y09-076
Ding, J., Tang, Q., Luo, B., Zhang, L., Lin, L., Han, L., et al. (2019). Klotho Inhibits
Angiotensin II-Induced Cardiac Hypertrophy, Fibrosis, and Dysfunction in
Mice through Suppression of Transforming Growth Factor-Beta1 Signaling
Pathway. Eur. J. Pharmacol. 859, 172549. doi:10.1016/j.ejphar.2019.172549
Ding, Y., and Choi, M. E. (2014). Regulation of Autophagy by TGF-β: Emerging
Role in Kidney Fibrosis. Seminars Nephrol. 34 (1), 62–71. doi:10.1016/j.
Disayabutr, S., Kim, E. K., Cha, S.-I., Green, G., Naikawadi, R. P., Jones, K. D., et al.
(2016). miR-34 miRNAs Regulate Cellular Senescence in Type II Alveolar
Epithelial Cells of Patients with Idiopathic Pulmonary Fibrosis. PloS one 11 (6),
Docherty, N. G., O’Sullivan, O. E., Healy, D. A., Fitzpatrick, J. M., and Watson, R.
W. G. (2006). Evidence that Inhibition of Tubular Cell Apoptosis Protects
against Renal Damage and Development of Fibrosis Following Ureteric
Obstruction. Am. J. physiology. Ren. physiology 290 (1), F4–F13. doi:10.
Du, R., Sun, W., Xia, L., Zhao, A., Yu, Y., Zhao, L., et al. (2012). Hypoxia-induced
Down-Regulation of microRNA-34a Promotes EMT by Targeting the Notch
Signaling Pathway in Tubular Epithelial Cells. PloS one 7 (2), e30771. doi:10.
Feili, X., Wu, S., Ye, W., Tu, J., and Lou, L. (2018). MicroRNA-34a-5p Inhibits Liver
Fibrosis by Regulating TGF-β1/Smad3 Pathway in Hepatic Stellate Cells. Cell
Biol. Int. 42 (10), 1370–1376. doi:10.1002/cbin.11022
Fu, S., Hu, X., Ma, Z., Wei, Q., Xiang, X., Li, S., et al. (2022). p53 in Proximal
Tubules Mediates Chronic Kidney Problems after Cisplatin Treatment. Cells 11
(4), 712. doi:10.3390/cells11040712
Gallant-Behm, C. L., Piper, J., Dickinson, B. A., Dalby, C. M., Pestano, L. A., and
Jackson, A. L. (2018). A Synthetic microRNA-92a Inhibitor (MRG-110)
Accelerates Angiogenesis and Wound Healing in Diabetic and Nondiabetic
Wounds. Wound Repair Regen. 26 (4), 311–323. doi:10.1111/wrr.12660
Ghosh, A. K., Quaggin, S. E., and Vaughan, D. E. (2013). Molecular Basis of Organ
Fibrosis: Potential Therapeutic Approaches. Exp. Biol. Med. (Maywood, N.J.)
238 (5), 461–481. doi:10.1177/1535370213489441
Gieseck, R. L., 3rd, Wilson, M. S., and Wynn, T. A. (2018). Type 2 Immunity in
Tissue Repair and Fibrosis. Nat. Rev. Immunol. 18 (1), 62–76. doi:10.1038/nri.
Guan, X., Nie, L., He, T., Yang, K., Xiao, T., Wang, S., et al. (2014). Klotho
Suppresses Renal Tubulo-Interstitial Fibrosis by Controlling Basic Fibroblast
Growth Factor-2 Signalling. J. Pathol. 234 (4), 560–572. doi:10.1002/path.4420
Harding, K. G., Moore, K., and Phillips, T. J. (2005). Wound Chronicity and
Fibroblast Senescence-Iimplications for Treatment. Int. wound J. 2 (4),
Harries, L. W. (2014). MicroRNAs as Mediators of the Ageing Process. Genes
(Basel) 5 (3), 656–670. doi:10.3390/genes5030656
Henderson, N. C., Rieder, F., and Wynn, T. A. (2020). Fibrosis: from Mechanisms
to Medicines. Nature 587 (7835), 555–566. doi:10.1038/s41586-020-2938-9
Hermeking, H. (2010). The miR-34 Family in Cancer and Apoptosis. Cell death
Differ. 17 (2), 193–199. doi:10.1038/cdd.2009.56
Hong, S.-W., Jung, K. H., Zheng, H.-M., Lee, H.-S., Suh, J.-K., Park, I.-S., et al.
(2010). The Protective Effect of Resveratrol on Dimethylnitrosamine-Induced
Liver Fibrosis in Rats. Archives pharmacal Res. 33 (4), 601–609. doi:10.1007/
Hou, Q., Zhou, L., Tang, J., Ma, N., Xu, A., Tang, J., et al. (2016). LGR4 Is a Direct
Target of MicroRNA-34a and Modulates the Proliferation and Migration of
Retinal Pigment Epithelial ARPE-19 Cells. PloS one 11 (12), e0168320. doi:10.
Hu, Y., Yu, C., Wu, F., Yu, W., Zhong, Y., Ying, H., et al. (2016). Antihepatoﬁbrotic
Effects of Aqueous Extract of Prunella Vulgaris on Carbon Tetrachloride-
Induced Hepatic Fibrosis in Rats. Planta medica. 82 (1-2), 97–105. doi:10.1055/
Huang, Y., Qi, Y., Du, J., and Zhang, D. (2014). MicroRNA-34a Regulates Cardiac
Fibrosis after Myocardial Infarction by Targeting Smad4. Expert Opin. Ther.
targets 18 (12), 1355–1365. doi:10.1517/14728222.2014.961424
Patel, K., et al. (2013). Treatment of HCV Infection by Targeting
microRNA. N. Engl. J. Med. 368 (18), 1685–1694. doi:10.1056/
Jesus, C.-R., Francisco, C., Dulce, C. M.-C., Laura, G.-F., Dolores, O.-M., Juan, V.
E., et al. (2019). Autophagy Stimulation as a Potential Strategy against. Intest.
Fibros. 8 (9), 1078. doi:10.3390/cells8091078
Jun, J.-I., and Lau, L. F. (2018). Resolution of Organ Fibrosis. J. Clin. investigation
128 (1), 97–107. doi:10.1172/JCI93563
Jun, J. I., and Lau, L. F. (2010). The Matricellular Protein CCN1/CYR61 Induces
Fibroblast Senescence and Restricts Fibrosis in Cutaneous Wound Healing.
Nat. Cell Biol. 12 (7), 676–685. doi:10.1038/ncb2070
Kim, D. Y., and Park, J. H. (2016). Genetic Mechanisms of ADPKD. Adv. Exp. Med.
Biol. 933, 13–22. doi:10.1007/978-981-10-2041-4_2
Kim, H. J., Joe, Y., Yu, J. K., Chen, Y., Jeong, S. O., Mani, N., et al. (2015). Carbon
Monoxide Protects against Hepatic Ischemia/reperfusion Injury by Modulating
the miR-34a/SIRT1 Pathway. Biochimica biophysica acta 1852 (7), 1550–1559.
Kota, A., Deshpande, D. A., Haghi, M., Oliver, B., and Sharma, P. (2017).
Autophagy and Airway Fibrosis: Is There a Link? F1000Res 6, 409. doi:10.
Krizhanovsky, V., Yon, M., Dickins, R. A., Hearn, S., Simon, J., Miething, C., et al.
(2008). Senescence of Activated Stellate Cells Limits Liver Fibrosis. Cell 134 (4),
Kumamoto, K., Spillare, E. A., Fujita, K., Horikawa, I., Yamashita, T., Appella, E.,
et al. (2008). Nutlin-3a Activates P53 to Both Down-Regulate Inhibitor of
Growth 2 and Up-Regulate Mir-34a, Mir-34b, and Mir-34c Expression, and
Induce Senescence. Cancer Res. 68 (9), 3193–3203. doi:10.1158/0008-5472.
Kyle, L.-W., Claire, J. C., Nigel, B. J., Karin, A. O., and Keith, W. N. (2009). Pathway
Analysis of Senescence-Associated miRNA Targets Reveals Common Processes
to Different Senescence Induction Mechanisms. Biochimica Biophysica Acta
1792 (4), 341–352. doi:10.1016/j.bbadis.2009.02.003
Lehmann, M., Korfei, M., Mutze, K., Klee, S., Skronska-Wasek, W., Alsafadi, H. N.,
et al. (2017). Senolytic Drugs Target Alveolar Epithelial Cell Function and
Attenuate Experimental Lung Fibrosis Ex Vivo.Eur. Respir. J. 50 (2), 1602367.
Li, A., Peng, R., Sun, Y., Liu, H., Peng, H., and Zhang, Z. (2018). LincRNA
1700020I14Rik Alleviates Cell Proliferation and Fibrosis in Diabetic
Nephropathy via miR-34a-5p/Sirt1/HIF-1alpha Signaling. Cell Death Dis. 9
(5), 461. doi:10.1038/s41419-018-0527-8
Li, B., Li, F., Gu, T., Guo, Y., Shen, B., Xu, X., et al. (2022). Speciﬁc Knockdown of
Y-Box Binding Protein 1 in Hepatic Progenitor Cells Inhibits Proliferation and
Alleviates Liver Fibrosis. Eur. J. Pharmacol. 921, 174866. doi:10.1016/j.ejphar.
Li, H., Xu, Y., Zhang, Q., Xu, H., Xu, Y., and Ling, K. (2019). Microvesicles
Containing miR-34a Induce Apoptosis of Proximal Tubular Epithelial Cells and
Participate in Renal Interstitial Fibrosis. Exp. Ther. Med. 17 (3), 2310–2316.
Li, J., Qu, X., Ricardo, S. D., Bertram, J. F., and Nikolic-Paterson, D. J. (2010).
Resveratrol Inhibits Renal Fibrosis in the Obstructed Kidney: Potential Role in
Deacetylation of Smad3. Am. J. pathology 177 (3), 1065–1071. doi:10.2353/
Li, W., Chen, C., Xu, M., Guo, J., Li, Y., Xia, Q., et al. (2011). The Rno-miR-34
Family Is Upregulated and Targets ACSL1 in Dimethylnitrosamine-Induced
Hepatic Fibrosis in Rats. FEBS J. 278 (9), 1522–1532. doi:10.1111/j.1742-4658.
Li, X., Chen, Y., Wu, S., He, J., Lou, L., Ye, W., et al. (2015). microRNA-34a and
microRNA-34c Promote the Activation of Human Hepatic Stellate Cells by
Targeting Peroxisome Proliferator-Activated Receptor γ.Mol. Med. Rep. 11 (2),
Sulﬁde Ameliorates Rat Myocardial Fibrosis Induced by Thyroxine
through PI3K/AKT Signaling Pathway. Endocr. J. 65 (7), 769–781.
Liu, Y., Bi, X., Xiong, J., Han, W., Xiao, T., Xu, X., et al. (2019). MicroRNA-34a
Promotes Renal Fibrosis by Downregulation of Klotho in Tubular Epithelial
Cells. Mol. Ther. J. Am. Soc. Gene Ther. 27 (5), 1051–1065. doi:10.1016/j.ymthe.
Frontiers in Physiology | www.frontiersin.org June 2022 | Volume 13 | Article 8952428
Zhao et al. MicroRNA-34a: Therapeutic Target in Fibrosis
Lv, X., Liu, S., and Hu, Z. (2017). Autophagy-inducing Natural Compounds: a
Treasure Resource for Developing Therapeutics against Tissue Fibrosis. J. Asian
Nat. Prod. Res. 19 (2), 101–108. doi:10.1080/10286020.2017.1279151
Lv, Y., Bing, Q., Lv, Z., Xue, J., Li, S., Han, B., et al. (2020). Imidacloprid-induced
Liver Fibrosis in Quails via Activation of the TGF-beta1/Smad Pathway. Sci.
Total Environ. 705, 135915. doi:10.1016/j.scitotenv.2019.135915
Madesh, M., Zong, W. X., Hawkins, B. J., Ramasamy, S., Venkatachalam, T.,
Mukhopadhyay, P., et al. (2009). Execution of Superoxide-Induced Cell Death
by the Proapoptotic Bcl-2-Related Proteins Bid and Bak. Mol. Cell Biol. 29 (11),
Martinez, F. J., Collard, H. R., Pardo, A., Raghu, G., Richeldi, L., Selman, M., et al.
(2017). Idiopathic Pulmonary Fibrosis. Nat. Rev. Dis. Prim. 3, 17074. doi:10.
Martins, V. R., Dias, M. S., and Hainaut, P. (2013). Tumor-cell-derived
Microvesicles as Carriers of Molecular Information in Cancer. Curr. Opin.
Oncol. 25 (1), 66–75. doi:10.1097/CCO.0b013e32835b7c81
Massague, J., Seoane, J., and Wotton, D. (2005). Smad Transcription Factors. Genes
Dev. 19 (23), 2783–2810. doi:10.1101/gad.1350705
Meng, F., Glaser, S. S., Francis, H., Yang, F., Han, Y., Stokes, A., et al. (2012).
Epigenetic Regulation of miR-34a Expression in Alcoholic Liver Injury. Am.
J. pathology 181 (3), 804–817. doi:10.1016/j.ajpath.2012.06.010
Oda, Y., Nakajima, M., Tsuneyama, K., Takamiya, M., Aoki, Y., Fukami, T., et al.
(2014). Retinoid X Receptor αin Human Liver Is Regulated by miR-34a.
Biochem. Pharmacol. 90 (2), 179–187. doi:10.1016/j.bcp.2014.05.002
Overstreet, J. M., Samarakoon, R., Meldrum, K. K., and Higgins, P. J. (2014). Redox
Control of P53 in the Transcriptional Regulation of TGF-Beta1 Target Genes
through SMAD Cooperativity. Cell Signal 26 (7), 1427–1436. doi:10.1016/j.
Pan, Y., Wang, J., He, L., and Zhang, F. (2021). MicroRNA-34 a Promotes EMT and
Liver Fibrosis in Primary Biliary Cholangitis by Regulating TGF-Beta1/smad
Pathway. J. Immunol. Res. 2021, 6890423. doi:10.1155/2021/6890423
Panigrahi, M., Thibault, P. A., and Wilson, J. A. (2022). MicroRNA 122 Affects
Both the Initiation and the Maintenance of Hepatitis C Virus Infections.
J. Virol. 96 (4), e0190321. doi:10.1128/JVI.01903-21
Piccolo, S. (2008). p53 Regulation Orchestrates the TGF-Beta Response. Cell 133
(5), 767–769. doi:10.1016/j.cell.2008.05.013
Qi, Y., Zhao, A., Yang, P., Jin, L., and Hao, C. (2020). miR-34a-5p Attenuates EMT
through Targeting SMAD4 in Silica-Induced Pulmonary Fibrosis. J. Cell Mol.
Med. 24 (20), 12219–12224. doi:10.1111/jcmm.15853
Ramos, K. J., Smith, P. J., McKone, E. F., Pilewski, J. M., Lucy, A., Hempstead, S. E.,
et al. (2019). Lung Transplant Referral for Individuals with Cystic Fibrosis:
Cystic Fibrosis Foundation Consensus Guidelines. J. Cyst. Fibros. 18 (3),
Recep, B., Katrien, V. R., and George, A. C. (2017). Cell-to-cell Communication:
microRNAs as Hormones. Mol. Oncol. 11 (12), 1673–1686. doi:10.1002/1878-
Richeldi, L., Collard, H. R., and Jones, M. G. (2017). Idiopathic Pulmonary Fibrosis.
Lancet 389 (10082), 1941–1952. doi:10.1016/s0140-6736(17)30866-8
Rieder, F., Kessler, S., Sans, M., and Fiocchi, C. (2012). Animal Models of Intestinal
Fibrosis: New Tools for the Understanding of Pathogenesis and Therapy of
Human Disease. Am. J. physiology. Gastrointest. liver physiology 303 (7),
Rottiers, V., and Naar, A. M. (2012). MicroRNAs in Metabolism and Metabolic
Disorders. Nat. Rev. Mol. Cell Biol. 13 (4), 239–250. doi:10.1038/nrm3313
Salminen, A., and Kaarniranta, K. (2009). SIRT1: Regulation of Longevity via
Autophagy. Cell Signal 21 (9), 1356–1360. doi:10.1016/j.cellsig.2009.02.014
Sharvit, E., Abramovitch, S., Reif, S., and Bruck, R. (2013). Ampliﬁed Inhibition of
Stellate Cell Activation Pathways by PPAR-γ, RAR and RXR Agonists. PloS one
8 (10), e76541. doi:10.1371/journal.pone.0076541
Shetty, S. K., Tiwari, N., Marudamuthu, A. S., Puthusseri, B., Bhandary, Y. P., Fu, J.,
et al. (2017). p53 and miR-34a Feedback Promotes Lung Epithelial Injury and
Pulmonary Fibrosis. Am. J. pathology 187 (5), 1016–1034. doi:10.1016/j.ajpath.
Shi, B., Deng, W., Long, X., Zhao, R., Wang, Y., Chen, W., et al. (2017). miR-21
Increases C-Kit(+) Cardiac Stem Cell Proliferation In Vitro through PTEN/
PI3K/Akt Signaling. PeerJ 5, e2859. doi:10.7717/peerj.2859
Simic, P., Williams, E. O., Bell, E. L., Gong, J. J., Bonkowski, M., and Guarente, L.
(2013). SIRT1 Suppresses the Epithelial-To-Mesenchymal Transition in Cancer
Metastasis and Organ Fibrosis. Cell Rep. 3 (4), 1175–1186. doi:10.1016/j.celrep.
Simone, B. A., Ly, D., Savage, J. E., Hewitt, S. M., Dan, T. D., Ylaya, K., et al. (2014).
microRNA Alterations Driving Acute and Late Stages of Radiation-Induced
Fibrosis in a Murine Skin Model. Int. J. Radiat. Oncol. Biol. Phys. 90 (1), 44–52.
Smith, E. S., Whitty, E., Yoo, B., Moore, A., Sempere, L. F., and Medarova, Z.
(2022). Clinical Applications of Short Non-Coding RNA-Based Therapies in
the Era of Precision Medicine. Cancers (Basel) 14 (6), 1588. doi:10.3390/
Song, L., Chen, T., Zhao, X., Xu, Q., Jiao, R., Li, J., et al. (2019). Pterostilbene
Prevents Hepatocyte Epithelial-Mesenchymal Transition in Fructose-Induced
Liver Fibrosis through Suppressing miR-34a/Sirt1/p53 and TGF-β1/Smads
Signalling. Br. J. Pharmacol. 176 (11), 1619–1634. doi:10.1111/bph.14573
Sutton, T. A., Hato, T., Mai, E., Yoshimoto, M., Kuehl, S., Anderson, M., et al.
(2013). p53 Is Renoprotective after Ischemic Kidney Injury by Reducing
Inﬂammation. J. Am. Soc. Nephrol. 24 (1), 113–124. doi:10.1681/ASN.
Tabuchi, T., Satoh, M., Itoh, T., and Nakamura, M. (2012). MicroRNA-34a
Regulates the Longevity-Associated Protein SIRT1 in Coronary Artery
Disease: Effect of Statins on SIRT1 and microRNA-34a Expression. Clin.
Sci. Lond. 123 (3), 161–171. doi:10.1042/CS20110563
Takano, M., Nekomoto, C., Kawami, M., and Yumoto, R. (2017). Role of miR-34a
in TGF-β1- and Drug-Induced Epithelial-Mesenchymal Transition in Alveolar
Type II Epithelial Cells. J. Pharm. Sci. 106 (9), 2868–2872. doi:10.1016/j.xphs.
Tang, G., Shen, X., Lv, K., Wu, Y., Bi, J., and Shen, Q. (2015). Different
Normalization Strategies Might Cause Inconsistent Variation in Circulating
microRNAs in Patients with Hepatocellular Carcinoma. Med. Sci. Monit. Int.
Med. J. Exp. Clin. Res. 21, 617–624. doi:10.12659/MSM.891028
Tarasov, V., Jung, P., Verdoodt, B., Lodygin, D., Epanchintsev, A., Menssen, A.,
et al. (2007). Differential Regulation of microRNAs by P53 Revealed by
Massively Parallel Sequencing: miR-34a Is a P53 Target that Induces
Apoptosis and G1-Arrest. Cell cycleGeorget. Tex.) 6 (13), 1586–1593. doi:10.
Termén, S., Tan, E. J., Heldin, C.-H., and Moustakas, A. (2013). p53 Regulates
Epithelial-Mesenchymal Transition Induced by Transforming Growth Factor
β.J. Cell. physiology 228 (4), 801–813. doi:10.1002/jcp.24229
Tian, X., Ji, F., Zang, H., and Cao, H. (2016). Activation of the miR-34a/SIRT1/p53
Signaling Pathway Contributes to the Progress of Liver Fibrosis via Inducing
Apoptosis in Hepatocytes but Not in HSCs. PloS one 11 (7), e0158657. doi:10.
Tsou, P.-S., Haak, A. J., Khanna, D., and Neubig, R. R. (2014). Cellular Mechanisms
of Tissue Fibrosis. 8. Current and Future Drug Targets in Fibrosis: Focus on
Rho GTPase-Regulated Gene Transcription. Am. J. physiology. Cell physiology
307 (1), C2–C13. doi:10.1152/ajpcell.00060.2014
Ucar, A., Gupta, S. K., Fiedler, J., Erikci, E., Kardasinski, M., Batkai, S., et al. (2012).
The miRNA-212/132 Family Regulates Both Cardiac Hypertrophy and
Cardiomyocyte Autophagy. Nat. Commun. 3, 1078. doi:10.1038/ncomms2090
Uhal, B. D. (2002). Apoptosis in Lung Fibrosis and Repair. Chest 122 (6 Suppl. l),
Valentijn, F. A., Knoppert, S. N., Pissas, G., Rodrigues-Diez, R. R., Marquez-
Exposito, L., Broekhuizen, R., et al. (2021). CCN2 Aggravates the Immediate
Oxidative Stress-DNA Damage Response Following Renal Ischemia-
Reperfusion Injury. Antioxidants (Basel) 10(12). 2020. doi:10.3390/
van Zandwijk, N., Pavlakis, N., Kao, S. C., Linton, A., Boyer, M. J., Clarke, S., et al.
(2017). Safety and Activity of microRNA-Loaded Minicells in Patients with
Recurrent Malignant Pleural Mesothelioma: a First-In-Man, Phase 1, Open-
Label, Dose-Escalation Study. Lancet Oncol. 18 (10), 1386–1396. doi:10.1016/
Villac Adde, F., Vidal Campos, S., de Oliveira Braga Teixeira, R. H., and Rodrigues,
J. C. (2018). Indications for Lung Resection Surgery and Lung Transplant in
South American Children with Cystic Fibrosis. Paediatr. Respir. Rev. 25, 37–42.
Wan, Y., McDaniel, K., Wu, N., Ramos-Lorenzo, S., Glaser, T., Venter, J., et al.
(2017). Regulation of Cellular Senescence by miR-34a in Alcoholic Liver Injury.
Am. J. pathology 187 (12), 2788–2798. doi:10.1016/j.ajpath.2017.08.027
Frontiers in Physiology | www.frontiersin.org June 2022 | Volume 13 | Article 8952429
Zhao et al. MicroRNA-34a: Therapeutic Target in Fibrosis
release Mitomycin C-Polylactic Acid Film Prevents Epidural Scar
Hyperplasia after Laminectomy by Inducing Fibroblast Autophagy and
Regulating the Expression of miRNAs. Eur. Rev. Med. Pharmacol. Sci. 21
(10), 2526–2537. doi:10.7666/d.Y3072421
Wang, J., Guo, L., Shen, D., Xu, X., Wang, J., Han, S., et al. (2017b). The Role of
C-SKI in Regulation of TGFbeta-Induced Human Cardiac Fibroblast
Proliferation and ECM Protein Expression. J. Cell Biochem. 118 (7),
Wang, P., Zhou, Y., and Richards, A. M. (2021). Effective Tools for RNA-Derived
Therapeutics: siRNA Interference or miRNA Mimicry. Theranostics 11 (18),
Waters, D. W., Blokland, K. E. C., Pathinayake, P. S., Burgess, J. K., Mutsaers, S. E.,
Prele, C. M., et al. (2018). Fibroblast Senescence in the Pathology of Idiopathic
Pulmonary Fibrosis. Am. J. Physiol. Lung Cell Mol. Physiol. 315 (2), L162–L172.
Weiskirchen, R., Weiskirchen, S., and Tacke, F. (2019). Organ and Tissue Fibrosis:
Molecular Signals, Cellular Mechanisms and Translational Implications. Mol.
Asp. Med. 65, 2–15. doi:10.1016/j.mam.2018.06.003
Wu, C., Chiang, W., Lai, C., Chang, F., Chen, Y., Chou, Y., et al. (2013).
Transforming Growth Factor β-1 Stimulates Proﬁbrotic Epithelial Signaling
to Activate Pericyte-Myoﬁbroblast Transition in Obstructive Kidney Fibrosis.
Am. J. pathology 182 (1), 118–131. doi:10.1016/j.ajpath.2012.09.009
Xie, T., Liang, J., Guo, R., Liu, N., Noble, P. W., and Jiang, D. (2011).
Comprehensive microRNA Analysis in Bleomycin-Induced Pulmonary
Fibrosis Identiﬁes Multiple Sites of Molecular Regulation. Physiol. genomics
43 (9), 479–487. doi:10.1152/physiolgenomics.00222.2010
Xue, M., Li, Y., Hu, F., Jia, Y., Zheng, Z., Wang, L., et al. (2018). High Glucose Up-
Regulates microRNA-34a-5p to Aggravate Fibrosis by Targeting SIRT1 in HK-
2 Cells. Biochem. biophysical Res. Commun. 498 (1), 38–44. doi:10.1016/j.bbrc.
Yamakuchi, M., Ferlito, M., and Lowenstein, C. J. (2008). miR-34a Repression of
SIRT1 Regulates Apoptosis. Proc. Natl. Acad. Sci. U. S. A. 105 (36),
Yan, G., Li, B., Xin, X., Xu, M., Ji, G., and Yu, H. (2015). MicroRNA-34a Promotes
Hepatic Stellate Cell Activation via Targeting ACSL1. Med. Sci. Monit. Int. Med.
J. Exp. Clin. Res. 21, 3008–3015. doi:10.12659/MSM.894000
Yan, G. (2016). MicroRNA-34a Bind ACSL1 to Affect Hepatic Fibrosis. Shanghai:
The Second Military Medical University.
34 Modulates Caenorhabditis elegans Lifespan via Repressing the
Autophagy Gene Atg9. Age Dordr. Neth. 35 (1), 11–22. doi:10.1007/
Yang, L., Besschetnova, T. Y., Brooks, C. R., Shah, J. V., and Bonventre, J. V. (2010).
Epithelial Cell Cycle Arrest in G2/M Mediates Kidney Fibrosis after Injury. Nat.
Med. 16 (5), 535–543. doi:10.1038/nm.2144
Zhang, C., Zhang, Y., Zhu, H., Hu, J., and Xie, Z. (2018). MiR-34a/miR-93 Target
C-Ski to Modulate the Proliferaton of Rat Cardiac Fibroblasts and Extracellular
Matrix Deposition In Vivo and In Vitro.Cell. Signal. 46, 145–153. doi:10.1016/j.
Zhang, F., Gao, F., Wang, K., Liu, X., and Zhang, Z. (2021a). MiR-34a Inhibitor
Protects Mesenchymal Stem Cells from Hyperglycaemic Injury through the
Activation of the SIRT1/FoxO3a Autophagy Pathway. Stem Cell Res. Ther. 12
(1), 115. doi:10.1186/s13287-021-02183-2
Zhang, G., Oldroyd, S. D., Huang, L. H., Yang, B., Li, Y., Ye, R., et al. (2001). Role of
Apoptosis and Bcl-2/Bax in the Development of Tubulointerstitial Fibrosis
during Experimental Obstructive Nephropathy. Exp. Nephrol. 9(2),71–80.
Zhang, J., Tian, X., Zhang, H., Teng, Y., Li, R., Bai, F., et al. (2014). TGF-β-induced
Epithelial-To-Mesenchymal Transition Proceeds through Stepwise Activation
of Multiple Feedback Loops. Sci. Signal. 7 (345), ra91. doi:10.1126/scisignal.
Zhang, J., Wang, H., Yao, L., Zhao, P., and Wu, X. (2021b). MiR-34a Promotes
Fibrosis of Hepatic Stellate Cells via the TGF-Beta Pathway. Ann. Transl. Med. 9
(20), 1520. doi:10.21037/atm-21-5005
Zhang, Q., Chang, X., Wang, H., Liu, Y., Wang, X., Wu, M., et al. (2019). TGF-beta1
Mediated Smad Signaling Pathway and EMT in Hepatic Fibrosis Induced by
Nano NiO In Vivo and In Vitro.Environ. Toxicol. 35 (4), 419–429. doi:10.1002/
Zhao, X., Kwan, J. Y. Y., Yip, K., Liu, P. P., and Liu, F. F. (2020). Targeting
Metabolic Dysregulation for Fibrosis Therapy. Nat. Rev. Drug Discov. 19 (1),
Zhou, B., Zuo, X. X., Li, Y. S., Gao, S. M., Dai, X. D., Zhu, H. L., et al. (2017).
Integration of microRNA and mRNA Expression Proﬁles in the Skin of
Systemic Sclerosis Patients. Sci. Rep. 7, 42899. doi:10.1038/srep42899
Zhou, Y., Xiong, M., Niu, J., Sun, Q., Su, W., Zen, K., et al. (2014). Secreted
Fibroblast-Derived miR-34a Induces Tubular Cell Apoptosis in Fibrotic
Kidney. J. Cell Sci. 127 (Pt 20), 4494–4506. doi:10.1242/jcs.155523
IV Protects H9C2(2-1) Cardiomyocytes from High Glucose-Induced
Injury via miR-34a-Mediated Autophagy Pathway. Artif. cells,
nanomedicine, Biotechnol. 47 (1), 4172–4181. doi:10.1080/21691401.
Zogg, H., Singh, R., and Ro, S. (2022). Current Advances in RNA Therapeutics for
Human Diseases. Int. J. Mol. Sci. 23 (5), 2736. doi:10.3390/ijms23052736
Zundler, S., Caioni, M., Müller, M., Strauch, U., Kunst, C., and Woelfel, G. (2016).
K+ Channel Inhibition Differentially Regulates Migration of Intestinal
Epithelial Cells in Inﬂamed vs. Non-Inﬂamed Conditions in a PI3K/Akt-
Mediated Manner. PloS one 11 (1), e0147736. doi:10.1371/journal.pone.
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Zhao et al. MicroRNA-34a: Therapeutic Target in Fibrosis