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ABSTRACT: Innate immune response is the first defense against pathogens via recognition by various conserved pattern recognition receptors, such as TLRs, to initiate a rapid and strong cytokine alarm. TLR signaling-mediated cytokine production must be properly regulated to prevent pathological conditions deriving from overproduction of cytokines. In this study, the role of specific microRNAs in TLR-signaling pathway was investigated to reveal the cross-interaction and -regulation in the MyD88 pathway. In peptidoglycan (PGN)/TLR2-stimulated THP-1 monocytes, PBMCs, and primary macrophages showed rapid and dramatic miR-132 and miR-212 (miR-132/-212) upregulation. This newly identified response appeared earlier in time than the characteristic miR-146a response in LPS-TLR4 stimulation. The rapid induction of miR-132/-212 was transcription factor CREB dependent, and the sustained expression of miR-132/-212 was responsible for inducing tolerance to subsequent PGN challenge. Cross-tolerance was observed by TLR5 ligand flagellin and heat-killed or live bacteria resulting from miR-132/-212 upregulation. Mechanistically, IRAK4 was identified and validated as a target of miR-132/-212 by luciferase reporter assay and seed-sequence mutagenesis of the reporter. Transfection of miR-132 or miR-212 alone mimicked PGN tolerance in monocytes, whereas transfected specific miRNA inhibitors tampered the tolerance effect. During bacterial infection, PGN-mediated TLR2 signaling induces miR-132/-212 to downregulate IRAK4, an early component in the MyD88-dependent pathway, whereas LPS/TLR4-induced miR-146a downregulates downstream components of the same MyD88-dependent pathway. The identification of miR-132/-212 and miR-146a together to prevent damaging consequences from the overproduction of proinflammatory cytokines by targeting a common signaling pathway is significant and will provide insights into future design and development of therapeutics.
The Journal of Immunology 12/2012; · 5.79 Impact Factor
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ABSTRACT: Toll-like receptors (TLRs) in innate immune cells are the prime cellular sensors for microbial components. TLR activation leads to the production of proinflammatory mediators and thus TLR signaling must be properly regulated by various mechanisms to maintain homeostasis. TLR4-ligand lipopolysaccharide (LPS)-induced tolerance or cross-tolerance is one such mechanism, and it plays an important role in innate immunity. Tolerance is established and sustained by the activity of the microRNA miR-146a, which is known to target key elements of the myeloid differentiation factor 88 (MyD88) signaling pathway, including IL-1 receptor-associated kinase (IRAK1), IRAK2 and tumor-necrosis factor (TNF) receptor-associated factor 6 (TRAF6). In this review, we comprehensively examine the TLR signaling involved in innate immunity, with special focus on LPS-induced tolerance. The function of TLR ligand-induced microRNAs, including miR-146a, miR-155 and miR-132, in regulating inflammatory mediators, and their impact on the immune system and human diseases, are discussed. Modulation of these microRNAs may affect TLR pathway activation and help to develop therapeutics against inflammatory diseases.
Cellular & molecular immunology 08/2011; 8(5):388-403. · 2.99 Impact Factor
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ABSTRACT: MicroRNAs (miRNAs) are endogenous, non-coding, single-stranded RNAs about 21 nucleotides in length. miRNAs have been shown to regulate gene expression and thus influence a wide range of physiological and pathological processes. Moreover, they are detected in a variety of sources, including tissues, serum, and other body fluids, such as saliva. The role of miRNAs is evident in various malignant and nonmalignant diseases, and there is accumulating evidence also for an important role of miRNAs in systemic rheumatic diseases. Abnormal expression of miRNAs has been reported in autoimmune diseases, mainly in systemic lupus erythematosus and rheumatoid arthritis. miRNAs can be aberrantly expressed even in the different stages of disease progression, allowing miRNAs to be important biomarkers, to help understand the pathogenesis of the disease, and to monitor disease activity and effects of treatment. Different groups have demonstrated a link between miRNA expression and disease activity, as in the case of renal flares in lupus patients. Moreover, miRNAs are emerging as potential targets for new therapeutic strategies of autoimmune disorders. Taken together, recent data demonstrate that miRNAs can influence mechanisms involved in the pathogenesis, relapse, and specific organ involvement of autoimmune diseases. The ultimate goal is the identification of a miRNA target or targets that could be manipulated through specific therapies, aiming at activation or inhibition of specific miRNAs responsible for the development of disease.
Arthritis research & therapy 07/2011; 13(4):229. · 4.27 Impact Factor
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ABSTRACT: Rheumatoid arthritis (RA) is a chronic and severe autoimmune disease that affects joint tissues, bone, and cartilage. However, the pathogenesis of RA is still unclear. Autoantibodies such as rheumatoid factor and anti-cyclic citrullinated peptide are useful tools for early diagnosis, monitoring disease activity, and predicting prognosis. Recently, many groups have focused their attention on the role of microRNAs in the pathogenesis of RA, as well as a potential biomarker to monitor RA. In fact, the expression of some microRNAs, such as miR-146a, is upregulated in different cell types and tissues in RA patients. MicroRNAs in RA could also be considered as possible future targets for new therapeutic approaches.
FEBS letters 05/2011; 585(23):3667-74. · 3.54 Impact Factor
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ABSTRACT: Human TLRs are critical sensors for microbial components leading to the production of proinflammatory cytokines that are controlled by various mechanisms. Monocytes pretreated with LPS exhibit a state of hyporesponsiveness, referred to as cross-tolerance, to both homologous and heterologous ligands, which play a broader role in innate immunity. To date, LPS-induced cross-tolerance has not been examined regarding microRNA expression kinetics. In this study, THP-1 monocytes treated with various inflammatory ligands showed a continuous amplification of microRNA (miR)-146a over 24 h that is inversely correlated to TNF-α production. In contrast, inhibition of miR-146a showed a reciprocal effect. Thus, the characteristic upregulation of miR-146a in LPS-exposed THP-1 monocytes was studied for cross-tolerance. Strikingly, in LPS-tolerized THP-1 monocytes, only miR-146a showed a continuous overexpression, suggesting its crucial role in cross-tolerance. Similarly, peptidoglycan-primed THP-1 cells showed homologous tolerance associated with miR-146a upregulation. Subsequently, interchangeable differential cross-regulation was observed among non-LPS ligands. TLR2 and TLR5 ligands showed both homologous and heterologous tolerance correlated to miR-146a overexpression. More importantly, inflammatory responses to TLR4, TLR2, and TLR5 ligands were reduced due to knockdown of miR-146a targets IL-1R-associated kinase 1 or TNFR-associated factor 6, suggesting the regulatory effect of miR-146a on these TLRs signaling. Transfection of miR-146a into THP-1 cells caused reduction of TNF-α production, mimicking LPS-induced cross-tolerance. Aside from individual ligands, a whole bacterial challenge in LPS-primed THP-1 monocytes was accompanied by less TNF-α production, which is conversely correlated to miR-146a expression. Our studies have thus demonstrated that miR-146a plays a crucial role for in vitro monocytic cell-based endotoxin-induced cross-tolerance.
The Journal of Immunology 02/2011; 186(3):1723-34. · 5.79 Impact Factor
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ABSTRACT: Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia are periodontal pathogens associated with the etiology of adult periodontitis as polymicrobial infections. Recent studies demonstrated that oral infection with P. gingivalis induces both periodontal disease and atherosclerosis in hyperlipidemic and proatherogenic ApoE(-/-) mice. In this study, we explored the expression of microRNAs (miRNAs) in maxillas (periodontium) and spleens isolated from ApoE(-/-) mice infected with P. gingivalis, T. denticola, and T. forsythia as a polymicrobial infection. miRNA expression levels, including miRNA miR-146a, and associated mRNA expression levels of the inflammatory cytokines tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β) were measured in the maxillas and spleens from mice infected with periodontal pathogens and compared to those in the maxillas and spleens from sham-infected controls. Furthermore, in response to these periodontal pathogens (as mono- and polymicrobial heat-killed and live bacteria), human THP-1 monocytes demonstrated similar miRNA expression patterns, including that of miR-146a, in vitro. Strikingly, miR-146a had a negative correlation with TNF-α secretion in vitro, reducing levels of the adaptor kinases IL-1 receptor-associated kinase 1 (IRAK-1) and TNF receptor-associated factor 6 (TRAF6). Thus, our studies revealed a persistent association of miR-146a expression with these periodontal pathogens, suggesting that miR-146a may directly or indirectly modulate or alter the chronic periodontal pathology induced by these microorganisms.
Infection and immunity 01/2011; 79(4):1597-605. · 4.21 Impact Factor
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ABSTRACT: The human toll-like receptor 4 (TLR4) pathway is activated in response to lipopolysaccharide (LPS), and subsequent signal
transductions lead to the production of cytokines such as tumor necrosis factor-α (TNF-α) by innate immune cells. Defects
in innate immune response may contribute to the overproduction of TNF-α leading to systemic inflammation and diseases. Thus,
the innate immune response needs to be tightly regulated by elaborate mechanisms to control its onset and termination. LPS
tolerance is a state of hyporesponsiveness to subsequent LPS challenge and is achieved by monocytic cells after prolonged
exposure to LPS. In this report, kinetics of endotoxin-responsive microRNAs expression analysis revealed a unique pattern
of gradual increase for miR-146a starting 4 h after LPS stimulation in THP-1 cells and continued up to 35-fold over 24 h.
Conversely, TNF-α increased up to 4 h and then decreased gradually implicating a negative correlation with miR-146a progression.
The characteristic up-regulation of miR-146a toward subsequent LPS challenge in THP-1 cells was studied. Strikingly, microRNA
expression analysis during the tolerized state of THP-1 cells showed only miR-146a overexpression suggesting its important
role in LPS tolerance. In addition, LPS tolerance was dependent on a LPS-priming dose and associated miR-146a up-regulation.
LPS-tolerized cells were observed to regain responsiveness in TNF-α production 22 h after LPS removal correlating with a decrease
in miR-146a level. Transfection of miR-146a into THP-1 cells mimicked LPS priming, whereas transfection of miR-146a inhibitor
largely abolished LPS tolerance. Thus our studies demonstrated that miR-146a is critical for the in vitro monocytic cell-based endotoxin tolerance.
Journal of Biological Chemistry 12/2009; 284(50):34590-34599. · 4.77 Impact Factor
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ABSTRACT: The human toll-like receptor 4 (TLR4) pathway is activated in response to lipopolysaccharide (LPS), and subsequent signal transductions lead to the production of cytokines such as tumor necrosis factor-alpha (TNF-alpha) by innate immune cells. Defects in innate immune response may contribute to the overproduction of TNF-alpha leading to systemic inflammation and diseases. Thus, the innate immune response needs to be tightly regulated by elaborate mechanisms to control its onset and termination. LPS tolerance is a state of hyporesponsiveness to subsequent LPS challenge and is achieved by monocytic cells after prolonged exposure to LPS. In this report, kinetics of endotoxin-responsive microRNAs expression analysis revealed a unique pattern of gradual increase for miR-146a starting 4 h after LPS stimulation in THP-1 cells and continued up to 35-fold over 24 h. Conversely, TNF-alpha increased up to 4 h and then decreased gradually implicating a negative correlation with miR-146a progression. The characteristic up-regulation of miR-146a toward subsequent LPS challenge in THP-1 cells was studied. Strikingly, microRNA expression analysis during the tolerized state of THP-1 cells showed only miR-146a overexpression suggesting its important role in LPS tolerance. In addition, LPS tolerance was dependent on a LPS-priming dose and associated miR-146a up-regulation. LPS-tolerized cells were observed to regain responsiveness in TNF-alpha production 22 h after LPS removal correlating with a decrease in miR-146a level. Transfection of miR-146a into THP-1 cells mimicked LPS priming, whereas transfection of miR-146a inhibitor largely abolished LPS tolerance. Thus our studies demonstrated that miR-146a is critical for the in vitro monocytic cell-based endotoxin tolerance.
Journal of Biological Chemistry 10/2009; 284(50):34590-9. · 4.77 Impact Factor
