Makoto Shimizu’s research while affiliated with The University of Tokyo and other places

Statins, HMG-CoA reductase inhibitors, have been widely prescribed to lower circulating low-density lipoprotein cholesterol levels and reduce the risk of cardiovascular disease. Although statins are well tolerated, statin-associated muscle symptoms (SAMS) are the major adverse effect and cause statin intolerance. Therefore, understanding the molecular mechanisms of SAMS and identifying effective strategies for its prevention are of significant clinical importance; however, both remain unclear. Here we establish a model of statin-induced myopathy (SIM) with human induced pluripotent stem cell (hiPSC)-derived myocytes (iPSC-MCs) and investigate the effect of statins on protein homeostasis (proteostasis) that affects skeletal muscle wasting and myotoxicity. We show that treating hiPSC-MCs with statins induces atrophic phenotype and myotoxicity, establishing a hiPSC-based SIM model. We then examine whether statins impair the balance between protein synthesis and degradation. The results show that statins not only suppress protein synthesis but also promote protein degradation by upregulating the expression of the muscle-specific E3 ubiquitin ligase Atrogin-1 in a mevalonate pathway-dependent manner. Mechanistically, blocking the mevalonate pathway inactivates the protein kinase Akt, leading to the inhibition of mTORC1 and GSK3β but the activation of FOXO1. These changes explain the statin-induced impairment in proteostasis. Finally, we show that pharmacological blockage of FOXO1 prevents SIM in hiPSC-MCs, implicating FOXO1 as a key mediator of SIM. Taken together, this study suggests that the mevalonate pathway is critical for maintaining skeletal muscle proteostasis and identifies FOXO1 as a potential target for preventing SIM.

Triokinase/FMN cyclase (Tkfc) is involved in fructose metabolism and is responsible for the phosphorylation of glyceraldehyde to glyceraldehyde-3-phosphate. In this study, we showed that refeeding induced hepatic expression of Tkfc in mice. Luciferase reporter gene assays using the Tkfc promoter revealed the existence of 2 hepatocyte nuclear factor 4α (HNF4α)-responsive elements (HNF4RE1 and HNF4RE2) and 1 carbohydrate-responsive element-binding protein (ChREBP)-responsive element (ChoRE1). Deletion and mutation of HNF4RE1 and HNF4RE2 or ChoRE1 abolished HNF4α and ChREBP responsiveness, respectively. HNF4α and ChREBP synergistically stimulated Tkfc promoter activity. ChoRE1 mutation attenuated but maintained HNF4α responsiveness, whereas HNF4RE1 and HNF4RE2 mutations abolished ChREBP responsiveness. Moreover, Tkfc promoter activity stimulation by ChREBP was attenuated upon HNF4α knockdown. Furthermore, Tkfc expression was decreased in the livers of ChREBP−/− and liver-specific HNF4−/− (Hnf4αΔHep) mice. Altogether, our data indicate that Tkfc is a target gene of ChREBP and HNF4α, and Tkfc promoter activity stimulation by ChREBP requires HNF4α.

Human liver organoids (HLOs) are reliable tools to represent physiological human liver biology. However, their use is limited especially in basic sciences. One of the reasons for this would be the insufficient systematic methodology to handle HLOs, including culture system, functional assessment, and gene transduction. Here, we generated and characterized mouse L cells stably and simultaneously overexpressing R‐spondin1, hepatocyte growth factor, fibroblast growth factor (FGF) 7, and FGF10 via lentiviral transduction. The conditioned medium of the cells contributed to HLO growth as a replacement of commercially available recombinant proteins, which leads to significant reduction of their culture cost. Proliferative and maturation phases of the cells were controlled by switching the medium to facilitate the evaluation of hepatocyte function, including insulin responsiveness and intracellular lipid accumulation. Gene expression analysis revealed that HLOs highly expressed genes involved in lipid metabolism. Importantly, HLOs secreted physiologically matured very low‐density lipoprotein, which is rarely observed in mice and in established cell lines. Efficient gene transduction into HLOs was achieved via a transient 2‐dimensional culture during viral infection. This study provides an invaluable platform for utilizing HLOs in various research fields, such as molecular biology, pharmacology, toxicology, and regenerative medicine. This article is protected by copyright. All rights reserved

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide, with an incidence of >25% of the adult population. NAFLD ranges from benign simple steatosis to non-alcoholic steatohepatitis (NASH). However, its transition mechanisms underlying the pathogenesis remain to be clarified. The expression of Cyp7b1 gene is downregulated in the liver of leptin-deficient mice and methionine and choline-deficient diet-fed mice based on previous microarray data. Thus, in this study, we investigated the effect of CYP7B1 restoration on the progression of NASH in mice fed MCD diet and its association with oxidative and lipid stresses. Our results suggest that restoration of CYP7B1 expression attenuates hepatitis and fibrosis and that lipid and oxidative stresses observed in the early stage of NASH suppresses Cyp7b1 transcription in hepatocytes.

Organoids are regarded as physiologically relevant cell models and useful for compound screening for drug development; however, their applications are currently limited because of the high cost of their culture. We previously succeeded in reducing the cost of human intestinal organoid culture using conditioned medium (CM) of L cells co-expressing Wnt3a, R-spondin1, and Noggin. Here, we further reduced the cost by replacing recombinant hepatocyte growth factor with CM. Moreover, we showed that embedding organoids in collagen gel, a more inexpensive matrix than Matrigel, maintains organoid proliferation and marker gene expression similarly when using Matrigel. The combination of these replacements also enabled the organoid-oriented monolayer cell culture. Furthermore, screening thousands of compounds using organoids expanded with the refined method identified several compounds with more selective cytotoxicity against organoid-derived cells than Caco-2 cells. The mechanism of action of one of these compounds, YC-1, was further elucidated. We showed that YC-1 induces apoptosis through the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway, the mechanism of which was distinct from cell death caused by other hit compounds. Our cost-cutting methodology enables large-scale intestinal organoid culture and subsequent compound screening, which could expand the application of intestinal organoids in various research fields.

The cholesterol metabolites oxysterols play central roles in cholesterol feedback control. They modulate the activity of two master transcription factors that control cholesterol homeostatic responses, sterol regulatory element-binding protein-2 (SREBP-2) and liver X receptor (LXR). Although the role of exogenous oxysterols in regulating these transcription factors has been well established, whether endogenously synthesized oxysterols similarly control both SREBP-2 and LXR remains poorly explored. Here, we carefully validate the role of oxysterols enzymatically synthesized within cells in cholesterol homeostatic responses. We first show that SREBP-2 responds more sensitively to exogenous oxysterols than LXR in CHO cells and rat primary hepatocytes. We then show that 25-hydroxycholesterol (25-HC), 27-HC, and 24S-HC endogenously synthesized by CH25H, CYP27A1, and CYP46A1, respectively, suppress SREBP-2 activity at different degrees by stabilizing Insig proteins, whereas 7α-HC has little impact on SREBP-2. These results demonstrate the role of site-specific hydroxylation of endogenous oxysterols. In contrast, the expression of CH25H, CYP46A1, CYP27A1, or CYP7A1 fails to induce LXR target gene expression. We also show the 25-HC production-dependent suppression of SREBP-2 using a tetracycline-inducible CH25H expression system. To induce 25-HC production physiologically, murine macrophages are stimulated with a toll-like receptor 4 ligand, and its effect on SREBP-2 and LXR is examined. The results also suggest that de novo synthesis of 25-HC preferentially regulates SREBP-2 activity. Finally, we quantitatively determine the specificity of the four cholesterol hydroxylases in living cells. Based on our current findings, we conclude that endogenous side-chain oxysterols primarily regulate the activity of SREBP-2, not LXR.

Background:Physiologically relevant cell models, including organoids, are considered to be reliable tools for recapitulating human biology. Although organoids are useful for cell-based compound screening, which may facilitate drug development, their applications are limited. Intestinal organoids are composed of multiple types of intestinal epithelial cells found in vivoand replicate organ structures and complexities. A major limitation of using organoids in screening studies is the high cost of their culture when commercially available recombinant proteins are used. Methods: We previously succeeded in reducing the cost of human intestinal organoid culture by using the conditioned medium (CM) of L cells that stably co-express Wnt3a, R-spondin1, and Noggin via lentiviral infection. Based on this, we worked on further cost reduction by replacing expensive materials with cheaper ones and expanded the organoids in a more cost-effective way for a large-scale assay. Results: We replaced recombinant hepatocyte growth factor protein with CM for human intestinal organoid culture.Moreover, collagen gel was used instead of Matrigel for organoid culture, and organoid proliferation rate, as well as marker gene expression, was largely unchanged. The combination of these replacements significantly contributed to cost reduction for culturing organoids and organoid-oriented monolayer cells. Furthermore, compound screening of thousands of known bioactive substances was performed using human intestinal organoids cultured with the refined cost-reduction strategies, and several compounds with more selective cytotoxicity against organoid-derived cells than Caco-2 cells were identified. The mechanism of action of one of these compounds, YC-1, was further elucidated. We showed that YC-1 induces apoptosis through the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway. Conclusions:These results indicate that our methodologies for cost reduction enable large-scale organoid culture and subsequent compound screening, which may further expand the application of intestinal organoids and organoids in general in various research fields, including both theoretical and applied science.

Skeletal muscle mass is negatively regulated by several TGF-β superfamily members. Myostatin (MSTN) is the most prominent negative regulator of muscle mass. Recent studies show that in addition to MSTN, GDF11, which shares high sequence identity with MSTN, induces muscle atrophy in vitro and in vivo at supraphysiological levels, whereas controversy regarding its roles exists. Furthermore, higher circulating GDF11 levels associate with frailty in humans. On the other hand, little is known about the effect of pathophysiological levels of GDF11 on muscle atrophy. Here we seek to determine whether pathophysiological levels of GDF11 are sufficient to activate Smad2/Smad3 signaling and induce muscle atrophy using human iPSC-derived myocytes (hiPSC-myocytes). We first show that incubating hiPSC-myocytes with pathophysiologic concentrations of GDF11 significantly reduces myocyte diameters. We next demonstrate that pathophysiological levels of GDF11 are sufficient to activate Smad2/3 signaling. Finally, we show that pathophysiological levels of GDF11 are capable of inducing the expression of Atrogin-1, an atrophy-promoting E3 ubiquitin ligase and that FOXO1 blockage reverses the GDF11-induced Atrogin-1 expression and atrophic phenotype. Collectively, our results suggest that GDF11 induces skeletal muscle atrophy at the pathophysiological level through the GDF11-FOXO1 axis.

Gut microbiota regulate physiological functions in various hosts, such as energy metabolism and immunity. Lactic acid bacteria, including Lactobacillus plantarum, have a specific polyunsaturated fatty acid saturation metabolism that generates multiple fatty acid species, such as hydroxy fatty acids, oxo fatty acids, conjugated fatty acids, and trans-fatty acids. How these bacterial metabolites impact host physiology is not fully understood. Here we investigated the ligand activity of lactic acid bacteria-produced fatty acids in relation to nuclear hormone receptors (NRs) expressed in the small intestine. Our reporter assays revealed two bacterial metabolites of γ-linolenic acid (GLA), 13-hydroxy-cis-6,cis-9-octadecadienoic acid (γHYD) and 13-oxo-cis-6,cis-9-octadecadienoic acid (γKetoD), activated peroxisome proliferator-activated receptor delta (PPARδ) more potently than GLA. We demonstrate that both γHYD and γKetoD bound directly to the ligand-binding domain of human PPARδ. A docking simulation indicated that four polar residues (T289, H323, H449, and Y473) of PPARδ donate hydrogen bonds to these fatty acids. Interestingly T289 does not donate a hydrogen bond to GLA, suggesting that bacterial modification of GLA introducing hydroxy and oxo group determines ligand selectivity. In human intestinal organoids, we determined γHYD and γKetoD increased the expression of PPARδ target genes, enhanced fatty acid β-oxidation, and reduced intracellular triglyceride accumulation. These findings suggest that γHYD and γKetoD, which gut lactic acid bacteria could generate, are naturally occurring PPARδ ligands in the intestinal tract, and may improve lipid metabolism in the human intestine.

Extracellular vesicles (EVs) contain various regulatory molecules and mediate intercellular communications. Although EVs are secreted from various cell types, including skeletal muscle cells, and present in the blood, their identity is poorly characterized in vivo, limiting the identification of their origin in the blood. Since the skeletal muscle is the largest organ in the body, it could substantially contribute to circulating EVs as their source. However, due to the lack of defined markers that distinguish skeletal muscle-derived EVs (SkM-EVs) from others, whether the skeletal muscle releases EVs in vivo and how much SkM-EVs account for plasma EVs remain poorly understood. In this work, we perform quantitative proteomic analyses on EVs released from C2C12 cells and human iPS cell-derived myocytes and identify potential marker proteins that mark SkM-EVs. These markers we identified apply to in vivo tracking of SkM-EVs. The results show that skeletal muscle makes only a subtle contribution to plasma EVs as their source in both control and exercise conditions in mice. On the other hand, we demonstrate that SkM-EVs are concentrated in the skeletal muscle interstitium. Furthermore, we show that interstitium EVs are highly enriched with the muscle-specific miRNAs and repress the expression of the paired box transcription factor Pax7, a master regulator for myogenesis. Taken together, our findings confirm previous studies showing that skeletal muscle cells release exosome-like EVs with specific protein and miRNA profiles in vivo and show that SkM-EVs mainly play a role within the muscle microenvironment where they accumulate.