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Department of Biochemistry and Molecular Biology, Institute of Human–Environment Interface Biology, Department of Rehabilitation Medicine, Seoul National University College of Medicine, 103 Daehak‐ro, Jongno‐Gu, Seoul 110‐799, Korea
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Department of Biochemistry and Molecular Biology, Institute of Human–Environment Interface Biology, Department of Rehabilitation Medicine, Seoul National University College of Medicine, 103 Daehak‐ro, Jongno‐Gu, Seoul 110‐799, Korea
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Glucocorticoids play a major role in the development of muscle atrophy in various medical conditions, such as cancer, burn injury, and sepsis, by inhibiting insulin signaling. In this study, we report a new pathway in which glucocorticoids reduce the levels of upstream insulin signaling components by downregulating the transcription of the gene encoding caveolin-1 (CAV1), a scaffolding protein present in the caveolar membrane. Treatment with the glucocorticoid dexamethasone (DEX) decreased CAV1 protein and Cav1 mRNA expression, with a concomitant reduction in insulin receptor alpha (IRα) and IR substrate 1 (IRS1) levels in C2C12 myotubes. On the basis of the results of promoter analysis using deletion mutants and site-directed mutagenesis a negative glucocorticoid-response element in the regulatory region of the Cav1 gene was identified, confirming that Cav1 is a glucocorticoid-target gene. Cav1 knockdown using siRNA decreased the protein levels of IRα and IRS1, and overexpression of Cav1 prevented the DEX-induced decrease in IRα and IRS1 proteins, demonstrating a causal role of Cav1 in the inhibition of insulin signaling. Moreover, injection of adenovirus expressing Cav1 into the gastrocnemius muscle of mice prevented DEX-induced atrophy. These results indicate that CAV1 is a critical regulator of muscle homeostasis, linking glucocorticoid signaling to the insulin signaling pathway, thereby providing a novel target for the prevention of glucocorticoid-induced muscle atrophy.
Search for other papers by Min Joo Kim in
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Innovative Research Institute for Cell Therapy, Seoul, Republic of Korea
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Innovative Research Institute for Cell Therapy, Seoul, Republic of Korea
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PERK is a pancreatic endoplasmic reticulum (ER) kinase. Its complete deletion in pancreatic β cells induces insulin deficiency; however, the effects of partial Perk suppression are unclear. We investigated the effect of partial PERK suppression using the specific PERK inhibitors GSK2606414 and GSK2656157. Low-dose GSK2606414 treatment for 24 h enhanced glucose-stimulated insulin secretion (GSIS), islet insulin content and calcium transit in mouse (at 40 nM) and human (at 50–100 nM) pancreatic islets. GSK2606414 also induced the expression of the ER chaperone BiP and the release of calcium from the ER. When Bip expression was inhibited using a Bip siRNA, the GSK2606414-induced augmentation of the ER calcium level, islet insulin contents, glucose-stimulated cytosolic calcium transit and GSIS were abrogated. In both wild-type and insulin-deficient Atg7-knockout mice, 8 weeks of GSK2656157 treatment enhanced GSIS and improved hyperglycemia without affecting body weight. In conclusion, partial PERK inhibition induced BiP expression in islets, increased glucose-stimulated calcium transit and islet insulin contents and enhanced GSIS, suggesting that low-dose PERK inhibitors could potentially be used to treat insulin deficiency.
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Dermcidin (DCD), an antimicrobial peptide that is secreted by sweat glands, is reportedly a human homolog of mouse proteolysis-inducing factor. This study was conducted to investigate the effect of DCD on body fat mobilization. The expression level of DCD in the livers of Ad-DCD-injected mice was higher than in those of Ad-β-galactosidase (Ad-β-gal)-injected mice 7 days after injection. In addition, injection with the Ad-DCD virus led to decreased body weight and epididymal fat mass when compared with controls. The plasma triglyceride level was decreased, whereas the free fatty acid and glycerol levels were increased in the Ad-DCD-injected group. Epididymal adipose tissues obtained from Ad-DCD-injected mice consisted of smaller adipocytes than tissues obtained from Ad-β-gal-injected mice. The gene expression profiles revealed an upregulation of hormone-sensitive lipase and adipose fatty acid-binding protein, both of which are involved in adipocyte lipolysis, in Ad-DCD-injected mice, and this lipolytic effect of DCD paralleled the increase of circulating tumor necrosis factor-α (TNF-α) level that was observed. The perilipin levels in adipose tissue were decreased in Ad-DCD-injected mice when compared with those of the control mice. Taken together, these results suggest that DCD-mediated body fat reduction might occur as a result of TNF-α-induced downregulation of perilipin in adipose tissue.
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Cysteamine (an aminothiol), which is derived from coenzyme A degradation and metabolized into taurine, has beneficial effects against cystinosis and neurodegenerative diseases; however, its role in diabetic complications is unknown. Thus, we sought to determine the preventive effect of cysteamine against hyperglycemia-induced vascular leakage in the retinas of diabetic mice. Cysteamine and ethanolamine, the sulfhydryl group-free cysteamine analogue, inhibited vascular endothelial growth factor (VEGF)-induced stress fiber formation and vascular endothelial (VE)-cadherin disruption in endothelial cells, which play a critical role in modulating endothelial permeability. Intravitreal injection of the amine compounds prevented hyperglycemia-induced vascular leakage in the retinas of streptozotocin-induced diabetic mice. We then investigated the potential roles of reactive oxygen species (ROS) and transglutaminase (TGase) in the cysteamine prevention of VEGF-induced vascular leakage. Cysteamine, but not ethanolamine, inhibited VEGF-induced ROS generation in endothelial cells and diabetic retinas. In contrast, VEGF-induced TGase activation was prevented by both cysteamine and ethanolamine. Our findings suggest that cysteamine protects against vascular leakage through inhibiting VEGF-induced TGase activation rather than ROS generation in diabetic retinas.
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C-peptide exerts protective effects against diabetic complications; however, its role in inhibiting hyperglycemic memory (HGM) has not been elucidated. We investigated the beneficial effect of C-peptide on HGM-induced vascular damage in vitro and in vivo using human umbilical vein endothelial cells and diabetic mice. HGM induced apoptosis by persistent generation of intracellular ROS and sustained formation of ONOO− and nitrotyrosine. These HGM-induced intracellular events were normalized by treatment with C-peptide, but not insulin, in endothelial cells. C-peptide also inhibited persistent upregulation of p53 and activation of mitochondrial adaptor p66shc after glucose normalization. Further, C-peptide replacement therapy prevented persistent generation of ROS and ONOO− in the aorta of diabetic mice whose glucose levels were normalized by the administration of insulin. C-peptide, but not insulin, also prevented HGM-induced endothelial apoptosis in the murine diabetic aorta. This study highlights a promising role for C-peptide in preventing HGM-induced intracellular events and diabetic vascular damage.
Asan Institute for Life Sciences, Seoul, Republic of Korea
Department of Cell and Developmental Biology, Dental Research Institute, Seoul National University, Seoul, Republic of Korea
Department of Thoracic and Cardiovascular Surgery, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Republic of Korea
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Asan Institute for Life Sciences, Seoul, Republic of Korea
Department of Cell and Developmental Biology, Dental Research Institute, Seoul National University, Seoul, Republic of Korea
Department of Thoracic and Cardiovascular Surgery, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Republic of Korea
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Asan Institute for Life Sciences, Seoul, Republic of Korea
Department of Cell and Developmental Biology, Dental Research Institute, Seoul National University, Seoul, Republic of Korea
Department of Thoracic and Cardiovascular Surgery, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Republic of Korea
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Asan Institute for Life Sciences, Seoul, Republic of Korea
Department of Cell and Developmental Biology, Dental Research Institute, Seoul National University, Seoul, Republic of Korea
Department of Thoracic and Cardiovascular Surgery, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Republic of Korea
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Asan Institute for Life Sciences, Seoul, Republic of Korea
Department of Cell and Developmental Biology, Dental Research Institute, Seoul National University, Seoul, Republic of Korea
Department of Thoracic and Cardiovascular Surgery, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Republic of Korea
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Asan Institute for Life Sciences, Seoul, Republic of Korea
Department of Cell and Developmental Biology, Dental Research Institute, Seoul National University, Seoul, Republic of Korea
Department of Thoracic and Cardiovascular Surgery, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Republic of Korea
Search for other papers by Yong Hee Kim in
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Asan Institute for Life Sciences, Seoul, Republic of Korea
Department of Cell and Developmental Biology, Dental Research Institute, Seoul National University, Seoul, Republic of Korea
Department of Thoracic and Cardiovascular Surgery, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Republic of Korea
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Asan Institute for Life Sciences, Seoul, Republic of Korea
Department of Cell and Developmental Biology, Dental Research Institute, Seoul National University, Seoul, Republic of Korea
Department of Thoracic and Cardiovascular Surgery, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Republic of Korea
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Growing evidence has shown a biochemical link between increased oxidative stress and reduced bone density. Although α-lipoic acid (α-LA) has been shown to act as a thiol antioxidant, its effect on bone cells has not been determined. Using proteomic analysis, we identified six differentially expressed proteins in the conditioned media of α-LA-treated human bone marrow stromal cell line (HS-5). One of these proteins, receptor activator of nuclear factor κB ligand (RANKL), was significantly up-regulated, as confirmed by immunoblotting with anti-RANKL antibody. ELISA showed that α-LA stimulated RANKL production in cellular extracts (membranous RANKL) about 5-fold and in conditioned medium (soluble RANKL) about 23-fold, but had no effect on osteoprotegerin (OPG) secretion. Despite increasing the RANKL/OPG ratio, α-LA showed a dose-dependent suppression of osteoclastogenesis, both in a coculture system of mouse bone marrow cells and osteoblasts and in a mouse bone marrow cell culture system, and reduced bone resorption in a dose-dependent manner. In addition, α-LA-induced soluble RANKL was not inhibited by matrix metalloprotease inhibitors, indicating that soluble RANKL is produced by α-LA without any posttranslational processing. In contrast, α-LA had no significant effect on the proliferation and differentiation of HS-5 cells. These results suggest that α-LA suppresses osteoclastogenesis by directly inhibiting RANKL–RANK mediated signals, not by mediating cellular RANKL production. In addition, our findings indicate that α-LA-induced soluble RANKL is not produced by shedding of membranous RANKL.
