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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.
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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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The steroid hormone, estrogen, plays an important role in various physiological events which are mediated via its nuclear estrogen receptors, ERalpha and ERbeta. However, the molecular mechanisms that are regulated by estrogen in the uterus remain largely unknown. To identify genes that are regulated by estrogen, the ovariectomized mouse uterus was exposed to 17beta-estradiol (E2) for 6 h and 12 h, and the data were analyzed by cDNA microarray. The present study confirms previous findings and identifies several genes with expressions not previously known to be influenced by estrogen. These genes include small proline-rich protein 2A, receptor-activity-modifying protein 3, inhibitor of DNA binding-1, eukaryotic translation initiation factor 2, cystatin B, decorin, secreted frizzled-related protein 2, integral membrane protein 2B and chemokine ligand 12. The expression patterns of several selected genes identified by the microarray analysis were confirmed by RT-PCR. In addition, laser capture microdissection (LCM) was conducted to determine the expression of selected genes in specific uterine cell types. Analysis of early and late responsive genes using LCM and cDNA microarray not only suggests direct and indirect effects of E2 on uterine physiological events, but also demonstrates differential regulation of E2 in specific uterine cell types. These results provide a basic background on global gene alterations or genetic pathways in the uterus during the estrous cycle and the implantation period.
