Upregulation of gene encoding adipogenic transcriptional factors C/EBPalpha and PPARgamma2 in denervated muscle.
Muscle denervation induces fatty degeneration in skeletal muscle. However, the possible mechanism(s) remains to be elucidated. To gain insight into the regulation of this process, this study was designed to characterize the expression pattern of genes encoding transcriptional factors that regulate adipogenesis and the terminal differentiation marker of adipocytes in denervated muscle. Female mice underwent surgery to transect the sciatic nerve, and then the gastrocnemius muscles were harvested 5, 10, 20 or 30 days after surgery. The extent of fatty degeneration was assessed as lipid accumulation by Oil Red O staining. The cellular localization of CCCAT/enhancer-binding protein alpha (C/EBPalpha) and peroxisome proliferator-activated receptor gamma2 (PPARgamma2), which play an important role in the regulation of adipocyte differentiation, was assessed by immunohistochemistry. The mRNA levels were analysed using a real-time polymerase chain reaction. After muscle denervation, most muscle fibres atrophied pathologically, and lipid accumulation was observed in the superficial region of the gastrocnemius muscle, suggesting that fatty degeneration occurs in this model. Both C/EBPalpha and PPARgamma2 proteins were observed in the interstitial space of denervated muscle but detected in small amounts in normal muscle. The expression levels of C/EBPalpha and PPARgamma2 were significantly upregulated 30 days after muscle denervation. The expression levels of fatty acid binding protein 4 (FABP4), which reflects fatty acid metabolism, were decreased slightly at 5 and 10 days and then returned to control levels 30 days after muscle denervation. These findings suggest that muscle denervation-induced fatty degeneration may be mediated through C/EBPalpha and PPARgamma2.
Wagatsuma
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Department of Biochemical Sciences, National Institute of Fitness and Sports, 1 Shiromizu, Kanoya, Kagoshima 891-2393, Japan. waga@nifs-k.ac.jp