Effect of transforming growth factor-β1 on decorin expression and muscle morphology during chicken embryonic and posthatch growth and development

Abstract

During skeletal muscle development, transforming growth factor-β1 (TGF-β1) is a potent inhibitor of muscle cell proliferation and differentiation, as well as a regulator of extracellular matrix (ECM) production. Decorin, a member of the small leucine-rich ECM proteoglycans, binds to TGF-β1 and modulates TGF-β1-dependent cell growth stimulation or inhibition. The expression of decorin can be regulated by TGF-β1 during muscle proliferation and differentiation. How TGF-β1 affects decorin and muscle growth, however, has not been well documented in vivo. The present study investigated the effect of TGF-β1 on decorin expression and intracellular connective tissue development during skeletal muscle growth. Exogenous TGF-β1 significantly decreased the number of myofibers in a given area at both 1 d and 6 wk posthatch. The TGF-β1-treated muscle had a significant decrease in decorin mRNA expression at embryonic day (ED) 10, whereas protein amounts decreased at 17 ED and 1 d posthatch compared to the control muscle. Decorin was localized in both the endomysium and perimysium in the control pectoralis major muscle. Transforming growth factor-β1 reduced decorin in both the endomysium and perimysium from 17 ED to 6 wk posthatch. Compared to the control muscle, the perimysium space in the pectoralis major muscle was dramatically decreased by TGF-β1 during embryonic development through posthatch growth. Because decorin regulates collagen fibrillogenesis, a major component of the ECM, the reduction of decorin by TGF-β1 treatment may cause the irregular formation of collagen fibrils, leading to the decrease in endomysium and perimysium space. The results from the current study suggest that the effect of TGF-β1 on decorin expression and localization was likely associated with altered development of the perimysium and the regulation of muscle fiber development.