We reported previously that IF chickens expressed lower IGF I and higher IGF IR mRNA in the gastrocnemius muscle on Day 14. Satellite cells isolated Baricitinib from the muscle showed similar responses with lower GHR, IGF 1 and higher IGF IR mRNA expression in the IF group. It was suggested that Inhibitors,Modulators,Libraries in chickens after hatching, hepatic gene expression of IGF I is GH dependent while muscu lar gene expression of IGF I is independent of GH and GHR. However, it is unknown whether IGF I ex pression in satellite cells is dependent on GHR. Here, expression of GHR and IGF I in satellite cells exhibited a similar pattern in response to feed restriction and re feeding, suggesting a possible regulatory link between these two genes. The role of the GHIGF I axis in the regulation of avian muscle growth remains obscure.

Inhibitors,Modulators,Libraries Growth hor mone can promote skeletal muscle satellite cell proli feration in vitro and in vivo, and modify GHR expression. Satellite cell proliferation was decreased in starved chicks along with a lower GHR gene expression, which were reversed with re feeding. IGF I stimulates the proliferation, and fusion of satellite cells in vitro. Inhibitors,Modulators,Libraries However, IGF I together with GH in culture showed no enhancement effect on DNA synthesis in chicken satellite cells. Since both myofibers and satellite cells are able to produce IGF I, the effects of paracrine and autocrine IGF I on satellite cell activity have to be considered, in addition to the role of endocrine IGF I. Recently, mechano growth factor E, derived from an isoform of IGF I, was reported to activate human muscle progenitor cells.

In addition to the GHIGF system, thyroid hormones were suggested to be involved in mediating the effect of nutrition on satellite cell function. Subcutaneous injections of T4 in rats would stimulate the number of total satellite cells and satellite cells per muscle fiber, while satellite cell numbers extracted from the hypothyroid Inhibitors,Modulators,Libraries rats were fewer and less active in prolifera tion and differentiation at the start of culture. How ever, it is unclear how expression of the thyroid hormone receptor in satellite Inhibitors,Modulators,Libraries cells responds to nutri tional status and thyroid hormone levels. We reported previously that serum concentrations of both T3 and T4 decreased with IF for 14 days in chicks. We observed a significant up regulation of TR mRNA expression in the IF group, which was completely restored with re feeding.

This up regulation of TR mRNA expression in satellite cells may represent a feedback regulation through decreased serum thyroid hormone levels. How ever, the TR mRNA expression in satellite cells was not coinciding with the viability of satellite cells. It is speculated that the thyroid hormone except recep tor activity, which determines the sensitivity of the satel lite cells to T3, may be blunted.