mTOR is necessary for proper satellite cell activity and skeletal muscle regeneration

Abstract

The serine/threonine kinase mammalian target of rapamycin (mTOR) is a key regulator of protein synthesis, cell proliferation and energy metabolism. As constitutive deletion of Mtor gene results in embryonic lethality, the function of mTOR in muscle stem cells (satellite cells) and skeletal muscle regeneration remains to be determined. In this study, we established a satellite cell specific Mtor conditional knockout (cKO) mouse model by crossing Pax7CreER and Mtorflox/flox mice. Skeletal muscle regeneration after injury was severely compromised in the absence of Mtor, indicated by increased number of necrotic myofibers infiltrated by Evans blue dye, and reduced number and size of regenerated myofibers in the Mtor cKO mice compared to wild type (WT) littermates. To dissect the cellular mechanism, we analyzed satellite cell-derived primary myoblasts grown on single myofibers or adhered to culture plates. The Mtor cKO myoblasts exhibited defective proliferation and differentiation kinetics when compared to myoblasts derived from WT littermates. At the mRNA and protein levels, the Mtor cKO myoblasts expressed lower levels of key myogenic determinant genes Pax7, Myf5, Myod, Myog than did the WT myoblasts. These results suggest that mTOR is essential for satellite cell function and skeletal muscle regeneration through controlling the expression of myogenic genes.

A novel bioreactor for the generation of highly aligned 3D skeletal muscle-like constructs through orientation of fibrin via application of static strain

“…This might account for the global increase of Pax7 expression between day 0 and day 3 of culture in all treatment groups. The increase in MyoD expression that is observed between day 0 and day 3 in all groups supports this theory, as proliferating satellite cells are characterized by co-expression of MyoD and Pax7 [81]. Additionally, it has been demonstrated that, even in immortalized cell lines such as C2C12, not all cells undergo myogenic differentiation as a subset remains in quiescence [82].…”

The Mechanistic Target of Rapamycin: The Grand ConducTOR of Metabolism and Aging

“…These cells are a small fraction of the muscle cells in a tissue, but can be studied in vivo after muscle damage or ex vivo in culture proliferation and differentiation models. The mTOR pathway has a stimulatory role at several steps in the differentiation process of satellite cells and a full description is beyond the scope of this review (Rodgers et al, 2014; Schiaffino et al, 2013; Zhang et al, 2015). Continued studies of the role of mTOR in muscle are important given that the signaling pathway is critical in both the metabolic functions of differentiated fibers, as well as regeneration of new ones.…”

Heat therapy promotes the expression of angiogenic regulators in human skeletal muscle

“…Approximately 30 mg of tissue was used for RNA extraction using the TRIzol Reagent (Invitrogen, Life Technologies), according to manufacturer's instructions. The quality and concentration of total RNA were measured by a spectrophotometer (Nanodrop 3000, ThermoFisher), as described previously (84). cDNA was prepared using the RT 2 first strand kit following the manufacturer's instructions (Qiagen, Valencia, CA).…”