SMAD2 Promotes Myogenin Expression and Terminal Myogenic Differentiation

Abstract

SMAD2 is a transcription factor whose activity is regulated by members of the Transforming Growth Factor beta (TGFβ) superfamily. While activation of SMAD2 and SMAD3 downstream of TGFβ or myostatin signaling is known to inhibit myogenesis, we find that SMAD2 in the absence of TGFβ signaling promotes terminal myogenic differentiation. We find that during myogenic differentiation, SMAD2 expression is induced. Knockout of SMAD2 expression in primary myoblasts did not affect the efficiency of myogenic differentiation but produced smaller myotubes with reduced expression of the terminal differentiation marker myogenin. Conversely, overexpression of SMAD2 stimulated myogenin expression, and enhanced both differentiation and fusion, and these effects were independent of classical activation by the TGFβ receptor complex. Loss of Smad2 in muscle satellite cells in vivo resulted in decreased muscle fiber caliber and impaired regeneration after acute injury. Taken together, we demonstrate that SMAD2 is an important positive regulator of myogenic differentiation, in part through the regulation of Myog.

Single-cell chromatin accessibility profiling reveals a self-renewing muscle satellite cell state

“…Upon activation of their receptors by members of the TGFβ superfamily, Smad4 forms heterodimers with one of the five R-Smads in the cytosol and together they are translocated to the nucleus to bind to their target genes ( Massagué, 2008 ). The function of SMADs, including SMAD4, has been studied in the processes of myoblast proliferation and differentiation ( Yanagisawa et al, 2011 ; Ono et al, 2011 ; Cohen et al, 2015 ; Lamarche et al, 2020 ; Paris et al, 2016 ; Stantzou et al, 2017 ). Nevertheless, whether and how the SMADs proteins causally regulate MuSC self-renewal was unknown.…”

Identification of a self-renewing muscle satellite cell state by single-cell chromatin accessibility profiling

“…Among the eight known Smad proteins in mammals, Smad4 is unique in that it functions as an indispensable Co-Smad for five R-Smads (receptor-regulated Smads, i.e., Smad1, 2, 3, 5, and 8): upon activation of their receptors by members of the TGFβ superfamily, Smad4 forms heterodimers with one of the five R-Smads in the cytosol and together they are translocated to the nucleus to bind to their target genes 48 . The function of SMADs, including SMAD4, has been studied in the processes of myoblast proliferation and differentiation [49][50][51][52][53][54] . Nevertheless, whether and how the SMADs proteins causally regulates MuSC self-renewal was unknown.…”

“…Intriguingly, the expression of TGFBR3 protein coincides with the decreased SMAD2/3 activity, indicated by less enriched binding motif of SMAD2/3 in the open chromatin sequences of the selfrenewing population. Although activation of SMAD2/3 via TGFβ or myostatin signaling inhibits myogenesis 55,56 , recent studies reported that SMAD2 and SMAD3 can promote myogenic differentiation independent of TGFβ signaling 52,[57][58][59] . Particularly, SMAD2 is identified as an important positive regulator of myogenic differentiation by driving Myog expression 52 .…”

“…Although activation of SMAD2/3 via TGFβ or myostatin signaling inhibits myogenesis 55,56 , recent studies reported that SMAD2 and SMAD3 can promote myogenic differentiation independent of TGFβ signaling 52,[57][58][59] . Particularly, SMAD2 is identified as an important positive regulator of myogenic differentiation by driving Myog expression 52 . These results suggested that in the early activated MuSCs engaged in self-renewal, the inactivation of SMAD2/3 could potentially block the myogenic differentiation fate to enable self-renewal.…”

Techniques, challenges and future prospects for cell-based meat

“…Because features, structure, and nutrient content, such as proteins, fatty acids, and vitamins, are signi cantly impacted by cell maturity, the maturity degree of the produced nal cells is a critical assessment criterion at this stage (Wuyi, 2019). Although muscle stem cells are thought to have a high potential for myogenic differentiation, the diameter, length, and protein content of ex vivo generated myo bers vary considerably depending on the culture conditions and may be substantially lower than actual muscle bers (Braga et al, 2017;Lamarche et al, 2021;Park et al, 2016).…”