miR-431 promotes differentiation and regeneration of old skeletal muscle by targeting Smad4

Abstract

The myogenic capacity of myoblasts decreases in skeletal muscle with age. In addition to environmental factors, intrinsic factors are important for maintaining the regenerative potential of muscle progenitor cells, but their identities are largely unknown. Here, comparative analysis of microRNA (miRNA) expression profiles in young and old myoblasts uncovered miR-431 as a novel miRNA showing markedly reduced abundance in aged myoblasts. Importantly, elevating miR-431 improved the myogenic capacity of old myoblasts, while inhibiting endogenous miR-431 lowered myogenesis. Bioinformatic and biochemical analyses revealed that miR-431 directly interacted with the 3 ′ untranslated region (UTR) of Smad4 mRNA, which encodes one of the downstream effectors of TGF-β signaling. In keeping with the low levels of miR-431 in old myoblasts, SMAD4 levels increased in this myoblast population. Interestingly, in an in vivo model of muscle regeneration following cardiotoxin injury, ectopic miR-431 injection greatly improved muscle regeneration and reduced SMAD4 levels. Consistent with the finding that the mouse miR-431 seed sequence in the Smad4 3 ′ UTR is conserved in the human SMAD4 3 ′ UTR, inhibition of miR-431 also repressed the myogenic capacity of human skeletal myoblasts. Taken together, our results suggest that the age-associated miR-431 plays a key role in maintaining the myogenic ability of skeletal muscle with age.

Smad4 restricts differentiation to promote expansion of satellite cell derived progenitors during skeletal muscle regeneration

“…Consistent with previous reports, Smad4 disruption did promote myogenic terminal commitment (Dey et al, 2012; Ono et al, 2011; Lee et al, 2015). However, declines in proliferating SCs and MPs during regeneration were also observed.…”

“…Previous studies have shown that knockdown of Smad4 or TGFβ superfamily ligand supplementation in myogenic cells is able to promote or impair terminal myogenic commitment, respectively (Ono et al, 2011; Dey et al, 2012; Lee et al, 2015; Trendelenburg et al, 2009). To examine the terminal myogenic fate decisions of Smad4-deficient SCs, FACs-purified adult P7:S4KO and Ctl SCs and MPs were cultured for 96 hr in plating media (10% horse serum, FGF2, DMEM), and supplemented with vehicle, TGFβ1, or BMP4 ligands (Chakkalakal et al, 2012, 2014; Zammit et al, 2004).…”

“…Furthermore, non-specific knockdown of Smad4 through siRNAs or viral delivery of shRNAs to regenerating aged skeletal muscle promotes myofiber hypertrophy (Dey et al, 2012; Lee et al, 2015). Therefore, we sought to examine whether specific disruption of Smad4 in aged SCs could promote aged skeletal muscle regeneration, presumably in an environment of high TGFβ ligand activity, suggesting that the implications of signaling loss could differ from results observed in adult mice.…”

“…In myogenic culture systems derived from immortalized cell lines or using sequential pre-plate techniques, knockdown of Smad4 promotes myogenic differentiation (Dey et al, 2012; Ono et al, 2011). Furthermore, global reduction of expression through direct intramuscular injection of Smad4 siRNAs or viral vectors with Smad4 shRNAs into injured mouse skeletal muscle can promote the formation of larger regenerated muscle fibers relative to controls (Dey et al, 2012; Lee et al, 2015). However, given that multiple non-myogenic cell types, such as inflammatory cells and fibro/adipogenic progenitors, also contribute to SC and MP fate decisions during skeletal muscle regeneration; It is unclear which cellular mechanisms promote hypertrophy of regenerated myofibers with non-targeted Smad4 loss.…”

SASP regulation by noncoding RNA

“…Through this broad impact on gene expression, microRNAs can regulate diverse physiologic processes such as embryonic development and cell proliferation, differentiation, and apoptosis [41–45]. Many microRNAs have also been implicated in pathological conditions including cancer, diabetes, cardiovascular disease, neurodegeneration, and immune diseases [46–48].…”