Skeletal muscle regeneration is delayed by reduction in Xin expression: consequence of impaired satellite cell activation?

Abstract

Xin is a striated muscle-specific actin-binding protein whose mRNA expression has been observed in damaged skeletal muscle. Here we demonstrate increased Xin protein expression early postinjury (≤ 12 h) and localization primarily to the periphery of damaged myofibers. At 1 day postinjury, Xin is colocalized with MyoD, confirming expression in activated satellite cells (SCs). By 5 days postinjury, Xin is evident in newly regenerated myofibers, with a return to preinjury levels by 14 days of regeneration. To determine whether the increased Xin expression is functionally relevant, tibialis anterior muscles of wild-type mice were infected with Xin-short hairpin RNA (shRNA) adenovirus, whereas the contralateral tibialis anterior received control adenovirus (Control). Four days postinfection, muscles were harvested or injured with cardiotoxin and collected at 3, 5, or 14 days thereafter. When compared with Control, Xin-shRNA infection attenuated muscle regeneration as demonstrated by Myh3 expression and fiber areas. Given the colocalization of Xin and MyoD, we isolated single myofibers from infected muscles to investigate the effect of silencing Xin on SC function. Relative to Control, SC activation, but not proliferation, was significantly impaired in Xin-shRNA-infected muscles. To determine whether Xin affects the G0-G1 transition, cell cycle reentry was assessed on infected C2C12 myoblasts using a methylcellulose assay. No difference in reentry was noted between groups, suggesting that Xin contributes to SC activation by means other than affecting G0-G1 transition. Together these data demonstrate a critical role for Xin in SC activation and reduction in Xin expression results in attenuated skeletal muscle repair.

Fad24, a Positive Regulator of Adipogenesis, Is Required for S Phase Re-entry of C2C12 Myoblasts Arrested in G0 Phase and Involved in p27^Kip1 Expression at the Protein Level

“…Finally, larger myotubes were formed in the regenerating regions at day 14 after CTX injection, suggesting that the skeletal muscle injury caused by CTX was repaired. In agreement with these results, the expression level of myogenic nuclear factor myoD, which has an important role in the proliferation of satellite cells in an adult skeletal muscle, increased after CTX injection as described previously 15,19) (Fig. 1B).…”

Decreased Satellite Cell Number and Function in Humans and Mice With Type 1 Diabetes Is the Result of Altered Notch Signaling

“…Single muscle fibers were obtained from Akita and WT mice at 12 weeks of age (8 weeks of diabetes) from the left and right extensor digitorum longus and peroneus muscles, as previously described (15). Fibers were fixed immediately after isolation (referred to as Control fibers) or placed in culture dishes with plating media (10% normal horse serum, 0.5% chick embryo extract in DMEM) overnight (18 h; referred to as Activated fibers).…”

“…SC activation was assessed in floating cultures by adding 10 mmol/L BrdU to the plating media and incubating newly isolated single fibers for 24 h. Fibers were fixed and stained for BrdU (Abcam, Cambridge, MA), as previously described (15). SCs that became activated and entered the cell cycle incorporated BrdU.…”

HMGB2 regulates satellite-cell-mediated skeletal muscle regeneration through IGF2BP2

“…Previous studies have demonstrated that all of them are validated for use (Aguilera et al, 2011;Averous et al, 2012;Della Pietra et al, 2015;Dixon et al, 2011;Gong et al, 2015;Kim et al, 2011;Li et al, 2012;Murphy et al, 2011;Nissar et al, 2012;Rao et al, 2014;Sarkar and Zohn, 2012;Takeda et al, 2014;Tan et al, 2011;Taniguchi et al, 2011;Wu et al, 2010;Zhang et al, 2011).…”