Syndecan‐4 influences mammalian myoblast proliferation by modulating myostatin signalling and G1/S transition

Abstract

Myostatin, a TGF‐β superfamily member, is a negative regulator of muscle growth. Here we describe how myostatin activity is regulated by syndecan‐4, a ubiquitous transmembrane heparan sulfate proteoglycan. During muscle regeneration the levels of both syndecan‐4 and promyostatin decline gradually after a sharp increase, concurrently with the release of mature myostatin. Promyostatin and syndecan‐4 co‐immunoprecipitate, and the interaction is heparinase‐sensitive. ShRNA‐mediated silencing of syndecan‐4 reduces C2C12 myoblast proliferation via blocking the progression from G1‐ to S‐phase of the cell cycle, which is accompanied by elevated levels of myostatin and p21(Waf1/Cip1), and decreases in cyclin E and cyclin D1 expression. Our results suggest that syndecan‐4 functions as a reservoir for promyostatin regulating the local bioavailability of mature myostatin.

Syndecan-4 Modulates Cell Polarity and Migration by Influencing Centrosome Positioning and Intracellular Calcium Distribution

“…Other studies observed reduced motility following syndecan-4 knockdown in different cell types, consistent with our current observations, whereas high syndecan-4 level promoted migration (Toba-Ichihashi et al, 2016;Yin et al, 2017;Jeyarajah et al, 2019). Previous analyses of C2C12 mouse myoblast cells revealed that syndecan-4 was the most prominent heparan sulfate proteoglycan in these cells when compared with syndecan-1, syndecan-2, syndecan-3, glypican, or perlecan (Keller-Pinter et al, 2018), thus suggesting an important role for syndecan-4 in this cell type. However, the observed upregulation of syndecan-1, syndecan-2, and syndecan-3 mRNAs after syndecan-4 silencing (Keller-Pinter et al, 2018) suggests that other members of the syndecan family may compensate at least partially for the loss of syndecan-4.…”

“…Although syndecan-4 knockout mice cannot regenerate damaged muscle tissue (Cornelison et al, 2004), the details of the underlying mechanism remain unknown. Previously, we reported that syndecan-4 affects myoblast proliferation by modulating myostatin signaling and the G1/S transition in cell cycle (Keller-Pinter et al, 2018), and directional persistence of random cell migration is affected by syndecan-4-mediated Tiam-1 expression and distribution (Becsky et al, 2020). In this study, we demonstrated that syndecan-4 knockdown induced nanoscale alterations in the lamellipodial actin fiber structure of migrating myoblasts.…”

“…Syndecans, a family of transmembrane proteoglycans, have been reported to play crucial roles in tissue regeneration (Chung et al, 2016). We demonstrated previously that syndecan-4 could influence myoblast proliferation, as syndecan-4 silencing reduced cell cycle progression from the G1 to the S phase and reduced the formation of mature myostatin, a negative regulator of muscle growth (Keller-Pinter et al, 2018). Syndecan-4 knockout mice also exhibited a decreased capacity for skin wound repair and angiogenesis (Echtermeyer et al, 2001), as well as inability to regenerate skeletal muscle following cardiotoxin-induced muscle necrosis (Cornelison et al, 2004).…”

Myoblast Migration and Directional Persistence Affected by Syndecan-4-Mediated Tiam-1 Expression and Distribution

“…It is noteworthy that the direct relationship between the syndecan-4 coordinated persistent migration and the Tiam1-mediated Rac1 activation remains unknown. Earlier, we reported that syndecan-4 binds and inhibits Tiam1, modulating the activity of Rac1 GTPase [24]. Thus, the syndecan-4-Tiam1 complex can regulate the local activity of Rac1.…”

“…We verified the effect of syndecan-4 (SDC4) silencing by qPCR technique and Western blotting in C2C12 mouse myoblast cell lines transfected stably with plasmids expressing shRNA specific for syndecan-4 (shSDC4#1 and shSDC4#2), and we also tested the effect of the scrambled sequence [24]. The syndecan-4 expression was significantly decreased in both shSDC4#1 and shSDC4#2 cell lines, with the reduction being less in the latter; whereas the scrambled sequence did not affect the syndecan-4 level [24].…”