Pannexin 1 and pannexin 3 channels regulate skeletal muscle myoblast proliferation and differentiation.
Bottom Line: Using HSMM, we found that Panx1 expression promotes this process, whereas it was impaired in the presence of probenecid or carbenoxolone.As for Panx3, its lower molecular weight species were prominent in adult skeletal muscle but very low in the fetal tissue and in undifferentiated skeletal muscle cells and myoblasts.On the other hand, a ∼70-kDa immunoreactive species of Panx3, likely glycosylated, sialylated, and phosphorylated, was highly expressed in proliferative myoblasts but strikingly down-regulated during their differentiation.
Affiliation: From the Department of Surgery, Division of Paediatric Surgery, University of Ottawa, Children's Hospital of Eastern Ontario, Ottawa, Ontario K1H 8L1, Canada, Apoptosis Research Center, Children's Hospital of Eastern Ontario, Ottawa, Ontario K1H 8L1, Canada.Show MeSH
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Mentions: In addition to their differential expression in fetal versus adult skeletal muscle tissue, we also show here that Panx levels are regulated during skeletal muscle myoblast differentiation in vitro. During development, embryonic muscle mass increases predominantly by proliferative growth of myoblasts that differentiate to eventually generate fully differentiated myofibers in adults. Skeletal muscle terminal differentiation is a temporally ordered process that follows an organized sequence of events including commitment, cell cycle withdrawal, expression of muscle-specific proteins, and myoblast fusion to form multinucleated myotubes (34). Our results clearly demonstrated that both Panx1 and Panx3 regulate skeletal muscle myoblast differentiation and proliferation, which are summarized in our proposed model in Fig. 10. Indeed, we have found that the levels of Panx1 are very low in undifferentiated and proliferative skeletal muscle myoblasts but increased drastically during their differentiation. Accordingly, its overexpression accelerated skeletal muscle myoblast differentiation through a process that likely involves its channel functions but did not regulate myoblast proliferation. As for Panx3, its lower molecular weight form was not detected or was below detectable levels in both undifferentiated and differentiated HSMM but was expressed in human skeletal muscle tissue, which may suggest that it is expressed further along the differentiation process. This form was also more abundant in adult versus fetal skeletal muscle tissue. When overexpressed in HSMM, it promoted their differentiation and inhibited their proliferation, suggesting that it may play a role in maintaining the skeletal muscle myoblasts in a differentiated and non-proliferative state. On the other hand, the ∼70-kDa immunoreactive species of Panx3 was found highly expressed in undifferentiated HSMM. Its levels were drastically down-regulated during differentiation, and its knockdown significantly inhibited HSMM proliferation, which may thus suggest a role in keeping the undifferentiated skeletal muscle myoblasts in a proliferative state. Altogether, our results thus indicate that various species of Panx1 and Panx3 are expressed in skeletal muscle tissue and that they differentially regulate skeletal muscle myoblast differentiation and proliferation.
Affiliation: From the Department of Surgery, Division of Paediatric Surgery, University of Ottawa, Children's Hospital of Eastern Ontario, Ottawa, Ontario K1H 8L1, Canada, Apoptosis Research Center, Children's Hospital of Eastern Ontario, Ottawa, Ontario K1H 8L1, Canada.