Ghrelin and Des-Acyl Ghrelin Promote Differentiation and Fusion of C2C12 Skeletal Muscle Cells

Abstract

Ghrelin is an acylated peptidyl gastric hormone acting on the pituitary and hypothalamus to stimulate appetite, adiposity, and growth hormone release, through activation of growth hormone secretagogue receptor (GHSR)-1a receptor. Moreover, ghrelin features several activities such as inhibition of apoptosis, regulation of differentiation, and stimulation or inhibition of proliferation of several cell types. Ghrelin acylation is absolutely required for both GHSR-1a binding and its central endocrine activities. However, the unacylated ghrelin form, des-acyl ghrelin, which does not bind GHSR-1a and is devoid of any endocrine activity, is far more abundant than ghrelin in plasma, and it shares with ghrelin some of its cellular activities. In here we show that both ghrelin and des-acyl ghrelin stimulate proliferating C2C12 skeletal myoblasts to differentiate and to fuse into multinucleated myotubes in vitro through activation of p38. Consistently, both ghrelin and des-acyl ghrelin inhibit C2C12 proliferation in growth medium. Moreover, the ectopic expression of ghrelin in C2C12 enhances differentiation and fusion of these myoblasts in differentiation medium. Finally, we show that C2C12 cells do not express GHSR-1a, but they do contain a common high-affinity binding site recognized by both acylated and des-acylated ghrelin, suggesting that the described activities on C2C12 are likely mediated by this novel, yet unidentified receptor for both ghrelin forms.

Ghrelin Gene Products in Acute and Chronic Inflammation

“…Both peptides promote the differentiation of skeletal myoblasts, preadipocytes, and embryonic stem cells toward cardiomyocytes (Filigheddu et al 2007;Gao et al 2012Gao et al , 2013Giovambattista et al 2008;Miegueu et al 2011). Moreover, they affect, either positively or negatively, proliferation of numerous cell types including osteoblasts, pancreatic b cells, islets and islet microendothelial cells, myoblasts, and adrenocortical tumor cells (Delhanty et al 2006(Delhanty et al , 2007Favaro et al 2012;Filigheddu et al 2007;Granata et al 2007).…”

“…Since unacylated ghrelin shares with ghrelin common high affinity binding sites in various cell lines, including cells lacking GHS-R1a (Baldanzi et al 2002;Cassoni et al 2001Cassoni et al , 2004Filigheddu et al 2007;Granata et al 2007;Jeffery et al 2002;Muccioli et al 2004), and they share biological activities in vivo, also in Ghsr null mice (Porporato et al 2013), both peptides act in all probability through a common, although yet unidentified, receptor.…”

Acylated and unacylated ghrelin do not directly stimulate glucose transport in isolated rodent skeletal muscle

“…Rather, AG is thought to potentially interact with the corticotropin‐releasing factor (CRF‐2) receptor in muscle (Filigheddu et al. 2007; Gershon and Vale 2014), while UnAG does not have an identified receptor, although it is not a ligand for GHS‐R1a and has been shown to have metabolic effects in peripheral tissues distinct from AG (Filigheddu et al. 2007; Lear et al.…”

“…2007; Gershon and Vale 2014), while UnAG does not have an identified receptor, although it is not a ligand for GHS‐R1a and has been shown to have metabolic effects in peripheral tissues distinct from AG (Filigheddu et al. 2007; Lear et al. 2010).…”

“…Acylated ghrelin (AG) acts through GHS‐R1a in nonmuscle peripheral tissues, and potentially the corticotropin‐releasing factor (CRF‐2) receptor in muscle (Filigheddu et al. 2007; Gershon and Vale 2014). Unacylated ghrelin (UnAG) is believed to act through an alternate receptor (Lear et al.…”