CRF type 2 receptors mediate the metabolic effects of ghrelin in C2C12 cells

Abstract

Objective Ghrelin is known to regulate appetite control and cellular metabolism. The Corticotropin-Releasing Factor (CRF) family is also known to regulate energy balance. In this study, we investigated the links between ghrelin and the CRF family in C2C12 cells, a mouse myoblast cell line. Design and methods C2C12 cells were treated with ghrelin in the presence or absence of CRF receptor antagonists and then subjected to different metabolic analyses. Results Ghrelin enhanced glucose uptake by C2C12 cells, induced GLUT4 translocation to the cell surface and decreased RBP4 expression. A CRF-R2 selective antagonist, anti-sauvagine-30, blocked ghrelin-induced glucose uptake, Ghrelin upregulated CRF-R2 but not CRF-R1 levels. Moreover, ghrelin-treated C2C12 cells displayed a cAMP and pERK activation in response to Ucn3, a CRF-R2 specific ligand, but not in response to CRF or stressin, CRF-R1 specific ligands. Ghrelin also induced UCP2 and UCP3 expression, which were blocked by anti-sauvagine-30. Ghrelin did not induce fatty acids uptake by C2C12 cells or ACC expression. Even though C2C12 cells clearly exhibited responses to ghrelin, the known ghrelin receptor, GHSR1a, was not detectable in C2C12 cells. Conclusion Our results suggest that, ghrelin plays a role in regulating muscle glucose and, raise the possibility that suppression of the CRF-R2 pathway might provide benefits in high ghrelin states.

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.…”

“…Gershon et al. reported an increase in GLUT4 translocation and glucose uptake in C2C12 muscle cells treated for 24 h with AG (Gershon and Vale 2014). Other groups have reported no change in the phosphorylation of insulin signaling markers, such as AKT, in acute response to ghrelin administration (Vestergaard et al.…”

“…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.…”

“…Unacylated ghrelin (UnAG) is believed to act through an alternate receptor (Lear et al. 2010; Gershon and Vale 2014) in peripheral tissues such as muscle. Ghrelin's effects on peripheral glucose utilization have not been extensively studied and are unclear.…”

“…There is also some, albeit limited evidence for a direct effect of ghrelin on isolated muscle cells. In C2C12 myocytes, direct exposure to AG for 24 h increases GLUT4 translocation to the cell surface and glucose transport (Gershon and Vale 2014). However, to date there has been no examination of ghrelin's direct and isolated effect on glucose transport in mature, intact skeletal muscle.…”