Ghrelin regulates proliferation and differentiation of osteoblastic cells

Abstract

It has previously been reported that growth hormone secretagogues (GHS) may have a role in the regulation of bone metabolism in animals and humans. In this study we evaluated the effect of ghrelin, the endogenous ligand of GHS receptors, on the proliferation rate and on osteoblast activity in primary cultures of rat calvaria osteoblasts. In the same experiments, we compared the effects of ghrelin with those of hexarelin (HEXA) and EP-40737, two synthetic GHS with different characteristics. Both ghrelin and HEXA (10 11 -10 8 M) significantly stimulated osteoblast proliferation at low concentrations (10 10 M). Surprisingly, EP-40737 demonstrated an antiproliferative effect at 10 9 -10 8 M, whereas lower concentrations had no effect on cell proliferation. Ghrelin and HEXA significantly increased alkaline phosphatase (ALP) and osteocalcin (OC) production. At variance with these peptides, EP-40737 did not significantly stimulate ALP and OC. The mRNA for GHS-R1a receptors and the corresponding protein were detected in calvarial osteoblasts by RT-PCR and Western blot respectively, indicating that ghrelin and GHS may bind and activate this specific receptor. We conclude that endogenous ghrelin and synthetic GHS modulate proliferation and differentiation of rat osteoblasts, probably by acting on their specific receptor.

AMP-activated protein kinase pathway and bone metabolism

“…Adiponectin, which increases osteoblast proliferation and differentiation (Oshima et al 2005) but has controversial effect on bone mass in vivo (Williams et al 2009), can stimulate AMPK phosphorylation in MC3T3-E1 osteoblastic cells (Kanazawa et al 2007). We showed that AMPK phosphorylation and activity in ROS17/2.8 cells was stimulated by ghrelin (Shah et al 2010), a hormone known to stimulate osteoblast differentiation and function (Maccarinelli et al 2005, van der Velde et al 2008. Dexamethasone, a synthetic glucocorticoid that has been shown to induce osteoblastic differentiation and bone formation in several culture systems (Delany et al 1994), stimulates AMPK phosphorylation in primary osteoblasts (unpublished results, M Shah, J Jeyabalan, B Viollet & C Chenu).…”

“…The bone loss in age-related osteoporosis is associated with more adipogenesis and less bone formation (Pei & Tontonoz 2004). Second, there are direct actions on bone of hormones produced by adipocytes, such as adiponectin and leptin, as well as of hormones released by the pancreas, gut and pituitary (Cornish et al 1996, Maccarinelli et al 2005, Williams et al 2009). In addition, the recent discovery that leptin can inhibit bone formation through hypothalamic and sympathetic nervous system relays , Takeda et al 2002, Elefteriou et al 2005 has demonstrated that bone can not only be directly affected by hormones which have receptors on bone cells, but can also be influenced by the same hormones acting on receptors in the central nervous system (CNS).…”

Ghrelin Levels in Patients with Rickets

“…Previous studies have reported a significant stimulation of osteoblast proliferation and an increased ALP activity in osteoblasts in response to ghrelin (7,17,18). Ghrelin stimulates growth hormone secretion both in vivo and in vitro, and may therefore have a positive effect on bone.…”

Ghrelin, des-acyl ghrelin and obestatin: Three pieces of the same puzzle

“…Ghrelin stimulates the proliferation and inhibits apoptosis of the H9c2 cardiomyocyte cell line [4], human adrenal zona glomerulosa cells [101], preadipocytes [76], osteoblastic cells [96] and pancreatic beta-cells [59] and rat fetal spinal cord [126] and skin cells [108]. Thus, peripheral actions of ghrelin result not only from modulation of function, but also from regulation of survival/proliferation of target cells.…”