The Endogenous Growth Hormone Secretagogue (Ghrelin) Is Synthesized and Secreted by Chondrocytes

J. E. Caminos, O. Gualillo, F. Lago, M. Otero, M. Blanco, R. Gallego, T. Garcia-Caballero, M. B. Goldring, F. F. Casanueva, J. J. Gomez-Reino, C. Dieguez
2005 Endocrinology  
Ghrelin, the endogenous ligand for the growth hormone secretagogue receptor (GHS-R), is a recently isolated hormone, prevalently expressed in stomach but also in other tissues such as hypothalamus and placenta. This novel acylated peptide acts at a central level to stimulate growth hormone secretion and, notably, to regulate food intake. However, the existence of further, as yet unknown, effects or presence of ghrelin in peripheral tissues cannot be ruled out. In this report, we provide clear
more » ... idence for the expression of ghrelin peptide and mRNA in human, mouse and rat chondrocytes. Immunoreactive ghrelin was identified by immunohistochemistry in rat cartilage, being localised prevalently in proliferative and maturative zone of the epiphyseal growth plate, and in mouse and human chondrocytic cell lines. Moreover, ghrelin mRNA was detected by RT-PCR and confirmed by Southern analysis in rat cartilage as well as in mouse and human chondrocytes cell lines. Ghrelin mRNA expression has been studied in rat along early life development showing a stable profile of expression throughout. Although ghrelin expression in chondrocytes suggests the presence of an unexpected autocrine/paracrine pathway, we failed to identify the functional growth hormone secretagogue receptor (GHS-R) type 1A by RT-PCR. On the other hand, binding analysis with 125 I ghrelin suggests the presence of specific receptors different from the 1A isotype. Scatchard analysis revealed the presence of two receptors with respectively high and low affinity. Finally, ghrelin, in vitro, was able to significantly stimulate cAMP production and inhibits chondrocytes metabolic activity both in human and murine chondrocytes. In addition ghrelin is able to actively decrease both spontaneous or insulin-induced long chain fatty acid uptake in human and mouse chondrocytes. This study is the first to provide evidence for the presence of this novel peptide in chondrocytes and suggests novel potential roles for this new recognised component of the GH axis in cartilage metabolism.
doi:10.1210/en.2004-1379 pmid:15576457 fatcat:okzhusmwnraifb5vclfrmx7eme