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PMID:16394173

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Citation

Delhanty, PJ, van der Eerden, BC, van der Velde, M, Gauna, C, Pols, HA, Jahr, H, Chiba, H, van der Lely, AJ and van Leeuwen, JP (2006) Ghrelin and unacylated ghrelin stimulate human osteoblast growth via mitogen-activated protein kinase (MAPK)/phosphoinositide 3-kinase (PI3K) pathways in the absence of GHS-R1a. J. Endocrinol. 188:37-47

Abstract

Recent studies demonstrate widespread expression of ghrelin among tissues and have uncovered its pleiotropic nature. We have examined gene expression of ghrelin and its two receptor splice variants, growth hormone secretagogue receptors (GHS-R) 1a and 1b, in human bone biopsies and in the human pre-osteoblastic SV-HFO cell line during differentiation. Additionally, we examined proliferative effects of ghrelin and unacylated ghrelin (UAG) in differentiating and non-differentiating cells. We detected GHS-R1b mRNA in human bone and osteoblasts but not ghrelin's cognate receptor GHS-R1a, using two different real-time PCR assays and both total RNA and mRNA. In osteoblasts GHS-R1b mRNA expression remained low during the first 14 days of culture, but increased 300% in differentiating cells by day 21. Both human bone biopsies and osteoblasts expressed ghrelin mRNA, and osteoblasts were found to secrete ghrelin. Overall, ghrelin gene expression was greater in differentiating than non-differentiating osteoblasts, but was not increased during culture in either group. Ghrelin and UAG induced thymidine uptake dose-dependently, peaking at 1 and 10 nM respectively, at day 6 of culture in both non-differentiating and differentiating osteoblasts. The proliferative response to ghrelin and UAG declined with culture time and state of differentiation. The proliferative effects of ghrelin and UAG were suppressed by inhibitors of extracellular-signal-regulated kinase (ERK) and phosphoinositide-3 kinase, and both peptides rapidly induced ERK phosphorylation. Overall, our data suggest new roles for ghrelin and UAG in modulating human osteoblast proliferation via a novel signal transduction pathway.

Links

PubMed Online version:10.1677/joe.1.06404

Keywords

Alkaline Phosphatase/metabolism; Analysis of Variance; Biological Markers/analysis; Biological Markers/metabolism; Cell Differentiation/drug effects; Cell Proliferation/drug effects; Cells, Cultured; DNA/biosynthesis; Femur Head; Ghrelin; Humans; Mitogen-Activated Protein Kinases/metabolism; Osteoblasts/cytology; Osteoblasts/drug effects; Peptide Hormones/pharmacology; Phosphatidylinositol 3-Kinases/metabolism; Receptors, G-Protein-Coupled/metabolism; Receptors, Ghrelin; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction/physiology; Stimulation, Chemical; Thymidine/analysis; Thymidine/metabolism

Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

HUMAN:GHRL

involved_in

GO:0042127: regulation of cell population proliferation

ECO:0000314: direct assay evidence used in manual assertion

P

Seeded From UniProt

complete


See also

References

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