Production of prostaglandin D(2) by human osteoblasts and modulation of osteoprotegerin, RANKL, and cellular migration by DP and CRTH2 receptors.
Human osteoblasts produce PGD(2), which acts on the DP receptor to decrease osteoprotegerin production and on the CRTH2 receptor to decrease RANKL expression and to induce osteoblast chemotaxis. These results indicate that activation of CRTH2 may lead to an anabolic response in bone.


BACKGROUND
Whereas the actions of prostaglandin (PG)E(2) as a modulator of bone and osteoblast function are relatively well characterized, little is known about PGD(2) and bone metabolism. The objectives of this study were to determine if human osteoblasts can produce PGD(2), which prostaglandin D(2) synthases are implicated in this synthesis, to identify the PGD(2) receptors (DP and CRTH2) on these cells and to characterize the biological effects resulting from their activation.


METHODS
RT-PCR analysis and immunohistochemistry were used to detect PGD(2) receptor and synthases in cultured human osteoblasts. Immunohistochemistry was used to identify the synthases and receptors in human bone tissue. Intracellular cAMP and calcium levels were determined to verify receptor activation. The cells were stimulated with PGD(2) or the specific agonists BW 245C (DP) and DK-PGD(2) (CRTH2), and the resulting effects on osteoprotegerin (OPG) secretion, RANKL expression, and chemotaxis were determined. Osteoblast production of PGD(2) was evaluated by measuring PGD(2) in the culture supernatants after stimulation with interleukin (IL)-1, TNF-alpha, PTH, vascular endothelial growth factor (VEGF), and insulin-like growth factor I (IGF-I).


RESULTS
Human osteoblasts in culture generated PGD(2) when stimulated. Both osteoblasts in culture and in situ present the lipocalin-type PGD(2) synthase only. Both DP and CRTH2 receptors were present in human osteoblasts in culture and in situ. Stimulation of DP resulted in an increase in cAMP, whereas CRTH2 increased the intracellular calcium level. OPG production was reduced by 60% after DP receptor stimulation, whereas CRTH2 receptor stimulation decreased RANKL expression on human osteoblasts. As reported for other cell types, CRTH2 was a potent inducer of chemotaxis for human osteoblasts in culture.


CONCLUSIONS
Human osteoblasts in culture produce PGD(2) under biologically relevant stimuli through the lipocalin-type PGD(2) synthase (L-PGDS) pathway. As an autacoid, PGD(2) can act on DP and CRTH2 receptors, both present on these cells. Specific activation of CRTH2 could lead directly and indirectly to an anabolic response in bone.
Gallant
Maxime A
MA
Division of Rheumatology, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, Québec, Canada.
Samadfam
Rana
R
Hackett
Josette A
JA
Antoniou
John
J
Parent
Jean-Luc
JL
de Brum-Fernandes
Artur J
AJ
D001842:Bone and Bones / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002633:Chemotaxis; D000242:Cyclic AMP / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism; D006133:Growth Substances / Q000494:pharmacology; D006801:Humans; D006827:Hydantoins / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007375:Interleukin-1 / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D053244:Osteoprotegerin; D015230:Prostaglandin D2 / Q000096:biosynthesis* / Q000235:genetics; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D011971:Receptors, Immunologic / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D011982:Receptors, Prostaglandin / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D042461:Vascular Endothelial Growth Factor A / Q000494:pharmacology
D002352:Carrier Proteins; D006023:Glycoproteins; D006133:Growth Substances; D006827:Hydantoins; D007375:Interleukin-1; D008562:Membrane Glycoproteins; D053244:Osteoprotegerin; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D011971:Receptors, Immunologic; D011982:Receptors, Prostaglandin; D018124:Receptors, Tumor Necrosis Factor; C505686:TNFRSF11A protein, human; C506030:TNFRSF11B protein, human; C505688:TNFSF11 protein, human; D014409:Tumor Necrosis Factor-alpha; D042461:Vascular Endothelial Growth Factor A; C058848:BW A868C; D007334:Insulin-Like Growth Factor I; D000242:Cyclic AMP; D015230:Prostaglandin D2; C036293:prostaglandin D2 receptor