Endogenous FGF-2 is critically important in PTH anabolic effects on bone.
Parathyroid hormone (PTH) increases fibroblast growth factor receptor-1 (FGFR1) and fibroblast growth factor-2 (FGF-2) expression in osteoblasts and the anabolic response to PTH is reduced in Fgf2-/- mice. This study examined whether candidate factors implicated in the anabolic response to PTH were modulated in Fgf2-/- osteoblasts. PTH increased Runx-2 protein expression in Fgf2+/+ but not Fgf2-/- osteoblasts. By immunocytochemistry, PTH treatment induced nuclear accumulation of Runx-2 only in Fgf2+/+ osteoblasts. PTH and FGF-2 regulate Runx-2 via activation of the cAMP response element binding proteins (CREBs). Western blot time course studies showed that PTH increased phospho-CREB within 15 min that was sustained for 24 h in Fgf2+/+ but had no effect in Fgf2-/- osteoblasts. Silencing of FGF-2 in Fgf2+/+ osteoblasts blocked the stimulatory effect of PTH on Runx-2 and CREBs phosphorylation. Studies of the effects of PTH on proteins involved in osteoblast precursor proliferation and apoptosis showed that PTH increased cyclinD1-cdk4/6 protein in Fgf2+/+ but not Fgf2-/- osteoblasts. Interestingly, PTH increased the cell cycle inhibitor p21/waf1 in Fgf2-/- osteoblasts. PTH increased Bcl-2/Bax protein ratio in Fgf2+/+ but not Fgf2-/- osteoblasts. In addition PTH increased cell viability in Fgf2+/+ but not Fgf2-/- osteoblasts. These data suggest that endogenous FGF-2 is important in PTH effects on osteoblast proliferation, differentiation, and apoptosis. Reduced expression of these factors may contribute to the reduced anabolic response to PTH in the Fgf2-/- mice. Our results strongly indicate that the anabolic PTH effect is dependent in part on FGF-2 expression.
Sabbieti
Maria Giovanna
MG
Department of Comparative Morphology and Biochemistry, University of Camerino, Camerino (MC), Italy.
Agas
Dimitrios
D
Xiao
Liping
L
Marchetti
Luigi
L
Coffin
J Douglas
JD
Doetschman
Thomas
T
Hurley
Marja M
MM
D045930:Anabolic Agents / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D051361:Cyclin-Dependent Kinase 6 / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D010281:Parathyroid Hormone / Q000378:metabolism / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D045930:Anabolic Agents; C494827:Bax protein, mouse; D050659:Core Binding Factor Alpha 1 Subunit; D017362:Cyclic AMP Response Element-Binding Protein; D010281:Parathyroid Hormone; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; C493716:Runx2 protein, mouse; D051028:bcl-2-Associated X Protein; D016222:Fibroblast Growth Factor 2; C495902:Cdk4 protein, mouse; C495912:Cdk6 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D048049:Extracellular Signal-Regulated MAP Kinases