BMP-2 differentially modulates FGF-2 isoform effects in osteoblasts from newborn transgenic mice

Abstract

We previously generated separate lines of transgenic mice that specifically overexpress either the Fibroblast growth factor (FGF)-2 low-molecular-mass isoform (TgLMW) or the high-mass isoforms (TgHMW) in the osteoblast lineage. Vector/control (TgVector) mice were also made. Here we report the use of isolated calvarial osteoblasts (COBs) from those mice to investigate whether the FGF-2 protein isoforms differentially modulate bone formation in vitro. Our hypothesis states that FGF-2 isoforms specifically modulate bone morphogenetic protein 2 (BMP-2) function and subsequently bone differentiation genes and their related signaling pathways. We found a significant increase in alkaline phosphatase-positive colonies in Tg LMW COBs compared with TgVector controls. BMP-2 treatment significantly increased mineralized colonies in TgVector and TgLMW COBs. BMP-2 caused a further significant increase in mineralized colonies in TgLMW COBs compared with TgVector COBs but did not increase alkaline phosphatase-positive colonies in TgHMW COBs. Time-course studies showed that BMP-2 caused a sustained increase in phosphorylated mothers against decapentaplegic- 1/5/8 (Smad/1/5/8), runt-related transcription factor-2 (Runx-2), and osterix protein in TgLMW COBs. BMP-2 caused a sustained increase in phospho-p38 MAPK in TgVector but only a transient increase in TgLMW and TgHMW COBs. BMP-2 caused a transient increase in phospho-p44/42 MAPK in TgVector COBs and no increase in TgLMW COBs, but a sustained increase was found in TgHMWCOBs. Basal expression of FGF receptor 1 protein was significantly increased in TgLMW COBs relative to TgVector COBs, and although BMP-2 caused a transient increase in FGF receptor 1 expression in TgVector COBs and TgHMW COBs, there was no further increase TgLMW COBs. Interestingly, although basal expression of FGF receptor 2 was similar in COBs from all genotypes, BMP-2 treatment caused a sustained increase in TgLMW COBs but decreased FGF receptor 2 in TgVector COBs and TgHMWCOBs. © 2013 by The Endocrine Society.