Induction of Rat Marrow Stromal Cells by FGF2 and Insulin Activates Transcription of runx2 Gene through ap1 Consensus Sequence

Background: Signaling transductions in bone development and regeneration are complicated and relied on various growth factors functioning in an orchestrated manner. FGF2 and insulin are bone anabolic agents. Co-induction of rat marrow stromal cells (rat MSCs) by FGF2 and insulin significantly enhances runx2 gene expression in vitro and bone formation in vivo. However, molecular mechanisms underlying these activations are scant at present.

Objective: To characterize the 5ʹ-upstream region of runx2 gene responsible for increasing bone formation followed by FGF2 and insulin induction.

Results: In vitro study showed that mRNA levels of genes including runx2, osterix, bone morphogenetic protein 7, β-catenin, axis inhibition protein 2, and dickkopf-1 increasingly expressed by FGF2 plus insulin induction in compared to that of FGF2 treatment. BMP-2 and alkaline phosphatase were significantly affected by these inducers, and mineralization was improved by about 2 folds. Improvement of bone regeneration in vivo was apparent for inductions using FGF2 or FGF2 plus insulin, followed by BMP-2. The insulin supplement was advantageous for forming new blood vessels, although it hindered bone formation to some extent.

Conclusion: Regulation of runx2 transcription by FGF2 and insulin seemed to mediate through the ap1 consensus locating on the 5ʹ-upstream region of runx2 gene. Supposedly, multiple impulses exhibit catabolic/anabolic effects on bone regeneration in rat MSCs following challenged by FGF2 and insulin.