895. The Differential Effect of BMP4 on C2C12 and NIH/3T3 Cells: Implications for Gene Therapy for Bone and Cartilage Repair

Abstract

Top of pageAbstract The present study was designed to compare the osteogenic potential of NIH/3T3 cells and C2C12 cells following BMP4 stimulation and their potential for bone and cartilage repair after genetic engineering to express BMP4. Using different concentrations of BMP4 protein, we observed that NIH/3T3 cells were able to undergo osteogenic differentiation in vitro. Compared to the myogenic C2C12 cell line, NIH/3T3 cells required much higher levels (10-fold) of BMP4 as well as a longer exposure time (4-fold) to induce osteogenic differentiation. We then investigated whether NIH/3T3 cells, retrovirally transduced to express BMP4, were capable of undergoing endochondral bone formation when injected into skeletal muscle. These results were compared to the bone forming ability of similarly transduced C2C12 cells. Although genetically altered C2C12 and NIH/3T3 cells demonstrated endochondral bone formation in vivo, we observed that NIH/3T3 cells had a prolonged cartilaginous intermediate while the C2C12 cells were rapidly differentiating toward an osteogenic lineage. It has been demonstrated in previous work that Runx2 knockout mice are capable of forming cartilage, but incapable of forming bone. We hypothesized that Runx2 may be involved in the observed differences between cell types. We found that C2C12 cells express high baseline levels of Runx2 while NIH/3T3 cells express very low levels. These results suggest that NIH/3T3 cells can undergo chondrogenic and osteogenic differentiation under the influence of BMP4, but the low expression of Runx2 in these cells seems to play an important role in favoring their chondrogenesis versus osteogenesis in vivo. Thus, following genetic engineering to express BMP4, myoblastic cells may be more effective for bone regeneration applications while NIH/3T3 cells may be optimal for cartilage repair.