280 OSTEOGENIC ACTIVITY OF IN HOUSE-PRODUCED PORCINE BMP2 ON ADIPOSE-DERIVED STEM CELLS

Abstract

In our laboratory, we extensively study the possibility of using adipose-derived stem cells (ASC) for maxillofacial bone regeneration. This includes also the tissue repair of large critical-size osteotomies requiring the use of tridimensional scaffolds. Bone regeneration in scaffolds can be greatly enhanced by the use of specific growth factors such as BMP2. In the present study, we compared the activity of commercially available human BMP2 (hBMP2) with in house-produced porcine BMP2 (pBMP2). The latter was synthesised using the BMP2 coding sequence from mRNA obtained from porcine ASC cell cultures. The coding sequence of the mature protein was cloned into a pET-21 plasmid and produced in E. coli as inclusion bodies. The activity of pBMP2 and hBMP2 was tested on ASC isolated from male pigs at passage 4 and at approximately 80% confluence in 48-well plates. Cells were treated in triplicate with hBMP2 or pBMP2 at 0.5, 5, 50, 500, or 1000 ng mL^–1, adipogenic medium (AM), osteogenic medium (OM), or normal DMEM medium supplemented with acetic acid (used to resuspend BMP2 as the control) for 5 or 17 days. Cells were harvested for Alizarin Red S (AR) quantification and expression of osteogenic genes. For the AR analysis, cells were fixed with formalin and treated with AR. The AR was then extracted by acetic acid and neutralized with ammonium hydroxide before spectrophotometer reading at an absorbance of 420 nm. Data were analysed using GLM of SAS (SAS Institute Inc., Cary, NC, USA) with treatment, time, concentration, and all interactions as main effects. Using an inverted robotic stage microscope, images of the entire well for each replicate were taken every 2 to 3 days. Images revealed formation of osteogenic nodules in OM and characteristic large cells filled with lipid droplets in AM. No evident nodule formation was observed in the other treated cells at any time point. The AR was higher than control in both hBMP2 and pBMP2 at 0.5, 50, and 1000 ng mL^–1 but not at 5 and 500 ng mL^–1. There was no overall difference between hBMP2 and pBMP2 but the former had the highest AR value at 5 days in cells treated with 0.5 ng mL^–1 and pBMP2 at 17 days with 1000 ng mL^–1. Interestingly, both had higher values compared to OM, particularly at 5 days. We also observed an increase of AR due to time in cells treated with acetic acid (control). Overall, the data appear to indicate an increase in calcium accumulation in cells treated with both hBMP2 and pBMP2, with an early increase in the former and a late and larger increase in the latter. This might indicate a larger but slower activity of pBMP2 compared with hBMP2. The lack of formation of osteogenic nodules by both BMP2 might indicate an insufficiency of BMP2 to induce osteogenesis in porcine ASC. This last observation, together with the lack of increased AR accumulation compared with control at the 5 and 50 ng mL^–1 doses, suggests the need for a more accurate analysis of BMP2 activity by measuring expression of BMP2-related genes. Finally, the data provide preliminary support for the equivalency of activity of pBMP2 and hBMP2 for in vivo bone regeneration.