Lmp3 Cooperates With Bmp7 To Promote Bone Regeneration

Gene transfer of key regulators of osteogenesis for mesenchymal stem cells (MSCs) represents a promising strategy to regenerate bone. LMP3, a transcription variant of LIM domain mineralization protein (LMP) lacking LIM domains, can induce osteogenesis in vitro and in vivo. Objectives: Since little is known about the effects of LMP3 on periodontal ligament (PDL) cell osteogenic differentiation, this study sought to explore whether gene delivery of LMP3 can promote PDL cell mineralization and osteogenesis. Methods: Human PDL cells were transduced by LMP3 adenovirus (AdLMP3) or control vector, and then induced to osteogenic differentiation. Osteogenesis was assessed by ALP staining, von Kossa staining, extracellular calcium measurement, and via marker gene expression. In order to examine whether AdLMP3 can induce ex vivo bone formation, PDL cells were transduced with either AdLMP3 or control vector, after which the cells were seeded in polymer scaffolds. For combinatory gene delivery, PDL cells were transduced with AdBMP7, AdBMP7/LacZ virus or AdBMP7/AdLMP3, then suspended into collagen scaffolds. The scaffolds were subcutaneously implanted into immunodeficient mice. After 3 or 4 weeks, scaffold constructs were harvested and bone formation was evaluated by µ-CT and histological staining. Results: Our results showed that gene transfer of LMP3 significantly up-regulated ALP, BSP, and BMP2 gene expression and increased in vitro matrix mineralization in human PDL. Although AdLMP3 gene delivery to PDL cells did not induce ectopic bone formation in vivo, we found that AdLMP3 augments new bone formation, when co-delivered with AdBMP7. Conclusions: Our study provides evidence that there is a synergistic effect between LMP3 and BMP-7 in vivo, suggesting that LMP3 delivery may be used to augment BMP-mediated osteogenesis. LMP3 and BMP-7 combinatory gene therapy may also have specific applications for oral and periodontal regenerative medicine. FUNDING SUPPORT: NIH DE13397, AR051456, ITI Foundation and University of Michigan Rackham Predoctoral Fellowship.