The focus of the present proposal is to utilize a mouse model of osteogenesis imperfecta (oim) as a model system to evaluate the potential of the bone marrow derived mesenchymal stem cells (BMSCs) to engraft and participate in repair and regeneration of bone. The mouse has a natural occurring mutation that results in non-expression of proa2(I) chains leading to the accumulation of al(I) homotrimers in tissues. The mouse exhibits osteopenia, cortical thinning and easy fracturing and is an excellent model for evaluating the potential of BMSCs as targets for the treatment of genetic and non-genetic diseases of bone. Recent clinical trial by Horwitz et al. using whole marrow in children with a severe form of OI, demonstrated that BMSCs may offer treatment options for O1. Therefore, the hypotheses to be tested are: BMSCs from normal donor mice administered systemically or locally into syngeneic recipient mice will engraft in the bones of the recipient mice, synthesize authentic bone extracellular matrix and contribute to the structural integrity of the host bone. The following specific aims will be used to test these hypotheses: 1) Demonstrate that the cells infused into oim mice will engraft in bone and in fracture sites created in oim mice 2) Demonstrate that the cells which engraft in bone differentiate into osteoblasts and synthesize the authentic bone extracellular matrix and 3) Demonstrate that the cells that engraft in bone contribute to the structural integrity of bone. To accomplish the above aims, BMSCs will be established from femurs and tibiae of normal donor mice and either marked with retroviruses expressing LacZ or GFP genes to aid in cell tracking or unmarked prior to infusion in oim mice. The fate of the infused cells will be tracked by following expression of the marker genes in tissue and by fluorescent in situ hybridization (fish). Differentiation of the transplanted cells into osteoblasts in vivo will be determined by co-localization of osteocalcin and marker genes and also by in situ hybridization. Synthesis of authentic extraceltular matrix by the infused cells will be analyzed by the determination of the presence of type I collagen comprised of 1 and 2 heterotrimers. Structural integrity of the host bone, will be determined by histophotometry, cross-linking, and collagen content and bone mineral density. The proposed studies may lead to the development of better treatments for genetic and non-genetic diseases of bone based on BMSCs.
