Differential Effects of BMPs on the Healing of Craniofacial Defects

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ABSTRACT An attractive modality for bone regeneration involves the use of pluripotent mesenchymal stem cells that are induced by osteogenic factors. Our overall goal is to investigate differential effects of bone morphogenetic proteins on bone healing in murine craniofacial defect models. This project is based on the hypothesis that there is a definable, differential profile of the osteogenic BMPs (BMP2, 4, 6, 7, 9) in regards to their capacity to induce healing of critical-sized craniofacial defects. To test this hypothesis, the following specific aims are proposed: 1) i. To construct recombinant adenoviruses expressing individual BMPs (BMP-2, -4, -6, -7, -9), ii. To determine the effect of stem cell transfection with the recombinant adenoviruses above on the expression levels of various proliferation and/or osteogenic differentiation markers in the stem cells, iii. To determine the differential effects of the various BMPs (2, 4, 6, 7, 9) on bone healing of critical sized defects in murine models. iv. To characterize this differential effect in areas of non-load bearing (calvarial) and areas of load-bearing (mandibular) craniofacial repair; 2) v. To generate primary cultures of calvarial/mandibular osteoblasts for in vitro stimulation with BMP, vi.To stimulate primary cultures of isolated osteoblasts with the various BMPs and measure the capacity of each BMP to induce osteogenesis in early and late stages of differentiation; 3) vii. To target canonical Wnt/beta catenin signaling via si-RNA technology and examine the effects of pathway inhibition both in vitro and in vivo. viii. To target SMAD4 signaling via si-RNA technology and examine the effects of SMAD4 inhibition both in vitro and in vivo. These specific aims will be addressed by the following experimental design: 1) Transfection of mesenchymal stem cells with adenovirus encoded with BMPs (Ad-BMPs); 2) Infection of mesenchymal stem cells with Ad-BMPs and testing of these stem cells in vitro for osteogenic differentiation; 3) Transfer of Ad-BMP induced mesenchymal stem cells into critical-sized murine craniofacial defects and evaluation of defect closure via micro-CT; 4) RT-PCR of downstream signalling elements important in BMP-induced stem cell osteogenesis; 5) siRNA knockdown of these critical signalling elements both in vitro and in vivo.