Role and regulation of PRX1 expressing cells during calvarial bone regeneration

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Craniofacial surgeons and neurosurgeons perform numerous bone regeneration procedures to treat calvarial congenital abnormalities or lesions due to trauma and cancer. Current procedures require therapeutic aids to foster bone regeneration, as healing of calvarial bone defects often results in fibrous non-unions unable to protect the brain from injuries. Unfortunately, the available therapeutic aids based on recombinant growth factors present with severe limitations in terms of efficacy and safety. Ex vivo manipulation and expansion of skeletal stem cells has also been proposed as an alternative to the growth-factor based therapies. However, these cell-based regenerative strategies have shown variability of the regenerative outcomes. Therefore, more effective bone regenerative strategies for craniofacial defects are critically needed. We have recently shown that PRX1 is a marker of stem cells residing in the sutures of the mouse calvaria. Postnatal PRX1 expressing cells (pnPRX1+ cells) reside exclusively within the calvarial sutures, are required for regeneration of calvarial bone defects, and decline in number with age. Our current data further indicates that pnPRX1+ cells respond to activation of Wnt signaling by differentiating into osteoblasts and to inhibition of Wnt signaling by proliferating. With these findings and with the goal of developing clinically viable alternatives to the current calvarial bone regeneration therapies, in Aim 1 we propose to study the Wnt-regulated cellular mechanisms that control the migration of pnPRX1+ cells from the suture niche to a calvarial bone defect located remotely from the suture. In Aim 2 we propose to test the ability of Wnt inhibitor small molecules or of small fragments of transplanted sutures to induce regeneration of calvarial bone defects. By understanding the molecular mechanisms that govern the contribution of the stem cells of the suture to the regeneration of a calvarial bone defect and by defining novel strategies to harness these stem cells within their niches, our studies may lead to the development of novel therapies for calvarial bone regeneration, helping craniofacial surgeons and neurosurgeons with their need to regenerate a part of the skeleton so vital for protection of the brain.