Evaluation of pigment epithelium derived factor and its derived peptide for bone healing

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Abstract The present exploratory application proposes to evaluate the use of two novel factors, Pigment epithelium derived factor (PEDF) and a 17 amino acid peptide derived from it (P17) for the acceleration of healing femur fractures created in serpinf1 knockout mice or wildtype mice. PEDF encoded by serpinf1 gene is synthesized by a wide variety of cells in fetal and adult tissues. Mutations in serpinf1 gene cause type VI osteogenesis imperfecta (OI) whose hallmark is excessive osteoid build up that fails to mineralize. Bone defects resulting from trauma, bone tumors, and cranial facial defects may heal but a large number of them result in delayed healing or nonunion. Autografts are usually used but there is a limited supply and tissue harvest may lead to donor site morbidity. Allografts can be used but there is potential for disease transmission. Bone morphogenetic proteins (BMPs) specifically, BMP-2 and BMP-7 have been approved for clinical use to augment bone fracture healing. BMPs are very expensive, their mode of application remains problematic and they are prone to inducing ectopic bone formation. We and others reported that PEDF promoted mesenchymal stem cell (MSCs) differentiation and increased osteoblast mineralization and reduced expression of Sost/Sclerostin by osteocytes. Preliminary data showed that P17, a peptide with affinity for PEDF-receptor promoted osteoblast differentiation, increased matrix mineralization in vitro, and suppressed Sost expression by osteocytes. P17 infused into serpinf1 knockout mice via the peritoneal cavity, increased stiffness of the femurs which were reported to possess reduced stiffness. We are thus proposing to explore whether PEDF or P17 possess ability to accelerate healing of delayed or nonunion bone fractures using two mice models. The global hypothesize is PEDF or the P17 peptide will accelerate healing of critical sized mouse femoral defects created in serpinf1 knockout mice or wildtype mice. PEDF possess antiangiogenic activity but the P17 peptide does not, the peptide may possess superior ability to accelerate healing and regeneration of murine femoral fractures. We will test the hypothesis through two aims. In aim 1, we will determine whether P17 or PEDF delivered via the peritoneal cavity will accelerate healing of femur fractures created in serpinf1 knockout mice. Critical sized fractures will be created in serpinf1 mice femurs; the mice will be injected with P17 or PEDF via peritoneal cavity. Control mice will be injected with saline. Some mice will be followed by radiographic analysis at weekly intervals to determine the extent of healing. At week 6, all mice will be sacrificed, femurs harvested and evaluated by histology, micro CT and biomechanical testing. In aim 2, similar approaches will be carried out but using wildtype mice. We predict that Both P17 and PEDF will accelerate healing of femur fractures in both mice models but P17 may be more effective because it does not possess antiangiogenic activity as PEDF. Completion of the exploratory studies will lead to the development of novel therapeutic approaches to treat bone fractures as well as other bone pathologies based on PEDF or PEDF-derived peptide or peptides. .