Regulation of Skeletal Growth and Regeneration - Growth, structure and regeneration of the skeleton remain areas of intense research activity, due to their importance and relevance to body function and quality of life. The major engines of skeletal growth are the growth plates that are composed of a top reserve zone rich in stem cells followed by proliferating, pre- hypertrophic and hypertrophic zones of chondrocyte maturation and ossification, with cells organized in columns. Growth plate-like structures also form during skeletal repair and regeneration as observed in bone fracture healing. Growth plate activity is regulated by multiple mechanisms including signaling proteins such as hedgehog and fibroblast growth factor family members; transcription factors including Runx2 and Mef2c; and local and systemic hormones. The growth plates normally remain active until the end of puberty and then undergo involution and close, establishing a fully grown skeleton. However, trauma, genetic disorders or drug treatment of certain pediatric pathologies can have side effects on growth plates, derange proliferation and maturation rates and cause slowdown and involution, often with severe skeletal consequences. For example, about 10% of adolescents with a growth plate injury in long bones develop asymmetric bone growth and require challenging surgical intervention. An example of genetic conditions is children affected by Crouzon in which the cranial base growth plates malfunction and cause skull defects. Drug-induced growth plate malfunction is observed in pediatric patients treated with pharmaceuticals that can have unwanted side effects on their growth plates, causing growth retardation. In sum, the growth plates are vulnerable to malfunction in several acquired and congenital pathologies, representing an unmet clinical need in search of solutions. In this new project, we have used a standard model of growth plate defect in juvenile mice that mimics a pathology seen in pediatric patients. Preliminary data suggest that growth plate dysfunction was caused by concurrent changes in mechanisms normally fine-tuning growth plate activity and functioning. Additional data suggest that systemic treatment with a drug targeting one such mechanism was able to maintain growth plate function and restore skeletal lengthening. Our hypothesis is that growth plate dysfunction is amenable to drug-based rescue. Aim 1 will assess growth plate dysfunction and genes involved in it. Aim 2 will delineate the cellular mechanisms underlying dysfunction and rescue. Aim 3 will test the overall effectiveness and safety of the pharmacological treatment and its range of action. We will use transgenic mouse lines, in situ hybridization, protein analysis and treatment, biochemical approaches, and cultures of primary cells to delineate the mechanisms of growth plate defects and means to counter them. We will utilize strict and unequivocal rules to ensure scientific rigor and robust and unbiased design, methodology, analysis, interpretation, and reporting of data. The project is geared to further test mechanisms of growth plate activity and will exploit the resulting information to test new tools of therapeutic intervention on growth plate defects.
