Osteoporosis is a prevalent age-related disease characterised by low bone mineral density (BMD) and fragility fractures. In the clinic there is a demand for new osteo-anabolic treatments to strengthen bones. A powerful way to identify new osteo-anabolic targets is by understanding the genetics of high bone mass (HBM), whereby individuals have naturally high BMD and are resistant to fractures. Recently, missense mutations in SMAD9, WDR5 and PIEZO1 were independently identified in HBM pedigrees. SMAD9 is an inhibiting transcription factor in the bone morphogenetic protein signalling pathway. WDR5 is a core scaffolding component of histone methyltransferase complexes involved in multiple cellular processes. PIEZO1 is a mechanosensitive ion channel protein important for mechanotransduction in many cellular systems. To determine whether these genes could be potential targets for osteoporosis treatment, functional studies were carried out using complementary in vitro and in vivo skeletal models. Primary human osteogenic mesenchymal stem cells are a suitable model for osteoblast differentiation. Zebrafish are a suitable model for studying in vivo bone homeostasis due to their similar skeletal physiology to mammals, their optical translucency and availability of fluorescent reporter lines allowing dynamic live imaging. Furthermore, the role of the HBM associated genes during fracture repair and bone regeneration can be modelled using the caudal fin of adult zebrafish. In this thesis I explored the roles of these HBM-associated genes in multiple skeletal contexts. I demonstrated that WDR5 controls both osteoblast-adipocyte cell fates and its importance in osteoblast maturation. I highlighted the importance of SMAD9 expression in osteochondral progenitors during development and bone formation. Finally, I confirmed PIEZO1 is involved in osteoblast differentiation and bone maturation. These studies improve our understanding of how bone homeostasis is regulated, and hence help determine whether SMAD9, PIEZO1 or WDR5 are suitable targets for osteo-anabolic therapies.
Functional Studies of High Bone Mass Associated Genes in Both In Vitro and In Vivo Skeletal Systems
Mcdonald, G. (Author). 23 Jan 2024
Student thesis: Doctoral Thesis › Doctor of Philosophy (PhD)