Investigating the role of Asporin in musculoskeletal development

Abstract

Understanding musculoskeletal development is of high importance, as it forms the foundation for understanding various skeletal disorders and can illuminate pathways involved in other musculoskeletal conditions including osteoarthritis (OA). This thesis focuses on the role of Asporin, a small leucine-rich proteoglycan (SLRP), expressed in the developing periosteum, perichondrium, tendons, and subchondral bone. Asporin possesses a unique ability among SLRPs to mineralise type I collagen fibres. A polymorphism associated with risk of OA and IDD was identified in GWAS studies increases Asporin function, moreover Asporin is significantly upregulated in OA cartilage in comparison to healthy cartilage. The study employs an in vitro approach utilising Asporin overexpression in cartilage and bone cells to replicate the conditions observed in OA. In addition, the research integrates the use of Asporin null mouse models and col2cre conditional knockout of Asporin to elucidate the role of Asporin in musculoskeletal development and specifically in cartilage and periosteal cells. This research shows the effect of Asporin in the mineralisation of the ECM and reduction of sulphated proteoglycan in the overexpression model, interesting for the role of Asporin in OA pathogenicity. Phenotyping of the global mouse model demonstrates that Asporin is not essential for endochondral ossification or cartilage structure, highlighting modulation of Asporin expression as potential therapeutic target of OA with minimal off target effects. Further, studying of the role of Asporin in bone using µCT, histomorphometric analysis and histological techniques to gain a well rounded understanding of its involvement in development showed that the loss of Asporin does not disrupt bone or spinal development nor affect the tendon structure. However, deletion of Asporin in type II collagen positive periosteal skeletal progenitor cells (under Col2Cre) hinders bone remodelling and appositional growth in the col2cre conditional Asporin knockout, suggesting a potential role for Asporin in bone homeostasis and fracture repair.