To advance development of effective disease modifying OA treatments, a better understanding of its pathophysiological mechanisms is necessary. By studyinga family with early onset OA and high... Show moreTo advance development of effective disease modifying OA treatments, a better understanding of its pathophysiological mechanisms is necessary. By studyinga family with early onset OA and high cartilage mineralization, a likely causal mutation in the TNF receptor superfamily member 11b (TNFRSF11B) encoding for osteoprotegerin (OPG) was identified. This mutation causes a 19 amino acid extension in the C-terminal domain of OPG (OPG-XL). OPG is a decoy receptor that competes with receptor activator of the nuclear KB factor (RANK) for the binding of nuclear factor KB ligand (RANKL). This triad is known for regulating the formation of osteoclasts, hence playing a critical role in bone remodeling. Given that TNFRSF11B is also one of the highest upregulated genes in OA lesioned cartilage as compared to preserved, this gene is likely underlying OA development and progression but its implication in cartilage homeostasis is as of yet unknown.Altogether, this thesis highlights the role of OPG in OA development by generating an OPG overexpression system in primary chondrocytes and by studying a rare mutation in TNFRSF11B. By further generating neo-cartilage, neo-bone and osteoclasts from the OPG-XL family members, we showed a bidirectional interplay of OPG-XL characterized by higher bone resorption and higher cartilage mineralization. Novel treatments for this family and extrapolation to common OA could be addressed on highly differentially expressed genes such as MGP and DIO2. Finally, the pleiotropy that OPG-XL showed indicates a beneficial or detrimental stage depending on the tissue, making OPG-XL, and likely OPG, a double-edged sword in OA development. Show less
This thesis aims to increase the understanding of human osteoarthritis pathophysiology by developing reliable biomimetic ex vivo human osteochondral explant models and focussing on the role of... Show moreThis thesis aims to increase the understanding of human osteoarthritis pathophysiology by developing reliable biomimetic ex vivo human osteochondral explant models and focussing on the role of osteoarthritis-relevant triggers (mechanical stress) and interacting genetic factors for developing treatment targets. Human aged joint tissues were collected in the Research in Articular Osteoarthritis Cartilage (RAAK) biobank. To add knowledge of the osteoarthritis pathophysiological processes, aged human ex vivo osteochondral explants were subject to three osteoarthritis-relevant triggers, being inflammation, hypertrophy and injurious mechanical stress. Next, knowledge on early initiating processes occurring in mechano-pathology was investigated by applying RNA-sequencing to cartilage of aged human osteochondral explants subjected to mechanical stress. In addition, to show that the human osteochondral explant model could also be used for genetic interaction studies, we investigated expression of the osteoarthritis risk gene MGP in relation to rs1800801 genotypes. By combining information from RNA-sequencing datasets of cartilage and bone with osteoarthritis-relevant triggers in cartilage and bone explants we investigated the role of MGP and vitamin K in osteoarthritis. Lastly, the injurious mechanical explant model was exploited to determine the effectivity of inhibiting the osteoarthritis risk gene DIO2 by iopanoic acid treatment either by burst or prolonged release from PLGA-PEG nanoparticles. Show less
The aim of this thesis was to combine transcriptomics, genetics and human disease modelling to obtain further insight into molecular processes underlying osteoarthritis. More specifically, we aimed... Show moreThe aim of this thesis was to combine transcriptomics, genetics and human disease modelling to obtain further insight into molecular processes underlying osteoarthritis. More specifically, we aimed to elucidate the role of long noncoding RNAs expression changes as aberrant epigenetic mechanism in regulating gene expression in chondrocytes. We identified previously unknown long noncoding RNAs associated with the osteoarthritic process and showed enrichment for cis¬-regulation of these long noncoding RNAs with target messenger RNAs.To provide insight in the etiology of osteoarthritis, causal pathways can be identified by unravelling the substantial genetic component. To this end, we investigated the biological functionality of the high-impact, pathogenic mutation identified in the gene fibronectin1 in an early-onset osteoarthritis family. We demonstrated that the identified causal missense mutation in the gelatin-binding domain of the extracellular matrix protein fibronectin resulted in significant decreased binding capacity to collagen type II.Finally, the common function of fibronectin1 was investigated in cartilage and what changes occur at the transcript level of fibronectin1 with osteoarthritis. Down-regulation of full-length fibronectin was unbeneficial for in vitro chondrogenesis, we hypothesize that this was caused by decreased availability of the classical integrin binding site of fibronectin. Show less
