Molecular and Tissue Engineering Strategies for Cartilage Repair in Osteoarthritis

Abstract

Osteoarthritis (OA) affects over 500 million individuals globally, yet most current clinical treatments remain largely palliative focused on alleviating pain without halting the progressive degradation of articular cartilage. This thesis investigates integrated molecular, cellular, and biomaterial strategies designed to both slow cartilage degeneration and promote long-term tissue regeneration. It first outlines the complex and multifactorial pathogenesis of OA, including mechanical overload, persistent low-grade inflammation, and dysregulation of Hippo-YAP1/TAZ and TGF-β/BMP signalling pathways. The thesis then critically evaluates emerging tissue-engineering approaches, identifying composite scaffolds, three-dimensional printing, and bioactive hydrogels as promising platforms. However, challenges such as poor graft integration, disruption of native cartilage zonal architecture, and inflammation-driven failure remain significant barriers to clinical success. The experimental work focuses on modulating intracellular signalling pathways relevant to cartilage degeneration and repair. siRNA was employed to silence YAP1, a gene upregulated by the inflammatory cytokine IL-1β. This intervention reduced pro-inflammatory mediator expression in human chondrocytes and enhanced the chondrogenic potential of MSCs, thereby offering a dual anti-inflammatory and regenerative effect. In contrast, exogenous administration of Noggin—a BMP pathway antagonist—successfully inhibited hypertrophic differentiation, but also markedly suppressed extracellular matrix production of MSCs, underscoring the need for precise regulation of TGF-β/BMP signalling balance. To bridge the gap between simplified in vitro systems and the complexity of in vivo conditions, an ex vivo osteochondral model using bovine tissue was developed. This model integrates mild enzymatic cartilage digestion with controlled multiaxial mechanical loading to recapitulate early OA features, including matrix loss, inflammation, and load-induced cell death. The system thus provides a physiologically relevant and ethically compliant platform for preclinical testing. Notably, the study demonstrated that self-assembling p5RHH peptide–siRNA nanocomplexes could penetrate full-thickness cartilage and achieve effective YAP1 silencing within the dense extracellular matrix. This finding supports the feasibility of minimally invasive, cartilage-targeted gene therapies. In conclusion, this thesis presents YAP1 as a promising target for simultaneous inhibition of cartilage catabolism and enhancement of regeneration. Noggin offers a tool for modulating hypertrophy, though with trade-offs in matrix synthesis. The developed ex vivo model offers a realistic and scalable testing platform, while the peptide-based delivery system enables deep tissue access for nucleic acid therapeutics. Together, these innovations contribute to a mechanistic and technological foundation for precision therapies that address the underlying drivers of OA, moving beyond symptomatic relief toward disease-modifying interventions.