CELLULAR AND MOLECULAR BIOLOGY OF BONE AND CARTILAGE: STRUCTURE, REMODELING, PATHOLOGICAL DEGENERATION, AND REGENERATIVE THERAPEUTIC STRATEGIES

Abstract

Background: Bone and cartilage are specialized connective tissues that form the structural and biomechanical foundation of the vertebrate musculoskeletal system. Despite their apparent rigidity, both tissues are metabolically dynamic, undergoing continuous remodeling throughout life. Disruption of this homeostasis underlies some of the most prevalent and disabling diseases in modern medicine, including osteoporosis—affecting over 200 million people worldwide—and osteoarthritis, estimated to affect 528 million individuals globally.

Objective: To provide a comprehensive, evidence-based review of the cellular and molecular biology of bone and cartilage, encompassing their extracellular matrix composition, key cell types, signaling pathways governing remodeling and degeneration, and current regenerative and pharmacological therapeutic strategies.

Methods: A systematic review of eight primary peer-reviewed sources was conducted, including original research articles, meta-analyses, and authoritative clinical practice guidelines published between 2000 and 2024.

Results: Bone tissue is maintained by the coordinated activity of osteoblasts, osteocytes, and osteoclasts, regulated by the RANK/RANKL/OPG axis, Wnt/β-catenin signaling, and parathyroid hormone (PTH). Articular cartilage, avascular and aneural, relies on chondrocytes and a proteoglycan- and collagen II-rich extracellular matrix for load distribution. In osteoporosis, uncoupled remodeling favors resorption, reducing bone mineral density (BMD) and increasing fracture risk. In osteoarthritis (OA), matrix metalloproteinase (MMP)- and ADAMTS-mediated degradation of aggrecan and type II collagen drives progressive cartilage loss. Pharmacological interventions include bisphosphonates, denosumab, and teriparatide for osteoporosis, and intra-articular corticosteroids and hyaluronic acid for OA. Emerging regenerative strategies encompass mesenchymal stem cell (MSC) transplantation, scaffold-based tissue engineering, and gene therapy.

Conclusion: Advances in molecular biology have transformed understanding of bone and cartilage pathophysiology, enabling targeted therapies that significantly reduce fracture incidence and slow cartilage degeneration. Future progress depends on translating stem cell and gene therapy innovations into safe, scalable clinical protocols.