Mapping articular cartilage maturation across postnatal development by proteomics.
OBJECTIVE: Articular cartilage has a specialised extracellular matrix that provides tensile strength and resistance to compression, but repair capacity is limited. Matrix remodelling during growth is essential for long-term tissue function, yet the underlying protein-level adaptations remain poorly characterised in large-animal models relevant to human joint biology. DESIGN: Using non-targeted, label-free mass spectrometry-based proteomics, we profiled full-thickness articular cartilage from goats across seven postnatal ages from neonatal to adult (n = 3 per age). Cartilage proteins were extracted using guanidine-based solubilisation and analysed by mass spectrometry. Selected proteins were further examined by immunohistochemistry. RESULTS: We identified 799 proteins across the seven ages, of which 157 matrisome components grouped into six categories. Development was associated with increased abundance of proteins involved in matrix organisation and stabilisation, including COL6A1, LOX, TIMP3 and CILP. Enrichment analysis revealed a shift from collagen biosynthesis and fibrillogenesis in early postnatal cartilage to elastic fibre organisation, integrin-matrix interactions and glycosaminoglycan metabolism in mature tissue, consistent with transition from matrix assembly to maintenance. Lysozyme increased with age, suggesting a structural role that warrants further study. Several proteins enriched in mature cartilage, including CILP, HTRA1, FN1 and SPP1, have also been implicated in osteoarthritis, suggesting that some molecular features of mature ECM maintenance are shared with diseased tissue. Immunohistochemistry confirmed stable COL2 localisation, loss of deep-zone COL10 staining with maturation and emergence of superficial PRG4 expression in adult cartilage. CONCLUSIONS: Our findings define the proteomic trajectory of cartilage maturation and provide a molecular reference for joint development and matrix ageing.