Osteoglycin (OGN) is a small leucine-rich proteoglycan (SLRP) functioning as a structural and signaling component of the extracellular matrix. Primary function: OGN induces bone formation in conjunction with TGF-β signaling and participates in skeletal and connective tissue development 1. Mechanism: OGN regulates tissue organization and cell behavior through multiple pathways. In lung myofibroblasts, OGN activates the TGF-β/Smad signaling pathway via integrin αv-mediated mechanisms, promoting fibrotic responses 2. During skin development, OGN marks progenitor-like cells (OGN+/UCHL1+) that give rise to hair placodes, suggesting roles in epithelial appendage morphogenesis 3. Disease relevance: OGN is upregulated in idiopathic pulmonary fibrosis and osteoarthritis/rheumatoid arthritis, implicating it in pathological fibrosis and inflammatory joint disease 24. OGN also associates with tumorigenesis, including cell proliferation, invasion, metastasis, and epithelial-mesenchymal transition 1. Clinical significance: Circulating OGN levels correlate with aerobic fitness and glucose metabolism across the lifespan, with higher levels in males and a U-shaped age-dependent pattern, suggesting potential biomarker utility for metabolic health 5. OGN knockdown attenuates experimental lung fibrosis in mouse models, indicating therapeutic potential through pathway inhibition 2.