GPRC6A and osteoarthritis: This review systematically catalogs GPCR expression and functional heterogeneity in key bone cells: 12 GPCRs in mesenchymal stem cells (MSCs) orchestrate lineage specification; 21 GPCRs in osteoblasts/osteocytes mediate matrix mineralization and mechanotransduction; 23 GPCRs in macrophages/osteoclasts regulate inflammatory bone resorption; 31 GPCRs in chondrocytes govern endochondral ossification and osteoarthritis pathogenesis; and 8 GPCRs in other cell types modulate bone-related physiological processes.