Species-specific roles of cellular communication network proteins in cartilage development: A comparative study using in vitro chondrogenic models.

Cellular communication network (CCN) proteins are key matricellular regulators of cartilage development, yet their species-specific roles and network-level context remain unclear. This study integrated bulk RNA sequencing from chicken and mouse embryonic limb bud micromass cultures and human mesenchymal stem cell chondrogenesis with co-expression, protein-protein interaction, and ortholog analyses to construct CCN-centered regulatory networks across models. CCN1 and CCN2 emerged as dominant, conserved hubs enriched in collagen-containing extracellular matrix, cartilage development, and growth factor signaling modules, whereas CCN3-CCN6 showed lower context-dependent expression and connectivity. Functional and ortholog analyses revealed moderate pathway conservation, with high conservation of IGF, EGFR, and HIF-1 signaling, but reduced overlap in hypoxia and mechanosensing/Hippo categories, indicating species-specific tuning of environmental sensing. A focused ortholog screen identified multifunctional conserved hubs, including COL2A1, TGFBR1, SMAD3, RUNX2, HIF1A, IGF1, SPP1, and CD44. Single-cell RNA-seq meta-analysis of human iPSC-derived chondrogenesis and embryonic limb datasets showed CCN1/2 expression and homologous network activity peaking in mesenchymal and early chondrocyte populations, consistent with model-dependent persistence into hypertrophic and ossification stages in vivo. Overall, this work defines a conserved CCN1/2-centered axis integrating extracellular matrix formation with growth factor and mechanical cues, providing a framework for model selection and CCN-targeted cartilage regeneration strategies.