Identification of Human Juvenile Chondrocyte-Specific Factors that Stimulate Stem Cell Growth

Although regeneration of human cartilage is inherently inefficient, age is an important risk factor for osteoarthritis. Recent reports have provided compelling evidence that juvenile chondrocytes (from donors below 13 years of age) are more efficient at generating articular cartilage as compared to adult chondrocytes. However, the molecular basis for such a superior regenerative capability is not understood. To identify the cell-intrinsic differences between juvenile and adult cartilage, we have systematically profiled global gene expression changes between a small cohort of human neonatal/juvenile and adult chondrocytes. No such study is available for human chondrocytes although young and old bovine and equine cartilage have been recently profiled. Our studies have identified and validated new factors enriched in juvenile chondrocytes as compared to adult chondrocytes including secreted extracellular matrix factors chordin-like 1 (CHRDL1) and microfibrillar-associated protein 4 (MFAP4). Network analyses identified cartilage development pathways, epithelial-mesenchymal transition, and innate immunity pathways to be overrepresented in juvenile-enriched genes. Finally, CHRDL1 was observed to aid the proliferation and survival of bone marrow-derived human mesenchymal stem cells (hMSC) while maintaining their stem cell potential. These studies, therefore, provide a mechanism for how young cartilage factors can potentially enhance stem cell function in cartilage repair.