Microenvironment-directed chondrogenesis of adipose-derived mesenchymal stem cells in hyaline, elastic, and fibrocartilage in vivo.

Cartilage exhibits remarkable subtype diversity-hyaline, fibrocartilage, and elastic-each with unique extracellular matrix architecture and mechanical function. Despite the clinical promise of adipose-derived mesenchymal stem cells (ADMSCs) for cartilage regeneration, whether distinct in vivo cartilage microenvironments can instruct ADMSC differentiation toward corresponding subtypes remains poorly defined. Green fluorescent protein-labeled human ADMSCs were encapsulated in a fibrin hydrogel and implanted into three representative cartilage sites-auricular (elastic), articular (hyaline), and meniscal (fibrocartilage)-in an immunodeficient rat model. Regenerated tissues were harvested at 4 weeks for histology (H&E), immunofluorescence analysis of hyaline (COL II, aggrecan), fibrocartilage (COL I, tenomodulin), and elastic (fibrillin-1, elastin) markers, and RT-PCR quantification of lineage-associated gene expression. ADMSCs survived and engrafted within all three microenvironments. Articular cartilage implants exhibited strong hyaline-like differentiation, characterized by intense COL II and aggrecan expression and upregulation of SOX9, COL2A1, and ACAN. Meniscal implants instead displayed a fibrocartilage-like profile with robust COL I and tenomodulin expression and elevated COL1A1, TNMD, and SCX transcripts. In contrast, auricular cartilage implants showed negligible expression of hyaline, fibrocartilage, or elastic markers, accompanied by global downregulation of chondrogenic and elastogenic genes. These results demonstrate that local cartilage niches exert distinct instructive effects on ADMSC fate: articular and meniscal environments effectively guide hyaline- and fibrocartilage-like differentiation, whereas the auricular niche under the tested conditions fails to support elastic or hyaline lineage commitment. Our findings highlight the decisive role of the tissue microenvironment in modulating ADMSC differentiation and underscore the need for bioengineered, niche-mimetic scaffolds to achieve subtype-specific cartilage regeneration-particularly for complex elastic tissues such as the auricle.