Microencapsulation-induced SOX9-DNA binding interaction in mediating mesenchymal condensation and chondrogenesis

Abstract

Chondrogenesis of human mesenchymal stem cells (MSCs) apparently include a crucial transitional stage called mesenchymal condensation (MC), which iscomplex and governed by specific transcription factors (TFs). Among these, SRY-Box 9 (SOX9) plays pivotal roles in mediating cell-cell and cell-matrix interactions during MC and chondrogenesis. In this study, we aimed at investigating the association of SOX9-DNA binding activity with specific chondrogenic markers, collagen type II (COL2A1) and aggrecan (ACAN), in 3D-microencapsulated hMSCs and demonstrated the time course for expression pattern and level for chondrogenic markers at 2.5e5, 5e5 and 1e6 cell densities. Under microencapsulation, it was visibly observed nuclear localization of SOX9 at 1-h, 1-d and 2-d post-microencapsulation and higher COL2A1 deposition with time and cell density. For chondrogenesis, results from qPCR data normalized by monolayer coated with collagen (2Dc) revealed the highest SOX9 expression at 1-h post-microencapsulation and a gradual reduction with time. Concordantly, ACAN showed a decreasing trend with time in spite of lower expression than 2Dc in the entire duration. Unlike ACAN, COL2A1 expression increased at early time-points, then fluctuated with time and reached a maximum at 7-d. Two-way ANOVA showed significant differences for SOX9, ACAN and COL2A1 separately in the three cell densities (p<0.0001 for SOX9 and ACAN; p=0.003 for COL2A1) and at the seven time points except COL2A1 (p<0.0001). Furthermore, chromatin-immunoprecipitation (ChIP) analyses exhibited stronger SOX9 binding activity with the promoter and intron-1 enhancer of COL2A1 in MSCs with 3D-microencapsulation than 2Dc. Altogether, this work suggests MC and chondrogenesis are presumably promoted by enhanced SOX9 binding activity due to microencapsulation-induced epigenetic modification on the regulatory sites of chondrogenic markers. Further studies on the interaction between 3D microencapsulation and SOX9 binding activity are warranted to a more understanding of the transcriptional regulation for hMSCs chondrogenesis.