SIRT1 activity orchestrates ECM expression during hESC-chondrogenic differentiation

Epigenetic modification is a key driver of differentiation and the deacetylase Sirtuin1 (SIRT1) is an established regulator of cell function, ageing and articular cartilage homeostasis. Here we investigate the role of SIRT1 during development of chondrocytes by using human embryonic stem cells (hESCs). HESC-chondroprogenitors were treated with SIRT1 activator; SRT1720, or inhibitor; EX527, at different development stages. Activation of SIRT1 during 3D-pellet culture led to significant increases in expression of ECM genes for type-II collagen (COL2A1) and aggrecan (ACAN), and chondrogenic transcription factors SOX5 and ARID5B, with SOX5 ChIP analysis demonstrating enrichment on the ACAN -10 enhancer. Unexpectedly, while ACAN was enhanced, GAG retention in the matrix was reduced when SIRT1 was activated. Significantly, ARID5B and COL2A1 were positively correlated, with Co-IP indicating binding of ARID5B to SIRT,1 suggesting that COL2A1 expression is promoted by an ARID5B and SIRT1 interaction. In conclusion, SIRT1 activation positively impacts on the expression of the main ECM components, whilst mitigating ECM organization and GAG content during cartilage development. These results suggest that SIRT1 activity is beneficial to cartilage development and matrix synthesis, but that use in cartilage regeneration would require tailoring.