Down Regulation of SUV39H1 and CITED2 Exerts Additive Effect on Promoting Adipogenic Commitment of Human Mesenchymal Stem Cells.

Abstract

Human adipogenesis is the process through which uncommitted human mesenchymal stem cells (hMSCs) differentiate into adipocytes. Through a siRNA-based high throughput screen that identifies adipogenic regulators whose expression knockdown leads to enhanced adipogenic differentiation of hMSCs, two new regulators, SUV39H1, a histone methyltransferase that catalyze H3K9Me3, and CITED2, a CBP/p300 interacting transactivator with Glu/Asp rich carboxy-terminal domain 2 were uncovered. Both SUV39H1 and CITED2 are normally down regulated during adipogenic differentiation of hMSCs. Further expression knockdown induced by siSUV39H1 or siCITED2 at the adipogenic initiation stage significantly enhanced adipogenic differentiation of hMSCs as compared to siControl treatment, with siSUV39H1 acting by both accelerating fat accumulation in individual adipocytes and increasing the total number of committed adipocytes, whereas siCITED2 acting predominantly by increasing the total number of committed adipocytes. In addition, both siSUV39H1 and siCITED2 were able to redirect hMSCs to undergo adipogenic differentiation in the presence of osteogenic inducing media, which normally only induces osteogenic differentiation of hMSCs in the absence of siSUV39H1 or siCITED2. Interestingly, simultaneous knockdown of both SUV39H1 and CITED2 resulted in even greater levels of adipogenic differentiation of hMSCs and expression of CEBPα and PPARγ, two master regulators of adipogenesis, as compared to those elicited by single gene knockdown. Furthermore, the effects of co-knockdown were equivalent to the additive effect of individual gene knockdown. Taken together, this study demonstrates that SUV39H1 and CITED2 are both negative regulators of human adipogenesis and down-regulation of both genes exerts an additive effect on promoting adipogenic differentiation of hMSCs through augmented commitment.