Homeostatic balance of histone acetylation and deconstruction of repressive chromatin marker H3K9me3 during adipocyte differentiation of 3T3-L1 cells.

Background Adipocyte differentiation is completed by changing gene expression. Chromatin is closely related to gene expression. Therefore, its structure might be changed for adipocyte differentiation. Mouse 3T3-L1 preadipocytes have been used as a cell model to study molecular mechanisms of adipogenesis. Objective To examine changes of chromatin modification and expression of histone modifying enzymes during adipocyte differentiation. Methods Microscopic analysis and Oil Red O staining were performed to determine distinct phenotype of adipocyte differentiation. RT-PCR and Western blot analysis were used to examine expression levels of histone modifying enzymes during adipocyte differentiation. Histone modifications were examined by immunostaining analysis. Results Expression levels of P300 and cbp were increased during adipocyte differentiation. However, acetylation of histones was not quantitatively changed postdifferentiation of 3T3-L1 cells compared to that at pre-differentiation. RT-PCR and Western blot analyses showed that expression levels of hdac2 and hdac3 were increased during adipocyte differentiation, suggesting histone acetylation at chromatin level was homeostatically controlled by increased expression of both HATs and HDACs. Tri-methylation level of H3K9 (H3K9me3), but not that of H3K27me3, was significantly decreased during adipocyte differentiation. Decreased expression of setdb1 was consistent with reduced pattern of H3K9me3. Knock-down of setdb1 induced adipocyte differentiation. This suggests that setdb1 is a key chromatin modifier that modulates repressive chromatin. Conclusion These results suggest that there exist extensive mechanisms of chromatin modifications for homeostatic balance of chromatin acetylation and deconstruction of repressive chromatin during adipocyte differentiation.