Abstract 433: HDAC7 is Essential for Stem Cell Differentiation into Smooth Muscle Cells
Background: Embryonic stem cells (ESCs) possess the potential to differentiate into specific cell lineages, such as vascular smooth muscle cells (SMCs). The homeostasis of histone acetylation and deacetylation mediated by histone deacetylase (HDAC) is known to play a central role in the regulation of gene expression, through co-operation with other transcription factors. However, it is unknown whether HDAC plays a role in mediating stem cell differentiation into SMCs.
Methods and results: Mouse ESCs were seeded on collagen IV-coated flasks and cultured in the absence of Leukemia Inhibitory Factor (LIF) in differentiation medium for 3 to 9 days in order to induce SMCs differentiation. Western blots and double-immunofluorescence staining demonstrated that HDAC7 expressed in parallel with SMC marker genes. Upregulation of HDAC7 expression resulted in increase in SMC marker expression, while downregulation of HDAC7 by siRNA caused decrease of SMC marker expression. In ex vivo culture of embryonic cells from SM22-LacZ transgenic mice, over-expression of HDAC7 significantly increased beta-gal positive cells, indicating a crucial role of HDAC7 in SMC differentiation during embryonic development. An important observation of this study is that HDAC7 undergoes alternative splicing during ESC differentiation, resulting in alternative translation from second ATG codon, giving rise to a short HDAC7 missing the N-terminal 22 amino acids. We also found that PDGF induced SMCs differentiation through the regulation of HDAC7 transcription and splicing, in which siHDAC7 knockdown ablated PDGF-induced SMC marker expression. Spliced HDAC7 increased SMC differentiation, while the short HDAC7 had no effect or even downregulated SMC differentiation. Further experiments revealed that the short HDAC7 isoform bound to MEF2C, while the full length HDAC7 did not, indicating that HDAC7 splicing can induce SMCs differentiation through the modulation of MEF2C-mediated gene expression.
Conclusions: Our findings provide novel information on the mechanism involved in SMC differentiation, and identify HDAC7 as a new target in therapeutic intervention on vascular disease, where inhibition of vascular progenitor cell differentiation into SMCs would be beneficial.