Abstract P023: HDAC Inhibition Promotes Cardiogenesis and the Survival of Embryonic Stem Cells Through Proteasome-Dependent Pathway

Abstract

Objectives: Histone deacetylase (HDAC) inhibition plays a crucial role in mediating cardiogenesis and myocardial protection, whereas HDAC degradation has recently attracted attention in mediating the biological function of HDACs. However, it remains unknown whether HDAC inhibition modulates cardiogenesis and embryonic stem cell (ESC) survival through the proteasome pathway. Methods and Results: Using the well-established mouse CGR8 mouse ESC culture, we evaluated the impact of HDAC inhibition and proteasome pathway on the cell death, viability and apoptosis in ESCs in response to oxidant stress (100μ mol/L hydrogen peroxides). We demonstrated that HDAC inhibitors, both TSA (50 nmol/L) and sodium butyrate (200 μ mol/L) that causes the pronounced reduction of HDAC4 activity, decreased cell death and increased viability of ESCs. HDAC inhibition reduced the cleaved caspase 3, 6, 9, PARP and TUNE-positive ESCs, which were abrogated with MG132 (0.5 μ mol/L), a specific proteasome inhibitor. Furthermore, we employed in vitro “hanging drop” methods to carry out two weeks of embryoid bodies (EB) culture to assess the effect of HDAC inhibition and proteasome pathway on cardiogenesis. HDAC inhibition stimulates the growth of EB, which is associated with faster spontaneous rhythmic contraction. HDAC inhibition increased the up-regulation of GATA4, MEF2, NKX2.5, cardiac actin, and α-SMA mRNA and protein levels that were abrogated by MG132. Immunostaining analysis demonstrates that trichostatin A and sodium butyrate resulted in a significant increase in cardiac lineage commitments that were blocked by the proteasome inhibition. Notably, HDAC inhibitors led to noticeable HDAC4 degradation, which was effectively prevented by MG132. Luciferase assay demonstrates an activation of MEF2 cardiac transcriptional factor by HDAC inhibition, which was repressed by MG132, revealing that the degradation of HDAC4 allows the activation of MEF2. Conclusions: Taken together, our study is the first to demonstrate that HDAC inhibition through proteasome pathway forms a novel signaling to determine the cardiac lineage commitment and elicit the survival pathway, which is dependent on specific HDAC4 degradation and subsequent MEF2 activation of ESCs.