HDAC inhibition promotes cardiogenesis and the survival of embryonic stem cells through proteasome-dependent pathway.

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. Using the well-established mouse ESC culture, we demonstrated that HDAC inhibitors, both trichostatin A (TSA,50  nmol/L) and sodium butyrate (NaB, 200  µmol/L) that causes the pronounced reduction of HDAC4 activity, decreased cell death and increased viability of ESCs in response to oxidant stress. HDAC inhibition reduced the cleaved caspases 3, 6, 9, PARP, and TUNEL positive ESCs, which were abrogated with MG132 (0.5  µmol/L), a specific proteasome inhibitor. Furthermore, HDAC inhibition stimulates the growth of embryoid bodies (EB), which are associated with a faster spontaneous rhythmic contraction. HDAC inhibition increases the up-regulation of GATA4, MEF2C, Nkx2.5, cardiac actin, and α-SMA mRNA and protein levels that were abrogated by MG132. TSA and NaB 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 for the activation of MEF2. 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 elicits the survival pathway.