Abstract 5613: Class IIa HDAC6 Contributes to Angiogenesis and Endothelial Cell Function
Acetylation of histone proteins contributes to the regulation of gene expression by alteration of chromatin structure. Histone deacetylases (HDACs) act as modulators of gene expression by deacetylation of histone proteins as well as non-histone proteins. Previous studies identified the class IIa histone deacetylases HDAC5 and HDAC7 as regulators of angiogenesis. The class IIb HDAC6 is the only HDAC that possesses two functional deacetylase domains and is known to be involved in lymphocyte chemotaxis and in cancer development. However, the function of HDAC6 in endothelial cells is unknown. Therefore, we analyzed the effect of HDAC6 for endothelial cell functions during angiogenesis. HDAC6 is mainly localized in the cytoplasm of human umbilical vein endothelial cells. Knockdown of HDAC6 with siRNA oligonucleotides significantly decreased endothelial cell sprouting from spheroids (42%±7, p<0.05, N=5), tube formation in matrigel assay (81%±2, p<0.05, N=3) and endothelial cell migration in a scratched wound assay (65%±5, p<0.05, N=3) without affecting cell viability. These results were confirmed using a second unrelated oligonucleotide. Consistently, overexpression of HDAC6 wild-type increased endothelial cell sprouting (122%±8, N=4), indicating that HDAC6 is a positive regulator of angiogenesis. The catalytic activity of the second HDAC-domain seems to be necessary for the pro-angiogenic effect of HDAC6, because overexpression of a deletion mutant, which lacks the second deacetylase domain, did not affect sprouting (95%±10, N=4). Because the second HDAC-domain is known to be responsible for α-tubulin deacetylation and acetylation of α-tubulin might play a role in cell migration, we assessed the effect of the HDAC6 specific tubulin deacetylation inhibitor tubacin on endothelial sprout formation. Application of tubacin did not affect sprouting, indicating that the mechanism is independent of α-tubulin deacetylation. In summary, we found that the cytoplasmic HDAC6 is necessary for in vitro angiogenesis as assessed by endothelial sprouting, tube formation and migration. Mechanistically, the pro-angiogenic effect of HDAC6 in endothelial cells requires the second deacetylase domain, but is independent of α-tubulin deacetylation.