Abstract 5565: Histone Deacetylase 5 Regulates Angiogenic Growth Factors And Guidance Molecules And Represses Angiogenesis
Posttranslational histone modification contributes to the regulation of gene transcription. Histone acetylation is regulated by histone deacetylases (HDACs). The class IIa HDACs are signal-responsive regulators of gene expression involved in vascular homeostasis. Therefore, we investigated the differential role of class IIa HDACs for the regulation of angiogenesis. We demonstrate that, among the HDAC isoforms tested, silencing of HDAC5 exhibited a unique pro-angiogenic effect evidenced by increased endothelial cell migration (121±5%, p<0,005), sprouting (216±35%, p<0,05) and vessel formation in vivo (159±13%, p<0,01). Consistently, overexpression of HDAC5 wt decreased sprout formation, indicating that HDAC5 is a negative regulator of angiogenesis. To analyze the mechanism, we transfected endothelial cells with different HDAC5 mutants. Overexpression of a nuclear HDAC5 mutant significantly suppressed sprout formation. Because myocyte enhancer factor-2 (MEF2) interacts with HDAC5 in cardiac myocytes, we tested whether MEF2 is required for HDAC5 function. Transfection of endothelial cells with HDAC5 ΔMEF2, which is not able to bind MEF2, still significantly decreased sprout formation. Moreover, transfection of an HDAC5 deacetylase-deficient mutant also significantly diminished sprout formation. Thus, the anti-angiogenic activity of HDAC5 was independent of MEF2 binding and deacetylase activity, but required a nuclear localization of HDAC5 indicating that HDAC5 might affect the transcriptional regulation of gene expression. To identify putative HDAC5 targets, we performed microarray expression analysis. Silencing of HDAC5 by siRNA increased expression of fibroblast growth factor 2 (FGF2) (484±27%, p<0,05) and angiogenic guidance factors including Slit2 (816±96%, p<0,05). CHIP assays demonstrate that HDAC5 binds to the promoter of FGF2 and Slit2. Antagonization of FGF2 or of Slit2 reduced sprout induction in response to HDAC5-siRNA. In summary, HDAC5 represses angiogenic genes, like FGF2 and Slit2, which causally contribute to capillary-like sprouting of endothelial cells. The de-repression of a set of angiogenic genes by HDAC5 inactivation may provide a useful therapeutic target for induction of angiogenesis.