Restoring vascular endothelial autophagic flux reduces atherosclerotic lesions

Atherosclerotic lesions preferentially develop in arterial areas exposed to low shear stress, where endothelial cells express a pro-inflammatory, apoptotic, and senescent phenotype. Autophagy is a lysosomal mechanism that recycles damaged organelles and protein aggregates to maintain cellular homeostasis. Stimulation of autophagy in high shear stress conditions is an atheroprotective process. Conversely, endothelial cells exposed to atheroprone low shear stress present a defective autophagic flux, which favors a pro-inflammatory phenotype and the formation of atherosclerotic lesions. Since an efficient autophagic flux is dependent on α-tubulin acetylation, which is reduced under low shear stress, we hypothesized that increasing α-tubulin acetylation could restore adequate levels of autophagy in endothelial cells exposed to low shear stress. We found that blocking Histone Deacetylase 6 (HDAC6) activity, either by pharmacological inhibition (Tubastatin-A) or genetic approaches (shHDAC6), raised levels of acetylated α-tubulin, as well as LC3-II/I ratio, LC3 punctae area and autophagic flux in cultured endothelial cells exposed to low shear stress. This effect was associated with a reduced expression of inflammatory markers (Intercellular adhesion molecule-1 (ICAM-1), Vascular cell Adhesion Protein-1 (VCAM-1) and Monocyte Chemoattractant Protein-1 (MCP-1)) in Tumor Necrosis Factor-alpha (TNF-α)-stimulated cells. We observed increased endothelial autophagic flux in the aortic arch of the HDAC6-/-/ApoE-/- mice. Subsequently, atherosclerotic plaque size was significantly reduced in the atheroprone areas of chimeric HDAC6-/-/ApoE-/- mice, transplanted with HDAC6+/+/ApoE-/- bone marrow, when compared to HDAC6+/+/ApoE-/- littermate controls. Taken together, these results indicate that targeting α-tubulin acetylation, via HDAC6-inhibition, may be an interesting strategy to restore endothelial autophagic flux and to promote an atheroprotective endothelial phenotype despite unfavorable shear stress conditions.