Sirtuin 6 mitigates thoracic aortic aneurysm progression via maintenance of mitochondria homeostasis in vascular smooth muscle cells

Aortic aneurysm and dissection (AAD) is a life-threatening disease without effective pharmacological treatments. The progressive loss of vascular smooth muscle cells (VSMCs) is the fundamental pathophysiological basis for AAD, but the underlying mechanisms are largely unknown. Sirtuin 6 (SIRT6), a class III histone deacetylase, is critical for maintenance of VSMC homeostasis and consequent prevention of vascular remodeling-related diseases. However, its role in AAD development requires further investigation. Here, we show that SIRT6 expression was significantly reduced in VSMCs of the thoracic aorta in AAD patients. Sirt6 deficiency in VSMCs dramatically accelerated angiotensin Ⅱ (Ang Ⅱ) infusion-induced AAD formation and rupture even without an Apoe-deficient background. In vitro studies demonstrated that Sirt6 deficiency led to mitochondrial dysfunction and accelerated VSMC senescence. Mechanistically, SIRT6 could bind and deacetylate NRF2, a key transcription factor for mitochondrial biogenesis, however, Sirt6 deficiency inhibited NRF2 and reduced mRNAs encoding mitochondrial complex. Notably, MDL-811, a newly developed small-molecule SIRT6 agonist, effectively reversed Ang Ⅱ-induced mitochondrial dysfunctions in human aortic smooth muscle cells. More importantly, MDL-811 also mitigated AAD progression in mice. These findings suggest that SIRT6 plays a protective role in AAD development and targeting SIRT6 with small-molecule activators such as MDL-811 could represent a promising therapeutic strategy for AAD.