Thiol redox signaling in aortic aneurysm

PROJECT SUMMARY/ABSTRACT Marfan syndrome is a connective tissue disorder caused by fibrillin-1 gene mutations, which predisposes to thoracic aortic aneurysm and aortic dissection (TAAD). Aortic aneurysm in MFS usually remains clinically silent, whilst progressively worsening until the aortic wall eventually dissects. Aortic dissections in MFS can occur even at aortic dimensions not considered eligible for surgical repair, leading to sudden deaths. Molecular and genetic culprits of TAAD are only partially understood, hampering the discovery of urgently needed therapies. Recent evidence indicates increased oxidants in aneurysmal aortas of patients and animal models of MFS; however, underlying redox mechanisms that may causally contribute to TAAD pathogenesis remain elusive. We found that oxidants-induced post-translational modifications of cysteine thiols, specifically glutathionylation, are significantly increased in aortas of individuals and a mouse model with Marfan syndrome (Fbn1mgR/mgR mice), and that sirtuin- 1 (Sirt1) is one of these glutathionylated proteins. Sirt1 is a NAD+-dependent lysine deacetylase essential to suppress inflammation, matrix metalloproteinases (MMP2/9) activation and vascular smooth muscle cell (VSMC) senescence. We hypothesize that oxidative inactivation of Sirt1 in VSMC is a redox mechanism contributing to TAAD pathogenesis in Marfan syndrome. Specifically, loss of Sirt1 activity in VSMC due to glutathionylation contributes to vascular media degeneration and aortic wall pathological remodeling by increasing VSMC phenotyping changes, inflammation and MMP2/9 hyperactivation leading to aortic wall mechanical failure and TAAD. We will study these aspects with two Specific Aims. In Aim 1, we will use Fbn1mgR/mgR mice in which Sirt1 is overexpressed and the de-glutathionylation enzyme glutaredoxin-1 (Glrx) is deleted, specifically in VSMC, to examine cause-and-effect between Sirt1 glutathionylation and TAAD development. We will also use novel genetic tools (adeno-associated viruses expressing a redox-resistant Sirt1 mutant or Glrx) to determine whether preventing Sirt1 glutathionylation ameliorates TAAD in Fbn1mgR/mgR mice by suppressing VSMC phenotypic changes and MMP2/9 activation. In Aim 2, we will use in vitro systems (human and mouse Marfan VSMC) to elucidate whether lack of Sirt1 activity in glutathionylated Sirt1 contributes to VSMC phenotypic changes and MMP2/9 hyperactivation via HMGA1, a newly identified Sirt1 deacetylation target. Overall, our innovative studies will fill knowledge gaps on redox mechanisms of TAAD and pave the way for targeted therapies to prevent TAAD in individuals at risk, such as those with Marfan syndrome, for which currently there are very limited treatment options.