Background: 

The class III histone deacetylase SIRT1 has been identified as a highly conserved key regulator of ageing and longevity in model organisms such as S. cerevisiae and C. elegans, in mammals and even in primates, which regulates cellular functions such as differentiation, senescence and metabolism. However, the role of SIRT1 in vascular homeostasis and in the development of vascular proliferative disease remains elusive.

Methods and Results: 

Strong expression of SIRT1 was detected in the media of a variety of healthy human vessels but was found downregulated in atherectomy specimens from carotid and coronary arteries as assessed by immunohistochemistry, qPCR and immunoblotting. Moreover, we detected a downregulation of SIRT1 mRNA and protein expression in proliferating human coronary smooth muscle cells (SMC) in vitro, in atherosclerotic plaques of ApoE/LDLr KO mice and following vascular injury in the mouse femoral artery. Pharmacological inhibition (nicotinamide) or silencing of endogenous SIRT1 using siRNA resulted in an increased proliferation and migration of SMC under basal as well as serum-induced conditions. Consistently, MEF cells isolated from SIRT^-/- mice showed an augmented proliferative response to serum stimulation compared to WT-MEF cells. In contrast, pharmacological activation using resveratrol or reconstitution of SIRT1 levels using adenoviral overexpression of the WT form but not a deacetylase-dead mutant prevented the proliferation and migration of SMC in vitro and significantly reduced neointima formation in dilated mouse femoral arteries (Ad-WT-SIRT1: 0.9 0.4 vs. Ad-control: 1.9 0.6; P<0.005). Interestingly, activation/reconstitution of SIRT1 also rendered SMC more resistant to H₂O₂-mediated apoptosis and resulted in a more differentiated, quiescent and contractile SMC phenotype. Mechanistically, following a protein-interaction screening, we demonstrate that SIRT1 directly interacts with (as shown by FRET analysis) and deacetylates (as shown by IP and MALDI-TOF) the transcription factor Stat3, thereby reducing its transcriptional activity (promoter-binding and luciferase assays). cDNA microarray- and subsequent qPCR and immunoblot analysis identified BIRC5 (survivin) as one of the most strongly upregulated genes following SIRT1 knock down and subsequent analysis revealed that survivin transactivation is regulated by Stat3. Further analyses, using Stat3 or Survivin knock down- or activation approaches respectively, confirmed that SIRT1-mediated inhibition of the Stat3-dependent transactivation of survivin represents the key mechanism of SIRT1's antiproliferative and re-differentiation-inducing effect.

Conclusion: 

Thus, our study describes for the first time that SIRT1 is a critical modulator of SMC function and vascular lesion formation and identifies SIRT1-Stat3-survivin axis as a novel potential target for the prevention or therapy of vascular proliferative diseases.