Cyclin-Dependent Kinase 5–Mediated Hyperphosphorylation of Sirtuin-1 Contributes to the Development of Endothelial Senescence and Atherosclerosis

Abstract

Background-Endothelial senescence represents one of the major characteristics of vascular aging and promotes the development of atherosclerosis. Sirtuin-1 (SIRT1) is an NAD-dependent deacetylase possessing antiaging activities. During the occurrence of endothelial senescence, both the expression and activity of SIRT1 are downregulated. The present study was designed to investigate the molecular mechanisms contributing to the loss-of-SIRT1 function in senescent endothelial cells. Methods and Results-After repetitive passages, primary cultures of porcine aortic endothelial cells exhibited a severe senescence phenotype. Western blotting revealed that phosphorylation of SIRT1 at serine 47 (S47) was significantly enhanced in senescent endothelial cells. S47 phosphorylation was stimulated by agents promoting senescence and attenuated by drugs with antisenescence properties. Mutation of S47 to nonphosphorable alanine (S47A) enhanced whereas replacing S47 with phospho-mimicking aspartic acid (S47D) abolished the antisenescent, growth-promoting, and LKB1-downregulating actions of SIRT1. Phosphorylation at S47 was critically involved in the nuclear retention of SIRT1 but abolished its association with the telomeric repeat-binding factor 2-interacting protein 1. Cyclin-dependent kinase 5 (CDK5) was identified as an SIRT1 kinase modulating S47 phosphorylation. Knockdown or inhibition of CDK5 reduced the number of senescent endothelial cells, promoted nuclear exportation of SIRT1, and attenuated the expression of inflammatory genes in porcine aortic endothelial cells. The truncated regulatory subunit of CDK5, P25, accumulated in senescent porcine aortic endothelial cells and atherosclerotic aortas. Long-term treatment with roscovitine, a CDK5 inhibitor, blocked the development of cellular senescence and atherosclerosis in aortas of hypercholesterolemic apolipoprotein E-deficient mice. Conclusion-CDK5-mediated

Rap1 induces cytokine production in pro-inflammatory macrophages through NFκB signaling and is highly expressed in human atherosclerotic lesions

“…14,36 Previous findings indicated that Rap1 directly binds to the IKK complex in Hela S3 carcinoma cells, 10 but directly associates with IkBa in primary culture of porcine aortic endothelial cells (PAECs). 37 The present results on macrophages are in line with the former observation that Rap1 binds directly to the IKK complex. Indeed, the present co-immunoprecipitation experiments revealed that Rap1 binds directly to both IKKa and IKKb, but not to IkBa.…”

“…[42][43][44] Indeed, in senescent PAECs, the amount of Rap1 in the cytosol is elevated compared with young PAECs. 37 Thus, it is tempting to speculate that as telomere length is reduced, the ratio between telomere-bound and "free" Rap1 (available for the cytoplasmic activation of the NFkB pathway) is affected. This hypothesis implies that Rap1 could be an important molecular switch that links aging to chronic inflammation.…”

SIRT1 and SIRT6 Signaling Pathways in Cardiovascular Disease Protection

“…In ECs, increased cyclin-dependent kinase 5-mediated hyperphosphorylation of SIRT1 at Ser-47 prevents its nuclear exportation and the interaction with telomeric repeat-binding factor 2-interacting protein 1 (TERF2IP), a regulator of telomere function and NF-jB signaling (12).…”

12th International Symposium on Resistance Arteries (ISRA 2017) Manchester, September 3-6, 2017: Abstracts

“…Abstract: Background-P25 is a 209-amino acid COOH-terminal fragment of the regulatory subunit 1 (p35) for CDK5, a proline-directed serine/threonine kinase. Upregulation of p25 triggers a sustained activation of CDK5 and hyperphosphorylation of various substrates including SIRT1, the longevity regulator, in endothelial cells (1). The present study investigated the role of endothelial p25 in regulating endothelial senescence and adverse arterial remodeling.…”