Investigation into the role of sirtuins in vascular calcification

Vascular calcification is a major health risk throughout the world and has long been associated with the development of type II diabetes. Previously thought to be a result of passive degeneration it is now understood to involve a host of complex signalling pathways, which regulate the promotors and inhibitors of osteogenesis within vascular smooth muscle cells (vSMCs). With 1 in 4 of the British population suggested to have diabetes, unpicking the molecular mechanism behind the development of this crippling pathology is required to develop further treatment of vascular calcification. Sirtuin 1 (SIRT1), an NAD+ dependent deacetylase has shown a beneficial role in insulin sensitivity and glucose homeostasis, as well as a known protective effect on inhibiting oxidative stress and inflammation within the vessel wall and therefore may be a promising candidate for regulation of vascular calcification within diabetic vessels. This study determined that SIRT1 is reduced within the diabetic patient ubiquitously, both within the vSMCs and serum when compared to non-diabetic controls. Furthermore, it confirms that vSMCs explanted from a diabetic vessel exhibit increased migratory and adhesive properties, presenting with extensive DNA damage and have an increased capacity to adopt a senescence associated secretory phenotype, in which osteogenic master transcription factor Runx2 is switched on, increasing trans-differentiation to an osteogenic phenotype. Additionally, the utilisation of a high glucose, phosphate and calcium vSMC tissue culture model demonstrates the induction of an osteogenic phenotype can be inhibited via the activation of SIRT1 using small molecular activator SRT1720 and conversely exacerbated by its inhibition using Sirtinol or siRNA. Furthermore, SIRT1 activation inhibits proliferative and migratory factors ERK and AKT activity within vSMCs, whilst increasing activation of DNA repair complex MRN and associated kinase ATM. These findings suggest that activation of SIRT1 within a diabetic vSMC model may reduce their migratory capacity, therefore reducing their development of a senescent phenotype through increasing repair of DNA damage, thus overall reducing the cells ability to promote calcification