SIRT1 Mutation Impairs Ca²⁺ Buffering in Coronary Smooth Muscle Cells of Ossabaw Miniature Swine

Abstract

Background Metabolic syndrome (MetS) impairs sarco‐endoplasmic reticulum Ca2+ ATPase (SERCA) activity in coronary smooth muscle (CSM) and is implicated in coronary atherosclerosis in Ossabaw miniature swine. Sirtuin 1 (SIRT1) is a deacetylase that has diverse roles in intracellular Ca2+ signaling, metabolism, and cardiovascular disease. SIRT1 impairment exacerbates MetS and vascular disease, including calcification. After Ca2+ is increased in CSM by Ca2+ influx or release from the sarcoplasmic reticulum (SR), the Ca2+ is then buffered by either Ca2+ efflux from the cell by the plasmalemmal Ca2+ ATPase or sequestration back into the SR via SERCA. SIRT1 inhibition hyper‐acetylates SERCA and decreases activity, thereby impairing the Ca2+ buffering capacity of the cell. Hypothesis MetS and SIRT1 mutation will impair Ca2+ buffering in CSM. Methods Using CRISPR/Cas9 methodology a point mutation (SIRT1L100P) was made in Ossabaw miniature swine to mimic the naturally occurring mutation in humans and decrease SIRT1 activity, thereby resulting in hyperacetylation of Ca2+transporters and impaired function. Four groups of pigs were used to analyze genotype and diet interactions: wild type lean, SIRT1 lean, wild type MetS, and SIRT1 MetS. Pigs were age 4 months at the start and fed normal chow (lean) or atherogenic diet (MetS) for 7 months. CSM cells were enzymatically dispersed and Ca2+ was measured with fura‐2. The main Ca2+ regulation protocol was the maximal release of Ca2+ from the SR by 5 mM caffeine and then assessment of Ca2+ efflux and sequestration. Time to half recovery of Ca2+ to baseline during caffeine exposure was measured to assess Ca2+ efflux (rapid phase Ca2+buffering) and deviation from baseline was measured to assess SERCA function (slow phase Ca2+buffering). Results There was no effect of MetS or SIRT1 mutation on Ca2+ efflux. Two‐way ANOVA showed SIRT1 mutation alone inhibits SERCA buffering of Ca2+ in CSM (p=0.0005). There was no effect of MetS diet (p=0.184) and no interactions of SIRT1 genotype and MetS diet (p=0.113) on SERCA activity. Conclusion SIRT1L100P mutation is likely to contribute to coronary atherosclerosis and SIRT1 activators may be effective therapies.