Atorvastatin Treatment Prevents Alterations in Coronary Smooth Muscle Nuclear Ca ²⁺ Signaling in Diabetic Dyslipidemia

Abstract

Atorvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, alters bulk myoplasmic Ca²⁺ regulation and inhibits phenotypic modulation and proliferation of vascular smooth muscle in culture. Nuclear Ca²⁺ (Ca_n) signaling is tightly coupled to transcriptional events and cell growth. Therefore, we hypothesized that in vivo treatment with atorvastatin would attenuate alterations in mitogen-induced Ca_n signaling associated with coronary atherosclerosis. Three groups of male Yucatan pigs were treated for 20 weeks: controls, alloxan-induced diabetics fed an atherogenic diet and diabetics fed an atherogenic diet plus atorvastatin (80 mg/day). Right coronary artery single-cell cytosolic Ca²⁺ (Ca_c) and Ca_n responses to the mitogen endothelin-1 (5 × 10^–8 M) were measured by laser confocal microscopy using the calcium indicator Fluo-4. We observed a 39% increase in Ca_c and a 52% increase in Ca_n responses to endothelin-1 in cells from diabetic dyslipidemic arteries compared to control. These alterations were prevented in animals treated with atorvastatin. We show that during proliferation, the nucleus of a smooth muscle cell becomes rounded and loses the characteristic multilobular shape, clefts and invaginations. Consistent with this, a redistribution of Ca²⁺ stores from a transnuclear morphology in controls to a more perinuclear morphology occurred in cells from diabetic dyslipidemic arteries and was prevented by atorvastatin. In addition, the peak Ca_n responses to endothelin-1 were inversely correlated (r = 0.712) with the extent of the transnuclear distribution of Ca²⁺ stores and directly correlated (r = 0.874) with the extent of atherosclerosis, as assessed in vivo by intravascular ultrasound. These findings indicate that chronic treatment with atorvastatin directly decreases mitogen-induced Ca_n mobilization, which we suggest is related to the spatial localization of Ca_n stores.