Atorvastatin Treatment Prevents Alterations in Coronary Smooth Muscle Nuclear Ca²⁺ 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^–8M) 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.

Increased atherosclerosis in diabetic dyslipidemic swine

“…This study is a significant extension of our previous work (19,20,22,23) and that of Gerrity et al (47) in several regards. First, we have shown in high fat/CH fed diabetic pigs a strong, direct association of LDL and LDL/HDL ratio with coronary atheroma quantified by the clinically used intravascular ultrasound method.…”

“…For VLDL, LDL, and by guest, on May 8, 2018 www.jlr.org Downloaded from HDL lipid content, fractions corresponding to these lipoproteins were collected and assayed for CH and TG concentration by standard enzymatic assay. Certain plasma lipid concentrations at 12 weeks for C, HF, DF, and DF ϩ A pigs were reported previously in studies directed at investigating calcium metabolism in coronary smooth muscle cells (20,23,24). Liver lipids were measured by the HPLC method of Homan and Anderson (25) using a 10 cm ϫ 4.6 mm silica gel column (Spherisorb), a SEDEX 55 evaporative light scattering detector (Richard Scientific, Inc.), and 1,2-di-O -hexadecyl-rac-glycerol as the internal standard.…”

“…1) nor insulin sensitivity (Otis, Wamhoff, Sturek, unpublished observations). We (19,20,23) and others (62,63) have suggested that Ca 2ϩ metabolism is altered in coronary smooth muscle cells of diabetics. Using cells isolated from the same pigs described in the current paper, Ca 2ϩ uptake into sarcoplasmic reticulum (measured in presence of caffeine) and into non-sarcoplasmic reticulum Ca 2ϩ stores (measured in presence of ionomycin) was increased in DF smooth muscle cells compared with cells from HF pigs.…”

“…Atorvastatin treatment reversed increases in Ca 2ϩ uptake into both storage sites (20). Alterations in coronary smooth muscle nuclear calcium signaling may be an important component in atherosclerosis development, possibly through induction of cell proliferation (23). Other reports have indicated that HMG-CoA reductase inhibitors affect the vessel wall independent of CH-lowering.…”

Lysophosphatidylcholine, a component of atherogenic lipoproteins, induces the change of calcium mobilization via TRPC ion channels in cultured human corporal smooth muscle cells

“…There are reports that ox-LDL increases intracellular free Ca 2 þ concentration ([Ca 2 þ ] i ) in various smooth muscle preparations. 19,20 To date, however, there is no report about ox-LDL effect in corporal smooth muscle preparation. In our study, we showed that LPC increased [Ca 2 þ ] i and Ca 2 þ influx in isolated myocytes, suggesting that the procontractile action of LPC could be endothelium independent.…”