Very-Low-Density Lipoprotein of Metabolic Syndrome Suppresses Store-Operated Calcium Entry through Modulations of STIM1 in HL-1 Atrial Myocytes

Abstract

Introduction: Metabolic syndrome (MetS) is a major risk for atrial myopathy and atrial fibrillation. Very-low-density lipoprotein (VLDL) of MetS (MetS-VLDL) exerts in vivo and in vitro cytotoxicity to atrial myocytes. Calcineurin-NFAT pathway, which is regulated by STIM1/Orai1-mediated store-operated calcium entry (SOCE), is pivotal in mediating adaptive cardiac hypertrophy. We hypothesized that MetS-VLDL can suppress SOCE and its downstream calcineurin-NFAT pathway. Methods & Results: The normal-VLDL and MetS-VLDL samples were isolated from peripheral blood of healthy volunteers and individuals with MetS, and used to incubate HL-1 atrial myocytes for 16 hours. Calcium imaging was facilitated with fura-2AM Ca2+ dye. After sarcoplasmic reticulum (SR) Ca2+ store was depleted with perfusion of thapsigarin and caffeine in a Ca2+ -free solution, SOCE was triggered upon reperfusion of a 1.8 mM Ca2+ solution. Protein expression of STIM1, Orai1, camodulin, CaMKII, NFAT, and calcineurin were quantified by Western blot. O-GlcNAylation of STIM1 and Orai1 were assessed by immunoprecipitation. The SR Ca2+ release was not changed in VLDLs-treated groups. SOCE was significantly attenuated by MetS-VLDL (0.59 ± 0.03 folds to control, p< 0.0001), through reduced membranous expression of STIM1 (0.32 ± 0.03 folds to control, p= 0.025), in conjunction with increased O-GlcNAylation modification. MetS-VLDL also reduced nuclear translocation of NFAT and intra-nuclear calcineurin (all p< 0.05). These changes were associated with derangement of myofilament proteins expression. Conclusions: The adaptive hypertrophy response in atrial myocytes was hampered by MetS-VLDL through inhibiting Ca2+-calcineurin-NFAT pathway. The VLDL-induced STIM 1 modulation and SOCE suppression may contribute to atrial myopathy in MetS.