Very Low-Density Lipoproteins of Metabolic Syndrome Modulates STIM1, Suppresses Store-Operated Calcium Entry, and Deranges Myofilament Proteins in Atrial Myocytes.

Individuals with metabolic syndrome (MetS) are at high risk for atrial myopathy and atrial fibrillation. Very low-density lipoproteins (VLDLs) of MetS (MetS-VLDLs) are cytotoxic to atrial myocytes in vivo and in vitro. The calcineurin-nuclear factor of activated T-cells (NFAT) pathway, which is regulated by stromal interaction molecule 1 (STIM1)/ calcium release-activated calcium channel protein 1 (Orai1)-mediated store-operated Ca2+ entry (SOCE), is a pivotal mediator of adaptive cardiac hypertrophy. We hypothesized that MetS-VLDLs could affect SOCE and the calcineurin-NFAT pathway. Normal-VLDL and MetS-VLDL samples were isolated from the peripheral blood of healthy volunteers and individuals with MetS. VLDLs were applied to HL-1 atrial myocytes for 18 h and were also injected into wild-type C57BL/6 male mouse tails three times per week for six weeks. After the sarcoplasmic reticulum (SR) Ca2+ store was depleted, SOCE was triggered upon reperfusion with 1.8 mM of Ca2+. SOCE was attenuated by MetS-VLDLs, along with reduced transcriptional and membranous expression of STIM1 (P = 0.025), and enhanced modification of O-GlcNAcylation on STIM1 protein, while Orai1 was unaltered. The nuclear translocation and activity of calcineurin were both reduced (P < 0.05), along with the alteration of myofilament proteins in atrial tissues. These changes were absent in normal-VLDL-treated cells. Our results demonstrated that MetS-VLDLs suppressed SOCE by modulating STIM1 at the transcriptional, translational, and post-translational levels, resulting in the inhibition of the calcineurin-NFAT pathway, which resulted in the alteration of myofilament protein expression and sarcomere derangement in atrial tissues. These findings may help explain atrial myopathy in MetS. We suggest a therapeutic target on VLDLs to prevent atrial fibrillation, especially for individuals with MetS.

The sodium-glucose co-transporter 2 inhibitor empagliflozin attenuates cardiac fibrosis and improves ventricular hemodynamics in hypertensive heart failure rats.

BACKGROUND: Sodium glucose co-transporter 2 inhibitor (SGLT2i), a new class of anti-diabetic drugs acting on inhibiting glucose resorption by kidneys, is shown beneficial in reduction of heart failure hospitalization and cardiovascular mortality. The mechanisms remain unclear. We hypothesized that SGLT2i, empagliflozin can improve cardiac hemodynamics in non-diabetic hypertensive heart failure. METHODS AND RESULTS: The hypertensive heart failure model had been created by feeding spontaneous hypertensive rats (SHR) with high fat diet for 32 weeks (total n = 13). Half SHRs were randomized to be administered with SGLT2i, empagliflozin at 20 mg/kg/day for 12 weeks. After evaluation of electrocardiography and echocardiography, invasive hemodynamic study was performed and followed by blood sample collection and tissue analyses. Empagliflozin exhibited cardiac (improved atrial and ventricular remodeling) and renal protection, while plasma glucose level was not affected. Empagliflozin normalized both end-systolic and end-diastolic volume in SHR, in parallel with parameters in echocardiographic evaluation. Empagliflozin also normalized systolic dysfunction, in terms of the reduced maximal velocity of pressure incline and the slope of end-systolic pressure volume relationship in SHR. In histological analysis, empagliflozin significantly attenuated cardiac fibrosis in both atrial and ventricular tissues. The upregulation of atrial and ventricular expression of PPARα, ACADM, natriuretic peptides (NPPA and NPPB), and TNF-α in SHR, was all restored by treatment of empagliflozin. CONCLUSIONS: Empagliflozin improves hemodynamics in our hypertensive heart failure rat model, associated with renal protection, attenuated cardiac fibrosis, and normalization of HF genes. Our results contribute some understanding of the pleiotropic effects of empagliflozin on improving heart function.

Simultaneous Electrocardiography Recording and Invasive Blood Pressure Measurement in Rats.

For studies related to cardiovascular physiology or pathophysiology, blood pressure (BP) and electrocardiography are basic observational parameters. Research focusing on cardiovascular disease models, potential cardiovascular therapeutic targets or pharmaceutical agents requires assessment of systemic arterial pressure and heart rhythm changes. In situations where radio telemetry systems are not available or affordable, the technique of femoral artery cannulation is an alternative way to obtain intra-arterial pressure waveform recordings and systemic BP measurements. This technique is economical and can be performed with standard equipment in animal facilities. However, invasive arterial pressure recording requires cannulation of small arteries, which can be a challenging surgical skill. Here, we present step-by-step protocols for femoral artery cannulation procedures. Key procedures include the calibration of the data acquisition system, tissue dissection and femoral artery cannulation, and setup of the arterial cannulation system for pressure recording. Surface electrocardiography recording procedures are also included. We also present examples of BP recordings from normotensive and hypertensive rats. This protocol allows reliable direct recordings of systemic BP with simultaneous electrocardiography.

High fat diet aggravates atrial and ventricular remodeling of hypertensive heart disease in aging rats.

BACKGROUND/PURPOSE: Left ventricular hypertrophy is a major cause of heart failure in aging population. This study is to determine whether an excess dietary fat is lipotoxic or lipoprotein to the hypertrophic aging heart. METHODS: At 44-week-old, a normal chow (12% fat) was replaced a high-fat diet (HFD; 45% fat) for randomly selective spontaneously hypertensive rats (SHR + HFD, n = 6) and Wistar-Kyoto rats (WKY + HFD, n = 6, normotensive control). Others (SHR, n = 11; WKY, n = 10) were continuously fed with normal diets. After 27 weeks, electrocardiogram, echocardiography, and femoral arterial catheterization were performed before rats being sacrificed for molecular biology analyses. RESULTS: HFD aggravated cardiac atrial, ventricular dilation and hypertrophy in SHR (LV mass: SHR + HFD 2026.0 ± 424.9 vs SHR 1449 ± 461.1 mg, unpaired t test P < 0.05). HFD caused significant atrial dilatation in both WKY (LA diameter, 5.38 ± 0.36 vs 4.11 ± 0.42 mm, P < 0.001) and SHR (6.13 ± 0.79 vs 4.69 ± 1.00, P < 0.01). Only in SHR, HFD induced significant left ventricular dilatation (LV diameter, 8.87 ± 1.25 vs 7.08 ± 1.00 mm, P < 0.01) and reduced ejection fraction (LVEF, 62.8 ± 11.6 vs 75.1 ± 9.2 mm, P < 0.05). The α-myosin heavy chain was significantly upregulated in atria and ventricles of HFD groups. HFD induced significant upregulation of PPARα, ACADM, and TNFα transcripts in atrial tissues (P < 0.05). CONCLUSION: Hypertensive heart disease in aging rats was aggravated by HFD with worse atrial, ventricular remodeling and associated with left ventricular systolic function impairment.