Downregulated myocardial connexin 43 and suppressed contractility in rabbits subjected to a cholesterol-enriched diet

Abstract

The effects of hypercholesterolemia on the myocardium per se include electrophysiological and mechanical alterations. Since gap junctions are essential in electromechanical coupling throughout the heart, we examined the correlation between the temporal expression of cardiac connexin 43 (Cx43), contractile function, and conduction velocity in cholesterol-fed rabbits. After a 12-week feeding period, serum cholesterol levels gradually increased (Po0.001). In contrast, expression of cardiomyocyte Cx43 protein progressively decreased (60% reduction at 12 weeks, Po0.001). Such a reduction was also demonstrated by immunoconfocal microscopy, which further showed redistribution of Cx43 gap junctions at the lateral cell membrane. The downregulation of Cx43 protein was associated with increased levels of Cx43 mRNA (3.5 -fold at 12 weeks, Po0.001) and phosphorylated c-Jun N-terminal kinase (three-fold at 12 weeks, P ¼ 0.001). Functionally, although fractional shortening of the left ventricle remained unchanged throughout the feeding protocol, the cholesterol-fed rabbits had a reduced cardiac cycle-dependent variation of integrated backscatters, a decreased mitral ring systolic velocity, and an increased modified Tei index (all Po0.001), all of which indicated impaired intrinsic myocardial contractility and attenuated ventricular systolic performance. In Langendorff-perfused hearts of cholesterol-fed rabbits, decreased conduction velocity was observed (Po0.005). Withdrawal of the cholesterol-enriched diet for 18 weeks restored the contractile parameters and Cx43 protein expression. These findings suggest that Cx43 is highly involved in the molecular mechanism of hypercholesterolemia-induced cardiac contractile dysfunction and dysrhythmias.

Short-Duration Therapeutic Hypothermia Causes Prompt Connexin43 Gap Junction Remodeling in Isolated Rabbit Hearts

“…In each specimen, we randomly selected at least 4 images with myocardial fiber orientation parallel to the long axis of cells for analysis. 10 In these areas, cell border and Cx43 GJs in the intercalated disk could be easily identified ( Figures 3A,5A, MH images as examples). 10, 12 Assisted by image analysis software (QWIN, Leica), we measured (1) the percentage of total tissue area occupied by Cx43 immunoreactive signals, and (2) the percentage of Cx43 signal located outside the end-to-end cell junctions (lateralization) (Figures 3A,5A).…”

“…In each square, epicardial conduction perpendicular to the propagating wavefronts was selected to measure the CV (cm/s) using depolarization isochronal maps ( Figure 1B). 6,10 The mean of the CVs from these 4 sites became the CV of the heart. 6 By plotting CV against different S1 pacing cycle lengths (PCLs) to construct a CVR curve, "maximal CV reduction (cm/s)", which was defined as the difference in CV at the longest and shortest S1 PCLs, could be obtained (see Figure 6B in reference 18).…”

“…10, 12 Assisted by image analysis software (QWIN, Leica), we measured (1) the percentage of total tissue area occupied by Cx43 immunoreactive signals, and (2) the percentage of Cx43 signal located outside the end-to-end cell junctions (lateralization) (Figures 3A,5A). 10,12,22 In each heart, the percentages were means of the 4 sites.…”

“…10 The protein was loaded with an equal amount (20 μg) per lane for electrophoresis. 10,14 After transferring the protein to nitrocellulose, membranes were blocked and probed for 60 min with mouse anti-T-Cx43 (1:250, BD Biosciences, Lexington, KY, USA) and mouse anti-NP-Cx43 (1:250, Cx43 dephosphorylated at Ser 368 ; Zymed, California, CA, USA) antibodies.…”

Statin Therapy Decreases Myocardial Function as Evaluated Via Strain Imaging

“…Advanced echocardiographic imaging with tissue Doppler (TDI) and speckle tracking technology have gained popularity in the clinical and research realms as highly efficient methods to quantify myocardial function 18 -20 and have been used with both human and animal models of hypercholesterolemia to evaluate for minor changes in both systolic and diastolic function. 21,22 Speckle tracking technology uses similar technology to further quantify systolic function in very small areas of the myocardium reflecting left ventricle (LV) tissue deformation or strain. 23 Recently, TDI and speckle tracking derived strain imaging (SI) imaging have been used to evaluate the improved left ventricular response in humans and animals on statin therapy that has correlated with decreasing serum cholesterol values.…”