Atrial fibrillation and its arrhythmogenesis associated with insulin resistance

Cardiovasc Diabetol. 2019 Sep 26;18(1):125. doi: 10.1186/s12933-019-0928-8.

Abstract

Background: Insulin resistance (IR) is considered as a risk factor for atrial fibrillation (AF) even before diabetes develops. The pathophysiology and underlying mechanism are largely unclear.

Methods: We investigated the corresponding mechanism in two IR models of rats fed 15-week high-fat (HFa) and high-fructose/cholesterol (HFr) diets. AF was evaluated and induced by burst atrial pacing. Isolated atrial myocytes were used for whole-cell patch clamp and calcium assessment. Ex vivo whole heart was used for optical mapping. Western blot and immunofluorescence were used for quantitative protein evaluation.

Results: Both HFa and HFr rat atria were vulnerable to AF evaluated by burst atrial pacing. Isolated atrial myocytes from HFa and HFr rats revealed significantly increased sarcoplasmic reticulum calcium content and diastolic calcium sparks. Whole-heart mapping showed prolonged calcium transient duration, conduction velocity reduction, and repetitive ectopic focal discharge in HFa and HFr atria. Protein analysis revealed increased TGF-β1 and collagen expression; increased superoxide production; abnormal upregulation of calcium-homeostasis-related proteins, including oxidized CaMKIIδ, phosphorylated-phospholamban, phosphorylated-RyR-2, and sodium-calcium exchanger; and increased Rac1 activity in both HFa and HFr atria. We observed that inhibition of CaMKII suppressed AF in both HF and HFr diet-fed rats. In vitro palmitate-induced IR neonatal cardiomyocytes and atrial fibroblasts expressed significantly more TGF-β1 than did controls, suggesting paracrine and autocrine effects on both myocytes and fibroblasts.

Conclusions: IR engenders both atrial structural remodeling and abnormal intracellular calcium homeostasis, contributing to increased AF susceptibility. The inhibition of CaMKII may be a potential therapeutic target for AF in insulin resistance.

Keywords: Atrial fibrillation; CaMKII; Insulin resistance; TGF-β.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials
  • Animals
  • Atrial Fibrillation / etiology*
  • Atrial Fibrillation / metabolism
  • Atrial Fibrillation / physiopathology
  • Atrial Remodeling*
  • Biomarkers / blood
  • Blood Glucose / metabolism
  • Calcium Signaling
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2 / metabolism
  • Cells, Cultured
  • Cholesterol, Dietary
  • Diet, High-Fat
  • Dietary Sugars
  • Disease Models, Animal
  • Fibroblasts / metabolism
  • Fibrosis
  • Fructose
  • Heart Conduction System / metabolism
  • Heart Conduction System / physiopathology*
  • Heart Rate*
  • Insulin / blood
  • Insulin Resistance*
  • Male
  • Myocytes, Cardiac / metabolism
  • Rats, Sprague-Dawley
  • Transforming Growth Factor beta1 / metabolism

Substances

  • Biomarkers
  • Blood Glucose
  • Cholesterol, Dietary
  • Dietary Sugars
  • Insulin
  • Tgfb1 protein, rat
  • Transforming Growth Factor beta1
  • Fructose
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2