Cholesterol depletion increased cardiomyocyte contractility associated with phosphorylation of cytosolic AKT

Introduction Sarcolemmal cholesterol is concentrated in lipid rafts and caveolae, which are flask-shaped invaginations of the plasma membrane and plays an important role for cell function. In cardiomyocyte the scaffolding protein caveolin- 3 permits the enrichment of cholesterol in caveolae, and caveolin-3 interactions with numerous proteins regulate their function. Hypothesis We hypothesized that acute cholesterol depletion increases cardiomyocyte intracellular Ca2+ and contractility. Methods Ventricular myocytes, isolated from adult Sprague Dawley rats, were treated with the cholesterol reducing agent methyl-β-cyclodextrin (MβCD, 5 mM, 1 hr, room temperature). Total cellular cholesterol levels, caveolin-3 localization, subcellular, AKT, ERK and p38 signaling, [Ca2+]i and contractility were assessed. Results Treatment with MβCD reduced ∼45% cholesterol and shifted caveolin-3 from cytoskeleton and triton-insoluble fractions to the triton-soluble fraction. Cholesterol depletion increased 2.4-fold AKT phosphorylation only in cytosolic fraction, an effect that was independent of total cytosolic AKT. Cholesterol depletion increased ERK isoform phosphorylation in cytoskeletal, cytosolic, tritonsoluble and triton-insoluble membrane fractions without altering their subcellular distributions. The primary effect of MβCD was on p38 subcellular distribution of p38α with little effect on p38 phosphorylation. Cholesterol depletion increased cardiomyocyte twitch amplitude and the rates of shortening and relaxation in conjunction with increased diastolic and systolic [Ca2+]i. Conclusion These results indicate that acute reductions in membrane cholesterol levels modulates subcellular caveolin-3, AKT, ERK, p38 signaling, as well as increasing [Ca2+]i and contractility