Phospholamban gene ablation improves calcium transients but not cardiac function in a heart failure model

Decreased amplitude and slower kinetics of cardiomyocyte intracellular calcium (Ca_i²⁺) transients may underlie the diminished cardiac function observed in heart failure. These alterations occur in humans and animals with heart failure, including the TNF1.6 mouse model, in which heart failure arises from cardiac-specific overexpression of tumor necrosis factor α (TNFα). Objective: Since ablation of phospholamban expression (PLBKO) removes inhibition of the sarcoplasmic reticulum (SR) Ca²⁺ pump, enhances SR Ca²⁺ uptake and increases contractility, we assessed whether ablation of phospholamban expression could improve cardiac function, limit remodeling, and improve survival in the TNF1.6 model of heart failure. Methods: We bred PLBKO with TNF1.6 mice and characterized the progeny for survival, cardiac function (echocardiography), cardiac remodeling (hypertrophy, dilation, fibrosis), and Ca_i²⁺ transients and contractile function of isolated cardiomyocytes. Results: PLB ablation did not improve survival, cardiac function, or limit cardiac chamber dilation and hypertrophy in TNF1.6 mice (TKO mice). However, contractile function and Ca _i²⁺ transients (amplitude and kinetics) of isolated TKO cardiomyocytes were markedly enhanced. This discordance between unimproved cardiac function, and enhanced Ca_i²⁺ cycling and cardiomyocyte contractile parameters may arise from a continued overexpression of collagen and decreased expression of gap junction proteins (connexin 43) in response to chronic TNFα stimulation. Conclusions: Enhancement of intrinsic cardiomyocyte Ca_i²⁺ cycling and contractile function may not be sufficient to overcome several parallel pathophysiologic processes present in the failing heart.