cAMP‐Dependent Protein Kinase A‐Stimulated Sarcoplasmic Reticulum Function in Heart Failure^a

Abstract

It is unclear whether decreased protein expression of SERCA2 (SR-Ca(2+)-ATPase) and phospholamban (PLB), or alterations in the phosphorylation state of PLB leading to increased inhibition of SERCA2 are responsible for the reduced SERCA2 function in failing human myocardium. In crude membrane preparations from patients with terminal heart failure due to idiopathic dilated cardiomyopathy (DCM) and control hearts (NF), SERCA2 activity was measured with a NADH coupled assay. Protein expression of SERCA2 and PLB and the phosphorylation state at the two phosphorylation sites, serine-16-PLB and threonine-17-PLB, were investigated with specific (phosphorylation) antibodies and Western blot technique. In NF, the Vmax and the Ca2+ sensitivity of SERCA2 activity were significantly higher compared to DCM. Protein expression of SERCA2 and PLB were unchanged, whereas the phosphorylation status at both serine-16-PLB and threonine-17-PLB were significantly reduced in DCM. The native phosphorylation status of PLB measured by the back-phosphorylation technique was reduced in DCM as well. After stimulation with protein kinase A only the Ca2+ sensitivity, but not Vmax, increased. The reduced phosphorylation state of PLB may lead to decreased Ca2+ sensitivity of SERCA2 in failing human myocardium. The altered regulation of the SR-CA(2+)-ATPase in human heart failure may offer an opportunity for an improvement in the therapy of heart failure.

Phosphorylation of phospholamban at threonine-17 reduces cardiac adrenergic contractile responsiveness in chronic pressure overload-induced hypertrophy

“…*P Ͻ 0.05. pacing rates, being largely responsible for these changes (40). Reduced SERCA abundance (24), decreased PLB phosphorylation (46), and increased RyR (30) and L-type Ca 2ϩ channel phosphorylation (12) appear to underlie these end-stage defects. Ca 2ϩ regulation in earlier stages of the cardiac response to stress is less well understood.…”

Treatment of Chronic Heart Failure With β-Adrenergic Receptor Antagonists

“…That approach was recently attempted in a Phase 3 trial using the phosphodiesterase 3 selective inhibitor enoximone in combination with ␤-blockade to couple inhibition of ␤ 1 -AR adverse biological signaling with restoration of 16 Ser phospholamban phosphorylation, 122 which is reduced in the failing heart. 123 Although this 1854-patient clinical trial was not positive on its primary end points, it demonstrated promise in patients with the most severe LV dysfunction. 124 …”

Ca handling during excitation–contraction coupling in heart failure

“…All these studies highlight the critical role of SERCA in abnormal Ca homeostasis and contractile dysfunction of HF. However, there are several publications that did not report any alteration in the SERCA expression level in human HF [56;82-84] and animal HF models [51;75]. Moreover, it has been shown that HF is also associated with a decrease in the PLB expression level [2;45;70], but to a lesser degree than SERCA [38;49;67].…”