Levels of SR proteins involved in calcium release (ryanodine receptor), calcium binding (calsequestrin, calreticulin), and calcium uptake (calcium ATPase, phospholamban) were measured by Western blot analysis in nonfailing human myocardium (n = 7) and in end-stage failing myocardium due to dilated cardiomyopathy (n = 14).
Studies with knockout and transgenic mice show that gain of inhibitory function of phospholamban alters cardiac contractility and could be a causal feature in some cardiomyopathies.
The unique interaction between phospholamban and increased adrenergic drive, elucidated herein, provides the first evidence that compensatory increases in catecholamine stimulation can, even in the absence of preexisting heart failure, be a primary causative factor in the development of cardiomyopathy and early mortality.
Here we report that an inherited human dilated cardiomyopathy with refractory congestive heart failure is caused by a dominant Arg --> Cys missense mutation at residue 9 (R9C) in phospholamban (PLN), a transmembrane phosphoprotein that inhibits the cardiac sarcoplasmic reticular Ca2+-adenosine triphosphatase (SERCA2a) pump.
To determine the cross-signaling between Ca2+ and cAMP pathways, the phosphorylation of Ser16-PLB and Thr17-PLB was studied at increasing stimulation frequencies as well as in the presence of beta-adrenergic stimulation in isolated ventricular trabeculae from failing (dilative cardiomyopathy, DCM, heart transplants, n=9) and non-failing human myocardium (donor hearts, NF, n=9).
Thus, by chronic suppression of sarcoplasmic reticulum Ca(2+)-ATPase activity, the nonreversible superinhibitory function of mutant PLN-R14Del may lead to inherited dilated cardiomyopathy and premature death in both humans and mice.
Transgenic mice overexpressing the mutant PLN-R14Del recapitulated human cardiomyopathy exhibiting similar histopathologic abnormalities and premature death.
Thus, by chronic suppression of sarcoplasmic reticulum Ca(2+)-ATPase activity, the nonreversible superinhibitory function of mutant PLN-R14Del may lead to inherited dilated cardiomyopathy and premature death in both humans and mice.
The variant AF177763.1:g.203A>C (at position -36 bp relative to the PLN transcriptional start site) was found only in the heterozygous form in 1 out of 296 normal subjects and in 22 out of 381 cardiomyopathy patients (heart failure at age of 18-44 years, ejection fraction=22+/-9%).