High Resolution Mapping of the Cardiac Transmural Proteome Using Reverse Phase Protein Microarrays

Abstract

The expression level of proteins governing the electrical excitability of and conduction within ventricular myocardium are known to vary as a function of distance through the heart wall. The expression patterns of a subset of these proteins are altered in disease. Precise measurement of such patterns is therefore essential to understanding structure-function relationships within the heart in health and disease. Here, we report a new experimental approach using reverse-phase protein microarrays to map the left ventricular transmural proteome. This approach can yield submillimeter spatial resolution, and when coupled with the method of array microenvironment normalization, reduces nonbiological components of variability to ∼10% of overall study variability. In addition, the experimental design provides sufficient statistical power to detect small, yet potentially biologically significant expression changes on the order of 1.1-fold. The usefulness of this technique is demonstrated by mapping the transmural expression of Serca2a in the left ventricle of 12 canine hearts, each in one of three states: normal, dyssynchronous heart failure, and dyssynchronous heart failure followed by cardiac resynchronization therapy. We confirm the existence of a 40% transmural gradient (epi>endo) of Serca2a, and demonstrate the ability of this technique to yield highly significant transmural expression differences within each individual heart. The expression level of proteins governing the electrical excitability of and conduction within ventricular myocardium are known to vary as a function of distance through the heart wall. The expression patterns of a subset of these proteins are altered in disease. Precise measurement of such patterns is therefore essential to understanding structure-function relationships within the heart in health and disease. Here, we report a new experimental approach using reverse-phase protein microarrays to map the left ventricular transmural proteome. This approach can yield submillimeter spatial resolution, and when coupled with the method of array microenvironment normalization, reduces nonbiological components of variability to ∼10% of overall study variability. In addition, the experimental design provides sufficient statistical power to detect small, yet potentially biologically significant expression changes on the order of 1.1-fold. The usefulness of this technique is demonstrated by mapping the transmural expression of Serca2a in the left ventricle of 12 canine hearts, each in one of three states: normal, dyssynchronous heart failure, and dyssynchronous heart failure followed by cardiac resynchronization therapy. We confirm the existence of a 40% transmural gradient (epi>endo) of Serca2a, and demonstrate the ability of this technique to yield highly significant transmural expression differences within each individual heart. The cardiac action potential (AP) 1The abbreviations used are:APaction potentialAMNarray microenvironment normalizationCRTcardiac resynchronization therapyCVcoefficient of variationDHFdyssynchronous heart failureendoendocardialepiepicardialHRSHhigh resolution single heartLRMHlow resolution multi heartLVleft ventricleRPMAreverse phase protein microarrayTPNtotal protein normalizationTPERtransmembrane protein extractionTCEPtris[2-carboxylethy]phosphine. is a rapid rise and slow decrease of cardiac myocyte trans-membrane electrical potential in response to changes in membrane conductance for specific ions. The resulting electrical wave propagates from the right and left atria to the ventricles, initiating the synchronized release of calcium (Ca2+) and subsequent contraction of the heart muscle. Isolated cardiac ventricular myocytes have been shown to exhibit disparate AP characteristics (shape and duration) as a function of transmural location (depth within the ventricle from surface to interior) (1Liu D.W. Gintant G.A. Antzelevitch C. Ionic bases for electrophysiological distinctions among epic