Cytoskeletal protein 4.1 isoforms, newly discovered in heart, are differentially overexpressed in the myocardium of patients with deteriorating heart failure

Abstract

Cytoskeletal proteins are thought to play an important role in cardiomyopathy. Proteins 4.1 and spectrin are required for maintenance of the structure of animal cell membranes. We have recently shown that the three genes encoding protein 4.1(4.1R, 4.1G and 4.1N) are expressed in the human heart. They form a complex with spectrins close to the Z-disc at the sarcoplasmic reticulum, considered to maintain SR integrity during heart contraction. The role of these proteins in heart failure is unknown. In an attempt to clarify this we used Quantitative Real-Time PCR to compare mRNA expression of these proteins in three groups: deteriorating heart failure patients undergoing LVAD support (n = 10), stable patients with advanced heart failure undergoing heart transplantation (ESHF, n = 17) and normal control donor hearts (n = 26). Protein expression and localisation were examined by confocal immunofluorescence microscopy. 4.1R and 4.1N were up-regulated 3.3-fold (p<0.01) and 1.8-fold (p<0.05) in the myocardium of patients undergoing LVAD support vs. ESHF. 4.1G expression and β-spectrin expression did not differ in LVAD vs. ESHF. Immunofluorescence microscopy for each 4.1 protein isoform indicated they are localised at the Z-disc. We compared measurements within the same samples with those for the pro-inflamatory cytokines TNF-α, IL1-β, IL-6, IL-4, IL-10 & IL-1R. Proteins 4.1G, 4.1R and 4.1N correlated with TNF-α, IL1-β and IL-1R within individual patients. In conclusion, differential overexpression of the cytoskeletal proteins 4.1R and 4.1N occurs in the myocardium of patients with deteriorating heart failure requiring LVAD insertion. This was associated with expression of pro-inflammatory cytokines. The mechanisms responsible require further investigation.