Abstract P494: Truncated Titin Protein In Dilated Cardiomyopathy

Abstract

Truncating variations in the gene coding for titin (TTNtv) have been known to cause dilated cardiomyopathy for nearly 20 years. Efforts to detect direct evidence of either haploinsufficiency or dominant negative mechanisms have thus far failed, leaving the mechanism open to controversy. By analyzing a collection of 184 post-transplant human hearts, 22 of which bear TTNtv’s, we show evidence supporting both haploinsufficient (lack of sufficient full length titin to maintain normal cardiomyocyte contractility) and dominant-negative (toxic gain of function due to truncated titin) mechanisms. Using allele specific proteomics as well as epitope specific agarose gel immunoblotting we show that TTNtv are present in human myocardium at the expected molecular weight and bear only the epitopes expected to be present in TTNtv protein. TTNtv associate with the sarcomere bearing insoluble fraction of human myocardium but are more weakly attached to the sarcomere than full length titin, consistent with their lack of thick filament and M-line attachment sites. We further show that DCM hearts bearing TTNtv have less full length titin than non-TTNtv bearing DCM hearts, by both total protein and in ratio to sarcomeric proteins, indicating TTN haploinsufficiency is also present in TTNtv hearts. This unambiguous detection of TTNtv protein in the myocardium of DCM combined with a reduction in full length titin supports a combined dominant negative and haploinsufficient mechanism of pathogenesis of TTNtv induced DCM.