Haas, J.; Schudy, S.; Rauscher, B.; Munoz, A.; Rosskopf, S.; Reich, C.; Doenmez Yalcin, G.; Yalcin, A.; Seeger, T.; Taft, M.; Freichel, M.; Grimm, D.; Manstein, D. J.; Backs, J.; Frey, N.; Steinmetz, L. M.; Meder, B.

Dysregulation of alternative splicing - mediated by factors such as RBM20 or SLM2 - can affect proper gene isoform control disrupts gene isoform homeostasis and underpins severe cardiomyopathy in both animal models and patients. Although innovative therapies target various sarcomeric components, the impact of isoform switching in cardiac disease remains poorly understood. Here, we applied nanopore long-read sequencing to map the full-length transcriptome of left ventricular tissue from thirteen nonfailing controls, ten patients with dilated cardiomyopathy (DCM), and ten with ischemic cardiomyopathy (ICM). Our analysis identified 78,520 transcripts, 31% of which represent novel isoforms of known genes. Notably, the transcriptomes of DCM and ICM were largely indistinguishable, indicating that end-stage heart failure is characterized by a convergent isoform landscape, irrespective of disease etiology. Among 11 prototypical sarcomere genes, 10 displayed highly significant isoform shifts (p= 5.23x10-45 - 2.89x10-200). Focusing on tropomyosin, we observed that while the predominant cardiac gene TPM1 showed moderate up-regulation of its transcript isoforms, transcripts derived from TPM3-typically expressed at lower levels in the healthy heart-were markedly increased in heart failure.