Genetic Studies of Sarcomere-based Cardiac Diseases

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Project Summary TITIN (TTN) truncating variants (TTNtvs) have been found to be the most common genetic factor for dilated cardiomyopathy (DCM). However, allelic heterogeneity (AH) of TTNtv DCM, i.e. TTNtvs are also found in reference populations, significantly confound diagnosis and therapeutic development of these patients. Pathogenic TTNtvs are mainly found in the C-terminal A-band region (TTNtv-As) but less in the N-terminal Z- disc region (TTNtv-Zs). Moreover, pathological signaling pathways for TTNtv DCM remain largely unknown. Here, we aim to leverage unique research opportunities enabled by zebrafish genetics to decipher underlying mechanisms of AH, discover pathological signaling pathways, and develop effective therapeutic avenues. Our preliminary studies showed that AH of TTNtv DCM can be recapitulated in both embryonic and adult zebrafish, opening the door for mechanistic studies of AH in vivo. From our screen of known cardiomyopathy signaling pathways, we identified mTOR, autophagy, MAPK and PDE1 as candidate signaling pathways that could be leveraged for therapeutic benefits. We also established a F0-based genetic assay using the Microhomology- mediated end joining (MMEJ) genome editing technology that enables us to rapidly discover new signaling pathways. Based on these preliminary studies, we proposed to leverage unique genetic and chemical genetic tools in zebrafish to prove that zebrafish is the first in vivo animal model for allelic heterogeneity of TTNtv DCM, which can be used to decipher primary damages incurred by TTNtvs, to discover sequential pathological signaling pathways, and to develop mechanism-based therapies. The proposal is organized into the 3 specific aims. In Specific Aim 1, we will decipher allelic heterogeneity of ttntv DCM via studying a panel of ttntv mutants and ttn null mutants. In Specific Aim 2, we propose to elucidate molecular basis of autophagy dysregulation in ttntv DCM and develop an autophagy-based therapy. In Specific Aim 3, we will confirm MAPK and PDE1 as candidate signalings and discover additional new genes and signaling pathways by carrying MMEJ-based F0 screens. Upon completion of the proposal, we anticipate the following deliverables: 1) provide in vivo evidence to clarify why TTNtv-As are more likely to cause DCM phenotypes than TTNtv-Zs; 2) obtain insights on autophagy, MAPK and PDE signaling pathways in ttntv DCM, and identify mechanism-based therapeutic avenues for ttntv DCM; 3) establish a F0-based genetic screening approach that is capable of systematically discovering new genes for ttntv DCM, opening an unprecedented opportunity for mechanistic studies of an inherited cardiomyopathy.