An mTOR-Tfeb-Fabp7a signaling axis can be harnessed to ameliorate bag3 cardiomyopathy in adult zebrafish

Abstract

Dysregulated proteostasis in cardiomyocytes is an important pathological event in BAG3 cardiomyopathy, which can be repaired by inhibiting mechanistic target of rapamycin (mTOR) for cardioprotective effects. Here, we aimed to uncover additional pathological events and therapeutic target genes via leveraging zebrafish genetics. We first assessed transcription factor EB (tfeb), a candidate gene that encodes a direct downstream phosphorylation target of mTOR signaling. We found that cardiomyocyte-specific transgenic overexpression of tfeb (Tg[cmlc2:tfeb]) is sufficient to repair defective proteostasis, attenuate accelerated cardiac senescence, a previously unrecognized phenotype in the bag3 cardiomyopathy model, and rescue cardiac dysfunction. Next, we compared cardiac transcriptomes between the Tg(cmlc2:tfeb) transgenic fish and the mtorxu015/+ mutant, and tested 4 commonly downregulated lipodystrophy genes using an F0-based genetic assay. We found that inhibition of the fatty acid binding protein a (fabp7a) gene, but not the other 3 genes, exerts therapeutic effects on bag3 cardiomyopathy. Conversely, fabp7a expression is elevated in bag3 cardiomyopathy model and cardiomyocyte-specific overexpression of fabp7a resulted in dysregulated proteostasis, accelerated cardiac senescence, as well as cardiac dysfunction. Together, these genetic studies in zebrafish uncovered Fabp7a activation and accelerated cardiac senescence as important pathological events in bag3 cardiomyopathy. The mTOR-Tfeb-Fabp7a signaling axis can be harnessed to repair these pathological changes and exert cardioprotective effects.