Galactokinase is a Novel Modifier of Calcineurin-Induced Cardiomyopathy in Drosophila

Abstract

Calcineurin is both necessary and sufficient to induce cardiac hypertrophy, an independent risk factor for arrhythmia, dilated cardiomyopathy, heart failure, and sudden cardiac death. However, current knowledge of the downstream effectors of calcineurin is limited. My study utilizes Drosophila melanogaster to 1) establish a reliable model for discovering novel modifiers of calcineurin-induced cardiomyopathy; and 2) discover and characterize novel modifiers of calcineurin-induced cardiomyopathy.In this study, I generated sensitized Drosophila lines expressing constitutively active calcineurin (CanAact) that was either fused to yellow fluorescent protein (YFP) or a Flag epitope (Flag-tagged) specifically in the heart using the cardiac-specific tinC driver (tinC-CanAact). These sensitized lines displayed significant cardiac enlargement as assayed via optical coherence tomography (OCT), histology, and confocal microscopy. The feasibility of this method was established by testing Drosophila expressing deficiency of a known calcineurin modifier, Mef2. Employing a targeted deficiency screen informed by calcineurin modifier screens in the eye and mesoderm, Galactokinase (Galk) was discovered as a novel modifier of calcineurin-induced cardiomyopathy in the fly through 1) genetic deficiencies, transposable elements, and RNAi disrupting Galk expression rescued tinC-CanAact-induced cardiomyopathy; and 2) transposable element in Galk rescued tinC-CanAact-induced decreased life span. Further characterization identified that the genetic disruption of Galk rescued CanAact-induced phenotypes driven in the posterior wing, but not ectodermaly, mesodermaly, or ubiquitously driven phenotypes. In a separate region, genetic disruption of the galactoside-binding lectin, galectin, was also found to rescue tinC-CanAact-induced cardiac enlargement.Together, these results characterize tinC-CanAact-induced cardiac enlargement in the fly, establish that the tinC-CanAact sensitized line is a reliable model for discovering novel calcineurin regulators and suggest that galactokinase and galectin-regulated glycosylation is important for calcineurin-induced cardiomyopathy. These results have the potential to provide insight into new treatments for cardiac hypertrophy.