The NADPH Metabolic Network Regulates Human <i>αB-crystallin</i> Cardiomyopathy and Reductive Stress in <i>Drosophila melanogaster</i>

<div><p>Dominant mutations in the <i>alpha-B crystallin</i> (<i>CryAB</i>) gene are responsible for a number of inherited human disorders, including cardiomyopathy, skeletal muscle myopathy, and cataracts. The cellular mechanisms of disease pathology for these disorders are not well understood. Among recent advances is that the disease state can be linked to a disturbance in the oxidation/reduction environment of the cell. In a mouse model, cardiomyopathy caused by the dominant <i>CryAB^R120G</i> missense mutation was suppressed by mutation of the gene that encodes glucose 6-phosphate dehydrogenase (G6PD), one of the cell's primary sources of reducing equivalents in the form of NADPH. Here, we report the development of a <i>Drosophila</i> model for cellular dysfunction caused by this <i>CryAB</i> mutation. With this model, we confirmed the link between G6PD and mutant <i>CryAB</i> pathology by finding that reduction of G6PD expression suppressed the phenotype while overexpression enhanced it. Moreover, we find that expression of mutant CryAB in the <i>Drosophila</i> heart impaired cardiac function and increased heart tube dimensions, similar to the effects produced in mice and humans, and that reduction of G6PD ameliorated these effects. Finally, to determine whether CryAB pathology responds generally to NADPH levels we tested mutants or RNAi-mediated knockdowns of phosphogluconate dehydrogenase (PGD), isocitrate dehydrogenase (IDH), and malic enzyme (MEN), the other major enzymatic sources of NADPH, and we found that all are capable of suppressing CryAB^R120G pathology, confirming the link between NADP/H metabolism and CryAB.</p>