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

Heng B Xie,Kent G Golic,Anthony Cammarato,Namakkal S Rajasekaran,Ho-Chen Lin,Sanford I Bernstein,Jennifer A Suggs,Huali Zhang,Ivor J Benjamin

doi:10.1371/journal.pgen.1003544

Abstract

Dominant mutations in the alpha-B crystallin (CryAB) 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 CryABR120G 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 Drosophila model for cellular dysfunction caused by this CryAB mutation. With this model, we confirmed the link between G6PD and mutant CryAB 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 Drosophila 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 CryABR120G pathology, confirming the link between NADP/H metabolism and CryAB.

Highlights

The maintenance and integrity of specialized functional structures such as sarcomeres, the basic unit of contractile force in striated muscles, are inextricably linked to the cellular machinery of molecular chaperones and protein quality control pathways
Our results show that Drosophila provides a suitable model in which to study the pathology of the human CryABR120G mutation
We found that a reduced level of glucose 6-phosphate dehydrogenase (G6PD) ameliorates many of the perturbed cardiac functional parameters in CryABR120G flies, just as it does in the CryABR120G mouse [7]

Summary

Introduction

The maintenance and integrity of specialized functional structures such as sarcomeres, the basic unit of contractile force in striated muscles, are inextricably linked to the cellular machinery of molecular chaperones and protein quality control pathways. Evidence for this notion is provided by the identification of myopathic mutations in genes that encode proteins with chaperone function, such as CryAB and Bag, and whose products have been localized to Z-discs. CryAB, a small molecular weight heat shock protein, is expressed constitutively in the lens and in non-lenticular tissues associated with high rates of oxidative metabolism, such as heart and type I and type II skeletal muscle fibers. Expression of either the mouse or human CryABR120G allele in the mouse heart produced cardiomyopathy, heart failure and shortened lifespan, all of which phenocopy the disease condition in Author Summary

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