Human αB-Crystallin Mutation Causes Oxido-Reductive Stress and Protein Aggregation Cardiomyopathy in Mice

Harvard University, Cambridge, Massachusetts, United States
Cell (Impact Factor: 32.24). 09/2007; 130(3):427-39. DOI: 10.1016/j.cell.2007.06.044
Source: PubMed


The autosomal dominant mutation in the human alphaB-crystallin gene inducing a R120G amino acid exchange causes a multisystem, protein aggregation disease including cardiomyopathy. The pathogenesis of cardiomyopathy in this mutant (hR120GCryAB) is poorly understood. Here, we show that transgenic mice overexpressing cardiac-specific hR120GCryAB recapitulate the cardiomyopathy in humans and find that the mice are under reductive stress. The myopathic hearts show an increased recycling of oxidized glutathione (GSSG) to reduced glutathione (GSH), which is due to the augmented expression and enzymatic activities of glucose-6-phosphate dehydrogenase (G6PD), glutathione reductase, and glutathione peroxidase. The intercross of hR120GCryAB cardiomyopathic animals with mice with reduced G6PD levels rescues the progeny from cardiac hypertrophy and protein aggregation. These findings demonstrate that dysregulation of G6PD activity is necessary and sufficient for maladaptive reductive stress and suggest a novel therapeutic target for abrogating R120GCryAB cardiomyopathy and heart failure in humans.

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    • "For example, mutations in α B -crystallin, a small heat shock protein, result in protein aggregation causing cardiomyopathy in mice. The mechanism underlying protein aggregation disease has been attributed to reductive stress associated with increased activity of glucose-6-phosphate dehydrogenase (G6PD) raising NADPH levels [10]. In studies of experimental heart failure, G6PD activity was found to be significantly elevated resulting in a two-fold increase in NADPH concentration and increased ROS production [9]. "
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    ABSTRACT: Both extremes of redox balance are known to cause cardiac injury, with mounting evidence revealing that the injury induced by both oxidative and reductive stress is oxidative in nature. During reductive stress, when electron acceptors are expected to be mostly reduced, some redox proteins can donate electrons to O2 instead, which increases reactive oxygen species (ROS) production. However, the high level of reducing equivalents also concomitantly enhances ROS scavenging systems involving redox couples such as NADPH/NADP(+) and GSH/GSSG. Here our objective was to explore how reductive stress paradoxically increases net mitochondrial ROS production despite the concomitant enhancement of ROS scavenging systems. Using recombinant enzymes and isolated permeabilized cardiac mitochondria, we show that two normally antioxidant matrix NADPH reductases, glutathione reductase and thioredoxin reductase, generate H2O2 by leaking electrons from their reduced flavoprotein to O2 when electron flow is impaired by inhibitors or because of limited availability of their natural electron acceptors, GSSG and oxidized thioredoxin. The spillover of H2O2 under these conditions depends on H2O2 reduction by peroxiredoxin activity, which may regulate redox signaling in response to endogenous or exogenous factors. These findings may explain how ROS production during reductive stress overwhelms ROS scavenging capability, generating the net mitochondrial ROS spillover causing oxidative injury. These enzymes could potentially targeted to increase cancer cell death or modulate H2O2-induced redox signaling to protect the heart against ischemia/reperfusion damage. Copyright © 2015. Published by Elsevier B.V.
    Full-text · Article · Feb 2015 · Biochimica et Biophysica Acta (BBA) - Bioenergetics
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    • "Protein damage resulting from stress causes breakdown of protein homeostasis [1]. There are multiple response mechanisms that protect cells against environment stress [2] [3]. A 'protein quality control' network consisting of molecular chaperones and proteases is responsible for limiting and repairing protein aggregation [1]. "
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    ABSTRACT: Small heat shock proteins (sHsps) are ubiquitous chaperones that play a vital role in protein homeostasis. sHSPs are characterized by oligomeric architectures and dynamic exchange of subunits. The flexible oligomeric assembling associating with function remains poorly understood. Based on the structural data, it is certainly agreed that two dimerization models depend on the presence or absence of a β6 strand to differentiate nonmetazoan sHSPs from metazoan sHSPs. Here, we report the Sulfolobus solfataricus Hsp20.1 ACD dimer structure, which shows a distinct dimeric interface. We observed that, in the absence of β6, Hsp20.1 dimer does not depend on β7 strand for forming dimer interface as metazoan sHSPs, nor dissociates to monomers. This is in contrast to other published sHSPs. Our structure reveals a variable, highly polar dimer interface that has advantages for rapid subunits exchange and substrate binding. Remarkably, we find that the C-terminal truncation variant has chaperone activity comparable to that of wild-type despite lack of the oligomer structure. Our further study indicates that the N-terminal region is essential for the oligomer and dimer binding to the target protein. Together, the structure and function of Hsp20.1 give more insight into the thermal protection mechanism of sHSPs. Copyright © 2015. Published by Elsevier Inc.
    Preview · Article · Feb 2015 · Biochemical and Biophysical Research Communications
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    • "Increased NADPH level facilitates the reduction of GSSG to GSH, which serves as an important antioxidant mechanism. However, it has been shown that excessive increases in GSH/GSSG ratio paradoxically elevate mitochondrial oxidation and cytotoxicity in cultured cells and cause cardiomyopathy in mice.42–44 Our data also raise a cautionary note in targeting the NADPH oxidase activity for cardioprotection as the reductive stress resulting from the excessive suppression of the system leads to greater I/R injury than activation of the system. "
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    ABSTRACT: The NADPH oxidase family (Nox) produces reactive oxygen species by adding the electron donated by NADPH to oxygen. Excessive reactive oxygen species production under a variety of pathological conditions has been attributed to increased Nox activity. Here, we aimed at investigating the role of Nox in cardiac ischemic injury through gain- and loss-of-function approaches. We modulated Nox activity in the heart by cardiac-specific expression of Nox4 and dominant negative Nox4. Modulation of Nox activity drastically changes the cellular redox status. Increasing Nox activity by cardiac-specific overexpression of Nox4 imposed oxidative stress on the myocardium [increased NAD(P)(+)/NAD(P)H and decreased glutathione/glutathione disulfide ratio] and worsened cardiac energetics and contractile function after ischemia-reperfusion. Overexpression of the dominant negative Nox4 (DN), which abolished the Nox function, led to a markedly reduced state [decreased NAD(P)(+)/NAD(P)H and increased glutathione/glutathione disulfide ratio] at baseline and paradoxically promoted mitochondrial reactive oxygen species production during ischemia resulting in no recovery of heart function after reperfusion. Limiting the generation of reducing equivalent through modulating carbon substrates availability partially restored the NAD(+)/NADH ratio and protected dominant negative Nox4 hearts from ischemic injury. This study reveals an important role of Nox in cardiac redox regulation and highlights the complexity of developing therapies that affect the intricately connected redox states.
    Full-text · Article · Dec 2014 · Journal of the American Heart Association
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