C-Terminal Heat Shock Protein 90 Inhibitor Decreases Hyperglycemia-induced Oxidative Stress and Improves Mitochondrial Bioenergetics in Sensory Neurons

Department of Pharmacology and Toxicology, The University of Kansas, Lawrence, Kansas 66045, United States.
Journal of Proteome Research (Impact Factor: 4.25). 03/2012; 11(4):2581-93. DOI: 10.1021/pr300056m
Source: PubMed


Diabetic peripheral neuropathy (DPN) is a common complication of diabetes in which hyperglycemia-induced mitochondrial dysfunction and enhanced oxidative stress contribute to sensory neuron pathology. KU-32 is a novobiocin-based, C-terminal inhibitor of the molecular chaperone, heat shock protein 90 (Hsp90). KU-32 ameliorates multiple sensory deficits associated with the progression of DPN and protects unmyelinated sensory neurons from glucose-induced toxicity. Mechanistically, KU-32 increased the expression of Hsp70, and this protein was critical for drug efficacy in reversing DPN. However, it remained unclear if KU-32 had a broader effect on chaperone induction and if its efficacy was linked to improving mitochondrial dysfunction. Using cultures of hyperglycemically stressed primary sensory neurons, the present study investigated whether KU-32 had an effect on the translational induction of other chaperones and improved mitochondrial oxidative stress and bioenergetics. A variation of stable isotope labeling with amino acids in cell culture called pulse SILAC (pSILAC) was used to unbiasedly assess changes in protein translation. Hyperglycemia decreased the translation of numerous mitochondrial proteins that affect superoxide levels and respiratory activity. Importantly, this correlated with a decrease in mitochondrial oxygen consumption and an increase in superoxide levels. KU-32 increased the translation of Mn superoxide dismutase and several cytosolic and mitochondrial chaperones. Consistent with these changes, KU-32 decreased mitochondrial superoxide levels and significantly enhanced respiratory activity. These data indicate that efficacy of modulating molecular chaperones in DPN may be due in part to improved neuronal mitochondrial bioenergetics and decreased oxidative stress.

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Available from: Huiping Zhao
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    • "*P , 0.05 versus vehicle (Veh) + Veh; ^P , 0.05 versus STZ + Veh; #P , 0.05 versus C57Bl/6 STZ + KU-32. hyperglycemically stressed primary sensory neurons, these factors may directly contribute to improving mtBE and SRC in diabetic mice (Zhang et al., 2012). In this regard, hyperglycemia can increase oxidative stress and the oxidative modification of amino acids (Akude et al., 2010) that may impair protein folding within mitochondria (Muchowski and Wacker, 2005), decrease mitochondrial protein import (Baseler et al., 2011), and promote mitochondrial dysfunction (Tomlinson and Gardiner, 2008). "
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    ABSTRACT: Impaired neuronal mitochondrial bioenergetics contributes to the pathophysiologic progression of diabetic peripheral neuropathy (DPN) and may be a focal point for disease management. We have demonstrated that modulating heat shock protein 90 (Hsp90) and Hsp70 with the small molecule drug, KU-32, ameliorates psychosensory, electrophysiologic, morphologic and bioenergetic deficits of DPN in animal models of Type 1 diabetes. The current study used mouse models of Type 1 and Type 2 diabetes to determine the relationship of changes in sensory neuron mitochondrial bioenergetics to the onset of and recovery from DPN. The onset of DPN showed a tight temporal correlation with a decrease in mitochondrial bioenergetics in a genetic model of Type 2 diabetes. In contrast, sensory hypoalgesia developed 10 weeks before the occurrence of significant declines in sensory neuron mitochondrial bioenergetics in the Type 1 model. KU-32 therapy improved mitochondrial bioenergetics in both the Type 1 and Type 2 models and this tightly correlated with a decrease in DPN. Mechanistically, improved mitochondrial function following KU-32 therapy required Hsp70 since the drug was ineffective in diabetic Hsp70 KO mice. Our data indicate that changes in mitochondrial bioenergetics may rapidly contribute to nerve dysfunction in Type 2 diabetes, but not Type 1 diabetes, and that modulating Hsp70 offers an effective approach toward correcting sensory neuron bioenergetic deficits and DPN in both Type 1 and Type 2 diabetes.
    Full-text · Article · Nov 2013 · Journal of Pharmacology and Experimental Therapeutics
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    • "Recent data suggest that KU-32 may improve neuronal function by enhancing mitochondrial respiratory capacity following hyperglycemic stress [12] [13]. Since emerging research indicates that diabetes (especially type 2 diabetes) increases oxidative stress and mitochondrial fission/fusion in sensory neurons [14], the actions of KU-32 are enticing as a possible novel pharmacological intervention to reverse diabetic peripheral neuropathy. "
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    ABSTRACT: KU-32 is a novel, novobiocin-based Hsp90 inhibitor that protects against neuronal glucotoxicity and reverses multiple clinical indices of diabetic peripheral neuropathy in a rodent model. However, any drug with potential for treating diabetic complications must also have no adverse effects on the function of pancreatic islets. Thus, the goal of the current study was to assess the effect of KU-32 on the in vitro viability and function of human islets. Treating human islets with KU-32 for 24 hours showed no toxicity as assessed using the alamarBlue assay. Confocal microscopy confirmed that with a minimum of 2-day exposure, KU-32 improved cellular viability by blocking apoptosis. Functionally, isolated human islets released more glucose-stimulated insulin when preincubated in KU-32. However, diabetic BKS-db/db mice, a model for type 2 diabetes, administered KU-32 for 10 weeks did not show any significant changes in blood glucose and insulin levels, despite having greater insulin staining/beta cell in the pancreas compared to untreated BKS db/db mice. In summary, KU-32 did not harm isolated human islets and may even be protective. However, the effect does not appear significant enough to alter the in vivo metabolic parameters of diabetic mice.
    Full-text · Article · Nov 2012 · Experimental Diabetes Research
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    ABSTRACT: Compound 2 (KU-32) is a first-generation novologue (a novobiocin-based, C-terminal, heat shock protein 90 (Hsp90) inhibitor) that decreases glucose-induced death of primary sensory neurons and reverses numerous clinical indices of diabetic peripheral neuropathy in mice. The current study sought to exploit the C-terminal binding site of Hsp90 to determine whether the optimization of hydrogen bonding and hydrophobic interactions of second-generation novologues could enhance neuroprotective activity. Using a series of substituted phenylboronic acids to replace the coumarin lactone of 2, we identified that electronegative atoms placed at the meta-position of the B-ring exhibit improved cytoprotective activity, which is believed to result from favorable interactions with Lys539 in the Hsp90 C-terminal binding pocket. Consistent with these results, a meta-3-fluorophenyl substituted novologue (13b) exhibited a 14-fold lower ED(50) for protection against glucose-induced toxicity of primary sensory neurons compared to 2.
    No preview · Article · Jun 2012 · Journal of Medicinal Chemistry
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