KU-596 decreases mitochondrial superoxide and improves bioenergetics following downregulation of manganese superoxide dismutase in diabetic sensory neurons

Neuronal mitochondrial dysfunction and oxidative stress are key pathophysiologic mechanisms of diabetic peripheral neuropathy (DPN). KU-596 is a small molecule modulator of heat shock protein 90 (Hsp90) that can reverse clinically relevant measures of DPN in diabetic animal models. Mechanistically, drug efficacy requires Hsp70 and correlates with improving mitochondrial maximal respiratory capacity (MRC) and decreasing oxidative stress in diabetic sensory neurons. The goal of this study was to determine if ex vivo treatment of diabetic neurons with KU-596 improves MRC by decreasing glucose-induced oxidative stress in an Hsp70-dependent manner. Sensory neurons were isolated from non-diabetic or diabetic mice wild type (WT) or Hsp70 knockout (Hsp70 KO) mice and treated with KU-596 in the presence of low or high glucose concentrations. In diabetic WT and Hsp70 KO neurons, hyperglycemia significantly increased superoxide levels, but KU-596 only decreased superoxide in WT neurons. Similarly, KU-596 significantly improved MRC in diabetic WT neurons maintained in high glucose but did not improve MRC in diabetic Hsp70 KO neurons under the same conditions. Since manganese superoxide dismutase (MnSOD) is the main mechanism to detoxify mitochondrial superoxide radicals, the cause and effect relationship between improved respiration and decreased oxidative stress was examined after knocking down MnSOD. Downregulating MnSOD in diabetic WT neurons increased hyperglycemia-induced superoxide levels, which was still significantly decreased by KU-596. However, KU-596 did not improve MRC following MnSOD knockdown. These data suggest that the ability of KU-596 to improve MRC is not necessarily dependent on decreasing mitochondrial superoxide in a MnSOD-dependent manner.