mGluR2/3 activation of the SIRT1 axis preserves mitochondrial function in diabetic neuropathy

Abstract

ObjectivesThere is a critical need to develop effective treatments for diabetic neuropathy. This study determined if a selective mGluR2/3 receptor agonist prevented or treated experimental diabetic peripheral neuropathy (DPN) through glutamate recycling and improved mitochondrial function.MethodsAdult male streptozotocin treated Sprague‐Dawley rats with features of type 1 diabetes mellitus (T1DM) or Low Capacity Running (LCR) rats with insulin resistance or glucose intolerance were treated with 3 or 10 mg/kg/day LY379268. Neuropathy end points included mechanical allodynia, nerve conduction velocities (NCV), and intraepidermal nerve fiber density (IENFD). Markers of oxidative stress, antioxidant response, glutamate recycling pathways, and mitochondrial oxidative phosphorylation (OXPHOS) associated proteins were measured in dorsal root ganglia (DRG).ResultsIn diabetic rats, NCV and IENFD were decreased. Diabetic rats treated with an mGluR2/3 agonist did not develop neuropathy despite remaining diabetic. Diabetic DRG showed increased levels of oxidized proteins, decreased levels of glutathione, decreased levels of mitochondrial DNA (mtDNA) and OXPHOS proteins. In addition, there was a 20‐fold increase in levels of glial fibrillary acidic protein (GFAP) and the levels of glutamine synthetase and glutamate transporter proteins were decreased. When treated with a specific mGluR2/3 agonist, levels of glutathione, GFAP and oxidized proteins were normalized and levels of superoxide dismutase 2 (SOD2), SIRT1, PGC‐1α, TFAM, glutamate transporter proteins, and glutamine synthetase were increased in DRG neurons.InterpretationActivation of glutamate recycling pathways protects diabetic DRG and this is associated with activation of the SIRT1‐PGC‐1α–TFAM axis and preservation of mitochondrial OXPHOS function.

Overexpression of Sirtuin 1 protein in neurons prevents and reverses experimental diabetic neuropathy

“…Mice were anaesthetized with isoflurane, 4-5% for induction and 1-2% for maintenance (Choi et al, 2014;Chandrasekaran et al, 2015Chandrasekaran et al, , 2017. During nerve conduction studies, the mice were provided with thermal support and isoflurane anaesthesia via facemask (1-2%).…”

“…Intraepidermal nerve fibre density (IENFD) was measured using PGP9.5 antibody staining in a blinded fashion, as previously described (Choi et al, 2014;Chandrasekaran et al, 2015Chandrasekaran et al, , 2017. To delineate fibre crossing at the dermoepidermal junction, slides were counterstained by dipping in eosin (Sigma-Aldrich Eosin Y solution HT110316).…”

“…To delineate fibre crossing at the dermoepidermal junction, slides were counterstained by dipping in eosin (Sigma-Aldrich Eosin Y solution HT110316). IENFD was calculated (as fibres/mm) by the number of complete baseline crossings of nerve fibres at the dermo-epidermal junction divided by the measured length of the epidermal surface using standardized validated methods (Lauria et al, 2005;England et al, 2009;Chandrasekaran et al, 2017).…”

“…L3 to L5 DRGs were homogenized in RIPA buffer with protease and phosphatase inhibitors in a tissue lyser (Qiagen Inc.) and extracts were centrifuged at 13 000g. Protein samples (20 mg) were analysed by western blot analysis (Choi et al, 2014;Chandrasekaran et al, 2017). The source and dilution of the various antibodies used in this study were: rabbit polyclonal anti-SIRT1 (Millipore 07-131, 1:1000), mouse monoclonal (m)Ab anti-DBC1 (Cell Signaling Technology #5857, 1:1000), rabbit mAb anti-PARP (Cell Signaling Technology #9532, 1:1000), goat polyclonal anti-CD38 (Santa Cruz Biotechnology, #SC7049S, 1:1000), rabbit polyclonal acetylated lysine antibody (Cell Signaling Technology, #9441, 1:1000), rabbit anti-seasonal polyclonal HA antibody (Origene #TA160089, 1:1000), rabbit polyclonal PGC-1 antibody (Novus Biologicals, #NBP1-04676, 1:1000), mouse mAb anti b-actin (Cell Signaling Technology, #3700, 1:1000) and rabbit mAb anti GAPDH (Cell Signaling Technology, #5174, 1:1000).…”

Interactions between and Shared Molecular Mechanisms of Diabetic Peripheral Neuropathy and Obstructive Sleep Apnea in Type 2 Diabetes Patients

“…A previous study showed that the excitatory neurotransmitter glutamate induced an increased magnitude of mitochondrial depolarization, but no increase in apoptosis was observed [ 201 ]. In DPN, glutamate release is related with increased oxidative stress and decreased mitochondrial function, which is associated with neuropathic pain and activation of the glutamate recycling pathway that protects diabetic dorsal root ganglion by activating the SIRT1-PGC-1 α -EFAM axis [ 202 ]. In OSA patients, higher glutamate levels were observed versus healthy subjects [ 203 ].…”