Diabetic peripheral neuropathy: evidence for apoptosis and associated mitochondrial dysfunction.

Abstract

We hypothesized that diabetic sensory neuropathy is associated with activation of apoptosis and concomitant mitochondrial dysfunction. Studies were performed in excised intact and acutely dissociated dorsal root ganglion (DRG) neurons from control and streptozotocininduced diabetic rats with decreased peripheral nerve conduction velocities (NCV). Apoptosis was increased in acutely dissociated DRG neurons from 3-to 6-weekold diabetic rats. Basal mitochondrial membrane potential (⌬) was significantly more positive in DRG neurons from diabetic rats. Depolarization with glutamate resulted in significantly more positive ⌬ and delayed recovery of ⌬ in neurons from diabetic rats. Restoration of euglycemia for 2 weeks with insulin implants normalized NCV, ⌬, and apoptosis. Intact and acutely dissociated neurons from diabetic rats demonstrated decreased Bcl-2 levels and translocation of cytochrome C from the mitochondria to the cytoplasm. Neither levels of Bax nor levels of Bcl-X L were altered in diabetic neuropathy. Apoptosis associated with mitochondrial dysfunction may contribute to the pathogenesis of diabetic sensory neuropathy.

Oxidative injury and neuropathy in diabetes and impaired glucose tolerance

“…An area of controversy is whether classical apoptosis in the peripheral nervous system is responsible for the neuropathic deficits observed in both animal models and human patients. Multiple studies report activation of caspases in DRG neurons both in vitro and in vivo (Russell et al, 1999;Srinivasan et al, 2000;Kishi et al, 2002;Russell et al, 2002;Cheng and Zochodne, 2003;Schmeichel et al, 2003;. Others detect some loss of DRG (Russell et al, 1999;Zochodne et al, 2001;Kishi et al, 2002) and in particular there is a statistically significant loss of large DRG neurons (Kishi et al, 2002).…”

“…These ROS are associated with membrane lipid peroxidation, nitration of proteins and DNA damage (for review see (Vincent and Feldman, 2004). Mitochondrial oxidative injury coupled with loss of insulin and neurotrophic support contributes to mitochondrial inner membrane depolarization in sensory neurons, ballooning of mitochondria, release of cytochrome c into the cytosol, and activation of caspases in DRG neurons Schmeichel et al, 2003Srinivasan et al, 2000Cheng and Zochodne, 2003; all of which are associated with neuronal or axonal injury (Sasaki et al, 1997;Fujimura et al, 1999;Russell et al, 1999;Kishi et al, 2002;Huang et al, 2003). In the current study, both DRG neurons and SC show evidence of caspase activation and positive TUNEL labeling.…”

Glial Cell Line-Derived Neurotrophic Factor Increases β-Cell Mass and Improves Glucose Tolerance

“…7B, C). To determine the mechanisms involved in insulin loss following STZ administration, β-cells apoptosis was assessed by a combination of TUNEL staining 19 with cleaved caspase-3 immunocytochemistry. GDNF-tg mice showed 4 fold less β-cell apoptosis than WT mice twelve days after injection with STZ as evidenced by the smaller number of TUNEL and cleaved caspase-3 positive β-cells in these mice (P<0.05; Fig.…”

Transforming growth factor-β induces cellular injury in experimental diabetic neuropathy

“…Explant cultures were grown by placing whole DRG onto collagen-coated 6-well culture dishes. Cultures were grown for 3 days in Neurobasal Medium containing 25 mM glucose (optimal basal glucose for neurons) (Russell et al, 1999;Russell et al, 2002;Srinivasan et al, 2000), with 0.5% B27 without antioxidants, 10 ng/ml Nerve Growth Factor, 0.5% Pen/Strep/Neo, and 0.7 mM l-glutamine, and 40 µM FUDR. Media was changed every 48 hours, and immediately before drug treatment.…”

“…Despite the significant pathology associated with nerve degeneration, the etiology of neuropathy is still unclear. Several pathways have been suggested to be associated with glucose neurotoxicity (Tomlinson and Gardiner 2008) and diabetic neuropathy, for example oxidative stress (Cameron et al, 1993;Coppey et al, 2001;Obrosova et al, 2005;Pop-Busui et al, 2006;Russell et al, 2002), altered polyol metabolism (Cameron and Cotter 1997), mitochondrial dysfunction (Huang et al, 2003a;Montal, 1998;Russell et al, 2002), activation of certain cysteine proteases (caspases) (Russell et al, 1999;Srinivasan et al, 2000) (Cheng and Zochodne 2003;Schmeichel et al, 2003), and regulation of growth factors and their intermediate signaling pathways (Sayers et al, 2003;Tomlinson et al, 1996). However, the role of cytokines such as transforming growth factor β (TGF-β) in development of diabetic neuropathy is not clearly defined.…”