GDNF rescues hyperglycemia-induced diabetic enteric neuropathy through activation of the PI3K/Akt pathway
Mallappa Anitha, Chetan Gondha, Roy Sutliff, Alexander Parsadanian, Simon Mwangi, Shanthi V. Sitaraman, Shanthi Srinivasan
Mallappa Anitha, Chetan Gondha, Roy Sutliff, Alexander Parsadanian, Simon Mwangi, Shanthi V. Sitaraman, Shanthi Srinivasan
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Research Article Endocrinology

GDNF rescues hyperglycemia-induced diabetic enteric neuropathy through activation of the PI3K/Akt pathway

Abstract

Diabetes can result in loss of enteric neurons and subsequent gastrointestinal complications. The mechanism of enteric neuronal loss in diabetes is not known. We examined the effects of hyperglycemia on enteric neuronal survival and the effects of glial cell line–derived neurotrophic factor (GDNF) on modulating this survival. Exposure of primary enteric neurons to 20 mM glucose (hyperglycemia) for 24 hours resulted in a significant increase in apoptosis compared with 5 mM glucose (normoglycemia). Exposure to 20 mM glucose resulted in decreased Akt phosphorylation and enhanced nuclear translocation of forkhead box O3a (FOXO3a). Treatment of enteric neurons with GDNF ameliorated these changes. In streptozotocin-induced diabetic mice, there was evidence of myenteric neuronal apoptosis and reduced Akt phosphorylation. Diabetic mice had loss of NADPH diaphorase–stained myenteric neurons, delayed gastric emptying, and increased intestinal transit time. The pathophysiological effects of hyperglycemia (apoptosis, reduced Akt phosphorylation, loss of inhibitory neurons, motility changes) were reversed in diabetic glial fibrillary acidic protein–GDNF (GFAP-GDNF) Tg mice. In conclusion, we demonstrate that hyperglycemia induces neuronal loss through a reduction in Akt-mediated survival signaling and that these effects are reversed by GDNF. GDNF may be a potential therapeutic target for the gastrointestinal motility disorders related to diabetes.

Authors

Mallappa Anitha, Chetan Gondha, Roy Sutliff, Alexander Parsadanian, Simon Mwangi, Shanthi V. Sitaraman, Shanthi Srinivasan

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Figure 1

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Hyperglycemia induces apoptosis in enteric neurons, and this is ameliora...
Hyperglycemia induces apoptosis in enteric neurons, and this is ameliorated by GDNF. To study the dose-dependent effects of hyperglycemia, different concentrations of glucose (5, 10, or 20 mM) were used in serum-free/glucose-free media. (A) Apoptosis was assessed by the Ret/Hoechst staining method. (B) Magnified view of neurons to show the DNA fragmentation (arrow) seen during apoptosis compared with a healthy neuron (on the right). (C) Apoptosis was assessed using the Ret/TUNEL method in the presence or absence of GDNF and the stated glucose or mannitol concentrations. (D) Representative photomicrographs of enteric neurons cultured in the presence of 5 mM and 20 mM glucose and assessed for apoptosis using the Ret/TUNEL method. Ret (red) staining was used as a neuronal marker. Arrows identify the apoptotic cells (yellow) with condensed nuclei. Figure shows results of 4 independent experiments. *P < 0.05; **P < 0.01; ***P < 0.001. Scale bars: 20 μm (B); 100 μm (D). Glu, glucose.