Abstract
The pathogenetic role of vascular endothelial growth factor (VEGF) in long-term retinal and kidney complications of diabetes has been demonstrated. Conversely, little is known in diabetic neuropathy. We examined the modulation of VEGF pathway at mRNA and protein level on dorsal root ganglion (DRG) neurons and Schwann cells (SC) induced by hyperglycaemia. Moreover, we studied the effects of VEGF neutralization on hyperglycemic DRG neurons and streptozotocin-induced diabetic neuropathy. Our findings demonstrated that DRG neurons were not affected by the direct exposition to hyperglycaemia, whereas showed an impairment of neurite outgrowth ability when exposed to the medium of SC cultured in hyperglycaemia. This was mediated by an altered regulation of VEGF and FLT-1 receptors. Hyperglycaemia increased VEGF and FLT-1 mRNA without changing their intracellular protein levels in DRG neurons, decreased intracellular and secreted protein levels without changing mRNA level in SC, while reduced the expression of the soluble receptor sFLT-1 both in DRG neurons and SC. Bevacizumab, a molecule that inhibits VEGF activity preventing the interaction with its receptors, restored neurite outgrowth and normalized FLT-1 mRNA and protein levels in co-cultures. In diabetic rats, it both prevented and restored nerve conduction velocity and nociceptive thresholds. We demonstrated that hyperglycaemia early affected neurite outgrowth through the impairment of SC-derived VEGF/FLT-1 signaling and that the neutralization of SC-secreted VEGF was protective both in vitro and in vivo models of diabetic neuropathy.
Highlights
Neuropathy is a chronic complication of both type 1 and type 2 diabetes that severely affects patients’ quality of life and increases morbidity and mortality [1]
Cells: ctrl 0.03960.007, glucose 45 mM 0.06060.01, glucose 90 mM 0.03960.005, glucose 135 mM 0.0460.006, glucose 180 mM 0.0460.006, Fig. 2C) at any of the concentration tested, whereas it increased Schwann cells (SC) apoptosis only at the highest concentrations both in coculture and in monoculture. Both neurons and SC showed high rate of apoptosis after exposure to cisplatin and paclitaxel demonstrating that absence of intrinsic resistance
Hyperglycaemia did not cause early loss of mitochondrial membrane potential differential Mitochondrial potential was assessed in dorsal root ganglion (DRG)-co-cultures 24 hours after glucose (45 mM) or toxic compound exposure
Summary
Neuropathy is a chronic complication of both type 1 and type 2 diabetes that severely affects patients’ quality of life and increases morbidity and mortality [1]. Diabetic axonal damage fails to recover due to a number of events, including the loss of innervated targets and the chronic denervation of Schwann cells (SC) [2]. Different mechanisms have been claimed as critical in the pathogenesis of diabetic neuropathy (DN), including abnormal metabolic and neurovascular pathways, growth factor deficiency, and extracellular matrix remodeling [3]. Previous studies showed that hyperglycaemia can directly affect SC inducing in vitro apoptosis [6], altering the secretion of growth factors [7,8] and interfering with proliferation and migration abilities [9], suggesting an effect on this cell type. Little is known on how hyperglycaemia interferes with the supporting role of SC on axonal growth in cultured dorsal root ganglion (DRG) neurons
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