Disruption of RAGE signaling prevents sympathetic neuron malfunction in high glucose conditions

Abstract

Diabetes, which is characterized by elevated plasma glucose, can have a devastating effect on peripheral nerves frequently leading to the clinical symptoms of neuropathy. Diabetic autonomic neuropathy (DAN) results from damage to autonomic nerves, and the most troubling forms of DAN often lead to cardiovascular abnormalities and premature death. Despite the prevalence of DAN and the impact to quality and life expectancy, the precise mechanisms underlying these pathologies are poorly understood. Recently, a new model for the onset of DAN was proposed where hyperglycemia-induced oxidative stress inactivates nicotinic acetylcholine receptors (nAChRs), the main receptor driving autonomic synaptic transmission at sympathetic ganglia. This inactivation leads to the depression of synaptic transmission, and consequently triggers the onset of autonomic neuropathy in diabetic mice. However, the source and pathways contributing to the elevation of reactive oxygen species (ROS) and oxidative stress remained unclear. In recent years it has been shown that the accelerated formation of advanced glycation end products (AGEs) and activation of their receptor (RAGE) in diabetes play a major role in the induction of oxidative stress in sensory nerve damage. Thus we hypothesized that the activation and up-regulation of RAGE during high glucose conditions is a major source of ROS production in sympathetic neurons leading to the inactivation of nAChRs and autonomic malfunction. In this thesis we show for the first time that RAGE is expressed in cultured sympathetic neurons and is also up-regulated during high glucose conditions. Our results further demonstrate that direct RAGE activation by its natural ligands leads to an increase in cytoplasmic ROS which in turn induces the inactivation of nAChRs in sympathetic neurons. We also report that high glucose-induced ROS generation and subsequent inactivation of nAChRs is prevented in sympathetic neurons from RAGE knock-out mice. The results of this dissertation suggest RAGE to be a pivotal source of ROS production leading to the functional deficits observed in sympathetic neurons during high glucose conditions.