The functional roles of gap junctional communication among astrocytes and other brain cells are believed to include trafficking of nutrients, energy metabolites, signaling molecules, and electrolytes. Although trafficking of biological molecules within the cellular syncytia in brain is not well understood due to the lack of sensitive assays for unlabeled or non-fluorescent molecules, hereditary mutations in connexin proteins that impair gap junctional signaling can cause deafness, underscoring the importance of trans-cellular communication among brain cells. Our initial findings demonstrate that gap junctional dye transfer is markedly reduced in cultured astrocytes after prolonged exposure to high levels of glucose and in brain slices from streptozotocin-treated diabetic rats. Disruption of syncytial trafficking and the slower onset of increased expression of endoplasmic reticulum chaperone proteins in experimental diabetes suggests that reduced communication among gap junction-coupled brain cells and endoplasmic reticulum stress may be unrecognized, 'subtle'complications of diabetes in the central nervous system. Gap junctional trafficking deficits in cultured astrocytes occurred after increased generation of reactive oxygen species (ROS) and could be prevented or restored by various pharmacological agents. These findings led to our overall hypothesis that diabetes-induced oxidative- nitrosative stress impairs gap junctional trafficking of biological molecules, gradually causes endoplasmic reticulum stress, and causes subtle impairment of brain function. The three specific aims are as follows, (1) establish roles of oxidative-nitrosative modification of cellular proteins in impairment of astrocytic gap junction communication and manifestation of endoplasmic reticulum stress, (2) establish impairment of gap junctional transfer of biological molecules during experimental diabetes, and (3) establish effects of experimental diabetes on auditory pathway functions. This proposal addresses some of the long-standing, basic issues related to connexin channel function - permeability of biological molecules, functions of syncytial communication in situ, and development of novel assays, tools, or probes for studies of connexin structure and function. It then assesses permeability of connexin channels to biological molecules in experimental diabetes. Our long-term goals are to understand the functions of the astrocytic syncytium in health and disease and improve knowledge of the cellular basis of metabolic brain images. Translational aspects of this study include potential treatment strategies for diabetes and improved interpretation of brain imaging and spectroscopic studies using technologies that detect signals arising from metabolic responses to changes in physiological activity. The anticipated results will lead to a better understanding of nutritional and signaling roles of gap junctions in astrocytes and other brain cells and how these functions are disrupted by hyperglycemia and experimental diabetes.
Complications of diabetes cause serious, progressive health problems and many diabetic patients acquire altered hearing characteristics and develop hearing loss. We found that experimental diabetes impairs the ability of brain cells to the shuttle nutrients and signaling compounds between different cells in the brain, and we test the hypothesis that disruption of cellular function by diabetes progressively interferes with communication between brain and inner ear cells, leading to hearing impairment. Therapeutic molecules will be tested for their ability to overcome these deficits with the goal of developing new treatment strategies to minimize diabetes-induced deficits in brain.
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