It has been suggested previously, that excessive release of glutamate and overactivation of glutamate receptors (mainly NMDA receptors, NMDAR) are primarily responsible for the secondary (delayed) neuronal death that occurs in the central nervous system during neuronal injuries, including ischemia, traumatic brain injury and epilepsy. Recently, based on our experimental data, we proposed novel hypothesis for the mechanisms of glutamate-dependent excitotoxicity. We suggested that, during neuronal injury, the main reason for glutamate-dependent neuronal death is not an overactivation of NMDARs per se, but rather the presence and increase in expression of neuronal gap junctions (GJ;electrical synapses). We also postulated that these mechanisms have universal character and are involved in neuronal death in different types of neuronal injuries. Currently, however, there i no definitive evidence that increase and decrease in neuronal GJ coupling would directly determine the increased and decreased neuronal death, respectively. In addition, the underlying mechanism for increase in neuronal GJ coupling during neuronal injury is not known. The centrality of neuronal GJs to neuronal death makes addressing these issues imperative, if blockade of neuronal GJ coupling is to be exploited clinically as a novel approach for neuroprotection. First, we will test the prediction that increase in neuronal GJ coupling augments, and decrease prevents, neuronal death caused by ischemia. This will be studied using oxygen-glucose deprivation as an in vitro model of ischemia, neuronal cultures prepared from the somatosensory cortex of wild-type and connexin 36 knockout mice, cell culture infections with lentiviral vectors, electrotonic coupling, western blots and analysis of neuronal death. Second, we will test the hypothesis that increase in neuronal gap junction coupling during ischemia is regulated via the mechanism of """"""""leaky scanning"""""""" of connexin 36 mRNA translation. This will be tested using electrotonic coupling, western blotting, neuronal staining, molecular biology and neuronal cultures prepared from the somatosensory cortex of wild-type mice. The analysis we propose fits the criteria of the R21 mechanism: there is risk that our hypothesis on the role of GJs in neuronal death might be wrong. However, if we are correct, we will have identified novel mechanism for glutamate-mediated excitotoxicity and novel approach for neuroprotection that targets neuronal GJs, rather than NMDARs.
This study is relevant to public health. It addresses the role of neuronal gap junctions (electrical synapses) in ischemic neuronal death and the mechanisms of regulation of neuronal gap junction coupling during ischemia. This research may have clinical importance given that neuronal gap junction coupling increases during ischemia, but the role and regulation of gap junctions in ischemia are not yet understood.
