The contribution of canonical transient receptor potential (TRPC) ion channels to ischemic brain injury

Abstract

Ischemic brain injury is the third leading cause of mortality and the leading cause of disability in Australia. However, there are no neuroprotective treatments to mitigate neuronal damage elicited by ischemic brain injury. This study investigated the putative role of canonical transient potential receptor (TRPC) ion channels in the pathophysiology of ischemic brain injury. TRPC ion channels are non-selective cation channels expressed in the central nervous system and other organs. These channels are coupled to the metabotropic glutamate receptor signalling pathway which is strongly activated by glutamate release during ischemia, brain trauma and epilepsy. Ischemic brain injury was mimicked in both in vitro and in vivo models in wildtype (WT; 129 SvEv) and transgenic mice lines having genetic deletion of TRPC3 (TRPC3 -/-) and TRPC1,3,6,7 (TRPC1,3,6,7 -/-) subunits. As an in vitro model, extracellular field excitatory post synaptic potentials were recorded from the hippocampal brain slices before, during and after glutamate treatment of slices from TRPC3 -/- and WT mice. Greater recovery of synaptic function in TRPC3 -/- slices following an excitotoxic insult, compared to the WT controls suggested that TRPC3 plays a role in excitotoxicity-mediated injury in the hippocampus. Focal ischemia in the cerebral cortex was achieved using a photothrombotic stroke model in which platelet aggregation in the brain microvessel endothelium is achieved via a tail vein injection of Rose Bengal dye, followed by irradiation with green laser light at the target brain surface. Longitudinal analysis of progression of the infarct volumes at different time points following injury were quantified using unstained darkfield cryosections and haematoxylin and eosin (H&E) staining, with the highest infarct volumes observed at 4 days post infarct (DPI). This correlated well with loss of neurons in the lesion core and infiltration by astrocytes and microglia indicative of tissue remodelling. Across three independent studies the infarct volumes of TRPC1,3,6,7 -/- mice at 4 DPI were significantly smaller than the WT. This confirmed the involvement of TRPC ion channels in cerebral ischemic brain injury. These studies provide compelling evidence that indicate the block of TRPC channels would confer neuroprotection from ischemic brain injury.