Abstract
Transient receptor potential canonical 6 (TRPC6) channels are permeable to Na+ and Ca2+ and are widely expressed in the brain. In this study, the role of TRPC6 was investigated following ischemia/reperfusion (I/R) and oxygen-glucose deprivation (OGD). We found that TRPC6 expression was increased in wild-type (WT) mice cortical neurons following I/R and in primary neurons with OGD, and that deletion of TRPC6 reduced the I/R-induced brain infarct in mice and the OGD- /neurotoxin-induced neuronal death. Using live-cell imaging to examine intracellular Ca2+ levels ([Ca2+]i), we found that OGD induced a significant higher increase in glutamate-evoked Ca2+ influx compared to untreated control and such an increase was reduced by TRPC6 deletion. Enhancement of TRPC6 expression using AdCMV-TRPC6-GFP infection in WT neurons increased [Ca2+]i in response to glutamate application compared to AdCMV-GFP control. Inhibition of N-methyl-d-aspartic acid receptor (NMDAR) with MK801 decreased TRPC6-dependent increase of [Ca2+]i in TRPC6 infected cells, indicating that such a Ca2+ influx was NMDAR dependent. Furthermore, TRPC6-dependent Ca2+ influx was blunted by blockade of Na+ entry in TRPC6 infected cells. Finally, OGD-enhanced Ca2+ influx was reduced, but not completely blocked, in the presence of voltage-dependent Na+ channel blocker tetrodotoxin (TTX) and dl-α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) blocker CNQX. Altogether, we concluded that I/R-induced brain damage was, in part, due to upregulation of TRPC6 in cortical neurons. We postulate that overexpression of TRPC6 following I/R may induce neuronal death partially through TRPC6-dependent Na+ entry which activated NMDAR, thus leading to a damaging Ca2+ overload. These findings may provide a potential target for future intervention in stroke-induced brain damage.
Highlights
Ischemic stroke is a devastating disease that is one of the leading causes of death
These results demonstrated that I/R and oxygen-glucose deprivation (OGD) induced a significant increase in Transient receptor potential canonical 6 (TRPC6) expression in neurons
The present study reports that deletion of TRPC6 protects against cerebral I/R-induced brain damage in vivo and OGD- and excitatory neurotoxininduced cell death in vitro
Summary
Ischemic stroke is a devastating disease that is one of the leading causes of death. A critical deficit of cerebral blood flow (CBF) during stroke rapidly triggers neuronal depolarization that releases a large amount of glutamate into the extracellular space (Drejer et al, 1985; Choi et al, 1990; Choi, 1992). Upon oxygen and glucose deprivation (OGD) which is a well-established in vitro model of ischemia (Tasca et al, 2015), glutamate is massively released by neurons, and the resulting increase in the intracellular Ca2+ concentration ([Ca2+]i) causes a delayed neuronal cell death (Caldeira et al, 2014). Treatments which blocks glutamate-ionotropic receptors can protect neurons from ischemic insult and reduce brain infarction in animals (Choi et al, 1988; Chen et al, 1992). Though the blockade of glutamate receptors shows dramatic neuroprotective effects in animal stroke and in vitro OGD models, clinical trials aimed at reducing ischemic brain injury by targeting NMDA and AMPA receptors, failed to achieve satisfactory effects (De Keyser et al, 1999; Gladstone et al, 2002; Lo et al, 2003). There is a great need to develop new, potential drug targets for the treatment of strokes (Roth and Liesz, 2016)
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