Blockade of TRPC Channels Limits Cholinergic-Driven Hyperexcitability and Seizure Susceptibility After Traumatic Brain Injury

Abstract

We investigated the contribution of excitatory transient receptor potential canonical (TRPC) cation channels to posttraumatic hyperexcitability in the brain 7 days following controlled cortical impact model of traumatic brain injury (TBI) to the parietal cortex in male adult mice. We investigated if TRPC1/TRPC4/TRPC5 channel expression is upregulated in excitatory neurons after TBI in contribution to epileptogenic hyperexcitability in key hippocampal and cortical circuits that have substantial cholinergic innervation. This was tested by measuring TRPC1/TRPC4/TRPC5 protein and messenger RNA (mRNA) expression, assays of cholinergic function, neuronal Ca2+ imaging in brain slices, and seizure susceptibility after TBI. We found region-specific increases in expression of TRPC1, TRPC4, and TRPC5 subunits in the hippocampus and cortex following TBI. The dentate gyrus, CA3 region, and cortex all exhibited robust upregulation of TRPC4 mRNA and protein. TBI increased cFos activity in dentate gyrus granule cells (DGGCs) and layer 5 pyramidal neurons both at the time of TBI and 7 days post-TBI. DGGCs displayed greater magnitude and duration of acetylcholine-induced rises in intracellular Ca2+ in brain slices from mice subjected to TBI. The TBI mice also exhibited greater seizure susceptibility in response to pentylenetetrazol-induced kindling. Blockade of TRPC4/TRPC5 channels with M084 reduced neuronal hyperexcitation and impeded epileptogenic progression of kindling. We observed that the time-dependent upregulation of TRPC4/TRPC5-containing channels alters cholinergic responses and activity of principal neurons acting to increase proexcitatory sensitivity. The underlying mechanism includes acutely decreased acetylcholinesterase function, resulting in greater Gq/11-coupled muscarinic receptor activation of TRPC channels. Overall, our evidence suggests that TBI-induced plasticity of TRPC channels strongly contributes to overt hyperexcitability and primes the hippocampus and cortex for seizures.

Post-Traumatic Epilepsy and Comorbidities: Advanced Models, Molecular Mechanisms, Biomarkers, and Novel Therapeutic Interventions

“…Neuronal loss was observed within the ipsilateral hippocampus, and aberrant mossy fiber sprouting was evident within the dentate gyrus. Similar data have now been collected from several laboratories ( Zhang et al, 2008 ; Andrade et al, 2017 ; Mukherjee et al, 2013 ; Shultz et al, 2013; Carver et al, 2021 ).…”

TRPC channels as emerging targets for seizure disorders

“…The expression of these TRPC channels in the brain indeed can be regulated by excitatory inputs. In a mouse model of TBI-induced seizures, the expression of TRPC4 and TRPC5 but not TRPC1 is consistently upregulated at both mRNA and protein levels in the cortex as well as hippocampal areas CA1, CA3, and dentate gyrus after TBI [35]. Treatment with TRPC4/TRPC5 dual inhibitor M084 (Figure 2) significantly decreases the post-TBI neuronal hyperexcitability featured by c-Fos activity and acetylcholine-induced rises in intracellular Ca 2+ in dentate gyrus granule cells.…”

“…Treatment with TRPC4/TRPC5 dual inhibitor M084 (Figure 2) significantly decreases the post-TBI neuronal hyperexcitability featured by c-Fos activity and acetylcholine-induced rises in intracellular Ca 2+ in dentate gyrus granule cells. Moreover, the TBI mice display greater seizure susceptibility in response to pentylenetetrazol (PTZ)-induced kindling, which can be reduced by blocking the TRPC4/TRPC5 channels using Trends in Pharmacological Sciences compound M084 (Table 2) [35]. These interesting findings suggest that the TBI-induced TRPC4 and TRPC5 are involved in the neuronal hyperexcitation and might lower the seizure threshold in post-traumatic epilepsy, thereby contributing to the epileptogenic processes in TBI-induced acquired epilepsy.…”

Direct modulation of TRPC ion channels by Gα proteins

“…Shapiro group put an emphasis on the role of TRPC in the G i signaling pathway in the brain, as well as M channels and GIRK channels ( Carver and Shapiro, 2019 ; Carver et al, 2020 ; Carver et al, 2021 ). Sohn group also suggested that TRPC5 mediates the effects of leptin and serotonin via POMC neurons ( Gao et al, 2017 ), and this effect is independent of altering GIRK channel activity ( Sohn et al, 2011 ).…”