Transient Receptor Potential Ankyrin-1 (TRPA1) Block Protects against Loss of White Matter Function during Ischaemia in the Mouse Optic Nerve

Abstract

Oligodendrocytes produce myelin, which provides insulation to axons and speeds up neuronal transmission. In ischaemic conditions, myelin is damaged, resulting in mental and physical disabilities. Recent evidence suggests that oligodendrocyte damage during ischaemia can be mediated by Transient Receptor Potential Ankyrin-1 (TRPA1), whose activation raises intracellular Ca2+ concentrations and damages compact myelin. Here, we show that TRPA1 is constitutively active in oligodendrocytes and the optic nerve, as the specific TRPA1 antagonist, A-967079, decreases basal oligodendrocyte Ca2+ concentrations and increases the size of the compound action potential (CAP). Conversely, TRPA1 agonists reduce the size of the optic nerve CAP in an A-967079-sensitive manner. These results indicate that glial TRPA1 regulates neuronal excitability in the white matter under physiological as well as pathological conditions. Importantly, we find that inhibition of TRPA1 prevents loss of CAPs during oxygen and glucose deprivation (OGD) and improves the recovery. TRPA1 block was effective when applied before, during, or after OGD, indicating that the TRPA1-mediated damage is occurring during both ischaemia and recovery, but importantly, that therapeutic intervention is possible after the ischaemic insult. These results indicate that TRPA1 has an important role in the brain, and that its block may be effective in treating many white matter diseases.

Transient receptor potential Ankyrin‐1 (TRPA1) agonists suppress myelination and induce demyelination in organotypic cortical slices

“…Using single cell calcium imaging (Hamilton et al, 2016;Lajoso et al, 2021; Figure 1a) we confirm that TRPA1 activation with either TRPA1 expression is not confined to glia in the cortex, where neuronal TRPA1-eGFP expression can be seen (Figure S1).…”

“…The data presented here, and that already published, also indicate that TRPA1 is expressed by oligodendrocyte lineage cells throughout the mouse lifetime. The evidence in young mice includes (1) in situ hybridization experiments for TRPA1 mRNA (Hamilton et al, 2016;Marques et al, 2016), (2) TRPA1 agonist induced oligodendrocyte calcium flux (Hamilton et al, 2016, Lajoso et al, 2021; Figure 1), and now (3) the organotypic brain slice experiments in this article (Figures 2-5). We now provide good evidence that TRPA1 continues to be expressed into adulthood by presenting data from the TRPA1-eGFP mice (Figure 1) and this finding supports reports of TRPA1 block protecting myelin in in vivo models of stroke (Xia et al, 2019).…”

“…Most, like JT010, are electrophilic agonists that bind to TRPA1 on the N-terminal by covalent modification. We, and others, have found that electrophilic TRPA1 agonists may need an intrinsic factor to be present in order to activate TRPA1 (Lajoso et al, 2021). In order to confirm that agonists that bind to TRPA1 in the traditional manner also cause demyelination, we applied carvacrol, which produces a robust TRPA1 mediated calcium concentration increase in oligodendrocytes (Figure 1).…”

“…Currently, intense research efforts are dedicated to understanding the mechanisms causing demyelination in order to prevent myelin degeneration (Amedei et al, 2012 ; Desai et al, 2016 ; Stangel et al, 2017 ). Recent evidence indicates that Transient Receptor Potential Ankyrin 1 (TRPA1) channels cause myelin damage and loss of white matter function during simulated ischemia (Hamilton et al, 2016 ; Lajoso et al, 2021 ), stroke (Xia et al, 2019 ), and a cytotoxic model of multiple sclerosis (Bölcskei et al, 2018 ; Kriszta et al, 2019 ; Sághy et al, 2016 ). Previously, TRPA1 was described as a non‐selective cation channel mainly expressed in primary sensory neurons, which plays a key role in physiological and pathological pain (Chen et al, 2011 ; Koivisto et al, 2014 , 2018 ; Talavera et al, 2020 ).…”

“…The "n" is one averaged data point from individual slices.the specific TRPA1 agonist JT010 (1 μM), or the nonspecific TRPA1 agonist, carvacrol (2 mM), causes a consistent increase in intracellular calcium concentration in corpus callosum oligodendrocytes (Δ[Ca 2+ ] i = ΔR/R 0 ; Figure1b). Differences in onset times are believed to be due to variances in binding sites on TRPA1 for these two drugs(Lajoso et al, 2021), but the mean responses are the same (0.30 ± 0.04 ΔR/R 0 Carvacrol; 0.35 ± 0.11 ΔR/R 0 JT010; Figure1c).To support these functional experiments and our previously published in situ hybridisation experiments showing TRPA1 mRNA in APC/CC1 positive cerebellar oligodendrocytes(Hamilton et al, 2016), we purchased TRPA1-eGFP mice (Gensat, Tg(Trpa1-EGFP)LT325Gsat/ Mmucd) that express eGFP when TRPA1 is expressed. Initial labeling for GFP with DAB staining showed that TRPA1-eGFP was located throughout the brain and especially in cells appearing to be oligodendrocytes in rows within the corpus callosum (Figure1d,d1).…”