Transient Receptor Potential Melastatin Subfamily Member 2 Cation Channel Regulates Detrimental Immune Cell Invasion in Ischemic Stroke

Abstract

Ischemic stroke is the second most common cause of death worldwide. Tissue damage is thought to follow a biphasic course. The initial hypoxic damage is determined by immediate neuronal cell death leading to the formation of the infarct core, whereas secondary infarct growth is considered to be a consequence of systemic and local sterile inflammation. 1 Ischemia in the central nervous system is characterized by oxidative stress and the release of a manifold of stress mediators, among them adenosine diphosphate ribose (ADPR) that is produced by poly-ADPR polymerase in response to oxidative stress, cyclic ADPR, calcium and nicotinic acid adenine dinucleotide phosphate.2 Because these factors modulate the open-probability of the calcium-permeable transient receptor potential melastatin subfamily member 2 (TRPM2) cation channel, this channel has been implicated in stroke pathophysiology. The highest expression levels of TRPM2 are found throughout the nervous system, such as neurons and microglial cells, 3 but it can also be detected in a variety of other tissues including cells of the peripheral immune system, 4 such as polymorphonuclear neutrophils and monocytes.Background and Purpose-Brain injury during stroke results in oxidative stress and the release of factors that include extracellular Ca 2+, hydrogen peroxide, adenosine diphosphate ribose, and nicotinic acid adenine dinucleotide phosphate. These alterations of the extracellular milieu change the activity of transient receptor potential melastatin subfamily member 2 (TRPM2), a nonselective cation channel expressed in the central nervous system and the immune system. Our goal was to evaluate the contribution of TRPM2 to the tissue damage after stroke. Methods-In accordance with current quality guidelines, we independently characterized Trpm2 in a murine ischemic stroke model in 2 different laboratories. Results-Gene deficiency of Trpm2 resulted in significantly improved neurological outcome and decreased infarct size.Besides an already known moderate neuroprotective effect of Trpm2 deficiency in vitro, ischemic brain invasion by neutrophils and macrophages was particularly reduced in Trpm2-deficient mice. Bone marrow chimeric mice revealed that Trpm2 deficiency in the peripheral immune system is responsible for the protective phenotype. Furthermore, experiments with mixed bone marrow chimeras demonstrated that Trpm2 is essential for the migration of neutrophils and, to a lesser extent, also of macrophages into ischemic hemispheres. Notably, the pharmacological TRPM2 inhibitor, N-(p-amylcinnamoyl)anthranilic acid, was equally protective in the stroke model. Therefore, TRPM2 might be involved in early ischemic neuronal cell death but also in the subsequent detrimental sterile inflammation. Involvement of TRPM2 in cerebral ischemic injury has recently been investigated, [5][6][7][8] showing a pathogenetic contribution of TRPM2 to ischemic stroke. However, these analyses focused on the role of TRPM2 in neuronal injury during ischemia. Of note, Trpm2 deficiency i...

Signalling mechanisms mediating Zn2+-induced TRPM2 channel activation and cell death in microglial cells

“…3a) was almost completely prevented by the necrosis inhibitor IM-54, suggesting necrotic cell death, a mechanism eliciting inflammatory responses. This is consistent with the findings from recent transgenic studies that the TRPM2 channel in microglial cells is engaged in inflammatory pain71 and post-ischemic stroke brain damage75 and AD8089.…”

“…We started with using immunofluorescent confocal microscopy to confirm the TRPM2 expression in microglial cells7172737475. Positive immunostaining was observed in cells labelled with an anti-TRPM2 antibody but not in control cells (Fig.…”

TRPM2 channel: A novel target for alleviating ischaemia‐reperfusion, chronic cerebral hypo‐perfusion and neonatal hypoxic‐ischaemic brain damage

“…The striatal infarct volume was also significantly reduced in the mice injected with lentivirus expressing TRPM2‐specific shRNA into the striatum 2‐3 weeks before ischaemia . Three independent studies compared MCAO‐R induced brain damage in the WT and TRPM2‐KO mice, and these studies provide independent but consistent evidence to show that ischaemia‐reperfusion brain damage was significantly protected by TRPM2‐KO . Furthermore, one of the studies noted no difference in brain damage between the WT and TRPM2‐KO mice that were subjected to permanent ischaemia without reperfusion .…”

Redox regulation of transient receptor potential channels in the endothelium

“…Clotrimazole impedes TRPM2 activity but has many additional effects including inhibition of cytochrome P450 enzymes 68 , block of intermediate conductance Ca 2+ activated K + channels 69 , L-type voltage gated Ca 2+ channels 70 , ATP-gated K + channels 71 , and TRPM8 72 channels, and activation of TRPV1 and TRPA1 channels 72 . A more convincing study using TRPM2 −/− mice showed reduced infarct after ischemia/reperfusion injury, which was a consequence of reduced neutrophil infiltration 73 . Interestingly, transplantation of wild type bone marrow into TRPM2 −/− mice reversed the protective effect of TRPM2 deletion, possibly due to increased neutrophil infiltration 73 .…”