TRPM2 in ischemic stroke: Structure, molecular mechanisms, and drug intervention

Figures & data

Figure 1. TRPM2 consists of four subunits and has six transmembrane domains with a reentry loop between the fifth and sixth helices. The N termini and C termini are located in the intracellular loops. The intracellular N-terminus includes four highly conserved common regions and an IQ motif that binds CaM and Ca²⁺. The intracellular C-terminus contains a TRP box (TRP), a coiled-coil domain (CCD), and the nucleoside diphosphate-linked moiety X-type homology motif (NUDT9-H)

Figure 2. Various stimuli can lead to TRPM2 activation. The elevation of ROS and H₂O₂ activate TRPM2 through production of intracellular ADPR. Extracellular factors including TNF-α and β-AP contribute to activation of TRPM2. Structural analogs of ADPR including NAADP, cADPR, OAADPR, and 2′-deoxy-ADPR activate TRPM2. Elevated Ca²⁺ and NAD⁺ can also participate in activation of TRPM2

Figure 3. Mechanisms of neuronal TRPM2 in ischemic stroke. TRPM2 modulates NMDAR-dependent survival and death signal pathways. TRPM2 participate in PKC/NOX‐mediated ROS generation, Zn²⁺ accumulation and subsequent a vicious positive feedback signaling mechanism for delayed cell death. TRPM2 involves in NLRP3 inflammasome activation and secretion of CXCL2 and caspase-1

Figure 4. Involvement of non-neuronal TRPM2 in immune responses. TRPM2 signaling control microglia cells and astrocytes function and responses through production of cytokines and chemotaxis. TRPM2 contributes to brain injury through activating peripheral immune cells including macrophages, neutrophils, and monocytes

Figure 5. The role of TRPM2 in blood–brain barrier damage. TRPM2 is involved in endothelial cell damage and microvascular pericyte injury

Table 1. Chemical synthesis compounds with TRPM2 inhibitory effects

Compound name	Structure	Animal/Cell	Mechanism of action	References
Flufenamic acid (FFA)		TRPM2-HEK293 cells/Rat insulinoma CRI-G1 cells	Partially reversible and voltage-independence on the inhibition of TRPM2 intracellularly Nonspecifically inhibits TRPM2 and activates TRPC6 and TRPA	[107–109]
2-(3-Methylphenyl) aminobenzoic acid (3-MFA)		TRPM2-HEK293 cells	Partially reversible and voltage-independence on the inhibition of TRPM2 intracellularly Nonspecific block of TRPM2 and slight inhibits the TRPC4 and TRPC5	[108,110]
N-(p-Amylcinnamoyl) anthranilic acid (ACA)		TRPM2-HEK293 cells/TRPM2-Human U937 cells	Partially reversible and voltage-independence on the inhibition of TRPM2 extracellularly Nonspecifically blocks TRPM2 and inhibits the other TRP channels in the order: TRPM8 > TRPC6 > TRPV1 Decreases the male hippocampal cell death and infarct size in ischemic stroke Suppresses neutrophil infiltration after ischemic stroke Attenuates okadaic acid-induced neuroinflammation and neurodegeneration in rats	[19,21,86,87,111–113]
Clotrimazole (Cltz)		TRPM2-HEK293 cells/Rat insulinoma CRI-G1 cells	Completely irreversible inhibition of TRPM2 and accelerates the inhibition effects as extracellular pH falls Nonselectively blocks TRPM2 and displays concentration dependence Decreases hippocampal cell death and infarct volume following cerebral ischemia	[19,22,53,114]
Econazole		TRPM2-HEK293 cells	Irreversible inhibition of TRPM2-mediated currents in a concentration-dependent manner Nonselective inhibition of TRPM2 by altering cytosolic Ca^2+ concentration	[114]
2-Aminoethoxydiphenyl borate (2-APB)		TRPM2-HEK293 cells	Voltage independent but reversibly inhibition of TRPM2 extracellularly Nonselectively blocks TRPM2 by altering cytosolic Ca^2+ accumulation Protects kidney function and decreases neutrophil infiltration after kidney I/R injury Decreases male hippocampal cell death following OGD Attenuates diabetes-induced cognitive dysfunction	[19,53,108,115,116]
Adenosine monophosphate (AMP)		Human neutrophils and T cells	Potent dose-dependent inhibition of ADPR-induced TRPM2 currents Specifically inhibits TRPM2 currents at the NUDIX domain	[95,117]
8-Bromoadenosine 5′-diphosphoribose (8‐Br‐cADPR)		Male Wistar albino rats	Completely suppressed cADPR and H2O2-induced TRPM2 currents but not ADPR-induced TRPM2 currents Specifically inhibits TRPM2 currents at the MHR1/2 domain Reduces renal damage after renal ischemia–reperfusion injury Decreases expressions of TRPM2, CD38, caspase‐3, TNF-α, IL‐1β	[94,95,117–119]
8-Phenyl-2′-deoxy- ADPR (8-Ph-ADPR)		TRPM2-HEK293 cells	Highly active specific NUDT9H- TRPM2 antagonist without affecting TRPM7, TRPM8 Inhibition of Ca^2+ signaling and chemotaxis in human neutrophils	[118,120]
Tat-M2NX	/	C57Bl/6 mice	Specifically inhibits ADPR-induced TRPM2 currents involved direct interactions with the NUDT9-H domain Reduction in infarct volume after ischemic stroke injury Efficiently cross the BBB	[98]
Scalaradial		TRPM2- HEK293 cells	Inhibition of TRPM2 currents in a concentration and time-dependent manner Specifically blocks TRPM2 Independence of phospholipase A2(sPLA2) and ERK and Akt pathways	[99]
JNJ-28,583,113		TRPM2-expressing HEK cells	Reversible inhibition of TRPM2 Causes the phosphorylation of the GSK3α and β subunits in microglia Protected cells from oxidative stress-induced cell death, cellular morphological changes and blunted microglia cytokine release in response to pro-inflammatory stimuli	[100]
7i		TRPM2-HEK293 cells	Dose-dependent inhibition of TRPM2 Interaction with NUDT9-H domain of TRPM2 Selective inhibition of TRPM2 currents without affecting TRPM7, TRPM8, TRPV1, and TRPV3	[120]
8a		TRPM2-HEK293 cells	Dose-dependent inhibition of TRPM2 Interaction with NUDT9-H domain of TRPM2 Selective inhibition of TRPM2 currents without affecting TRPM7, TRPM8, TRPV1, and TRPV3	[120]
2,3-Dihydroquinazolin-4(1 H)-one (D9)		TRPM2-HEK293 cells	Specific inhibitor of TRPM2 without affecting the TRPM8 currents	[101]
N-Acetyl-L-cysteine		Rats induced by global cerebral ischemia	Reduction in global cerebral ischemia-induced neuronal death cascades, such as lipid peroxidation, microglia, and astroglia activation, free zinc accumulation, and TRPM2 over-activation	[121]
AG490		TRPM2-HEK293 cells/Primary neurons were cultured from E16 CD-1 mice	Reduction in TRPM2 currents and infarct volume Improvement in overall brain morphology, general health, and short-term neurobehavioral performance	[122]
AG-related compounds (AG555, AG556)	/	Human monocytic U937 cells	Blocks H2O2-induced TRPM2 activation by scavenging of the hydroxyl radical Inhibits H2O2-induced CXCL8 secretion following ERK activation, which is mediated by TRPM2-dependent and independent mechanisms in U937 cells	[123]

Table 2. Literature review of various plants/herbs and marketed drugs showing TRPM2 inhibition effects

Compound name	Structure	Disease	Pharmacological activity	References
Duloxetine		Cerebral I/R injury Depression	Reduction in TRPM2-mediated inward currents during the channel-opening state Reduction in Ca^2+ concentration, caspase-3, caspase-9, mitochondrial depolarization, and intracellular ROS production Attenuates brain injury via TRPM2 inhibition	[103,124]
Dexmedetomidine		Cerebral ischemia	Reduction in TRPM2 densities and cytosolic calcium ion accumulation Decrease in caspase-3, caspase-9, ROS production, and depolarization of mitochondrial membrane potential in the hippocampus and dorsal root ganglion (DRG) neurons	[59]
Melatonin and selenium		Neuropathic pain	Decrease in Ca^2+ concentration, caspase-3, caspase-9, the current density in TRPM2 and amelioration of apoptosis and mitochondrial depolarization Reduction of glutathione, lipid peroxidation, and intracellular ROS production Prevents IFNγ-mediated microglia TRPM2 activation and cytokine generation	[125–127]
17β-Estradiol		Neurodegenerative disease in postmenopausal women	Decreases Ca^2+ influx, TRPM2 capacitances, caspase-3, caspase-9, mitochondrial membrane depolarization, and cell viability	[128]
Tamoxifen		Neurodegenerative disease in postmenopausal women	Dcrease in Ca^2+concentration, TRPM2 capacitance, caspase-3, caspase-9, and mitochondrial depolarization	[128]
Raloxifene		Neurodegenerative disease in postmenopausal women	Decrease in Ca^2+ concentration, TRPM2 current density, caspase-3, caspase-9, and mitochondrial membrane depolarization	[128]
Curcumin		Liver I/R injury Drug-induced hepatitis Nonalcoholic steatohepatitis	Inhibition of TRPM2 currents and increased Ca^2+ in rat hepatocytes	[102]
		Cisplatin-induced optic nerve damage	Decreases TRPM2 current density, Ca^2+ concentration, mitochondrial membrane depolarization, and ROS production	[129]
		Chronic kidney disease	Inhibition of albumin-induced Ca^2+ oscillations, cytokine production, ROS production, mitochondrial membrane potential, and NF-κB signaling related to cell death via TRPM2 inhibition	[130]
Salidroside		Liver disease	Inhibition of the increases in TRPM2 protein and mRNA expressions, Ca^2+ increase, and p-CaMKII protein expression Increase in the relative expression of LC3B-II and reduction of p62, and LC3B-II/LC3B-I ratio Alleviates PA-induced lipid accumulation, IL-1β and IL-6 mRNA expression in hepatic L02 cells	[131]
Resveratrol		Acute hypoxia	Reduction of intracellular Ca^2+ and improves mitochondrial function Suppression of the generation of cytokines (IL-1β and TNF-α), Zn^2+ concentration, PARP-1 activity, TRPM2 expression, caspase-3, and caspase-9 levels, and mitochondrial ROS production in SH-SY5Y cells	[132]
Hypericum perforatum (HP)		Spinal cord injury	Reduction of the SCI-induced TRPM2 currents and cytosolic-free Ca^2+ concentration Reduces the increase in apoptosis, caspase 3, caspase 9, cytosolic ROS production, and mitochondrial membrane depolarization values in the DRG of the spinal cord injury group	[133]

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