Longstanding evidence have demonstrated a strong correlation between altered ROS and Ca²⁺ systems and brain diseases, including aging and neurodegenerative disorders (Patel, 2016; Cobley et al., 2018; Franco and Vargas, 2018; Madreiter-Sokolowski et al., 2020). Given its role in sensing and responding to oxidative stress, many research groups investigated the potential role of TRPM2 in oxidative stress-mediated brain diseases. One of the most markers of aging is probably the dramatic decline of the antioxidant Glutathione (GSH). In this context, Belrose and coworkers showed that the loss of GSH-mediated neuronal senescence is associated with increased TRPM2 current density in cultured hippocampal neurons, suggesting a cellular connexion between activation of TRPM2 and neuronal senescence (Belrose et al., 2012). Furthermore, Kaneko’s group demonstrated that knocking out the TRPM2 channel attenuates cognitive dysfunction and prevents age-related damage in the white matter and hippocampus of normal and chronic cerebral hypoperfusion mouse models, suggesting that activation of TRPM2 has a deleterious effect on the pathophysiology of the aging brain (Miyanohara et al., 2018; Kakae et al., 2019). Activation of TRPM2 has also been associated with the establishment of long-term depression (LTD), a specific form of NMDAR-dependent synaptic plasticity that requires endocytosis of AMPA receptors (AMPAR) (Xie et al., 2011). Mechanistically, the authors showed that loss of TRPM2 impairs NMDAR-dependent LTD through the inactivation of GSK-3β and reduction of PSD95 and AMPAR Glu1 expression (Xie et al., 2011). The genetic etiology of TRPM2 has also been associated with increased susceptibility to bipolar disorder (BD). Indeed, a family-based association study showed the association between D543E mutation of Trpm2 and type-1 BD (McQuillin et al., 2006; Xu et al., 2009). Using TRPM2 KO mice, Jong and colleagues demonstrated that loss of TRPM2 is associated with the behavioral manifestations of BD, including increased anxiety and impaired social interaction (Jang et al., 2015). Mechanistically, the authors provided evidence that loss of TRPM2 induces the inhibitory phosphorylation of GSK-3 via calcineurin, a known kinases in bipolar disorder (Li et al., 2010; Pandey et al., 2010), and suggest that loss of TRPM2 has a deleterious effects on BD (Jang et al., 2015).

TRPM2 has also been associated with Alzheimer’s disease (AD), a common neurodegenerative disorder primarily associated with the accumulation of β-amyloid (Aβ) plaques, Ca²⁺ overload, and increased ROS (Gibson, 2002; Leclerc et al., 2009; Zhao and Zhao, 2013; Tong et al., 2018). For instance, inhibition of TRPM2 has been shown to reduce Aβ-mediated cytosolic Ca²⁺ overload and cytotoxicity in rat striatal cells, suggesting a key role of TRPM2 in Aβ-induced cytotoxicity (Fonfria et al., 2005). In support, another study also demonstrated that TRPM2-mediated massive Ca²⁺ entry is required for Aβ-mediated cerebrovascular dysfunction, confirming the role of the activation of TRPM2 in the deleterious cerebrovascular effects of Aβ (Park et al., 2014). Mechanistically, the authors showed that Aβ-mediated oxidative–nitrosative stress triggers PARP activity, DNA damage, and ADPR overproduction, which in turn activates TRPM2-mediated Ca²⁺ overload in cerebrovascular cells, ultimately impairing cerebral blood flow (Park et al., 2014).

Another hallmark of AD is microglia’s failure to phagocyte Aβ (Chen and Trapp, 2016; Sarlus and Heneka, 2017), due to the failure of Aβ-mediated NLRP3 activation and cognitive dysfunction (Halle et al., 2008; Gold and El Khoury, 2015). In this context, Amizadeh and coworkers demonstrated that the DPQ TRPM2 inhibitor decreases Aβ-mediated ROS and Ca²⁺ elevation, together with decreased NLRP3 activation and proinflammatory cytokines IL-1β secretion in microglial cells (Aminzadeh et al., 2018). Meanwhile, Ostapchenko and collaborators showed that Aβ-mediated decreases in the presynaptic marker synaptophysin and reduced microglial activation critically depend on TRPM2 current activation in cultured neurons. Using a Barnes maze analysis, the authors further show that inhibition of TRPM2 prevents the pathological and behavioral deficits observed in older (12–15 months) APP/PS1 AD mouse models, supporting a causative relationship between Aβ and the TRPM2 activation in Aβ-induced neurotoxicity and cognitive dysfunction (Ostapchenko et al., 2015). Interestingly, Li and Jiang showed that Aβ-mediated primary hippocampal neuron toxicity involves TRPM2-mediated lysosomal Zn²⁺ release (Li and Jiang, 2018). The authors demonstrated that Aβ-mediated neuron toxicity is ablated in TRPM2 KO mice and provided evidence that lysosomal TRPM2-mediated Zn²⁺ release causes lysosomal dysfunction and cytoplasmic Zn²⁺ overload, which in leads to mitochondrial Zn²⁺ accumulation and loss of mitochondrial function (Li and Jiang, 2018). Collectively, these results highlight the therapeutic potential of TRPM2 and suggest the inhibition of TRPM2 as promising strategy to counteract the deleterious effects of in brain diseases.

Ischemic stroke is characterized by sudden neurological deficits and occurs when the arteries supplying blood to the brain become blocked, resulting in neuronal necrosis (Dirnagl et al., 1999; Paul and Candelario-Jalil, 2021). A crucial mechanism involved in ischemic stroke is the excessive release of the neurotransmitter glutamate, which leads to overactivation of NMDA (N-methyl-D-aspartate) receptors (NMDAR) and subsequently to excessive Ca²⁺ influx and overproduction of ROS in neurons (Wu and Tymianski, 2018; Ge et al., 2020). Given the potential link between the Ca²⁺/ROS system and TRPM2 on the one hand and NMDAR-mediated ischemic stroke on the other, the role of TRPM2 in ischemic stroke has been investigated in detail (Turlova et al., 2018; Zong et al., 2022a; Xu et al., 2022). The first evidence linking TRPM2 with ischemic stroke was provided by Fonfria and collaborators, who showed increased TRPM2 mRNA expression and function after ischemic injury in the microglia of the transient middle cerebral artery occlusion (tMCAO) rat stroke model. They suggested that TRPM2 activation during ischemic brain injury may mediate key aspects of microglial pathophysiological responses (Fonfria et al., 2006). A similar result was also observed in neonatal mice, where genetic deletion of TRPM2 reduced brain injury and improved functional behavior after neonatal hypoxic-ischemic brain injury, suggesting TRPM2 inhibition as a promising therapeutic target for the ischemic brain injury (Huang et al., 2017). Intriguingly, the therapeutic benefit of TRPM2 inhibition in ischemic cell death appears sex-dependent (Yuan et al., 2009; Liu et al., 2011). Indeed, Jia and coworkers demonstrated that TRPM2-mediated ischemic cell death is male-specific and does not contribute to damage in female neurons or brain tissue. Using pharmacological and genetic detection of TRPM2, the authors demonstrated significant protection only for male neurons following in vitro ischemia (oxygen–glucose deprivation, OGD), while having no effect on female neurons (Jia et al., 2011). One explanation for this sex-dependent TRPM2 effect in stroke cell death may reside in a greater sensitivity to ADPR in males and/or activation of different signaling pathways in males versus females after ischemic injury (Lang and McCullough, 2008). Indeed, deletion of PARP, a potent signal for TRPM2 activation, has been shown to be neuroprotective in males and deleterious in females (McCullough et al., 2005), where stroke-mediated cell death involves caspase-dependent apoptosis (Renolleau et al., 2007; Liu et al., 2011).

​Mechanistically, TRPM2-mediated ischemic stroke has been associated with the expression and signalling of NMDARs (Ge et al., 2020; Xu et al., 2022). Among the numerous subunits, GluN2A and GluN2B are the most important types of NMDARs and have been shown to control signalling pathways leading to cell survival and death, respectively (Sun et al., 2018). Using an in vivo stroke model, Alim and coworkers demonstrated a shift in the GluN2A/GluN2B ratio toward the induction of GluN2A subunits and activation of the downstream prosurvival signalling pathways Akt and ERK1/2 in TRPM2 KO mice (Alim et al., 2013). A recent study further revealed that TRPM2 directly interacts with GluN2A to modulate its membrane expression (Boyce and Thompson, 2022; Zong et al., 2022b). The interaction between TRPM2 and GluN2A occurs via the unique EE3 motif at the N-terminus of TRPM2 and the KKR motifs at the C-terminus of GluN2A, requiring the recruitment of PKCγ to selectively increase NMDAR subunit activity and membrane expression (Zong et al., 2022b). Utilizing the TRPM2-derived interfering peptide TAT-EE3, the authors demonstrated that disruption of the TRPM2-NMDAR interaction effectively prevented phosphorylated CREB and ERK1/2 levels, inhibited neuronal excitotoxicity, and protected mice from ischemic stroke in vitro and in vivo (Zong et al., 2022b). This confirms the neuroprotective role of TRPM2 inhibition in stroke and suggests that peptide-based uncoupling of TRPM2-NMDAR association is a promising therapeutic strategy for ischemic stroke (Wu and Tymianski, 2018; Zong et al., 2022b). Overall, inhibition of TRPM2 could be an effective therapeutic target for the treatment of stroke in men.

Myocardial infarctions are caused by sudden blood obstruction, leading to cardiac ischemia, which results from a decreased oxygen and glucose supply (Heusch, 2016; Heusch, 2019). After the ischemic episode, effective blood flow is restored, and the ischemic tissue is reperfused. However, this process leads to a secondary effect called ischemia/reperfusion (I/R) injury, characterized by ROS and Ca²⁺ overload, excessive production of inflammatory cytokines, and ultimately cardiomyocyte cell death (Hausenloy et al., 2017; Wu et al., 2018). Given the role of TRPM2 in the ROS/Ca²⁺ system, many research groups investigated the role of TRPM2 in the pathophysiology of I/R injury (Zhan et al., 2016). Yang and coworkers provided the first evidence that TRPM2 channels are functionally present in the plasmalemma of myocytes and are involved in ROS-mediated cardiomyocyte death. They showed that increased ROS triggers PAPR-induced ADPR production, which subsequently activates TRPM2, leading to mitochondrial Ca²⁺/Na⁺ uptake and accumulation. This process disrupts mitochondrial permeability, causing cytochrome C release and caspase 3 activation, ultimately triggering apoptotic cell death (Yang et al., 2006). Similarly, TRPM2 has also been associated with TNF-ɑ-mediated cardiomyocyte death (Roberge et al., 2014), an important proinflammatory cytokine involved in I/R (Kleinbongard et al., 2011). The authors showed that TNF-ɑ activates PARP and TRPM2, resulting in a massive Ca²⁺ influx that likely leads to mitochondrial Ca²⁺ overload. This, in turn, results in increased mitochondrial ROS production, caspase 8 activation, and ultimately cardiomyocyte death (Roberge et al., 2014). Collectively, these findings emphasize the significance of PARP and TRPM2 in I/R-mediated cardiomyocyte apoptosis and propose TRPM2 as a promising approach to mitigate I/R-mediated cardiovascular damage. However, Miller’s group conducted a series of studies that meticulously demonstrated that TRPM2 may actually play a protective role in I/R-mediated cardiovascular damage (Miller et al., 2013; Miller et al., 2014; Hoffman et al., 2015). They employed a cardiac ischemia period followed by reperfusion in WT and TRPM2-KO mice. They discovered that TRPM2-KO mice exhibit altered expression of proteins involved in contractility (higher Na⁺-Ca²⁺ exchanger, decreased α1-subunit of Na⁺-K⁺-ATPase), ROS scavenging (lower SOC1/2 and increased NOX1), and mitochondrial bioenergetics and mitophagy (lower complexes I, III, and IV, and increased complexes II and V; lower MCU and BNIP3). Consequently, TRPM2-KO mice have reduced mitochondrial function, including lower oxygen consumption rate, decreased ATP production, and increased mitochondrial ROS production. Importantly, rescue experiments with ectopic TRPM2 injections in TRPM2-KO mice confirmed that only TRPM2-WT, and not TRPM2-E960D silent pore, can rescue and restore myocyte mitochondrial function, corroborating the protective role of TRPM2-mediated Ca²⁺ entry in cardiomyocyte survival after I/R. In summary, these results suggest that TRPM2-mediated Ca²⁺ influx into myocytes serves a dual protective function against I/R injury by maintaining mitochondrial function and energy production and by promoting antioxidant defense and reducing ROS production.

Numerous studies have established the critical role of ROS/Ca²⁺ signaling in the immune system, covering aspects from immune cell activation to suppression of immune responses (Vig and Kinet, 2009; Nathan and Cunningham-Bussel, 2013; Yang et al., 2013; Morris et al., 2022). TRPM2, positioned at the intersection of ROS and Ca²⁺ systems, has quickly emerged as a target for investigating immune physiology (Knowles et al., 2013; Syed Mortadza et al., 2015). Early evidence from Perraud’s group and others provide indicates that TRPM2 is functionally expressed in inflammatory cells, including monocytes, neutrophils, and phagocytes (Perraud et al., 2001; Sano et al., 2001; Heiner et al., 2003; Massullo et al., 2006). Yamamato and colleagues showed that silencing TRPM2 prevents the H₂O₂-induced Ca²⁺ influx and the downstream Ca²⁺-dependent tyrosine kinase Pyk2. This, in turn, leads to NF-KB nuclear translocation and CXCL8 chemo-cytokine production in human U937 cells. These observations were further confirmed in vivo using TRPM2 TRPM2-KO mice. Notably, TRPM2-KO monocytes exhibited reduced CXCL2 production and exacerbated dextran sulfate sodium (DSS)-induced ulcerative colitis. However, TRPM2 KO neutrophil maintained their functions, including migration and infiltration from bone marrow in response to chemokines, suggesting that the protective role of TRPM2 inhibition may be primarily attributed to a defect in monocyte cytokine production (Yamamoto et al., 2008).

Using the carrageenan-induced inflammatory pain model, Haraguchi and coworkers showed that TRPM2-mediated inflammation critically depends on macrophage and microglial CXCL2 production and subsequent neutrophil infiltration (Haraguchi et al., 2012). Interestingly, TRPM2 deficiency had no effect on the production of H₂O₂, TNF-α and CCL2 involved in inflammatory pain (Ren and Dubner, 2010), suggesting that TRPM2 inhibition specifically reduces the inflammatory response. Another study also reported the involvement of TRPM2-mediated Ca²⁺ influx in lipopolysaccharide (LPS)-induced production of numerous cytokines (IL-6, IL-8, IL-10, and TNF-α) in primary monocyte THP-1 cells (Wehrhahn et al., 2010). Similarly, Yonezawa and collaborators demonstrated that inhibiting TRPM2 reduces bleomycin (BLM)-induced lung inflammation through decreased polymorphonuclear leukocyte (PMN) recruitment and reduced secretion of inflammatory cytokines, including IL-1β, MIP-2, and TNF-α (Yonezawa et al., 2016). In support, Malik’s group demonstrated that TRPM2-mediated Ca²⁺ influx is required for VE-cadherin phosphorylation at Y73, a process necessary for the disassembly of adherens junctions and opening of the paracellular pathways, thereby allowing PMN adhesion and transmigration (Mittal et al., 2017). Indeed, when challenged with LPS injection, TRPM2-depleted mice exhibited reduced PMN accumulation, inflammation, and mortality, suggesting a protective role of TRPM2 inhibition (Mittal et al., 2017). Using the 8-Br-cADPR TRPM2 antagonist, Eraslan and colleagues also showed the therapeutic benefits of TRPM2 inhibition, as it prevented ischemic acute kidney inflammation through reduced production of TNF-α, IL-1β, and myeloperoxidase activity (Eraslan et al., 2019). Moreover, suppression of TRPM2 alleviated fibrosis accumulation and the associated inflammatory response in a unilateral urethral obstruction (UUO) mice model, primarily by reducing transforming growth factor (TGF)-β1-mediated JNK activation and decreasing NF-kB expression and downstream fibrotic genes, including α-smooth muscle actin (α-SMA), connective tissue growth factor (CTGF), fibronectin (FN), and Collagen 1alpha 1 (Col1α1) (Wang et al., 2019). In accordance, inhibition of TRPM2 protected Apoe−/− mice from high-fat diet (HFD)-induced atherosclerosis by suppressing of CD36 signaling and the activation of macrophage pro-inflammatory activity (Zong et al., 2022c), further consolidating the benefits of TRPM2 inhibition in mitigating severe inflammatory responses.

In striking contrast, other studies have associated the loss of TRPM2 with the aggravation of inflammatory responses. For instance, Di and collaborators showed exacerbated proinflammatory cytokine production of CXCL2, TNFα, and IL-6 in the lungs and poor survival of TRPM2-deficient mice compared to WT mice in response to endotoxin LPS (Nathan and Cunningham-Bussel, 2013). Mechanistically, the authors showed that LPS activates TRPM2-mediated Ca²⁺/Na⁺ influx, which depolarizes the plasma membrane to inhibit NADPH oxidase and ROS production, proposing a negative feedback mechanism in which TRPM2 activation buffers LPS-induced ROS and proinflammatory activity (Wu and Tymianski, 2018). In another study, the inhibition of TRPM2 was associated with LPS-induced inflammation, neutrophil migration, and neutrophil-mediated vascular injury through a mechanism independent of TRPM2 cation channel activity (Wang et al., 2016a). The authors showed that LPS-induced ROS in neutrophils negatively regulates neutrophil migration by oxidizing TRPM2 at Cys549 of its N-terminal region (Wang et al., 2016a), which triggers interaction and internalization of the chemoattractant receptor FPR1, a key regulator of the inflammatory environment (Dorward et al., 2015). This finding suggests that TRPM2 activation may serve as a strategy mitigate neutrophil-induced inflammatory injury (Wang et al., 2016a).

In addition to its contribution to innate immunity, TRPM2 has also been shown to play a crucial role in defense against infections. For example, Knowles and colleagues reported that TRPM2-depleted mice were more susceptible to infection with Listeria monocytogenes (LM) and exhibited lower production of the cytokines IL -12 and IFNγ compared with WT mice, suggesting a role for TRPM2 in combating LM infections (Knowles et al., 2011). Partida-Sanchez’s group further showed that the increased susceptibility of TRPM2-KO mice to LM-induced lethality was associated with enhanced neutrophil migration, accumulation, and inflammatory TNF-α, IL -6, and IL -10 production in the liver and spleen. Interestingly, the authors demonstrated that in vivo depletion of neutrophils in TRPM2 KO mice prevented LM -mediated systemic inflammation, confirming the benefit of TRPM2 activation in neutrophils for combating LM dissemination and preventing neutrophil-mediated tissue damage during Listeria infection (Robledo-Avila et al., 2020). Using H. pylori as an infection model, the same group showed that the loss of TRPM2 resulted in increased macrophage-mediated inflammatory gastritis and decreased H. pylori colonization compared to WT mice (Beceiro et al., 2017). In this context, the authors showed that H. pylori activates TRPM2-mediated Ca²⁺ influx, which in turn reduces NADPH oxidase-mediated ROS production and macrophage inflammatory activities. In TRPM2-depleted macrophages, H. pylori induces excessive Ca²⁺ overload and enhanced MAPK and NADPH oxidase activities, exacerbating macrophage production of inflammatory cytokines, suggesting that TRPM2 activation may represent a promising therapeutic strategy to control macrophage-mediated excessive inflammation and tissue damage in response to H. pylori (Beceiro et al., 2017). Similar enhanced inflammatory activity has also been observed in TRPM2 KO mice in response to other infection models, including lung infection triggered by P. aeruginosa (Di et al., 2017), sepsis triggered by E. coli (Zhang et al., 2017), or polymicrobial sepsis (Qian et al., 2014).

The role of TRPM2 in the immune system is indeed multifaceted, as it has been shown to exert both proinflammatory and anti-inflammatory functions. The discrepancies between various reports may be attributed to factors such as the genetic background of the animal models employed, the specific context of inflammation under study, and the different pathways and doses of endotoxin-mediated inflammation. Consequently, additional research is required to evaluate the therapeutic potential of manipulating TRPM2 more accurately is innate inflammation and infection. This further investigation will facilitate a deeper understanding of TRPM2’s role and inform the development of targeted therapies for a range of inflammatory and infectious conditions.

In addition to providing energy in the form of ATP, mitochondria produce ROS from various sources, including the electron transport chain (ETC), mainly complexes I and III (Murphy, 2009; Zorov et al., 2014). Among the many factors that contribute to mitochondrial function and ATP production, Ca²⁺ plays an essential role coordinating oxidative phosphorylation and activating the respiratory chain, leading to increased ATP production (Brookes et al., 2004). In cancer, mitochondrial function is further stimulated to increase ATP production, which is required for sustained cell proliferation and survival, thereby also increasing ROS production and the risk of cytotoxicity (Sabharwal and Schumacker, 2014). In response, cells enhance antioxidant proteins to detoxify themselves from elevated ROS and cytotoxicity. In this context, Miller’s group have demonstrated a delicate role for TRPM2-mediated Ca²⁺ entry in mitochondrial bioenergetics and redox balance (Miller, 2019). In neuroblastoma cells, Miller’s group showed that inhibition or silencing of TRPM2 decreased hypoxia-inducible factor-1/2 (HIF)-1/2 and its downstream mitochondrial membrane proteins involved in mitophagy (BNIP3), ROS-scavenging (SOD1/2), and ATP synthesis (ETC., complexes) (Chen et al., 2014; Bao et al., 2016). In addition, downregulation of TRPM2 was associated with inhibition of Pyk2 and the downstream MCU, reducing mitochondrial Ca²⁺ uptake and altering the mitochondrial membrane potential (Hirschler-Laszkiewicz et al., 2018). Loss of TRPM2-mediated altered mitochondrial membrane proteins was also linked to altered mitochondrial function, as it resulted in significant reductions in oxygen consumption rate (OCR) and OCR-mediated ATP production, thereby suppressing energy production and ultimately reducing tumor survival and progression in vitro and in vivo (Chen et al., 2014; Bao et al., 2016; Hirschler-Laszkiewicz et al., 2018). Importantly, in rescue experiments using WT TRPM2 but not the silent E960D TRPM2 mutant, mitochondrial function and tumor survival were restored in vitro and in vivo, suggesting a direct link between TRPM2-mediated Ca²⁺ influx, mitochondrial bioenergetics, and cancer progression (Bao et al., 2016; Hirschler-Laszkiewicz et al., 2018). Similar observations have been made in acute myeloid leukemia (AML) (Xu et al., 2022), gastric cancer (Almasi et al., 2018), and breast cancer (unpublished data, El Hiani’s laboratory). Taken together, these data indicate that TRPM2 promotes cancer progression by enhancing mitochondrial function and ATP production. To mitigate the potential ROS accumulation associated with increased ATP production, cancer cells upregulate their antioxidant system, a key process in which TRPM2 has been shown to play a pivotal role. Indeed, Miller’s group demonstrated a critical role for TRPM2-mediated Ca²⁺ influx in maintaining the activity of Nuclear factor (erythroid-derived 2)-Related Factor-2 (Nrf2) (Bao et al., 2019), a master transcription factor that regulates crucial genes important for antioxidant enzymes and cofactors necessary to reduce excessive ROS levels in tumor cells (Abdul-Aziz et al., 2015; Tonelli et al., 2018). In neuroblastoma, the authors showed that loss of TRPM2 reduced the expression of Nrf2 and expression of its regulatory proteins IQ motif containing GTPase activating protein 1 (IQGAP1) and Kelch-like ECH-associated protein 1 (Keap1), as well as the expression of Nrf2 downstream antioxidant proteins NADP⁺, NADPH, NAD⁺, NADH, and GSH, leading to ROS accumulation. Moreover, ectopic expression of WT -TRPM2, but not the pore-silent TRPM2 E960D mutant, in TRPM2-depleted neuroblastoma cells restored cell viability and reconstituted expression of the antioxidants NADP⁺, NADPH, NAD ⁺, NADH, and GSH, while reducing ROS production, demonstrating the critical role of TRPM2-mediated Ca²⁺ entry in Nrf2 activity and downstream antioxidant proteins (Bao et al., 2019).

Collectively, these studies have shown that TRPM2 supports cancer survival through a dual function: Elevated cancer ROS activates TRPM2-mediated Ca²⁺ influx to 1) directly couple with mitochondrial Ca²⁺ uptake and ATP production to promote cancer progression, and 2) potentiate the NFR2 and downstream antioxidant proteins NADPH and GSH to reduce ROS production. On the one hand, increased ROS production ensures the enhancement of TRPM2 activity and thus increased ATP production via a positive feedback mechanism; on the other hand, TRPM2-mediated Ca²⁺ entry triggers ROS-scavenging proteins that prevent ROS from reaching cell-damaging levels (Figure 2).

Another specific adaptive system that cancer cells use to withstand elevated ROS -mediated cell death is autophagy. Autophagy plays an important role in controlling ROS levels (by eliminating dysfunctional proteins, recycling damaged organelles) and even in the induction of drug resistance (by removing DNA damage and eliminating mutant cells), thereby providing a survival advantage for cancer cell progression (Kumar et al., 2015; Chang and Zou, 2020; Redza-Dutordoir and Averill-Bates, 2021). However, there is also growing evidence that sustained autophagy may act as a suppressor of tumor development through excessive elimination of essential proteins and organelles, and the induction of caspase-independent autophagic cell death (Eskelinen, 2011; Singh et al., 2018; Yun et al., 2020; Zhou et al., 2020). Mechanistically, autophagy can be activated under various stress conditions, including nutrient starvation and hypoxia, and involves divers signalling pathways, particularly mTOR (mechanistic target of rapamycin) and ULK1 (unc-51-like kinase) (Dikic and Elazar, 2018; Yu et al., 2018). Since Ca²⁺ and ROS have been implicated in autophagic signalling pathways (Bootman et al., 2018; Hasan et al., 2022), many groups have investigated the role of TRPM2 in the autophagy of different types of cancer.

In this context, Miller’s group was the first to report a key role of TRPM2 in the link between autophagy and tumor growth (Chen et al., 2014; Bao et al., 2016). In neuroblastoma, this group demonstrated that inhibition of TRPM2 triggers cell death and is associated with a decrease in HIF-1/2 and its downstream target BNIP3, leading to the accumulation of Hsp60 and Tom20 proteins, two key indicators of decreased autophagy and mitophagy (Chen et al., 2014). Genetic deletion of TRPM2 in these cells also led to a decrease in HIF-1/2 and BNIP3, confirming the role of TRPM2 in autophagy (Bao et al., 2016). In support, Almasi and coworkers showed that silencing TRPM2-mediated cell death was associated with decreased autophagy flux and autophagy markers (e.g., ATGs 3, 5, 7, and 12) through an mTOR-independent JNK-dependent mechanism (Almasi et al., 2018). In acute myeloid leukemia (AML), Chen and coworkers also show that cell death mediated by knocking down TRPM2 is associated with decreased autophagy through inhibition of the CREB and ATF4, which are important transcription factors for autophagosome biogenesis, leading to a decrease in ULK1 and autophagy markers (ATGs 5, 7, and 13) (Chen et al., 2020). In striking contrast, Tektemur and coworkers showed that silencing TRPM2 induces apoptotic genes along with key autophagic genes, including ATG5, BECN1, and ULK1/2, suggesting a correlation between TRPM2 inhibition and autophagy induction (Tektemur et al., 2019). Using the TRPM2 antagonists CLT or 8-Br-ADPR, Wang and coworkers also showed that oxidative stress-mediated death of HeLa cells is accompanied by a TRPM2-dependent Ca²⁺ influx that activates CAMK2 (Ca²⁺/calmodulin-dependent protein kinase II) and its downstream target BECN1/Beclin 1, which in turn binds BCL2 to inhibit autophagy, making the cells more prone to death (Wang et al., 2016b). Collectively, these findings indicates that TRPM2 plays a pivotal role in cancer survival through a dual role in autophagy, which varies depending on the specific type of cancer.

In addition to its role in cell survival, numerous studies have shown that autophagy is involved in the efficacy of various chemotherapeutic agents and the development of drug resistance. While the mechanisms underlying autophagy’s impact on the effectiveness of anticancer drugs are not fully understood, a potential explanation could reside in the link between autophagy and ROS. Indeed, chemotherapeutic agents act primarily by inducing ROS to kill cells (Yang et al., 2018; Perillo et al., 2020). However, as mentioned above, TRPM2-mediated NRF2 and autophagy decrease ROS levels and increase the ROS-induced damage threshold, thereby buffering the cytotoxicity of anticancer drugs. This reduction in the efficacy of chemotherapeutic agents contributes to drug resistance. Targeting the TRPM2 function could, therefore, represent a tipping point that can be exploited for improved cancer therapy (Table 1). Accordingly, numerous studies have shown that inhibition of TRPM2 increased the efficacy of anticancer drugs. In neuroblastoma, Miller’s group demonstrated that inhibition of TRPM2 increased the cytotoxicity of doxorubicin (Chen et al., 2014; Bao et al., 2016; Hirschler-Laszkiewicz et al., 2018; Bao et al., 2019; Hirschler-Laszkiewicz et al., 2022), a widely used anticancer drug in chemotherapy to treat various cancers (Minotti et al., 2004). A similar result was reported in myeloid leukemia, where knockdown of TRPM2 enhanced doxorubicin-mediated cell death (Chen et al., 2020). In breast cancer, inhibition of TRPM2 increased cell death after doxorubicin and tamoxifen (Koh et al., 2015), another commonly used chemotherapeutic agent in breast cancer therapy (Howell and Howell, 2023). In gastric cancer, inhibition of TRPM2 has been shown to increase the efficacy of doxorubicin and paclitaxel (Almasi et al., 2018), a widely used anticancer drug in cancer therapy (Mekhail and Markman, 2002). Overall, these studies suggest that inhibition of TRPM2 is a novel strategy to increase the efficacy of anticancer drugs and improve cancer therapy. However, other studies show the opposite, with the activation of TRPM2 increasing the efficacy of chemotherapeutic agents. Most of these studies were conducted by Naziroglu’s research group, showing that the activation of TRPM2 enhanced the anticancer drug-mediated ROS production and cell death in various types of cancers. For instance, curcumin-mediated TRPM2 activation enhanced ROS production and cell death in laryngeal squamous cancer cells (LSCC) after treatment with cisplatin (Gokce Kutuk et al., 2019), one of the most commonly used drugs for the treatment of squamous cell carcinoma (Pendleton and Grandis, 2013). Interestingly, paclitaxel-mediated ROS production and cell death in LSCC also involved TRPM2 activation (Kumbul and Naziroglu, 2022). In glioblastoma cells, the combination of paclitaxel with and resveratrol, a naturally occurring phytochemical that has been shown to sensitize multiple cell lines to numerous chemotherapeutic agents (Xiao et al., 2018), potentiated paclitaxel-mediated cytotoxicity and cell death through the activation of TRPM2 channel (Ozturk et al., 2019). The combination of cisplatin and Eicosapentaenoic acid, a component of omega-3 polyunsaturated fatty acids recently shown to influence the effects of many anticancer drugs (Ghoreishi et al., 2012; Bennouna et al., 2019), also enhanced cisplatin-mediated oxidant effects and cell death through TRPM2 activation in glioblastoma cells (Ocal and Naziroglu, 2022). Selenium-mediated TRPM2 activation also enhanced ROS production and cell death in glioblastoma cells after treatment with docetaxel (Ertilav et al., 2019), an important antineoplastic agent used in the management of multiple metastatic and non-resectable tumor types (Farha and Kasi, 2023). Similarly, honeybee venom melittin and silver nanoparticles enhanced cisplatin-mediated oxidant actions and cell death in glioblastoma cells through the activation of TRPM2 (Akyuva and Naziroglu, 2023; Ertilav and Naziroglu, 2023). Finally, the TRPM2 agonist cumene hydroperoxide (CMPx) increased the sensitivity of breast and colon cancer cells to 5-fluorouracil (5-FU) and leucovorin (LV), both individually and in combination (Guler and Ovey, 2018), both of which are widely used drugs in breast and digestive tract cancers (Machover, 1997; Sethy and Kundu, 2021). Collectively, these studies clearly suggest that activation of TRPM2 is a promising strategy to improve the efficacy of many anticancer drugs. However, the drugs used in these studies to activate and inhibit TRPM2 function are far from specific to TRPM2, and genetic knockdowns and/or overexpression are necessary to confirm this role of TRPM2 in pro-anticancer drug effects.