The TRPM family: key players and mechanisms in energy metabolism.

The transient receptor potential melastatin (TRPM) subfamily belongs to the TRP cation channels family. Since the first cloning of TRPM1 in 1989, tremendous progress has been made in identifying novel members of the TRPM subfamily and their functions. The TRPM subfamily is composed of eight members consisting of four six-transmembrane domain subunits, resulting in homomeric or heteromeric channels. From a structural point of view, based on the homology sequence of the coiled-coil in the C-terminus, the eight TRPM members are clustered into four groups: TRPM1/M3, M2/M8, M4/M5 and M6/M7. TRPM subfamily members have been involved in several physiological functions. However, they are also linked to diverse pathophysiological human processes. Alterations in the expression and function of TRPM subfamily ion channels might generate several human diseases including cardiovascular and neurodegenerative alterations, organ dysfunction, cancer and many other channelopathies. These effects position them as remarkable putative targets for novel diagnostic strategies, drug design and therapeutic approaches. Here, we review the current knowledge about the main characteristics of all members of the TRPM family, focusing on their actions in human diseases.

Background: Cold air is a major environmental factor that exacerbates bronchial asthma. Transient receptor potential melastatin family member 8 (TRPM8) receptor is a cold- and menthol-sensing cation channel expressed in sensory neurons as well as bronchial epithelial cells. Objectives: We sought to explore the role of TRPM8 receptor expressed in bronchial epithelial cells in airway inflammation. Methods: Human airway epithelial cell line, BEAS-2B, was treated with menthol, TRPM8 antagonist (BCTC, N-(4-tert-butylphenyl)-4-(3-chloropyridin-2-yl) piperazine-1-carboxamide) and dexamethasone in dose- and time- dependent manner. The mRNA of TRPM8 and proinflammatory cytokines such as IL-4, 6, 8, 13, 25, 33 was determined by real-time quantitative PCR. The expression of TRPM8 in bronchial epithelial cells was determined by western blotting and immunofluorescence. ELISA of TRPM8 performed using the induced sputum of asthmatics and normal controls. Results: TRPM8 protein expression was significantly increased in patients with asthma compared with healthy controls using ELISA of sputum supernatants. TRPM8 receptor was expressed primarily in bronchial epithelial cells at both mRNA and protein levels with statistical significances. Activating TRPM8 receptors by menthol was coupled with enhanced expression of the inflammatory cytokines of some IL and treatment with BCTC and dexamethasone attenuated the expression of the inflammatory cytokines. Conclusions: Activation of TRPM8 receptor of bronchial epithelial cells induces airway inflammatory cytokines, suggesting the TRPM8 receptor may involve in cold induced asthma exacerbations.

Plasma membrane protein channels provide a passageway for ions to access the intracellular milieu. Rapid entry of calcium ions into cells is controlled mostly by ion channels, while Ca2+-ATPases and Ca2+ exchangers ensure that cytosolic Ca2+ levels ([Ca2+]cyt) are maintained at low (~100 nM) concentrations. Some channels, such as the Ca2+-release-activated Ca2+ (CRAC) channels and voltage-dependent Ca2+ channels (CACNAs), are highly Ca2+-selective, while others, including the Transient Receptor Potential Melastatin (TRPM) family, have broader selectivity and are mostly permeable to monovalent and divalent cations. Activation of CRAC channels involves the coupling between ORAI1-3 channels with the endoplasmic reticulum (ER) located Ca2+ store sensor, Stromal Interaction Molecules 1-2 (STIM1/2), a pathway also termed store-operated Ca2+ entry (SOCE). The TRPM family is formed by 8 members (TRPM1-8) permeable to Mg2+, Ca2+, Zn2+ and Na+ cations, and is activated by multiple stimuli. Recent studies indicated that SOCE and TRPM structure-function are interlinked in some instances, although the molecular details of this interaction are only emerging. Here we review the role of TRPM and SOCE in Ca2+ handling and highlight the available evidence for this interaction.

Transient receptor potential melastatin 7 (TRPM7) cation channel is a unique protein that has the dual ability to act as a channel to regulate transmembrane Mg 2+ transport and also as a kinase to promote cellular signaling. Despite increasing awareness of the importance of Mg 2+ in cardiovascular biology nothing is known about TRPM7 and its kinase domain in the pathophysiology of hypertension. We previously demonstrated that Ang II regulates TRPM7 in vitro . Here we studied TRPM7 kinase-deficient mice to explore the role of the TRPM7 kinase domain in Ang II-induced hypertension. TRPM7 kinase deficient mice (TRPM7 +/- ) and wild type (WT) counterparts were infused with Ang II (400 ng/kg/min; minipumps) for 4 weeks. Blood pressure (BP) was measured by tail cuff. Vascular reactivity and structure studies were performed by myography in mesenteric arteries. Although baseline BP tended to be higher in TRPM7 +/- versus WT mice (127 ± 6.0 vs 119 ± 2.2 mmHg), significance was not achieved. TRPM7 +/- mice displayed earlier onset of BP increase by Ang II (2 weeks; WT-Ang II: 145 ± 5 vs TRPM7 +/- Ang II: 178 ± 9; mmHg). After 4 weeks, BP was significantly higher in TRPM7 +/- (174 ± 10 mmHg) than in WT mice (147 ± 8 mmHg). Ang II-induced hypertension was associated with cardiac hypertrophy, an effect that was exaggerated in TRPM7 +/- mice (WT: 4.4 ± 0.1; WT-Ang II: 5.0 ± 0.2; TRPM7 +/- : 4.5 ± 0.1; TRPM7 +/- Ang II: 5.7 ± 0.1 g/body weight). Mesenteric arteries from Ang II-infused TRPM7 +/- mice exhibited decreased sensitivity to acetylcholine (pD2; WT-Ang II: 7.6 ± 0.3 vs. TRPM7 +/- Ang II: 6.7 ± 0.4), and reduced maximal relaxation compared to WT mice (WT-Ang II: 88 ± 8% vs TRPM7 +/- Ang II: 59 ± 10%). Ang II induced a leftward shift in the stress-strain relationship for both WT and TRPM7 +/- mice in a similar fashion. Plasma analysis revealed that TRPM7 +/- mice were hypomagnesemic, and that Ang II increased Mg 2+ levels to a greater extent in WT than in TRPM7 +/- mice (WT: 0.65 ± 0.02; WT-Ang II: 0.74 ± 0.04; TRPM7 +/- : 0.60 ± 0.01; TRPM7 +/- Ang II: 0.64 ± 0.02; mmol/L). In conclusion, our findings demonstrate that hypertension, cardiac hypertrophy and endothelial dysfunction are exaggerated by Ang II in TRPM7 +/- hypomagnesemic mice, suggesting a novel role for TRPM7 kinase domain in cardiovascular pathophysiology.

A structural overview of the ion channels of the TRPM family

Transient receptor potential melastatin-2 (TRPM2) is a plasma membrane cation channel with important physiologic roles in noncancerous cells. However, in MCF-7 and MDA-MB-231 human breast adenocarcinoma cells, we previously demonstrated that TRPM2 was present in the nucleus, and pharmacologic inhibition or RNAi silencing of TRPM2 led to decreased proliferation. In this study, we evaluated the ability of TRPM2 inhibition to produce cell death in normal breast epithelial cells and breast adenocarcinoma cells. Further, we analyzed the cell death pathways induced. Treatment with the DNA alkylating agent, N-methyl-N’-nitro-N-nitrosoguanidine (MNNG), or doxorubicin (Dox) led to increased levels of cell death in MDA-MB-231 breast adenocarcinoma cells pretreated with TRPM2 inhibitors, but not in noncancerous mammary epithelial cells after pretreatment. Similar increases in cell death were observed after RNAi silencing of TRPM2 in both MDA-MB-231 and MCF-7 breast adenocarcinoma cells after Dox or tamoxifen treatment, respectively. Investigation of apoptosis after TRPM2 inhibition demonstrated decreased levels of caspase activity and no significant effect of Q-VD-OPh, a pan-caspase inhibitor, on cell death induced by TRPM2 inhibition. Further, pretreatment with 3-methyl adenine, an inhibitor of autophagy, also produced no significant effect on cell death induced by TRPM2 inhibition. These studies indicate that apoptosis or autophagy are not the primary cell death pathways induced by TRPM2 inhibition in breast cancer cells. Also, RNAi silencing of poly(ADP-ribose) glycohydrolase (PARG) and apoptosis-inducing factor (AIF), two proteins involved in initiating or facilitating alternative pathways of cell death, produced minimal changes in cell death induced by TRPM2 inhibition. Taken together, this study demonstrated that TRPM2 inhibition selectively increases cell death in breast adenocarcinoma cells. Further, the data suggests that apoptosis, autophagy, and PARG/AIF-mediated cell death are not the primarily cell death pathways involved in the cytotoxicity caused by TRPM2 inhibition. The results therefore suggest that TRPM2 is a potential target in breast cancer, where its inhibition may cause the selective eradication of breast adenocarcinoma cells. Citation Format: David W. Koh, Daniel P. Powell, Steven D. Blake, Joy L. Hoffman, Xiaoxing Feng. Selective induction of breast adenocarcinoma cell death via inhibition of the transient receptor potential melastatin-2 (TRPM2) cation channel. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1717. doi:10.1158/1538-7445.AM2015-1717

Objective: Transient receptor potential (TRP) melastatin 7 (TRPM7) cation channel, a dual-function ion channel/protein kinase, regulates vascular smooth muscle cell (VSMC) Mg2+ homeostasis and mitogenic signaling. Mechanisms regulating vascular growth effects of TRPM7 are unclear, but epidermal growth factor (EGF) may be important because it is a magnesiotropic hormone involved in cellular Mg2+ regulation and VSMC proliferation. Here we sought to determine whether TRPM7 is a downstream target of EGF in VSMCs and if EGF receptor (EGFR) through TRPM7 influences VSMC function.Approach and results: Studies were performed in primary culture VSMCs from rats and humans and vascular tissue from mice deficient in TRPM7 (TRPM7+/Δkinase and TRPM7R/R). EGF increased expression and phosphorylation of TRPM7 and stimulated Mg2+ influx in VSMCs, responses that were attenuated by gefitinib (EGFR inhibitor) and NS8593 (TRPM7 inhibitor). Co-immunoprecipitation (IP) studies, proximity ligation assay (PLA) and live-cell imaging demonstrated interaction of EGFR and TRPM7, which was enhanced by EGF. PP2 (c-Src inhibitor) decreased EGF-induced TRPM7 activation and prevented EGFR–TRPM7 association. EGF-stimulated migration and proliferation of VSMCs were inhibited by gefitinib, PP2, NS8593 and PD98059 (ERK1/2 inhibitor). Phosphorylation of EGFR and ERK1/2 was reduced in VSMCs from TRPM7+/Δkinase mice, which exhibited reduced aortic wall thickness and decreased expression of PCNA and Notch 3, findings recapitulated in TRPM7R/R mice.Conclusions: We show that EGFR directly interacts with TRPM7 through c-Src-dependent processes. Functionally these phenomena regulate [Mg2+]i homeostasis, ERK1/2 signaling and VSMC function. Our findings define a novel signaling cascade linking EGF/EGFR and TRPM7, important in vascular homeostasis.

Millions of new cases of cancer are diagnosed worldwide each year, making it a serious public health concern. Developments in customized therapy and early detection have significantly enhanced treatment for and results from cancer. Therefore, it is important to investigate new molecular biomarkers. In this study, we created an efficient transient receptor potential melastatin (TRPM) family members-related TRPM-Score for 17 solid tumors. CCNE1, produced from TRPM-Score, was found to be an exceptional biomarker through several sophisticated machine learning and deep learning computational techniques. TRPM-Score and CCNE1 immunotherapeutic prediction, immunological characteristics, and predictive value were thoroughly assessed. In most cancer types, CCNE1 was a substantially dangerous marker. Additional in vitro tests validated CCNE1’s immunomodulatory properties, demonstrating that silencing impeded macrophage movement and decreased PD-L1 expression. Additionally, CCNE1 may accurately predict responses to cancer immunotherapy. These findings indicate that the TRPM family—particularly CCNE1, which is associated with TRPM—is a significant player in the pan-cancer domain and can be utilized as a therapeutic target and prognostic biomarkers, especially in immuno-oncology. The thorough characterization of the TRPM family and the discovery of CCNE1 as a crucial downstream effector mark important developments in our comprehension of pan-cancer biology.

The cation channel transient receptor potential melastatin 4 (TRPM4) is a calcium-activated non-selective cation channel and acts in cardiomyocytes as a negative modulator of the L-type Ca2+ influx. Global deletion of TRPM4 in the mouse led to increased cardiac contractility under β-adrenergic stimulation. Consequently, cardiomyocyte-specific inactivation of the TRPM4 function appears to be a promising strategy to improve cardiac contractility in heart failure patients. The aim of this study was to develop a gene therapy approach in mice that specifically silences the expression of TRPM4 in cardiomyocytes. First, short hairpin RNAmiR30 (shRNAmiR30) sequences against the TRPM4 mRNA were screened in vitro using lentiviral transduction for a stable expression of the shRNA cassettes. Western blot analysis identified three efficient shRNAmiR30 sequences out of six, which reduced the endogenous TRPM4 protein level by up to 90 ± 6%. Subsequently, the most efficient shRNAmiR30 sequences were delivered into cardiomyocytes of adult mice using adeno-associated virus serotype 9 (AAV9)-mediated gene transfer. Initially, the AAV9 vector particles were administered via the lateral tail vein, which resulted in a downregulation of TRPM4 by 46 ± 2%. Next, various optimization steps were carried out to improve knockdown efficiency in vivo. First, the design of the expression cassette was streamlined for integration in a self-complementary AAV vector backbone for a faster expression. Compared to the application via the lateral tail vein, intravenous application via the retro-orbital sinus has the advantage that the vector solution reaches the heart directly and in a high concentration, and eventually a TRPM4 knockdown efficiency of 90 ± 7% in the heart was accomplished by this approach. By optimization of the shRNAmiR30 constructs and expression cassette as well as the route of AAV9 vector application, a 90% reduction of TRPM4 expression was achieved in the adult mouse heart. In the future, AAV9-RNAi-mediated inactivation of TRPM4 could be a promising strategy to increase cardiac contractility in preclinical animal models of acute and chronic forms of cardiac contractile failure.

Radiation-induced aortic valve deleterious remodeling may occur years after radiotherapy. The transient receptor potential melastatin 4 (TRPM4) cation channel participates in aortic valve radiation-induced remodeling in mice in vivo. Valvular interstitial cells (VICs) are involved in valve leaflet thickening and calcification leading to aortic stenosis. TRPM4 favors their remodeling toward an osteogenic phenotype in vitro. Here, we evaluated whether radiation-induced remodeling involves TRPM4 in human valvular interstitial cells (hVICs). VICs were isolated from aortic valves and maintained in procalcifying media supplemented or not with 9-phenanthrol (a TRPM4 inhibitor) or small hairpin RNA (shRNA)-TRPM4. Cells were irradiated at 0 Gy or 8 Gy. Ten days after irradiation, cell surface, viability, cycle, and proliferation were measured. Senescence was evaluated by β-galactosidase activity measurements. Osteogenic markers [bone morphogenetic protein 2 (BMP2), runt-related transcription factor 2 (Runx2), and alkaline phosphatase (ALP)] and TRPM4 mRNA levels were quantified by quantitative polymerase chain reaction (qPCR). VIC surface increased after radiation, whereas cell density decreased. Radiation had no effect on viability but induced an increase in the proportion of cells in G0 cell cycle phase. An increase of cell senescence was observed after irradiation. Finally, irradiation induced an increase of TRPM4, BMP2, Runx2, and ALP mRNA. All these effects were partly prevented by 9-phenanthrol or shRNA-TRPM4. Interestingly, VIC density on aortic valve leaflets from mice submitted to X-ray treatment in vivo was decreased in treated animals compared with untreated ones, and this was not observed in animals with disruption of the Trpm4 gene. TRPM4 participates in radiation-induced hVICs remodeling by promoting cell senescence and osteogenic transition. TRPM4 may, thus, be evaluated as a therapeutic target to diminish valvular effects of radiotherapy.NEW & NOTEWORTHY The paper demonstrates, by pharmacological and molecular approaches, that the TRPM4 cation channel is involved in radiation-induced osteogenic remodeling of human valvular interstitial cells in culture. Osteogenic remodeling and cell senescence are prevented by TRPM4 inhibition. Since interstitial cells participate in aortic valve remodeling leading to aortic stenosis such as observed in some patients treated for cancer with radiotherapy, TRPM4 inhibition might be evaluated as an interesting new target to avoid this deleterious side effect.

The transient receptor potential melastatin 4 (TRPM4) is a Ca2+-activated nonselective monovalent cation channel belonging to the TRP channel superfamily. TRPM4 is widely expressed in various tissues and most abundantly expressed in the heart. TRPM4 plays a critical role in cardiac conduction. Patients carrying a gain-of-function or loss-of-function mutation of TRPM4 display impaired cardiac conduction. Knockout or over-expression of TRPM4 in mice recapitulates conduction defects in patients. Moreover, recent studies have indicated that TRPM4 plays a role in hypertrophy and heart failure. Whereas the role of TRPM4 mediated by cardiac myocytes has been well investigated, little is known about TRPM4 and its role in cardiac fibroblasts. Here we show that in human left ventricular fibroblasts, TRPM4 exhibits typical Ca2+-activation characteristics, linear current-voltage (I-V) relation, and monovalent permeability. TRPM4 currents recorded in fibroblasts from heart failure patients (HF) are more than 2-fold bigger than those from control individuals (CTL). The enhanced functional TRPM4 in HF is not resulted from changed channel properties, as TRPM4 currents from both HF and CTL fibroblasts demonstrate similar sensitivity to intracellular calcium activation and extracellular 9-phenanthrol (9-phen) blockade. Consistent with enhanced TRPM4 activity, the protein level of TRPM4 is about 2-fold higher in HF than that of CTL hearts. Moreover, TRPM4 current in CTL fibroblasts is increased after 24 hours of TGFβ1 treatment, implying that TRPM4 in vivo may be upregulated by fibrogenesis promotor TGFβ1. The upregulated TRPM4 in HF fibroblasts suggests that TRPM4 may play a role in cardiac fibrogenesis under various pathological conditions.

The transient receptor potential melastatin-2 (TRPM2) cation channel was previously identified as a potential target in various cancers, where its pharmacologic inhibition caused increased DNA damage and the selective eradication of cancer cells. In this study, we utilized several human primary metastatic melanoma cell lines, in which we analyzed TRPM2 and its isoforms, and evaluated the ability of TRPM2 inhibition to modulate cell death. As TRPM2 is known to exist as a plasma membrane cation channel in noncancerous cells, we investigated the localization of TRPM2 in melanoma cells. In three lines of primary human metastatic melanoma cells, TRPM2 was localized in the nucleus, as compared to an extra-nuclear localization in noncancerous primary epidermal keratinocyes. Because TRPM2 exists in several isoforms in cancer cells, we investigated the cellular localization of these isoforms. Subcellular fractionations demonstrated that only full-length TRPM2 was localized to the nucleus in primary human metastatic melanoma cells, whereas two smaller isoforms were localized exclusively in the cytoplasmic fraction. Treatment with the TRPM2 inhibitor, clotrimazole, caused decreased proliferation in all three lines of primary human metastatic melanoma cells. Further, treatment with the DNA alkylating agent, temozolomide (TMZ), led to increased levels of cell death in melanoma cells pretreated with clotrimazole, but not in noncancerous primary epidermal keratinocyes after pretreatment. Similar increases in cell death were observed after RNAi silencing of TRPM2 followed by TMZ treatment. Taken together, this study demonstrated that TRPM2 inhibition selectively increases cell death in primary human metastatic melanoma cells. Further, the data suggests that, similar to our previous results in breast adenocarcinoma cells, full-length TRPM2 appears to have a novel role in melanoma cell growth and survival. The results therefore suggest that TRPM2 is a potential target in melanoma, where its inhibition may cause the selective eradication of metastatic melanoma. Citation Format: David W. Koh, Steven D. Blake, Daniel P. Powell. Enhanced cytotoxicity in primary human metastatic melanoma cells via inhibition of the transient receptor potential melastatin-2 (TRPM2) channel. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1269.

Transient receptor potential melastatin 3 (TRPM3) is a nonselective cation channel that is inhibited by Gβγ subunits liberated following activation of Gαi/o protein-coupled receptors. Here, we demonstrate that TRPM3 channels are also inhibited by Gβγ released from Gαs and Gαq Activation of the Gs-coupled adenosine 2B receptor and the Gq-coupled muscarinic acetylcholine M1 receptor inhibited the activity of TRPM3 heterologously expressed in HEK293 cells. This inhibition was prevented when the Gβγ sink βARK1-ct (C terminus of β-adrenergic receptor kinase-1) was coexpressed with TRPM3. In neurons isolated from mouse dorsal root ganglion (DRG), native TRPM3 channels were inhibited by activating Gs-coupled prostaglandin-EP2 and Gq-coupled bradykinin B2 (BK2) receptors. The Gi/o inhibitor pertussis toxin and inhibitors of PKA and PKC had no effect on EP2- and BK2-mediated inhibition of TRPM3, demonstrating that the receptors did not act through Gαi/o or through the major protein kinases activated downstream of G-protein-coupled receptor (GPCR) activation. When DRG neurons were dialyzed with GRK2i, which sequesters free Gβγ protein, TRPM3 inhibition by EP2 and BK2 was significantly reduced. Intraplantar injections of EP2 or BK2 agonists inhibited both the nocifensive response evoked by TRPM3 agonists, and the heat hypersensitivity produced by Freund's Complete Adjuvant (FCA). Furthermore, FCA-induced heat hypersensitivity was completely reversed by the selective TRPM3 antagonist ononetin in WT mice and did not develop in Trpm3-/- mice. Our results demonstrate that TRPM3 is subject to promiscuous inhibition by Gβγ protein in heterologous expression systems, primary neurons and in vivo, and suggest a critical role for this ion channel in inflammatory heat hypersensitivity.SIGNIFICANCE STATEMENT The ion channel TRPM3 is widely expressed in the nervous system. Recent studies showed that Gαi/o-coupled GPCRs inhibit TRPM3 through a direct interaction between Gβγ subunits and TRPM3. Since Gβγ proteins can be liberated from other Gα subunits than Gαi/o, we examined whether activation of Gs- and Gq-coupled receptors also influence TRPM3 via Gβγ. Our results demonstrate that activation of Gs- and Gq-coupled GPCRs in recombinant cells and sensory neurons inhibits TRPM3 via Gβγ liberation. We also demonstrated that Gs- and Gq-coupled receptors inhibit TRPM3 in vivo, thereby reducing pain produced by activation of TRPM3, and inflammatory heat hypersensitivity. Our results identify Gβγ inhibition of TRPM3 as an effector mechanism shared by the major Gα subunits.

The calcium-permeable cation channel TRPM8 (transient receptor potential melastatin 8) is a member of the TRP superfamily of cation channels that is upregulated in various types of cancer with high levels of autophagy, including prostate, pancreatic, breast, lung, and colon cancers. Autophagy is closely regulated by AMP-activated protein kinase (AMPK) and plays an important role in tumor growth by generating nutrients through degradation of intracellular structures. Additionally, AMPK activity is regulated by intracellular Ca2+ concentration. Considering that TRPM8 is a non-selective Ca2+-permeable cation channel and plays a key role in calcium homoeostasis, we hypothesized that TRPM8 may control AMPK activity thus modulating cellular autophagy to regulate the proliferation and migration of breast cancer cells. In this study, overexpression of TRPM8 enhanced the level of basal autophagy, whereas TRPM8 knockdown reduced the level of basal autophagy in several types of mammalian cancer cells. Moreover, the activity of the TRPM8 channel modulated the level of basal autophagy. The mechanism of regulation of autophagy by TRPM8 involves autophagy-associated signaling pathways for activation of AMPK and ULK1 and phagophore formation. Impaired AMPK abolished TRPM8-dependent regulation of autophagy. TRPM8 interacts with AMPK in a protein complex, and cytoplasmic C-terminus of TRPM8 mediates the TRPM8–AMPK interaction. Finally, basal autophagy mediates the regulatory effects of TRPM8 on the proliferation and migration of breast cancer cells. Thus, this study identifies TRPM8 as a novel regulator of basal autophagy in cancer cells acting by interacting with AMPK, which in turn activates AMPK to activate ULK1 in a coordinated cascade of TRPM8-mediated breast cancer progression.

Transient receptor potential melastatin 4 (TRPM4) cation channels act in cardiomyocytes as a negative modulator of the L-type Ca2+ current. Ubiquitous Trpm4 deletion in mice leads to an increased β-adrenergic inotropy in healthy mice as well as after myocardial infarction. In this study, we set out to investigate cardiac inotropy in mice with cardiomyocyte-specific Trpm4 deletion. The results guided us to investigate the relevance of TRPM4 for catecholamine-evoked Ca2+ signaling in cardiomyocytes and inotropy in vivo in TRPM4-deficient mouse models of different genetic background. Cardiac hemodynamics were investigated using pressure–volume analysis. Surprisingly, an increased β-adrenergic inotropy was observed in global TRPM4-deficient mice on a 129SvJ genetic background, but the inotropic response was unaltered in mice with global and cardiomyocyte-specific TRPM4 deletion on the C57Bl/6N background. We found that the expression of TRPM4 proteins is about 78 ± 10% higher in wild-type mice on the 129SvJ versus C57Bl/6N background. In accordance with contractility measurements, our analysis of the intracellular Ca2+ transients revealed an increase in ISO-evoked Ca2+ rise in Trpm4-deficient cardiomyocytes of the 129SvJ strain, but not of the C57Bl/6N strain. No significant differences were observed between the two mouse strains in the expression of other regulators of cardiomyocyte Ca2+ homeostasis. We conclude that the relevance of TRPM4 for cardiac contractility depends on homeostatic TRPM4 expression levels or the genetic endowment in different mouse strains as well as on the health/disease status. Therefore, the concept of inhibiting TRPM4 channels to improve cardiac contractility needs to be carefully explored in specific strains and species and prospectively in different genetically diverse populations of patients.