TRPM离子通道与人类疾病

TRPM蛋白家族是一类表达于多种哺乳动物细胞中广泛存在的离子通道。近年来发现它们在维持某些特定生理功能中起关 键作用且与人类疾病密切相关。研究显示氧化应激可使TRPM离子通道功能异常导致疾病发生、发展。TRPM亚家族的三个成 员,TRPM2,TRPM4 和TRPM7 均受氧化应激的调控,其功能改变、增加或缺失与炎症及免疫系统的激活、神经退行性疾病和神经 系统疾病、心血管疾病、癌症及糖尿病,代谢紊乱和骨疾病等疾病紧密联系。本文就近年来氧化应激调控的TRPM离子通道与人 类疾病的关系做简要综述。此外,文章也将探讨它们作为药物设计靶点和工具的应用前景。     

Oxidative stress-modulated TRPM ion channels in cell dysfunction and pathological conditions in humans

The transient receptor potential melastatin (TRPM) protein family is an extensive group of ion channels expressed in several types of mammalian cells. Many studies have shown that these channels are crucial for performing several physiological functions. Additionally, a large body of evidence indicates that these channels are also involved in numerous human diseases, known as channelopathies.A characteristic event frequently observed during pathological states is the raising in intracellular oxidative agents over reducing molecules, shifting the redox balance and inducing oxidative stress. In particular, three members of the TRPM subfamily, TRPM2, TRPM4 and TRPM7, share the remarkable feature that their activities are modulated by oxidative stress.Because of the increase in oxidative stress, these TRPM channels function aberrantly, promoting the onset and development of diseases.Increases, absences, or modifications in the function of these redox-modulated TRPM channels are associated with cell dysfunction and human pathologies. Therefore, the effect of oxidative stress on ion channels becomes an essential part of the pathogenic mechanism. Thus, oxidative stress-modulated ion channels are more susceptible to generating pathological states than oxidant-independent channels.This review examines the most relevant findings regarding the participation of the oxidative stress-modulated TRPM ion channels, TRPM2, TRPM4, and TRPM7, in human diseases. In addition, the potential roles of these channels as therapeutic tools and targets for drug design are discussed.     

TRPM7 and its role in neurodegenerative diseases

Calcium (Ca²⁺) and magnesium (Mg²⁺) ions have been shown to play an important role in regulating various neuronal functions. In the present review we focus on the emerging role of transient potential melastatin-7 (TRPM7) channel in not only regulating Ca²⁺ and Mg²⁺ homeostasis necessary for biological functions, but also how alterations in TRPM7 function/expression could induce neurodegeneration. Although eight TRPM channels have been identified, the channel properties, mode of activation, and physiological responses of various TRPM channels are quite distinct. Among the known 8 TRPM channels only TRPM6 and TRPM7 channels are highly permeable to both Ca²⁺ and Mg²⁺; however here we will only focus on TRPM7 as unlike TRPM6, TRPM7 channels are abundantly expressed in neuronal cells. Importantly, the discrepancy in TRPM7 channel function and expression leads to various neuronal diseases such as Alzheimer disease (AD) and Parkinson disease (PD). Further, it is emerging as a key factor in anoxic neuronal death and in other neurodegenerative disorders. Thus, by understanding the precise involvement of the TRPM7 channels in different neurodegenerative diseases and by understanding the factors that regulate TRPM7 channels, we could uncover new strategies in the future that could evolve as new drug therapeutic targets for effective treatment of these neurodegenerative diseases.     

TRPM7 and its role in neurodegenerative diseases

Calcium (Ca²⁺) and magnesium (Mg²⁺) ions have been shown to play an important role in regulating various neuronal functions. In the present review we focus on the emerging role of transient potential melastatin-7 (TRPM7) channel in not only regulating Ca²⁺ and Mg²⁺ homeostasis necessary for biological functions, but also how alterations in TRPM7 function/expression could induce neurodegeneration. Although eight TRPM channels have been identified, the channel properties, mode of activation, and physiological responses of various TRPM channels are quite distinct. Among the known 8 TRPM channels only TRPM6 and TRPM7 channels are highly permeable to both Ca²⁺ and Mg²⁺; however here we will only focus on TRPM7 as unlike TRPM6, TRPM7 channels are abundantly expressed in neuronal cells. Importantly, the discrepancy in TRPM7 channel function and expression leads to various neuronal diseases such as Alzheimer disease (AD) and Parkinson disease (PD). Further, it is emerging as a key factor in anoxic neuronal death and in other neurodegenerative disorders. Thus, by understanding the precise involvement of the TRPM7 channels in different neurodegenerative diseases and by understanding the factors that regulate TRPM7 channels, we could uncover new strategies in the future that could evolve as new drug therapeutic targets for effective treatment of these neurodegenerative diseases.     

TRPM channels, calcium and redox sensors during innate immune responses

Melastatin-related TRPM ion channels have emerged as novel therapeutic targets due to their potential ability to modulate the function and fate of immune cells during inflammation, innate, and adaptive immunity. Four family members, TRPM1, TRPM2, TRPM4 and TRPM7 have a strong presence in the immune system. TRPM channels regulate ion-homeostasis by sensing cellular redox status and cytoplasmic calcium levels. TRPM2 for example, is highly expressed in phagocytes. This channel is activated by intracellular ADP-ribose upon exposure to oxidative stress and induces cell death. Here we will review the functional links between TRPM-mediated ion conductance, chemotaxis, apoptosis, and innate immunity.     

TRPM7 and TRPM2-Candidate susceptibility genes for Western Pacific ALS and PD?

Recent findings implicating TRPM7 and TRPM2 in oxidative stress-induced neuronal death thrust these channels into the spotlight as possible therapeutic targets for neurodegenerative diseases. In this review, we describe how the functional properties of TRPM7 and TRPM2 are interconnected with calcium (Ca(2+)) and magnesium (Mg(2+)) homeostasis, oxidative stress, mitochondrial dysfunction, and immune mechanisms, all principal suspects in neurodegeneration. We focus our discussion on Western Pacific Amyotrophic Lateral Sclerosis (ALS) and Parkinsonism Dementia (PD) because extensive studies conducted over the years strongly suggest that these diseases are ideal candidates for a gene-environment model of etiology. The unique mineral environment identified in connection with Western Pacific ALS and PD, low Mg(2+) and Ca(2+), yet high in transition metals, creates a condition that could affect the proper function of these two channels.     

TRPM7 and TRPM2—Candidate susceptibility genes for Western Pacific ALS and PD?

Recent findings implicating TRPM7 and TRPM2 in oxidative stress-induced neuronal death thrust these channels into the spotlight as possible therapeutic targets for neurodegenerative diseases. In this review, we describe how the functional properties of TRPM7 and TRPM2 are interconnected with calcium (Ca²⁺) and magnesium (Mg²⁺) homeostasis, oxidative stress, mitochondrial dysfunction, and immune mechanisms, all principal suspects in neurodegeneration. We focus our discussion on Western Pacific Amyotrophic Lateral Sclerosis (ALS) and Parkinsonism Dementia (PD) because extensive studies conducted over the years strongly suggest that these diseases are ideal candidates for a gene-environment model of etiology. The unique mineral environment identified in connection with Western Pacific ALS and PD, low Mg²⁺ and Ca²⁺, yet high in transition metals, creates a condition that could affect the proper function of these two channels.     

A structural overview of the ion channels of the TRPM family

The TRPM (transient receptor potential melastatin) family belongs to the superfamily of TRP cation channels. The TRPM subfamily is composed of eight members that are involved in diverse biological functions such as temperature sensing, inflammation, insulin secretion, and redox sensing. Since the first cloning of TRPM1 in 1998, tremendous progress has been made uncovering the function, structure, and pharmacology of this family. Complete structures of TRPM2, TRPM4, and TRPM8, as well as a partial structure of TRPM7, have been determined by cryo-EM, providing insights into their channel assembly, ion permeation, gating mechanisms, and structural pharmacology. Here we summarize the current knowledge about channel structure, emphasizing general features and principles of the structure of TRPM channels discovered since 2017. We also discuss some of the key unresolved issues in the field, including the molecular mechanisms underlying voltage and temperature dependence, as well as the functions of the TRPM channels’ C-terminal domains.     

Transient receptor potential melastatin 6 and 7 channels, magnesium transport, and vascular biology: implications in hypertension

Magnesium, an essential intracellular cation, is critically involved in many biochemical reactions involved in the regulation of vascular tone and integrity. Decreased magnesium concentration has been implicated in altered vascular reactivity, endothelial dysfunction, vascular inflammation, and structural remodeling, processes important in vascular changes and target organ damage associated with hypertension. Until recently, very little was known about mechanisms regulating cellular magnesium homeostasis, and processes controlling transmembrane magnesium transport had been demonstrated only at the functional level. Two cation channels of the transient receptor potential melastatin (TRPM) cation channel family have now been identified as magnesium transporters, TRPM6 and TRPM7. These unique proteins, termed chanzymes because they possess a channel and a kinase domain, are differentially expressed, with TRPM6 being found primarily in epithelial cells and TRPM7 occurring ubiquitously. Vascular TRPM7 is modulated by vasoactive agents, pressure, stretch, and osmotic changes and may be a novel mechanotransducer. In addition to its magnesium transporter function, TRPM7 has been implicated as a signaling kinase involved in vascular smooth muscle cell growth, apoptosis, adhesion, contraction, cytoskeletal organization, and migration, important processes involved in vascular remodeling associated with hypertension and other vascular diseases. Emerging evidence suggests that vascular TRPM7 function may be altered in hypertension. This review discusses the importance of magnesium in vascular biology and implications in hypertension and highlights the transport systems, particularly TRPM6 and TRPM7, which may play a role in the control of vascular magnesium homeostasis. Since the recent identification and characterization of Mg2+-selective transporters, there has been enormous interest in the field. However, there is still a paucity of information, and much research is needed to clarify the exact mechanisms of magnesium regulation in the cardiovascular system and the implications of aberrant transmembrane magnesium transport in the pathogenesis of hypertension and other vascular diseases.     

Functional transient receptor potential melastatin 7 channels are critical for human mast cell survival

Mast cells play a significant role in the pathophysiology of many diverse diseases such as asthma and pulmonary fibrosis. Ca2+ influx is essential for mast cell degranulation and release of proinflammatory mediators, while Mg2+ plays an important role in cellular homeostasis. The channels supporting divalent cation influx in human mast cells have not been identified, but candidate channels include the transient receptor potential melastatin (TRPM) family. In this study, we have investigated TRPM7 expression and function in primary human lung mast cells (HLMCs) and in the human mast cell lines LAD2 and HMC-1, using RT-PCR, patch clamp electrophysiology, and RNA interference. Whole cell voltage-clamp recordings revealed a nonselective cation current that activated spontaneously following loss of intracellular Mg2+. The current had a nonlinear current-voltage relationship with the characteristic steep outward rectification associated with TRPM7 channels. Reducing external divalent concentration from 3 to 0.3 mM dramatically increased the size of the outward current, whereas the current was markedly inhibited by elevated intracellular Mg2+ (6 mM). Ion substitution experiments revealed cation selectivity and Ca2+ permeability. RT-PCR confirmed the presence of mRNA for TRPM7 in HLMC, LAD2, and HMC-1 cells. Adenoviral-mediated knockdown of TRPM7 in HLMC with short hairpin RNA and in HMC-1 with short interfering RNA markedly reduced TRPM7 currents and induced cell death, an effect that was not rescued by raising extracellular Mg2+. In summary, HLMC and human mast cell lines express the nonselective cation channel TRPM7 whose presence is essential for cell survival.     

瞬时受体电位M8离子通道功能及其翻译后修饰调节机制

瞬时受体电位M8(transient receptor potential melastatin 8, TRPM8)又称冷及薄荷醇感受器,位于细胞膜或细胞器膜上,是瞬时受体电位(transient receptor potential, TRP)通道超家族中的一员。TRPM8通道分布广泛,是一个非选择性阳离子通道,可作为冷热传感器和冷痛传感器进行信号传导,参与众多生物过程的调节,在维持细胞内外稳态、控制离子进出细胞方面具有重要作用。研究发现,蛋白质翻译后修饰(post-translational modification, PTM)通过调控TRPM8通道的功能,进而影响多种疾病的发生和发展。因此,探究TRPM8的翻译后修饰的过程,对深入了解TRPM8的功能及调控机制是十分必要的。目前,已报道的TRPM8翻译后修饰包括磷酸化、泛素化和糖基化等,它们能够调控蛋白质的相互作用和改变TRPM8离子通道的活性,从而调控细胞增殖、迁移和凋亡。值得注意的是,TRPM8的表达与前列腺癌、膀胱癌和乳腺癌等多种癌症密切相关。本文将从TRPM8离子通道的结构出发,系统地阐述TRPM8蛋白翻译后修饰和激动剂、...     

The oncogenic roles of TRPM ion channels in cancer

Transient receptor potential (TRP) proteins are a diverse family of ion channels present in multiple types of tissues. They function as gatekeepers for responses to sensory stimuli including temperature, vision, taste, and pain through their activities in conducting ion fluxes. The TRPM (melastatin) subfamily consists of eight members (i.e., TRPM1–8), which collectively regulate fluxes of various types of cations such as K⁺, Na⁺, Ca²⁺, and Mg²⁺. Growing evidence in the past two decades indicates that TRPM ion channels, their isoforms, or long noncoding RNAs encoded within the locus may be oncogenes involved in the regulation of cancer cell growth, proliferation, autophagy, invasion, and epithelial–mesenchymal transition, and their significant association with poor clinical outcomes of cancer patients. In this review, we describe and discuss recent findings implicating TRPM channels in different malignancies, their functions, mechanisms, and signaling pathways involved in cancers, as well as summarizing their normal physiological functions and the availability of ion channel pharmacological inhibitors.     

The super-cooling agent icilin reveals a mechanism of coincidence detection by a temperature-sensitive TRP channel

TRPM8, a member of the transient receptor potential family of ion channels, depolarizes somatosensory neurons in response to cold. TRPM8 is also activated by the cooling agents menthol and icilin. When exposed to menthol or cold, TRPM8 behaves like many ligand-gated channels, exhibiting rapid activation followed by moderate Ca(2+)-dependent adaptation. In contrast, icilin activates TRPM8 with extremely variable latency followed by extensive desensitization, provided that calcium is present. Here, we show that, to achieve full efficacy, icilin requires simultaneous elevation of cytosolic Ca2+, either via permeation through TRPM8 channels or by release from intracellular stores. Thus, two stimuli must be paired to elicit full channel activation, illustrating the potential for coincidence detection by TRP channels. Determinants of icilin sensitivity map to a region of TRPM8 that corresponds to the capsaicin binding site on the noxious heat receptor TRPV1, suggesting a conserved molecular logic for gating of these thermosensitive channels by chemical agonists.     

Alternative splicing switches the divalent cation selectivity of TRPM3 channels

TRPM3 is a poorly understood member of the large family of transient receptor potential (TRP) ion channels. Here we describe five novel splice variants of TRPM3, TRPM3alpha1-5. These variants are characterized by a previously unknown amino terminus of 61 residues. The differences between the five variants arise through splice events at three different sites. One of these splice sites might be located in the pore region of the channel as indicated by sequence alignment with other, better-characterized TRP channels. We selected two splice variants, TRPM3alpha1 and TRPM3alpha2, that differ only in this presumed pore region and analyzed their biophysical characteristics after heterologous expression in human embryonic kidney 293 cells. TRPM3alpha1 as well as TRPM3alpha2 induced a novel, outwardly rectifying cationic conductance that was tightly regulated by intracellular Mg(2+). However, these two variants are highly different in their ionic selectivity. Whereas TRPM3alpha1-encoded channels are poorly permeable for divalent cations, TRPM3alpha2-encoded channels are well permeated by Ca(2+) and Mg(2+). Additionally, we found that currents through TRPM3alpha2 are blocked by extracellular monovalent cations, whereas currents through TRPM3alpha1 are not. These differences unambiguously show that TRPM3 proteins constitute a pore-forming channel subunit and localize the position of the ion-conducting pore within the TRPM3 protein. Although the ionic selectivity of ion channels has traditionally been regarded as rather constant for a given channel-encoding gene, our results show that alternative splicing can be a mechanism to produce channels with very different selectivity profiles.     

The transmembrane segment S6 determines cation versus anion selectivity of TRPM2 and TRPM8

TRPM2 and TRPM8, closely related members of the transient receptor potential (TRP) family, are cation channels activated by quite different mechanisms. Their transmembrane segments S5 and S6 are highly conserved. To identify common structures in S5 and S6 that govern interaction with the pore, we created a chimera in which the S5-pore-S6 region of TRPM8 was inserted into TRPM2, along with a lysine at each transition site. Currents through this chimera were induced by ADP-ribose (ADPR) in cooperation with Ca(2+). In contrast to wild-type TRPM2 channels, currents through the chimera were carried by Cl(-), as demonstrated in ion substitution experiments using the cation N-methyl-D-glucamine (NMDG) and the anion glutamate. Extracellular NMDG had no effects. The substitution of either intracellular or extracellular Cl(-) with glutamate shifted the reversal potential, decreased the current amplitude and induced a voltage-dependent block relieved by depolarization. The lysine in S6 was responsible for the anion selectivity; insertion of a lysine into corresponding sites within S6 of either TRPM2 or TRPM8 created anion channels that were activated by ADPR (TRPM2 I1045K) or by cold temperatures (TRPM8 V976K). The positive charge of the lysine was decisive for the glutamate block because the mutant TRPM2 I1045H displayed cation currents that were blocked at acidic but not alkaline intracellular pH values. We conclude that the distal part of S6 is crucial for the discrimination of charge. Because of the high homology of S6 in the whole TRP family, this new role of S6 may apply to further TRP channels.     

Roles of TRPM2 in oxidative stress

Reactive oxygen species (ROS) play critical roles in cell death, diseases, and normal cellular processes. TRPM2 is a member of transient receptor potential (TRP) protein superfamily and forms a Ca²⁺-permeable nonselective cation channel activated by ROS, specifically by hydrogen peroxide (H₂O₂), and at least in part via second-messenger mechanisms. Accumulating evidence has indicated that TRPM2 mediates multiple cellular responses, after our finding that Ca²⁺ influx via TRPM2 regulates H₂O₂-induced cell death. Recently, we have demonstrated that Ca²⁺ influx through TRPM2 induces chemokine production in monocytes and macrophages, which aggravates inflammatory neutrophil infiltration in mice. However, understanding is still limited for in vivo physiological or pathophysiological significance of ROS-induced TRPM2 activation. In this review, we summarize mechanisms underlying activation of TRPM2 channels by oxidative stress and downstream biological responses, and discuss the biological importance of oxidative stress-activated TRP channels.     

On potential interactions between non-selective cation channel TRPM4 and sulfonylurea receptor SUR1

The sulfonylurea receptor SUR1 associates with Kir6.2 or Kir6.1 to form K(ATP) channels, which link metabolism to excitability in multiple cell types. The strong physical coupling of SUR1 with Kir6 subunits appears exclusive, but recent studies argue that SUR1 also modulates TRPM4, a member of the transient receptor potential family of non-selective cation channels. It has been reported that, following stroke, brain, or spinal cord injury, SUR1 is increased in neurovascular cells at the site of injury. This is accompanied by up-regulation of a non-selective cation conductance with TRPM4-like properties and apparently sensitive to sulfonylureas, leading to the postulation that post-traumatic non-selective cation currents are determined by TRPM4/SUR1 channels. To investigate the mechanistic hypothesis for the coupling between TRPM4 and SUR1, we performed electrophysiological and FRET studies in COSm6 cells expressing TRPM4 channels with or without SUR1. TRPM4-mediated currents were Ca(2+)-activated, voltage-dependent, underwent desensitization, and were inhibited by ATP but were insensitive to glibenclamide and tolbutamide. These properties were not affected by cotransfection with SUR1. When the same SUR1 was cotransfected with Kir6.2, functional K(ATP) channels were formed. In cells cotransfected with Kir6.2, SUR1, and TRPM4, we measured K(ATP)-mediated K(+) currents and Ca(2+)-activated, sulfonylurea-insensitive Na(+) currents in the same patch, further showing that SUR1 controls K(ATP) channel activity but not TRPM4 channels. FRET signal between fluorophore-tagged TRPM4 subunits was similar to that between Kir6.2 and SUR1, whereas there was no detectable FRET efficiency between TRPM4 and SUR1. Our data suggest that functional or structural association of TRPM4 and SUR1 is unlikely.