TRPM2 channel membrane currents in primary rat megakaryocytes were activated by the agonist ADP-ribose but not oxidative stress

Angiotensin type 1 receptor activation promotes neuronal and glial alpha-synuclein aggregation and transmission

The brain renin-angiotensin system (RAS) has been related to dopaminergic degeneration, and high expression of the angiotensin II (AngII) type 1 receptor (AT1) gene is a marker of the most vulnerable neurons in humans. However, it is unknown whether AngII/AT1 overactivation affects α-synuclein aggregation and transmission. In vitro, AngII/AT1 activation increased α-synuclein aggregation in dopaminergic neurons and microglial cells, which was related to AngII-induced NADPH-oxidase activation and intracellular calcium raising. In mice, AngII/AT1 activation was involved in MPTP-induced increase in α-synuclein expression and aggregation, as they significantly decreased in mice treated with the AT1 blocker telmisartan and AT1 knockout mice. Cell co-cultures (transwells) revealed strong transmission of α-synuclein from dopaminergic neurons to astrocytes and microglia. AngII induced a higher α-synuclein uptake by microglial cells and an increase in the transfer of α-synuclein among astroglial cells. However, AngII did not increase the release of α-synuclein by neurons. The results further support brain RAS dysregulation as a major mechanism for the progression of Parkinson's disease, and AT1 inhibition and RAS modulation as therapeutic targets.

Low molecular weight heparin treatment reduced apoptosis and oxidative cytotoxicity in the thrombocytes of patients with recurrent pregnancy loss and thrombophilia: Involvements of TRPM2 and TRPV1 channels

AIM

Recurrent pregnancy loss (RPL) is known to be associated with increased thrombophilia and oxidative toxicity. However, the mechanism of thrombophilia apoptosis and oxidative toxicity is still unclear. In addition, the treatment of heparin induced regulator roles on intracellular free Ca²⁺ ([Ca²⁺ ]_i ) and cytosolic reactive oxygen species (cytROS) concentrations in several diseases. TRPM2 and TRPV1 channels are activated by different stimuli, including oxidative toxicity. The aim of this study was to investigate the effects of low molecular weight heparin (LMWH) via modulation of TRPM2 and TRPV1 on calcium signaling, oxidative toxicity, and apoptosis in the thrombocytes of RPL patients.

STUDY DESIGN

Thrombocyte and plasma samples collected from 10 patients with RPL and 10 healthy controls were used in the current study.

MAIN FINDINGS

The [Ca²⁺ ]_i concentration, cytROS (DCFH-DA), mitochondrial membrane potential (JC-1), apoptosis, caspase-3, and caspase-9 levels were high in the plasma and thrombocytes of RPL patients, although they were diminished by the treatments of LMWH, TRPM2 (N-(p-amylcinnamoyl)anthranilic acid) and TRPV1 (capsazepine) channel blockers.

CONCLUSIONS

The current study results suggest that the treatment of LMWH is useful against apoptotic cell death and oxidative toxicity in the thrombocytes of patients with RPL, which seem to be dependent on increased levels of [Ca²⁺ ]_i concentration via the activation of TRPM2 and TRPV1.

TRP channel function in platelets and megakaryocytes: basic mechanisms and pathophysiological impact

Transient receptor potential (TRP) proteins form a superfamily of cation channels that are expressed in a wide range of tissues and cell types. During the last years, great progress has been made in understanding the molecular complexity and the functions of TRP channels in diverse cellular processes, including cell proliferation, migration, adhesion and activation. The diversity of functions depends on multiple regulatory mechanisms by which TRP channels regulate Ca²⁺ entry mechanisms and intracellular Ca²⁺ dynamics, either through membrane depolarization involving cation influx or store- and receptor-operated mechanisms. Abnormal function or expression of TRP channels results in vascular pathologies, including hypertension, ischemic stroke and inflammatory disorders through effects on vascular cells, including the components of blood vessels and platelets. Moreover, some TRP family members also regulate megakaryopoiesis and platelet production, indicating a complex role of TRP channels in pathophysiological conditions. In this review, we describe potential roles of TRP channels in megakaryocytes and platelets, as well as their contribution to diseases such as thrombocytopenia, thrombosis and stroke. We also critically discuss the potential of TRP channels as possible targets for disease prevention and treatment.

Effects and Molecular Mechanism of L-Type Calcium Channel on Fluoride-Induced Kidney Injury

This study aimed to investigate the role and molecular mechanism of L-type calcium channel (LTCC) on fluoride exposure-induced kidney injury. Subchronic and chronic fluoride exposures were included in the experiment. Each part contained 140 ICR male mice. They were randomly divided into 7 groups: control group, high-fluoride group (NaF 30 mg/L), low-fluoride group (NaF 5 mg/L), high/low-fluoride + agonist (FPL64176) group, high/low-fluoride + inhibitor (nifedipine) group. One week before the end of fluoride exposure, each mouse in the fluoride exposure group was injected intraperitoneally with LTCC agonist (FPL64176) or inhibitor (nifedipine) (5 mg/kg day). The apoptosis of kidney cell was observed by TUNEL, and the protein expression levels of Cav1.2 and CaM, CaMKII, Bcl-2, and Bax were detected by Western blot. Compared with the control group, the protein expression levels of Cav1.2, CaM, and Bax significantly increased, and those of CaMKII and Bcl-2 significantly decreased, the ratio of Bax/Bcl-2 also significantly increased, and the number of apoptotic kidney cells significantly increased in the high/low-fluoride group and in the high/low-fluoride + agonist group. The above indicators and fluoride exposure concentrations showed in time- and dose-dependent changes. Compared with the high/low-fluoride + agonist group, the protein expression level of the molecular in the kidney cells above mentioned was significantly opposite and the number of apoptotic kidney cells significantly decreased in the high/low-fluoride + inhibitor group. In conclusion, LTCC mediates the kidney injury induced by fluoride exposure in mice. Fluoride exposure induced abnormal expression of the Cav1.2 protein, Ca²⁺ signal transduction pathway, and apoptosis-regulated proteins, which is one of the molecular mechanisms. Nifedipine may be a new and effective anti-fluoride drug.

The role of TRPM2 channels in neurons, glial cells and the blood-brain barrier in cerebral ischemia and hypoxia

Stroke is one of the major causes of mortality and morbidity worldwide, yet novel therapeutic treatments for this condition are lacking. This review focuses on the roles of the transient receptor potential melastatin 2 (TRPM2) ion channels in cellular damage following hypoxia-ischemia and their potential as a future therapeutic target for stroke. Here, we highlight the complex molecular signaling that takes place in neurons, glial cells and the blood-brain barrier following ischemic insult. We also describe the evidence of TRPM2 involvement in these processes, as shown from numerous in vitro and in vivo studies that utilize genetic and pharmacological approaches. This evidence implicates TRPM2 in a broad range of pathways that take place every stage of cerebral ischemic injury, thus making TRPM2 a promising target for drug development for stroke and other neurodegenerative conditions of the central nervous system.

Transient receptor potential melastatin-2 and temperature participate in the process of CD38-regulated oxytocin secretion

In recent studies, oxytocin showed potential for the treatment of mental diseases. CD38 is essential for oxytocin release, and hence plays a critical role in social behavior. CD38 catalyzes β-NAD into cyclic ADP ribose (cADPR), which could elevate the intracellular Ca by Ca-permeable channels for oxytocin secretion. The temperature-sensitive cation channel, transient receptor potential melastatin-2 (TRPM2), is a cation-nonselective cation and has been shown to affect oxytocin indirectly. The aim of the present study was to verify the participation of temperature and TRPM2 in CD38-regulated oxytocin release. The crude membranes were prepared to isolate the nerve terminals from the posterior pituitary. At 34°C, 37°C, and 39°C, agonists (β-NAD, ADPR, cADPR) and antagonists (8-Br-cADPR, 2-APB) were used to stimulate the nerve terminals. Oxytocin releases were investigated by enzyme-linked immunosorbent assay. In addition, the expression of TRPM2 and CD38 in the hypothalamus and pituitary was detected by western blotting and quantitative PCR. CD38 agonists (β-NAD, cADPR) and antagonist (8-Br-cADPR) could increase or reduce the oxytocin release, respectively. TRPM2 agonist (ADPR) and antagonist (2-APB) alone could also regulate oxytocin release. Furthermore, temperature could increase agonist stimulation and attenuate the antagonist inhibition on oxytocin release. In addition, CD38 and TRPM2 were expressed in the hypothalamus and pituitary at both the mRNA and the protein level. TRPM2 in pituitary nerve terminals plays a role in oxytocin release. Temperature- enhanced oxytocin release by CD38 and TRPM2. TRPM2 might be involved in the process of CD38-regulated oxytocin release.

Fluoride affects calcium homeostasis and osteogenic transcription factor expressions through L-type calcium channels in osteoblast cell line

Osteoblast L-type voltage-dependent calcium channels (VDCC) play important roles in maintaining intracellular homeostasis and influencing multiple cellular processes. In particular, they contribute to the activities and functions of osteoblasts (OBs). In order to study how L-type VDCC modulate calcium ion (Ca(2+)) homeostasis and the expression of osteogenic transcription factors in OBs exposed to fluoride, MC3T3-E1 cells were exposed to a gradient of concentrations of fluoride (0, 2.0, 5.0, 10.0 mg/L) in combination with 10 μM nifedipine, a specific inhibitor of VDCC, for 48 h. We examined messenger RNA (mRNA) and protein levels of Cav1.2, the main subunit of VDCC, and c-fos, c-jun, runt-related transcription factor 2 (Runx2), osterix (OSX), and intracellular free Ca(2+) ([Ca(2+)]i) concentrations in MC3T3-E1 cells. Our results showed that [Ca(2+)]i levels increased in a dose-dependent manner with increase in concentration of fluoride. Meantime, results indicated that lower concentrations of fluoride (less than 5 mg/L, especially 2 mg/L) can lead to high expression of Cav1.2 and enhance osteogenic function, while high concentration of fluoride (10 mg/L) can induce decreased Cav1.2 and osteogenic transcriptional factors in MC3T3E1 cells exposed to fluoride. However, the levels of [Ca(2+)]i, Cav1.2, c-fos, c-jun, Runx2, and OSX induced by fluoride were significantly altered and even reversed in the presence of nifedipine. These results demonstrate that L-type calcium channels play a crucial role in Ca(2+) homeostasis and they affect the expression of osteogenic transcription factors in fluoride-treated osteoblasts.

A cell permeable NPE caged ADP-ribose for studying TRPM2

Transient potential receptor melastatin-2 (TRPM2) is a non-selective Ca²⁺-permeable cation channel of the TRPM channel subfamily and is mainly activated by intracellular adenosine diphosphate ribose (ADPR). Here we synthesized a 1-(2-nitrophenyl)ethyl caged ADPR (NPE-ADPR) and found that uncaging of NPE-ADPR efficiently stimulated Ca²⁺, Mg²⁺, and Zn²⁺ influx in a concentration-dependent manner in intact human Jurkat T-lymphocytes. The cation influx was inhibited by inhibitors or knockdown of TRPM2. Likewise, uncaging of NPE-ADPR markedly induced cation entry in HEK 293 cells that overexpress TRPM2. As expected, high temperature increased the ability of the photolyzed NPE-ADPR to induce cation entry, whereas acidic pH inhibited. Moreover, the absence of extracellular Ca²⁺ significantly inhibited Mg²⁺ and Zn²⁺ influx after uncaging NPE-ADPR. On the other hand, the absence of extracellular Na⁺ or Mg²⁺ had no effect on photolyzed NPE-ADPR induced Ca²⁺ entry. Taken together, our results indicated that NPE-ADPR is a cell permeable ADPR analogue that is useful for studying TRPM2-mediated cation entry in intact cells.

Melatonin modulates apoptosis and TRPM2 channels in transfected cells activated by oxidative stress

Transient receptor potential melastatin-like 2 (TRPM2) is a non-selective Ca(2+) permeable cation channel and is known to be activated by H(2)O(2), one of the most important indicators of intracellular oxidative stress. A neurohormone melatonin may have a modulator role on TRPM2 channels activated by oxidative stress because it is a strong antioxidant. In this study we investigated the effects of melatonin on apoptosis, whole cell currents and Ca(2+) influx arising from TRPM2 channels activated by H(2)O(2). In whole-cell patch clamp experiments, TRPM2 channels in transfected Chinese hamster ovary (CHO) cells were activated by H(2)O(2). However, the currents were inhibited either by intracellular or by extracellular melatonin. When intracellular melatonin was introduced by pipette, TRPM2 channel currents were not activated by H(2)O(2) although H(2)O(2)-induced Ca(2+) gating and release were not blocked 2-aminoethyldiphenyl borate (2-APB). Cytosolic Ca(2+) release was measured by Fura-2 and was higher in H(2)O(2) groups than in control. Melatonin also inhibited apoptosis in the transfected cells. In conclusion, we observed modulator roles of intracellular and extracellular melatonin on Ca(2+) influx and apoptosis through a TRPM2 channel in transfected CHO cells.

TRPM channels: same ballpark, different players, and different rules in immunogenetics

Transient receptor potential (TRP) channels belong to a large family of cation channels and are the "border guards" predominantly localized to the plasma membrane. Research over the years has considerably and highly developed the knowledge of expression and functional aspects of the TRPM channels. A closer look at the channel dynamics has dismantled undeniable substantiation for multifaceted roles for TRPM channel-mediated extracellular Ca(2+) influx in several physiological and pathophysiological functions. Given the wealth of literature unfolding the multiple roles of TRP channels in physiology in a very extensive range of different mammalian tissues, this review confines itself to the literature describing the multiple roles of TRPM channels in diabetes, smooth muscle cell regulation, immunological responses, and emerging aspects of cancer. We also focus on differential activities of TRPM channels after post-transcriptional and post-translational processing and their exquisite roles at various cellular and molecular levels.