TRPM7 is an essential regulator for volume-sensitive outwardly rectifying anion channel.

Animal cells can regulate their volume after swelling by the regulatory volume decrease (RVD) mechanism. In epithelial cells, RVD is attained through KCl release mediated via volume-sensitive outwardly rectifying Cl- channels (VSOR) and Ca2+-activated K+ channels. Swelling-induced activation of TRPM7 cation channels leads to Ca2+ influx, thereby stimulating the K+ channels. Here, we examined whether TRPM7 plays any role in VSOR activation. When TRPM7 was knocked down in human HeLa cells or knocked out in chicken DT40 cells, not only TRPM7 activity and RVD efficacy but also VSOR activity were suppressed. Heterologous expression of TRPM7 in TRPM7-deficient DT40 cells rescued both VSOR activity and RVD, accompanied by an increase in the expression of LRRC8A, a core molecule of VSOR. TRPM7 exerts the facilitating action on VSOR activity first by enhancing molecular expression of LRRC8A mRNA through the mediation of steady-state Ca2+ influx and second by stabilizing the plasmalemmal expression of LRRC8A protein through the interaction between LRRC8A and the C-terminal domain of TRPM7. Therefore, TRPM7 functions as an essential regulator of VSOR activity and LRRC8A expression.

The evolution of a series of behavioral traits is associated with autism-risk genes in cavefish.

BACKGROUND: An essential question in evolutionary biology is whether shifts in a set of polygenic behaviors share a genetic basis across species. Such a behavioral shift is seen in the cave-dwelling Mexican tetra, Astyanax mexicanus. Relative to surface-dwelling conspecifics, cavefish do not school (asocial), are hyperactive and sleepless, adhere to a particular vibration stimulus (imbalanced attention), behave repetitively, and show elevated stress hormone levels. Interestingly, these traits largely overlap with the core symptoms of human autism spectrum disorder (ASD), raising the possibility that these behavioral traits are underpinned by a similar set of genes (i.e. a repeatedly used suite of genes). RESULT: Here, we explored whether modification of ASD-risk genes underlies cavefish evolution. Transcriptomic analyses revealed that > 58.5% of 3152 cavefish orthologs to ASD-risk genes are significantly up- or down-regulated in the same direction as genes in postmortem brains from ASD patients. Enrichment tests suggest that ASD-risk gene orthologs in A. mexicanus have experienced more positive selection than other genes across the genome. Notably, these positively selected cavefish ASD-risk genes are enriched for pathways involved in gut function, inflammatory diseases, and lipid/energy metabolism, similar to symptoms that frequently coexist in ASD patients. Lastly, ASD drugs mitigated cavefish's ASD-like behaviors, implying shared aspects of neural processing. CONCLUSION: Overall, our study indicates that ASD-risk genes and associated pathways (especially digestive, immune and metabolic pathways) may be repeatedly used for shifts in polygenic behaviors across evolutionary time.

Altered functional properties of a TRPM2 variant in Guamanian ALS and PD.

Two related neurodegenerative disorders, Western Pacific amyotrophic lateral sclerosis (ALS) and parkinsonism-dementia (PD), originally occurred at a high incidence on Guam, in the Kii peninsula of Japan, and in southern West New Guinea more than 50 years ago. These three foci shared a unique mineral environment characterized by the presence of severely low levels of Ca(2+) and Mg(2+), coupled with high levels of bioavailable transition metals in the soil and drinking water. Epidemiological studies suggest that genetic factors also contribute to the etiology of these disorders. Here, we report that a variant of the transient receptor potential melastatin 2 (TRPM2) gene may confer susceptibility to these diseases. TRPM2 encodes a calcium-permeable cation channel highly expressed in the brain that has been implicated in mediating cell death induced by oxidants. We found a heterozygous variant of TRPM2 in a subset of Guamanian ALS (ALS-G) and PD (PD-G) cases. This variant, TRPM2(P1018L), produces a missense change in the channel protein whereby proline 1018 (Pro(1018)) is replaced by leucine (Leu(1018)). Functional studies revealed that, unlike WT TRPM2, P1018L channels inactivate. Our results suggest that the ability of TRPM2 to maintain sustained ion influx is a physiologically important function and that its disruption may, under certain conditions, contribute to disease states.

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.

A TRPM7 variant shows altered sensitivity to magnesium that may contribute to the pathogenesis of two Guamanian neurodegenerative disorders.

Guamanian amyotrophic lateral sclerosis (ALS-G) and parkinsonism dementia (PD-G) have been epidemiologically linked to an environment severely deficient in calcium (Ca2+) and magnesium (Mg2+). Transient receptor potential melastatin 7 (TRPM7) is a bifunctional protein containing both channel and kinase domains that has been proposed to be involved in the homeostatic regulation of intracellular Ca2+, Mg2+, and trace metal ion concentration. There is evidence that TRPM7 is constitutively active and that the number of available channels is dependent on intracellular free Mg2+ levels. We found a TRPM7 variant in a subset of ALS-G and PD-G patients that produces a protein with a missense mutation, T1482I. Recombinant T1482I TRPM7 exhibits the same kinase catalytic activity as WT TRPM7. However, heterologously expressed T1482I TRPM7 produces functional channels that show an increased sensitivity to inhibition by intracellular Mg2+. Because the incidence of ALS-G and PD-G has been associated with prolonged exposure to an environment severely deficient in Ca2+ and Mg2+, we propose that this variant TRPM7 allele confers a susceptibility genotype in such an environment. This study represents an initial attempt to address the important issue of gene-environment interactions in the etiology of these diseases.

TRPM7 provides an ion channel mechanism for cellular entry of trace metal ions.

Trace metal ions such as Zn(2+), Fe(2+), Cu(2+), Mn(2+), and Co(2+) are required cofactors for many essential cellular enzymes, yet little is known about the mechanisms through which they enter into cells. We have shown previously that the widely expressed ion channel TRPM7 (LTRPC7, ChaK1, TRP-PLIK) functions as a Ca(2+)- and Mg(2+)-permeable cation channel, whose activity is regulated by intracellular Mg(2+) and Mg(2+).ATP and have designated native TRPM7-mediated currents as magnesium-nucleotide-regulated metal ion currents (MagNuM). Here we report that heterologously overexpressed TRPM7 in HEK-293 cells conducts a range of essential and toxic divalent metal ions with strong preference for Zn(2+) and Ni(2+), which both permeate TRPM7 up to four times better than Ca(2+). Similarly, native MagNuM currents are also able to support Zn(2+) entry. Furthermore, TRPM7 allows other essential metals such as Mn(2+) and Co(2+) to permeate, and permits significant entry of nonphysiologic or toxic metals such as Cd(2+), Ba(2+), and Sr(2+). Equimolar replacement studies substituting 10 mM Ca(2+) with the respective divalent ions reveal a unique permeation profile for TRPM7 with a permeability sequence of Zn(2+) approximately Ni(2+) >> Ba(2+) > Co(2+) > Mg(2+) >/= Mn(2+) >/= Sr(2+) >/= Cd(2+) >/= Ca(2+), while trivalent ions such as La(3+) and Gd(3+) are not measurably permeable. With the exception of Mg(2+), which exerts strong negative feedback from the intracellular side of the pore, this sequence is faithfully maintained when isotonic solutions of these divalent cations are used. Fura-2 quenching experiments with Mn(2+), Co(2+), or Ni(2+) suggest that these can be transported by TRPM7 in the presence of physiological levels of Ca(2+) and Mg(2+), suggesting that TRPM7 represents a novel ion-channel mechanism for cellular metal ion entry into vertebrate cells.

Dissociation of the store-operated calcium current I(CRAC) and the Mg-nucleotide-regulated metal ion current MagNuM.

Rat basophilic leukaemia cells (RBL-2H3-M1) were used to study the characteristics of the store-operated Ca(2+) release-activated Ca(2+) current (I(CRAC)) and the magnesium-nucleotide-regulated metal cation current (MagNuM) (which is conducted by the LTRPC7 channel). Pipette solutions containing 10 mM BAPTA and no added ATP induced both currents in the same cell, but the time to half-maximal activation for MagNuM was about two to three times slower than that of I(CRAC). Differential suppression of I(CRAC) was achieved by buffering free [Ca(2+)](i) to 90 nM and selective inhibition of MagNuM was accomplished by intracellular solutions containing 6 mM Mg.ATP, 1.2 mM free [Mg(2+)](i) or 100 microM GTP-gamma-S, allowing investigations on these currents in relative isolation. Removal of extracellular Ca(2+) and Mg(2+) caused both currents to be carried significantly by monovalent ions. In the absence or presence of free [Mg(2+)](i), I(CRAC) carried by monovalent ions inactivated more rapidly and more completely than MagNuM carried by monovalent ions. Since several studies have used divalent-free solutions on either side of the membrane to study selectivity and single-channel behaviour of I(CRAC), these experimental conditions would have favoured the contribution of MagNuM to monovalent conductance and call for caution in interpreting results where both I(CRAC) and MagNuM are activated.