Magnesium-Induced Cell Survival Is Dependent on TRPM7 Expression and Function

Abstract

Mg 2+ homeostasis is essential for cell survival and the loss of this regulation has been associated with many neurodegenerative diseases, including loss of dopaminergic neurons. Although the neurotoxin-mediated loss of dopaminergic neurons in Parkinson disease models is extensively studied, the ion channel(s) that regulate Mg 2+ homeostasis and thus could prevent neuronal cell death is not yet identified. Here, we show that TRPM7 (transient receptor potential melastatin 7) is involved in regulating Mg 2+ homeostasis in dopaminergic cells. Importantly, transient loss of TRPM7 decreased intracellular Mg 2+ levels and decreased dopaminergic cells/neurons survival. We provide further evidence that both increases in extracellular Mg 2+ or transiently increasing TRPM7 levels protected dopaminergic SH-SY5Y cells against neurotoxin-mediated cell death. Neurotoxin treatment significantly decreased TRPM7 levels in both SH-SY5Y cells and the substantia nigra pars compacta region of mice, along with a decrease in Mg 2+ influx. Moreover, Mg 2+ supplementation showed a concentration-dependent decrease in caspase-3 activity, an increase in cell survival, restored mitochondrial membrane potential, and increase TRPM7 levels in neurotoxin-treated cells. In contrast, transient silencing of TRPM7 inhibited the positive effect of Mg 2+ supplementation in protecting against neurotoxins. Whereas, TRPM7 overexpression not only maintained Mg 2+ homeostasis but also inhibited caspase 3 activity that induced cell survival. Overall, these results suggest a significant role of TRPM7 channels in Mg 2+ homeostasis and the survival of neurotoxininduced loss of dopaminergic cells.

Isoproterenol-Dependent Activation of TRPM7 Protects Against Neurotoxin-Induced Loss of Neuroblastoma Cells

“…Importantly, the decrease in TRPM7 expression was specific, since no change in actin levels were observed upon neurotoxintreatment. Consistent with these studies a decrease in TRPM7 expression has also been shown in PD patients and in the samples from neurotoxin-induced substantia nigra pars compacta regions (Sun et al, 2019), which further suggests that loss of TRPM7 could lead to neurodegeneration. Similarly, mutations in TRPM7 has been reported in some familial PD patients (Hermosura et al, 2005), and although the expression and/or function of TRPM7 was not identified in this study, a decrease in TRPM7 expression and/or function could be the reason for the observed neuronal loss.…”

“…Similarly, TRPM7 mutants in zebrafish have decreased DA neurons (Decker et al, 2014), suggesting that changes in the Mg 2+ influx could induce neurodegeneration. Consistent with this observation, decreased Mg 2+ intake induced DA neuron loss, whereas Mg 2+ supplementation prevented neurotoxin-mediated decrease in DA neurons (Oyanagi and Hashimoto, 2011;Sun et al, 2019). These results suggest that TRPM7-mediated regulation of intracellular Mg 2+ could promote neuronal survival, however, its regulation, specifically TRPM7 activation in DA cells is not fully identified.…”

“…Neurotoxin treatment has been well used as a model for PD and using this in vitro model we have here established the significance of β−AR-mediated activation of TRPM7 in the loss of neuroblastoma cells. We have previously shown that Mg 2+ homeostasis prevents neurotoxin-induced cell death (Sun et al, 2019), however, the mechanisms for TRPM7 activation are not known. Importantly, increasing Mg 2+ concentration has been shown to protect against neurotoxin-induced loss of dopaminergic cells (Hashimoto et al, 2008;Muroyama et al, 2009), suggesting that Mg 2+ influx leads to the survival of dopaminergic neurons.…”

“…Recent studies have shown that intracellular Mg 2+ concentration is mediated through TRPM6/7 channels (Sun et al, 2019). Whole-cell current recordings were used to further establish the channel identity that is responsible for Mg 2+ influx.…”

“…The properties of the currents were similar as observed with TRPM6/7 channels. 2APB has been previously used to differentiate TRPM6/7 currents as addition of 2APB potentiates TRPM6 function, but inhibits TRPM7 currents (Mishra et al, 2009;Sun et al, 2019). Thus, to differentiate between these two Mg 2+ channels we further studied the effects of 2-APB that further decreased these currents, suggesting that these currents FIGURE 1 | Isoproterenol treatment induces survival of neuroblastoma cells: (A) Cell survival under conditions as labeled was performed using MTT assays on control and MPP + (500µM for 24 h) treated SH-SY5Y cells.…”