Are the transient receptor potential melastatin (TRPM) channels important in magnesium homeostasis following traumatic brain in

Illustrations

Figure 1 Potential mechanisms of TRPM channel-mediated cell death in traumatic brain injury (TBI). Following TBI, the entry of Ca²⁺ into cells via the n-methyl-D-aspartate receptor (NMDAR) stimulates neuronal nitric oxide synthase (nNOS) leading to the production of nitric oxide (NO). Rises in intracellular Ca²⁺ concentration ([Ca²⁺]_i) promote O_2- release from mitochondria, which reacts with NO to produce highly reactive peroxynitrite radicals (ONOO^-). Free radicals damage cellular macromolecules and further activate TRPM2 and TRPM7 channels, allowing the influx of even more Ca²⁺. Mitochondria also produce adenosine diphosphate ribose (ADPR), which stimulates TRPM2. TBI causes [Mg²⁺]_i depletion and decreases in cellular pH, which activates TRPM7 and TRPM6 (and TRPM7/TRPM6 dimers). The kinase domains (K) of TRPM7 and TRPM6 may also influence signaling processes and inflammation. Disruption to the BBB allows water, proteins and metal ions to enter the brain (not shown); toxic trace metals (such as Zn²⁺⁾ may enter cells through TRPM7, while inflammatory mediators (such as tumor necrosis factor-α) further activate TRPM2. Prolonged depletion of Mg²⁺ and excess production of ROS and RNS could exacerbate this positive feedback loop and overactivate TRPM2 and TRPM7 (and potentially TRPM2/TRPM7 dimers). The resultant unregulated Ca²⁺ influx leads to excitotoxicity, enhances oxidative stress and inflammatory processes, and eventually activates pro-apoptotic signaling cascades that result in cell death.