Residues at the tip of the pore loop of NR3B-containing NMDA receptors determine Ca2+ permeability and Mg2+ block

<p>Abstract</p> <p>Background</p> <p>Members of the complex N-methyl-D-aspartate receptor (NMDAR) subfamily of ionotropic glutamate receptors (iGluRs) conventionally assemble from NR1 and NR2 subunits, the composition of which determines receptor properties. Hallmark features of conventional NMDARs include the requirement for a coagonist, voltage-dependent block by Mg²⁺, and high permeability for Ca²⁺. Both Mg²⁺sensitivity and Ca²⁺permeability are critically dependent on the amino acids at the N and N+1 positions of NR1 and NR2. The recently discovered NR3 subunits feature an unprecedented glycine-arginine combination at those critical sites within the pore. Diheteromers assembled from NR1 and NR3 are not blocked by Mg²⁺and are not permeable for Ca²⁺.</p> <p>Results</p> <p>Employing site-directed mutagenesis of receptor subunits, electrophysiological characterization of mutants in a heterologous expression system, and molecular modeling of the NMDAR pore region, we have investigated the contribution of the unusual NR3 N and N+1 site residues to the unique functional characteristics of receptors containing these subunits. Contrary to previous studies, we provide evidence that both the NR3 N and N+1 site amino acids are critically involved in mediating the unique pore properties. Ca²⁺permeability could be rescued by mutating the NR3 N site glycine to the NR1-like asparagine. Voltage-dependent Mg²⁺block could be established by providing an Mg²⁺coordination site at either the NR3 N or N+1 positions. Conversely, "conventional" receptors assembled from NR1 and NR2 could be made Mg²⁺insensitive and Ca²⁺impermeable by equipping either subunit with the NR3-like glycine at their N positions, with a stronger contribution of the NR1 subunit.</p> <p>Conclusions</p> <p>This study sheds light on the structure-function relationship of the least characterized member of the NMDAR subfamily. Contrary to previous reports, we provide evidence for a critical functional involvement of the NR3 N and N+1 site amino acids, and propose them to be the essential determinants for the unique pore properties mediated by this subunit.</p

TRPM2 cation channels modulate T cell effector functions and contribute to autoimmune CNS inflammation.

TRPM2, a highly Ca(2+)-permeable member of the transient receptor potential melastatin-related (TRPM) family of cation channels, is expressed in cells of the immune system. We demonstrate firstly that TRPM2 cation channels on T cells critically influence T cell proliferation and proinflammatory cytokine secretion following polyclonal T cell receptor stimulation. Consistently, trpm2-deficient mice exhibited an attenuated clincal phenotype of experimental autoimmune encephalomyelitis (EAE) with reduced inflammatory and demyelinating spinal cord lesions. Importantly, trmp2-deficient T cells were as susceptible as wildtype T cells to oxidative stress-induced cell death as it occurs in inflammatory CNS lesions. This supports the notion that the attenuated EAE phenotype is mainly due to reduced T cell effector functions but unaffected by potential modulation of T cell survival at the site of inflammation. Our findings suggest TRPM2 cation channels as a potential target for treating autoimmune CNS inflammation

TRPM2 cation channels critically determine proliferation and proinflammatory cytokine secretion following various strengths of polyclonal T cell receptor triggering.

<p>(<b>A–D</b>) Proliferation as determined by ³[H]-thymidine uptake (<b>A</b>; bead:cell ratio of 1∶4) and secretion of proinflammatory IL-2 (<b>B</b>), IFN-γ (<b>C</b>) and IL-17 (<b>D</b>) determined by ELISA from the supernatants were significantly reduced in spleenocytes from trpm2-deficient as compared to wildtype mice following anti-CD3/CD28 bead-stimulation for 3 days at various bead:cell ratios (1∶1 to 1∶16; n = 3 for all experiments). P-values ≤0.05 were considered significant (*). P-values ≤0.01 and ≤0.001 were considered highly significant (** and ***, respectively).</p

Translational imaging of TSPO reveals pronounced innate inflammation in human and murine CD8 T cell-mediated limbic encephalitis.

Autoimmune limbic encephalitis (ALE) presents with new-onset mesial temporal lobe seizures, progressive memory disturbance, and other behavioral and cognitive changes. CD8 T cells are considered to play a key role in those cases where autoantibodies (ABs) target intracellular antigens or no ABs were found. Assessment of such patients presents a clinical challenge, and novel noninvasive imaging biomarkers are urgently needed. Here, we demonstrate that visualization of the translocator protein (TSPO) with [18F]DPA-714-PET-MRI reveals pronounced microglia activation and reactive gliosis in the hippocampus and amygdala of patients suspected with CD8 T cell ALE, which correlates with FLAIR-MRI and EEG alterations. Back-translation into a preclinical mouse model of neuronal antigen-specific CD8 T cell-mediated ALE allowed us to corroborate our preliminary clinical findings. These translational data underline the potential of [18F]DPA-714-PET-MRI as a clinical molecular imaging method for the direct assessment of innate immunity in CD8 T cell-mediated ALE