3-Hydroxykynurenine targets kainate receptors to promote defense against infection.

Bacterial infection involves a complex interaction between the pathogen and host where the outcome of infection is not solely determined by pathogen eradication. To identify small molecules that promote host survival by altering the host-pathogen dynamic, we conducted an in vivo chemical screen using zebrafish embryos and found that treatment with 3-hydroxykynurenine (3-HK) protects from lethal bacterial infection. 3-HK, a metabolite produced through host tryptophan metabolism, has no direct antibacterial activity but enhances host survival by restricting bacterial expansion in macrophages through a systemic mechanism that targets kainate-sensitive glutamate receptors. These findings reveal a new pathway by which tryptophan metabolism and kainate-sensitive glutamate receptors function and interact to modulate immunity, with important implications for the coordination between the immune and nervous systems in pathological conditions.

A tryptophan metabolite modulates the host response to bacterial infection via kainate receptors.

Bacterial infection involves a complex interaction between the pathogen and host where the outcome of infection is not solely determined by pathogen eradication. To identify small molecules that promote host survival by altering the host-pathogen dynamic, we conducted an in vivo chemical screen using zebrafish embryos and found that treatment with 3-hydroxy-kynurenine protects from lethal gram-negative bacterial infection. 3-hydroxy-kynurenine, a metabolite produced through host tryptophan metabolism, has no direct antibacterial activity but enhances host survival by restricting bacterial expansion in macrophages by targeting kainate-sensitive glutamate receptors. These findings reveal new mechanisms by which tryptophan metabolism and kainate-sensitive glutamate receptors function and interact to modulate immunity, with significant implications for the coordination between the immune and nervous systems in pathological conditions.

TMEM163 Regulates ATP-Gated P2X Receptor and Behavior.

Fast purinergic signaling is mediated by ATP and ATP-gated ionotropic P2X receptors (P2XRs), and it is implicated in pain-related behaviors. The properties exhibited by P2XRs vary between those expressed in heterologous cells and in vivo. Several modulators of ligand-gated ion channels have recently been identified, suggesting that there are P2XR functional modulators in vivo. Here, we establish a genome-wide open reading frame (ORF) collection and perform functional screening to identify modulators of P2XR activity. We identify TMEM163, which specifically modulates the channel properties and pharmacology of P2XRs. We also find that TMEM163 is required for full function of the neuronal P2XR and a pain-related ATP-evoked behavior. These results establish TMEM163 as a critical modulator of P2XRs in vivo and a potential target for the discovery of drugs for treating pain.

ABC transporters control ATP release through cholesterol-dependent volume-regulated anion channel activity.

Purinergic signaling by extracellular ATP regulates a variety of cellular events and is implicated in both normal physiology and pathophysiology. Several molecules have been associated with the release of ATP and other small molecules, but their precise contributions have been difficult to assess because of their complexity and heterogeneity. Here, we report on the results of a gain-of-function screen for modulators of hypotonicity-induced ATP release using HEK-293 cells and murine cerebellar granule neurons, along with bioluminescence, calcium FLIPR, and short hairpin RNA-based gene-silencing assays. This screen utilized the most extensive genome-wide ORF collection to date, covering 90% of human, nonredundant, protein-encoding genes. We identified two ABCG1 (ABC subfamily G member 1) variants, which regulate cellular cholesterol, as modulators of hypotonicity-induced ATP release. We found that cholesterol levels control volume-regulated anion channel-dependent ATP release. These findings reveal novel mechanisms for the regulation of ATP release and volume-regulated anion channel activity and provide critical links among cellular status, cholesterol, and purinergic signaling.

Homer proteins accelerate Ca2+ clearance mediated by the plasma membrane Ca2+ pump in hippocampal neurons.

The plasma membrane Ca(2+) ATPase (PMCA) is responsible for maintaining basal intracellular Ca(2+) concentration ([Ca(2+)](i)) and returning small increases in [Ca(2+)](i) back to resting levels. The carboxyl terminus of some PMCA splice variants bind Homer proteins; how binding affects PMCA function is unknown. Here, we examined the effects of altered expression of Homer proteins on PMCA-mediated Ca(2+) clearance from rat hippocampal neurons in culture. The kinetics of PMCA-mediated recovery from the [Ca(2+)](i) increase evoked by a brief train of action potentials was determined in the soma of single neurons using indo-1-based photometry. Exogenous expression of Homer 1a, Homer 1c or Homer 2a did not affect PMCA function. However, shRNA mediated knockdown of Homer 1 slowed PMCA mediated Ca(2+) clearance by 28% relative to cells expressing non-silencing shRNA. The slowed recovery rate in cells expressing Homer 1 shRNA was reversed by expression of a short Homer 2 truncation mutant. These results indicate that constitutively expressed Homer proteins tonically stimulate PMCA function in hippocampal neurons. We propose a model in which binding of short or long Homer proteins to the carboxyl terminus of the PMCA stimulates Ca(2+) clearance rate. PMCA-mediated Ca(2+) clearance may be stimulated following incorporation of the pump into Homer organized signaling domains and following induction of the Homer 1a immediate early gene.