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Kainate receptors (KARs) are a subtype of ionotropic glutamate receptor (iGluR) channels, a superfamily of ligand-gated ion channels which mediate the majority of excitatory neurotransmission in the central nervous system. KARs modulate neuronal circuits and plasticity during development and are implicated in neurological disorders, including epilepsy, depression, schizophrenia, anxiety, and autism. Calcium-permeable KARs undergo ion channel block, but the therapeutic potential of channel blockers remains underdeveloped, mainly due to limited structural knowledge. Here, we present closed-state structures of GluK2 KAR homotetramers in complex with ion channel blockers NpTx-8, PhTx-74, Kukoamine A, and spermine. We find that blockers reside inside the GluK2 ion channel pore, intracellular to the closed M3 helix bundle-crossing gate, with their hydrophobic heads filling the central cavity and positively charged polyamine tails spanning the selectivity filter. Molecular dynamics (MD) simulations of our structures illuminate interactions responsible for different affinity and binding poses of the blockers. Our structures elucidate the trapping mechanism of KAR channel block and provide a template for designing new blockers that can selectively target calcium-permeable KARs in neuropathologies. Kainate receptors (KARs) contribute to excitatory neurotransmission, neuronal plasticity and neurological disorders. Here, Gangwar et al. present KAR structures in complex with channel blockers NpTx8, PhTx74, KukoA, and spermine, which become trapped inside the channel upon its closure. [ABSTRACT FROM AUTHOR]

Small molecule polyamines are abundant in all life forms and participate in diverse aspects of cell growth and differentiation. Spermidine/spermine acetyltransferase (SAT1) is the rate-limiting enzyme in polyamine catabolism and a primary genetic risk factor for suicidality. Here, using genome-wide screening, we find that SAT1 selectively controls nicotinic acetylcholine receptor (nAChR) biogenesis. SAT1 specifically augments assembly of nAChRs containing α7 or α4β2, but not α6 subunits. Polyamines are classically studied as regulators of ion channel gating that engage the nAChR channel pore. In contrast, we find polyamine effects on assembly involve the nAChR cytosolic loop. Neurological studies link brain polyamines with neurodegenerative conditions. Our pharmacological and transgenic animal studies find that reducing polyamines enhances cortical neuron nAChR expression and augments nicotine-mediated neuroprotection. Taken together, we describe a most unexpected role for polyamines in regulating ion channel assembly, which provides a new avenue for nAChR neuropharmacology. Small molecule polyamines participate in diverse aspects of cell growth and differentiation and are known to regulate ion channel gating. Here authors reveal that cellular polyamines control nicotinic acetylcholine receptor (nAChR) biogenesis, and either catabolic degradation or inhibition of polyamine production augments nAChR assembly. [ABSTRACT FROM AUTHOR]

The roles of glia and polyamines (PA) in brain function and dysfunction are highlighted in this review. We emphasize that PA accumulation preferentially in glia, but not in neurons, is clearly evolutionarily determined; it is found throughout the brain, retina, peripheral nervous system, and in glial-neuronal co-cultures of multiple species, including man. This phenomenon raises key questions: (i) What are the mechanisms that underlie such uneven distribution, accumulation and release from glia? (ii) What are the consequences of PA fluxes within the brain on neuronal function? (iii) What are the roles of PAs in brain disorders and diseases? This review includes suggestions on the roles of PAs, such as putrescine (PT), spermidine (SPD), spermine (SPM) and their derivatives as novel glio-transmitters in brain since PA affect many neuronal and glial receptors, channels and transporters. Polyamines hitherto have been neglected, although it is evident that these molecules are key elements for normal brain function and their metabolic disorders, apparently, cause the development of many pathological syndromes and diseases. The study of endogenous PA allows one to put forward the basic principles of scientific research on glio-neuronal interactions and clinical therapies, which are based on the exclusivity of glial cells in terms of accumulation of PA and PA-dependent functions. [ABSTRACT FROM AUTHOR]

Impairments to glutamatergic synaptic transmission are seen in many pathological CNS states. Excess glutamate actions, inducing persistent depolarization of neurons and massive calcium influx, can lead to cell death. Despite the obvious importance of developing antiglutamate agents as neuroprotectors, the only one of the ionotropic glutamate receptor antagonists which has been introduced into practice is memantine. One of the causes of the multiple side effects occurring when glutamate receptor antagonists are used is that these pharmacological agents inhibit the whole of the receptor pool, both those receptors involved in pathological processes and those performing normal physiological functions. One possible approach to overcoming this problem consists of developing pharmacological agents whose actions are enhanced in potential pathological states, such as high-frequency stimulation of receptors, high glutamate concentrations, decreases in neuron membrane potential, etc. The efficacies of many types of antagonists, such as channel blockers, depends on the membrane potential and the nature of receptor activation. The present article provides a discussion of some of the characteristics of the mechanisms of blockade of glutamate receptor ion channels from the point of view of the potential to create neuroprotective agents. In particular, blockers with different interactions with channel gate structures and different types of blockade voltage dependence are compared, with analysis of the characteristics of the actions of blockers able to penetrate channels to enter cells. We suggest that only detailed study of the mechanisms of action of antagonists on glutamate receptors can bring us towards the ability to predict the results of using blockers in vivo on the basis of data obtained in vitro. [ABSTRACT FROM AUTHOR]