Zinc(II) interactions with brain-derived neurotrophic factor N-terminal peptide fragments: inorganic features and biological perspectives

Diverse Functions of Multiple Bdnf Transcripts Driven by Distinct Bdnf Promoters

The gene encoding brain-derived neurotrophic factor (Bdnf) consists of nine non-coding exons driven by unique promoters, leading to the expression of nine Bdnf transcripts that play different roles in various brain regions and physiological stages. In this manuscript, we present a comprehensive overview of the molecular regulation and structural characteristics of the multiple Bdnf promoters, along with a summary of the current knowledge on the cellular and physiological functions of the distinct Bdnf transcripts produced by these promoters. Specifically, we summarized the role of Bdnf transcripts in psychiatric disorders, including schizophrenia and anxiety, as well as the cognitive functions associated with specific Bdnf promoters. Moreover, we examine the involvement of different Bdnf promoters in various aspects of metabolism. Finally, we propose future research directions that will enhance our understanding of the complex functions of Bdnf and its diverse promoters.

Environmental Enrichment Engages Vesicular Zinc Signaling to Enhance Hippocampal Neurogenesis

Zinc is highly concentrated in synaptic vesicles throughout the mammalian telencephalon and, in particular, the hippocampal dentate gyrus. A role for zinc in modulating synaptic plasticity has been inferred, but whether zinc has a particular role in experience-dependent plasticity has yet to be determined. The aim of the current study was to determine whether vesicular zinc is important for modulating adult hippocampal neurogenesis in an experience-dependent manner and, consequently, hippocampal-dependent behaviour. We assessed the role of vesicular zinc in modulating hippocampal neurogenesis and behaviour by comparing ZnT3 knockout (KO) mice, which lack vesicular zinc, to wild-type (WT) littermates exposed to either standard housing conditions (SH) or an enriched environment (EE). We found that vesicular zinc is necessary for a cascade of changes in hippocampal plasticity following EE, such as increases in hippocampal neurogenesis and elevations in mature brain-derived neurotrophic factor (mBDNF), but was otherwise dispensable under SH conditions. Using the Spatial Object Recognition task and the Morris Water task we show that, unlike WT mice, ZnT3 KO mice showed no improvements in spatial memory following EE. These experiments demonstrate that vesicular zinc is essential for the enhancement of adult hippocampal neurogenesis and behaviour following enrichment, supporting a role for zincergic neurons in contributing to experience-dependent plasticity in the hippocampus.

Neurotrophic Activity and Its Modulation by Zinc Ion of a Dimeric Peptide Mimicking the Brain-Derived Neurotrophic Factor N-Terminal Region

Brain-derived neurotrophic factor (BDNF) is a neurotrophin (NT) essential for neuronal development and synaptic plasticity. Dysregulation of BDNF signaling is implicated in different neurological disorders. The direct NT administration as therapeutics has revealed to be challenging. This has prompted the design of peptides mimicking different regions of the BDNF structure. Although loops 2 and 4 have been thoroughly investigated, less is known regarding the BDNF N-terminal region, which is involved in the selective recognition of the TrkB receptor. Herein, a dimeric form of the linear peptide encompassing the 1-12 residues of the BDNF N-terminal (d-bdnf) was synthesized. It demonstrated to act as an agonist promoting specific phosphorylation of TrkB and downstream ERK and AKT effectors. The ability to promote TrkB dimerization was investigated by advanced fluorescence microscopy and molecular dynamics (MD) simulations, finding activation modes shared with BDNF. Furthermore, d-bdnf was able to sustain neurite outgrowth and increase the expression of differentiation (NEFM, LAMC1) and polarization markers (MAP2, MAPT) demonstrating its neurotrophic activity. As TrkB activity is affected by zinc ions in the synaptic cleft, we first verified the ability of d-bdnf to coordinate zinc and then the effect of such complexation on its activity. The d-bdnf neurotrophic activity was reduced by zinc complexation, demonstrating the role of the latter in tuning the activity of the new peptido-mimetic. Taken together our data uncover the neurotrophic properties of a novel BDNF mimetic peptide and pave the way for future studies to understand the pharmacological basis of d-bdnf action and develop novel BDNF-based therapeutic strategies.

The Role of Metals in the Neuroregenerative Action of BDNF, GDNF, NGF and Other Neurotrophic Factors

Mature neurotrophic factors and their propeptides play key roles ranging from the regulation of neuronal growth and differentiation to prominent participation in neuronal survival and recovery after injury. Their signaling pathways sculpture neuronal circuits during brain development and regulate adaptive neuroplasticity. In addition, neurotrophic factors provide trophic support for damaged neurons, giving them a greater capacity to survive and maintain their potential to regenerate their axons. Therefore, the modulation of these factors can be a valuable target for treating or preventing neurologic disorders and age-dependent cognitive decline. Neuroregenerative medicine can take great advantage by the deepening of our knowledge on the molecular mechanisms underlying the properties of neurotrophic factors. It is indeed an intriguing topic that a significant interplay between neurotrophic factors and various metals can modulate the outcome of neuronal recovery. This review is particularly focused on the roles of GDNF, BDNF and NGF in motoneuron survival and recovery from injuries and evaluates the therapeutic potential of various neurotrophic factors in neuronal regeneration. The key role of metal homeostasis/dyshomeostasis and metal interaction with neurotrophic factors on neuronal pathophysiology is also highlighted as a novel mechanism and potential target for neuronal recovery. The progress in mechanistic studies in the field of neurotrophic factor-mediated neuroprotection and neural regeneration, aiming at a complete understanding of integrated pathways, offers possibilities for the development of novel neuroregenerative therapeutic approaches.

Amphetamine sensitization alters hippocampal neuronal morphology and memory and learning behaviors

It is known that continuous abuse of amphetamine (AMPH) results in alterations in neuronal structure and cognitive behaviors related to the reward system. However, the impact of AMPH abuse on the hippocampus remains unknown. The aim of this study was to determine the damage caused by AMPH in the hippocampus in an addiction model. We reproduced the AMPH sensitization model proposed by Robinson et al. in 1997 and performed the novel object recognition test (NORt) to evaluate learning and memory behaviors. After the NORt, we performed Golgi-Cox staining, a stereological cell count, immunohistochemistry to determine the presence of GFAP, CASP3, and MT-III, and evaluated oxidative stress in the hippocampus. We found that AMPH treatment generates impairment in short- and long-term memories and a decrease in neuronal density in the CA1 region of the hippocampus. The morphological test showed an increase in the total dendritic length, but a decrease in the number of mature spines in the CA1 region. GFAP labeling increased in the CA1 region and MT-III increased in the CA1 and CA3 regions. Finally, we found a decrease in Zn concentration in the hippocampus after AMPH treatment. An increase in the dopaminergic tone caused by AMPH sensitization generates oxidative stress, neuronal death, and morphological changes in the hippocampus that affect cognitive behaviors like short- and long-term memories.

Zinc induced structural changes in the intrinsically disordered BDNF Met prodomain confer synaptic elimination

Human brain derived neurotrophic factor (BDNF) encodes a protein product consisting of a C-terminal mature domain (mature BDNF) and an N-terminal prodomain, which is an intrinsically disordered protein. A common single nucleotide polymorphism in humans results in a methionine substitution for valine at position 66 of the prodomain, and is associated with memory deficits, depression and anxiety disorders. The BDNF Met66 prodomain, but not the Val66 prodomain, promotes rapid structural remodeling of hippocampal neurons' growth cones and dendritic spines by interacting directly with the SorCS2 receptor. While it has been reported that the Met66 and Val66 prodomains exhibit only modest differences in structural propensities in the apo state, here we show that Val66 and Met66 prodomains differentially bind zinc (Zn). Zn2+ binds with higher affinity and more broadly impacts residues on the Met66 prodomain compared to the Val66 prodomain as shown by NMR and ITC. Zn2+ binding to the Met66 and Val66 prodomains results in distinct conformational and macroscopic differences observed by NMR, light scattering and cryoEM. To determine if Zn2+ mediated conformational change in the Met66 prodomain is required for biological effect, we mutated His40, a Zn2+ binding site, and observed a loss of Met66 prodomain bioactivity. As the His40 site is distant from the known region of the prodomain involved in receptor binding, we suggest that Met66 prodomain bioactivity involves His40 mediated stabilization of the multimeric structure. Our results point to the necessity of a Zn2+-mediated higher order molecular assembly of the Met66 prodomain to mediate neuronal remodeling.

The Role of Copper (II) on Kininogen Binding to Tropomyosin in the Presence of a Histidine-Proline-Rich Peptide

The antiangiogenic activity of the H/P domain of histidine-proline-rich glycoprotein is mediated by its binding with tropomyosin, a protein exposed on endothelial cell-surface during the angiogenic switch, in presence of zinc ions. Although it is known that copper ion serum concentration is significantly increased in cancer patients, its role in the interaction of H/P domain with tropomyosin, has not yet been studied. In this paper, by using ELISA assay, we determined the modulating effect of TetraHPRG peptide, a sequence of 20 aa belonging to H/P domain, on the binding of Kininogen (HKa) with tropomyosin, both in absence and presence of copper and zinc ions. A potentiometric study was carried out to characterize the binding mode adopted by metal ions with TetraHPRG, showing the formation of complex species involving imidazole amide nitrogen atoms in metal binding. Moreover, circular dichroism showed a conformational modification of ternary systems formed by TetraHPRG, HKa and copper or zinc. Interestingly, slight pH variation influenced the HKa-TetraHPRG-tropomyosin binding. All these results indicate that both metal ions are crucial in the interaction between TetraHPRG, tropomyosin and HKa.

The change of conditions does not affect Ros87 downhill folding mechanism

Downhill folding has been defined as a unique thermodynamic process involving a conformations ensemble that progressively loses structure with the decrease of protein stability. Downhill folders are estimated to be rather rare in nature as they miss an energetically substantial folding barrier that can protect against aggregation and proteolysis. We have previously demonstrated that the prokaryotic zinc finger protein Ros87 shows a bipartite folding/unfolding process in which a metal binding intermediate converts to the native structure through a delicate barrier-less downhill transition. Significant variation in folding scenarios can be detected within protein families with high sequence identity and very similar folds and for the same sequence by varying conditions. For this reason, we here show, by means of DSC, CD and NMR, that also in different pH and ionic strength conditions Ros87 retains its partly downhill folding scenario demonstrating that, at least in metallo-proteins, the downhill mechanism can be found under a much wider range of conditions and coupled to other different transitions. We also show that mutations of Ros87 zinc coordination sphere produces a different folding scenario demonstrating that the organization of the metal ion core is determinant in the folding process of this family of proteins.

Substitution of the Native Zn(II) with Cd(II), Co(II) and Ni(II) Changes the Downhill Unfolding Mechanism of Ros87 to a Completely Different Scenario

The structural effects of zinc replacement by xenobiotic metal ions have been widely studied in several eukaryotic and prokaryotic zinc-finger-containing proteins. The prokaryotic zinc finger, that presents a bigger βββαα domain with a larger hydrophobic core with respect to its eukaryotic counterpart, represents a valuable model protein to study metal ion interaction with metallo-proteins. Several studies have been conducted on Ros87, the DNA binding domain of the prokaryotic zinc finger Ros, and have demonstrated that the domain appears to structurally tolerate Ni(II), albeit with important structural perturbations, but not Pb(II) and Hg(II), and it is in vitro functional when the zinc ion is replaced by Cd(II). We have previously shown that Ros87 unfolding is a two-step process in which a zinc binding intermediate converts to the native structure thorough a delicate downhill folding transition. Here, we explore the folding/unfolding behaviour of Ros87 coordinated to Co(II), Ni(II) or Cd(II), by UV-Vis, CD, DSC and NMR techniques. Interestingly, we show how the substitution of the native metal ion results in complete different folding scenarios. We found a two-state unfolding mechanism for Cd-Ros87 whose metal affinity K_d is comparable to the one obtained for the native Zn-Ros87, and a more complex mechanism for Co-Ros87 and Ni-Ros87, that show higher K_d values. Our data outline the complex cross-correlation between the protein-metal ion equilibrium and the folding mechanism proposing such an interplay as a key factor in the proper metal ion selection by a specific metallo-protein.

Structural Insight of the Full-Length Ros Protein: A Prototype of the Prokaryotic Zinc-Finger Family

Ros/MucR is a widespread family of bacterial zinc-finger (ZF) containing proteins that integrate multiple functions such as virulence, symbiosis and/or cell cycle transcription. NMR solution structure of Ros DNA-binding domain (region 56–142, i.e. Ros87) has been solved by our group and shows that the prokaryotic ZF domain shows interesting structural and functional features that differentiate it from its eukaryotic counterpart as it folds in a significantly larger zinc-binding globular domain. We have recently proposed a novel functional model for this family of proteins suggesting that they may act as H-NS-‘like’ gene silencers. Indeed, the N-terminal region of this family of proteins appears to be responsible for the formation of functional oligomers. No structural characterization of the Ros N-terminal domain (region 1–55) is available to date, mainly because of serious solubility problems of the full-length protein. Here we report the first structural characterization of the N-terminal domain of the prokaryotic ZF family examining by means of MD and NMR the structural preferences of the full-length Ros protein from Agrobacterium tumefaciens.

Brain-derived Neurotrophic Factor and TrkB Levels in Mice that Lack Vesicular Zinc: Effects of Age and Sex

In certain neurons, zinc ions are stored in synaptic vesicles by zinc transporter 3 (ZnT3). Vesicular zinc can then be released synaptically to modulate myriad targets. In vitro evidence indicates that these targets may include brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin receptor kinase B (TrkB). But the effects of vesicular zinc on BDNF and TrkB in the intact brain are unclear. Studies of mice that lack ZnT3 - and, as a result, vesicular zinc - have shown abnormalities in BDNF and TrkB levels, but results have been mixed and are therefore difficult to interpret. This might be caused by differences in the age or sex of mice tested. In the present study, we measured BDNF and TrkB levels in the hippocampus and neocortex, comparing wild type and ZnT3 knockout mice of both sexes at two ages (5 and 12 weeks). We also examined BDNF mRNA expression and protein levels at an intermediate age (8-10 weeks). We found that, regardless of age or sex, BDNF and TrkB protein levels did not differ between wild type and ZnT3 knockout mice. There were sex-specific differences in BDNF protein and mRNA expression, however. BDNF protein levels increased with age in female mice but not in males. And in females, but not males, ZnT3 KO mice exhibited great hippocampal BDNF mRNA expression than wild type mice. We conclude that, at least in naïve mice housed under standard laboratory conditions, elimination of vesicular zinc does not affect BDNF or TrkB protein levels.

The curious case of opossum prion: a physicochemical study on copper(ii) binding to the bis-decarepeat fragment from the protein N-terminal domain

The opossum is a peculiar model of immunity to prion diseases. Here we scrutinised the bis-decarepeat peptide sequence of the opossum prion (Op_bis-deca) protein by a multitechnique approach, with a combined experimental (potentiometry, UV-visible, circular dichroism, NMR and EPR spectroscopy, quartz crystal microbalance with dissipation monitoring and confocal microscopy) and simulation (DFT calculations) approach. Results showed that the macrochelate structures formed upon the binding to Cu(ii) by the analogous bis-octarepeat peptide sequence of human prion (Hu_bis-octa) are not found in the case of Op_bis-deca. At physiological pH and equimolar amount of copper ions, the [CuLH-2] is the major species formed by Op_bis-deca. In this species one imidazole and two amide nitrogen atoms are involved in metal coordination and its stability constant value is lower than that of the analogous species formed by Hu_bis-octa, due to the presence of an extra proline residue. Moreover, the study on the interaction of the peptides or the peptide/Cu(ii) complexes with the model cell membranes made of supported lipid bilayers disclosed different levels of interaction, monitored by the viscoelastic changes of the membranes, which exhibited a similar viscoelastic response at the interface of the two complexes, while in the absence of Cu(ii), the Hu_bis-octa/SLB interface was more viscoelastic than the Op_bis-deca one.

Coordination of a bis-histidine-oligopeptide to Re(i) and Ga(iii) in aqueous solution

We have spectroscopically analyzed the chemistry in aqueous solution and the properties of the histidine-based chelator pHis2 complexed to the fac-[Re(H₂O)₃(CO)₃]⁺ and Ga(iii) to unveil the molecular determinants of their coordination.

Binding of Zn(II) to Tropomyosin Receptor Kinase A in Complex with Its Cognate Nerve Growth Factor: Insights from Molecular Simulation and in Vitro Essays

The binding of the human nerve growth factor (NGF) protein to tropomyosin receptor kinase A (TrkA) is associated with Alzhemeir's development. Owing to the large presence of zinc(II) ions in the synaptic compartments, the zinc ions might be bound to the complex in vivo. Here, we have identified a putative zinc binding site using a combination of computations and experiments. First, we have predicted structural features of the NGF/TrkA complex in an aqueous solution by molecular simulation. Metadynamics free energy calculations suggest that these are very similar to those in the X-ray structure. Here, the "crab" structure of the NGF shape binds tightly to two TrkA "pincers". Transient conformations of the complex include both more extended and more closed conformations. Interestingly, the latter features facial histidines (His60 and His61) among the N-terminal D1-D3 domains, each of which is a potential binding region for biometals. This suggests the presence of a four-His Zn binding site connecting the two chains. To address this issue, we investigated the binding of a D1-D3 domains' peptide mimic by stability constant and nuclear magnetic resonance measurements, complemented by density functional theory-based calculations. Taken together, these establish unambiguously a four-His coordination of the metal ion in the model systems, supporting the presence of our postulated binding site in the NGF/TrkA complex.

Co(II) Coordination in Prokaryotic Zinc Finger Domains as Revealed by UV-Vis Spectroscopy

Co(II) electronic configuration allows its use as a spectroscopic probe in UV-Vis experiments to characterize the metal coordination sphere that is an essential component of the functional structure of zinc-binding proteins and to evaluate the metal ion affinities of these proteins. Here, exploiting the capability of the prokaryotic zinc finger to use different combinations of residues to properly coordinate the structural metal ion, we provide the UV-Vis characterization of Co(II) addition to Ros87 and its mutant Ros87_C27D which bears an unusual CysAspHis₂ coordination sphere. Zinc finger sites containing only one cysteine have been infrequently characterized. We show for the CysAspHis₂ coordination an intense d-d transition band, blue-shifted with respect to the Cys₂His₂ sphere. These data complemented by NMR and CD data demonstrate that the tetrahedral geometry of the metal site is retained also in the case of a single-cysteine coordination sphere.

Copper, differently from zinc, affects the conformation, oligomerization state and activity of bradykinin

The sole role of bradykinin (BK) as an inflammatory mediator is controversial, as recent data also support an anti-inflammatory role for BK in Alzheimer's disease (AD). The involvement of two different receptors (B1R and B2R) could be a key to understand this issue. However, although copper and zinc dyshomeostasis has been demonstrated to be largely involved in the development of AD, a detailed study of the interaction of BK with these two metal ions has never been addressed. In this work, we have applied mass spectrometry, circular dichroism as well as computational methods in order to assess if copper and zinc have the ability to modulate the conformation and oligomerization of BK. In addition, we have correlated the chemical data with the effect of metals on the activity of BK analyzed in cell cultures by biochemical procedures. The biochemical analyses on monocyte/macrophage cell culture (THP-1 Cell Line human) in line with the effect of metals on the conformation of BK showed that the presence of copper can affect the signaling cascade mediated by the BK receptors. The results obtained show a further role of metal ions, particularly copper, in the development and outcome of neuroinflammatory diseases. The possible implications in AD are discussed.

The Inorganic Side of NGF: Copper(II) and Zinc(II) Affect the NGF Mimicking Signaling of the N-Terminus Peptides Encompassing the Recognition Domain of TrkA Receptor

The nerve growth factor (NGF) N-terminus peptide, NGF(1–14), and its acetylated form, Ac-NGF(1–14), were investigated to scrutinize the ability of this neurotrophin domain to mimic the whole protein. Theoretical calculations demonstrated that non-covalent forces assist the molecular recognition of TrkA receptor by both peptides. Combined parallel tempering/docking simulations discriminated the effect of the N-terminal acetylation on the recognition of NGF(1–14) by the domain 5 of TrkA (TrkA-D5). Experimental findings demonstrated that both NGF(1–14) and Ac-NGF(1–14) activate TrkA signaling pathways essential for neuronal survival. The NGF-induced TrkA internalization was slightly inhibited in the presence of Cu²⁺ and Zn²⁺ ions, whereas the metal ions elicited the NGF(1–14)-induced internalization of TrkA and no significant differences were found in the weak Ac-NGF(1–14)-induced receptor internalization. The crucial role of the metals was confirmed by experiments with the metal-chelator bathocuproine disulfonic acid, which showed different inhibitory effects in the signaling cascade, due to different metal affinity of NGF, NGF(1–14) and Ac-NGF(1–14). The NGF signaling cascade, activated by the two peptides, induced CREB phosphorylation, but the copper addition further stimulated the Akt, ERK and CREB phosphorylation in the presence of NGF and NGF(1–14) only. A dynamic and quick influx of both peptides into PC12 cells was tracked by live cell imaging with confocal microscopy. A significant role of copper ions was found in the modulation of peptide sub-cellular localization, especially at the nuclear level. Furthermore, a strong copper ionophoric ability of NGF(1–14) was measured. The Ac-NGF(1–14) peptide, which binds copper ions with a lower stability constant than NGF(1–14), exhibited a lower nuclear localization with respect to the total cellular uptake. These findings were correlated to the metal-induced increase of CREB and BDNF expression caused by NGF(1–14) stimulation. In summary, we here validated NGF(1–14) and Ac-NGF(1–14) as first examples of monomer and linear peptides able to activate the NGF-TrkA signaling cascade. Metal ions modulated the activity of both NGF protein and the NGF-mimicking peptides. Such findings demonstrated that NGF(1–14) sequence can reproduce the signal transduction of whole protein, therefore representing a very promising drug candidate for further pre-clinical studies.

Influence of the N-terminus acetylation of Semax, a synthetic analog of ACTH(4-10), on copper(II) and zinc(II) coordination and biological properties

Semax is a heptapeptide (Met-Glu-His-Phe-Pro-Gly-Pro) that encompasses the sequence 4-7 of N-terminal domain of the adrenocorticotropic hormone and a C-terminal Pro-Gly-Pro tripeptide. N-terminal amino group acetylation (Ac-Semax) modulates the chemical and biological properties of parental peptide, modifying the ability of Semax to form complex species with Cu(II) ion. At physiological pH, the main complex species formed by Ac-Semax, [CuLH_-2]^2-, consists in a distorted CuN₃O chromophore with a weak apical interaction of the methionine sulphur. Such a complex differs from the Cu(II)-Semax complex system, which exhibits a CuN₄ chromophore. The reduced ligand field affects the [CuLH_-2]^2- formal redox potential, which is more positive than that of Cu(II)-Semax corresponding species. In the amino-free form, the resulting complex species is redox-stable and unreactive against ascorbic acid, unlike the acetylated form. Semax acetylation did not protect from Cu(II) induced toxicity on a SH-SY5Y neuroblastoma cell line, thus demonstrating the crucial role played by the free NH₂ terminus in the cell protection. Since several brain diseases are associated either to Cu(II) or Zn(II) dyshomeostasis, here we characterized also the complex species formed by Zn(II) with Semax and Ac-Semax. Both peptides were able to form Zn(II) complex species with comparable strength. Confocal microscopy imaging confirmed that peptide group acetylation does not affect the Zn(II) influx in neuroblastoma cells. Moreover, a punctuate distribution of Zn(II) within the cells suggests a preferred subcellular localization that might explain the zinc toxic effect. A future perspective can be the use of Ac-Semax as ionophore in antibody drug conjugates to produce a dysmetallostasis in tumor cells.

The prokaryotic zinc-finger: structure, function and comparison with the eukaryotic counterpart

Classical zinc finger (ZF) domains were thought to be confined to the eukaryotic kingdom until the transcriptional regulator Ros protein was identified in Agrobacterium tumefaciens. The Ros Cys2 His2 ZF binds DNA in a peculiar mode and folds in a domain significantly larger than its eukaryotic counterpart consisting of 58 amino acids (the 9-66 region) arranged in a βββαα topology, and stabilized by a conserved, extensive, 15-residue hydrophobic core. The prokaryotic ZF domain, then, shows some intriguing new features that make it interestingly different from its eukaryotic counterpart. This review will focus on the prokaryotic ZFs, summarizing and discussing differences and analogies with the eukaryotic domains and providing important insights into their structure/function relationships.

Homeostatic regulation of KCC2 activity by the zinc receptor mZnR/GPR39 during seizures

The aim of this study was to investigate the role of the synaptic metabotropic zinc receptor mZnR/GPR39 in physiological adaptation to epileptic seizures. We previously demonstrated that synaptic activation of mZnR/GPR39 enhances inhibitory drive in the hippocampus by upregulating neuronal K(+)/Cl(-) co-transporter 2 (KCC2) activity. Here, we first show that mZnR/GPR39 knockout (KO) adult mice have dramatically enhanced susceptibility to seizures triggered by a single intraperitoneal injection of kainic acid, when compared to wild type (WT) littermates. Kainate also substantially enhances seizure-associated gamma oscillatory activity in juvenile mZnR/GPR39 KO hippocampal slices, a phenomenon that can be reproduced in WT tissue by extracellular Zn(2+) chelation. Importantly, kainate-induced synaptic Zn(2+) release enhances surface expression and transport activity of KCC2 in WT, but not mZnR/GPR39 KO hippocampal neurons. Kainate-dependent upregulation of KCC2 requires mZnR/GPR39 activation of the Gαq/phospholipase C/extracellular regulated kinase (ERK1/2) signaling cascade. We suggest that mZnR/GPR39-dependent upregulation of KCC2 activity provides homeostatic adaptation to an excitotoxic stimulus by increasing inhibition. As such, mZnR/GPR39 may provide a novel pharmacological target for dampening epileptic seizure activity.