Alterations in the expression of neuronal chloride transporters may contribute to schizophrenia

Spatiotemporal expression patterns of genes coding for plasmalemmal chloride transporters and channels in neurological diseases

Neuronal voltage changes which are dependent on chloride transporters and channels are involved in forming neural functions during early development and maintaining their stability until adulthood. The intracellular chloride concentration maintains a steady state, which is delicately regulated by various genes coding for chloride transporters and channels (GClTC) on the plasmalemma; however, the synergistic effect of these genes in central nervous system disorders remains unclear. In this study, we first defined 10 gene clusters with similar temporal expression patterns, and identified 41 GClTC related to brain developmental process. Then, we found 4 clusters containing 22 GClTC were enriched for the neuronal functions. The GClTC from different clusters presented distinct cell type preferences and anatomical heterogeneity. We also observed strong correlations between clustered genes and diseases, most of which were nervous system disorders. Finally, we found that one of the most well-known GClTC, SLC12A2, had a more profound effect on glial cell-related diseases than on neuron-related diseases, which was in accordance with our observation that SLC12A2 was mainly expressed in oligodendrocytes during brain development. Our findings provide a more comprehensive understanding of the temporal and spatial expression characteristics of GClTC, which can help us understand the complex roles of GClTC in the development of the healthy human brain and the etiology of brain disorders.

NKCC1 to KCC2 mRNA Ratio in Schizophrenia and Its Psychopathology: a Case-Control Study

Schizophrenia (SCZ) is a debilitating, destructive, and chronic mental disorder and affects approximately one percent of the human population. Diagnosis in psychiatry is based on the patient's descriptions of his/her symptoms, interviewer's observations, history of disorder over time, and response to treatment. All of these data measure phenotype-based functions. But it appears that accurate diagnosis of such a complex disorder must be based on valid and reliable factors. In the present study, gene selection was based on the possible role of γ-aminobutyric acid (GABA) in psychopathology of SCZ and expression in blood. We evaluated the association of Na⁺-K⁺-Cl^- co-transporter 1 (NKCC1) and K⁺-Cl^- co-transporter 2 (KCC2) genes' messenger ribonucleic acid (mRNA) levels, and also the NKCC1/KCC2 ratio with positive and negative syndrome scale (PANSS) and brief psychiatric rating scale (BPRS) scores in an SCZ group. By using real-time PCR (RT-PCR), the present study is the first attempt to explore levels of NKCC1 and KCC2 expression at mRNA level and their relative expression in human peripheral blood of patients with SCZ. Our results showed that the NKCC1 to KCC2 mRNA ratio is significantly increased (but based on the delta cycle of threshold [∆Ct] is significantly lower) in the total sample of cases rather than controls (p = 0.045) and also higher in male sample cases rather than male controls (p = 0.016). In female samples, we found a trend toward a significant effect between the case and control participants (p = 0.075). We also found statistically significant association between mRNA of NKCC1 and KCC2 genes and NKCC1/KCC2 mRNA ratio with the positive and negative syndrome scale (PANSS) and brief psychiatric rating scale (BPRS) scores.

Dysregulation of GABAergic Signaling in Neurodevelomental Disorders: Targeting Cation-Chloride Co-transporters to Re-establish a Proper E/I Balance

The construction of the brain relies on a series of well-defined genetically and experience- or activity -dependent mechanisms which allow to adapt to the external environment. Disruption of these processes leads to neurological and psychiatric disorders, which in many cases are manifest already early in postnatal life. GABA, the main inhibitory neurotransmitter in the adult brain is one of the major players in the early assembly and formation of neuronal circuits. In the prenatal and immediate postnatal period GABA, acting on GABA_A receptors, depolarizes and excites targeted cells via an outwardly directed flux of chloride. In this way it activates NMDA receptors and voltage-dependent calcium channels contributing, through intracellular calcium rise, to shape neuronal activity and to establish, through the formation of new synapses and elimination of others, adult neuronal circuits. The direction of GABA_A-mediated neurotransmission (depolarizing or hyperpolarizing) depends on the intracellular levels of chloride [Cl⁻]_i, which in turn are maintained by the activity of the cation-chloride importer and exporter KCC2 and NKCC1, respectively. Thus, the premature hyperpolarizing action of GABA or its persistent depolarizing effect beyond the postnatal period, leads to behavioral deficits associated with morphological alterations and an excitatory (E)/inhibitory (I) imbalance in selective brain areas. The aim of this review is to summarize recent data concerning the functional role of GABAergic transmission in building up and refining neuronal circuits early in development and its dysfunction in neurodevelopmental disorders such as Autism Spectrum Disorders (ASDs), schizophrenia and epilepsy. In particular, we focus on novel information concerning the mechanisms by which alterations in cation-chloride co-transporters (CCC) generate behavioral and cognitive impairment in these diseases. We discuss also the possibility to re-establish a proper GABA_A-mediated neurotransmission and excitatory (E)/inhibitory (I) balance within selective brain areas acting on CCC.

Common Pathways for Pain and Depression-Implications for Practice

BACKGROUND

Pain and depression have a high impact on caring for the people who need palliative care, but both of these are neglected compared with the approach for other symptoms encountered by these patients.

AREAS OF UNCERTAINTY

There are few studies in humans that support the existence of common neural circuits between depression and pain that also explore the use of drugs with effects in both conditions. More knowledge is needed about the relationship of these clinical entities that will lead to the optimization of the treatment and improvement of quality of life.

DATA SOURCES

We conducted a search in PubMed to identify relevant articles and reviews that have been published in the last 5 years, concerning the topic of common pathways between depression and pain (2014-April 2019).

THERAPEUTIC ADVANCES

The connections between the 2 clinical entities start at the level of the cortical regions. The hippocampus is the main site of neural changes, modification of the immune system, neuromodulators, neurotransmitters, and signaling pathways implicated in both conditions. Increased levels of peripheral proinflammatory cytokines and neuroinflammatory changes are related to the physiopathology of these entities. Inflammation links depression and pain by altering neural circuits and changes in their common cortical regions. Antidepressants are used to treat depression and chronic, pain but more experimental studies are needed to determine which antidepressant drugs are the most effective in treating the 2 entities.

CONCLUSIONS

Pharmacological and nonpharmacological interventions targeting cortical changes in pain and depression are promising, but more clinical studies are needed to validate their usefulness.

The Link between Depression and Chronic Pain: Neural Mechanisms in the Brain

Chronic pain, as a stress state, is one of the critical factors for determining depression, and their coexistence tends to further aggravate the severity of both disorders. Unfortunately, their association remains unclear, which creates a bottleneck problem for managing chronic pain-induced depression. In recent years, studies have found considerable overlaps between pain- and depression-induced neuroplasticity changes and neurobiological mechanism changes. Such overlaps are vital to facilitating the occurrence and development of chronic pain and chronic pain-induced depression. In this review, we summarized the role of neuroplasticity in the occurrence and development of the two disorders in question and explored individualized application strategies of analgesic drugs and antidepressants that have different pharmacological effects in the treatment of chronic pain-induced depression. Therefore, this review may provide new insights into the understanding of association between chronic pain and depression.

Expanding Spectrum of Sodium Potassium Chloride Co-transporters in the Pathophysiology of Diseases

Sodium potassium chloride co-transporter (NKCC) belongs to cation-dependent chloride co-transporter family, whose activation allows the entry of Na(+), K(+) and 2Cl(-) inside the cell. It acts in concert with K(+) Cl(-) co-transporter (KCC), which extrudes K(+) and Cl(-) ions from cell. NKCC1 is widely distributed throughout the body, while NKCC2 is exclusively present in kidney. Protein kinase A, protein kinase C, Ste20-related proline-alanine-rich kinase, oxidative stress responsive kinases, With No K=lysine kinase and protein phosphatase type 1 control the phosphorylation/dephosphorylation of key threonine residues of in regulatory domain of NKCC1. The selective inhibitors of NKCC1 including bumetanide and furosemide are conventionally employed as diuretics. However, recent studies have indicated that NKCC1 may be involved in the pathophysiology of anxiety, cerebral ischemia, epilepsy, neuropathic pain, fragile X syndrome, autism and schizophrenia. The inhibitors of NKCC1 are shown to produce anxiolytic effects; attenuate cerebral ischemia-induced neuronal injury; produce antiepileptic effects and attenuate neuropathic pain. In the early developing brain, GABAA activation primarily produces excitatory actions due to high NKCC1/KCC2 ratio. However, as the development progresses, the ratio of NKCC1/KCC2 ratio reverses and there is switch in the polarity of GABAA actions and latter acquires the inhibitory actions. The recapitulation of developmental-like state during pathological state may be associated with increase in the expression and functioning of NKCC1, which decreases the strength of inhibitory GABAergic neurotransmission. The present review describes the expanding role and mechanism of NKCC1 in the pathophysiology of different diseases.

Failure of the Nemo Trial: Bumetanide Is a Promising Agent to Treat Many Brain Disorders but Not Newborn Seizures

The diuretic bumetanide failed to treat acute seizures due to hypoxic ischemic encephalopathy (HIE) in newborn babies and was associated with hearing loss (NEMO trial, Pressler et al., 2015). On the other hand, clinical and experimental observations suggest that the diuretic might provide novel therapy for many brain disorders including Autism Spectrum Disorders (ASD), schizophrenia, Rett syndrome, and Parkinson disease. Here, we discuss the differences between the pathophysiology of severe recurrent seizures in the neonates and neurological and psychiatric disorders stressing the uniqueness of severe seizures in newborn in comparison to other disorders.

Spines slow down dendritic chloride diffusion and affect short-term ionic plasticity of GABAergic inhibition

Cl⁻ plays a crucial role in neuronal function and synaptic inhibition. However, the impact of neuronal morphology on the diffusion and redistribution of intracellular Cl⁻ is not well understood. The role of spines in Cl⁻ diffusion along dendritic trees has not been addressed so far. Because measuring fast and spatially restricted Cl⁻ changes within dendrites is not yet technically possible, we used computational approaches to predict the effects of spines on Cl⁻ dynamics in morphologically complex dendrites. In all morphologies tested, including dendrites imaged by super-resolution STED microscopy in live brain tissue, spines slowed down longitudinal Cl⁻ diffusion along dendrites. This effect was robust and could be observed in both deterministic as well as stochastic simulations. Cl⁻ extrusion altered Cl⁻ diffusion to a much lesser extent than the presence of spines. The spine-dependent slowing of Cl⁻ diffusion affected the amount and spatial spread of changes in the GABA reversal potential thereby altering homosynaptic as well as heterosynaptic short-term ionic plasticity at GABAergic synapses in dendrites. Altogether, our results suggest a fundamental role of dendritic spines in shaping Cl⁻ diffusion, which could be of relevance in the context of pathological conditions where spine densities and neural excitability are perturbed.

Mild KCC2 Hypofunction Causes Inconspicuous Chloride Dysregulation that Degrades Neural Coding

Disinhibition caused by Cl⁻ dysregulation is implicated in several neurological disorders. This form of disinhibition, which stems primarily from impaired Cl⁻ extrusion through the co-transporter KCC2, is typically identified by a depolarizing shift in GABA reversal potential (E_GABA). Here we show, using computer simulations, that intracellular [Cl⁻] exhibits exaggerated fluctuations during transient Cl⁻ loads and recovers more slowly to baseline when KCC2 level is even modestly reduced. Using information theory and signal detection theory, we show that increased Cl⁻ lability and settling time degrade neural coding. Importantly, these deleterious effects manifest after less KCC2 reduction than needed to produce the gross changes in E_GABA required for detection by most experiments, which assess KCC2 function under weak Cl⁻ load conditions. By demonstrating the existence and functional consequences of “occult” Cl⁻ dysregulation, these results suggest that modest KCC2 hypofunction plays a greater role in neurological disorders than previously believed.

[The relationship between schizophrenia and epilepsy: the history and current state of the problem]

The review deals with the background and current state of the relationship between schizophrenia and epilepsy. The author presents results of recent epidemiological, neuropsychological, neurophysiological and genetic studies, indicating that these diseases may be different clinical variants of a common etiologic process (neurodevelopmental brain abnormalities), while epilepsy with chronic psychotic symptoms can be considered as an experimental model of schizophrenia pathogenesis.

Kinase-KCC2 coupling: Cl- rheostasis, disease susceptibility, therapeutic target

The intracellular concentration of Cl(-) ([Cl(-)]i) in neurons is a highly regulated variable that is established and modulated by the finely tuned activity of the KCC2 cotransporter. Despite the importance of KCC2 for neurophysiology and its role in multiple neuropsychiatric diseases, our knowledge of the transporter's regulatory mechanisms is incomplete. Recent studies suggest that the phosphorylation state of KCC2 at specific residues in its cytoplasmic COOH terminus, such as Ser940 and Thr906/Thr1007, encodes discrete levels of transporter activity that elicit graded changes in neuronal Cl(-) extrusion to modulate the strength of synaptic inhibition via Cl(-)-permeable GABAA receptors. In this review, we propose that the functional and physical coupling of KCC2 to Cl(-)-sensitive kinase(s), such as the WNK1-SPAK kinase complex, constitutes a molecular "rheostat" that regulates [Cl(-)]i and thereby influences the functional plasticity of GABA. The rapid reversibility of (de)phosphorylation facilitates regulatory precision, and multisite phosphorylation allows for the control of KCC2 activity by different inputs via distinct or partially overlapping upstream signaling cascades that may become more or less important depending on the physiological context. While this adaptation mechanism is highly suited to maintaining homeostasis, its adjustable set points may render it vulnerable to perturbation and dysregulation. Finally, we suggest that pharmacological modulation of this kinase-KCC2 rheostat might be a particularly efficacious strategy to enhance Cl(-) extrusion and therapeutically restore GABA inhibition.

Effects of SPAK knockout on sensorimotor gating, novelty exploration, and brain area-dependent expressions of NKCC1 and KCC2 in a mouse model of schizophrenia

SPAK (Sterile 20/SPS1-related proline/alanine-rich kinase) is a protein kinase belonging to the mitogen-activated protein kinase (MAPK) superfamily that has been found to be extensively distributed across the body. The SPAK downstream substrates NKCC1 and KCC2 in the central nervous system are important in the interpretation of developmental mental disorders. The present study aimed to clarify the role of SPAK-NKCC1/KCC2 using a rodent schizophrenia-like model. The mouse paradigm of isolation rearing (IR) was employed, as it simulates the sensorimotor gating abnormalities of schizophrenia. SPAK transgenic mice were used and were divided into four groups: social-wild type, social-SPAK(-/-), isolation-wild type, and isolation-SPAK(-/-). The prepulse inhibition (PPI) test and the novel object recognition test (NORT) were used to measure schizophrenia-associated dysfunctions in gating ability and the novelty recognition, respectively. Finally, the protein expressions of NKCC1/KCC2 in the prefrontal cortex and hippocampus were detected to determine correlations with the behavioral data. Our results demonstrated that SPAK-null mice had superior PPI and novelty recognition relative to wild type controls, with a concomitant increase in KCC2 in the prefrontal cortex. IR disrupted PPI and NORT performances with an associated increase in KCC2. Furthermore, rearing environment and gene manipulation had mutually interactive effects, as the IR-induced effects on PPI and NORT were reversed by SPAK knockout, and the increase in KCC2 and the decreased in the NKCC1/KCC2 ratio in the prefrontal cortex induced by SPAK knockout were reversed by IR. Our data supported the gene-environment hypothesis and demonstrated the potential value of SPAK manipulation in future schizophrenia studies.

Neuroinflammation and comorbidity of pain and depression

Comorbid depression and chronic pain are highly prevalent in individuals suffering from physical illness. Here, we critically examine the possibility that inflammation is the common mediator of this comorbidity, and we explore the implications of this hypothesis. Inflammation signals the brain to induce sickness responses that include increased pain and negative affect. This is a typical and adaptive response to acute inflammation. However, chronic inflammation induces a transition from these typical sickness behaviors into depression and chronic pain. Several mechanisms can account for the high comorbidity of pain and depression that stem from the precipitating inflammation in physically ill patients. These mechanisms include direct effects of cytokines on the neuronal environment or indirect effects via downregulation of G protein-coupled receptor kinase 2, activation of the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase that generates neurotropic kynurenine metabolites, increased brain extracellular glutamate, and the switch of GABAergic neurotransmission from inhibition to excitation. Despite the existence of many neuroimmune candidate mechanisms for the co-occurrence of depression and chronic pain, little work has been devoted so far to critically assess their mediating role in these comorbid symptoms. Understanding neuroimmune mechanisms that underlie depression and pain comorbidity may yield effective pharmaceutical targets that can treat both conditions simultaneously beyond traditional antidepressants and analgesics.

General anaesthetics do not impair developmental expression of the KCC2 potassium-chloride cotransporter in neonatal rats during the brain growth spurt

BACKGROUND

The developmental transition from depolarizing to hyperpolarizing γ-aminobutyric acid-mediated neurotransmission is primarily mediated by an increase in the amount of the potassium-chloride cotransporter KCC2 during early postnatal life. However, it is not known whether early neuronal activity plays a modulatory role in the expression of total KCC2 mRNA and protein in the immature brain. As general anaesthetics are powerful modulators of neuronal activity, the purpose of this study was to explore how these drugs affect KCC2 expression during the brain growth spurt.

METHODS

Wistar rat pups were exposed to either a single dose or 6 h of midazolam, propofol, or ketamine anaesthesia at postnatal days 0, 5, 10, or 15. KCC2 expression was assessed using immunoblotting, immunohistochemistry, or quantitative polymerase chain reaction analysis up to 3 days post-exposure in the medial prefrontal cortex.

RESULTS

There was a progressive and steep increase in the expression of KCC2 between birth and 2 weeks of age. Exposure to midazolam, propofol, or ketamine up to 6 h at any investigated stages of the brain growth spurt did not influence the expression of this cotransporter protein.

CONCLUSION

I.V. general anaesthetics do not seem to influence developmental expression of KCC2 during the brain growth spurt.

Evidence for shared susceptibility to epilepsy and psychosis: a population-based family study

BACKGROUND

There is emerging evidence of an etiological overlap between a range of neurodevelopmental disorders, including schizophrenia and epilepsy. Here we investigate shared familial vulnerability to psychotic illness and epilepsy in a family-based study.

METHODS

The study population consisted of parents and their children born in Helsinki between 1947 and 1990. The Finnish Hospital Discharge Register was used to determine psychiatric and neurological outcomes in adulthood for all offspring. Parental history of psychosis and epilepsy was determined by linking the Hospital Discharge Register and the Finnish Population Register.

RESULTS

Our total sample comprised 9653 families and 23,404 offspring. Individuals with epilepsy had a 5.5-fold increase in the risk of having a broadly defined psychotic disorder, an almost 8.5-fold increase in the risk of having schizophrenia, and a 6.3-fold increase in the risk of having bipolar disorder. There was strong evidence of clustering of the association between epilepsy and psychosis within families. Individuals with a parental history of epilepsy had a 2-fold increase in the risk of developing psychosis, compared with individuals without a parental history of epilepsy. Individuals with a parental history of psychosis had, reciprocally, a 2.7-fold increase in the risk of having a diagnosis of generalized epilepsy, compared with individuals without a parental history of psychosis. Post hoc analyses showed that these associations were not driven by the comorbidity of epilepsy and psychosis in the parents.

CONCLUSIONS

These findings support recent evidence of overlapping etiological factors between epilepsy and schizophrenia, especially recent evidence of a genetic overlap between these disorders.

Transcript-specific associations of SLC12A5 (KCC2) in human prefrontal cortex with development, schizophrenia, and affective disorders

The neuron-specific K(+)-Cl(-) cotransporter SLC12A5, also known as KCC2, helps mediate the electrophysiological effects of GABA. The pattern of KCC2 expression during early brain development suggests that its upregulation drives the postsynaptic switch of GABA from excitation to inhibition. We previously found decreased expression of full-length KCC2 in the postmortem hippocampus of patients with schizophrenia, but not in the dorsolateral prefrontal cortex (DLPFC). Using PCR and rapid amplification of cDNA ends, we discovered several previously unrecognized alternative KCC2 transcripts in both human adult and fetal brain in addition to the previously identified full-length (NM_020708.3) and truncated (AK098371) transcripts. We measured the expression levels of four relatively abundant truncated splice variants, including three novel transcripts (ΔEXON6, EXON2B, and EXON6B) and one previously described transcript (AK098371), in a large human cohort of nonpsychiatric controls across the lifespan, and in patients with schizophrenia and affective disorders. In SH-SY5Y cell lines, these transcripts were translated into proteins and expressed at their predicted sizes. Expression of the EXON6B transcript is increased in the DLPFC of patients with schizophrenia (p = 0.03) but decreased in patients with major depression (p = 0.04). The expression of AK098371 is associated with a GAD1 single nucleotide polymorphism (rs3749034) that previously has been associated with GAD67 expression and risk for schizophrenia. Our data confirm the developmental regulation of KCC2 expression, and provide evidence that KCC2 transcripts are differentially expressed in schizophrenia and affective disorders. Alternate transcripts from KCC2 may participate in the abnormal GABA signaling in the DLPFC associated with schizophrenia.

Association study of the KCNJ3 gene as a susceptibility candidate for schizophrenia in the Chinese population

We recently reported the results of a genome-wide association study (GWAS) of schizophrenia in the Japanese population. In that study, a single nucleotide polymorphism (SNP) (rs3106653) in the KCNJ3 (potassium inwardly rectifying channel, subfamily J, member 3) gene located at 2q24.1 showed association with schizophrenia in two independent sample sets. KCNJ3, also termed GIRK1 or Kir3.1, is a member of the G protein-activated inwardly rectifying K(+) channel (GIRK) group. GIRKs are widely distributed in the brain and play an important role in regulating neural excitability through the activation of various G protein-coupled receptors. In this study, we set out to examine this association using a different population. We first performed a gene-centric association study of the KCNJ3 gene, by genotyping 38 tagSNPs in the Chinese population. We detected nine SNPs that displayed significant association with schizophrenia (lowest P = 0.0016 for rs3106658, Global significance = 0.036). The initial marker SNP (rs3106653) examined in our prior GWAS in the Japanese population also showed nominally significant association in the Chinese population (P = 0.028). Next, we analyzed transcript levels in the dorsolateral prefrontal cortex of postmortem brains from patients with schizophrenia and bipolar disorder and from healthy controls, using real-time quantitative RT-PCR. We found significantly lower KCNJ3 expression in postmortem brains from schizophrenic and bipolar patients compared with controls. These data suggest that the KCNJ3 gene is genetically associated with schizophrenia in Asian populations and add further evidence to the "channelopathy theory of psychiatric illnesses".

Synaptic conversion of chloride-dependent synapses in spinal nociceptive circuits: roles in neuropathic pain

Electrophysiological conversion of chloride-dependent synapses from inhibitory to excitatory function, as a result of aberrant neuronal chloride homeostasis, is a known mechanism for the genesis of neuropathic pain. This paper examines theoretically how this type of synaptic conversion can disrupt circuit logic in spinal nociceptive circuits. First, a mathematical scaling factor is developed to represent local aberration in chloride electrochemical driving potential. Using this mathematical scaling factor, electrophysiological symbols are developed to represent the magnitude of synaptic conversion within nociceptive circuits. When inserted into a nociceptive circuit diagram, these symbols assist in understanding the generation of neuropathic pain associated with the collapse of transmembrane chloride gradients. A more generalized scaling factor is also derived to represent the interplay of chloride and bicarbonate driving potentials on the function of GABAergic and glycinergic synapses. These mathematical and symbolic representations of synaptic conversion help illustrate the critical role that anion driving potentials play in the transduction of pain. Using these representations, we discuss ramifications of glial-mediated synaptic conversion in the genesis, and treatment, of neuropathic pain.