Expression of GABA signaling molecules KCC2, NKCC1, and GAD1 in cortical development and schizophrenia

Section on Neuropathology, Clinical Brain Disorders Branch, Genes, Cognition and Psychosis Program, Intramural Research Program, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland 20892, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 07/2011; 31(30):11088-95. DOI: 10.1523/JNEUROSCI.1234-11.2011
Source: PubMed


GABA signaling molecules are critical for both human brain development and the pathophysiology of schizophrenia. We examined the expression of transcripts derived from three genes related to GABA signaling [GAD1 (GAD67 and GAD25), SLC12A2 (NKCC1), and SLC12A5 (KCC2)] in the prefrontal cortex (PFC) and hippocampal formation of a large cohort of nonpsychiatric control human brains (n = 240) across the lifespan (from fetal week 14 to 80 years) and in patients with schizophrenia (n = 30-31), using quantitative RT-PCR. We also examined whether a schizophrenia risk-associated promoter SNP in GAD1 (rs3749034) is related to expression of these transcripts. Our studies revealed that development and maturation of both the PFC and hippocampal formation are characterized by progressive switches in expression from GAD25 to GAD67 and from NKCC1 to KCC2. Previous studies have demonstrated that the former leads to GABA synthesis, and the latter leads to switching from excitatory to inhibitory neurotransmission. In the hippocampal formation, GAD25/GAD67 and NKCC1/KCC2 ratios are increased in patients with schizophrenia, reflecting a potentially immature GABA physiology. Remarkably, GAD25/GAD67 and NKCC1/KCC2 expression ratios are associated with rs3749034 genotype, with risk alleles again predicting a relatively less mature pattern. These findings suggest that abnormalities in GABA signaling critical to brain development contribute to genetic risk for schizophrenia.

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    • "A point worth of emphasis is that CCCs are gaining an increasing amount of interest as potential drug targets (Gagnon et al. 2013; Töllner et al. 2014), especially with regard to the design of novel anticonvulsant drugs (Löscher et al. 2013a, 2013b). In this context, our data on the fetal onset of KCC2 expression in human supraspinal brain structures (see also Vanhatalo et al. 2005; Bayatti et al. 2008; Robinson et al. 2010; Hyde et al. 2011) refute the view (cf. Dzhala et al. 2005) that the poor efficacy of anticonvulsants in the term human neonate is attributable to a lack of KCC2. "
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    ABSTRACT: Work on rodents demonstrated that steep upregulation of KCC2, a neuron-specific Cl(-) extruder of cation-chloride cotransporter (CCC) family, commences in supraspinal structures at around birth, leading to establishment of hyperpolarizing GABAergic responses. We describe spatiotemporal expression profiles of the entire CCC family in human brain. KCC2 mRNA was observed already at 10th postconceptional week (PCW) in amygdala, cerebellum, and thalamus. KCC2-immunoreactive (KCC2-ir) neurons were abundant in subplate at 18 PCW. By 25 PCW, numerous subplate and cortical plate neurons became KCC2-ir. The mRNA expression profiles of α- and β-isoforms of Na-K ATPase, which fuels cation-chloride cotransport, as well of tropomyosin receptor kinase B (TrkB), which promotes developmental upregulation of KCC2, were consistent with data from studies on rodents about their interactions with KCC2. Thus, in human brain, expression of KCC2 and its functionally associated proteins begins in early fetal period. Our work facilitates translation of results on CCC functions from animal studies to human and refutes the view that poor efficacy of anticonvulsants in the term human neonate is attributable to the lack of KCC2. We propose that perinatally low threshold for activation of Ca(2+)-dependent protease calpain renders neonates susceptible to downregulation of KCC2 by traumatic events, such as perinatal hypoxia ischemia.
    Cerebral Cortex 10/2015; DOI:10.1093/cercor/bhv218 · 8.67 Impact Factor
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    • "Alterations observed include a shift from facilitative towards repressive chromatin-associated histone modifications, and changes in DNA methylation signatures, often in conjunction with altered GAD1 expression in the prefrontal cortex (PFC) of the affected SCZ cases (Huang and Akbarian, 2007; Huang et al., 2007; Tang et al., 2011; Grayson and Guidotti, 2013). It is also noteworthy that common polymorphisms in the proximal GAD1 promoter conferred genetic risk for SCZ, impaired working memory performance and accelerated loss of gray matter (Addington et al., 2005; Straub et al., 2007), possibly in conjunction with altered expression of the cation chloride co-transporters NKCC1/KCC2, two key regulators of postsynaptic GABA A receptor-mediated currents (Hyde et al., 2011). These findings, taken together, would suggest that the genetic and epigenetic architecture of the GAD1 promoter is a potential factor for the gene's dysregulated expression in at least some cases with SCZ. "
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    ABSTRACT: Expression of GAD1 GABA synthesis enzyme is highly regulated by neuronal activity and reaches mature levels in the prefrontal cortex not before adolescence. A significant portion of cases diagnosed with schizophrenia show deficits in GAD1 RNA and protein levels in multiple areas of adult cerebral cortex, possibly reflecting molecular or cellular defects in subtypes of GABAergic interneurons essential for network synchronization and cognition. Here, we review 20 years of progress towards a better understanding of disease-related regulation of GAD1 gene expression. For example, deficits in cortical GAD1 RNA in some cases of schizophrenia are associated with changes in the epigenetic architecture of the promoter, affecting DNA methylation patterns and nucleosomal histone modifications. These localized chromatin defects at the 5′ end of GAD1 are superimposed by disordered locus-specific chromosomal conformations, including weakening of long-range promoter-enhancer loopings and physical disconnection of GAD1 core promoter sequences from cis-regulatory elements positioned 50 kilobases further upstream. Studies on the 3-dimensional architecture of the GAD1 locus in neurons, including developmentally regulated higher order chromatin compromised by the disease process, together with exploration of locus-specific epigenetic interventions in animal models, could pave the way for future treatments of psychosis and schizophrenia.
    Schizophrenia Research 10/2014; DOI:10.1016/j.schres.2014.10.020 · 3.92 Impact Factor
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    • "Using quantitative PCR and laser microdissection to collect RNA from individual Layer 3 PCs of monkey DLPFC, we found that the levels of KCC2 and NKCC1 mRNA were constant during postnatal development (Supplementary Fig. 6A). These data, together with previous studies (Hyde et al. 2011), suggest that in human and monkey DLPFC the hyperpolarizing shift in V in occurs before birth. However, mRNA levels do not give information on protein expression, and, indeed, KCC2 protein levels in human neocortex increase during postnatal development (Dzhala et al. 2005). "
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    ABSTRACT: Development of inhibition onto pyramidal cells may be crucial for the emergence of cortical network activity, including gamma oscillations. In primate dorsolateral prefrontal cortex (DLPFC), inhibitory synaptogenesis starts in utero and inhibitory synapse density reaches adult levels before birth. However, in DLPFC, the expression levels of γ-aminobutyric acid (GABA) synapse-related gene products changes markedly during development until young adult age, suggesting a highly protracted maturation of GABA synapse function. Therefore, we examined the development of GABA synapses by recording GABAAR-mediated inhibitory postsynaptic currents (GABAAR-IPSCs) from pyramidal cells in the DLPFC of neonatal, prepubertal, peripubertal, and adult macaque monkeys. We found that the decay of GABAAR-IPSCs, possibly including those from parvalbumin-positive GABA neurons, shortened by prepubertal age, while their amplitude increased until the peripubertal period. Interestingly, both GABAAR-mediated quantal response size, estimated by miniature GABAAR-IPSCs, and the density of GABAAR synaptic appositions, measured with immunofluorescence microscopy, were stable with age. Simulations in a computational model network with constant GABA synapse density showed that the developmental changes in GABAAR-IPSC properties had a significant impact on oscillatory activity and predicted that, whereas DLPFC circuits can generate gamma frequency oscillations by prepubertal age, mature levels of gamma band power are attained at late stages of development.
    Cerebral Cortex 06/2014; 25(11). DOI:10.1093/cercor/bhu122 · 8.67 Impact Factor
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