Transcript-Specific Associations of SLC12A5 (KCC2) in Human Prefrontal Cortex with Development, Schizophrenia, and Affective Disorders

Abstract

The neuron-specific K ϩ -Cl Ϫ 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 (⌬EXON6, 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 ϭ 0.03) but decreased in patients with major depression (p ϭ 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.

KCC2 rescues functional deficits in human neurons derived from patients with Rett syndrome

“…A disruption in KCC2 mRNA level has been reported in patients with schizophrenia (27,28). Difference in the expression levels of specific KCC2 transcripts has been linked to schizophrenia and affective disorders (38). We have previously discovered a significant decrease of KCC2 expression induced by a neuroligin 2 mutation found in patients with schizophrenia (39,40), suggesting a potential role of KCC2 in the pathogenesis of schizophrenia.…”

Cation-chloride cotransporters in neuronal development, plasticity and disease

“…The cell adhesion molecule neuroligin 2 (NLGN2) 217,218 appears to maintain dendritic spines by promoting KCC2 expression 71 . Alterations in the regulation of NLGN2 and/ or KCC2 may turn out to be relevant in developmental neuropsychiatric disorders, such as autism and schizophrenia 37–39,219 . Whether the recently discovered interactions between KCC2 and the kainate-type glutamate receptor (KAR) auxiliary subunit NETO2 (REF.…”

Neurodevelopment, GABA System Dysfunction, and Schizophrenia

“…As GABA is excitatory early in development and inhibitory after birth, changes in GABA system function should have opposing consequences on activity-dependent gene expression depending on when they occur. Recent studies showing that NKCC1 and KCC2, the ion transporters responsible for the excitatory/inhibitory switch, are dysregulated in schizophrenia, further complicating the possible interpretational framework Hyde et al, 2011;Tao et al, 2012). More studies are needed to determine how the specific developmental timing of environmental insults interact with genetic susceptibility, and we need a better understanding how altered chloride transporter expression in the adult brain impacts schizophrenia-relevant behaviors.…”