K+ CHANNEL MODEL FOR TRINUCLEOTIDE-EXPANSION DISEASES

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Several human hereditary neurological diseases are caused by expanded CAG repeats although the pathophysiological mechanism remains uncertain. Longer CAG alleles have also been reported to be over-represented in patients with bipolar disorder and schizophrenia, but the defective gene(s) remain unidentified. We isolated a human gene encoding a calcium-activated potassium channel (hSKCa3), found in neurons and containing a novel CAG repeat. Encoding a polyglutamine repeat near the amino terminus, this CAG repeat is highly polymorphic in normals, and long alleles are over-represented in schizophrenia and bipolar disorder. We now propose to combine the strengths of the four principal investigators in molecular biology, human genetics, neuroanatomy, biochemistry, and electrophysiology, to develop a detailed biophysical and pharmacological "fingerprint" of this channel. Using a chimeric strategy between hKCa3 and its "repeat-free" relative, hKCa4, coupled with site-specific mutagenesis, we will define functional domains within these proteins, and determine the effects of longer polyglutamine repeats on channel function. In-situ hybridization studies on human brains, from controls and patients with schizophrenia, will ascertain the neuronal distribution of hKCa3 in relation to neurotransmitter receptors and other channels, and potentially pinpoint key anatomical areas that might be implicated in schizophrenia. By defining the intron/exon organization of this gene, we will be able to initiate screening studies to identify point mutations in hKCa3 that might be associated with schizophrenia. We will also define the precise location of this gene with respect to other genetic markers for schizophrenia. The identification of the native promoter for hKCa3 will set the stage for the generation of transgenic mice that over-express hKCa3 with long polyglutamine repeats in the relevant regions of the brain; such mice might exhibit altered behavior. These experiments provide the framework for understanding the role of polyglutamine repeats in a protein of known function. The long term goal of these studies is to understand the role of hKCa3 in the pathogenesis of schizophrenia, and to develop specific modulators of this channel for potential use in the therapy of this debilitating neuropsychiatric disorder.