Elsevier

Neuroscience

Volume 120, Issue 3, 1 September 2003, Pages 695-704
Neuroscience

Biochemical analysis of GABAA receptor subunits α1, α5, β1, β2 in the hippocampus of patients with Alzheimer's disease neuropathology

https://doi.org/10.1016/S0306-4522(03)00030-7Get rights and content

Abstract

Alzheimer's disease (AD) is characterized by selective vulnerability of specific neuronal populations within particular brain regions. For example, hippocampal glutamatergic cell populations within the CA1/subicular pyramidal cell fields have been found to be particularly vulnerable early in AD progression. In contrast, hippocampal GABA-ergic neurons and receptors appear resistant to neurodegeneration. Despite relative sparing of GABAA receptors in AD, it is possible that the specific subunit composition of these receptors may undergo alterations with disease progression. In order to address this issue, we employed quantitative Western blot analysis to examine protein levels of GABAA receptor subunits α1, α5, β1, β2 in the hippocampus of subjects displaying increasing severity of AD neuropathology. Subjects were categorized into three groups based upon Braak staging pathologic criteria: pathologically mild (stages I/II, n=9); moderate (stages III/IV, n=8); and severe (stages V/VI, n=7). Across all subject groups, levels of subunit protein were heterogeneously distributed throughout the five hippocampal subregions analyzed (subiculum, CA1–3, dentate gyrus). Statistical analyses revealed differential preservation of GABAA receptor subunits in AD. In particular, α1, β1, and β2 displayed little difference in protein levels among pathologically mild, moderate, and severe subject groups. In contrast, although relatively modest, protein levels of the α5 subunit were significantly reduced between subjects with severe neuropathology compared with pathologically mild subjects (13.5% reduction). Collectively, our data provide evidence for heterogeneous distribution and relative sparing of GABAA receptor subunits in the hippocampus of AD patients.

Section snippets

Subjects

Postmortem midregion hippocampal tissue was obtained from 23 elderly subjects (mean age 75±9.3 years; mean postmortem interval 7.13 h) with increasing neuropathologic severity of AD (Table 1). All subjects had a clinical diagnosis of AD, as assessed by a longitudinal research program maintained by the University of Pittsburgh Alzheimer's Disease Research Center. All patients underwent periodic neuropsychological and neurological evaluation. As described previously (in Mizukami et al., 1997,

Quantitative analyses

As specified in the Experimental Procedures section, extracts from membrane punches 2, 4, 6, 8, and 9 were separated by SDS-PAGE and probed with GABAA receptor subunit antibodies. An example of the electrophoretic activity of the four subunits analyzed and the standard curve of bovine cortex for punch two is provided in Fig. 2. The α5 antibody yielded only a single target band (approximately 52 kDa). As shown in the figure, antibodies against the α1, β1, and β2 subunits often yielded a

Discussion

To our knowledge, this study represents the first biochemical assessment of GABAA receptors in the AD brain. We employed quantitative Western blot analysis to examine the protein levels of GABAA receptor subunits α1, α5, β1, and β2 in the AD hippocampus. These receptor subunits were chosen because of their prevalence in the human and rodent hippocampus De Blas et al., 1988, Olsen and Tobin, 1990, Wisden et al., 1992, Moreno et al., 1994, Fritschy and Mohler, 1995, Miralles et al., 1999. In

Acknowledgements

Grant sponsor: NIH AG-15472 and AG-13398 to D. M. Armstrong and A. L. De Blas, respectively.

References (37)

  • E.A. Barnard et al.

    International Union of PharmacologyXV. Subtypes of GABAA receptor: classification on the basis of subunit structure and receptor function

    Pharmacol Rev

    (1998)
  • T.P. Bonnert et al.

    θ, A novel γ-aminobutyric acid type A receptor subunit

    Proc Natl Acad Sci

    (1999)
  • H. Braak et al.

    Neuropathological staging of Alzheimer-related changes

    Acta Neuropath

    (1991)
  • A.L. De Blas et al.

    Localization of the GABAA receptor in the rat brain with a monoclonal antibody to the 57,000 Mr peptide of the GABAA receptor/benzodiazepine receptor/Cl− channel complex

    J Neurosci

    (1988)
  • A.L. De Blas

    Brain GABAA receptors studied with subunit specific antibodies

    Mol Neurobiol

    (1996)
  • M. Ewert et al.

    Subunit specificity and epitope characterization of monoclonal antibodies directed against the GABAA/benzodiazepine receptor

    J Cell Biol

    (1990)
  • J.M. Fritschy et al.

    GABAA receptor heterogeneity in the adult rat braindifferential regional and cellular distribution of seven major subunits

    J Comp Neurol

    (1995)
  • J.T. Greenamyre et al.

    Dementia of the Alzheimer typechanges in hippocampal L-[3H]glutamate binding

    J Neurochem

    (1987)

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    Present address: Institute for Brain Aging and Dementia, University of California, 1226 Gillespie Neuroscience Research Facility, Irvine, CA 92697, USA.

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