Authors: Landfield, Philip W.; Blalock, Eric M.; Chen, Kuey-Chu; Porter, Nada M.

Source: Current Alzheimer Research, Volume 4, Number 2, April 2007 , pp. 205-212(8)

Publisher: Bentham Science Publishers

Abstract:

The original glucocorticoid (GC) hypothesis of brain aging and Alzheimer's disease proposed that chronic exposure to GCs promotes hippocampal aging and AD. This proposition arose from a study correlating increasing plasma corticosterone with hippocampal astrocyte reactivity in aging rats. Numerous subsequent studies have found evidence consistent with this hypothesis, in animal models and in humans. However, several results emerged that were inconsistent with the hypothesis, highlighting the need for a more definitive test with a broader panel of biomarkers. We used microarray analyses to identify a panel of hippocampal gene expression changes that were aging-dependent, and also corticosterone- dependent. These data enabled us to test a key prediction of the GC hypothesis, namely, that the expression of most target biomarkers of brain aging should be regulated in the same direction (increased or decreased) by both GCs and aging. This prediction was decisively contradicted, as a majority of biomarker genes were regulated in opposite directions by aging and GCs, particularly inflammatory and astrocyte-specific genes. Thus, the initial hypothesis of simple positive cooperativity between GCs and aging must be rejected. Instead, our microarray data suggest that in the brain GCs and aging interact in more complex ways that depend on the cell type. Therefore, we propose a new version of the GC-brain aging hypothesis; its main premise is that aging selectively increases GC efficacy in some cell types (e.g., neurons), enhancing catabolic processes, whereas aging selectively decreases GC efficacy in other cell types (e.g., astrocytes), weakening GC anti-inflammatory activity. We also propose that changes in GC efficacy might be mediated in part by cell type specific shifts in the antagonistic balance between GC and insulin actions, which may be of relevance for Alzheimer's disease pathogenesis.

Keywords: Corticosterone; hippocampus; insulin; inflammation; astrocyte; microarray; cognition; Alzheimer's

Document Type: Research article

DOI: http://dx.doi.org/10.2174/156720507780362083

Affiliations: 1: Department of Molecular and Biological Pharmacology, University of Kentucky College of Medicine, 800 Rose Street, MS-310, Lexington, Kentucky, 40536, USA.

Publication date: 2007-04-01

More about this publication?

• Current Alzheimer Research publishes peer-reviewed frontier review and research articles on all areas of Alzheimer's disease. This multidisciplinary journal will help in understanding the neurobiology, genetics, pathogenesis, and treatment strategies of Alzheimer's disease. The journal publishes objective reviews written by experts and leaders actively engaged in research using cellular, molecular, and animal models. The journal also covers original articles on recent research in fast emerging areas of molecular diagnostics, brain imaging, drug development and discovery, and clinical aspects of Alzheimer's disease. Manuscripts are encouraged that relate to the synergistic mechanism of Alzheimer's disease with other dementia and neurodegenerative disorders. Book reviews, meeting reports and letters-to-the-editor are also published. The journal is essential reading for researchers, educators and physicians with interest in age-related dementia and Alzheimer's disease. Current Alzheimer Research provides a comprehensive 'bird's-eye view' of the current state of Alzheimer's research for neuroscientists, clinicians, health science planners, granting, caregivers and families of this devastating disease.

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