Caspase Cleavage of GFAP within Degenerating Astrocytes of the Alzheimer's Disease Brain

Publication Date

4-2006

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Biology

Department

Biology

Supervisory Committee Chair

Troy Rohn

Supervisory Committee Member

Julia Oxford

Supervisory Committee Member

Denise Wingett

Abstract

Recent studies demonstrate a role for the activation of caspases and cleavage of cellular proteins within neurons of the Alzheimer's disease (AD) brain. To determine whether a similar role for caspases also occurs within glial cells in AD, we designed a site-directed caspase-cleavage antibody to glial fibrillary acidic protein (GFAP), a cytoskeletal protein specifically expressed in astrocytes. Using both a cell-free system and a cell model system of apoptosis, in vitro characterization of this antibody (termed GFAP caspase cleavage product or GFAP-CCP Ab), demonstrated immunolabeling of the predicted caspase-cleavage fragment but not full-length GFAP by Western blot analysis. To determine whether caspases cleave GFAP in vivo, sections from control and AD tissues were examined by immunohistochemistry using the GFAP-CCP Ab. Two prominent features of staining were strong immunolabeling of degenerating astrocytes in proximity to blood vessels and staining within plaque-rich regions of the AD brain. Furthermore, co-localization of the GFAP-CCP Ab and an antibody to active caspase-3 was demonstrated within damaged astrocytes of the AD brain. Detection of the predicted 20 kDa caspase-cleaved fragment of GFAP in AD human brain extracts following Western blot analysis was used to confirm the immunohistochemical data. Prior studies suggest that the activation of caspases and cleavage of cellular proteins including GFAP may contribute to the injury and damage of astrocytes in the AD brain, possibly contributing to the compromization of the blood brain barrier, and subsequent cognitive impairment associated with Alzheimer’s disease.

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