Abstract 2254: Very Brief Focal Ischemia Simulating Human TIAs Induces Aβ Aggregate and Activates Prolonged Autophagy in Rats
Objective Very brief periods of focal ischemia in humans called Transient Ischemic Attacks (TIAs) are viewed as being benign. However, our recent animal studies demonstrate that brief periods of focal ischemia can produce microinfarcts associated with neuronal apoptosis and glial Hsp70 positive inclusions. Recent studies of inclusions show they are associated with misfolded proteins that can aggregate and form inclusions, or the proteins can be destroyed via the catabolic process of autophagy. These processes have been shown to occur in Alzheimer’s Disease (AD) where evidence of β amyloid (Aβ) aggregates and cellular autophagy are described. Since there is increasing evidence that cerebral ischemia is linked to AD, we postulated that protein aggregates possibly including Aβ and autophagy would occur following cerebral ischemia. The aims of this study were to demonstrate that brief focal cerebral ischemia induces: Aβ aggregation; Aβ cleavage into “non-toxic” and toxic Aβ 1-42 fragments; and autophagy of cells in brain.
Methods Middle cerebral artery occlusion (MCAO) was produced in adult SD rats using the suture method. Rats subjected to 20 minutes of ischemia were sacrificed at 4 or 8 weeks. Antibodies against Rodent Aβ (R Aβ, detects all cleaved fragments of Aβ), Aβ 1-42 (detects only the toxic fragment), and LC3b (Atg8 marker of autophagy) were used.
Results All immunoreactive cells were ipsilateral to the MCAO. No immunoreactivity was observed contralateral to the MCAO in the opposite hemisphere. 1. At 4 weeks post ischemia, R Aβ was expressed in focal areas of the caudate-putamen, globus pallidum and cortex. Aβ 1-42 staining was negative at 4 weeks in all structures. At 8 weeks post ischemia, the pattern of the R Aβ expression was similar to 4 weeks except that it appeared in CA1 hippocampal neurons. At 8 weeks Aβ 1-42 was induced in caudate-putamen, globus pallidum, hippocampal CA1 region, and cortex where it partially co-localized with R Aβ. R Aβ and Aβ 1-42 co-localization in hippocampus occurred in few cells, possibly GABAergic interneurons. 2. LC3b, an autophagy marker, was expressed in the penumbra of microinfarcts of the cortex at 8 weeks. Almost all Aβ 1-42 positive aggregates co-localized with LC3b.
Conclusions 1. Brief focal ischemia induced Aβ only on the ischemic side of the brain; 2. Brief ischemia produced “non-toxic” and toxic Aβ 1-42 fragments; 3. Most cells expressing Aβ 1-42 are undergoing autophagy.
- © 2012 by American Heart Association, Inc.