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Inability to detect beta-amyloid protein precursor mRNA in Alzheimer plaque-associated microglia
S A Scott1, S A Johnson, C Zarow
1Department of Neurology, University of Southern California School of Medicine, Los Angeles 90033.
Abstract:
A close association between Alzheimer senile plaques and microglia (the resident mononuclear phagocytic system cells of the brain) is well documented. To determine whether microglia contain detectable beta-amyloid protein precursor (beta-APP) mRNA, the present study combined immunocytochemistry (LN3 antibody to label microglia) with in situ hybridization (full-length cRNA probe to detect all forms of beta-APP mRNA). We report that immunolabeled microglia, including those clustered around senile plaques, generally lack detectable beta-APP mRNA--suggesting that microglia are not synthesizing the plaque-associated amyloid. The possibility that, analogous to the process in other forms of amyloidosis, the resident mononuclear phagocytic cells ingest an amyloidogenic precursor and secrete amyloid was not examined. Recent demonstrations of interactions between immune-related factors and Alzheimer lesions suggest that beta-APP and its breakdown products, along with microglia and their secretory products, may work synergistically in an AD pathogenetic cascade.
Insights
Microglia, brain immune cells, do not appear to produce the amyloid precursor linked to Alzheimer disease. This suggests other mechanisms may be involved in amyloid plaque formation in the brain.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Alzheimer disease is characterized by senile plaques.
- Microglia are the brain's resident immune cells and are found near these plaques.
Purpose of the Study:
- To investigate if microglia synthesize beta-amyloid precursor protein (beta-APP) mRNA.
- To determine the role of microglia in the pathogenesis of Alzheimer disease-associated amyloid plaques.
Main Methods:
- Combined immunocytochemistry (using LN3 antibody) to identify microglia.
- In situ hybridization (using a full-length cRNA probe) to detect beta-APP mRNA within microglia.
Main Results:
- Microglia, even those near plaques, generally lacked detectable beta-APP mRNA.
- Findings suggest microglia are not the source of the amyloid associated with plaques.
Conclusions:
- Microglia may not synthesize the amyloidogenic precursor protein found in Alzheimer plaques.
- Further research is needed to explore if microglia ingest and process amyloid precursors.
- Interactions between immune factors and Alzheimer lesions suggest a synergistic role in disease progression.