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Uptake of fibrillar beta-amyloid by microglia isolated from MSR-A (type I and type II) knockout mice
H Chung1, M I Brazil, M C Irizarry
1Department of Biochemistry, Weill Medical College of Cornell University, Room E215, 1300 York Avenue, New York, NY 10021, USA.
Abstract:
To characterize the receptors involved in binding fibrillar amyloid A-beta (fA beta), we compared the uptake of fA beta in microglia from wildtype (MSR-A+/+) and MSR-A knockout (MSR-A-/-) mice. On average, there was a 60% reduction in the uptake of Cy3-fA beta in microglia from the MSR-A-/- mice. Cy3-fA beta uptake in the MSR-A-/- mice was still competable by scavenger receptor ligands, including acetylated low-density lipoprotein (Ac-LDL) and fucoidan. This indicates that uptake by MSR-B and/or other MSRs is also involved in the uptake of fA beta by microglia. However, the significant reduction in the uptake of fA beta in the MSR-A-/- microglia suggests that fA beta gets internalized mostly by MSR-As in microglia. Uptake of modified fA beta (ClqA beta) was similar in the MSR-A-/- microglia as in the wildtype indicating that the uptake of the opsonized fA beta is independent of MSR-A.
Insights
Microglia primarily internalize fibrillar amyloid beta (fAβ) via scavenger receptors A (MSR-A). However, other scavenger receptors also contribute to fAβ uptake, particularly for modified forms.
Area of Science:
- Neuroimmunology
- Molecular Biology
- Alzheimer's Disease Research
Background:
- Amyloid beta (Aβ) plaques are a hallmark of Alzheimer's disease.
- Microglia, the brain's immune cells, play a role in clearing Aβ.
- Scavenger receptors (MSRs) are implicated in microglial Aβ uptake.
Purpose of the Study:
- To identify the specific scavenger receptors involved in fibrillar Aβ (fAβ) uptake by microglia.
- To determine the contribution of MSR-A to fAβ internalization.
Main Methods:
- Compared uptake of fluorescently labeled fAβ (Cy3-fAβ) in microglia from wildtype and MSR-A knockout mice.
- Assessed competition of Cy3-fAβ uptake using known scavenger receptor ligands (Ac-LDL, fucoidan).
- Evaluated uptake of opsonized fAβ (ClqAβ) in both genotypes.
Main Results:
- Microglia from MSR-A knockout mice showed a 60% reduction in Cy3-fAβ uptake compared to wildtype.
- fAβ uptake in MSR-A knockout microglia was still inhibited by other scavenger receptor ligands, suggesting involvement of MSR-B and other MSRs.
- Uptake of opsonized fAβ (ClqAβ) was similar in both knockout and wildtype microglia, indicating MSR-A independence.
Conclusions:
- MSR-A is the primary scavenger receptor mediating fibrillar Aβ uptake in microglia.
- Other scavenger receptors, like MSR-B, also contribute to fAβ internalization.
- MSR-A is not involved in the uptake of MSR-A-independent opsonized fAβ.