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Impaired lysosomal processing of beta2-microglobulin by infiltrating macrophages in dialysis amyloidosis
M García-García1, Argilés, A Gouin-Charnet
1Institut de Génétique Humaine, Montpellier, France.
Background:
Macrophages may participate in amyloid fibril formation by processing the protein precursor. Although this theory seems to apply for amyloidosis, in which proteolytic cleavage is a prerequisite for amyloid fibril formation, it has not been demonstrated for beta2-microglobulin (beta2m) amyloidosis. We aimed to establish the role played by macrophages in beta2m amyloidosis.
Methods:
We used a double immunogold electron microscopy technique, including mouse antihuman CD68, rabbit antihuman beta2m, amyloid P component, and lysosome-associated membrane protein (LAMP-1) antibodies. Differential density labeling studies of beta2m and amyloid P component were performed extra- and intracellularly to assess protein processing by macrophages.
Results:
The cells surrounding amyloid fibrils were found to be mostly CD68 positive, suggesting that they were of monocyte-macrophage lineage. Intracellular accumulation of amyloid fibrils was also observed; these fibrils were constantly surrounded by LAMP-1-linked gold particles, demonstrating that intracellular beta2m was almost exclusively lysosomal. The rough-surface endoplasmic reticulum was not labeled by beta2m antibody, suggesting that there was no active synthesis of beta2m by the cells. As a marker of endocytosis, protruded cytoplasmic processes in close relation with the intracellular accumulations of beta2m amyloid fibrils were observed. No difference in density labeling (extracellular vs. intracellular) was observed for beta2m, whereas intracellular P component labeling was significantly decreased.
Conclusions:
All of these data are strongly suggestive of phagocytosis and not synthesis of amyloid fibrils by macrophages. Further, they demonstrate an impaired lysosomal processing specific for beta2m, as other compounds of the amyloid fibrils (P component) are significantly cleared.
Insights
Macrophages engulf beta2-microglobulin (beta2m) amyloid fibrils, rather than synthesizing them. This study reveals impaired lysosomal processing of beta2m by macrophages in beta2m amyloidosis.
Area of Science:
- Immunology
- Cell Biology
- Protein Biochemistry
Background:
- Macrophages are implicated in amyloid fibril formation through protein precursor processing.
- This mechanism is established for some amyloidosis types but not for beta2-microglobulin (beta2m) amyloidosis.
- The specific role of macrophages in beta2m amyloidosis requires elucidation.
Purpose of the Study:
- To investigate the role of macrophages in the pathogenesis of beta2-microglobulin (beta2m) amyloidosis.
- To determine whether macrophages synthesize or phagocytose beta2m amyloid fibrils.
- To assess the intracellular processing of beta2m by macrophages.
Main Methods:
- Utilized double immunogold electron microscopy with specific antibodies (anti-CD68, anti-beta2m, anti-amyloid P component, anti-LAMP-1).
- Conducted differential density labeling studies to compare extracellular and intracellular beta2m and amyloid P component.
- Analyzed cellular localization and processing of beta2m within macrophage lysosomes.
Main Results:
- Cells surrounding amyloid fibrils were predominantly CD68-positive, indicating macrophage lineage.
- Intracellular beta2m amyloid fibrils were localized within lysosomes (LAMP-1 positive).
- No evidence of beta2m synthesis by macrophages; observed cytoplasmic processes suggest endocytosis.
- Intracellular amyloid P component labeling was decreased, while beta2m labeling showed no difference, suggesting specific processing defects.
Conclusions:
- Macrophages phagocytose beta2m amyloid fibrils, contradicting the synthesis hypothesis.
- Demonstrated impaired lysosomal processing of beta2m by macrophages.
- Amyloid P component, another amyloid fibril component, is cleared more effectively, highlighting a specific defect in beta2m processing.