Related Experiment Videos
Modulation of apoprotein E secretion in response to receptor-mediated endocytosis in resident and inflammatory
Abstract:
We have determined the effect of various endocytic ligands on the secretion of ApoE by macrophages. ApoE was a major secreted protein of resident macrophages, but BCG-activated macrophages secreted little ApoE and periodate-elicited macrophages secreted intermediate amounts of ApoE. Resident, periodate-elicited, and BCG-activated mouse peritoneal macrophages were incubated with AcLDL, EIgG, EIgMC, dextran sulfate, latex, or zymosan, and the resulting protein secretion patterns were analyzed by [35S]methionine labeling and SDS-polyacrylamide gel electrophoresis. AcLDL increased total [35S]methionine incorporation into secreted proteins. Although AcLDL increased the secretion of ApoE by resident macrophages less than or equal to fivefold in a dose-dependent manner, with maximal stimulation at 4.8 micrograms/ml, it decreased the secretion of ApoE by periodate-elicited macrophages to almost nothing and did not affect the low rate of secretion of ApoE by BCG-activated macrophages. However, EIgG, which increases cellular cholesterol content of macrophages as AcLDL does, did not increase ApoE secretion, and dextran sulfate, which is recognized by the same receptor as AcLDL, also did not increase ApoE secretion. The binding and uptake of EIgG, dextran sulfate, zymosan, latex, and EIgMC all decreased the secretion of ApoE. These endocytic ligands also altered the pattern of secreted and cellular proteins other than ApoE. The pattern of response was ligand-specific. However, increased secretion of polypeptides of Mr 62,000 and 68,000 was common to many stimuli. We conclude that receptor-mediated endocytosis modulates the secretion of ApoE and other proteins pleiotypically in resident, inflammatory, and activated macrophages.
Insights
Endocytic ligands differentially regulate apolipoprotein E (ApoE) secretion by macrophages. Receptor-mediated endocytosis impacts ApoE secretion in a ligand-specific manner across various macrophage activation states.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Apolipoprotein E (ApoE) is a crucial secreted protein synthesized by macrophages.
- Macrophage activation status significantly influences ApoE secretion levels.
- Understanding the regulation of ApoE secretion is vital for macrophage function.
Purpose of the Study:
- To investigate the impact of various endocytic ligands on ApoE secretion by macrophages.
- To determine if receptor-mediated endocytosis modulates ApoE secretion.
- To explore ligand-specific effects on protein secretion patterns in different macrophage populations.
Main Methods:
- Incubation of resident, periodate-elicited, and BCG-activated mouse peritoneal macrophages with diverse endocytic ligands (AcLDL, EIgG, EIgMC, dextran sulfate, latex, zymosan).
- Analysis of secreted and cellular protein patterns using [35S]methionine labeling and SDS-polyacrylamide gel electrophoresis.
- Dose-response analysis of AcLDL effects on ApoE secretion.
Main Results:
- AcLDL demonstrated a dose-dependent increase in ApoE secretion by resident macrophages but decreased it in periodate-elicited macrophages and had no effect on BCG-activated macrophages.
- Other endocytic ligands (EIgG, dextran sulfate, zymosan, latex, EIgMC) generally decreased ApoE secretion.
- Ligand binding and uptake altered protein secretion patterns in a ligand-specific manner, with common increases in 62,000 and 68,000 Mr polypeptides observed.
- EIgG and dextran sulfate did not increase ApoE secretion, despite AcLDL-like properties.
Conclusions:
- Receptor-mediated endocytosis plays a significant role in modulating ApoE secretion by macrophages.
- The effect of endocytic ligands on ApoE secretion is pleiotropic and depends on both the ligand and the macrophage activation state.
- These findings highlight the complex interplay between endocytosis and protein secretion in macrophages.