Plasma apolipoprotein secretion by human monocyte-derived macrophages

Area of Science:

• Cell Biology
• Immunology
• Biochemistry

Background:

• Apolipoprotein E is a major secretory protein produced by human monocyte macrophages.
• The synthesis of other plasma apolipoproteins by these cells remains largely undocumented.

Purpose of the Study:

• To investigate the synthesis and secretion of various apolipoproteins (A-I, B, C-II, C-III, and E) by cultured human monocyte macrophages.
• To determine the effect of malondialdehyde-modified low-density lipoprotein (MDA-LDL) on apolipoprotein secretion.

Main Methods:

• Cultured human monocyte macrophages were incubated with or without MDA-LDL.
• Culture media were analyzed for apolipoproteins using specific radioimmunoassays.
• Confirmation of apolipoprotein E identity was performed using [35S]methionine labeling, affinity chromatography, and SDS-gel electrophoresis.

Main Results:

• Significant levels of apolipoprotein E were detected, with baseline production ranging from 0.64 to 2.82 µg/mg cell protein per 24 h.
• MDA-LDL significantly stimulated apolipoprotein E secretion by 1.6-3.0 fold.
• No apolipoprotein B, A-I, C-II, or C-III was detected, despite sensitive assays.

Conclusions:

• Human monocyte macrophages synthesize and secrete apolipoprotein E.
• These cells do not appear to synthesize apolipoproteins A-I, B, C-II, or C-III.
• MDA-LDL enhances apolipoprotein E secretion by macrophages.