Interferon-gamma down-regulates the lipoprotein(a)/apoprotein(a) receptor activity on macrophage foam cells. Evidence for disruption of ligand-induced receptor recycling by interferon-gamma.

P.J Skiba,G.A Keesler,I Tabas

doi:10.1016/s0021-9258(17)31619-8

Abstract

Cholesterol loading of macrophages, such as occurs in atheroma foam cells, has recently been shown to upregulate a novel receptor activity that mediates the internalization degradation of the atherogenic lipoprotein, lipoprotein(a) (Lp(a)), and its protein moiety, apoprotein(a), (apo(a)). Herein, the regulation of this receptor activity by macrophage activation and interferon-gamma (IFN-gamma) was investigated. Compared with control foam cells, 125I-recombinant-apo(a) (r-apo(a)) degradation assayed after 5 h of incubation was 3-6-fold less in foam cells derived from thioglycollate- or concanavalin A-elicited mouse peritoneal macrophages. In vitro treatment of foam cells derived from resident mouse peritoneal macrophages or from human monocyte-derived macrophages with IFN-gamma also led to a substantial decrease in the ability of these cells to degrade 125I-rapo(a); similar results were obtained with 125I-Lp(a). In contrast, IFN-gamma-treated foam cells that were incubated for 10 min with 125I-r-apo(a) and then chased for 2 h in the absence of ligand degraded similar amounts of 125I-r-apo(a) as untreated foam cells. To reconcile these data, we hypothesized that the apo(a) receptor activity undergoes ligand-induced recycling and that IFN-gamma disrupts this recycling. To test this idea, control and IFN-gamma-treated foam cells were incubated for 10 min with unlabeled r-apo(a), and then 125I-r-apo(a) receptor activity was assayed at various times thereafter. Untreated foam cells showed clear evidence of ligand-induced recycling of the apo(a) receptor activity, whereas recycling was markedly diminished in the IFN-gamma-treated foam cells. Thus, by disrupting ligand-induced receptor recycling, IFN-gamma leads to down-regulation of the foam cell Lp(a)/apo(a) receptor activity. Since T cells are known to be present in atherosclerotic lesions, these findings raise the possibility that the degradation by atheroma foam cells of Lp(a) and other possible ligands for the receptor may be reversibly regulated by IFN-gamma.

Highlights

From the Departments of Medicine and Anatomy & Cell Biology, Columbia University College of Physicians and Surgeons, New York, New York 10032
Sincemacpresent in atherosclerotic lesions, these findings raise rophages can exist in several different stateosf activation inthe possibility that the degradation by atheroma foam duced by local stimuli or conditions, it is reasonable to believe cells of Lp(a)and other possible ligands for the receptor that macrophage foam cells in lesions may exist in different may be reversibly regulated by IFN-y
To determine if receptor down-regulation was reversible, lZ5I-experiment, we found that cells pulsed for 20 min exhibited a r-apo(a) receptor activity was assayed in both IFN-y-treated similar amount of eventual ''51-r-apo(a) degradation as those foam cells and foam cells derived from concanavalinA-elicited pulsed for 10 min, indicating thatbinding of r-apo(a) to these macrophages that were maintained in culturefor 3 days in the functional sites had reached equilibrium by 10 min at 37 "C

Summary

EXPERIMENTAL PROCEDURES

Materials-Tissue culture media and reagents were purchased from Life Technologies, Inc., tissue culture plates were from Corning, and defined fetal bovine serum was from HycloneLaboratories, Inc. (Logan, UT). Materials-Tissue culture media and reagents were purchased from Life Technologies, Inc., tissue culture plates were from Corning, and defined fetal bovine serum was from HycloneLaboratories, Inc. Cells-Residentmouse peritoneal macrophages from female ICR mice (22-25 g) were plated in DMEM, 10%fetal calf serum, containing penicillin (100unitdml), streptomycin (100pg/ml), and glutamine MM) at 1x lo6celld22-mmwell [22].ConcanavalinAand thioglycollateelicited macrophages were harvested from the peritoneum of female ICRmice 3 days after the intraperitoneal injection of 40pg of con-. The cells were placedonice and washed twice with ice-cold PBS. The cells wetrheen washed twice with ice-cold PBSand dissolved in 1ml of 0.1 N NaOH. CanavalinA[23] or 4 days after the intraperitoneal injection of 40 mgof thioglycollatein 1ml of sterile PBS and plated as described above.

RESULTS

Unloaded Ug

Foam cell

Findings

DISCUSSION