Native low-density lipoprotein uptake by macrophage colony-stimulating factor-differentiated human macrophages is mediated by macropinocytosis and micropinocytosis.
OBJECTIVE
To examine the pinocytotic pathways mediating native low-density lipoprotein (LDL) uptake by human macrophage colony-stimulating factor-differentiated macrophages (the predominant macrophage phenotype in human atherosclerotic plaques).


RESULTS
We identified the kinase inhibitor SU6656 and the Rho GTPase inhibitor toxin B as inhibitors of macrophage fluid-phase pinocytosis of LDL. Assessment of macropinocytosis by time-lapse microscopy revealed that both drugs almost completely inhibited macropinocytosis, although LDL uptake and cholesterol accumulation by macrophages were only partially inhibited (approximately 40%) by these agents. Therefore, we investigated the role of micropinocytosis in mediating LDL uptake in macrophages and identified bafilomycin A1 as an additional partial inhibitor (approximately 40%) of macrophage LDL uptake that targeted micropinocytosis. When macrophages were incubated with both bafilomycin A1 and SU6656, inhibition of LDL uptake was additive (reaching 80%), showing that these inhibitors target different pathways. Microscopic analysis of fluid-phase uptake pathways in these macrophages confirmed that LDL uptake occurs through both macropinocytosis and micropinocytosis.


CONCLUSIONS
Our findings show that human macrophage colony-stimulating factor-differentiated macrophages take up native LDL by macropinocytosis and micropinocytosis, underscoring the importance of both pathways in mediating LDL uptake by these cells.
Anzinger
Joshua J
JJ
Section of Experimental Atherosclerosis, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Md 20892-1422, USA.
Chang
Janet
J
Xu
Qing
Q
Buono
Chiara
C
Li
Yifu
Y
Leyva
Francisco J
FJ
Park
Bum-Chan
BC
Greene
Lois E
LE
Kruth
Howard S
HS
D001693:Biological Transport, Active / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008077:Lipoproteins, LDL / Q000378:metabolism*; D018942:Macrolides / Q000494:pharmacology; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D008264:Macrophages / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D010873:Pinocytosis / Q000187:drug effects / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology
D007211:Indoles; D008077:Lipoproteins, LDL; D018942:Macrolides; C416927:SU 6656; D013449:Sulfonamides; D016173:Macrophage Colony-Stimulating Factor; C040929:bafilomycin A1