Degradation of aggregated LDL occurs in complex extracellular sub-compartments of the lysosomal synapse

Journal of Cell Science
Rajesh K SinghAbigail S Haka

Abstract

Monocyte-derived cells use an extracellular, acidic, lytic compartment (a lysosomal synapse) for initial degradation of large objects or species bound to the extracellular matrix. Akin to osteoclast degradation of bone, extracellular catabolism is used by macrophages to degrade aggregates of low density lipoprotein (LDL) similar to those encountered during atherogenesis. However, unlike osteoclast catabolism, the lysosomal synapse is a highly dynamic and intricate structure. In this study, we use high resolution three dimensional imaging to visualize compartments formed by macrophages to catabolize aggregated LDL. We show that these compartments are topologically complex, have a convoluted structure and contain sub-regions that are acidified. These sub-regions are characterized by a close apposition of the macrophage plasma membrane and aggregates of LDL that are still connected to the extracellular space. Compartment formation is dependent on local actin polymerization. However, once formed, compartments are able to maintain a pH gradient when actin is depolymerized. These observations explain how compartments are able to maintain a proton gradient while remaining outside the boundaries of the plasma membrane.

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Citations

Apr 6, 2016·Journal of Lipid Research·Abigail S HakaFrederick R Maxfield
May 26, 2017·Arteriosclerosis, Thrombosis, and Vascular Biology·Hanrui Zhang, Muredach P Reilly
Oct 28, 2019·Arteriosclerosis, Thrombosis, and Vascular Biology·Trent D EvansBabak Razani
Oct 31, 2019·Traffic·Frederick R MaxfieldRajesh K Singh
Oct 11, 2019·Arteriosclerosis, Thrombosis, and Vascular Biology·Rajesh K SinghFrederick R Maxfield
Dec 26, 2019·MBio·Melissa Cruz-AcuñaJamal S Lewis
Aug 18, 2017·Journal of Lipid Research·Rajesh K SinghFrederick R Maxfield

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Methods Mentioned

BETA
electron
scanning electron microscopy
electron microscopy
confocal microscopy
GTPase
RAP

Software Mentioned

ImageJ
Avizo
SerialEM tomography
Protomo
Elements C
Auto Slice and View G3
softWoRx
NIS
MetaMorph

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