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Modified LDLs induce and bind to membrane ruffles on macrophages
N L Jones1, N S Allen, M C Willingham
1Department of Pathology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1092, USA. njones@wfubmc.edu
Abstract:
Macrophage foam cell formation in vitro requires uptake of modified low density lipoproteins (LDL) such as acetylated LDL (AcLDL) and moderately oxidized LDL (OxLDL), or beta-migrating very low density lipoprotein (betaVLDL), a naturally occurring lipoprotein. Incubation ofmacrophages with AcLDL and OxLDL resulted in stimulation of membrane ruffle formation, while betaVLDL primarily resulted in increased numbers of microvilli. Time-lapse Allen video enhanced contrast differential interference contrast (AVEC-DIC) light microscopy and correlative whole mount intermediate-voltage transmission electron microscopy (IVEM) was used to examine the dynamics ofAcLDL stimulated membrane ruffling and membrane ruffle ultrastructure. Stereo 3D surface replicas confirmed that AcLDL bound to these AcLDL-induced membrane ruffles. Quantification of the plasma membrane surface area after incubation with AcLDL, betaVLDL or LDL confirmed that AcLDL stimulated membrane ruffling, while betaVLDL and LDL stimulated microvilli formation. These studies suggest that modified LDLs induce circular membrane ruffles and modified LDLs bind to these ligand-induced membrane ruffles.
Insights
Modified lipoproteins like acetylated LDL (AcLDL) trigger macrophage membrane ruffles, while others like beta-migrating very low density lipoprotein (betaVLDL) increase microvilli. AcLDL specifically binds to these induced ruffles.
Area of Science:
- Cell Biology
- Lipid Metabolism
- Atherosclerosis Research
Background:
- Macrophage foam cell formation is crucial in atherosclerosis.
- Modified low-density lipoproteins (LDL) are key in this process.
- Specific modified LDLs, including acetylated LDL (AcLDL), oxidized LDL (OxLDL), and beta-migrating very low density lipoprotein (betaVLDL), are implicated.
Purpose of the Study:
- To investigate the dynamic cellular responses of macrophages to different modified LDLs.
- To examine the ultrastructure and binding characteristics of AcLDL-induced membrane structures.
- To differentiate the effects of AcLDL, OxLDL, and betaVLDL on macrophage plasma membrane morphology.
Main Methods:
- Time-lapse Allen video enhanced contrast differential interference contrast (AVEC-DIC) light microscopy.
- Correlative whole mount intermediate-voltage transmission electron microscopy (IVEM).
- Stereo 3D surface replica analysis to confirm ligand binding.
Main Results:
- AcLDL and OxLDL significantly stimulated membrane ruffle formation in macrophages.
- betaVLDL primarily increased the number of microvilli on the macrophage surface.
- AcLDL was observed to bind specifically to the induced membrane ruffles, confirmed by 3D surface replicas.
- Quantification revealed AcLDL promotes ruffling, while betaVLDL and LDL promote microvilli formation.
Conclusions:
- Modified LDLs induce distinct changes in macrophage plasma membrane morphology.
- AcLDL specifically induces and binds to circular membrane ruffles.
- These findings provide insights into the cellular mechanisms of modified LDL uptake and foam cell formation.