Abstract 663: Modified Low Density Lipoproteins Elicited Macrophage InflammatoryResponses is Regulated by the Glycerolipid Synthesis Enzyme Lipin-1

Modified low density lipoproteins (modLDL) elicit macrophage generation into foam cells that release pro-inflammatory mediators driving atherosclerotic lesion progression causing cardiovascular disease. The molecular mechanisms that elicit foam cell inflammatory responses have not yet been fully elucidated. The lipid-laden phenotype that is characteristic of macrophage foam cells is due to lipid droplet biogenesis in response to excess cholesterol. Lipid droplet biogenesis is a process that is thought to be symptomatic of, but not drive atherosclerosis. Lipid droplet biogenesis requires glycerolipid synthesis, during which, lipin-1 converts phosphatidate into diglyceride as the penultimate step of lipid droplet generation. We had previously demonstrated lipin-1 is also required for modLDL-elicited pro-inflammatory response from macrophages. We hypothesized that modLDL elicits chronic diglyceride generation, via lipin-1 enzymatic activity, that activates signaling cascades responsible for foam cell pro-inflammatory responses. To test our hypotheses we stimulated wild type and lipin-1 depleted bone marrow-derived macrophages (BMDMs) with oxidized LDLs (oxLDLs). Stimulation of wild type BMDMs resulted in chronic activation of the signaling kinases PKCα/βII, ERK1/2 and the AP-1 transcription factor subunit cJun (up to 48 hours after stimulation). This pathway was not observed to be active in BMDMs depleted of lipin-1 either genetically or with siRNA. The pharmacological inhibition of lipin-1, PKCα/βII, ERK1/2 strongly suggest lipin-1- PKCα/βII-ERK1/2-cJun represents a signaling axis. Finally, each of these proteins were required for oxLDL-elicited pro-inflammatory responses by macrophages. These results suggest that augmented glycerolipid synthesis in macrophages due to modLDL stimulation is not just symptomatic of atherosclerosis but promote inflammatory responses that drive lesion progression

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Abstract 382: Lipin-1 Links Pro-inflammatory Responses and Foam Cell Formation by Oxidized-Low Density Lipoprotein-Elicited Macrophages

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvb.35.suppl_1.382 ◽

2015 ◽

Vol 35 (suppl_1) ◽

Author(s):

Aaron R Navratil ◽

Aimee E Vozenilek ◽

James A Cardelli ◽

Jonette M Green ◽

A W Orr ◽

...

Keyword(s):

Lipid Droplet ◽

Inflammatory Cytokine ◽

Cytokine Production ◽

Inflammatory Responses ◽

Foam Cell ◽

Cell Formation ◽

Foam Cell Formation ◽

Wild Type ◽

Inflammatory Cytokine Production ◽

Lipin 1

Atherosclerosis is a chronic inflammatory disease of large and medium-sized arteries and one of the underlying causes of cardiovascular disease (CVD). Macrophages participate decisively in the development and promotion of atherosclerosis. Macrophages infiltrate the arterial intima to ingest modified low density lipoproteins (e.g. oxLDLs) via scavenger receptors. The scavenging of oxLDLs results in foam cell formation due to enhanced lipid droplet biogenesis. These foam cells eventually release pro-inflammatory cytokines that promote atherosclerosis. However, it is currently unknown whether there is a link between lipid droplet biogenesis and pro-inflammatory cytokine production in macrophages that scavenge oxLDL. Lipin-1, a phosphatidate phosphohydrolase enzyme, partially contributes to macrophage pro-inflammatory cytokine production following stimulation with bacteria. Lipin-1 is also required for lipid droplet biogenesis in macrophages. Finally, we observed lipin-1 protein within macrophages from human atherosclerotic plaques. Thus, we hypothesized that lipid droplet biogenesis, via lipin-1 activity, directly contributes to foam cell pro-inflammatory cytokine production. To test this hypothesis we compared lipid droplet biogenesis and pro-inflammatory cytokine responses of oxLDL-stimulated wild type and lipin-1-depleted macrophages. Depletion of lipin-1 inhibited oxLDL-induced foam cell generation by reducing lipid droplet number, area, and staining intensity. There were no differences in scavenger receptor expression or uptake of oxLDL between wild type and lipin-1-depleted cells. In addition, depletion of lipin-1 also ablated oxLDL-elicited production of the pro-atherogenic cytokines tumor necrosis factor-α and interleukin-6. These findings demonstrate a critical role for lipin-1 in the regulation of macrophage inflammatory responses to oxLDL. Furthermore, these data begin to link foam cell formation, via lipid droplet biogenesis, and pro-inflammatory cytokine production within oxLDL stimulated macrophages. Thus, our studies suggest that lipid droplet biogenesis may be an ideal therapeutic target to inhibit inflammation associated with atherosclerosis to treat CVD.

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Uptake of modified low-density lipoproteins alters actin distribution and locomotor forces in macrophages

AJP Cell Physiology ◽

10.1152/ajpcell.00177.2002 ◽

2003 ◽

Vol 284 (2) ◽

pp. C555-C561 ◽

Cited By ~ 23

Author(s):

Celina V. Zerbinatti ◽

Robert W. Gore

Keyword(s):

Foam Cells ◽

Force Transducer ◽

Low Density Lipoproteins ◽

Low Density ◽

Force Frequency ◽

Modified Low Density Lipoproteins ◽

Generating Capacity ◽

Induced Changes ◽

Isometric Forces ◽

Modified Forms

It is postulated that macrophage-derived foam cells accumulate in the arterial wall because they lose the ability to migrate after excessive ingestion of modified forms of low-density lipoproteins (LDL). To assess changes in locomotor force generating capacity of foam cells, we measured isometric forces in J774A.1 macrophages after cholesterol loading with oxidized (Ox-LDL) or aggregated (Agg-LDL) LDL using a novel magnetic force transducer. Ox-LDL loading reduced the ability of J774A.1 macrophages to generate isometric forces by 50% relative to control cells. Changes in force frequency consistent with reduced motility were detected as well. Agg-LDL loading was also detrimental to J774A.1 motility but to a lesser extent than Ox-LDL. Ox-LDL loading significantly reduced total actin levels and induced changes in the F-actin to G-actin distribution, whereas Agg-LDL loaded cells had significantly increased levels of total actin. These data provide evidence that cholesterol loading and subsequent accumulation decreases macrophage motility by reducing the cells' force generating capacity and that Ox-LDL appears to be more effective than Agg-LDL in disrupting the locomotor machinery.

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