Cholesterol Accumulation In Foam Cells Research Articles

Hydroxytyrosol Reduces Foam Cell Formation and Endothelial Inflammation Regulating the PPARγ/LXRα/ABCA1 Pathway.

Cholesterol accumulation in macrophages leads to the formation of foam cells and increases the risk of developing atherosclerosis. We have verified whether hydroxytyrosol (HT), a phenolic compound with anti-inflammatory and antioxidant properties, can reduce the cholesterol build up in THP-1 macrophage-derived foam cells. We have also investigated the potential mechanisms. Oil Red O staining and high-performance liquid chromatography (HPLC) assays were utilized to detect cellular lipid accumulation and cholesterol content, respectively, in THP-1 macrophages foam cells treated with HT. The impact of HT on cholesterol metabolism-related molecules (SR-A1, CD36, LOX-1, ABCA1, ABCG1, PPARγ and LRX-α) in foam cells was assessed using real-time PCR (RT-qPCR) and Western blot analyses. Finally, the effect of HT on the adhesion of THP-1 monocytes to human vascular endothelial cells (HUVEC) was analyzed to study endothelial activation. We found that HT activates the PPARγ/LXRα pathway to upregulate ABCA1 expression, reducing cholesterol accumulation in foam cells. Moreover, HT significantly inhibited monocyte adhesion and reduced the levels of adhesion factors (ICAM-1 and VCAM-1) and pro-inflammatory factors (IL-6 and TNF-α) in LPS-induced endothelial cells. Taken together, our findings suggest that HT, with its ability to interfere with the import and export of cholesterol, could represent a new therapeutic strategy for the treatment of atherosclerotic disease.

FGF21 induces autophagy-mediated cholesterol efflux to inhibit atherogenesis via RACK1 up-regulation.

Fibroblast growth factor 21 (FGF21) acts as an anti‐atherosclerotic agent. However, the specific mechanisms governing this regulatory activity are unclear. Autophagy is a highly conserved cell stress response which regulates atherosclerosis (AS) by reducing lipid droplet degradation in foam cells. We sought to assess whether FGF21 could inhibit AS by regulating cholesterol metabolism in foam cells via autophagy and to elucidate the underlying molecular mechanisms. In this study, ApoE−/− mice were fed a high‐fat diet (HFD) with or without FGF21 and FGF21 + 3‐Methyladenine (3MA) for 12 weeks. Our results showed that FGF21 inhibited AS in HFD‐fed ApoE−/− mice, which was reversed by 3MA treatment. Moreover, FGF21 increased plaque RACK1 and autophagy‐related protein (LC3 and beclin‐1) expression in ApoE−/− mice, thus preventing AS. However, these proteins were inhibited by LV‐RACK1 shRNA injection. Foam cell development is a crucial determinant of AS, and cholesterol efflux from foam cells represents an important defensive measure of AS. In this study, foam cells were treated with FGF21 for 24 hours after a pre‐treatment with 3MA, ATG5 siRNA or RACK1 siRNA. Our results indicated that FGF21‐induced autophagy promoted cholesterol efflux to reduce cholesterol accumulation in foam cells by up‐regulating RACK1 expression. Interestingly, immunoprecipitation results showed that RACK1 was able to activate AMPK and interact with ATG5. Taken together, our results indicated that FGF21 induces autophagy to promote cholesterol efflux and reduce cholesterol accumulation in foam cells through RACK1‐mediated AMPK activation and ATG5 interaction. These results provided new insights into the molecular mechanisms of FGF21 in the treatment of AS.

Biology of High-Density Lipoproteins: An Update49High density lipoproteins exert pro-inflammatory effects on macrophages via passive cholesterol depletion and PKC-NF-kB/STAT1-IRF1 signaling50Homocysteine accelerated the formation of THP-1 macrophages-derived foam cells and cholesterol disorder via regulating the expressions of LXRa, ABCA1 and ABCG151Protein components of HDL as markers of cardiovascular damage in patients with arterial hypertension

Biology of High-Density Lipoproteins: An Update49High density lipoproteins exert pro-inflammatory effects on macrophages via passive cholesterol depletion and PKC-NF-kB/STAT1-IRF1 signaling50Homocysteine accelerated the formation of THP-1 macrophages-derived foam cells and cholesterol disorder via regulating the expressions of LXRa, ABCA1 and ABCG151Protein components of HDL as markers of cardiovascular damage in patients with arterial hypertension

Alpha-linolenic acid increases cholesterol efflux in macrophage-derived foam cells by decreasing stearoyl CoA desaturase 1 expression: evidence for a farnesoid-X-receptor mechanism of action

Increased cholesterol efflux from macrophage-derived foam cells (MDFCs) is an important protective mechanism to decrease lipid load in the atherosclerotic plaque. Dietary alpha-linolenic acid (ALA), an omega-3 polyunsaturated fatty acid (PUFA), decreases circulating cholesterol, but its role in cholesterol efflux has not been extensively studied. Stearoyl CoA desaturase 1 (SCD1) is the rate-limiting enzyme in the synthesis of monounsaturated fatty acids (MUFAs). Endogenous MUFAs are preferentially incorporated into triglycerides, phospholipids and cholesteryl ester, which are abundant in atherosclerotic plaque. This study investigated the mechanisms by which ALA regulated SCD1 and subsequent effect on cholesterol storage and transport in MDFCs. Small interfering RNA (siRNA) also was applied to modify SCD1 expression in foam cells. Alpha-linolenic acid treatment and SCD1 siRNA significantly decreased SCD1 expression in MDFCs. The reduction of SCD1 was accompanied with increased cholesterol efflux and decreased intracellular cholesterol storage within these cells. Alpha-linolenic acid activated the nuclear receptor farnesoid-X-receptor, which in turn increased its target gene small heterodimer partner (SHP) expression, and decreased liver-X-receptor dependent sterol regulatory element binding protein 1c transcription, ultimately resulting in repressed SCD1 expression. In conclusion, repression of SCD1 by ALA favorably increased cholesterol efflux and decreased cholesterol accumulation in foam cells. This may be one mechanism by which dietary omega-3 PUFAs promote atherosclerosis regression.

Interleukin‐10 inhibits the down‐regulation of ATP binding cassette transporter A1 by tumour necrosis factor‐alpha in THP‐1 macrophage‐derived foam cells

It is suggested that cholesterol efflux mediated by ATP binding cassette transporter A1 (ABCA1) plays an important role in anti-atherogenesis. However, the effects of inflammatory cytokines on ABCA1 expression and cholesterol accumulation in foam cells are little known. This study investigates the effects of tumour necrosis factor-alpha (TNF-alpha) and interleukin-10 (IL-10) on ABCA1 expression and cholesterol content in THP-1 macrophage-derived foam cells. ABCA1mRNA and protein levels were determined by RT-PCR and Western blot, respectively. The total cholesterol content in THP-1 macrophage-derived foam cells was detected by the zymochemistry method. Results revealed that TNF-alpha could increase cholesterol content by down-regulating ABCA1 expression in a time-dependent manner in THP-1 macrophage-derived foam cells, which may contribute to its pro-atherosclerotic effect. In addition IL-10 time-dependently decreased cholesterol accumulation by up-regulating ABCA1 expression and inhibited the down-regulation of ABCA1 by TNF-alpha in THP-1 macrophage-derived foam cells, which may be one of the mechanisms of IL-10 contributing to its anti-atherosclerotic action.