Human carotid atherosclerotic lesion protein components decrease cholesterol biosynthesis rate in macrophages through 3-hydroxy-3-methylglutaryl-CoA reductase regulation

Targeting macrophagic 17β-HSD7 by fenretinide for the treatment of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide and macrophage polarization plays an important role in its pathogenesis. However, which molecule regulates macrophage polarization in NAFLD remains unclear. Herein, we showed NAFLD mice exhibited increased 17β-hydroxysteroid dehydrogenase type 7 (17β-HSD7) expression in hepatic macrophages concomitantly with elevated M1 polarization. Single-cell RNA sequencing on hepatic non-parenchymal cells isolated from wild-type littermates and macrophage-17β-HSD7 knockout mice fed with high fat diet (HFD) for 6 weeks revealed that lipid metabolism pathways were notably changed. Furthermore, 17β-HSD7 deficiency in macrophages attenuated HFD-induced hepatic steatosis, insulin resistance and liver injury. Mechanistically, 17β-HSD7 triggered NLRP3 inflammasome activation by increasing free cholesterol content, thereby promoting M1 polarization of macrophages and the secretion of pro-inflammatory cytokines. In addition, to help demonstrate that 17β-HSD7 is a potential drug target for NAFLD, fenretinide was screened out from an FDA-approved drug library based on its 17β-HSD7 dehydrogenase inhibitory activity. Fenretinide dose-dependently abrogated macrophage polarization and pro-inflammatory cytokines production, and subsequently inhibited fat deposition in hepatocytes co-cultured with macrophages. In conclusion, our findings suggest that blockade of 17β-HSD7 signaling by fenretinide would be a drug repurposing strategy for NAFLD treatment.

Aqueous or lipid components of atherosclerotic lesion increase macrophage oxidation and lipid accumulation

INTRODUCTION AND OBJECTIVE

Understanding the interactions among atherosclerotic plaque components and arterial macrophages, is essential for elucidating the mechanisms involved in the development of atherosclerosis. We assessed the effects of lesion extracts on macrophages.

METHODS

Mouse peritoneal macrophages from atherosclerotic normoglycemic or hyperglycemic apoE(-/-) mice were incubated with aortic aqueous or with aortic lipidic extracts (mAAE or mALE) derived from these mice. In parallel, J774A.1 cultured macrophages were incubated with increasing concentrations of extracts prepared from human carotid lesions: polar lesion aqueous extract (hLAE), nonpolar lesion lipid extract (hLLE), or with their combination. In all the above systems we performed analyses of macrophage oxidative status, cholesterol, and triglyceride metabolism.

RESULTS

Aqueous or lipid extracts from either mice aorta or from human carotid lesions significantly increased macrophage oxidative stress as determined by reactive oxygen species (ROS) analysis. In parallel, a compensatory increase in the cellular antioxidant paraoxonase2 (PON2) activity and in macrophage glutathione content were observed following incubation with all extracts. Macrophage triglyceride mass and triglyceride biosynthesis rate were both significantly increased following treatment with the lipid extracts, secondary to upregulation of DGAT1. All extracts decreased cholesterol biosynthesis rate, through downregulation of HMGCR, the rate limiting enzyme in cholesterol biosynthesis. The combination of the human lesion extracts had the most significant effects.

CONCLUSION

The present study demonstrates that atherosclerotic plaque constituents enhance macrophage cellular oxidative stress, and accumulation of cholesterol and triglycerides, as shown in both in vivo and in vitro model systems.

Human carotid atherosclerotic plaque protein(s) change HDL protein(s) composition and impair HDL anti-oxidant activity

High density lipoprotein (HDL) anti-atherogenic functions are closely associated with cardiovascular disease risk factor, and are dictated by its composition, which is often affected by environmental factors. The present study investigates the effects of the human carotid plaque constituents on HDL composition and biological functions. To this end, human carotid plaques were homogenized and incubated with HDL. Results showed that after incubation, most of the apolipoprotein A1 (Apo A1) protein was released from the HDL, and HDL diameter increased by an average of approximately 2 nm. In parallel, HDL antioxidant activity was impaired. In response to homogenate treatment HDL could not prevent the accelerated oxidation of LDL caused by the homogenate. Boiling of the homogenate prior to its incubation with HDL abolished its effects on HDL composition changes. Moreover, tryptophan fluorescence quenching assay revealed an interaction between plaque component(s) and HDL, an interaction that was reduced by 50% upon using pre-boiled homogenate. These results led to hypothesize that plaque protein(s) interacted with HDL-associated Apo A1 and altered the HDL composition. Immuno-precipitation of Apo A1 that was released from the HDL after its incubation with the homogenate revealed a co-precipitation of three isomers of actin. However, beta-actin alone did not significantly affect the HDL composition, and yet the active protein within the plaque was elusive. In conclusion then, protein(s) in the homogenate interact with HDL protein(s), leading to release of Apo A1 from the HDL particle, a process that was associated with an increase in HDL diameter and with impaired HDL anti-oxidant activity.