Macrophage SR-BI modulates autophagy via VPS34 complex and PPARα transcription of Tfeb in atherosclerosis
Huan Tao, … , Kasey C. Vickers, MacRae F. Linton
Huan Tao, … , Kasey C. Vickers, MacRae F. Linton
Published March 4, 2021
Citation Information: J Clin Invest. 2021;131(7):e94229. https://doi.org/10.1172/JCI94229.
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Research Article Cardiology Vascular biology

Macrophage SR-BI modulates autophagy via VPS34 complex and PPARα transcription of Tfeb in atherosclerosis

Abstract

Autophagy modulates lipid turnover, cell survival, inflammation, and atherogenesis. Scavenger receptor class B type I (SR-BI) plays a crucial role in lysosome function. Here, we demonstrate that SR-BI regulates autophagy in atherosclerosis. SR-BI deletion attenuated lipid-induced expression of autophagy mediators in macrophages and atherosclerotic aortas. Consequently, SR-BI deletion resulted in 1.8- and 2.5-fold increases in foam cell formation and apoptosis, respectively, and increased oxidized LDL–induced inflammatory cytokine expression. Pharmacological activation of autophagy failed to reduce lipid content or apoptosis in Sr-b1–/– macrophages. SR-BI deletion reduced both basal and inducible levels of transcription factor EB (TFEB), a master regulator of autophagy, causing decreased expression of autophagy genes encoding VPS34 and Beclin-1. Notably, SR-BI regulated Tfeb expression by enhancing PPARα activation. Moreover, intracellular macrophage SR-BI localized to autophagosomes, where it formed cholesterol domains resulting in enhanced association of Barkor and recruitment of the VPS34–Beclin-1 complex. Thus, SR-BI deficiency led to lower VPS34 activity in macrophages and in atherosclerotic aortic tissues. Overexpression of Tfeb or Vps34 rescued the defective autophagy in Sr-b1–/– macrophages. Taken together, our results show that macrophage SR-BI regulates autophagy via Tfeb expression and recruitment of the VPS34–Beclin-1 complex, thus identifying previously unrecognized roles for SR-BI and potentially novel targets for the treatment of atherosclerosis.

Authors

Huan Tao, Patricia G. Yancey, John L. Blakemore, Youmin Zhang, Lei Ding, W. Gray Jerome, Jonathan D. Brown, Kasey C. Vickers, MacRae F. Linton

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Figure 8

SR-BI impacts autophagy by enhancing Barkor–cholesterol domain interaction.

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SR-BI impacts autophagy by enhancing Barkor–cholesterol domain interacti...
(A and B) Sr-b1–expressing or control plasmid was transfected for 48 hours into WT or Sr-b1–/– macrophages using jetPEI-Macrophage DNA Transfection reagent. Cells were then incubated for 24 hours with 100 μg/mL acetylated LDL and 5 μg/mL Sandoz 58035. SR-BI, Barkor, cholesterol domains (CT-B), VPS34, and LC3II were detected by Western blotting. The blots are representative, and the numbers are the mean of 3 independent experiments in which the values are normalized to WT basal levels (green, regular font). (C–E) Cells were incubated with DMEM with 10% FBS or enriched in FC by incubation for 24 hours with 100 μg/mL acetylated LDL and 5 μg/mL Sandoz 58035. The intracellular localization of cholesterol domains, Barkor, and SR-BI were examined by confocal fluorescence microscopy in cholesterol-normal (–) and FC-enriched (+) WT and Sr-b1–/– macrophages. (C) Shown are representative images of SR-BI (purple), Barkor (green), cholesterol domains (red), and merged images. Scale bar: 1 μm. (D and E) Quantitation of the average number of intracellular puncta positive for cholesterol domains alone (D) or positive for both Barkor and cholesterol domains (E) in 50 cells. **P < 0.01, ***P < 0.001 by Kruskal-Wallis test with Dunn’s multiple-comparison test. The data are presented as mean ± SEM (n = 50 per group from 3 independent experiments).