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 6

The effects of TFEB on autophagic activity in WT versus Sr-b1–/– macrophages and in atherosclerotic lesions.

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The effects of TFEB on autophagic activity in WT versus Sr-b1–/– macroph...
(A and B) Hematopoietic SR-BI deletion lowers the expression of TFEB in atherosclerotic lesions. Apoe–/– mice were constituted with Apoe–/– or Sr-b1–/– Apoe–/– (DKO) bone marrow and fed an atherogenic diet for 8 weeks. (A) Proximal aortic sections were stained using anti-TFEB primary antibody and FITC-labeled secondary antibody (green). Nuclei were counterstained with Hoechst (blue). Scale bar: 100 μm. (B) The TFEB-positive cells were quantitated by ImageJ software. Data are presented as mean ± SEM (n = 6 mice per group). ***P < 0.001 by unpaired Student’s t test. (C–F) Tfeb-expressing or control plasmid was transfected for 48 hours into WT or Sr-b1–/– macrophages using jetPEI-Macrophage DNA Transfection reagent. Cells were enriched with FC by incubation for 24 hours with 100 μg/mL acetylated LDL and 5 μg/mL Sandoz 58035. (C and D) Cytoplasmic and nuclear levels of TFEB in response to FC enrichment were analyzed by Western blotting and dot quantitation. (C) The blots are representative, and (D) the data are presented as mean ± SEM from 3 independent experiments (n = 3 per group). **P < 0.01 by 1-way ANOVA with Bonferroni’s post hoc test. (E) The mRNA levels for TFEB, VPS34, LC3, and Rab7 were measured by real-time PCR in Tfeb- or control plasmid–transfected cells with or without FC enrichment. The data are expressed as mean ± SEM from 3 independent experiments (n = 3 per group). *P < 0.05, **P < 0.01, ***P < 0.001 by 1-way ANOVA with Bonferroni’s post hoc test. (F) Tfeb overexpression rescues defective autophagy in Sr-b1–/– macrophages as examined by Western blotting of LC3II and TFEB levels. The blots are representative, and the numbers are the mean of 3 experiments, in which the values are normalized to WT basal levels (green, regular font).