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 7

Macrophage SR-BI regulates autophagy via the VPS34 complex.

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Macrophage SR-BI regulates autophagy via the VPS34 complex. (A) WT macro...
(A) WT macrophages were treated with acetylated LDL and Sandoz 58035 for 24 hours and SR-BI and LC3II subcellular localization were examined by immunofluorescence confocal microscopy. Scale bar: 1 μm. (B) Plasma membrane, lysosome, ER, and nuclear fractions were isolated from WT macrophages by density-gradient ultracentrifugation, and SR-BI distribution was detected by Western blotting. LAMP-1 was used as a lysosomal marker. (C) FC-enriched WT macrophage lysates were cross-linked and immunoprecipitated with anti–SR-BI antibody or IgG and protein A/G magnetic beads. VPS34, Beclin-1, Barkor, Rab7, Bif-1, LC3, ATG5, and SR-BI were then detected in immunoprecipitated proteins by Western blotting. (D) SR-BI and Barkor are associated with cholesterol domains. FC-enriched WT macrophages were incubated with cholera toxin B (CT-B), which interacts with lipid rafts. Cell lysates were cross-linked and immunoprecipitated with anti–CT-B antibody or IgG and protein A/G magnetic beads. Barkor and SR-BI were then detected in immunoprecipitated proteins by Western blotting. In A–D, data are representative of 3 experiments. (E) VPS34 activity was measured using the Class III PI3K ELISA Kit in macrophages treated with or without 100 μg/mL oxLDL or 300 nM rapamycin for 24 hours. Data are expressed as mean ± SEM (n = 6 per group from 3 independent experiments). *P < 0.05, **P < 0.01 by 1-way ANOVA with Bonferroni’s post hoc test. (F) VPS34 activity was measured in aortic arch tissue lysates from Ldlr–/– mice reconstituted with WT or Sr-b1–/– bone marrow and fed either a chow or Western diet for 16 weeks. Data are expressed as mean ± SEM (n = 6 mice per group). *P < 0.05 by 1-way ANOVA with Bonferroni’s post hoc test.