Monocyte-derived alveolar macrophage apolipoprotein E participates in pulmonary fibrosis resolution
Huachun Cui, Dingyuan Jiang, Sami Banerjee, Na Xie, Tejaswini Kulkarni, Rui-Ming Liu, Steven R. Duncan, Gang Liu
Huachun Cui, Dingyuan Jiang, Sami Banerjee, Na Xie, Tejaswini Kulkarni, Rui-Ming Liu, Steven R. Duncan, Gang Liu
View: Text | PDF
Research Article Pulmonology

Monocyte-derived alveolar macrophage apolipoprotein E participates in pulmonary fibrosis resolution

Abstract

Recent studies have presented compelling evidence that it is not tissue-resident, but rather monocyte-derived alveolar macrophages (TR-AMs and Mo-AMs, respectively) that are essential to development of experimental lung fibrosis. However, whether apolipoprotein E (ApoE), which is produced abundantly by Mo-AMs in the lung, plays a role in the pathogenesis is unclear. In this study, we found that pulmonary ApoE was almost exclusively produced by Mo-AMs in mice with bleomycin-induced lung fibrosis. We showed that, although ApoE was not necessary for developing maximal fibrosis in bleomycin-injured lung, it was required for the resolution of this pathology. We found that ApoE directly bound to Collagen I and mediated Collagen I phagocytosis in vitro and in vivo, and this process was dependent on low-density lipoprotein receptor–related protein 1 (LPR1). Furthermore, interference of ApoE/LRP1 interaction impaired the resolution of lung fibrosis in bleomycin-treated WT mice. In contrast, supplementation of ApoE promoted this process in ApoE–/– animals. In conclusion, Mo-AM–derived ApoE is beneficial to the resolution of lung fibrosis, supporting the notion that Mo-AMs may have distinct functions in different phases of lung fibrogenesis. The findings also suggest a potentially novel therapeutic target for treating lung fibrosis, to which effective remedies remain scarce.

Authors

Huachun Cui, Dingyuan Jiang, Sami Banerjee, Na Xie, Tejaswini Kulkarni, Rui-Ming Liu, Steven R. Duncan, Gang Liu

×

Figure 6

ApoE promotes type I Collagen phagocytosis by macrophages, which is dependent on LRP1.

Options: View larger image (or click on image) Download as PowerPoint
ApoE promotes type I Collagen phagocytosis by macrophages, which is depe...
(A and B) FITC-conjugated type I Collagen or albumin (50 μg/mL) was preincubated with conditioned media with or without mouse ApoE. The mixtures were then incubated with mouse alveolar macrophages for 4 hours. After extensive wash, flow cytometry was performed in the presence of 0.02% trypan blue. Cells without incubation with Collagen I were used as a negative control (neg.) (A). Collagen I or albumin uptake was reflected by mean fluorescence index (MFI) (B). n = 3; mean ± SD; **P < 0.01 by 2-tailed Student’s t test. (C) Six-week-old WT and ApoE–/– male mice were i.t. instilled with BLM. Four weeks later, mice were i.t. injected with 50 μg FITC-conjugated type I Collagen. Two hours later, AMs were isolated, and representative images of the AMs demonstrating Collagen I uptake are shown. Original magnification, ×200. Scale bars: 100 μm. (D) Quantitation of single cell fluorescence intensity was performed by ImageJ with a minimum of 200 cells analyzed and average calculated. Relative levels of Collagen I uptake are shown. ***P < 0.001 by 2-tailed Student’s t test. (E) Alveolar macrophages were preincubated with 2 μg/mL BSA, COG133, or LRPAP1 for 30 minutes. The cells were then incubated with conditioned media with or without ApoE for 30 minutes. After extensive wash, cell surface–bound ApoE was determined by flow cytometry. n = 3 for each group; mean ± SD. (F) A 96-well high-binding plate was precoated with 10 μg/mL Collagen I overnight at 4°C. Wells were washed and incubated with 50 ng/mL BSA or 50 ng/mL ApoE together with the indicated amounts of COG133 or LRPAP1, followed by incubation with ApoE antibody and HRP-conjugated secondary antibody and development with TMB substrate. n = 3; mean ± SD. (G) Alveolar macrophages were preincubated with 2 μg/mL BSA, COG133, or LRPAP1 for 30 minutes. The cells were then incubated with mixture of type I Collagen with control or ApoE conditioned media for 4 hours, followed by flow cytometry as in A and B. n = 3; mean ± SD. (H and I) Alveolar macrophages were treated as in G. Original magnification, ×400. Scale bars: 50 μm (H). Quantitation of single cell fluorescence intensity was performed by ImageJ and average calculated. Relative levels of Collagen I uptake are shown (I). *P < 0.05, **P < 0.01, ***P < 0.001 by 1-way ANOVA with Bonferroni’s post hoc test (E–I). The box-and-whisker plots depict the 25th and 75th percentiles and median, minimum, and maximum values (D and I).