BACKGROUND@#
Macrophages are involved in the pathogenesis of
idiopathic pulmonary fibrosis, partially by activating
lung fibroblasts. However, how
macrophages communicate with
lung fibroblasts is largely unexplored.
Exosomes can mediate intercellular
communication, whereas its
role in
lung fibrogenesis is unclear. Here we aim to investigate whether
exosomes can mediate the crosstalk between
macrophages and
lung fibroblasts and subsequently induce
fibrosis.@*
METHODS@#In vivo,
bleomycin (BLM)-induced
lung fibrosis model was established and
macrophages infiltration was examined. The effects of GW4869, an
exosomes inhibitor, on
lung fibrosis were assessed. Moreover,
macrophage exosomes were injected into
mice to observe its pro-fibrotic effects.
In vitro,
exosomes derived from
angiotensin II (Ang II)-stimulated
macrophages were collected. Then,
lung fibroblasts were treated with the
exosomes. Twenty-four hours later,
protein levels of α-
collagen I,
angiotensin II type 1 receptor (AT1R),
transforming growth factor-β (TGF-β), and phospho-Smad2/3 (p-Smad2/3) in
lung fibroblasts were examined. The
Student's t test or
analysis of variance were used for
statistical analysis.@*RESULTS@#In vivo, BLM-treated
mice showed enhanced infiltration of
macrophages, increased fibrotic alterations, and higher levels of Ang II and AT1R. GW4869 attenuated BLM-induced
pulmonary fibrosis.
Mice with
exosomes injection showed fibrotic features with higher levels of Ang II and AT1R, which was reversed by
irbesartan.
In vitro, we found that
macrophages secreted a great number of
exosomes. The
exosomes were taken by
fibroblasts and resulted in higher levels of AT1R (0.22 ± 0.02 vs. 0.07 ± 0.02, t = 8.66, P = 0.001), TGF-β (0.54 ± 0.05 vs. 0.09 ± 0.06, t = 10.00, P < 0.001), p-Smad2/3 (0.58 ± 0.06 vs. 0.07 ± 0.03, t = 12.86, P < 0.001) and α-
collagen I (0.27 ± 0.02 vs. 0.16 ± 0.01, t = 7.01, P = 0.002), and increased Ang II
secretion (62.27 ± 7.32 vs. 9.56 ± 1.68, t = 12.16, P < 0.001). Interestingly, Ang II increased the number of
macrophage exosomes, and the
protein levels of Alix (1.45 ± 0.15 vs. 1.00 ± 0.10, t = 4.32, P = 0.012), AT1R (4.05 ± 0.64 vs. 1.00 ± 0.09, t = 8.17, P = 0.001), and
glyceraldehyde-3-phosphate dehydrogenase (2.13 ± 0.36 vs. 1.00 ± 0.10, t = 5.28, P = 0.006) were increased in
exosomes secreted by the same number of
macrophages, indicating a positive loop between Ang II and
exosomes production.@*CONCLUSIONS@#
Exosomes mediate intercellular
communication between
macrophages and
fibroblasts plays an important
role in BLM-induced
pulmonary fibrosis.