Lung Epithelial Cell–Derived Microvesicles Regulate Macrophage Migration via MicroRNA-17/221–Induced Integrin β1 Recycling

Abstract

Robust lung inflammation is one of the prominent features in the pathogenesis of acute lung injury (ALI). Macrophage migration and recruitment are often seen at the early stage of lung inflammatory responses in response to noxious stimuli. Using an acid-inhalation induced lung injury model, we explored the mechanisms by which acid exposure initiates macrophage recruitment and migration during development of ALI. The lung epithelium comprises a large surface area and functions as a first-line defense against noxious insults. We found that acid exposure induced a remarkable microvesicle (MV) release from lung epithelium as detected in bronchoalveolar lavage fluid (BALF). Significantly elevated RNA, rather than protein, was found in these epithelium-derived MVs after acid and included several highly elevated microRNAs (miRNAs) including miR-17 and miR-221. Acid-induced-epithelial MV release promoted macrophage migration in vitro and recruitment into the lung in vivo and required, in part, MV-shuttling of miR-17 and/or miR-221. Mechanistically, acid-induced epithelial MV-miR-17/221 promoted β1 integrin recycling and presentation back onto the surface of macrophages, in part via a Rab11-mediated pathway. Integrin β1 is known to play an essential role in regulating macrophage migration. Taken together, acid-induced ALI results in epithelial MV-shuttling of miR-17/221 that in turn modulates macrophage β1 integrin recycling promoting macrophage recruitment and ultimately contribute to lung inflammation.

The role of microvesicles containing microRNAs in vascular endothelial dysfunction

“…miRNAs must be actively secreted from cells and selectively packaged into appropriate carriers, such as EVs (exosomes, MVs and apoptosis bodies), lipoproteins (LDL, HDL) and other ribonucleoprotein complexes . Selective and precise transport of miRNAs by MVs is the key step of extracellular miRNA‐mediated intercellular communication . Multiple miRNAs can be incorporated into one MV, but the exact mechanism of packaging is unclear .…”

“…Kuhn S et al provided first evidence that anti‐inflammatory adenosine significantly increased miR‐142‐3p levels in MMVs . Furthermore, a study found miR‐221, miR‐320a, miR‐92a and miR‐17 were significantly higher (greater than twofold) in hydrochloric acid‐induced MV release from lung epithelium . Secondly, in addition to inflammatory factors, other factors can also regulate the transfer of miRNA in MVs.…”

“…The places labelled with question marks are proposed but not clear transport of miRNAs by MVs is the key step of extracellular miRNAmediated intercellular communication. 66,67 Multiple miRNAs can be incorporated into one MV, but the exact mechanism of packaging is unclear. 68 Changes in miRNA content between MVs and their parental cells indicate a selective packaging of miRNAs into MVs.…”

“…67 Furthermore, a study found miR-221, miR-320a, miR-92a and miR-17 were significantly higher (greater than twofold) in hydrochloric acid-induced MV release from lung epithelium. 66 In addition, packing of miRNAs into specific MVs may also be affected by diseases. 118,119 For instance, miR-222 was demonstrated to be transported into recipient ECs by EMVs and functionally regulated expression of ICAM-1.…”

Fibronectin (FN) cooperated with TLR2/TLR4 receptor to promote innate immune responses of macrophages via binding to integrin β1

“…Cell surfacebound bacteria were quenched with trypan blue (2 mg/ml). After incubation periods, macrophage samples were fixed with 3.7% paraformaldehyde after cultured for 25,30,35,40,45,50,55,60,65,70,75,80,85 and 90 minutes at 37°C or a fixed time. To determine the kinetics of phagosome maturation, the co-localization of AF488-labeled E. coli with Lysotracker Red (a marker of acidic compartments) was examined by confocal microscopy (LSM 710, Carl Zeiss) at every minute interval from mixing macrophages with FITC-conjugated E. coli plus LPS and FN or PGN and FN up to 50 min.…”