MEK1 regulates pulmonary macrophage inflammatory responses and resolution of acute lung injury
Matthew E. Long, … , W. Conrad Liles, Anne M. Manicone
Matthew E. Long, … , W. Conrad Liles, Anne M. Manicone
Published December 5, 2019
Citation Information: JCI Insight. 2019;4(23):e132377. https://doi.org/10.1172/jci.insight.132377.
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Research Article Inflammation Pulmonology

MEK1 regulates pulmonary macrophage inflammatory responses and resolution of acute lung injury

Abstract

The MEK1/2–ERK1/2 pathway has been implicated in regulating the inflammatory response to lung injury and infection, and pharmacologic MEK1/2 inhibitor compounds are reported to reduce detrimental inflammation in multiple animal models of disease, in part through modulation of leukocyte responses. However, the specific contribution of myeloid MEK1 in regulating acute lung injury (ALI) and its resolution remain unknown. Here, the role of myeloid Mek1 was investigated in a murine model of LPS-induced ALI (LPS-ALI) by genetic deletion using the Cre-floxed system (LysMCre × Mekfl), and human alveolar macrophages from healthy volunteers and patients with acute respiratory distress syndrome (ARDS) were obtained to assess activation of the MEK1/2–ERK1/2 pathway. Myeloid Mek1 deletion results in a failure to resolve LPS-ALI, and alveolar macrophages lacking MEK1 had increased activation of MEK2 and the downstream target ERK1/2 on day 4 of LPS-ALI. The clinical significance of these findings is supported by increased activation of the MEK1/2–ERK1/2 pathway in alveolar macrophages from patients with ARDS compared with alveolar macrophages from healthy volunteers. This study reveals a critical role for myeloid MEK1 in promoting resolution of LPS-ALI and controlling the duration of macrophage proinflammatory responses.

Authors

Matthew E. Long, Ke-Qin Gong, William E. Eddy, Joseph S. Volk, Eric D. Morrell, Carmen Mikacenic, T. Eoin West, Shawn J. Skerrett, Jean Charron, W. Conrad Liles, Anne M. Manicone

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Figure 1

Mek1flLysMCre reduces alveolar macrophage MEK1 and decreases proinflammatory gene expression following LPS stimulation.

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Mek1flLysMCre reduces alveolar macrophage MEK1 and decreases proinflamm...
(A) Protein lysates from alveolar macrophages were recovered from naive female and male mice by bronchoalveolar lavage (BAL) and were used to detect total MEK1, MEK2, and GAPDH levels by Western blot. (B) Quantification by band densitometry revealed significant reduction in MEK1 without changes in MEK2 in Mek1flLysMCre mice compared with Mek1fl mice. Data points show values derived from an individual mouse (n = 4 for Mek1fl and n = 10 for Mek1flLysMCre), and the bars represent the mean ± SEM. (C) Quantitation of alveolar macrophages recovered from BAL of naive Mek1fl mice (n = 4 female, n = 5 male) and Mek1flLysMCre (n = 5 female, n = 5 male) reveal no differences in the total number of cells recovered. (D) Alveolar macrophages collected from the same mice as in C were allowed to attached to tissue culture plates and were stimulated with 50 ng/mL E. coli LPS for 4 hours. RNA was isolated and cDNA used as the template in qPCR reactions to measure proinflammatory gene expression. Relative Cxcl1, Il1b, Nos2, Ccl5, Ifit1, and Cxcl10 were compared to Hprt, and data are normalized to Mek1fl samples. Data points show values derived from an individual mouse and the bars represent the mean ± SEM. In A–D, statistical analysis used an unpaired t test. **P < 0.01, ***P < 0.001, ****P < 0.0001; ns, not significant.