EMC3 coordinates surfactant protein and lipid homeostasis required for respiration
Xiaofang Tang, … , Xinhua Lin, Jeffrey A. Whitsett
Xiaofang Tang, … , Xinhua Lin, Jeffrey A. Whitsett
Published December 1, 2017; First published October 30, 2017
Citation Information: J Clin Invest. 2017;127(12):4314-4325. https://doi.org/10.1172/JCI94152.
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Research Article Angiogenesis Pulmonology

EMC3 coordinates surfactant protein and lipid homeostasis required for respiration

Abstract

Adaptation to respiration at birth depends upon the synthesis of pulmonary surfactant, a lipid-protein complex that reduces surface tension at the air-liquid interface in the alveoli and prevents lung collapse during the ventilatory cycle. Herein, we demonstrated that the gene encoding a subunit of the endoplasmic reticulum membrane complex, EMC3, also known as TMEM111 (Emc3/Tmem111), was required for murine pulmonary surfactant synthesis and lung function at birth. Conditional deletion of Emc3 in murine embryonic lung epithelial cells disrupted the synthesis and packaging of surfactant lipids and proteins, impaired the formation of lamellar bodies, and induced the unfolded protein response in alveolar type 2 (AT2) cells. EMC3 was essential for the processing and routing of surfactant proteins, SP-B and SP-C, and the biogenesis of the phospholipid transport protein ABCA3. Transcriptomic, lipidomic, and proteomic analyses demonstrated that EMC3 coordinates the assembly of lipids and proteins in AT2 cells that is necessary for surfactant synthesis and function at birth.

Authors

Xiaofang Tang, John M. Snowball, Yan Xu, Cheng-Lun Na, Timothy E. Weaver, Geremy Clair, Jennifer E. Kyle, Erika M. Zink, Charles Ansong, Wei Wei, Meina Huang, Xinhua Lin, Jeffrey A. Whitsett

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Figure 5

Loss of Emc3 induced the unfolded protein response in EpCAM+ sorted epithelial cells.

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Loss of Emc3 induced the unfolded protein response in EpCAM+ sorted epit...
(A and B) Heatmap of the mRNAs (A, blue/red) and proteins (B, blue/yellow) involved in the UPR pathway are shown. Proteomic and RNA sequencing data were obtained from EpCAM+ sorted epithelial cells from control and Emc3-cKO mice at E18.5. Genes and proteins were categorized by ToppGene. P values and fold changes for each mRNA and protein are listed in Supplemental Table 2. (C–H) Immunohistochemical staining for ATF3 (C and D), ATF4 (E and F), and ATF6 (G and H) was performed on lung sections from E18.5 control and Emc3-cKO embryos. ATF3 and ATF4 staining was increased and ATF6 staining was unaltered in the mutant lungs. Scale bars: 100 μm. (I) Western blots using EpCAM+ cell lysates from control and mutant lungs at E18.5 were performed using the indicated antibodies. (J) Increased Xbp1 splicing in Emc3-cKO mice. Levels of the spliced Xbp1 transcript [Xbp1(S)] were normalized to that of the full-length Xbp1 by qPCR. mRNAs were isolated from E18.5 control and Emc3-cKO EpCAM+ cells. Data are the mean ± SEM. *P < 0.05 using unpaired, 2-tailed Student’s t test. n = 4/group. (K) Model for the induction of UPR in Emc3-cKO AT2 cells. The model was built based on the integration of RNA sequencing and proteomic data. Relationships between differentially expressed genes and proteins were determined by Genomatix Pathway System (GePS) and Ingenuity Pathway Analysis (IPA) suites. System models were created using IPA’s Path Designer.