JNK suppresses pulmonary fibroblast elastogenesis during alveolar development

Sheng Liu,Sarah M Young,Brian M Varisco,Harikrishnan Parameswaran

doi:10.1186/1465-9921-15-34

Sheng Liu, Sarah M Young + Show 2 more

Open Access

https://doi.org/10.1186/1465-9921-15-34

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Abstract

BackgroundThe formation of discrete elastin bands at the tips of secondary alveolar septa is important for normal alveolar development, but the mechanisms regulating the lung elastogenic program are incompletely understood. JNK suppress elastin synthesis in the aorta and is important in a host of developmental processes. We sought to determine whether JNK suppresses pulmonary fibroblast elastogenesis during lung development.MethodsAlveolar size, elastin content, and mRNA of elastin-associated genes were quantitated in wild type and JNK-deficient mouse lungs, and expression profiles were validated in primary lung fibroblasts. Tropoelastin protein was quantitated by Western blot. Changes in lung JNK activity throughout development were quantitated, and pJNK was localized by confocal imaging and lineage tracing.ResultsBy morphometry, alveolar diameters were increased by 7% and lung elastin content increased 2-fold in JNK-deficient mouse lungs compared to wild type. By Western blot, tropoelastin protein was increased 5-fold in JNK-deficient lungs. Postnatal day 14 (PND14) lung JNK activity was 11-fold higher and pJNK:JNK ratio 6-fold higher compared to PN 8 week lung. Lung tropoelastin, emilin-1, fibrillin-1, fibulin-5, and lysyl oxidase mRNAs inversely correlated with lung JNK activity during alveolar development. Phosphorylated JNK localized to pulmonary lipofibroblasts. PND14 JNK-deficient mouse lungs contained 7-fold more tropoelastin, 2,000-fold more emilin-1, 800-fold more fibrillin-1, and 60-fold more fibulin-5 than PND14 wild type lungs. Primarily lung fibroblasts from wild type and JNK-deficient mice showed similar differences in elastogenic mRNAs.ConclusionsJNK suppresses fibroblast elastogenesis during the alveolar stage of lung development.

Highlights

The formation of discrete elastin bands at the tips of secondary alveolar septa is important for normal alveolar development, but the mechanisms regulating the lung elastogenic program are incompletely understood
The enlarged distal airspaces and reduced numbers of secondary alveolar septal crests in JNK-deficient mice support a role for JNK in alveolar septation
JNK reduces lung elastin content To test whether JNK suppresses lung elastogenesis, elastin was morphometrically quantitated in Postnatal day 14 (PND14) wild type, JNK1−/− and JNK2&3−/− elastin-stained lung sections

Summary

Introduction

The formation of discrete elastin bands at the tips of secondary alveolar septa is important for normal alveolar development, but the mechanisms regulating the lung elastogenic program are incompletely understood. Beginning at approximately 35 weeks gestation and continuing for several years postnatally [1], large saccular air spaces in the lung are progressively divided into smaller ones by secondary alveolar septa leading to a twentyfold increase in alveolar surface area [2]. This exponential increase in gas-exchange capacity is essential to meeting the bioenergetic needs of ex utero growth and development. We hypothesized that activation of JNK suppresses elastogenesis during alveolar lung development contributing to the localization of elastin to alveolar septal tips. We assessed JNK activation during lung development, localized phosphorylated JNK by confocal microscopy, quantitated alveolar development and elastin localization in JNK deficient mice, and quantitated mRNA levels of elastin-associated genes in JNK deficient mouse lungs and primary fibroblasts

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Conclusion