Glucocorticoids Repress the Extracellular Matrix Proteoglycan Versican-V1 Isoform during Mouse Lung Development

Presentation Number: OR02-5
Date of Presentation: April 4th, 2017

Timothy James Cole*1, Kelly Short1 and Anthony Daniel Bird2
1Monash University, Melbourne, Australia, 2Hudson Institute, Melbourne, Australia

Abstract

Development of the functional human lung requires regulation of cellular proliferation and differentiation in specific germ layer compartments. Important endocrine regulators of mammalian lung development are glucocorticoid (GC) steroids such as cortisol. Previous work using global or conditional mouse knockouts of the glucocorticoid receptor (GR) gene have established that GR-mediated GC signalling in the mesenchymal compartment of the lung is crucial for normal respiratory development. Whole tissue and primary lung cell screens using NGS RNA-sequencing analysis from GR lung-mesenchyme and GR lung-epithelial cell targeted mouse models has profiled specific subsets of GR-regulated downstream gene target networks. These include mesenchymal regulation of ECM genes such as versican (Vcan), tropoelastin, and fibrillin 2, and epithelial cell regulation of surfactant metabolism, cell differentiation and growth factors such as midkine (1). We hypothesise that the severe mesenchymal cell hyperplasia observed during the saccular-stage of the GRmesKO fetal mouse lung is partially due to the lack of normal GR-mediated repression of the Vcan gene therefore driving inappropriate midkine-Vcan directed mesenchyme over-proliferation. GRmesKO mice were used to investigate in more detail Vcan as a potential GR regulated gene target. Alternative exon splicing of the Vcan gene generates 5 isoforms V0, V1, V2, V3 and V4 that vary in structure and function. Using isoform specific qPCR we observed that mRNA levels for all Vcan isoforms in the fetal mouse lung decline from E14.5 to P0.5. We also showed by immunohistochemistry that the V1 isoform containing the β GAG domain of Vcan is far more abundant in E16.5 lung than E18.5 suggesting that the β domain is spatially regulated in late lung development. All four Vcan isoform mRNA levels showed an increase in E18.5 GRmesKO lungs relative to controls. We did not detect large differences in protein immunostaining of Vcan between GRmesKO, GRnull and controls, but observed localised regions of strong overexpression of Vcan β GAG isoforms in both the E18.5 GRmesKO and total GR-deficient lung. In summary, GC steroids regulate the repression of the ECM protein Vcan V1 to contribute to coordinated mesenchymal thinning and the normal maturation of the respiratory system in mammals.

1. Bird AD et al. (2015) Molecular Endocrinology, 29(2): 158-171.

 

Nothing to Disclose: TJC, KS, ADB