Grainyhead-like 2 (GRHL2) distribution reveals novel pathophysiological differences between human idiopathic pulmonary fibrosis and mouse models of pulmonary fibrosis

Abstract

Chronic injury of alveolar lung epithelium leads to epithelial disintegrity in idiopathic pulmonary fibrosis (IPF). We had reported earlier that Grhl2, a transcriptional factor, maintains alveolar epithelial cell integrity by directly regulating components of adherens and tight junctions and thus hypothesized an important role of GRHL2 in pathogenesis of IPF. Comparison of GRHL2 distribution at different stages of human lung development showed its abundance in developing lung epithelium and in adult lung epithelium. However, GRHL2 is detected in normal human lung mesenchyme only at early fetal stage (week 9). Similar mesenchymal reexpression of GRHL2 was also observed in IPF. Immunofluorescence analysis in serial sections from three IPF patients revealed at least two subsets of alveolar epithelial cells (AEC), based on differential GRHL2 expression and the converse fluorescence intensities for epithelial vs. mesenchymal markers. Grhl2 was not detected in mesenchyme in intraperitoneal bleomycin-induced injury as well as in spontaneously occurring fibrosis in double-mutant HPS1 and HPS2 mice, whereas in contrast in a radiation-induced fibrosis model, with forced Forkhead box M1 (Foxm1) expression, an overlap of Grhl2 with a mesenchymal marker was observed in fibrotic regions. Grhl2's role in alveolar epithelial cell plasticity was confirmed by altered Grhl2 gene expression analysis in IPF and further validated by in vitro manipulation of its expression in alveolar epithelial cell lines. Our findings reveal important pathophysiological differences between human IPF and specific mouse models of fibrosis and support a crucial role of GRHL2 in epithelial activation in lung fibrosis and perhaps also in epithelial plasticity.

Epithelial–mesenchymal transition, a spectrum of states: Role in lung development, homeostasis, and disease

“…However, the presence of these cells co‐expressing epithelial and mesenchymal markers denotes an incomplete transition, and not necessarily a complete transition of an epithelial cell into a ECM‐producing myofibroblast. Similar to these reports of incomplete transition, cells in alveolar epithelium of IPF lungs co‐expressed epithelial marker GRHL2 with EMT markers VIM or ZEB1 (Varma et al, ), indicating a hybrid E/M phenotype. Similarly, bronchiolar basal metaplastic cells in IPF patients lose E‐cadherin expression only partially (Morbini et al, ).…”

Mutations in GRHL2 Result in an Autosomal-Recessive Ectodermal Dysplasia Syndrome

“…4,[8][9][10][11]18,27,28 With regard to the clinical phenotype in our affected individuals, aside from the changes affecting the skin and oral mucosa, the other main features comprised deafness and asthma, although this was variably present. Three subjects (ED-01 IV-4 and IV-5 and ED-02 VI-3) had deafness that developed in early infancy (c.f.…”

“…3,4 Biologically, GRHL2 contributes to formation of the epithelial barrier and wound healing, as well as neural-tube closure, maintenance of the mucociliary airway epithelium, and tumor suppression. [5][6][7][8][9][10][11] GRHL2 (MIM 608576) has been shown to regulate TERT (MIM 187270) expression and to enhance proliferation of epidermal keratinocytes; it also impairs keratinocyte differentiation through transcription inhibition of genes clustered at the epidermal differentiation complex 12 and regulates epithelial morphogenesis by establishing functional tight junctions. 13 GRHL2 is also present in the cochlear duct, 14 and mutations in human GRHL2 have been found in progressive autosomal-dominant hearing loss (DFNA28 [MIM 608641]), 15,16 and other polymorphic sequence variants in GRHL2 have been implicated in age-related hearing impairment and noise-induced hearing loss.…”

Genome-wide identification of Grainy head targets in Drosophila reveals regulatory interactions with the POU-domain transcription factor, Vvl

“…Additionally, Grhl mutant mice are extensively used to model epithelial disease, ranging from hearing loss to cancer (Gordon et al, 2014). Studies of Grhl2 downstream genes in mice and in human bronchial cells revealed its key role in epithelial morphogenesis, cell adhesion, and motility (Gao et al, 2013;Varma et al, 2014;Aue et al, 2015;Gao et al, 2015).…”