Epithelial heparan sulfate regulates Sonic Hedgehog signaling in lung development

Abstract

The tree-like structure of the mammalian lung is generated from branching morphogenesis, a reiterative process that is precisely regulated by numerous factors. How the cell surface and extra cellular matrix (ECM) molecules regulate this process is still poorly understood. Herein, we show that epithelial deletion of Heparan Sulfate (HS) synthetase Ext1 resulted in expanded branching tips and reduced branching number, associated with several mesenchymal developmental defects. We further demonstrate an expanded Fgf10 expression and increased FGF signaling activity in Ext1 mutant lungs, suggesting a cell non-autonomous mechanism. Consistent with this, we observed reduced levels of SHH signaling which is responsible for suppressing Fgf10 expression. Moreover, reactivating SHH signaling in mutant lungs rescued the tip dilation phenotype and attenuated FGF signaling. Importantly, the reduced SHH signaling activity did not appear to be caused by decreased Shh expression or protein stability; instead, biologically active form of SHH proteins were reduced in both the Ext1 mutant epithelium and surrounding wild type mesenchymal cells. Together, our study highlights the epithelial HS as a key player for dictating SHH signaling critical for lung morphogenesis.

Multiple roles of epithelial heparan sulfate in stomach morphogenesis

“…In our recent study, we examined the role of epithelial HS in lung branching morphogenesis and demonstrated a surprisingly expanded distribution of Fgf10 expression and increased Fgf signaling activity in lung buds (He et al, 2017). The data shown here are very different from what we observed in the lung buds, raising an interesting question of the specific activities of HS in regulation of the Fgf signaling pathway.…”

“…Mice deficient in one allele of Ext1 appeared to be normal in terms of the gastrointestinal morphology, therefore Ext1 fl/+ ; Shh-Cre mice were used as controls. In contrast, Ext1 mutant mice died shortly after birth due to respiratory defects (He et al, 2017), and exhibited several gastrointestinal anomalies, e.g. small stomach and abnormal intestines ( Fig.…”

“…The zebrafish Glypican4 (knypek) mutant exhibits severe cardiac defects, which are attributed to elevated Bmp and canonical Wnt signaling in the presumptive cardiac mesoderm (Strate et al, 2015). In mouse embryonic lungs, ablation of epithelial HS decreases the biological activity of Shh in the underlying mesenchyme and causes lung dysplasia through Shh-Fgf signaling (He et al, 2017). Therefore, we sought to determine whether lack of epithelial HS affects Hh, Bmp and Wnt signaling pathways during stomach morphogenesis.…”

Extracellular Matrix Remodeling During Palate Development

“…80 Genetically abolish heparan sulfate in the lung epithelial cells leads to reduced SHH production in the epithelial and expanded Fgf10 expression in the underlying mesenchyme in the lung development. 83 Shh secreted by the palatal epithelium signals to the underlying palatal mesenchyme and regulate Fgfs expression. 1 Fgfs, in return, can either positively or negatively regulate SHH expression in the epithelium.…”

Taking the Occam’s Razor Approach to Hedgehog Lipidation and Its Role in Development

“…HSPG-modulated shedding also represents a useful model to explain functional links between cell-surface HS biosynthesis and Hh bioactivation in lung [ 106 ], spinal cord [ 60 ] and fly wing [ 59 ] development in vivo. Moreover, Scube2-regulated shedding provides an explanation for the compensated loss of embryonic Hh function as a consequence of simultaneous knockdown of all three Scube genes in triple MO embryos [ 68 ] by increased ligand expression.…”