He Hua, Huang Meina, Sun Shenfei, Wu Yihui, Lin Xinhua
State Key Laboratory of Membrane Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.
University of Chinese Academy of Sciences, Beijing, China.
PLoS Genet. 2017 Aug 31;13(8):e1006992. doi: 10.1371/journal.pgen.1006992. eCollection 2017 Aug.
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.
哺乳动物肺的树状结构由分支形态发生产生，这是一个由多种因素精确调控的重复过程。细胞表面和细胞外基质（ECM）分子如何调节这一过程仍知之甚少。在此，我们表明硫酸乙酰肝素（HS）合成酶Ext1的上皮细胞缺失导致分支尖端扩张和分支数量减少，并伴有多种间充质发育缺陷。我们进一步证明，在Ext1突变肺中Fgf10表达增加且FGF信号活性增强，提示一种细胞非自主机制。与此一致，我们观察到负责抑制Fgf10表达的SHH信号水平降低。此外，在突变肺中重新激活SHH信号可挽救尖端扩张表型并减弱FGF信号。重要的是，SHH信号活性降低似乎不是由Shh表达或蛋白质稳定性降低引起的；相反，在Ext1突变上皮细胞和周围野生型间充质细胞中，生物活性形式的SHH蛋白均减少。总之，我们的研究强调上皮HS是决定对肺形态发生至关重要的SHH信号的关键因素。
