Deciphering the interaction between FGF10 and CTNNB1 signalling during early lung branching morphogenesis

Objectives:

Lung regeneration after injury recapitulates many of the signalling pathways used during lung development. It is therefore vital to understand the basic mechanisms regulating the developing lung, to better understand the mechanisms potentially involved in lung repair. Fibroblast growth factor 10 (FGF10) signalling, in cooperation with Wnt/ß-catenin, plays an essential regulatory role during lung branching morphogenesis in the mouse. However, the exact mechanisms of signalling interaction during morphogenesis remain obscure. Through the use of a dominant negative transgenic mouse model (Rosa26rtTA; Tet(o)solFgfr2b), we conditionally inhibited FGF10/FGFR2b signalling in E12.5 embryonic lungs, in vivo. We also conducted in vitro experiments to further investigate our in vivo findings. In so doing, we aim to elucidate novel mechanisms by which FGF10 regulates branching morphogenesis via Wnt/ß-catenin in the developing lung.

Results:

Gene array, immunofluorescence, electron microscopy and in-silico results show that FGF10 tightly controlled epithelial cellular adhesion and arrangement, in our in vivo model. In particular, FGF10 regulated the expression of the adherens-junction protein complex composed of catenin delta-2 (CTNND2), E-cadherin (CDH1), and ß-catenin (CTNNB1). In vitro Ctnnd2 siRNA-based loss-of-function experiments are being carried out. We are also investigating whether CDH1 inhibition or ß-catenin overexpression in the epithelium can rescue the branching defects observed upon FGFR2b signalling inhibition. Finally, the use of IQ1, a pharmacological inhibitor of the CTNNB1/P300 interaction, is being evaluated. Preliminary results from these in vitro experiments indicate that either inhibition of CTNNB1/P300 or knock-down of Ctnnd2 was sufficient to significantly phenocopy the in vivo inhibition of FGF10 signalling.

Conclusions:

The connection between FGF10 and Wnt/ß-catenin signalling via CTNND2/CDH1/P300/CTNNB1 regulation has never been characterized in the context of lung branching morphogenesis. Therefore, our results might suggest a novel signalling axis important during early lung development.