Fig. 6.

Canonical WNT pathway regulates AE polarity and barrier function.

a-b) WNT activation impaired PIGR gene expression at all time periods (a) and decreased SC release (b), while WNT inhibition increased PIGR expression (a) and SC release (b), used as indices of basal-to-apical polarity as this system allows the transcytosis of polymeric IgA and IgM across the epithelial layer.

c-f) CHIR99021-induced WNT activation also decreased the expression of key components of tight and adherens junctions, namely TJP1 (c) and CDH1 (d), and resulted in diminished E-cadherin protein levels (e-f), while WNT inhibition increased TJP1 (c) and E-cadherin (e-f), underscoring the importance of WNT in the epithelial barrier function and tightness.

g) Representative pictures of ALI-reconstituted epithelium, cultured under vehicle condition (DMSO), WNT activation (CHIR99021) or WNT inhibition regimen (XAV939), and immunostained for markers of polarity (pIgR, left panel) and tightness/barrier function (occludin, right panel). WNT activation decreased pIgR and occludin, while WNT inhibition increased pIgR. Occludin staining shows both junctional occludin (cell membrane) and off-target nuclear occludin 1B, an alternatively spliced transcript.

*, ** indicate p-values of less than 0•05 and 0•01, respectively (analysed using the Mann-Whitney test). Columns and bars in the graphs represent medians ± interquartile range. Scale bars, 20 µm. CHIR^act, CHIR99021-induced WNT activation condition; HKG, housekeeping genes; XAV^inh, XAV939-induced inhibition condition.