Desmoplakin Maintains Transcellular Keratin Scaffolding and Protects From Intestinal Injury

Abstract

Background & aims: Desmosomes are intercellular junctions connecting keratin intermediate filaments of neighboring cells. The cadherins desmoglein 2 (Dsg2) and desmocollin 2 mediate cell-cell adhesion, whereas desmoplakin (Dsp) provides the attachment of desmosomes to keratins. Although the importance of the desmosome-keratin network is well established in mechanically challenged tissues, we aimed to assess the currently understudied function of desmosomal proteins in intestinal epithelia.

Methods: We analyzed the intestine-specific villin-Cre DSP (DSP^ΔIEC) and the combined intestine-specific DSG2/DSP^ΔIEC (ΔDsg2/Dsp) knockout mice. Cross-breeding with keratin 8-yellow fluorescent protein knock-in mice and generation of organoids was performed to visualize the keratin network. A Dsp-deficient colorectal carcinoma HT29-derived cell line was generated and the role of Dsp in adhesion and mechanical stress was studied in dispase assays, after exposure to uniaxial cell stretching and during scratch assay.

Results: The intestine of DSP^ΔIEC mice was histopathologically inconspicuous. Intestinal epithelial cells, however, showed an accelerated migration along the crypt and an enhanced shedding into the lumen. Increased intestinal permeability and altered levels of desmosomal proteins were detected. An inconspicuous phenotype also was seen in ΔDsg2/Dsp mice. After dextran sodium sulfate treatment, DSP^ΔIEC mice developed more pronounced colitis. A retracted keratin network was seen in the intestinal epithelium of DSP^ΔIEC/keratin 8-yellow fluorescent protein mice and organoids derived from these mice presented a collapsed keratin network. The level, phosphorylation status, and solubility of keratins were not affected. Dsp-deficient HT29 cells had an impaired cell adhesion and suffered from increased cellular damage after stretch.

Conclusions: Our results show that Dsp is required for proper keratin network architecture in intestinal epithelia, mechanical resilience, and adhesion, thereby protecting from injury.

Keywords: Apical Junctional Complex; Cell Adhesion; Desmosome; Intestinal Epithelial Barrier; Keratin.