Plectin ensures intestinal epithelial integrity and protects colon against colitis

Abstract

Plectin, a highly versatile cytolinker protein, provides tissues with mechanical stability through the integration of intermediate filaments (IFs) with cell junctions. Here, we hypothesize that plectin-controlled cytoarchitecture is a critical determinant of the intestinal barrier function and homeostasis. Mice lacking plectin in an intestinal epithelial cell (IEC; PleΔIEC) spontaneously developed colitis characterized by extensive detachment of IECs from the basement membrane (BM), increased intestinal permeability, and inflammatory lesions. Moreover, plectin expression was reduced in the colons of ulcerative colitis (UC) patients and negatively correlated with the severity of colitis. Mechanistically, plectin deficiency in IECs led to aberrant keratin filament (KF) network organization and the formation of dysfunctional hemidesmosomes (HDs) and intercellular junctions. In addition, the hemidesmosomal α6β4 integrin (Itg) receptor showed attenuated association with KFs, and protein profiling revealed prominent downregulation of junctional constituents. Consistent with the effects of plectin loss in the intestinal epithelium, plectin-deficient IECs exhibited remarkably reduced mechanical stability and limited adhesion capacity in vitro. Feeding mice with a low-residue liquid diet that reduced mechanical stress and antibiotic treatment successfully mitigated epithelial damage in the PleΔIEC colon.

Identifying Plectin Isoform Functions through Animal Models

“…Two mouse models have been generated to study plectin in single epithelia. In one, plectin was deleted in the liver [ 23 ], in the other, in the intestinal epithelium [ 24 ]. The deletion in the liver was achieved by crossing plectin floxed mice with Alb-Cre transgenic mice in which the expression of the Cre recombinase is under the control of the albumin promoter [ 25 ].…”

“…To generate an intestinal epithelium conditional KO mouse, plectin floxed mice were crossed with villin-Cre transgenic mice [ 29 ] in which the expression of the Cre recombinase is driven by the promoter of villin, a protein which is highly expressed in the adult intestine. The most significant phenotype of the resulting Villin-Cre/cKO (plec ΔIEC ) mice was the weakening of the intestinal barrier with concomitant loss of its selective permeability, leading to chronic inflammation and colitis [ 24 ]. Mechanistically, this is due to the downregulation of the hemidesmosomal and junctional components integrin α6β4, ZO-1, E-cadherin, desmoglein-2 and desmoplakin, resulting in abnormal HD formation, leaky intercellular junctions, and unanchored keratin filaments.…”

“…Mechanistically, this is due to the downregulation of the hemidesmosomal and junctional components integrin α6β4, ZO-1, E-cadherin, desmoglein-2 and desmoplakin, resulting in abnormal HD formation, leaky intercellular junctions, and unanchored keratin filaments. As these structures are no longer able to hold the IECs attached to the basement membrane and subjacent lamina propia, or hold the IECs together, an extensive detachment of the IECs ensues, weakening the intestinal barrier [ 24 ]. The depletion of plectin in the intestinal epithelium results in a phenotype that is more severe compared to plectin deficiency in the liver [ 23 ] but less severe compared to integrin α6β4 deficiency in the intestinal epithelium [ 30 ].…”

“…However, in contrast to plectin-cKO mice, the lesions in α6-cKO mice spontaneously degenerate into adenocarcinoma. In humans, plectin expression is significantly reduced in colon biopsies of patients with ulcerative colitis [ 24 ].…”

Desmoplakin Maintains Transcellular Keratin Scaffolding and Protects From Intestinal Injury

“…This was somewhat surprising given that intestinal epithelial-specific loss of plectin, another cytolinker connecting keratin filaments with cell junctions, led to spontaneous colitis. 18 Therefore, we decided to systematically study the impact of Dsp loss on keratin network architecture as well as the susceptibility to intestinal injury. To that end, DSP ΔIEC mice were cross-bred with the reporter K8-yellow fluorescent protein (YFP) knock-in mouse 19 or subjected to dextran sodium sulfate (DSS)-induced colitis.…”