Roles of the cellular prion protein in the regulation of cell-cell junctions and barrier function

The cellular prion protein was historically characterized owing to its misfolding in prion disease. Although its physiological role remains incompletely understood, PrP(C) has emerged as an evolutionary conserved, multifaceted protein involved in a wide-range of biological processes. PrP(C) is a GPI-anchored protein targeted to the plasma membrane, in raft microdomains, where its interaction with a repertoire of binding partners, which differ depending on cell models, mediates its functions. Among identified PrP(C) partners are cell adhesion molecules. This review will focus on the multiple implications of PrP(C) in cell adhesion processes, mainly the regulation of cell-cell junctions in epithelial and endothelial cells and the consequences on barrier properties. We will show how recent findings argue for a role of PrP(C) in the recruitment of signaling molecules, which in turn control the targeting or the stability of adhesion complexes at the plasma membrane.

Requirement of cellular prion protein for intestinal barrier function and mislocalization in patients with inflammatory bowel disease

BACKGROUND & AIMS

Cell adhesion is one function regulated by cellular prion protein (PrP(c)), a ubiquitous, glycosylphosphatidylinositol-anchored glycoprotein. PrP(c) is located in cell-cell junctions and interacts with desmosome proteins in the intestinal epithelium. We investigated its role in intestinal barrier function.

METHODS

We analyzed permeability and structure of cell-cell junctions in intestine tissues from PrP(c) knockout (PrP(c-/-)) and wild-type mice. PrP(c) expression was knocked down in cultured human Caco-2/TC7 enterocytes using small hairpin RNAs. We analyzed colon samples from 24 patients with inflammatory bowel disease (IBD).

RESULTS

Intestine tissues from PrP(c-/-) mice had greater paracellular permeability than from wild-type mice (105.9 ± 13.4 vs 59.6 ± 10.1 mg/mL fluorescein isothiocyanate-dextran flux; P < .05) and impaired intercellular junctions. PrP(c-/-) mice did not develop spontaneous disease but were more sensitive than wild-type mice to induction of colitis with dextran sulfate (32% mortality vs 4%, respectively; P = .0033). Such barrier defects were observed also in Caco-2/TC7 enterocytes following PrP(c) knockdown; the cells had increased paracellular permeability (1.5-fold over 48 hours; P < .001) and reduced transepithelial electrical resistance (281.1 ± 4.9 vs 370.6 ± 5.7 Ω.cm(2); P < .001). Monolayer shape and cell-cell junctions were altered in cultures of PrP(c) knockdown cells; levels of E-cadherin, desmoplakin, plakoglobin, claudin-4, occludin, zonula occludens 1, and tricellulin were decreased at cell contacts. Cell shape and junctions were restored on PrP(c) re-expression. Levels of PrP(c) were decreased at cell-cell junctions in colonic epithelia from patients with Crohn's disease or ulcerative colitis.

CONCLUSIONS

PrP(c) regulates intestinal epithelial cell-cell junctions and barrier function. Its localization is altered in colonic epithelia from patients with IBD, supporting the concept that disrupted barrier function contributes to this disorder.

Acetabular revision using a press-fit dual mobility cup

INTRODUCTION

Dual mobility cups are especially indicated in total hip replacement revision, the risk of recurrent instability being greater than in primary surgery. In revision, however, primary cup fixation is uncertain without routine anchoring screws.

HYPOTHESIS

The stability of dual mobility cups impacted without cement, supplementary screw(s) or anchoring pegs fixation is satisfactory in total hip arthroplasty acetabular component revision, and prevents instability accidents.

PATIENTS AND METHODS

Twenty three patients were operated on by the same surgeon between January 1999 and December 2006 and prospectively followed up to a mean 4 1/2 years (range,2-10 yrs). A Collégia cup (Wright Medical France, Créteil, France) was impacted in 23 total hip arthroplasty acetabular component revisions, including 17 cases of SOFCOT grade-1 bone-stock loss and six of grade 2.

RESULTS

There were six clinically poor results on the Merle D'Aubigné scale. One case of early migration occurred, in a multioperated acetabulum. There was one isolated dislocation and one recurrent dislocation associated with loose greater trochanter nonunion, but tolerated as it was infrequent.

DISCUSSION

This option simplifies revision surgery and limits the risk of dislocation if the abductor muscles unit is continuous. It is indicated when local bone-site compromise encompass a wall-contained cavitary defect at most. A medial wall defect, if moderate, does not in our view preclude using a primary cup, impacted with a certain degree of protrusion. Longer-term follow-up will be needed to confirm these medium-term findings.

LEVEL OF EVIDENCE

Level IV. Prospective non comparative therapeutic study.