The actomyosin cytoskeleton serves as a key regulator of the integrity and remodeling of epithelial barriers by controlling assembly and functions of intercellular junctions and cell‐matrix adhesions. Although biochemical mechanisms that regulate the activity of non‐muscle myosin II (NM‐II) in epithelial cells have been extensively investigated, little is known about assembly of the contractile myosin structures at the epithelial adhesion sites. UNC‐45A is a cytoskeletal chaperone that is essential for proper folding of NM‐II heavy chains and myofilament assembly. We found abundant expression of UNC‐45A in human intestinal epithelial cell (IEC) lines and in the epithelial layer of the normal human colon. Interestingly, protein level of UNC‐45A was decreased in colonic epithelium of patients with ulcerative colitis. CRISPR/Cas9‐mediated knock‐out of UNC‐45A in HT‐29cf8 and SK‐CO15 IEC disrupted epithelial barrier integrity, impaired assembly of epithelial adherence and tight junctions and attenuated cell migration. Consistently, decreased UNC‐45 expression increased permeability of the Drosophila gut in vivo. The mechanisms underlying barrier disruptive and anti‐migratory effects of UNC‐45A depletion involved disorganization of the actomyosin bundles at epithelial junctions and the migrating cell edge. Loss of UNC‐45A also decreased contractile forces at apical junctions and matrix adhesions. Expression of deletion mutants revealed roles for the myosin binding domain of UNC‐45A in controlling IEC junctions and motility. Our findings uncover a novel mechanism that regulates integrity and restitution of the intestinal epithelial barrier, which may be impaired during mucosal inflammation.

Introduction: Most serrated polyps (SPs) fall into two categories: hyperplastic polyps (HPs) and sessile serrated polyps (SSPs), the former lacking precancerous potential while the latter is precancerous. These subtypes can be difficult to diagnose histologically. Inaccuracy in SP diagnosis can lead to incorrect colonoscopy surveillance recommendations that can increase the risk of colorectal cancer. In this study, we present GI pathologists with previously diagnosed SPs and aim to quantify the frequency of diagnostic change of SPs and diagnostic agreement. Methods: Polyp pathology data was utilized from a colonoscopy quality database from colonoscopies performed from 2012-2020. 167 serrated polyps (either HP or SSP) were selected for analysis balanced on previous histology, size and location, excluding those found in patients with known polyposis syndromes. Polyp specimens underwent re-diagnosis from a five member GI pathology team, their experience ranging from fellow to experienced attending. Each pathologist reviewed pathological specimens independently without knowledge of the original diagnosis and made their diagnosis of SSPs following WHO definition. Effort was made to keep diagnostic conditions like real-world practice. Statistical analysis was performed in SPSS. Kappa analysis was performed for inter-observer agreement. Kappa values were grouped as poor (, 0.2), fair (0.21-0.40), moderate (0.41-0.60), good (0.61-0.80), and perfect ( .0.80). Means were compared using independent samples t-test. A p value less than 0.05 was considered significant. (Table ) Results: On average, the five GI pathologists re-diagnosed 163 SPs matching the previous diagnosis about 74.1% of all polyps. The mean kappa value for variability in SSP diagnoses between original diagnosis and each GI pathologist was 0.497. Kappa value for polyps less than 1 cm was 0.313 versus 0.692 for polyps greater than 1 cm (p50.006). The mean kappa value between all pathologists in their re-diagnosis was 0.669. There was no significant difference in kappa when stratified by proximal versus distal colon. Conclusion: Re-diagnosis of SSPs resulted in only moderate level agreement between GI pathologists and the previous diagnosis. Interestingly, inter-observer agreement among pathologists was at a good level, and there was increased agreement for larger polyps, but not for location. While moderate to good level of agreement is above what is reported in literature, our study highlights the need for improved diagnostic reproducibility of SSPs.

No abstract

No abstract

No abstract