Abstract
Murine models describe a defined host/pathogen interaction for urinary tract infection, but human cell studies are scant. Although recent human urothelial organoid models are promising, none demonstrate long-term tolerance to urine, the natural substrate of the tissue and of the uropathogens that live there. We developed a novel human organoid from progenitor cells which demonstrates key structural hallmarks and biomarkers of the urothelium. After three weeks of transwell culture with 100% urine at the apical interface, the organoid stratified into multiple layers. The apical surface differentiated into enlarged and flattened umbrella-like cells bearing characteristic tight junctions, structures resembling asymmetric unit membrane plaques, and a glycosaminoglycan layer. The apical cells also expressed cytokeratin-20, a spatial feature of the mammalian urothelium. Urine itself was necessary for full development, and undifferentiated cells were urine-tolerant despite the lack of membrane plaques and a glycosaminoglycan layer. Infection with Enterococcus faecalis revealed the expected invasive outcome, including urothelial sloughing and the formation of intracellular colonies similar to those previously observed in patient cells. This new biomimetic model could help illuminate invasive behaviours of uropathogens, and serve as a reproducible test bed for disease formation, treatment and resolution in patients.
Highlights
UTIs are amongst the most common infectious diseases worldwide, but despite being associated with substantial economic and human cost[1,2], they are grossly understudied relative to other human diseases
UTI is problematic in more vulnerable subgroups: the risk of UTI dramatically increases in people with multiple sclerosis (MS)[6,7], spinal injury[8], renal transplant patients[9] and anyone requiring urinary catheterization or other indwelling devices[10]
Our laboratory studies the uropathogen Enterococcus faecalis. This bacterium is commonly implicated in chronic UTI in the elderly and is frequently associated with multi-drug resistance, hospital-acquired infection, and catheter-associated biofilm formation; we previously demonstrated that it exhibits intracellular invasion in patient cells[54,55,56,57,58,59,60,61,62]
Summary
UTIs are amongst the most common infectious diseases worldwide, but despite being associated with substantial economic and human cost[1,2], they are grossly understudied relative to other human diseases. Among healthy young women who suffer from their first UTI, the risk of recurrence within 6 months is 24%2; in another study, 2% of women studied had six or more episodes in a two-year period[5] These findings suggest that current treatment regimens are not ideal. The urinary bladder is lined by a specialised transitional urothelium comprising 3–7 layers of cells: basal cells (above the basement membrane), intermediate cells (above basal cells) and morphologically distinct, highly specialised, often binucleated umbrella cells at the apical surface, which face outward into the bladder lumen[17] These enlarged, flattened urothelial umbrella cells (or ‘facet cells’) partition urine and are thought to act as a powerful barrier to protect underlying tissue from harmful waste compounds[18]. Only heparan sulphate was detected in the luminal portion of calf bladders, elucidating possible differences between species[24]
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