Fig. 1.

E. coli infectioninduced significant upregulation of tight junction proteins in vitamin D sufficient mice and human urinary bladders. Expression of the tight junction proteins occludin and claudin-14 in the mouse urinary bladder during vitamin D deficiency (n = 6) and sufficiency (n = 6) (a, a’, b,b’) without and (a”, a”’, b”,b”’) with transurethrally induced E. coli urinary tract infection. Bladder biopsies were obtained from postmenopausal women (n = 7) with insufficient vitamin D (25D₃) levels before and after 12 weeks vitamin D supplementation. Biopsies were either (c, c’, d, and d’) uninfected or (c”, c”’, d”,d”’) E. coli infected ex vivo. Immunohistochemistry revealed no significant difference in (a, a’, b,b’) uninfected mice and (c, c’, d,d’) human bladders with or without sufficient vitamin D. Contrary, a significant upregulation as measured with densitometry of occludin and claudin-14 was observed in the urinary bladders of (a””, b””) E. coli infected vitamin D sufficient mice and (c”’, d””) ex vivo E. coli infected human bladder biopsies. Occludin and claudin-14 were localized in the superficial uroepithelium including the larger umbrella cells, lining the bladder lumen. Representative tissue samples are shown. Average mean fluorescence intensity per unit area is depicted in the right panel from three random view fields of each section. Images were captured at 40 × magnification and occludin and claudin-14 were stained with AlexaFluor 594 (red) and the cell nucleus with DAPI (blue). Zoomed images are shown as inserts, at 4 × further magnification. Data are shown as mean + SEM, **P < 0.01, ****P < 0.0001