Investigation of facilitative urea transporters in the human gastrointestinal tract

Abstract

The symbiotic relationship between humans and their intestinal microbiome is supported by urea nitrogen salvaging. Previous studies have shown that colonic UT‐B urea transporters play a significant role in this important physiological process. This current study investigated UT‐A and UT‐B urea transporter expression along the human gastrointestinal tract. Initial end‐point PCR experiments determined that UT‐A RNA was predominantly expressed in the small intestine, while UT‐B RNA was expressed in stomach, small intestine, and colon. Using western blotting experiments, a strong 40–60 kDa UT‐B signal was found to be abundant in both ileum and colon. Importantly, this signal was deglycosylated by PNGaseF enzyme treatment to a core protein of 30 kDa in both tissues. Further immunolocalization studies revealed UT‐B transporter proteins were present at the apical membrane of the villi in the ileum, but predominantly at the basolateral membrane of the colonic surface epithelial cells. Finally, a blind scoring immunolocalization study suggested that there was no significant difference in UT‐B abundance throughout the colon (NS, ANOVA, N = 5–21). In conclusion, this current study suggested UT‐B to be the main human intestinal urea transporter. Intriguingly, these data suggested that the same UT‐B isoform was present in all intestinal epithelial cells, but that the precise cellular location varied.

Regional investigation of UT-B urea transporters in the rat brain

“…Finally, the 100 kDa was predominantly found in cytosolic fractions for both C6 and RT4 cells, rather than the membrane fraction, and was weakly expressed in RT4 cells, which are known for their high level of UT-B protein [ 25 ]. These outcomes are supported by our previous studies that have reported similar 100 kDa bands in UT-B-deficient tissues, including the human liver [ 27 ]. Moreover, other groups’ investigations using similar antibodies targeted to the C-terminal of UT-B have observed similar 100 kDa signals in UT-B knockout mice [ 28 , 29 ].…”

Urea transport and hydrolysis in the rumen: A review

“…Rumen based urea transporter proteins are generated from 2 closely related genes; solute carrier family 14 member 1 ( SLC14a1 ) or the urea transporter B ( UT-B ), and SLC14a2 or the urea transporter A (UT-A) ( Lu et al., 2005 ; Strugatsky et al., 2013 ). Walpole et al. (2018) reported that both AQP and UT-B facilitated urea transportation into the rumen ( Fig.…”

Physiological functions of urea transporter B

“…High-protein diets can increase urea concentration, which may be a carcinogen for rat bladder [42, 70]. UT-B-/- mice were generated by disrupting the UT-B gene, evidenced by PCR analysis and lack of UT-B protein expression in all organs [86]. Transmission electron microscopy (TEM) analysis reveals that medullary sheath is observed in urothelial cells of UT-B-/- mice, which may cause urothelial cell shrinking, chromatin condensation, and apoptosis [91].…”

“…Firstly, UT-B protein is detected in human small intestine, colon, and colonic recesses [64]. Furthermore, UT-B protein is detected in human intestinal Caco-2 cells and epithelial cells, particularly higher expression in ascending colon than in descending colon [10, 86]. UT-B has shown to promote the transportation of urea from blood to the gastrointestinal tract in the ruminants and other mammals [45, 51, 83] and the gastrointestinal UT-B in humans may participate in the process of urea nitrogen salvaging (UNS).…”