Effect of dietary increased Vitamin a on urothelial regeneration after Cyclophosphamide induced injury in mice

Vitamin A, predominantly present as all-trans retinol, is an essential nutrient with wide-ranging physiological roles in embryonic development, vision, immunity, reproduction, cell differentiation and proliferation, apoptosis and maintenance of epithelial integrity. In this study the effects of an increased dietary Vitamin A on the regeneration of urinary bladder urothelial cells after severe cyclophosphamide (CP)-induced injury are investigated, focusing on proliferation, apoptosis and differentiation. After one week on a vitamin A-enriched diet, a high dose of CP (150 mg/kg) was administered to mice to induce acute urothelial injury. The effects of increased vitamin A intake on urothelial regeneration were analysed one and three days after the injury at both the RNA and protein levels using RNA sequencing, qPCR, immunohistochemistry and scanning electron microscopy. RNA sequencing revealed that the vitamin A-enriched diet upregulated two KEGG signalling pathways related to cell proliferation: the cell cycle and the PI3K-Akt pathway. We confirmed this by qPCR, which showed a significantly upregulated expression of the genes Itga3 and Areg, both of which are part of the PI3k-Akt signaling pathway. Furthermore, immunohistochemistry demonstrated increased proliferation rates in the urothelium of mice fed a vitamin A-enriched diet. Although RNA sequencing revealed significantly higher gene expression in apoptosis in mice on the vitamin A-enriched diet, this was not conformed by qPCR. Similarly, no significant effect of the vitamin A-enriched diet was observed on the expression of markers for highly differentiated urothelial cells, such as uroplakins, Krt20 and the percentage of the urothelial surface covered with microridges. Our results suggest that a vitamin A-enriched diet may accelerate urothelial regeneration by promoting cell proliferation in the early stages of regeneration. Overall design: To investigate the effect of Vitamin A on urothelial regeneration we established the mouse model of acute cystitis, where mice were fed with a vitamin A-enriched diet (a diet containing 36× higher amount of Vitamin A in the form of retinyl palmitate) prior the cyclophosphamide injection. Half of the mice ate a normal diet. We examined early stages of regeneration, so we collected mice's urinary bladders 1 and 3 days after injection of cyclophosphamide (or saline in the case of control mice).