Aldose reductase protects renal collecting tubule epithelial cells from hyperosmolality-induced DNA damage

Abstract

Background: Aldose reductase (AR) is a renal osmoresponsive gene that accu-mulates sorbitol to counteract hypertonicity-induced cellular damage. Loss of AR in the knockout mice (KO) led to the development of polydipsia and polyuria(Ho et al., 2000), although the mechanisms remained obscure. More recently, ithas been demonstrated both in vitro and in vivo that the renal medullary cells areconstantly living with many DNA breaks as a result of exposure to hyperosmo-lality or concentrated urine (Dmitrieva et al., 2004). We therefore hypothesizedthat AR might offer osmoprotection to renal cells by protecting them from hyper-osmolality-induced DNA damage.Method: Genomic DNA integrity was evaluated in the kidneys of three groupsof mice by fluorescent TUNEL assays as well as the Comet assays of renal primarycell culture. These mice included the wildtype (WT) and the KO mice and aline of bitransgenic mice (BT) that carry both the knockout mutation and atransgene that expresses AR collecting tubule epithelial cell (CTEC)-specifically.Results: TUNEL assays indicated that CTEC DNA breaks can be detected asearly as 3 weeks postnatal that were not seen in other types of renal cells. By the age of 5 weeks, significantly more CTECs of the KO mice have DNA breaksthan that of the WT, indicating more severe DNA damage and/or apoptosis. Incontrast the BT mice almost have no DNA damage in the CTECs while the epithelial-specific AR expression largely but incompletely rescued the poy-dipsia and polyuria. Preliminary Comet assays on CTECs also suggested that AR deficient cells are more susceptible to the hyperosmolality-induced DNAdamage.Conclusion: These data suggest that AR contributes to renal osmoprotection bypreventing hypertonicity-induced kidney DNA damage. Loss of this protectionin the KO mice very likely is one of the underlying mechanisms for the devel-opment of polyuira and polydipsia.