Aim: Vascular senescence, which is accelerated in individuals with chronic kidney disease (CKD), contributes to the development of cardio-renal syndrome, and various uremic toxins may play important roles in the mechanisms underlying this phenomenon. We recently reported that indoxyl sulfate (IS), a uremic toxin, directly activates aryl hydrocarbon receptor (AhR) and generates oxidative stress through NADPH oxidase-4 in human umbilical vein endothelial cells (HUVECs). In the current study, we sought to examine whether IS regulates sirtuin 1 (Sirt1) and affects endothelial senescence via AhR activation.
Methods: HUVECs were incubated with 500 μmol/L of IS for the indicated time periods. In order to evaluate changes in the senescence of the HUVECs, the number of senescence-associated β-galactosidase (SA β-gal)-positive cells was determined using an image analysis software program. The intracellular nicotinamide phosphoribosyltransferase (iNampt) activity, cellular NAD^＋/NADPH ratio and Sirt1 activity were analyzed according to a colorimetric assay to determine the mechanism of cellular senescence. Furthermore, we evaluated the involvement of AhR in the senescence-related changes induced by IS using AhR antagonists.
Results: IS decreased the iNampt activity, NAD^＋/NADPH ratio and Sirt1 activity, resulting in an increase in the percentage of SA β-gal-positive cells. On the other hand, the AhR antagonists restored the IS-induced decrease in the NAD^＋ content in association with an improvement in the iNampt activity and ameliorated the senescence-related changes. Taken together, these results indicate that IS impairs the iNampt-NAD^＋-Sirt1 system via AhR activation, which in turn promotes endothelial senescence.
Conclusions: The IS-AhR pathway induces endothelial senescence. Therefore, blocking the effects of AhR in the endothelium may provide a new therapeutic tool for treating cardio-renal syndrome.