Tumor Necrosis Factor and Interferon-γ Down-regulate Klotho in Mice With Colitis

Background & Aims: Klotho (KL) is an anti-inflammatory protein that protects the endothelium from nitric oxide (NO)-induced dysfunction, reduces the expression of endothelial adhesion molecules, and potentially regulates T-cell functions. KL deficiency leads to premature senescence and impaired Ca2+/Pi homeostasis, which can lead to inflammatory bowel disease (IBD)-associated osteopenia/osteoporosis. We investigated the changes in renal expression of Kl as a consequence of colitis. Methods: We studied 3 mouse models of IBD: colitis induced by trinitrobenzene sulfonic acid, colitis induced by microflora (in gnotobiotic interleukin-10^-/-), and colitis induced by adoptive transfer of CD4⁺CD45RB^high T cells. Effects of the tumor necrosis factor (TNF) and interferon (IFN)-γ on Kl expression and the activity of its promoter were examined in renal epithelial cells (mpkDCT4 and mIMCD3). Results: Renal expression of Kl messenger RNA (mRNA) and protein was reduced in all 3 models of IBD. Reduced level of KL correlated with the severity of colitis; the effect was reversed by neutralizing antibodies against TNF. In vitro, TNF inhibited Kl expression, an effect potentiated by IFN-γ. The combination of TNF and IFN-γ increased expression of inducible nitric oxide synthase (iNOS) and increased NO production. The effect of IFN-γ was reproduced by exposure to an NO donor and reversed by the iNOS inhibitor. In cells incubated with TNF and/or IFN-γ, Kl mRNA stability was unaffected, whereas Kl promoter activity was reduced, indicating that these cytokines regulate Kl at the transcriptional level. Conclusions: The down-regulation of KL that occurs during inflammation might account for the extraintestinal complications such as abnormalities in bone homeostasis that occur in patients with IBD.