Temporal and tissue-specific activation of aryl hydrocarbon hydroxylase signaling may be visualized in discrete mouse models of kidney disease

Abstract: Emerging evidence in animal models of chronic kidney disease (CKD) implicates Aryl Hydrocarbon Receptor (AHR) signaling as a mediator of uremic toxicity. However, details about its tissue-specific and time-dependent activation in response to various renal pathologies remain poorly defined. Here, a comprehensive analysis of AHR induction was conducted in response to discrete models of kidney diseases using a transgenic mouse line expressing the AHR responsive-promoter tethered to a β-galactosidase reporter gene. Following validation using a canonical AHR ligand (a dioxin derivative), the transgenic mice were subjected to adenine-induced and ischemia/reperfusion-induced injury models representing CKD and acute kidney injury (AKI), respectively, in humans. Indoxyl sulfate was artificially increased in mice through the drinking water and by inhibiting its excretion into the urine. Adenine-fed mice showed a distinct and significant increase in β-galactosidase in the proximal and distal renal tubules, cardiac myocytes, hepatocytes and microvasculature in the cerebral cortex. The pattern of β-galactosidase increase coincided with the changes in serum indoxyl sulfate levels. Machine-learning based image quantification revealed positive correlations between indoxyl sulfate levels and β-galactosidase expression in various tissues. This pattern of β-galactosidase expression was recapitulated in the indoxyl sulfate-specific model. The ischemia/reperfusion injury model showed increase in β-galactosidase in renal tubules that persisted despite reduction in serum indoxyl sulfate and blood urea nitrogen levels. Thus, our results demonstrate a relationship between AHR activation in various tissues of mice with CKD or AKI and the levels of indoxyl sulfate. This study demonstrates the use of a reporter gene mouse to probe tissue-specific manifestations of uremia in translationally-relevant animal models and provide hypothesis-generating insights into the mechanism of uremic toxicity that warrant further investigation.