Dynamic regulation of serum aryl hydrocarbon receptor agonists in MS

Abstract

Objective: Several factors influence the clinical course of autoimmune inflammatory diseases such as MS and inflammatory bowel disease. Only recently, the complex interaction between the gut microbiome, dietary factors, and metabolism has started to be appreciated with regard to its potential to modulate acute and chronic inflammation. One of the molecular sensors that mediates the effects of these environmental signals on the immune response is the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor with key functions in immune cells.

Methods: In this study, we analyzed the levels of AHR agonists in serum samples from patients with MS and healthy controls in a case-control study.

Results: We detected a global decrease of circulating AHR agonists in relapsing-remitting MS patients as compared to controls. However, during acute CNS inflammation in clinically isolated syndrome or active MS, we measured increased AHR agonistic activity. Moreover, AHR ligand levels in patients with benign MS with relatively mild clinical impairment despite longstanding disease were unaltered as compared to healthy controls.

Conclusions: Collectively, these data suggest that AHR agonists in serum are dynamically modulated during the course of MS. These findings may guide the development of biomarkers to monitor disease activity as well as the design of novel therapeutic interventions for MS.

Figure 1. Detection of aryl hydrocarbon receptor ligands from different sources

Aryl hydrocarbon receptor (AHR) agonistic activity was measured for a collection of AHR ligands from exogenous and exogenous sources, including the pollutant 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) (A), the diet-derived ligand Indole-3-carbinol (I3C) (B), ligands derived from microbial and host tryptophan metabolism Indole (C), Indoxyl-3-sulfate (I3S) (D), Indirubin (E), and 2′Z-Indirubin (F), the mucosal ligand 2-(1′H-indole-3′-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) (G), and the endogenous metabolite Kynurenine (H). Data are normalized to 100% (maximum activity per ligand) and are representative of 2 independent experiments.

Figure 2. Aryl hydrocarbon receptor ligand levels are decreased in patients with relapsing-remitting MS

Aryl hydrocarbon receptor (AHR) agonistic activity in serum samples of healthy controls (controls, n = 26) and relapsing-remitting MS (RRMS) patients (RRMS, n = 91) was assessed in duplicates using an AHR ligand–sensitive luciferase assay. Relative activity was calculated by dividing firefly luciferase activity (pGud-Luc) by Renilla luciferase activity (pTK-Renilla). Values are means of duplicate measurements. Lines represent mean and error bars standard error of the mean (SEM). Significance levels were derived using the Student t test. **p < 0.01.

Figure 3. Aryl hydrocarbon receptor ligand levels are modulated by disease activity

Aryl hydrocarbon receptor (AHR) agonistic activity in serum samples of healthy controls (controls, n = 26), relapsing-remitting MS (RRMS) patients during remission (RRMS remission, n = 32), and patients with RRMS with active disease (RRMS active, n = 20) was assessed in duplicates using an AHR ligand–sensitive luciferase assay. Values are means of duplicate measurements. Lines represent mean and error bars standard error of the mean (SEM). Significance levels were derived using 1-way analysis of variance followed by the Tukey multiple comparisons test. ****p < 0.0001.

Figure 4. Aryl hydrocarbon receptor ligand levels are increased in clinically isolated syndrome as compared to healthy controls

Aryl hydrocarbon receptor agonistic activity in serum samples of healthy controls (controls, n = 33) and patients with clinically isolated syndrome (CIS, n = 15) was assessed in duplicates. Values are means of duplicate measurements. Lines represent mean and error bars standard error of the mean (SEM). Significance level was derived by the Student t test. **p < 0.01.

Figure 5. Aryl hydrocarbon receptor ligand levels in patients with benign relapsing-remitting MS are unchanged as compared to healthy controls

Aryl hydrocarbon receptor agonistic activity in serum samples of healthy controls (controls, n = 7) and patients with benign relapsing-remitting MS as defined by low EDSS scores despite longstanding disease (benign MS, n = 11) was assessed in duplicates. Values are means of duplicate measurements. Lines represent mean and error bars standard error of the mean (SEM). Significance level was derived by the Student t test. n.s. = not significant.

Figure 6. Dynamic modulation of aryl hydrocarbon receptor ligand levels in patients with relapsing-remitting MS

(A) Serum aryl hydrocarbon receptor (AHR) agonistic activity is increased during the first relapse of the disease but decreases below control levels in remission. Further relapses increase AHR ligand levels during the relapse. (B) Benign courses of MS have control levels of AHR agonistic activity and might be increased during relapses. RRMS = relapsing-remitting MS.