Peroxisome proliferator-activated receptors mediate phytochemical-induced upregulation of farnesoid X receptor expression and activity in colonic epithelial cells

Abstract

Introduction: The nuclear bile acid receptor, farnesoid X receptor (FXR), is expressed on intestinal epithelial cells where its potential as a new drug target for treatment of intestinal and metabolic disorders, such as chronic diarrhoea, colitis, colon cancer, obesity and diabetes, has been well-established. We have previously shown that pentacyclic triterpenes (PCTs), a class of dietary phytochemical, enhance the expression and activity of colonic epithelial FXR. Here, we investigated if another common class of dietary phytochemical, polyunsaturated fatty acids (PUFAs), also modulate FXR signalling in these cells. Furthermore, since peroxisome proliferator-activated receptors (PPARs) have been shown to regulate FXR expression in other cell types, we investigated their potential in mediating the effects of PCTs and PUFAs on FXR expression in the colonic epithelium. Methods: All experiments were conducted on monolayers of T 84 colonic epithelial cells grown on permeable supports. Alpha-linolenic acid (ALA; 100 μM) and hederagenin (HG; 5 μM) were used as prototypical PUFAs or PCTs, respectively. Rosiglitazone (1 μM) and WY14643 (1 – 20 μM) were employed as PPARγ and PPARα agonists, whereas GW9662 (20 μM) and GW6471 (1 μM) were used as PPARγ and PPARα antagonists, respectively. Levels of FXR, FGF19, an index of FXR activation, and ANGPTL4, a PPAR target gene, were measured by qRT-PCR, western blotting, or ELISA. Results: Similar to our previous studies with HG, treatment of T 84 cells with ALA upregulated FXR mRNA and protein expression to 11.43 ± 2.1 fold (n = 7, p < 0.01) and 6.4 ± 1.2 fold (n = 6, p < 0.05) of that in control cells, respectively. ALA treatment also enhanced the effects of an FXR agonist, GW4064 (5 μM), on FGF19 mRNA and protein expression by 4.4 ± 1.6 (n = 7) and 6.5 ± 1.4 fold (n = 8, p < 0.05), respectively. Treatment with HG and ALA (3 hrs) also increased mRNA expression of the PPAR target gene, ANGPTL4, to 5.7 ± 1.0 (n = 5; p < 0.05) and 66.3 ± 9.5 fold (n = 7; p < 0.01) of that in untreated cells, respectively. Furthermore, the effects of the phytochemicals on FXR expression were mimicked by the PPARγ and PPARα agonists, rosiglitazone and WY14643, respectively. The PPARγ antagonist, GW9662, inhibited ALA-induced FXR mRNA expression by 0.5 ± 0.1 fold (n = 11; p < 0.001) but did not alter responses to HG. In contrast, the PPARα antagonist, GW6471, inhibited both ALA and HG-induced FXR mRNA expression by 0.71 ± 0.1 and 0.58 ± 0.1 fold (n = 4; p < 0.05) of that in control cells, respectively. Conclusion: The dietary phytochemicals, HG and ALA, upregulate colonic epithelial FXR through mechanisms that appear to involve differential activation of PPARs. By virtue of their ability to upregulate FXR expression and activity, foods or food supplements, rich in such PCTs and PUFAs have excellent potential for development as a new class of “FXR-targeted nutraceutical” for treatment and prevention of intestinal and metabolic disorders. Science Foundation Ireland This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.