👤 B M Stenson

Plasma accumulation of the gut microbial metabolite 4-ethylphenylsulfate (4EPS), derived from dietary amino acid, tyrosine, has been associated with cardiovascular, renal, metabolic, and neurological disorders. AngII (angiotensin II) infusion increases circulating 4EPS in mice, suggesting a potential mechanistic role. We hypothesized that 4EPS modulates AngII-regulated pathophysiology and disease progression by directly inhibiting AT1R (angiotensin II type 1 receptor). This hypothesis was tested by combining AT1R pharmacology, cell signaling assays, ex vivo vascular studies, an AngII-induced aortic aneurysm growth model, and plasma proteomics analysis. in vitro, 4EPS reduced the binding of both AngII and the antagonist candesartan to AT1R and suppressed AngII-induced calcium signaling. Ex vivo, 4EPS attenuated AngII-mediated vasoconstriction. In vivo, high-fat diet-fed ApoE-null mice coinfused with AngII and 4EPS showed significant blunting of blood pressure elevation and a marked reduction in aortic aneurysm-related mortality compared with mice infused with AngII alone. Analysis of aortic remodeling revealed increased elastin preservation and decreased thickening of the intimal and medial layers in 4EPS-treated animals. Plasma proteomics indicated alterations in actin-cytoskeletal signaling pathways consistent with reduced activation of ERK (extracellular-regulated kinase) 1/2, filamin-A, and proteins involved in vascular smooth muscle cell motility. These findings identify 4EPS as a benign, endogenous AT1R antagonist that diminishes AngII-mediated hemodynamic and vascular pathology. By suppressing cytoskeletal signaling associated with vascular remodeling, 4EPS provides significant protection against hypertension and aortic aneurysm progression in mice, revealing a previously unrecognized protective role for a gut microbial metabolite in modulating renin-angiotensin system activity. Show less

Obesity increases the risk of developing type 2 diabetes mellitus, characterised by impaired insulin-mediated glucose uptake in peripheral tissues. Liver X receptor (LXR) is a positive regulator of adipocyte glucose transport in murine models and a possible target for diabetes treatment. However, the levels of LXRα are increased in obese adipose tissue in humans. We aimed to investigate the transcriptome of LXR and the role of LXR in the regulation of glucose uptake in primary human adipocytes. The insulin responsiveness of human adipocytes differentiated in vitro was characterised, adipocytes were treated with the LXR agonist GW3965 and global transcriptome profiling was determined by microarray, followed by quantitative RT-PCR (qRT-PCR), western blot and ELISA. Basal and insulin-stimulated glucose uptake was measured and the effect on plasma membrane translocation of glucose transporter 4 (GLUT4) was assayed. LXR activation resulted in transcriptional suppression of several insulin signalling genes, such as AKT2, SORBS1 and CAV1, but caused only minor changes (<15%) in microRNA expression. Activation of LXR impaired the plasma membrane translocation of GLUT4, but not the expression of its gene, SLC2A4. LXR activation also diminished insulin-stimulated glucose transport and lipogenesis in adipocytes obtained from overweight individuals. Furthermore, AKT2 expression was reduced in obese adipose tissue, and AKT2 and SORBS1 expression was inversely correlated with BMI and HOMA index. In contrast to murine models, LXR downregulates insulin-stimulated glucose uptake in human adipocytes from overweight individuals. This could be due to suppression of Akt2, c-Cbl-associated protein and caveolin-1. These findings challenge the idea of LXR as a drug target in the treatment of diabetes. Show less

The Liver X receptor (LXR) is an important regulator of carbohydrate and lipid metabolism in humans and mice. We have recently shown that activation of LXR regulates cellular fuel utilization in adipocytes. In contrast, the role of LXR in human adipocyte lipolysis, the major function of human white fat cells, is not clear. In the present study, we stimulated in vitro differentiated human and murine adipocytes with the LXR agonist GW3965 and observed an increase in basal lipolysis. Microarray analysis of human adipocyte mRNA following LXR activation revealed an altered gene expression of several lipolysis-regulating proteins, which was also confirmed by quantitative real-time PCR. We show that expression and intracellular localization of perilipin1 (PLIN1) and hormone-sensitive lipase (HSL) are affected by GW3965. Although LXR activation does not influence phosphorylation status of HSL, HSL activity is required for the lipolytic effect of GW3965. This effect is abolished by PLIN1 knockdown. In addition, we demonstrate that upon activation, LXR binds to the proximal regions of the PLIN1 and HSL promoters. By selective knock-down of either LXR isoform, we show that LXRα is the major isoform mediating the lipolysis-related effects of LXR. In conclusion, the present study demonstrates that activation of LXRα up-regulates basal human adipocyte lipolysis. This is at least partially mediated through LXR binding to the PLIN1 promoter and down-regulation of PLIN1 expression. Show less