Requirement for sphingosine kinase 1 in mediating phase 1 of the hypotensive response to anandamide in the anaesthetised mouse

In the isolated rat carotid artery, the endocannabinoid anandamide induces endothelium-dependent relaxation via activation of the enzyme sphingosine kinase (SK). This generates sphingosine-1-phosphate (S1P) which can be released from the cell and activates S1P receptors on the endothelium. In anaesthetised mice, anandamide has a well-characterised triphasic effect on blood pressure but the contribution of SK and S1P receptors in mediating changes in blood pressure has never been studied. Therefore, we assessed this in the current study. The peak hypotensive response to 1 and 10 mg/kg anandamide was measured in control C57BL/6 mice and in mice pretreated with selective inhibitors of SK1 (BML-258, also known as SK1-I) or SK2 ((R)-FTY720 methylether (ROMe), a dual SK1/2 inhibitor (SKi) or an S1P1 receptor antagonist (W146). Vasodilator responses to S1P were also studied in isolated mouse aortic rings. The hypotensive response to anandamide was significantly attenuated by BML-258 but not by ROMe. Antagonising S1P1 receptors with W146 completely blocked the fall in systolic but not diastolic blood pressure in response to anandamide. S1P induced vasodilation in denuded aortic rings was blocked by W146 but caused no vasodilation in endothelium-intact rings. This study provides evidence that the SK1/S1P regulatory-axis is necessary for the rapid hypotension induced by anandamide. Generation of S1P in response to anandamide likely activates S1P1 to reduce total peripheral resistance and lower mean arterial pressure. These findings have important implications in our understanding of the hypotensive and cardiovascular actions of cannabinoids

The Role of O-Glcnacylation in Perivascular Adipose Tissue Dysfunction of Offspring of High Fat Diet-Fed Rats.

Perivascular adipose tissue (PVAT), which reduces vascular contractility, is dysfunctional in the male offspring of rats fed a high-fat diet (HFD), partially due to a reduced NO bioavailability. O-GlcNAcylation of eNOS decreases its activity, thus we investigated the role of O-GlcNAcylation in the prenatal programming of PVAT dysfunction. Female Sprague-Dawley rats were fed either a control (10% fat) or an obesogenic HFD (45% fat) diet for 12 weeks prior to mating, and throughout pregnancy and lactation. Offspring were weaned onto the control diet and were killed at 12 and 24 weeks of age. Mesenteric arteries from the 12-week-old offspring of HFD dams (HFDO) contracted less to U46619; these effects were mimicked by glucosamine in control arteries. PVAT from 12- and 24-week-old controls, but not from HFDO, exerted an anticontractile effect. Glucosamine attenuated the anticontractile effect of PVAT in the vessels from controls but not from HFDO. AMP-activated protein kinase (AMPK) activation (with A769662) partially restored an anticontractile effect in glucosamine-treated controls and HFDO PVAT. Glucosamine decreased AMPK activity and expression in HFDO PVAT, although phosphorylated eNOS expression was only reduced in that from males. The loss of anticontractile effect of HFDO PVAT is likely to result from increased O-GlcNAcylation, which decreased AMPK activity and, in males, decreased NO bioavailability.</jats:p

Deoxycholic acid supplementation impairs glucose homeostasis in mice

<div><p>Bile acids are critical contributors to the regulation of whole body glucose homeostasis; however, the mechanisms remain incompletely defined. While the hydrophilic bile acid subtype, ursodeoxycholic acid, has been shown to attenuate hepatic endoplasmic reticulum (ER) stress and thereby improve glucose regulation in mice, the effect of hydrophobic bile acid subtypes on ER stress and glucose regulation <i>in vivo</i> is unknown. Therefore, we investigated the effect of the hydrophobic bile acid subtype, deoxycholic acid (DCA), on ER stress and glucose regulation. Eight week old C57BL/6J mice were fed a high fat diet supplemented with or without DCA. Glucose regulation was assessed by oral glucose tolerance and insulin tolerance testing. In addition, circulating bile acid profile and hepatic insulin and ER stress signaling were measured. DCA supplementation did not alter body weight or food intake, but did impair glucose regulation. Consistent with the impairment in glucose regulation, DCA increased the hydrophobicity of the circulating bile acid profile, decreased hepatic insulin signaling and increased hepatic ER stress signaling. Together, these data suggest that dietary supplementation of DCA impairs whole body glucose regulation by disrupting hepatic ER homeostasis in mice.</p></div

Fasting serum bile acid profile.

<p>Total bile acid concentration (A), 12αOH:non-12αOH ratio (B) and hydrophobicity index (C) in fasting serum samples. Relative proportions of bile acid subtypes in fasting serum samples from HFD (D) and DCA treated (E) mice. Data are expressed as mean ± SEM, **<i>P</i><0.01, ****<i>P</i><0.0001 by Student’s t-test, <i>n</i> = 6 per group. TCA, taurocholic acid; TLCA, taurolitocholic acid; HDCA, hyodeoxycholic acid; GUDCA, glycoursodeoxycholic acid; CDCA, chenodeoxycholic acid; UDCA, ursodeoxycholic acid; αω MCA, αω muricholic acid; βMCA, β-muricholic acid and Tαβ MCA, tauro-αβ muricholic acid.</p

Food intake, body weight and adiposity.

<p>Energy intake (days 1–17, A), body weight (B), body weight gain (C) and adipose depot weights (subcutaneous (SQ), mesenteric (Mes), epididymal (Epi), retroperitoneal (RP) and brown adipose tissue (BAT)) (D). Data are expressed as mean ± SEM, <i>n</i> = 6 per group.</p

DCA supplementation impairs glucose homeostasis.

<p>Absolute blood glucose concentrations (A) and percentage change from baseline blood glucose concentrations (B) during an insulin tolerance test. (C) Blood glucose concentrations during an oral glucose tolerance test. Data are expressed as mean ± SEM, *<i>P</i><0.05 by two-factor ANOVA, ^#<i>P</i><0.05 by Student’s t-test, <i>n</i> = 8 per group.</p

DCA increases hepatic ER stress signaling and decreases hepatic insulin signaling.

<p>Phosphorylated to total IRE (A) and spliced XBP1 (sXBP1) expression normalized to tubulin (B). BiP (C) and TNFα (D) expression normalized to tubulin and phosphorylated to total Akt expression (E). Data are expressed as mean ± SEM, *<i>P</i><0.05, **<i>P</i><0.01 by Student’s t-test, <i>n</i> = 6 per group.</p

β Cell GLP-1R Signaling Alters α Cell Proglucagon Processing after Vertical Sleeve Gastrectomy in Mice

Summary: Bariatric surgery, such as vertical sleeve gastrectomy (VSG), causes high rates of type 2 diabetes remission and remarkable increases in postprandial glucagon-like peptide-1 (GLP-1) secretion. GLP-1 plays a critical role in islet function by potentiating glucose-stimulated insulin secretion; however, the mechanisms remain incompletely defined. Therefore, we applied a murine VSG model to an inducible β cell-specific GLP-1 receptor (GLP-1R) knockout mouse model to investigate the role of the β cell GLP-1R in islet function. Our data show that loss of β cell GLP-1R signaling decreases α cell GLP-1 expression after VSG. Furthermore, we find a β cell GLP-1R-dependent increase in α cell expression of the prohormone convertase required for the production of GLP-1 after VSG. Together, the findings herein reveal two concepts. First, our data support a paracrine role for α cell-derived GLP-1 in the metabolic benefits observed after VSG. Second, we have identified a role for the β cell GLP-1R as a regulator of α cell proglucagon processing. : The mechanisms by which GLP-1 enhances insulin secretion remain incompletely defined. Garibay et al. show that β cell GLP-1R signaling regulates α cell PC1/3 expression and GLP-1 production, pointing to an intra-islet paracrine positive feedback loop by which GLP-1-potentiated insulin secretion is amplified. Keywords: GLP-1, prohormone convertase 1/3, vertical sleeve gastrectomy, β cel