Altered adiponectin signaling and chronic sympathetic hyperactivity have both been proposed as key factors in the pathogenesis of metabolic syndrome. We recently reported that activation of I1 imidazoline receptors (I1R) improves several symptoms of the metabolic syndrome through sympathoinhibition and increases adiponectin plasma levels in a rat model of metabolic syndrome (Fellmann L, Regnault V, Greney H, et al. J Pharmacol Exp Ther 346: 370-380, 2013). The present study was designed to explore the peripheral component of the beneficial actions of I1R ligands (i.e., sympathoinhibitory independent effects). Aged rats displaying insulin resistance and glucose intolerance were treated with LNP509, a peripherally acting I1R agonist. Glucose tolerance, insulin sensitivity, and adiponectin signaling were assessed at the end of the treatment. Direct actions of the ligand on hepatocyte and adipocyte signaling were also studied. LNP509 reduced the area under the curve of the intravenous glucose tolerance test and enhanced insulin hypoglycemic action and intracellular signaling (Akt phosphorylation), indicating improved glucose tolerance and insulin sensitivity. LNP509 stimulated adiponectin secretion acting at I1R on adipocytes, resulting in increased plasma levels of adiponectin; it also enhanced AMPK phosphorylation in hepatic tissues. Additionally, I1R activation on hepatocytes directly enhanced AMPK phosphorylation. To conclude, I1R ligands can improve insulin sensitivity acting peripherally, independently of sympathoinhibition; stimulation of adiponectin and AMPK pathways at insulin target tissues may account for this effect. This may open a promising new way for the treatment of the metabolic syndrome.

Background: Pathological cardiac hyper trophy is a wor ldwide problem and an independent risk factor that predisposes the hear t to failure. Enhanced activit y or expression of the sodium proton exchanger isoform 1 (NHE1) has been implicated in conditions of cardiac hyper trophy. Induction of cGMP has previousl y been demonstrated to reduce NHE1 activit y and expression, which could be through the expression of heme oxygenase isoform 1 (HO-1), a stress-induced enz yme that shows cardioprotective proper ties. In our study, we aimed to investigate the role of inducing HO-1 in a cardiac hyper trophy model that expresses active NHE1 to determine whether HO-1 could protect against NHE1 induced cardiomyoc yte hyper trophy.Methods: H9c2 cardiomyoc ytes were infected with the active form of the NHE1 adenovir us in the presence and absence of protopor phyrin (CoPP). W hich was used to induce HO-1. Protein and mRNA expression of HO-1 were invested in H9c2 cardiomyoc ytes in the presence and absence of the expression of the active form of the NHE1 adenovir us. The effects of HO-1 induction on NHE1 protein expression and cardiomyoc yte hyper trophic markers were measured respectivel y by western blotting and anal y zing the cell surface area of H9c2.Results: O ur results showed a significant decrease in HO-1 mRNA expression in cardiomyoc ytes expressing active NHE1 (74.84 ± 9.19 % vs. 100 % normal NHE1 expression, p<0.05). However, we did not see any changes in NHE1 protein expression following HO-1 induction. A trend towards decrease in cardiomyoc yte hyper trophy was obser ved in H9c2 cardiomyoblasts infected with the active form of NHE1 following stimulation with HO-1 (NHE1, 154.93 ± 14.87 % vs. NHE1 + CoPP, 109 ± 16.44 %).Conc lusion: In our model, HO-1 maybe a useful means to reduce NHE1 induced cardiomyoc yte hyper trophy, although the mechanism by which it does that requires fur ther investigation. Health and Biomedical

Osteopontin regulates hypoxic induction of NHE1 activity in H9C2 cells. Soumaya Bouchoucha, Fatima Mraiche Hypoxia, an important component of ischemia, is the result of an imbalance between oxygen supply and demand. Severe impairment of oxygen supply may result in a maladaptive cardiac phenotype. During myocardial ischemia, the Na+/H+ exchanger isoform 1 (NHE1), the main regulator of pHi, has been shown to be increased. It has been shown recently that NHE1 elevation increases Osteopontin (OPN) expression, a matricellular protein and proinflammatory cytokine that has been reported to have a protective role in ischemic injury. In this study we tested the hypothesis that hypoxic induction of NHE1 expression and subsequent alterations in H9c2 cells are mediated by OPN. H9c2 cardiomyoblasts were infected with GFP, NHE1 in the presence and absence of OPN adenoviruses following a hypoxic insult using cobalt chloride (CoCl2). Western blotting was performed to investigate the expression of OPN and NHE1. NHE1 activity was measured using BCECF-AM. H9c2 infected cells exposed to hypoxia were characterized by measuring cell viability. Inducing hypoxia for 6 hours caused a significant decrease in cell viability in H9c2 cells (GFP: 87±2.5% Vs 70.76±8.17% GFP + hypoxia; P<0.05). In NHE1 + hypoxia infected cells, viability was significantly lower than the control (NHE1 + hypoxia: 69.36±13.71% Vs 100.0 GFP + hypoxia; P<0.05). Interestingly, when overexpressing both OPN and NHE1+hypoxia, cell viability tended to increase. Compared to the control groups, CoCl2 increased the rate of recovery, which reflects the activity of NHE1, in all groups. These results were accompanied by an increase in OPN expression in the NHE1+ hypoxia infected cells (NHE1 + hypoxia: 167.36±10.01% Vs. 100.0 GFP + hypoxia; P<0.05), which validates that NHE1 activates the expression of OPN under hypoxic conditions. These results reveal a suspected role of osteopontin in protecting cell against ischemic injury owing to the increase of NHE1 expression and activity. Taken together, identified osteopontin may function as a survival factor against hypoxic induction of NHE1 cell death. Keywords: NHE1, Osteopontin, hypoxia.