Transcription factor Nrf2 regulates SHP and lipogenic gene expression in hepatic lipid metabolism.

Nuclear factor erythroid-2 related factor 2 (Nrf2) plays a pivotal role in cytoprotection against both endogenous and exogenous stresses. Here, we establish a novel molecular link between Nrf2, nuclear receptor small heterodimer partner (SHP; NROB2), lipogenic genes, and hepatic lipid homeostasis. Deletion of Nrf2 (Nrf2⁻(/)⁻) in mice resulted in a reduced liver weight, a decrease in fatty acid content of hepatic triacylglycerol, as well as concomitant increases in the levels of serum VLDL-triglyceride (TG), HDL cholesterol, and ketone bodies at 6 mo of age. Liver weight and hepatic TG content were consistently lower in Nrf2⁻(/)⁻ mice upon a high-fat challenge. This phenotype was accompanied by downregulation of genes in lipid synthesis and uptake and upregulation of genes in lipid oxidation in older Nrf2⁻(/)⁻ mice. Interestingly, SHP expression was induced with age in Nrf2(+/+) mice but decreased by Nrf2 deficiency. Forced expression and activation of Nrf2 by Nrf2 activators consistently induced SHP expression, and Nrf2 was identified as a novel activator of the SHP gene transcription. We also identified PPAR-γ, Fas, Scd1, and Srebp-1 as direct targets of Nrf2 activation. These findings provide evidence for a role of Nrf2 in the modulation of hepatic lipid homeostasis through transcriptional activation of SHP and lipogenic gene expression.

Overexpression of nuclear receptor SHP in adipose tissues affects diet-induced obesity and adaptive thermogenesis.

The orphan nuclear receptor small heterodimer partner (SHP) regulates metabolic pathways involved in hepatic bile acid production and both lipid and glucose homeostasis via the transcriptional repression of other nuclear receptors. In the present study, we generated fat-specific SHP-overexpressed transgenic (TG) mice and determined the potential role of SHP activation, specifically in adipocytes, in the regulation of adipose tissue function in response to stressors. We determined in 2 mo-old SHP TG mice body weight, fat mass index, adipose tissues morphology, thermogenic and metabolic gene expression, metabolic rates at baseline and in response to beta adrenergic receptor agonists, and brown fat ultrastructural changes in response to cold exposure (6-48 h). Mice were fed a 10-wk high-fat diet (HFD; 42% fat). Weight gain, fat mass index, adipose tissues morphology, glucose tolerance, and metabolic rates were determined at the end of the feeding. Young TG mice had increased body weight and adiposity; however, their energy metabolism was increased and brown fat function was enhanced in response to cold exposure through the activation of thermogenic genes and mitochondrial biogenesis. SHP overexpression exacerbated the diet-induced obesity phenotype as evidence by marked weight gain over time, increased adiposity, and severe glucose intolerance compared with wild-type mice fed a HFD. In addition, SHP-TG mice fed HFD had decreased diet-induced adaptive thermogenesis, increased food intake, and decreased physical activity. In conclusion, SHP activation in adipocytes strongly affects weight gain and diet-induced obesity. Developing a synthetic compound to antagonize the effect of SHP may prove to be useful in treating obesity.

Captopril normalizes insulin signaling and insulin-regulated substrate metabolism in obese (ob/ob) mouse hearts.

The goal of this study was to determine whether inhibiting the renin-angiotensin system would restore insulin signaling and normalize substrate use in hearts from obese ob/ob mice. Mice were treated for 4 wk with Captopril (4 mg/kg x d). Circulating levels of free fatty acids, triglycerides, and insulin were measured and glucose tolerance tests performed. Rates of palmitate oxidation and glycolysis, oxygen consumption, and cardiac power were determined in isolated working hearts in the presence and absence of insulin, along with levels of phosphorylation of Akt and AMP-activated protein kinase (AMPK). Captopril treatment did not correct the hyperinsulinemia or impaired glucose tolerance in ob/ob mice. Rates of fatty acid oxidation were increased and glycolysis decreased in ob/ob hearts, and insulin did not modulate substrate use in hearts of ob/ob mice and did not increase Akt phosphorylation. Captopril restored the ability of insulin to regulate fatty acid oxidation and glycolysis in hearts of ob/ob mice, possibly by increasing Akt phosphorylation. Moreover, AMPK phosphorylation, which was increased in hearts of ob/ob mice, was normalized by Captopril treatment, suggesting that in addition to restoring insulin sensitivity, Captopril treatment improved myocardial energetics. Thus, angiotensin-converting enzyme inhibitors restore the responsiveness of ob/ob mouse hearts to insulin and normalizes AMPK activity independently of effects on systemic metabolic homeostasis.

Aortic banding in rat as a model to investigate malnutrition associated with heart failure.

Heart failure is a severe pathology, which has displayed a dramatic increase in the occurrence of patients with chronic heart disease in developed countries, as a result of increases in the population's average age and in survival time. This pathology is associated with severe malnutrition, which worsens the prognosis. Although the cachexia associated with chronic heart failure is a well-known complication, there is no reference animal model of malnutrition related to heart failure. This study was designed to evaluate the nutritional status of rats in a model of loss of cardiac function obtained by ascending aortic banding. Cardiac overload led to the development of cardiac hypertrophy, which decompensates to heart failure, with increased brain natriuretic peptide levels. The rats displayed hepatic dysfunction and an associated renal hypotrophy and renal failure, evidenced by the alteration in renal function markers such as citrullinemia, creatininemia, and uremia. Malnutrition has been evidenced by the alteration of protein and amino acid metabolism. A muscular atrophy with decreased protein content and increased amino acid concentrations in both plasma and muscle was observed. These rats with heart failure displayed a multiorgan failure and malnutrition, which reflected the clinical situation of human chronic heart failure.

Prevention of heart failure in rats by trimetazidine treatment: a consequence of accelerated phospholipid turnover?

Heart failure is known for alteration of cardiac catecholamine responsiveness involving adrenergic receptor (AR) down-regulation. Trimetazidine, a metabolically active anti-ischemic drug, accelerates the turnover of phospholipids. The present study evaluated the consequences of trimetazidine treatment (supposed to increase phospholipid synthesis) on AR in heart failure in rats. In control rats, trimetazidine (7.5 mg/day supplied in the diet) induced after 8 weeks a significant increase in both beta- (+54%) and alpha-AR (+30%) density, although after 12 weeks, the receptor density was normalized. Heart failure was obtained by ascending aortic banding. These heart failure rats developed a severe cardiac hypertrophy, mainly affecting the left ventricle, which was significantly reduced in the trimetazidine-treated group. The plasma level of brain natriuretic peptide (BNP), a marker of heart failure severity, was significantly increased in the heart failure group as compared with the sham group (900 and 1200% after 8 and 12 weeks, respectively). In the trimetazidine-treated group, the plasma BNP increase was significantly lower. The development of heart failure was associated with a decrease in beta- and alpha-AR sites (-23 and -36% versus sham, respectively) after 8 weeks and continued to decrease after 12 weeks (-37 and -48% versus sham, respectively). This down-regulation was prevented by trimetazidine without alteration in affinity. These results suggest that trimetazidine prevents AR desensitization and cardiac hypertrophy, in a pressure-overload model of heart failure. This cytoprotection suggests that membrane homeostasis preservation may be considered as a therapeutic target in the treatment of heart failure.

Trimetazidine effect on phospholipid synthesis in ventricular myocytes: consequences in alpha-adrenergic signaling.

The anti-anginal drug trimetazidine (TMZ) has been shown to increase the synthesis of phospholipids in ventricular myocytes, including phosphatidyl-inositol (PI). This study focused on the consequences of increasing PI metabolism on alpha-adrenergic signaling pathway in cultured rat cardiomyocytes. In the cells treated with TMZ, the synthesis of PI from inositol was largely increased as compared with the control (+55% in 60 min). The stimulation of alpha-adrenergic receptors by phenylephrine (PE) induced a dose-dependent production of inositide phosphates (IPs) by phospholipase C (PLC) activation. However, the amount of available IPs was significantly lower in TMZ-treated cells, in a dose-dependent manner. This effect was observed in the presence and absence of the IP1-phosphatase inhibitor LiCl. The in vitro determination of PLC activity revealed that this effect could not be attributed to the direct inhibition of the enzyme by TMZ. The TMZ-induced reduction of IPs in the PE-stimulated cardiomyocytes should be attributed to the increase of inositol recycling and incorporation in membrane structures, elicited by increased phospholipid synthesis. The consequences of this reduction in IPs availability were investigated on the cardiomyocyte hypertrophy induced by alpha-adrenergic chronic stimulation. Acute stimulation with PE increased protein synthesis (+50%), but this increase was largely prevented by TMZ. In conclusion, TMZ reduces cell available IPs, by accelerating their recycling in membranes as PI. This effect results in a cytoprotection in the pathological process of hypertrophy elicited by chronic alpha-adrenergic stimulation.