M L Bonet

Up-regulation of muscle uncoupling protein 3 gene expression in mice following high fat diet, dietary vitamin A supplementation and acute retinoic acid-treatment

OBJECTIVE: To analyse the impact of vitamin A supplementation of both a normal fat (NF) diet and a high fat (HF) diet and of acute retinoic acid (RA)-treatment on the expression of uncoupling protein 3 (UCP3) in mice.DESIGN: C57BL/6J mice were fed for 18 weeks a NF or a HF diet (10 and 45 energy% as fat, respectively), both with the normal vitamin A content or an excess vitamin A (8 mg and 320 mg retinyl palmitate/kg diet, respectively). Body weight and energy intake were recorded periodically. UCP3 mRNA and UCP3 protein levels in skeletal muscle (soleus/gastrocnemius) were analysed, as well as UCP1, UCP2 and UCP3 mRNA levels in interscapular brown adipose tissue (BAT), and UCP2 mRNA, UCP2 protein and leptin mRNA levels in white adipose tissue (WAT) depots. The effect of acute RA-treatment (100 mg/kg/day, 4 days) on UCP3 mRNA levels in skeletal muscle and BAT of NMRI mice was also assessed.RESULTS: Vitamin A supplementation of a NF diet led to increased levels of UCP3 mRNA and UCP3 protein in muscle, UCP1 mRNA in BAT, and UCP2 mRNA in inguinal WAT, but had no impact on body weight or adiposity of B6 mice. HF diet promoted obesity and increased levels of UCP3 mRNA and UCP3 protein in skeletal muscle, and of the mRNAs for all three UCPs in BAT. Supplementing the HF diet with vitamin A had little effect on the final obesity reached and did not lead to further increases of muscle UCP3 mRNA nor BAT UCP1 mRNA over the levels achieved with the non-supplemented HF diet. Adipose leptin mRNA levels were down regulated after vitamin A supplementation, independently of the fat content of the diet. Up-regulation of muscle, but not BAT, UCP3 mRNA levels was also found after acute RA-treatment in NMRI mice.CONCLUSION: The results provide evidence of a stimulatory effect of retinoids on muscle UCP3 expression in vivo, and a differential retinoid-regulation of the UCP3 gene in muscle and BAT.

Stimulation of uncoupling protein 1 expression in brown adipocytes by naturally occurring carotenoids

OBJECTIVE: To assess the effect of naturally occurring carotenoids on brown adipocyte proliferation and differentiation. The rationale behind is that certain carotenoids have provitamin A activity in mammals, and that one of the active forms of vitamin A, (retinoic acid) is known to behave as a transcriptional activator of the key gene for brown fat thermogenesis, the one encoding the uncoupling protein thermogenin (UCP1).DESIGN: Confluent primary cultures of mice brown adipocytes were treated with various concentrations of carotenoids. Cell morphology, total culture protein content, the DNA synthesis rate, and the levels of UCP1, retinoic acid receptor α (RARα) and retinoid X receptor α (RXRα) were analysed.RESULTS:Treatment with β-carotene, α-carotene and lutein promoted UCP1 expression in a dose-dependent manner, with an effectiveness that was related to their potency as vitamin A precursors. Cell morphology, total culture protein content at confluence and DNA synthesis rate were unaffected after carotenoid treatment up to 10 μM.CONCLUSION:The results indicate that carotenoids can positively affect the expression of UCP1 without altering brown adipocyte proliferation.

Retinol-binding protein 4 and nicotinamide phosphoribosyltransferase/visfatin in rat obesity models.

Retinol-binding protein 4 (RBP4) and nicotinamide phosphoribosyltransferase/visfatin (Nampt/visfatin) are adipocyte-secreted proteins (adipokines) whose relevance to the metabolic syndrome and regulation in obesity remain controversial. Here, we tested the hypothesis that adipose tissue expression and circulating levels of these two adipokines are elevated in obesity by analyzing their changes in both a genetic and a diet-induced model of obesity in the rat (obese FA/ FA Zucker rats and Wistar rats fed a cafeteria diet, respectively). Compared with lean controls, obese FA/ FA rats were hyperleptinemic, hyperinsulinemic, and insulin resistant and had reduced RBP4 serum levels and mRNA levels in adipose depots, unchanged Nampt/visfatin serum levels, and reduced Nampt/visfatin mRNA levels selectively in the inguinal adipose depot. Cafeteria diet-induced obesity resulted in increased fed blood glucose levels, a variable degree of insulin resistance, unchanged serum Nampt/visfatin and RBP4 levels, and reduced mRNA levels of both adipokines in several adipose depots. Hence, increases in RBP4 or Nampt/visfatin do not accompany obesity and insulin resistance in the models examined.

In vivo effects of CGP-12177 on the expression of leptin and uncoupling protein genes in mouse brown and white adipose tissues.

OBJECTIVE: To assess the effect of chronic treatment with CGP-12177 a β3-adrenergic receptor (AR) agonist with β2/β1-AR antagonist action, on the expression of the leptin gene and of genes coding for uncoupling proteins (ucp1, ucp2 and ucp3) in brown and white adipose tissues.DESIGN: NMRI mice received a daily subcutaneous injection of CGP-12177 at a dose of 0.05, 0.2, 0.5 or 1 mg/kg for 15 days. The specific levels of the mRNAs of interest were analysed in interscapular brown adipose tissue (BAT) and in two white adipose tissue (WAT) depots, inguinal (IWAT) and epididymal (EWAT).RESULTS: No changes in food intake or body weight were detected at any dose of CGP-12177. In the two WAT depots, the treatment led to enhanced expression of ucp1 and ucp3, but not of ucp2. In BAT, low doses (0.05 and 0.2 mg/kg) led to a decreased expression of the three ucp genes, whereas a slight stimulatory effect on the three ucp genes was elicited with a high dose (1 mg/kg). Treated animals displayed increased expression of leptin in BAT and, to a lesser extent, in IWAT, but not in EWAT.CONCLUSION: The results reveal that simultaneous stimulation of the expression of certain ucp genes and the leptin gene can be achieved, and suggest that adrenergic regulation of the leptin gene and of genes of the ucp family in adipose tissues is the result of complex interactions between the different β-AR pathways.

Vitamin A supplementation in early life affects later response to an obesogenic diet in rats.

Objective:To assess the influence of supplementation with a moderate dose of vitamin A in early life on adipose tissue development and the response to an obesogenic diet later in life.Methods:During the suckling period, rat pups received a daily oral dose of retinyl palmitate corresponding to three times the vitamin A ingested daily from maternal milk. Control rats received the vehicle (olive oil). Short-term effects of treatment on gene expression and morphology of white adipose tissue (WAT) were analyzed in animals on the day after weaning (day 21). To study long-term effects, control and vitamin A-treated rats were fed, after weaning, a normal fat or a high-fat (HF) diet for 16 weeks.Results:WAT of vitamin A-treated young rats (day 21) was enriched in small adipocytes with a reduced expression of adipogenic markers (peroxisome proliferator-activated receptor γ and lipoprotein lipase) and an increased cell proliferation potential as indicated by increased expression of proliferating cell nuclear antigen. Increased retinoic acid (RA)-induced transcriptional responses were present in the tissues of vitamin A-treated young rats (day 21) including WAT. Vitamin A-treated rats developed higher adiposity than control rats on a HF diet as indicated by body composition analysis and increased WAT depot mass, adipocyte diameter, WAT DNA content, leptinemia and adipose leptin gene expression. Excess adiposity gain in vitamin A-treated rats developed in the absence of changes in body weight and was attributable to excess adipocyte hyperplasia. No differences in adiposity were observed between vitamin A-treated rats and control rats on a normal fat diet. Total retinol levels in WAT of vitamin A-treated rats were elevated at weaning (day 21) and normalized by day 135 of age.Conclusion:Vitamin A intake in the early stages of postnatal life favors subsequent HF diet-induced adiposity gain through mechanisms that may relate to changes in adipose tissue development, likely mediated by RA.

Nutritional potential of metabolic remodelling of white adipose tissue.

Purpose of reviewRecent findings in animals suggest that diet-related factors can programme adipose tissue features in early life and remodel white adipose tissue (WAT) towards a brown adipose tissue (BAT)-like phenotype in adulthood, while impacting on body fat content and susceptibility to obesity. The purpose of this review is to address the significance of these results and their applicability in humans. Recent findingsNutritional conditions in the perinatal period influence sympathetic innervation to WAT and WAT cellularity in rodents. Leptin intake during the suckling period prevents obesity and other metabolic alterations in later life in rats through mechanisms that include increased sensitivity of adipose tissues to leptin. Recent data support the thermogenic functionality of inducible brown-like cells in rodent WAT and functional thermogenic beige adipogenesis from human progenitor cells. Diet-related factors and exercise can promote BAT activation and/or WAT-to-BAT remodelling (WAT browning) in animals. SummaryAnimal studies suggest that adipose tissue health and whole body adiposity might be influenced by early life nutrition and lifestyle factors in adulthood impacting energy metabolism in adipose tissues. For this knowledge to be translated to humans, biomarkers allowing early detection of the programming status of the individual and technologies allowing measuring of the thermogenic activity of adipose tissue depots in vivo are required.

Diminished response to food deprivation of the rat brown adipose tissue mitochondrial uncoupling system with age

The aim of the present work is to investigate the effect of starvation on brown adipose tissue thermogenic activity with aging. Interscapular brown adipose tissue from female Wistar rats of different ages was used; half of them were fed and the other half were starved for 24 hours. Mitochondria were isolated and mitochondrial protein content, GDP‐binding, Cytochrome‐c Oxidase activity and uncoupling protein levels were measured. Results show a decrease of all studied parameters, indicating a diminished thermogenic activity with age. The response to starvation is almost the same in all the parameters studied: a general reduction with starvation and a progressive disappearance of this response to starvation with aging. On the whole, these results would indicate a deficient regulation of brown adipose tissue thermogenic activity in old animals, as it happens in other animal models with an alterated thermogenesis.

Programming of the Beige Phenotype in White Adipose Tissue of Adult Mice by Mild Resveratrol and Nicotinamide Riboside Supplementations in Early Postnatal Life

SCOPE Resveratrol (RSV) and nicotinamide riboside (NR) are food compounds with anti-obesity actions in adult rodents. Here, the long-term effects of RSV and NR mild supplementation throughout lactation on adiposity-related parameters and the appearance of the beige phenotype in white adipose tissue (WAT) in adulthood are assessed. METHODS AND RESULTS Newborn mice received orally RSV or NR from day 2 to 20 of life. Control littermates received the vehicle. All animals are weaned onto a chow diet on day 21. On day 90, half the animals of each group are assigned to a high-fat diet (HFD) for 10 weeks, while the other remained on a normal-fat diet. Energy-balance-related parameters, blood parameters, and gene expression and immunohistochemical analysis of WAT are assessed. Treated male mice show an improved response to the HFD, such as delayed body weight gain, a blunted increase in the plasma leptin/adiponectin ratio, and a decreased lipolytic response, together with signs of white-to-brown fat remodeling in inguinal WAT. These effects are absent in female mice. CONCLUSION RSV and NR supplementations in early postnatal life affect WATs thermogenic/oxidative transcriptional phenotype and metabolic responses in adulthood, with upregulatory and beneficial effects evidenced in male animals.

Thermogenesis and the Metabolic Syndrome

Reduced energy expenditure may contribute to obesity, which is a major feature of the Metabolic Syndrome. Adaptive thermogenesis, the regulated production of heat in response to changes in environmental factors such as cold or diet, is one of the components of energy expenditure and its activation represents a crucial defense against obesity in rodents, but the situation in humans is less clear. The best known mechanism of adaptive thermogenesis is mediated by UCP1, a mitochondrial uncoupling protein uniquely expressed in brown adipocytes, cells that are scarce in adult humans. UCP2 and UCP3 are UCP1 homologues of wider tissue distribution in both rodents and humans, but a role for them in the regulation of energy expenditure has not unequivocally been probed.