PubMed Health⌕ Search

Biomedical subjects

M L Bonet

Publications and source records attributed to M L Bonet.

At least 19 recordsLinked to original sources
PubMed2003

Vitamin A and the regulation of fat reserves.

Beyond their classical nutritional roles, nutrients modify gene expression and function in target cells and, by so doing, affect many fundamental biological processes. An emerging example, which is the focus of this review, is the involvement of vitamin A in the regulation of the level and functioning of body fat reserves. Retinoic acid, the carboxylic acid form of vitamin A, is a transcriptional activator of the genes encoding uncoupling proteins, and results in animals indicate that whole body thermogenic capacity is related to the vitamin A status. Retinoic acid also influences adipocyte differentiation and survival, with high doses inhibiting and low doses promoting adipogenesis of preadipose cells in culture. Moreover, vitamin A status can influence the development and function of adipose tissues in whole animals, with a low vitamin A status favouring increased fat deposition.

Adipocytes↗
PubMed2003

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.

Adipose Tissue↗
PubMed2001

Changes of adiposity in response to vitamin A status correlate with changes of PPAR gamma 2 expression.

OBJECTIVE: To gain insight into the in vivo modulation of the expression of the adipogenic transcription factors PPAR gamma 2, C/EBP alpha, and ADD1/SREBP1c by retinoids and its relationship with whole-body adiposity. RESEARCH METHODS AND PROCEDURES: Three-week-old mice were fed with standard chow or a vitamin A-deficient diet for 10 weeks. During the 4 days immediately before they were killed, the animals were treated either with all-trans retinoic acid (tRA; 100 mg/kg per day, subcutaneously) or vehicle. The specific levels of the mRNAs for the three transcription factors were analyzed in epididymal white adipose tissue (eWAT) and inguinal white adipose tissue and in brown adipose tissue (BAT). Other parameters determined were leptin and UCP2 levels in white adipose tissue depots, total cholesterol and triglyceride serum levels, energy intake, body weight, and adiposity. RESULTS: Vitamin A-deficient diet feeding led to a marked increase of adiposity and to a small increase of body weight. Hypertrophy of white adipose tissue depots correlated with enhanced PPAR gamma 2 expression. Hypertrophy of BAT, in contrast, correlated with a decrease of PPAR gamma 2 expression that may contribute to the known reduced thermogenic potential of BAT under conditions of vitamin A restriction. Treatment with tRA triggered a reduction of adiposity and body weight that correlated with a down-regulation of PPAR gamma 2 expression in all adipose tissues. The effects of tRA were more pronounced in eWAT, where C/EBP alpha and ADD1/SREBP1c levels were also reduced. The response to tRA was impaired in the eWAT and BAT of animals fed the vitamin A-deficient diet. DISCUSSION: The results emphasize the importance of retinoids as physiological regulators of adipose tissue development and function in intact animals.

Adipose Tissue↗
PubMed2000

Obesity: molecular bases of a multifactorial problem.

Obesity could well become the most common health problem of the 21st century. There are more opportunities to consume large quantities of food: big portions of tasty, varied food, at reasonable prices, are available everywhere. Moreover, our bodies are better adapted to combat weight loss than to combat weight gain, since for thousands of years our species evolved in circumstances where nutrients were in short supply. The response of each individual to diet and other environmental factors varies considerably, depending on the characteristics of his/her body weight control mechanisms. The differentiating element in the future, especially as regards the dietary and pharmacological control of obesity, will be knowledge of an individual's possible response depending on his/her genetic background. Obesity can occur as a result of genetic or acquired changes in three main types of biochemical processes, which are the main focus of this review: a)feeding control, which determines the sensations of satiety and hunger through processes that depend on an interplay between internal signals (notably leptin) and environmental factors; b) energy efficiency, in particular the activation of thermogenesis mediated by uncoupling proteins (UCPs) that makes it possible to dissipate part of the energy contained in food as heat instead of accumulating it as fat, and c) adipogenesis, the process by which cells specialised in fat storage (adipocytes) are formed, which is controlled by an interplay of transcription factors, including members of the C/EBP, PPARgamma and ADD families. The knowledge of a growing number of genes and molecules implicated in these three types of processes and of their metabolic relationships is leading toward a molecular understanding of the body weight regulatory system, and is paving the way for new methods of obesity control, especially pharmacological but also nutritional and possibly involving genetic intervention.

Adipose Tissue↗
PubMed2000

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 beta3-adrenergic receptor (AR) agonist with beta2/beta1-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 beta-AR pathways.

Adipose Tissue↗
PubMed2000

Opposite effects of feeding a vitamin A-deficient diet and retinoic acid treatment on brown adipose tissue uncoupling protein 1 (UCP1), UCP2 and leptin expression.

The relationship between interscapular brown adipose tissue (IBAT) thermogenic potential and vitamin A status was investigated by studying the effects of feeding a vitamin A-deficient diet and all-trans retinoic acid (tRA) treatment on body weight and IBAT parameters in mice. Feeding a vitamin A-deficient diet tended to trigger opposite effects to those of tRA treatment, namely increased body weight, IBAT weight, adiposity and leptin mRNA expression, and reduced IBAT thermogenic potential in terms of uncoupling protein 1 (UCP1) mRNA and UCP2 mRNA expression. The results emphasize the importance of retinoids as physiological regulators of brown adipose tissue.

Adipose Tissue, Brown↗
PubMed1999

Brown adipose tissue response to cafeteria diet-feeding involves induction of the UCP2 gene and is impaired in female rats as compared to males.

Noradrenaline-dependent brown adipose tissue (BAT) thermogenesis is activated by the cold and excess energy intake, largely depends on the activity of the uncoupling protein 1 (UCP1), and is mediated mainly through the beta3-adrenoceptor (beta3-AR). We investigated the expression of ucp2, a gene that encodes a putative UCP1-like uncoupling protein, along with that of ucp1 and beta3-ar, in the interscapular BAT (IBAT) of male and female rats chronically fed a cafeteria diet. After 3 months on this diet, male rats attained a 34% excess body mass and showed IBAT hypertrophy and increased IBAT thermogenic potential, in terms of both UCP1 and UCP2 mRNA expression (both by 1.6-fold), UCP1 protein expression (by 1.75-fold) and GDP binding to IBAT mitochondria (by 2.2-fold); female rats attained a larger excess body weight (50%) and their IBAT, although hypertrophied, showed no signs of increased thermogenic potential per gram of tissue. Interestingly, the IBAT of female rats was already activated compared to males. Treatment of mouse brown adipocytes in primary culture with noradrenaline also triggered a dose-dependent increase of the levels of UCP1 mRNA and UCP2 mRNA. Retroregulatory down-regulation of the beta3-AR mRNA levels was found in the two models used. The results support a physiological role for UCP2, along with UCP1, in rodent BAT thermogenesis.

Adipose Tissue, Brown↗
PubMed1999

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 alpha (RARalpha) and retinoid X receptor alpha (RXRalpha) were analysed. RESULTS: Treatment with beta-carotene, alpha-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 microM. CONCLUSION: The results indicate that carotenoids can positively affect the expression of UCP1 without altering brown adipocyte proliferation.

Adipocytes↗
PubMed1998

Stimulation of uncoupling protein synthesis in white adipose tissue of mice treated with the beta 3-adrenergic agonist CGP-12177.

The effects of chronic treatment with the beta 3-adrenergic receptor agonist CGP-12177 on uncoupling protein (UCP) synthesis in interscapular brown adipose tissue (IBAT), various white fat depots and skeletal muscle have been examined in the mouse (daily injection for 15 days at a dose of 0.5 mg/kg). The treatment increased the IBAT UCP content and led to the expression of UCP in inguinal white adipose tissue. The increase in IBAT UCP content took place in the absence of tissue hypertrophy, and despite the increase in total body UCP content, no changes in body weight were observed after the treatment. The results confirm that ectopic expression of UCP in non-BAT tissues can be induced after chronic adrenergic stimulation.

Adipose Tissue↗
PubMed1998

Involvement of the retinoblastoma protein in brown and white adipocyte cell differentiation: functional and physical association with the adipogenic transcription factor C/EBPalpha.

We investigated the expression of the retinoblastoma protein (pRB) in adipocytes and its possible interaction with the adipogenic transcription factor CCAAT/enhancer-binding protein alpha (C/EBPalpha) in controlling the acquisition of the terminally differentiated adipocyte phenotype. The pRB was expressed (as measured by immunoblotting and/or immunofluorescence) in mice brown and white adipose tissue and in cultured adipocytes that showed lipid accumulation and expressed specific differentiation markers such as aP2 (measured using a specific cDNA probe) and in the case of brown adipocytes UCP-1 (measured using specific antibodies), but was undetectable in proliferative undifferentiated preadipocytes. Transient transfection experiments revealed a functional interaction between pRB and C/EBPalpha affecting transcription from the ucp-1 gene promoter. Thus, in immortalized brown adipocytes, co-transfection of both a C/EBPalpha and a pRB expression vectors maximally enhanced the expression of reporter chloramphenicol acetyltransferase driven by the ucp-1 promoter. Interestingly, C/EBPalpha inhibited reporter gene expression in CHO cells in an effect that was also potentiated in the presence of pRB. A positive effect of pRB on transcription from the ucp-1 promoter could be detected in C/EBPalpha-/-fibroblasts only after forced to overexpress C/EBPalpha, suggesting that the effect of pRB is dependent on its interaction with C/EBPalpha. We also found evidence that pRB and C/EBPalpha can directly bind to each other in vitro. Our results show that the expression of pRB is restricted to differentiated adipocytes, and provide evidence of a physical and functional interaction between pRB and C/EBPalpha that affects the transcriptional activity of the later on a brown adipocyte-specific gene.

3T3 Cells↗
PubMed1998

The uncoupling protein, thermogenin.

The uncoupling protein (UCP) or thermogenin is a 33 kDa inner-membrane mitochondrial protein exclusive to brown adipocytes in mammals that functions as a proton transporter, allowing the dissipation as heat of the proton gradient generated by the respiratory chain and thereby uncoupling oxidative phosphorylation. Thermogenesis (heat production) in brown adipose tissue, which is activated in response to cold exposure or chronic overeating, depends largely on UCP activity. Norepinephrine, released from sympathetic terminals and acting via beta-adrenoceptors and cAMP, is the main positive regulator of both UCP synthesis and activity. Brown fat thermogenesis plays a critical role in thermoregulation and in overall energy balance, at least in rodents. Manipulation of thermogenesis, whether through UCP or through analogous uncoupling proteins, could be an effective strategy against obesity.

Adipose Tissue, Brown↗
PubMed1997

Retinoic acid modulates retinoid X receptor alpha and retinoic acid receptor alpha levels of cultured brown adipocytes.

A novel potential regulatory pathway of brown adipose tissue (BAT) thermogenesis was recently recognized after identifying retinoic acid (RA) as a transcriptional activator of the uncoupling protein (UCP) gene. Here we provide evidence that the UCP responsiveness to RA in primary cultures of brown adipocytes involves RA receptor alpha (RAR alpha), and show, in the same system and also in CHO cells, that RA down-regulates the steady-state levels of RAR alpha and especially of retinoid X receptor alpha, suggesting autoregulation of the retinoid pathway and therefore supporting the idea of a physiological role for it in controlling the thermogenic capacity of BAT.

Adipocytes↗
PubMed1997

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.

Adipose Tissue↗
PubMed1996

In vitro and in vivo induction of brown adipocyte uncoupling protein (thermogenin) by retinoic acid.

The effects of retinoic acid (RA) isomers (all-trans-RA and 9-cis-RA) on the appearance of uncoupling protein (UCP; thermogenin), the only unequivocal molecular marker of the brown adipocyte differentiated phenotype, have been investigated in primary cultures of brown adipocytes, in the brown adipocyte cell line HIB 1B and directly in intact mice. The results obtained with cultured cells indicate that retinoids function as inducers of the appearance of UCP and, at the same time, partially inhibit brown adipocyte cell proliferation. The two RA isomers displayed similar effectiveness as UCP inducers, their effect being comparable with that triggered by noradrenaline, so far considered to be the main modulator of UCP gene expression. The effectiveness of retinoids as UCP inducers was dependent on the stage of brown adipocyte differentiation, being maximal in confluent primary cells and in the medium-late differentiation stage of HIB 1B cells. Corroborating the results obtained in vitro, we show that administration of all-trans-RA or 9-cis-RA to mice leads to an increase in their brown adipose tissue specific UCP content. 9-cis-RA treatment also prevented the loss of UCP on cold deacclimation. To our knowledge, this is the first report of a stimulatory effect of retinoid compounds on UCP induction in vivo.

Adipocytes↗
PubMed1995

Selective loss of the uncoupling protein from light versus heavy mitochondria of brown adipocytes after a decrease in noradrenergic stimulation in vivo and in vitro.

The relative stability against a decrease in adrenergic stimulation of the uncoupling protein (UCP) incorporated into different mitochondrial fractions was investigated in brown-fat-cell cultures. Cultures were initiated with undifferentiated cells from young mice and were acutely stimulated with noradrenaline at confluence (day 7). Cells were harvested just after the finish of the 24 h stimulation treatment or 24 h later, and three mitochondrial fractions were isolated by differential centrifugation: the M1 fraction (1000 g), the M3 fraction (3000 g) and the M15 fraction (15,000 g). The results obtained in vitro indicate that removal of adrenergic stimulation determines a selective loss of UCP from the lightest mitochondrial fractions (M3 and M15). Similar results were obtained in a situation in vivo (24 h starvation in mice) which is known to lead to a decreased noradrenaline input to brown adipose tissue, with decreased UCP levels. Thus brown adipocytes possess different mitochondrial subpopulations, which exhibit characteristic changes in their UCP turnover in response to thermogenic signals.

Adipose Tissue, Brown↗
PubMed1994

Kinetic mechanism of Halobacterium halobium Mn(2+)-activated alkaline phosphatase.

The extreme halophilic archaebacterium Halobacterium halobium contains an atypical alkaline phosphatase which is selectively activated by Mn2+ ions (Bonet et al., 1991: Int. J. Biochem. 23, 1445-1451). Enzyme kinetic mechanism in the presence of Mn2+ with p-nitrophenylphosphate as substrate was analysed by initial rate and product and competitive inhibition studies. The results indicate that there is an ordered addition of activator and substrate, Mn2+ being first in binding to the phosphatase, and that inorganic phosphate is the last product in leaving the enzyme active site. Strong inhibition by vanadate suggests that a phosphoenzyme intermediate is formed during enzymatic phosphohydrolysis of substrate.

Alkaline Phosphatase↗
PubMed1993

Effects of genetic replacements of charged and H-bonding residues in the retinal pocket on Ca2+ binding to deionized bacteriorhodopsin.

Metal cations are known to be required for proton pumping by bacteriorhodopsin (bR). Previous studies found that bR has two high-affinity and four to six low-affinity Ca(2+)-binding sites. In our efforts to find the location of these Ca2+ sites, the effects of replacing charged (Asp-85, Asp-212, and Arg-82) and H-bonding (Tyr-185) residues in the retinal pocket on the color control and binding affinity of Ca2+ ions in Ca(2+)-regenerated bR were examined. The important results are as follows: (i) The removal of Ca2+ from recombinant bR in which charged residues were replaced by neutral ones shifted the retinal absorption to the blue, opposite to that observed in wild-type bR or in recombinant bR in which the H-bonding residue, Tyr-185, was replaced by a non-H-bonding amino acid (Phe). (ii) Similar to the observation in wild-type bR, the binding of Ca2+ to the second site gave the observed color change in the recombinant bR samples in which charged residues were replaced by neutral ones. (iii) The residue replacements had no effect on the affinity constants of the four to six weakly bound Ca2+. (iv) The two high-affinity sites exhibited reduced affinity with substitutions; while the extent of the reduction depended on the specific substitution, each site was reduced by the same factor for each of the charged residue substitutions but by different factors for the mutant where Tyr-185 was replaced with Phe(Y185F). The above results suggest that the two Ca2+ ions in the two high-affinity sites are within interaction distance with one another and with the charged residues in the retinal pocket. The results further suggest that, while the interaction between Tyr-185 and the high-affinity Ca2+ ions is relatively short range and specific (with more coupling to the Ca2+ ion in the second affinity site), between the charged residues and Ca2+ ions it seems to be of the electrostatic (e.g., ion-ion) long range, nonspecific type. Although neither Asp-85, Asp-212, nor Arg-82 is individually directly involved in the binding of Ca2+ in these two sites, they might all participate in it. Together with the protonated Schiff base, the charged residues along with Tyr-185 and one or two Ca2+ ions (and probably a few water molecules) seem to form an electrostatically coupled system that is part of a cavity that controls the color and function of bR.

Amino Acid Sequence↗