Ana M. Proenza

Gender dimorphism in high-fat-diet-induced insulin resistance in skeletal muscle of aged rats.

Muscle resistance to insulin plays a key role in the metabolic dysregulation associated to obesity. A pro-inflammatory and pro-oxidant status has been proposed to be the link between dietary obesity and insulin resistance. Given the gender differences previously found in mitochondrial function and oxidative stress, the aim of the present study was to investigate whether this gender dimorphism leads to differences in the development of high-fat-diet-induced insulin resistance in rat skeletal muscle. Male and female rats of 15 months of age were fed with a high-fat-diet (32% fat) for 14 weeks. Control male rats showed a more marked insulin resistance status compared to females, as indicated by the glucose tolerance curve profile and the serum insulin, resistin and adiponectin levels. High-fat-diet feeding induced an excess of body weight of 16.2% in males and 38.4% in females, an increase in both muscle mitochondrial hydrogen peroxide production and in oxidative damage, together with a decrease in the Mn-superoxide dismutase activity in both genders. However, high-fat-diet fed female rats showed a less marked insulin resistance profile than males, higher mitochondrial oxygen consumption and cytochrome c oxidase activity, and a better capacity to counteract the oxidative-stress-dependent insulin resistance through an overexpression of both muscle UCP3 and GLUT4 proteins. These results point to a gender dimorphism in the insulin resistance status and in the response of skeletal muscle to high-fat-diet feeding which could be related to a more detrimental effect of age in male rats.

Breast and lung cancer are associated with a decrease in blood cell amino acid content

The description of different plasma amino acid profiles for specific types of cancer suggests that the metabolic alterations brought about by each type of tumor determine their own, distinctive profile of plasma amino acids. However, the blood cell pool represents an important percentage of the total amount of amino acids and has been reported to undergo significant changes in several physiological situations, thus raising the question of what effect a situation like cancer could have on amino acid blood compartmentation. We determined the levels of individual amino acids in blood, plasma and blood cell compartment of 14 lung cancer patients, 16 breast cancer patients and the corresponding healthy controls (n = 14 and 18, respectively). Cancer, a situation of increased amino acid demand, was accompanied by a decrease in the amino acid availability, of which the blood cell pool would be the main contributor. Thus, the fact that the blood cell pool reflects more intensely than plasma the changes in amino acid availability and undergoes changes according to the demand of amino acids, reinforces the important role of the cell pool in blood amino acid compartmentation and handling. The profiles of blood amino acids characteristic of different types of tumors that have been proposed by some authors could be extended to other compartments-in addition to the plasma-and even be more informative.

Sex Steroid Receptor Expression Profile in Brown Adipose Tissue. Effects of Hormonal Status

Recent investigations suggest that sex hormones play an important role in the brown adipose tissue (BAT) thermogenic program by acting on several steps of the lipolytic signal cascade and on the UCP1 transcription control. However, the number of studies focusing on steroid receptor status in brown adipose tissue is negligible. In the present study, we analyze steroid receptor mRNA levels in brown adipose tissue in male and female rats and in pregnant and lactating females, all of them models with a different hormonal background. The direct effect of sex hormones on the expression of their receptors was studied in vitro in primary culture of brown adipocytes. Oestrogen receptor (ERα) and androgen receptor (AR) densities were higher in male than in female BAT. PR A+B mRNA expression was downregulated in lactation, suggesting a role of progesterone signalling in thermogenesis impairment at this stage. In vitro studies showed that progesterone decreased PR A+B mRNA and that testosterone downregulated ERα mRNA. The results highlighted in this study demonstrate the presence of steroid receptor mRNA in BAT and in brown cell cultured adipocytes, supporting the idea that changes in steroid receptor expression would be important for the understanding of sex hormone effects on BAT physiology.

Long-term High-fat-diet Feeding Impairs Mitochondrial Biogenesis in Liver of Male and Female Rats

Background/Aims: Mitochondrial biogenesis includes both mitochondrial proliferation and differentiation and its regulation under different physiological conditions is not clear. Given the sexual dimorphism previously found in mitochondrial function, the aim of this study was to investigate the gender-dependent effect of chronic high-fat-diet (HFD) feeding on rat liver mitochondrial function and biogenesis. Methods: Ten-week old male and female rats were fed a HFD (26% fat) or a control diet (2.9% fat) for 26 weeks. Mitochondrial morphology was studied. Mitochondrial DNA and protein content, hydrogen peroxide production, oxidative capacity, antioxidant defenses, as well as markers of oxidative damage and mitochondrial biogenesis were analyzed. Results: Female rats showed higher levels of mitochondrial protein and an enhanced oxidative capacity per mitochondrion than males. In both genders, HFD feeding increased mtDNA content and decreased mitochondrial differentiation markers. Conclusion: In comparison to male rats, females show higher oxidative capacity as a consequence of their greater mitochondrial differentiation under both control and obese status. In response to HFD feeding, the oxidative capacity of the whole mitochondrial population is maintained in both genders. This is obtained by means of an enhancement of mitochondrial proliferation, which counteracts the diet-induced impairment of the function of each mitochondrion.

Sex differences in the effect of high-fat diet feeding on rat white adipose tissue mitochondrial function and insulin sensitivity.

Obesity-induced mitochondrial dysfunction in white adipose tissue (WAT) leads to a dysregulation of adipokine secretion, which is involved in insulin resistance development. Taking into account the sex differences previously found both in mitochondrial function and for the insulin sensitivity profile in different tissues, the aim of this study was to investigate whether a sex-dependent effect of a long-term high-fat diet (HFD) feeding exists on WAT mitochondrial function. Indeed, HFD effects on the levels of the key components of the insulin and adiponectin signaling pathways, and the consequences of these effects on the systemic profile of insulin sensitivity were also studied. Wistar rats of both sexes were fed a standard diet or an HFD. Serum markers of insulin sensitivity, protein, and mRNA levels of the main elements of the insulin and adiponectin signaling pathways, and the markers of mitochondrial function and biogenesis, were measured. Our results indicate that different physiological strategies are adopted by male and female rats in response to HFD. In this regard, HFD induced mitochondrial proliferation in males and mitochondrial differentiation in females, as well as a greater retroperitoneal WAT expandability capacity, which allows them to preserve a better insulin sensitivity profile than male rats for both control and HFD groups. Moreover, female WAT showed a decrease in adiponectin and insulin signaling pathway element levels. This sexual dimorphism suggests that there are different strategies for retroperitoneal WAT to maintain the energetic and metabolic homeostasis in response to HFD feeding.

Skeletal muscle and liver oxidative metabolism in response to a voluntary isocaloric intake of a high fat diet in male and female rats.

High fat diets (HFD) usually lead to hyperphagia and body weight gain. However, macronutrient proportions in the diet can modulate energy intake and body fat deposition. The aim of the study was to investigate muscle and liver oxidative metabolism in response to an isocaloric intake of a HFD and to elucidate the possible gender-dependent response. Eight week-old male and female rats were fed either standard chow or HFD for 14 weeks. Energy intake, body weight and whole animal oxygen consumption were determined periodically. Mitochondrial oxygen consumption, hydrogen peroxide production, TBARS levels, Cytochrome-c-oxidase, Citrate synthase and antioxidant enzyme activities were measured in muscle and liver. UCP1 and UCP3 protein levels were analyzed in brown adipose tissue and muscle, respectively. Male rats showed higher energy efficiency, enhanced adiposity, greater hydrogen peroxide production and less effective antioxidant machinery compared to females. HFD feeding increased energy expenditure but did not modify either tissue oxidative metabolism or oxidative damage in either gender. HFD animals over-expressed uncoupling proteins in order to maintain energy balance (brown adipose tissue UCP1) and to avoid oxidative stress (skeletal muscle UCP3), thus counteracting the alterations induced by the modification of the proportion of macronutrients in the diet.

Estradiol stimulates mitochondrial biogenesis and adiponectin expression in skeletal muscle.

Sexual dimorphism has been found in mitochondrial features of skeletal muscle, with female rats showing greater mitochondrial mass and function compared with males. Adiponectin is an insulin-sensitizing adipokine whose expression has been related to mitochondrial function and that is also expressed in skeletal muscle, where it exerts local metabolic effects. The aim of this research was to elucidate the role of sex hormones in modulation of mitochondrial function, as well as its relationship with adiponectin production in rat skeletal muscle. An in vivo study with ovariectomized Wistar rats receiving or not receiving 17β-estradiol (E2) (10 μg/kg per 48 h for 4 weeks) was carried out, in parallel with an assay of cultured myotubes (L6E9) treated with E2 (10 nM), progesterone (Pg; 1 μM), or testosterone (1 μM). E2 upregulated the markers of mitochondrial biogenesis and dynamics, and also of mitochondrial function in skeletal muscle and L6E9. Although in vivo E2 supplementation only partially restored the decreased adiponectin expression levels induced by ovariectomy, these were enhanced by E2 and Pg treatment in cultured myotubes, whereas testosterone showed no effects. Adiponectin receptor 1 expression was increased by E2 treatment, both in vivo and in vitro, but testosterone decreased it. In conclusion, our results are in agreement with the sexual dimorphism previously reported in skeletal muscle mitochondrial function and indicate E2 to be its main effector, as it enhances mitochondrial function and diminishes oxidative stress. Moreover, our data support the idea of the existence of a link between mitochondrial function and adiponectin expression in skeletal muscle, which could be modulated by sex hormones.

Gender related differences in paraoxonase 1 response to high-fat diet-induced oxidative stress.

Objective: To evaluate the influence of the pro‐oxidant and proinflammatory state related to dietary obesity on serum paraoxonase 1 (PON1) activity in male and female rats.

Depot- and gender-related differences in the lipolytic pathway of adipose tissue from severely obese patients.

The present study was performed to analyze in detail gender- and site-related alterations in the adrenergic signal transduction pathway of lipolysis in fat cells isolated from subcutaneous abdominal and visceral fat depots from severely obese patients. The study group consisted of 30 morbidly obese subjects (9 men and 21 women) aged 41.1±1.9 years, with a body mass index (BMI) of 54.7±1.7 kg/m2, who had undergone abdominal surgery. Protein levels of hormone-sensitive lipase (HSL) and adrenergic receptors (AR), as well as HSL activity and the lipolytic response to adrenergic agents were analyzed. Both fat depots had similar basal lipolysis, but the capacity of catecholamines to activate lipolysis was greater in visceral fat, both at AR and postreceptor levels. Basal lipolysis and lipolytic activity induced by dibutyryl cyclic AMP were higher in men than in women. However, the visceral depot of women showed a higher maximal stimulation by noradrenaline than that of men, in accordance with higher ß1- and ß3-AR protein levels. In conclusion, the main gender-related differences were located in the visceral depot, with women exhibiting a higher sensitivity to catecholamines associated with an increased provision of ß-AR, while men showed an enhanced lipolytic capacity at the postreceptor level.

Opposite effects of 17-β estradiol and testosterone on mitochondrial biogenesis and adiponectin synthesis in white adipocytes

Sexual dimorphism has been found in both mitochondrial functionality and adiponectin expression in white adipose tissue, with female rats presenting more functional mitochondria than males and greater adiponectin expression. However, little is known about the role of sex hormones in this dimorphism. The aim was to elucidate the role of sex hormones in mitochondrial biogenesis and dynamics and in adiponectin synthesis in white adipocytes, and also to provide new evidence of the link between these processes. 3T3-L1 preadipocytes were differentiated and treated either with 17-β estradiol (E₂; 10  nM), progesterone (Pg), testosterone (1  μM both), or a combination of Pg or testosterone with flutamide (FLT; 10  μM) or E₂ (1  μM). The markers of mitochondrial biogenesis and dynamics and adiponectin expression were analyzed. E₂ induced mitochondrial proliferation and differentiation in 3T3-L1, although testosterone showed opposite effects. Pg treatment stimulated proliferation but impaired differentiation. In concerns mitochondrial dynamics, these hormones promoted fusion over fission. FLT treatment indicated that Pg elicits its effects on mitochondrial dynamics through the androgen receptor. E₂ coadministration with testosterone or Pg reversed its effects. In conclusion, our results show that E₂ induces stimulation of mitochondrial biogenesis in white adipocytes in vitro, especially in situations that imply an impairment of mitochondrial function, whereas testosterone would have opposite effects. Moreover, testosterone and Pg alter mitochondrial dynamics by promoting fusion over fission, while E₂ stimulates both processes. All these alterations run in parallel with changes in adiponectin expression, thus suggesting the existence of a link between mitochondrial biogenesis and dynamics and adiponectin synthesis in white adipocytes.