A large proportion of mediastinal and perirenal visceral fat of Siberian adult people is formed by UCP1 immunoreactive multilocular and paucilocular adipocytes

Journal of Physiology and Biochemistry - Many deleterious consequences for health of excessive fat accumulation are due to visceral fat. Browning of visceral fat is mainly cold dependent and has...     

Effects of 6-month daily supplementation with oral beta-carotene in combination or not with benzo[a]pyrene on cell-cycle markers in the lung of ferrets

Epidemiological studies have demonstrated that people who eat more fruits and vegetables (rich in carotenoids) and people who have higher serum beta-carotene (BC) levels have a lower risk of cancer, particularly lung cancer. However, the two main human intervention studies of BC supplementation (the ATBC and the CARET trials) revealed an increased risk of lung cancer among smokers and asbestos workers. Previous studies carried out in the ferret have reported that BC effects are related to dose. Here, we treated ferrets with two concentrations of oral BC (0.8 and 3.2 mg/kg body weight per day) for 6 months, using BC in a formulation also containing dl-alpha-tocopherol and ascorbyl palmitate. The effect of the smoke-derived carcinogenic agent benzo[a]pyrene (BP), with or without low-dose BC, was also analysed. We determined the protein levels and mRNA expression levels of activator protein 1 (c-Jun and c-Fos), c-Myc, cyclin D1, proliferating cellular nuclear antigen and retinoic acid receptor beta. We did not find higher levels of cell proliferation markers in the lung of ferrets treated with BC or signals of squamous metaplasia lesions either. On the other hand, although no evident signals of pulmonary carcinogenesis were observed in animals exposed to BP, BC supplementation in these animals may prevent against excess cell proliferation, since this reestablishes Jun protein and cyclin D1 mRNA levels in the lung of BP-exposed animals. In summary, these results show that the combination of BC with alpha-tocopherol and ascorbyl palmitate does not induce pro-oxidant effects in the lung of ferrets.     

CL316,243 and cold stress induce heterogeneous expression of UCP1 mRNA and protein in rodent brown adipocytes.

Uncoupling protein 1 (UCP1), the mammalian thermogenic mitochondrial protein, is found only in brown adipocytes, but its expression by immunohistochemistry is not homogeneous. Here we present evidence that the non-homogeneous pattern of immunostaining for UCP1 (referred to as the "Harlequin phenomenon") is particularly evident after acute and chronic cold (4C) stimulus and after administration of a specific beta(3)-adrenoceptor agonist (CL316,243). Accordingly, mRNA in situ expression confirmed the UCP1 non-homogeneous pattern of gene activation under conditions of adrenergic stimulus. Furthermore, morphometric analysis of immunogold-stained thin sections showed that UCP1-gold particle density was different among neighboring brown adipocytes with mitochondria of the same size and density. When the adrenergic stimulus was reduced in warm-acclimated animals (28C), UCP1 protein and mRNA expression was reduced and consequently the Harlequin phenomenon was barely visible. These data suggest the existence of an alternative and controlled functional recruitment of brown adipocytes in acute adrenergically stressed animals, possibly to avoid heat and metabolic damage in thermogenically active cells. Of note, the heat shock protein heme oxygenase 1 (HO1) is heterogeneously expressed in adrenergically stimulated brown adipose tissue and, specifically, cells expressing strong immunoreactivity for UCP1 also strongly express HO1.     

Expression of human alpha 2-adrenergic receptors in adipose tissue of beta 3-adrenergic receptor-deficient mice promotes diet-induced obesity

Catecholamines play an important role in controlling white adipose tissue function and development. beta- and alpha 2-adrenergic receptors (ARs) couple positively and negatively, respectively, to adenylyl cyclase and are co-expressed in human adipocytes. Previous studies have demonstrated increased adipocyte alpha 2/beta-AR balance in obesity, and it has been proposed that increased alpha 2-ARs in adipose tissue with or without decreased beta-ARs may contribute mechanistically to the development of increased fat mass. To critically test this hypothesis, adipocyte alpha 2/beta-AR balance was genetically manipulated in mice. Human alpha 2A-ARs were transgenically expressed in the adipose tissue of mice that were either homozygous (-/-) or heterozygous (+/-) for a disrupted beta 3-AR allele. Mice expressing alpha 2-ARs in fat, in the absence of beta 3-ARs (beta 3-AR -/- background), developed high fat diet-induced obesity. Strikingly, this effect was due entirely to adipocyte hyperplasia and required the presence of alpha2-ARs, the absence of beta 3-ARs, and a high fat diet. Of note, obese alpha 2-transgenic beta 3 -/- mice failed to develop insulin resistance, which may reflect the fact that expanded fat mass was due to adipocyte hyperplasia and not adipocyte hypertrophy. In summary, we have demonstrated that increased alpha 2/beta-AR balance in adipocytes promotes obesity by stimulating adipocyte hyperplasia. This study also demonstrates one way in which two genes (alpha 2 and beta 3-AR) and diet interact to influence fat mass.     

Hormone‐induced mitochondrial fission is utilized by brown adipocytes as an amplification pathway for energy expenditure

Adrenergic stimulation of brown adipocytes (BA) induces mitochondrial uncoupling, thereby increasing energy expenditure by shifting nutrient oxidation towards thermogenesis. Here we describe that mitochondrial dynamics is a physiological regulator of adrenergically‐induced changes in energy expenditure. The sympathetic neurotransmitter Norepinephrine (NE) induced complete and rapid mitochondrial fragmentation in BA, characterized by Drp1 phosphorylation and Opa1 cleavage. Mechanistically, NE‐mediated Drp1 phosphorylation was dependent on Protein Kinase‐A (PKA) activity, whereas Opa1 cleavage required mitochondrial depolarization mediated by FFAs released as a result of lipolysis. This change in mitochondrial architecture was observed both in primary cultures and brown adipose tissue from cold‐exposed mice. Mitochondrial uncoupling induced by NE in brown adipocytes was reduced by inhibition of mitochondrial fission through transient Drp1 DN overexpression. Furthermore, forced mitochondrial fragmentation in BA through Mfn2 knock down increased the capacity of exogenous FFAs to increase energy expenditure. These results suggest that, in addition to its ability to stimulate lipolysis, NE induces energy expenditure in BA by promoting mitochondrial fragmentation. Together these data reveal that adrenergically‐induced changes to mitochondrial dynamics are required for BA thermogenic activation and for the control of energy expenditure.     

Erythrocyte glutathione transferase: a potential new biomarker in chronic kidney diseases which correlates with plasma homocysteine

The erythrocyte glutathione S-transferase (e-GST) is a member of a superfamily of inducible enzymes involved in cell detoxification that shows an increased expression in chronic kidney disease (CKD) patients. We propose a new automated analysis procedure for e-GST activity that has been validated in 72 CKD patients and 62 maintenance hemodialysis patients (MHD). Regression analysis was carried out to assess association between e-GST activity data, main clinical variables, and plasma homocysteine (Hcy), a modified sulfur amino acid known as potential risk factor for cardiovascular disease that is increased above normal levels in more than 90% of the uremic patients. An increased e-GST activity was confirmed in MHD patients (N=62; 10.2±0.4 U/gHb) compared with healthy subjects (N=80; 5.8±0.4 U/gHb), and as an original finding, a significant increase of e-GST activity was observed in pre-dialysis CKD patients with a positive correlation with disease severity weighted according to the four stages of "Kidney Disease Outcomes Quality Initiative" classification (7.4±0.5, 8±1, 9.5±0.6, 12±1 U/gHb, respectively). No correlation was found between e-GST activity and hemoglobin, transferrin, blood iron and the markers of systemic inflammation and renal function such as alpha-1 acid glycoprotein and high-sensitive C-Reactive Protein, beta-2 microglobulin and the index of malnutrition-inflammation PINI, while a significant correlation was observed for the first time between plasma Hcy and e-GST activity (r2=0.64, P<0.0001) in MHD patients. Hcy, however, was not identified as an inhibitor of e-GST enzyme. The results in this study suggest the potential for automated e-GST analysis as a valuable tool to further explore phase II-related uremic toxicity in CKD and MHD patients.     

Foetal bovine intermuscular adipose tissue exhibits histological and metabolic features of brown and white adipocytes during the last third of pregnancy

This study reports the metabolic and morphological characteristics of bovine intermuscular adipose tissue (AT) throughout foetal growth. Our hypothesis was that the histological and molecular features of intermuscular AT would be different from those previously reported for foetal perirenal AT, based on its anatomical location near the muscle and the recent identification of two distinct adipocyte precursors in mouse AT depending on their locations. To address this question, intermuscular AT was sampled from Charolais and Blond d'Aquitaine foetuses at 180, 210 and 260 days post conception (dpc). The two bovine breeds were chosen because of the higher adiposity of Charolais than Blond d'Aquitaine cattle during the postnatal life. Regardless of the breed, adipocyte volume increased slightly (+38%, P < 0.01) with increasing foetal age. This was concomitant with a decrease (P < 0.05) in the activity of enzymes involved in de novo fatty acid (FA) synthesis (FA synthase and glucose-6-phosphate dehydrogenase) and FA esterification (glycerol-3-phosphate dehydrogenase) when expressed per million adipocytes, and with an increase (P ⩽ 0.01) in mRNA abundances for uncoupling protein 1, adiponectin and leptin (LEP) between 180 and 260 dpc. No difference was observed in the adipocyte volume between breeds, which was consistent with the lack of major between-breed differences in mRNA abundances or activities of enzymes involved in lipid metabolism. The mRNA abundance of lipoprotein lipase was maintained across ages, suggesting a storage of circulating FA rather than of FA synthesized de novo. Plasma LEP increased with foetal age, but only in the Charolais breed (+71%, P ⩽ 0.01), and was two- to threefold higher in Charolais than Blond d'Aquitaine foetuses. Regardless of the breed, bovine intermuscular AT contained predominantly unilocular adipocytes believed to be white adipocytes that were larger at 260 dpc than at 180 dpc. These data thus challenge current concepts of the largely brown nature of bovine foetal AT (based on histological and metabolic features of perirenal AT as previously reported a few days before or after birth).