Androgen receptor deficiency in monocytes/macrophages does not alter adiposity or glucose homeostasis in male mice.

Androgen deprivation in men leads to increased adiposity, but the mechanisms underlying androgen regulation of fat mass have not been fully defined. Androgen receptor (AR) is expressed in monocytes/macrophages, which are resident in key metabolic tissues and influence energy metabolism in surrounding cells. Male mice bearing a cell-specific knockout of the AR in monocytes/macrophages (M-ARKO) were generated to determine whether selective loss of androgen signaling in these cells would lead to altered body composition. Wild-type (WT) and M-ARKO mice (12-22 weeks of age, n = 12 per group) were maintained on a regular chow diet for 8 weeks and then switched to a high-fat diet for 8 additional weeks. At baseline and on both the regular chow and high-fat diets, no differences in lean mass or fat mass were observed between groups. Consistent with the absence of differential body weight or adiposity, no differences in food intake (3.0 ± 0.5 g per day for WT mice vs 2.8 ± 0.4 g per day for M-ARKO mice) or total energy expenditure (0.6 ± 0.1 Kcal h-1 for WT mice vs 0.5 ± 0.1 Kcal h-1 for M-ARKO mice) were evident between groups during high-fat feeding. Liver weight was greater in M-ARKO than that in WT mice (1.5 ± 0.1 g vs 1.3 ± 0.0 g, respectively, P = 0.02). Finally, M-ARKO mice did not exhibit impairments in glucose tolerance or insulin sensitivity relative to WT mice at any study time point. In aggregate, these findings suggest that AR signaling specifically in monocytes/macrophages does not contribute to the regulation of systemic energy balance, adiposity, or insulin sensitivity in male mice.

Rosiglitazone Improves Insulin Resistance Mediated by 10,12 Conjugated Linoleic Acid in a Male Mouse Model of Metabolic Syndrome.

Trans-10, cis-12 conjugated linoleic acid (10,12 CLA) is a dietary fatty acid that promotes weight loss and disproportionate fat loss. Obese mice fed a high-fat, high-sucrose (HFHS) diet containing 10,12 CLA are resistant to weight gain and contain markedly reduced subcutaneous fat and adiponectin, with a concurrent lack of improvement in insulin sensitivity despite significant weight loss. Taken together, 10,12 CLA promotes a phenotype resembling peroxisome proliferator-activated receptor (PPAR)γ antagonism. Because thiazolidinediones such as rosiglitazone (Rosi) are used clinically to improve insulin sensitivity by activating PPARγ, with particular efficacy in subcutaneous white adipose tissue, we hypothesized that Rosi would improve glucose metabolism in mice losing weight with 10,12 CLA. Obese low-density lipoprotein receptor-deficient mice were fed a HFHS control diet, or supplemented with 1% 10,12 CLA with or without Rosi (10 mg/kg) for 8 weeks. Body composition, glucose and insulin tolerance tests, tissue gene expression, and plasma lipid analyses were performed. Mice consuming 10,12 CLA with Rosi lost weight and body fat compared with control groups, but with a healthier redistribution of body fat toward more subcutaneous adipose tissue than with 10,12 CLA alone. Further, Rosi improved 10,12 CLA-mediated insulin resistance parameters and increased plasma and subcutaneous adipose tissue adiponectin levels without adverse effects on plasma or hepatic lipids. We conclude that cotreatment of mice with 10,12 CLA and Rosi promotes fat loss with a healthier fat distribution that leads to improved insulin sensitivity, suggesting that the combination treatment strategy of 10,12 CLA with Rosi could have therapeutic potential for obesity treatment.

Metabolically distinct weight loss by 10,12 CLA and caloric restriction highlight the importance of subcutaneous white adipose tissue for glucose homeostasis in mice.

BACKGROUND: Widely used as a weight loss supplement, trans-10,cis-12 conjugated linoleic acid (10,12 CLA) promotes fat loss in obese mice and humans, but has also been associated with insulin resistance. OBJECTIVE: We therefore sought to directly compare weight loss by 10,12 CLA versus caloric restriction (CR, 15-25%), an acceptable healthy method of weight loss, to determine how 10,12 CLA-mediated weight loss fails to improve glucose metabolism. METHODS: Obese mice with characteristics of human metabolic syndrome were either supplemented with 10,12 CLA or subjected to CR to promote weight loss. Metabolic endpoints such as energy expenditure, glucose and insulin tolerance testing, and trunk fat distribution were measured. RESULTS: By design, 10,12 CLA and CR caused equivalent weight loss, with greater fat loss by 10,12 CLA accompanied by increased energy expenditure, reduced respiratory quotient, increased fat oxidation, accumulation of alternatively activated macrophages, and browning of subcutaneous white adipose tissue (WAT). Moreover, 10,12 CLA-supplemented mice better defended their body temperature against a cold challenge. However, 10,12 CLA concurrently induced the detrimental loss of subcutaneous WAT without reducing visceral WAT, promoted reduced plasma and WAT adipokine levels, worsened hepatic steatosis, and failed to improve glucose metabolism. Obese mice undergoing CR were protected from subcutaneous-specific fat loss, had improved hepatic steatosis, and subsequently showed the expected improvements in WAT adipokines, glucose metabolism and WAT inflammation. CONCLUSIONS: These results suggest that 10,12 CLA mediates the preferential loss of subcutaneous fat that likely contributes to hepatic steatosis and maintained insulin resistance, despite significant weight loss and WAT browning in mice. Collectively, we have shown that weight loss due to 10,12 CLA supplementation or CR results in dramatically different metabolic phenotypes, with the latter promoting a healthier form of weight loss.

Both STAT3 activation and cholesterol efflux contribute to the anti-inflammatory effect of apoA-I/ABCA1 interaction in macrophages.

ABCA1 exports excess cholesterol from cells to apoA-I and is essential for HDL synthesis. Genetic studies have shown that ABCA1 protects against cardiovascular disease. We have previously shown that the interaction of apoA-I with ABCA1 activates signaling molecule Janus kinase 2 (JAK2), which optimizes the cholesterol efflux activity of ABCA1. ABCA1-mediated activation of JAK2 also activates signal transducer and activator of transcription 3 (STAT3), which significantly attenuates proinflammatory cytokine expression in macrophages. To determine the mechanisms of the anti-inflammatory effects of apoA-I/ABCA1 interaction, we identified two special ABCA1 mutants, one with normal STAT3-activating capacity but lacking cholesterol efflux ability and the other with normal cholesterol efflux ability but lacking STAT3-activating capacity. We showed that activation of STAT3 by the interaction of apoA-I/ABCA1 without cholesterol efflux could significantly decrease proinflammatory cytokine expression in macrophages. Mechanistic studies showed that the anti-inflammatory effect of the apoA-I/ABCA1/STAT3 pathway is suppressor of cytokine signaling 3 dependent. Moreover, we showed that apoA-I/ABCA1-mediated cholesterol efflux without STAT3 activation can also reduce proinflammatory cytokine expression in macrophages. These findings suggest that the interaction of apoA-I/ABCA1 activates cholesterol efflux and STAT3 branch pathways to synergistically suppress inflammation in macrophages.

Hematopoietic ABCA1 deletion promotes monocytosis and worsens diet-induced insulin resistance in mice.

Low-grade chronic inflammation plays an important role in the pathogenesis of obesity-induced insulin resistance. ABCA1 is essential for reverse cholesterol transport and HDL synthesis, and protects against macrophage inflammation. In the present study, the effects of ABCA1 deficiency in hematopoietic cells on diet-induced inflammation and insulin resistance were tested in vivo using bone marrow transplanted (BMT)-WT and BMT-ABCA1(-/-) mice. When challenged with a high-fat high-carbohydrate diabetogenic diet with added cholesterol (HFHSC), BMT-ABCA1(-/-) mice displayed enhanced insulin resistance and impaired glucose tolerance as compared with BMT-WT mice. The worsened insulin resistance and impaired glucose tolerance in BMT-ABCA1(-/-) mice were accompanied by increased macrophage accumulation and inflammation in adipose tissue and liver. Moreover, BMT-ABCA1(-/-) mice had significantly higher hematopoietic stem cell proliferation, myeloid cell expansion, and monocytosis when challenged with the HFHSC diet. In vitro studies indicated that macrophages from ABCA1(-/-) mice showed significantly increased inflammatory responses induced by saturated fatty acids. Taken together, these studies point to an important role for hematopoietic ABCA1 in modulating a feed-forward mechanism in obesity such that inflamed tissue macrophages stimulate the production of more monocytes, leading to an exacerbation of inflammation and associated disease processes.

Genetic determinants of atherosclerosis, obesity, and energy balance in consomic mice.

Metabolic diseases such as obesity and atherosclerosis result from complex interactions between environmental factors and genetic variants. A panel of chromosome substitution strains (CSSs) was developed to characterize genetic and dietary factors contributing to metabolic diseases and other biological traits and biomedical conditions. Our goal here was to identify quantitative trait loci (QTLs) contributing to obesity, energy expenditure, and atherosclerosis. Parental strains C57BL/6 and A/J together with a panel of 21 CSSs derived from these progenitors were subjected to chronic feeding of rodent chow and atherosclerotic (females) or diabetogenic (males) test diets, and evaluated for a variety of metabolic phenotypes including several traits unique to this report, namely fat pad weights, energy balance, and atherosclerosis. A total of 297 QTLs across 35 traits were discovered, two of which provided significant protection from atherosclerosis, and several dozen QTLs modulated body weight, body composition, and circulating lipid levels in females and males. While several QTLs confirmed previous reports, most QTLs were novel. Finally, we applied the CSS quantitative genetic approach to energy balance, and identified three novel QTLs controlling energy expenditure and one QTL modulating food intake. Overall, we identified many new QTLs and phenotyped several novel traits in this mouse model of diet-induced metabolic diseases.

Obesity and weight loss result in increased adipose tissue ABCG1 expression in db/db mice.

The prevalence of obesity has reached epidemic proportions and is associated with several co-morbid conditions including diabetes, dyslipidemia, cancer, atherosclerosis and gallstones. Obesity is associated with low systemic inflammation and an accumulation of adipose tissue macrophages (ATMs) that are thought to modulate insulin resistance. ATMs may also modulate adipocyte metabolism and take up lipids released during adipocyte lipolysis and cell death. We suggest that high levels of free cholesterol residing in adipocytes are released during these processes and contribute to ATM activation and accumulation during obesity and caloric restriction. Db/db mice were studied for extent of adipose tissue inflammation under feeding conditions of ad libitum (AL) and caloric restriction (CR). The major finding was a marked elevation in epididymal adipose ABCG1 mRNA levels with obesity and CR (6-fold and 16-fold, respectively) over that seen for lean wild-type mice. ABCG1 protein was also elevated for CR as compared to AL adipose tissue. ABCG1 is likely produced by cholesterol loaded ATMs since this gene is not highly expressed in adipocytes and ABCG1 expression is sterol mediated. Our data supports the concept that metabolic changes in adipocytes due to demand lipolysis and cell death lead to cholesterol loading of ATMs. Based on finding cholesterol-loaded peritoneal leukocytes with elevated levels of ABCG1 in CR as compared to AL mice, we suggest that pathways for cholesterol trafficking out of adipose tissue involve ATM egress as well as ABCG1 mediated cholesterol efflux. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

Roles for cathepsins S, L, and B in insulitis and diabetes in the NOD mouse.

We developed a panel of non-obese diabetic (NOD) mice deficient in major lysosomal cysteine proteases (cathepsins S, L and B) to identify protease enzymes essential for autoimmune diabetes. Null alleles for cathepsins (Cts) S, L or B were introgressed onto the NOD genetic background with 19 Idd markers at homozygosity. Diabetes onset was determined among females aged up to 6 months. We evaluated insulitis and sialadenitis in tissues using histology and computer assisted morphology. NOD mice deficient in Ctss or Ctsb were partially protected from diabetes with incidence at 33% and 28%, respectively, versus wild-type NOD (69%; p < 0.00001). NODs lacking cathepsin L (Ctsl-/-) are completely protected from IDDM, as originally shown by others. Ctsl, Ctss, or Ctsb heterozygous mice were able to develop IDDM, although incidence levels were significantly lower for Ctsb+/- (50%) and Ctsl+/- (55%) as compared to NODs (69%; p < 0.03). Ctsl-/- mice contain functional, diabetogenic T cells and an enriched Foxp3+ regulatory T cell population, and diabetes resistance was due to the presence of an expanded population of regulatory T cells. These data provide additional information about the potency of the diabetogenic T cell population in Ctsl-/- mice which were comparable in potency to wild-type NOD mice. These data illustrate the critical contribution of each of these proteases in determining IDDM in the NOD mouse and provide a useful set of models for further studies.