Expressions of leptin and insulin-like growth factor-I are highly correlated and region-specific in adipose tissue of growing rats

Adipose tissue as a therapeutic target for vascular damage in Alzheimer's disease

Adipose tissue has recently been recognized as an important endocrine organ that plays a crucial role in energy metabolism and in the immune response in many metabolic tissues. With this regard, emerging evidence indicates that an important crosstalk exists between the adipose tissue and the brain. However, the contribution of adipose tissue to the development of age-related diseases, including Alzheimer's disease, remains poorly defined. New studies suggest that the adipose tissue modulates brain function through a range of endogenous biologically active factors known as adipokines, which can cross the blood-brain barrier to reach the target areas in the brain or to regulate the function of the blood-brain barrier. In this review, we discuss the effects of several adipokines on the physiology of the blood-brain barrier, their contribution to the development of Alzheimer's disease and their therapeutic potential. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Effects of Greenshell Mussel (Perna canaliculus) Intake on Pathological Markers of Multiple Phenotypes of Osteoarthritis in Rats

The prevalence of metabolic osteoarthritis has been increasing worldwide, particularly among women. The aim of this study was to investigate the effects of the New Zealand greenshell mussel (Perna canaliculus; GSM) on osteoarthritis (OA) prevention in a rat model. One-hundred-and-eight female rats aged 12 weeks were divided into four test groups, containing 24 rats each, plus an additional control group. Each test group received one of the four experimental diets: normal control diet (ND), normal control diet supplemented with GSM (ND + GSM), high fat/high sugar diet (HFHS), or high fat/high sugar diet supplemented GSM (HFHS + GSM), for 36 weeks (end of the study). After 8 weeks on experimental diets, half of each group was subjected to ovariectomy (OVX) and the remaining half received a sham operation (ovaries left intact). The study evaluated body composition, bone mass, plasma cytokines, adipokines, HbA1c, CTX-II, and knee joint’s histopathology. HFHS diet and OVX significantly induced body weight gain and leptin production. OVX rats lost bone mineral density but increased adiponectin, HbA1C, and MCP-1. The OVX rats fed HFHS showed the highest Mankin scores. Importantly, inclusion of GSM reduced these pathological features. In conclusion, GSM might be beneficial in halting the progression of OA.

Insulin-like Growth Factor-I Receptor and Thyroid-Associated Ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is a complex disease process presumed to emerge from autoimmunity occurring in the thyroid gland, most frequently in Graves disease (GD). It is disfiguring and potentially blinding, culminating in orbital tissue remodeling and disruption of function of structures adjacent to the eye. There are currently no medical therapies proven capable of altering the clinical outcome of TAO in randomized, placebo-controlled multicenter trials. The orbital fibroblast represents the central target for immune reactivity. Recent identification of fibroblasts that putatively originate in the bone marrow as monocyte progenitors provides a plausible explanation for why antigens, the expressions of which were once considered restricted to the thyroid, are detected in the TAO orbit. These cells, known as fibrocytes, express relatively high levels of functional TSH receptor (TSHR) through which they can be activated by TSH and the GD-specific pathogenic antibodies that underpin thyroid overactivity. Fibrocytes also express insulin-like growth factor I receptor (IGF-IR) with which TSHR forms a physical and functional signaling complex. Notably, inhibition of IGF-IR activity results in the attenuation of signaling initiated at either receptor. Some studies suggest that IGF-IR-activating antibodies are generated in GD, whereas others refute this concept. These observations served as the rationale for implementing a recently completed therapeutic trial of teprotumumab, a monoclonal inhibitory antibody targeting IGF-IR in TAO. Results of that trial in active, moderate to severe disease revealed dramatic and rapid reductions in disease activity and severity. The targeting of IGF-IR with specific biologic agents may represent a paradigm shift in the therapy of TAO.

IGFBP4 Is Required for Adipogenesis and Influences the Distribution of Adipose Depots

Insulinlike growth factor (IGF) I induces adipogenesis in vitro. IGF-binding protein 4 (IGFBP4) is highly expressed in adipocytes and osteoblasts and is inhibitory of IGFs in vitro. We previously reported that Igfbp4 null mice (Igfbp4-/-) had decreased fat proportions at 8 and 16 weeks of age. However, the mechanism leading to the reduced adiposity remains unknown. The purpose of this study was to elucidate how IGFBP4 mediates adipose tissue development in vivo. Our results showed that inguinal and gonadal white adipose tissue (gWAT) from Igfbp4-/- mice had decreased weights and Pparγ expression. Cultures of primary bone marrow stromal cells (BMSCs) and ear mesenchymal stem cells (eMSCs) from mutant mice showed reduced adipogenesis. Both BMSCs and eMSC had a strong induction of Igfbp4 expression during adipogenesis. Furthermore, the increase in phosphorylated Akt (p-Akt), a downstream target of IGF-I signaling, in wild-type cells, was blunted in mutant eMSCs. On a high-fat diet (HFD) there were sexual differences in adipocyte expansion of Igfbp4-/- mice. Mutant males gained weight by expanding their white fat depots. However, Igfbp4-/- female mice were protected against diet-induced obesity. Ovariectomized Igfbp4-/- female mice gained weight in a manner similar to that seen in ovariectomized controls. Thus, Igfbp4 is required for inguinal fat expansion in female mice but not in male mice. However, gWAT expansion, which is prevented by estrogen during HFD, does not require Igfbp4.

Preservation of high-fat diet-induced femoral trabecular bone loss through genetic target of TNF-α

Obesity and osteoporosis are two common chronic diseases, however, the basis for the correlation between them remains largely unknown. The pro-inflammation cytokine tumor necrosis factor-alpha (TNF-α) plays important roles in lipid and bone metabolisms, which may be a good candidate in the correlation between obesity and osteoporosis. We investigated the pathological roles of TNF-α in high-fat diet (HFD)-induced bone loss. Wild-type (WT) mice and TNF-α knockout (TNF-α(-/-)) mice were fed with the standard diet or the HFD for 12 weeks. Bone marrow stromal cells (BMSCs) from both genotypes were induced to differentiate into osteoblasts and treated with palmitic acid (PA). Bone mass and microstructure of femurs were evaluated by micro-CT. Lipid and bone metabolisms were investigated by histological and plasma analyses, and real-time PCR. On the HFD, both TNF-α(-/-) and WT mice presented notable visceral obesity, dyslipidemia. Adipogenesis and osteoclastogenesis were enhanced, while osteoblastogenesis was reduced in both genotypes. However, the changes were significantly different between TNF-α(-/-) and WT mice after the HFD. The gain of body and fat-pad weight was less and adipocyte area was smaller by 22 % in TNF-α(-/-) mice. Osteoclast numbers and plasma CTX level were lower by 40 % and by 23 % in TNF-α(-/-) mice. There were more ALP positive cells in the PA-treated TNF-α(-/-) BMSCs. mRNA expression of PPAR-γ was lower while that of Runx2 was higher in the bone from TNF-α(-/-) HFD group and in the PA-treated TNF-α(-/-) BMSCs, compared to WT on the same treatment. Furthermore, femoral trabecular bone mass and trabecular bone number were significantly decreased in WT mice on the HFD, whereas they were increased by 1.56-fold and 1.53-fold, respectively, in TNF-α(-/-) mice on the same diet (P < 0.05). Our results demonstrated that TNF-α gene knockout retained HFD-induced femoral trabecular bone loss mainly by suppressing adipogenesis and osteoclastogenesis, and enhancing osteoblastogenesis, which suggests that TNF-α plays a critical role in the development of HFD-related bone metabolic disorders and it may be a new potential therapeutic target for obesity-related bone loss.

Qualitative and quantitative differences of adipose-derived stromal cells from superficial and deep subcutaneous lipoaspirates: a matter of fat

BACKGROUND AIMS

Subcutaneous fat represents a valuable reservoir of adipose-derived stem cells (ASCs) in the stromal vascular fraction (SVF), widely exploited in regenerative medicine applications, being easily harvested through lipoaspiration. The lack of standardized procedures for autologous fat grafting guided research efforts aimed at identifying possible differences related to the harvesting site, which may affect cell isolation yield, cell growth properties and clinical outcomes. Subcutaneous fat features a complex architecture: the superficial fascia separates superficial adipose tissue (SAT) from deep layer tissue (DAT). We aimed to unravel the differences between SAT and DAT, considering morphological structure, SVF composition, and ASC properties.

METHODS

SAT and DAT were collected from female donors and comparatively analyzed to evaluate cellular yield and viability, morphology, immunophenotype and molecular profile. ASCs were isolated in primary culture and used for in vitro differentiation assays. SAT and DAT from cadaver donors were also analyzed through histology and immunohistochemistry to assess morphology and cell localization within the hypoderm.

RESULTS

Liposuctioned SAT contained a higher stromal tissue compound, along with a higher proportion of CD105-positive cells, compared with DAT from the same harvesting site. Also, cells isolated from SAT displayed increased multipotency and stemness features. All differences were mainly evidenced in specimens harvested from the abdominal region. According to our results, SAT features overall increased stem properties.

CONCLUSIONS

Given that subcutaneous adipose tissue is currently exploited as the gold standard source for high-yield isolation of adult stem cells, these results may provide precious hints toward the definition of standardized protocols for microharvesting.

Increased adiposity and insulin correlates with the progressive suppression of pulsatile GH secretion during weight gain

Pathological changes associated with obesity are thought to contribute to GH deficiency. However, recent observations suggest that impaired GH secretion relative to excess calorie consumption contributes to progressive weight gain and thus may contribute to the development of obesity. To clarify this association between adiposity and GH secretion, we investigated the relationship between pulsatile GH secretion and body weight; epididymal fat mass; and circulating levels of leptin, insulin, non-esterified free fatty acids (NEFAs), and glucose. Data were obtained from male mice maintained on a standard or high-fat diet. We confirm the suppression of pulsatile GH secretion following dietary-induced weight gain. Correlation analyses reveal an inverse relationship between measures of pulsatile GH secretion, body weight, and epididymal fat mass. Moreover, we demonstrate an inverse relationship between measures of pulsatile GH secretion and circulating levels of leptin and insulin. The secretion of GH did not change relative to circulating levels of NEFAs or glucose. We conclude that impaired pulsatile GH secretion in the mouse occurs alongside progressive weight gain and thus precedes the development of obesity. Moreover, data illustrate key interactions between GH secretion and circulating levels of insulin and reflect the potential physiological role of GH in modulation of insulin-induced lipogenesis throughout positive energy balance.

The insulin-like growth factors in adipogenesis and obesity

Adipose tissue has been recognized as a major target of growth hormone (GH) action. GH was shown to inhibit adipocyte differentiation but stimulated preadipocyte proliferation in vitro. GH acts directly via its receptor or via upregulating insulin-like growth factor (IGF)-I, which is a critical mediator of preadipocyte proliferation, differentiation, and survival. Results from clinical studies on GH treatment in patients with GH deficiency or GH insensitivity syndrome can be used to dissect GH and IGF as well as IGF-binding protein (IGFBP) actions in vivo. In this article, changes of the GH/IGF system during adipocyte differentiation in vitro as well as related signaling pathways and their impact on adipose tissue growth and function are discussed. Clinical considerations include the effects of GH and IGF-I on adipose tissue during treatment of GH deficiency, differences in the IGF system between visceral and subcutaneous adipose tissue depots as well as the recently emerging role for adipose tissue in the regulation of glucose homeostasis.

Leptin and reproductive function

Adipose tissue plays a dynamic role in whole-body energy homeostasis by acting as an endocrine organ. Collective evidence indicates a strong link between neural influences and adipocyte expression and secretion of leptin. Developmental changes in these relationships are considered important for pubertal transition in reproductive function. Leptin augments secretion of gonadotropin hormones, which are essential for initiation and maintenance of normal reproductive function, by acting centrally at the hypothalamus to regulate gonadotropin-releasing hormone (GnRH) neuronal activity and secretion. The effects of leptin on GnRH are mediated through interneuronal pathways involving neuropeptide-Y, proopiomelanocortin and kisspeptin. Increased infertility associated with diet induced obesity or central leptin resistance are likely mediated through the kisspeptin-GnRH pathway. Furthermore, Leptin regulates reproductive function by altering the sensitivity of the pituitary gland to GnRH and acting at the ovary to regulate follicular and luteal steroidogenesis. Thus leptin serves as a putative signal that links metabolic status with the reproductive axis. The intent of this review is to examine the biological role of leptin with energy metabolism, and reproduction.

The IGF-I regulatory system and its impact on skeletal and energy homeostasis

Insulin-like growth factor (IGF)-I is important in the acquisition and maintenance of both soft and hard tissues. Skeletal remodeling requires energy and recent work has demonstrated that bone can influence insulin sensitivity and thereby regulate metabolic processes. New insights from mouse models into the role of IGF-binding proteins (IGFBPs) as more than mere depots for the IGFs has reignited investigations into the metabolic targets influenced by the IGF regulatory system and the pathways that link bone to adipose tissue. Although there remains continued uncertainty about the relative balance between the effects of circulating versus tissue IGF-I actions, the role of the IGFBPs has been redefined both as modulators of IGF-I action and as independent signaling factors. This review highlights several recent findings that shed new light on the physiologic role of the IGF regulatory system and its influence on skeletal and fat metabolism.

Diet-genotype interactions in the early development of obesity and insulin resistance in mice with a genetic deficiency in tumor necrosis factor-alpha

The onset of insulin resistance, the sites of action, and the mechanisms through which tumor necrosis factor-alpha (TNF-alpha) exacerbates the increase in adiposity and the development of insulin resistance in mice fed high-fat (HF) diet remain unclear. Here we investigated the effect of TNF-alpha deficiency on adiposity and insulin resistance during the initial 1 to 4 weeks of HF feeding. We examined body weight; the distribution of white adipose tissue (WAT); homeostasis model assessment; and levels of leptin, resistin, and adiponectin in the initial 4 weeks of HF feeding in TNF-alpha knockout (KO) mice and wild-type (WT) controls. Through 4 weeks of HF feeding, KO mice, unlike WT mice, maintained normal insulin sensitivity. Although WT-HF and KO-HF mice had similar levels of WAT at this time, KO-HF mice had more subcutaneous and less epididymal fat than WT-HF mice. The KO-HF mice also had less liver fat than the WT-HF mice. Finally, KO-HF mice had lower plasma levels of resistin than WT-HF mice. These data demonstrate that genetic lack of TNF-alpha protects insulin sensitivity during the early phase of HF feeding in the absence of altered total WAT. The data also suggest that the mechanism maintaining insulin sensitivity in the absence of TNF-alpha may involve redirection of the fat deposition to the metabolically more inert subcutaneous depot or decreases in circulating resistin and resultant decrease in liver fat deposition. The efficacy of therapeutic measures designed to counteract the effects of TNF-alpha may be increased during the early stages of obesity and insulin resistance.

Molecular cloning and expression of bovine (Bos taurus) leptin receptor isoform mRNAs

We characterized Bos taurus leptin receptor (Ob-R) isoform mRNAs as well as their expression in different tissues, including some adipose depots (perirenal, subcutaneous and intermuscular adipose tissues). Based on the GenBank database sequences of the bovine partial Ob-R, primers were designed to amplify cDNAs of bovine Ob-R isoforms. The full-length cDNAs of bovine the Ob-R isoforms were cloned by combination with 3'-and 5'-RACE. Three bovine Ob-R isoform cDNAs were cloned and the sequence analyses revealed that these cDNAs were bovine Ob-R isoforms, i.e., the long form (Ob-Rb), the middle form (Ob-Ra) and the short form (Ob-Rc). The open reading frames of Ob-Ra, Ob-Rb and Ob-Rc gene were 2688, 3498 and 2673 bp, respectively. The deduced amino acid sequences suggested that the isoforms were single transmembrane proteins, and differed in the C-terminal amino acid sequences. The amino acid sequence of these bovine Ob-R isoforms showed 73-75% identity compared with the corresponding mouse isoforms. The tissue-specific expression of the bovine Ob-R isoforms were measured by semi-quantitative RT-PCR. Expression of Ob-Rb was highest in liver, heart, spleen and kidney, with lower expression in lung and testis, and slight expression in muscle. Ob-Ra was highly expressed in liver and spleen, whereas moderate expression was observed in heart, testis, and muscle, and its expression was the lowest in lung and kidney. Ob-Rc mRNA was expressed in the liver, heart, testis, kidney and muscle, but not in the lung and spleen. In adipose tissues, higher expression of Ob-Ra and Ob-Rb mRNA was observed in intermuscular adipose tissue than in subcutaneous or perirenal adipose tissues. Ob-Ra mRNA level was positively correlated with Ob-Rb mRNA level in the adipose tissues (r=0.81, P<0.05). The results demonstrated that each Ob-R isoform mRNA was differentially expressed in various tissues of cattle, which may be involved in the difference of peripheral actions for leptin.

Adiposity dependent apelin gene expression: relationships with oxidative and inflammation markers

It has been reported that apelin functions as an adipokine, which has been associated to obesity and insulin resistance. The objective of this study was to analyze the apelin mRNA expression in white adipose tissue (WAT) from high-fat (Cafeteria) fed rats, in order to examine potential relationships with obesity markers and other related risk factors. Animals fed on the high-fat diet during 56 days increased their body weight, total body fat and WAT depots weights when compared to controls. Apelin subcutaneous mRNA expression was higher in the Cafeteria than in the Control fed group and this increase was partially reversed by dietary vitamin C supplementation. Statistically significant associations between subcutaneous apelin gene expression and almost all the studied variables were identified, being of special interest the correlations found with serum leptin (r=0.517), liver malondialdehyde (MDA) levels (r=0.477), and leptin, IRS-3 and IL-1ra retroperitoneal mRNA expression (r=0.701; r=0.692 and r=0.561, respectively). These associations evidence a possible role for apelin in the excessive weight gain induced by high-fat feeding and increased adiposity, insulin-resistance, liver oxidative stress and inflammation.

Dietary fat source regulatesobgene expression in white adipose tissue of rats under hyperphagic feeding

This work was designed to investigate the effect of different lipid sources onobgene expression and serum leptin levels in rats with two different feeding protocols: (1) free access to food; or (2) energy-controlled feeding. Male Wistar rats were fed diets containing 40 % energy as fat (olive oil, sunflower oil or beef tallow), for 4 weeks. In Expt 1 rats had free access to food, and in Expt 2 rats were fed a controlled amount of food (16 g/d, equivalent to 300 kJ/d). Insulin and leptin were determined by ELISA andobmRNA by Northern blot. When rats had free access to food,obmRNA levels were higher in animals fed either olive oil or sunflower oil than in those fed beef tallow. In marked contrast with feedingad libitum, no differences were found among dietary fat groups in rats fed energy-controlled diets. When both feeding protocols were compared, free access to food induced an increased expression ofobmRNA in perirenal and/or epididymal adipose tissues from rats fed either olive oil or sunflower oil, but not from rats fed beef tallow. Dietary lipid type did not induce modifications in serum leptin concentrations. A tendency to higher serum leptin levels was observed more in rats with free access to food than in rats fed energy-controlled feeding. No differences were found in insulin levels. Dietary fat type importantly affectsobmRNA expression in rat white adipose tissue under hyperphagic conditions. Further study is needed in order to elucidate the mechanism underlying this effect.

Lipid metabolism and secretory function of porcine intramuscular adipocytes compared with subcutaneous and perirenal adipocytes

The function of adipocytes interspersed between myofiber fasciculi in skeletal muscle physiology and physiopathology is poorly documented. Because regional differences in adipocyte features have been reported in various species, we hypothesized that lipid metabolism and secretory function of intramuscular (IM) adipocytes differ from that of nonmuscular adipocytes. In the present study, adipocytes isolated from trapezius muscle were compared with subcutaneous and perirenal adipocytes in growing pigs. Between 80 and 210 days of age, gene expressions and/or activities of enzymes involved in lipogenesis or lipolysis were much lower (P < 0.05) in adipocytes isolated from muscle than in those from other locations. Insulin-induced lipogenesis and lipolytic efficiency after catecholamine addition were also the lowest (P < 0.05) in IM adipocytes. In these cells, the age-related increase (+300%) in the ratio of mRNA levels of fatty acid synthase to hormone-sensitive lipase paralleled the enlargement of adipocyte diameters (+70%, P < 0.05) and the increase in lipid content in muscle (+135%, P < 0.05) during growth. Expressions of genes coding for leptin, adiponectin, and IGF-I, as well as for various hormonal receptors, were lower (P < 0.05) in IM adipocytes than in other adipocytes, whereas levels of TNF-alpha mRNA did not differ between sites. Interestingly, IGF-II mRNA levels were higher (P < 0.05) in IM adipocytes than in other adipocytes. These data support the view that IM fat is not just an ectopic extension of other fat locations but displays specific biological features during growth.

Peripheral metabolic responses to prolonged weight reduction that promote rapid, efficient regain in obesity-prone rats

Weight regain after weight loss is the most significant impediment to long-term weight reduction. We have developed a rodent paradigm that models the process of regain after weight loss, and we have employed both prospective and cross-sectional analyses to characterize the compensatory adaptations to weight reduction that may contribute to the propensity to regain lost weight. Obese rats were fed an energy-restricted (50–60% kcal) low-fat diet that reduced body weight by 14%. This reduced weight was maintained for up to 16 wk with limited provisions of the low-fat diet. Intake restriction was then removed, and the rats were followed for 56 days as they relapsed to the obese state. Prolonged weight reduction was accompanied by 1) a persistent energy gap resulting from an increased drive to eat and a reduced expenditure of energy, 2) a higher caloric efficiency of regain that may be linked with suppressed lipid utilization early in the relapse process, 3) preferential lipid accumulation in adipose tissue accompanied by adipocyte hyperplasia, and 4) humoral adiposity signals that underestimate the level of peripheral adiposity and likely influence the neural pathways controlling energy balance. Taken together, long-term weight reduction in this rodent paradigm is accompanied by a number of interrelated compensatory adjustments in the periphery that work together to promote rapid and efficient weight regain. These metabolic adjustments to weight reduction are discussed in the context of a homeostatic feedback system that controls body weight.

Leptin in pregnancy: an update

Leptin influences satiety, adiposity, and metabolism and is associated with mechanisms regulating puberty onset, fertility, and pregnancy in various species. Maternal hyperleptinemia is a hallmark of mammalian pregnancy, although both the roles of leptin and the mechanisms regulating its synthesis appear to be taxa specific. In pregnant humans and nonhuman primates, leptin is produced by both maternal and fetal adipose tissues, as well as by the placental trophoblast. Specific receptors in the uterine endometrium, trophoblast, and fetus facilitate direct effects of the polypeptide on implantation, placental endocrine function, and conceptus development. A soluble isoform of the receptor may be responsible for inducing maternal leptin resistance during pregnancy and/or may facilitate the transplacental passage of leptin for the purpose of directly regulating fetal development. The steroid hormones are linked to the regulation of leptin and the leptin receptor and probably interact with other pregnancy-specific, serum-borne factors to regulate leptin dynamics during pregnancy. In addition to its effects on normal conceptus development, leptin is linked to mechanisms affecting a diverse array of pregnancy-specific pathologies that include preeclampsia, gestational diabetes, and intrauterine growth restriction. Association with these anomalies and with mechanisms pointing to a fetal origin for a range of conditions affecting the individual's health in adult life, such as obesity, diabetes mellitus, and cardiovascular disease, reiterate the need for continued research dedicated to elucidating leptin's roles and regulation throughout gestation.

New Lactobacillus acidophilus isolates reduce the release of leptin by murine adipocytes leading to lower interferon-gamma production

Leptin produced by adipocytes increases Th1-dependent immunostimulation and autoimmune diseases. Lactobacilli are known to promote or suppress Th1 responses according to the isolates. We have investigated whether the sensitivity of Suriss Jim Lambert (SJL) mice to Th1-dependent immune diseases, when compared with C57BL/6 mice, may be modulated by selected lactobacilli able to decrease leptin release by adipocytes. White adipocytes were isolated from both C57BL/6 and SJL mice and incubated with bacterial extracts from new CBA4P and TPA3P isolates of Lactobacillus acidophilus and L. rhamnosus 9595 (LR), or with conditioned media (CM) from lactobacillus-treated macrophages. Immunomodulation induced by supernatants of treated adipocytes was determined by metabolic activity of syngenic splenic lymphocytes. Leptin produced by adipocytes, tumour necrosis factor (TNF)-alpha and interleukin (IL)-1beta by macrophages, and IFN-gamma and IL-4 by lymphocytes were quantified by enzyme-linked immunosorbent assay (ELISA) tests. Results revealed that supernatants from CBA4P- and LR-treated adipocytes decreased the metabolic activity of lymphocytes from SJL mice, whereas adipocytes incubated with CM from CBA4P-treated macrophages showed no stimulation of lymphocytes. Such effects correlated with leptin levels. Lower levels of leptin were produced by adipocytes from SJL mice in the presence of CBA4P and LR extracts. Lymphocytes from SJL mice produced low levels of IFN-gamma when incubated with supernatants from CBA4P-treated cells. Such immunosuppressive effects were dependent on levels of TNF-alpha and IL-1beta produced by lactobacillus-treated macrophages. Taken together, these results suggest that the CBA4P isolate reduces levels of leptin in SJL mice, leading to lower IFN-gamma production. Therefore, the CBA4P isolate of L. acidophilus is a promising new probiotic strain for the control of Th1 inflammatory diseases.

The yellow agouti mutation alters some but not all responses to diet and exercise

OBJECTIVE

Effects of ectopic expression of the agouti signaling protein were studied on responses to diet restriction and exercise in C57BL/6J (B6) mice and obese B6 mice congenic for the yellow agouti mutation [B6.Cg-Ay (Ay)].

RESEARCH METHODS AND PROCEDURES

Adult male Ay mice were either kept sedentary or exercised on a running wheel and fed ad libitum or diet restricted until weight matched to ad libitum-fed B6 control mice. Body composition, plasma lipids, leptin, and adiponectin were measured. mRNA levels for leptin, adiponectin, lipoprotein lipase, and pyruvate dehydrogenase kinase 4 were measured in a visceral (epididymal) and a subcutaneous (femoral) fat depot by real-time polymerase chain reaction.

RESULTS

Correlations among traits exhibited one of three patterns: similar lines for B6 and Ay mice, different slopes for B6 and Ay mice, and/or different intercepts for B6 and Ay mice. Correlations involving plasma leptin, mesenteric and epididymal adipose weights, or low-density lipoprotein-cholesterol were most likely to have different slopes and/or intercepts in B6 and Ay mice. mRNA levels for leptin, Acrp30, pyruvate dehydrogenase kinase 4, and lipoprotein lipase in epididymal adipose tissue were not correlated with corresponding levels in femoral adipose tissue.

DISCUSSION

The agouti protein interferes with leptin signaling at melanocortin receptors in the hypothalamus of Ay mice. Our results are consistent with the hypothesis that the melanocortin portion of the leptin-signaling pathway mediates effects primarily on certain fat depots and on some, but not all, components of cholesterol homeostasis.

Regulation of development and metabolism of adipose tissue by growth hormone and the insulin-like growth factor system

White adipose tissue plays a key role in the regulation of the energy balance of vertebrates. This tissue is also now recognized to secrete a variety of factors such as leptin, which is thought to be involved in the modulation of adipose mass. Unlike other tissues, adipose tissue mass has considerable capacity to expand. The review deals primarily on the regulation of development and metabolism of adipose tissue by growth hormone (GH) and the insulin-like growth factor (IGF) system, with a special focus on the pig. The anti-insulin effects of GH are well-documented in pigs as in other species. In vitro exposure of adipose precursor cells to GH leads to a decrease in differentiation of those cells in pigs, in contrast to data obtained in murine cell lines. In vivo treatment and prolonged in vitro incubation of adipose tissue or isolated adipocytes with GH result in a decrease in glucose transport and lipogenesis, especially at the level of the fatty acid synthase gene, resulting in a reduction of the lipid content and adipose tissue mass. The mechanism by which GH antagonizes insulin stimulation of lipogenesis is still unresolved, as it is not mediated by protein kinase A, protein kinase C and Janus kinase-2 at the signaling level, or upstream stimulatory factor 1 or sterol regulatory element binding protein-1 at the transcriptional level. GH is apparently the main regulator of IGF-I mRNA expression in adipose tissue, however, the effects of IGF-I on this tissue are rather unclear.

Differences in mRNA expression of adipocyte-derived factors in response to fasting, refeeding and leptin

The present study examines whether and to what extent the profiles of adipose-derived factors are altered in epididymal and subcutaneous adipose tissues of long-term fasted/refed and of fasted rats treated by recombinant leptin. Fasting was characterized by three successive metabolic phases. Minor differences in the time-course and magnitude of response were detected between the two adipose sites. Leptin, adiponectin, resistin, adiponutrin, and insulin-like growth factor-1 (IGF-1) gene expressions differentially decreased according to the fasting duration. mRNA levels reached a minimum in late fasting for these secreted factors, being decreased by 60-90% for adiponectin, resistin, and IGF-1, 95-98% for leptin and by 100% for adiponutrin. Refeeding partially or totally restored their mRNA expression in epididymal adipose. Expression levels of apolipoprotein E (ApoE), angiotensinogen (AGT), adipsin and macrophage migration inhibitory factor (MIF) were either unchanged or slightly affected. In leptin-treated rats, leptin mRNA concentrations were significantly decreased in phase 2 of fasting (by 85%) from levels in control phosphate-buffered saline (PBS)-treated rats in both tissues. Leptin treatment also decreased resistin mRNA levels (by 78% in P2L and 63% in P3L relative to control groups) in subcutaneous adipose. These data suggest that adiponectin, resistin, adiponutrin, and IGF-1 could be involved in overall energy homeostasis during prolonged fasting, as leptin is. The mechanisms that underlie the expressions of these adipose-secreted factors remain to be determined.

Cooperative activation of cultured vagal afferent neurons by leptin and cholecystokinin

To test the hypothesis that leptin can directly activate vagal afferent neurons, we used fluorescence imaging to detect acute changes in cytosolic calcium after leptin application to primary cultures of vagal afferent neurons dissociated from adult rat nodose ganglia. We found that approximately 40% of vagal afferent neurons exposed to leptin (40 ng/ml) responded with rapid and reversible increases in cytosolic calcium. These responses were dependent upon extracellular calcium. As previously reported, about 35% of vagal afferents increase cytosolic calcium in response to the gut-peptide cholecystokinin (CCK). A majority (74%) of neurons that responded to CCK also exhibited increases in cytosolic calcium in response to leptin. In addition, synergistic increases in cytosolic calcium were observed when leptin and CCK were applied in combination. These results demonstrate that leptin acts directly on vagal afferent neurons to trigger acute influxes of extracellular calcium. Our results also suggest cooperation between leptin and CCK in the activation of some vagal afferent neurons. Acute activation of vagal afferents by leptin alone and in combination with CCK may contribute to modulation of visceral reflexes and control of food intake.

The regulation of IGF-1 by leptin in the pig is tissue specific and independent of changes in growth hormone

A combination of in vivo and in vitro experiments were performed to determine the extent to which exogenous leptin regulates serum growth hormone (GH) and insulin-like growth factor I (IGF-1) concentrations, and the abundance of IGF-1 mRNA in major peripheral tissues. Initially (Experiment 1), a recombinant human leptin analog was administered i.m. to young growing pigs (approximately 27 kg body weight) for 15 days at 0 (control), 0.003, 0.01 and 0.03 mg. kg(-1). day(-1). Although there was no sustained effect of leptin on serum GH, there was a reduction (P < 0.02) in serum IGF-1 at the intermediate dose that paralleled a decrease (P < 0.09) in hepatic IGF-1 expression. Leptin, at these doses, did not reduce feed intake (P > 0.57), nor was there an effect of leptin on dietary nitrogen retention (P > 0.97). In a second experiment, pigs were injected with vehicle or a higher dose of leptin (0.05 mg. kg(-1). day(-1)) for 14 days. A third treatment group was injected with vehicle and pair-fed to the intake of the group treated with leptin. In this study, exogenous leptin resulted in a sustained increase in serum leptin (P < 0.0001) and reduction in feed intake of approximately 30% (P < 0.0001). Serum IGF-1 was depressed in both the leptin-treated and pair-fed groups, relative to the group allowed ad-libitum intake (P < 0.01). Furthermore, there was no difference among treatments in the relative abundance of IGF-1 mRNA in skeletal muscle (P > 0.42) or adipose tissue (P > 0.26), and liver mRNA abundance was actually increased (P < 0.01) by leptin, despite the lower feed intake. Finally, to determine whether leptin altered the secretion of IGF-1 by isolated pig hepatocytes, primary cultures were incubated with leptin for 24 to 48 hr (Experiment 3). Leptin (100 nM) caused a sharp reduction (P < 0.0001) in dexamethasone-induced IGF-1 secretion at 24 hr (47% reduction) and at 48 hr (40% reduction). Collectively, these data indicate that leptin may regulate hepatic IGF-1 production in the pig, independent of GH, but that hepatocyte sensitivity to leptin may be depend on dose and in vitro vs. in vivo conditions.

Effects of supplemental rumen-protected conjugated linoleic acid or linoleic acid on feedlot performance, carcass quality, and leptin concentrations in beef cattle1

Thirty-six Angus x Hereford heifers (365 kg) were used to determine effects of dietary lipid supplementation from two sources during the final 32 or 60 d of feeding on serum and adipose tissue leptin concentrations, animal performance, and carcass characteristics. Following an initial feeding period of 56 d, heifers were fed one of three diets in a 3 x 2 factorial arrangement: 1) basal diet, 2) basal diet plus 4% (DM basis) corn oil, or 3) basal diet plus 2% (DM basis) rumen-protected conjugated linoleic acid (a mixture of Ca-salts of palm oil fatty acids with 31% conjugated linoleic acid). Jugular blood samples were collected at 28-d intervals (d 28 to 118) and serum subsequently harvested for leptin quantification via RIA. Real-time ultrasound measurements were collected at 28-d intervals across time on feed. At slaughter, samples were obtained from various adipose depots. Data were analyzed with dietary treatment, length of supplementation, adipose depot (when appropriate), and all two- and three-way (when appropriate) interactions in the repeated measures model. Measures of feedlot performance, including ADG, DMI, and gain:feed did not differ (P > 0.23) with dietary treatment or supplementation length. Heifers supplemented with corn oil tended (P < 0.07) to have higher marbling scores following 32 d of treatment than those supplemented with rumen-protected conjugated linoleic acid, with controls intermediate. Quality grade and hot carcass weight did not differ (P > 0.15) with treatment or length of supplementation. Leptin concentrations were higher (P < 0.05) from d 57 to 118 on feed than the initial period (d 0 to 56) of dietary adaptation when all animals received the basal diet. Circulating leptin concentrations were not affected by dietary treatment. However, leptin concentrations in adipose tissues were greater (P < 0.05) for heifers supplemented with corn oil than either control or rumen-protected conjugated linoleic acid diets, which did not differ. Compared with adipose tissues from rumen-protected conjugated linoleic acid-supplemented animals, tissues from heifers fed corn oil contained 68% greater leptin concentration. Correlations between performance, carcass traits, and serum leptin concentrations were low. Serum leptin concentrations across time on feed were not associated with carcass and performance data, including ADG, DMI, and gain:feed. Based on these data, concentrations of leptin are not related to indices of feedlot performance and carcass quality in beef cattle.

Regional fat pad growth and cellularity in obese zucker rats: modulation by caloric restriction

OBJECTIVE

To investigate, in young obese male Zucker rats, the effects of chronic food restriction and subsequent refeeding on: 1). parameters of nonadipose and adipose growth, 2). regional adipose depot cellularity [fat cell volume (FCV) and number], and 3). circulating leptin levels.

RESEARCH METHODS AND PROCEDURES

Obese (fa/fa) and lean (Fa/?) male Zucker rats were studied from age 5 to 19 weeks. After baseline food intake monitoring, 10 obese rats were subjected to 58 days of marked caloric restriction from ad libitum levels [obese-restricted (OR)], followed by a return to ad libitum feeding for 22 days. Ten lean control rats and 10 obese control rats were fed ad libitum for the entire experiment. All rats were fed using a computer-driven automated feeding system designed to mimic natural eating patterns.

RESULTS

After food restriction, OR rats weighed significantly less than did lean and obese rats and showed a significant diminution in body and adipose growth as compared with obese rats. Relative adiposity was not different between obese and OR rats and was significantly higher than that of lean rats. The limitation in growth of the adipose tissue mass in OR rats was due mostly to suppression of fat cell proliferation because the mean FCV in each of the four depots was not affected. Serum leptin levels of OR and obese rats were not different from each other but were significantly higher than those of lean rats.

DISCUSSION

Marked caloric restriction affects obese male Zucker rats in a manner different from that of nongenetic rodent models (i.e., Wistar rats). In comparison with the response to caloric deprivation of Wistar rats, these calorically restricted obese male Zucker rats appeared to defend their relative adiposity and mean FCV at the expense of fat cell number. These findings indicate that genetic and/or tissue-specific controls override the general consequences of food restriction in this genetic model of obesity.

Effects of TNF-alpha on glucose metabolism and lipolysis in adipose tissue and isolated fat-cell preparations

We hypothesized that exposure to tumor necrosis factor-alpha (TNF-alpha) would significantly increase lactate production by adipose-tissue (AT) fragments and isolated adipocytes. We therefore examined the effects of TNF-alpha on the metabolism of epididymal AT explants during 24-hour tissue incubation. We also studied the effects of this 24-hour TNF-alpha tissue exposure on subsequent glucose metabolism and lipolysis by isolated adipocytes. Glycerol release into the medium was significantly increased (50%, P =.027) by exposure of the AT fragments to TNF-alpha (4 nmol/L) for 24 hours. During this time, glucose uptake from the medium and lactate release into the medium tended to increase, whereas leptin release into the medium tended to decrease, but these effects of TNF-alpha were not statistically significant. After the 24-hour AT-explant incubation, adipocytes were isolated by means of collagenase digestion from the AT fragments and subsequently tested in a short-term (60-minute) metabolic incubation. Prior exposure to TNF-alpha resulted in a significant increase in adipocyte glycerol release (P =.044), total glucose metabolism (P =.019), and lactate production (P =.037). With the exception of lactate, TNF-alpha produced no significant stimulation of the metabolites of glucose. The pattern of glucose metabolism elicited by TNF-alpha exposure differs from that usually attributed to a lipolytic hormone and suggests that the effects of TNF-alpha on glucose metabolism involve pathways separate from, or in addition to, its effects on lipolytic stimulation.

Body composition, fasting leptin, and sex steroid administration determine GH sensitivity in peripubertal short children

Serum IGF-I levels in GH-treated subjects demonstrate a wide range of responsiveness to GH. However, the factors influencing GH sensitivity are not well known. The aim of this work was 1) to test whether body composition (determined by dual energy x-ray absorptiometry) or factors related to body composition (fasting blood glucose, FFA, C-peptide, leptin, and insulin sensitivity determined by an insulin tolerance test) influence GH sensitivity; and 2) to study the effect of sex steroid priming on GH sensitivity. We measured serum IGF-I at baseline and 24 h after a single administration of GH (2 mg/m(2)) in 60 healthy prepubertal and early pubertal children (height, -2.1 +/- 1.0 SD score). GH sensitivity, as estimated by the increase in serum IGF-I after GH administration (difference between stimulated and baseline serum IGF-I = delta IGF-I), was also determined after a short-term administration of oral ethinyl E2 in girls and im T in boys. The serum IGF-I concentration was 297 +/- 114 microg/liter at baseline and increased to 429 +/- 160 microg/liter, corresponding to a 46 +/- 29% increase over the baseline value (P < 0.0001, stimulated vs. baseline serum IGF-I). delta IGF-I was not different between gender or pubertal stage. There were positive correlations (P < 0.001) between delta IGF-I and adiposity (total body fat, r = 0.62; trunk fat, r = 0.62), fasting leptin (r = 0.64), and C-peptide (r = 0.54), and a negative correlation with fasting FFA (r = -0.33; P < 0.05) even after adjustment for age, gender, and pubertal stage. These factors remained significant independent predictors of the absolute as well as the percent increase in serum IGF-I in multiple regression analyses. Priming with T and ethinyl E2 had a similar stimulating effect on the serum GH peak in response to the insulin tolerance test. In boys, serum baseline IGF-I increased by 60%, and delta IGF-I was similar after vs. before T administration. By contrast, in girls, serum baseline IGF-I was similar, and delta IGF-I was 60% less after vs. before ethinyl E2 administration. This study indicates that 1) GH sensitivity is determined by fat mass, serum fasting leptin, C-peptide, and FFA; and 2) oral ethinyl E2 and im T have divergent effects on the IGF-I response to a single administration of GH.