Growth hormone (GH) is known to interact with adipose tissue and to induce lipolysis. Adipocytes produce leptin which regulates appetite and energy expenditure. In order to elucidate the role of GH in leptin production, we studied the effect of GH on leptin gene expression and body fat in fatty Zucker rats, a model of obesity with resistance to both leptin and insulin. Recombinant human GH administered subcutaneously at 0.5 mg/kg per day (low dose) as well as at 1.65 mg/kg per day (high dose) reduced leptin mRNA levels in epididymal fat tissue but not in subcutaneous fat tissue after 7 days. GH administration only at the high dose reduced percentage body fat. Insulin-like growth factor-I infusion (200 microg/kg per day) did not change percentage body fat or leptin mRNA levels in epididymal fat. These observations suggest that GH directly interacts with adipose tissue and reduces leptin gene expression in visceral fat tissue.
O Isozaki, T Tsushima, M Miyakawa, Y Nozoe, H Demura and H Seki
Ruben Rodriguez, Jacqueline N Minas, Jose Pablo Vazquez-Medina, Daisuke Nakano, David G Parkes, Akira Nishiyama and Rudy M Ortiz
Obesity is associated with the inappropriate activation of the renin-angiotensin system (RAS), which increases arterial pressure, impairs insulin secretion and decreases peripheral tissue insulin sensitivity. RAS blockade reverses these detriments; however, it is not clear whether the disease state of the organism and treatment duration determine the beneficial effects of RAS inhibition on insulin secretion and insulin sensitivity. Therefore, the objective of this study was to compare the benefits of acute vs chronic angiotensin receptor type 1 (AT1) blockade started after the onset of obesity, hyperglycemia and hypertension on pancreatic function and peripheral insulin resistance. We assessed adipocyte morphology, glucose intolerance, pancreatic redox balance and insulin secretion after 2 and 11 weeks of AT1 blockade in the following groups of rats: (1) untreated Long-Evans Tokushima Otsuka (lean control; n = 10), (2) untreated Otsuka Long-Evans Tokushima Fatty (OLETF; n = 12) and (3) OLETF + ARB (ARB; 10 mg olmesartan/kg/day by oral gavage; n = 12). Regardless of treatment duration, AT1 blockade decreased systolic blood pressure and fasting plasma triglycerides, whereas chronic AT1 blockade decreased fasting plasma glucose, glucose intolerance and the relative abundance of large adipocytes by 22, 36 and 70%, respectively. AT1 blockade, however, did not improve pancreatic oxidative stress or reverse impaired insulin secretion. Collectively, these data show that AT1 blockade after the onset of obesity, hyperglycemia and hypertension improves peripheral tissue insulin sensitivity, but cannot completely reverse the metabolic derangement characterized by impaired insulin secretion once it has been compromised.
Esther Paulo, Dongmei Wu, Peter Hecker, Yun Zhang and Biao Wang
Numerous studies have suggested that beige adipocyte abundance is correlated with improved metabolic performance, but direct evidence showing that beige adipocyte expansion protects animals from the development of obesity is missing. Previously, we have described that the liver kinase b1 (LKB1) regulates beige adipocyte renaissance in subcutaneous inguinal white adipose tissue (iWAT) through a class IIa histone deacetylase 4 (HDAC4)-dependent mechanism. This study investigates the physiological impact of persistent beige adipocyte renaissance in energy homeostasis in mice. Here we present that the transgenic mice H4-TG, overexpressing constitutively active HDAC4 in adipocytes, showed beige adipocyte expansion in iWAT at room temperature. H4-TG mice exhibited increased energy expenditure due to beige adipocyte expansion. They also exhibited reduced adiposity under both normal chow and high-fat diet (HFD) feeding conditions. Specific ablation of beige adipocytes reversed the protection against HFD-induced obesity in H4-TG mice. Taken together, our results directly demonstrate that beige adipocyte expansion regulates adiposity in mice and targeting beige adipocyte renaissance may present a novel strategy to tackle obesity in humans.
Johanna L Barclay, Hadiya Agada, Christina Jang, Micheal Ward, Neil Wetzig and Ken K Y Ho
Clinical cases of glucocorticoid (GC) excess are characterized by increased fat mass and obesity through the accumulation of white adipocytes. The effects of GCs on growth and function of brown adipose tissue are unknown and may contribute to the negative energy balance observed clinically. This study aims to evaluate the effect of GCs on proliferation, differentiation, and metabolic function of brown adipocytes. Human brown adipocytes sourced from supraclavicular fat biopsies were grown in culture and differentiated to mature adipocytes. Human white adipocytes sourced from subcutaneous abdominal fat biopsies were cultured as controls. Effects of dexamethasone on growth, differentiation (UCP1, CIDEA, and PPARGC1A expression), and function (oxygen consumption rate (OCR)) of brown adipocytes were quantified. Dexamethasone (1 μM) significantly stimulated the proliferation of brown preadipocytes and reduced that of white preadipocytes. During differentiation, dexamethasone (at 0.1, 1, and 10 μM) stimulated the expression of UCP1, CIDEA, and PPARGC1A in a concentration-dependent manner and enhanced by fourfold to sixfold the OCR of brown adipocytes. Isoprenaline (100 nM) significantly increased (P<0.05) expression of UCP1 and OCR of brown adipocytes. These effects were significantly reduced (P<0.05) by dexamethasone. Thus, we show that dexamethasone stimulates the proliferation, differentiation, and function of human brown adipocytes but inhibits adrenergic stimulation of the functioning of brown adipocytes. We conclude that GCs exert complex effects on development and function of brown adipocytes. These findings provide strong evidence for an effect of GCs on the biology of human brown adipose tissue (BAT) and for the involvement of the BAT system in the metabolic manifestation of Cushing's syndrome.
Johannes Klein, Sören Westphal, Daniel Kraus, Britta Meier, Nina Perwitz, Volker Ott, Mathias Fasshauer and H Harald Klein
Metformin is an anti-diabetic drug with anorexigenic properties. The precise cellular mechanisms of its action are not entirely understood. Adipose tissue has recently been recognized as an important endocrine organ that is pivotal for the regulation of insulin resistance and energy homeostasis. Due to its thermogenic capacity brown adipose tissue contributes to the regulation of energy metabolism and is an attractive target tissue for pharmacological approaches to treating insulin resistance and obesity. Leptin is the prototypic adipocyte-derived hormone inducing a negative energy balance. We investigated effects of metformin on adipocyte metabolism, signalling, and leptin secretion in a brown adipocyte model. Metformin acutely stimulated p44/p42 mitogen-activated protein (MAP) kinase in a dose- (3.2-fold at 1 mmol/l, P< 0.05) as well as time-dependent (3.8-fold at 5 min, P< 0.05) manner. This stimulation was highly selective since phosphorylation of intermediates in the stress kinase, janus kinase (JAK)–signal transducer and activator of transcription (STAT), and phosphatidylinositol (PI) 3-kinase signalling pathways such as p38 MAP kinase, STAT3, and Akt was unaltered. Furthermore, chronic metformin treatment for 12 days dose-dependently inhibited leptin secretion by 35% and 75% at 500 μmol/l and 1 mmol/l metformin respectively (P< 0.01). This reduction was not caused by alterations in adipocyte differentiation. Moreover, the impairment in leptin secretion by metformin was reversible within 48 h after removal of the drug. Pharmacological inhibition of p44/p42 MAP kinase prevented the metformin-induced negative effect on leptin secretion. Taken together, our data demonstrate direct acute effects of metformin on adipocyte signalling and endocrine function with robust inhibition of leptin secretion. They suggest a selective molecular mechanism that may contribute to the anorexigenic effect of this antidiabetic compound.
Hui Yu, Zoe Thompson, Sylee Kiran, Graham L Jones, Lakshmi Mundada, Surbhi, Marcelo Rubinstein and Malcolm J Low
Proopiomelanocortin (POMC) neurons in the hypothalamic arcuate nucleus (ARC) are essential for normal energy homeostasis. Maximal ARC Pomc transcription is dependent on neuronal Pomc enhancer 1 (nPE1), located 12 kb upstream from the promoter. Selective deletion of nPE1 in mice decreases ARC Pomc expression by 70%, sufficient to induce mild obesity. Because nPE1 is located exclusively in the genomes of placental mammals, we questioned whether its hypomorphic mutation would also alter placental Pomc expression and the metabolic adaptations associated with pregnancy and lactation. We assessed placental development, pup growth, circulating leptin and expression of Pomc, Agrp and alternatively spliced leptin receptor (LepR) isoforms in the ARC and placenta of Pomc∆1/∆1 and Pomc+/+ dams. Despite indistinguishable body weights, lean mass, food intake, placental histology and Pomc expression and overall pregnancy outcomes between the genotypes, Pomc ∆1/∆1 females had increased pre-pregnancy fat mass that paradoxically decreased to control levels by parturition. However, Pomc∆1/∆1 dams had exaggerated increases in circulating leptin, up to twice of that of the typically elevated levels in Pomc+/+ mice at the end of pregnancy, despite their equivalent fat mass. Pomc∆1/∆1dams also had increased placental expression of soluble leptin receptor (LepRe), although the protein levels of LEPRE in circulation were the same as Pomc+/+ controls. Together, these data suggest that the hypomorphic Pomc∆1/∆1 allele is responsible for the perinatal super hyperleptinemia of Pomc∆1/∆1 dams, possibly due to upregulated leptin secretion from individual adipocytes.
Yuichi Kikuchi, Muneharu Yamada, Toshihiko Imakiire, Taketoshi Kushiyama, Keishi Higashi, Naomi Hyodo, Kojiro Yamamoto, Takashi Oda, Shigenobu Suzuki and Soichiro Miura
Fasudil, a Rho-kinase inhibitor, may improve insulin signaling. However, its long-term effect on metabolic abnormalities and its preventive effect on diabetic nephropathy are still unknown. We assessed these effects of fasudil in insulin-resistant diabetic rats, comparing them with those of an angiotensin II receptor blocker, olmesartan. Male Otsuka Long–Evans Tokushima fatty (OLETF) and Long–Evans Tokushima Otsuka, non-diabetic control, rats at 15 weeks of age were used. OLETF rats were randomized to receive a low or a high dose of fasudil or olmesartan for 25 weeks. To examine the therapeutic effects after the development of diabetes, OLETF rats at 30 weeks of age were given fasudil for 10 weeks. Administration of high-dose fasudil completely suppressed the development of diabetes, obesity, and dyslipidemia and increased serum adiponectin levels in OLETF rats. High-dose olmesartan also decreased hemoglobin A1c and increased serum adiponectin. There was a significant correlation between hemoglobin A1c and serum adiponectin or free fatty acid levels. The treatment with high-dose fasudil ameliorated proteinuria, glomerulosclerosis, renal interstitial fibrosis, and macrophage infiltration in OLETF rats. Olmesartan, even at the low dose, suppressed renal complications. The treatment with fasudil after the development of diabetes improved the metabolic abnormalities in OLETF rats, but could not suppress the progression of nephropathy. We conclude that the long-term treatment with fasudil prevents the development of diabetes, at least in part, by improving adipocyte differentiation in insulin-resistant diabetic rats. Early use of fasudil may prevent diabetic nephropathy.
KW Siddals, M Westwood, JM Gibson and A White
IGF action in vivo is acutely regulated by IGF-binding protein-1 (IGFBP-1) and its phosphorylation state is implicated in modulating these effects. Since IGFs have an important regulatory role in adipocyte function, we investigated the effects of phosphorylated IGFBP-1 (pIGFBP-1) and non-phosphorylated IGFBP-1 (npIGF BP-1) on 3T3-L1 preadipocyte proliferation and adipocyte metabolism. IGFs stimulated clonal expansion of 3T3-L1 cells (IGF-I more potently than IGF-II (EC(50): 30 nM and 50 nM)). npIGFBP-1 inhibited IGF-I (50 nM) clonal expansion at a 5:1 molar ratio (P<0.01), whereas pIGFBP-1 (purified from HepG2 cell medium) abolished clonal expansion at a 1:1 molar ratio (P<0.005). In contrast, IGF-II-induced clonal expansion was inhibited 100% at a 1:1 molar ratio of npIGFBP-1. In mature adipocytes, IGF-I was equipotent with insulin in stimulating glucose uptake (EC(50): 10 nM) and inhibiting isoproterenol-induced lipolysis (EC(50): 15 nM). npIGFBP-1 completely reversed IGF-I effects at a 1:1 molar ratio (P<0.01). In summary, IGFs rather than insulin are potent regulators of clonal expansion in 3T3-L1 preadipocytes. Importantly, IGFs are equipotent with insulin in regulating adipocyte metabolism. IGFBP-1 inhibits IGF effects on preadipocyte proliferation and adipocyte metabolism, with pIGFBP-1 being more potent than npIGFBP-1 at inhibiting mitogenic actions. Since IGFBP-1 is acutely regulated by insulin, this could have important consequences in hyperinsulinaemic and insulin-resistant states.
Gulizar Issa Ameen and Silvia Mora
Obesity leads to adipose tissue dysfunction, insulin resistance and diabetes. Adipose tissue produces adipokines that contribute to regulate insulin sensitivity. In turn, insulin stimulates the production and release of some adipokines. Casitas-b-lymphoma proteins (c-Cbl, Cbl-b and Cbl3) are intracellular adaptor signalling proteins that are rapidly phosphorylated by activation of tyrosine kinase receptors. c-Cbl is rapidly phosphorylated by insulin in adipocytes. Here, we tested the hypothesis that Cbl signalling regulates adipokine expression in adipose tissue. We determined the adipokine profile of WAT of Cbl−/− and Cbl+/+ mice in the C57BL6 background. Female Cbl−/− mice exhibited altered expression of adiponectin, leptin and RBP4 in visceral adipose tissue, while no significant changes were seen in male mice. TNFα and IL6 levels were unaffected by Cbl depletion. RBP4 expression was unchanged in liver. Adipose tissue of Cbl−/− animals showed increased basal activation of extracellular regulated kinases (ERK1/2) compared to Cbl+/+. c-Cbl knockdown in 3T3L1 adipocytes also increased basal ERK phosphorylation and RBP4 expression. Inhibition of ERK1/2 phosphorylation in Cbl-depleted 3T3L1 adipocytes or in adipose tissue explants of Cbl−/− mice reduced RBP4 mRNA. 17β-Estradiol increased RBP4 mRNA in adipocytes. Cbl depletion did not change ER expression but increased phosphorylation of ERα at S118, a target site for ERK1/2. ERK1/2 inhibition reduced phosphoER and RBP4 levels. These findings suggest that Cbl contributes to regulate RBP4 expression in adipose of female mice through ERK1/2-mediated activation of ERα. Since Cbl signalling is compromised in diabetes, these data highlight a novel mechanism that upregulates RBP4 locally.
L Bouraoui, J Gutiérrez and I Navarro
Here, we describe optimal conditions for the culture of rainbow trout (Oncorhynchus mykiss) pre-adipocytes obtained from adipose tissue and their differentiation into mature adipocytes, in order to study the endocrine control of adipogenesis. Pre-adipocytes were isolated by collagenase digestion and cultured on laminin or 1% gelatin substrate. The expression of proliferating cell nuclear antigen was used as a marker of cell proliferation on various days of culture. Insulin growth factor-I stimulated cell proliferation especially on days 5 and 7 of culture. Tumor necrosis factor α (TNFα) slightly enhanced cell proliferation only at a low dose. We verified the differentiation of cells grown in specific medium into mature adipocytes by oil red O (ORO) staining. Quantification of ORO showed an increase in triglycerides throughout culture. Immunofluorescence staining of cells at day 11 revealed the expression of CCAAT/enhancer-binding protein and peroxisome proliferator–activator receptor γ, suggesting that these transcriptional factors are involved in adipocyte differentiation in trout. We also examined the effect of TNFα on the differentiation of these adipocytes in primary culture. TNFα inhibited the differentiation of these cells, as indicated by a decrease in glycerol-3-phosphate dehydrogenase activity, an established marker of adipocyte differentiation. In conclusion, the culture system described here for trout pre-adipocytes is a powerful tool to study the endocrine regulation of adipogenesis in this species.