There is a high incidence of metabolic syndrome among patients with primary aldosteronism (PA), which has recently been associated with an unfavorable cardiometabolic profile. However, the underlying mechanisms have not been clarified in detail. Characterizing aldosterone (Ald) target genes in adipocytes will help us to elucidate the deleterious effects associated with excess Ald. Apelin, a novel adipokine, exerts beneficial effects on obesity-associated disorders and cardiovascular homeostasis. The objective of this study was to investigate the effects of high Ald levels on apelin expression and secretion and the underlying mechanisms involved in adipocytes. In vivo, a single-dose Ald injection acutely decreased apelin serum levels and adipose tissue apelin production, which demonstrates a clear inverse relationship between the levels of plasma Ald and plasma apelin. Experiments using 3T3-L1 adipocytes showed that Ald decreased apelin expression and secretion in a time- and dose-dependent manner. This effect was reversed by glucocorticoid receptor (GR) antagonists or GR (NR3C1) knockdown; furthermore, putative HREs were identified in the apelin promoter. Subsequently, we verified that both glucocorticoids and mineralocorticoids regulated apelin expression through GR activation, although no synergistic effect was observed. Additionally, detailed potential mechanisms involved a p38 MAPK signaling pathway. In conclusion, our findings strengthen the fact that there is a direct interaction between Ald and apelin in adipocytes, which has important implications for hyperaldosteronism or PA-associated cardiometabolic syndrome and hoists apelin on the list of potent therapeutic targets for PA.
He Jiang, Xiao-Ping Ye, Zhong-Yin Yang, Ming Zhan, Hai-Ning Wang, Huang-Min Cao, Hui-Jun Xie, Chun-Ming Pan, Huai-Dong Song and Shuang-Xia Zhao
Yueting Dong, Zhiye Xu, Ziyi Zhang, Xueyao Yin, Xihua Lin, Hong Li and Fenping Zheng
Liver X receptors (LXR) are deemed as potential drug targets for atherosclerosis, whereas a role in adipose tissue expansion and its relation to insulin sensitivity remains unclear. To assess the metabolic effects of LXR activation by the dual LXRα/β agonist T0901317, C57BL/6 mice fed a high-fat diet (HFD) were treated with T0901317 (30 mg/kg once daily by intraperitoneal injection) for 3 weeks. Differentiated 3T3-L1 adipocytes were used for analysing the effect of T0901317 on glucose uptake. The following results were obtained from this study. T0901317 reduced fat mass, accompanied by a massive fatty liver and lower serum adipokine levels in HFD mice. Increased adipocyte apoptosis was found in epididymal fat of T0901317-treated HFD mice. In addition, T0901317 treatment promoted basal lipolysis, but blunted the anti-lipolytic action of insulin. Furthermore, LXR activation antagonised PPARγ target genes in epididymal fat and PPARγ-PPRE-binding activity in 3T3-L1 adipocytes. Although the glucose tolerance was comparable to that in HFD mice, the insulin response during IPGTT was significantly higher and the insulin tolerance was significantly impaired in T0901317-treated HFD mice, indicating decreased insulin sensitivity by T0901317 administration, and which was further supported by impaired insulin signalling found in epididymal fat and decreased insulin-induced glucose uptake in 3T3-L1 adipocytes by T0901317 administration. In conclusion, these findings reveal that LXR activation impairs adipose expansion by increasing adipocyte apoptosis, lipolysis and antagonising PPARγ-mediated transcriptional activity, which contributes to decreased insulin sensitivity in whole body. The potential of LXR activation being a therapeutic target for atherosclerosis might be limited by the possibility of exacerbating insulin resistance.
Dong-Jae Jun, Kyung-Yoon Na, Wanil Kim, Dongoh Kwak, Eun-Jeong Kwon, Jong Hyuk Yoon, Kyungmoo Yea, Hyeongji Lee, Jaeyoon Kim, Pann-Gill Suh, Sung Ho Ryu and Kyong-Tai Kim
Interleukin 6 (IL6) is a pleiotropic cytokine that not only affects the immune system, but also plays an active role in many physiological events in various organs. Notably, 35% of systemic IL6 originates from adipose tissues under noninflammatory conditions. Here, we describe a previously unknown function of melanocortins in regulating Il6 gene expression and production in 3T3-L1 adipocytes through membrane receptors which are called melanocortin receptors (MCRs). Of the five MCRs that have been cloned, MC2R and MC5R are expressed during adipocyte differentiation. α-Melanocyte-stimulating hormone (α-MSH) or ACTH treatment of 3T3-L1 adipocytes induces Il6 gene expression and production in a time- and concentration-dependent manner via various signaling pathways including the protein kinase A, p38 mitogen-activated protein kinase, cJun N-terminal kinase, and IκB kinase pathways. Specific inhibition of MC2R and MC5R expression with short interfering Mc2r and Mc5r RNAs significantly attenuated the α-MSH-induced increase of intracellular cAMP and both the level of Il6 mRNA and secretion of IL6 in 3T3-L1 adipocytes. Finally, when injected into mouse tail vein, α-MSH dramatically increased the Il6 transcript levels in epididymal fat pads. These results suggest that α-MSH in addition to ACTH may function as a regulator of inflammation by regulating cytokine production.
Raghunath Chatterjee, Paramita Bhattacharya, Oksana Gavrilova, Kimberly Glass, Jaideep Moitra, Max Myakishev, Stephanie Pack, William Jou, Lionel Feigenbaum, Michael Eckhaus and Charles Vinson
Adipose-specific inactivation of both AP-1 and CCAAT-enhancer-binding protein (C/EBP) families of B-ZIP transcription factors in transgenic mice causes severe lipoatrophy. To evaluate whether inactivation of only C/EBP members was critical for lipoatrophy, A-C/EBP, a dominant-negative protein that specifically inhibits the DNA binding of the C/EBP members, was expressed in adipose tissue. For the first 2 weeks after birth, aP2-A-C/EBP mice had no white adipose tissue (WAT), drastically reduced brown adipose tissue (BAT), and exhibited marked hepatic steatosis, hyperinsulinemia, and hyperlipidemia. However, WAT appeared during the third week, coinciding with significantly improved metabolic functioning. In adults, BAT remained reduced, causing cold intolerance. At 30 weeks, the aP2-A-C/EBP mice had only 35% reduced WAT, with clear morphological signs of lipodystrophy in subcutaneous fat. Circulating leptin and adiponectin levels were less than the wild-type levels, and these mice exhibited impaired triglyceride clearance. Insulin resistance, glucose intolerance, and reduced free fatty acid release in response to β3-adrenergic agonist suggest improper functioning of the residual WAT. Gene expression analysis of inguinal WAT identified reduced mRNA levels of several enzymes involved in fatty acid synthesis and glucose metabolism that are known C/EBPα transcriptional targets. There were increased levels for genes involved in inflammation and muscle differentiation. However, when dermal fibroblasts from aP2-A-C/EBP mice were differentiated into adipocytes in tissue culture, muscle markers were elevated more than the inflammatory markers. These results demonstrate that the C/EBP family is essential for adipose tissue development during the early postnatal period, the regulation of glucose and lipid homeostasis in adults, and the suppression of the muscle lineage.
Yingkai Sun, Rui Wang, Shaoqian Zhao, Wen Li, Wen Liu, Lingyun Tang, Zhugang Wang, Weiqing Wang, Ruixin Liu, Guang Ning, Jiqiu Wang and Jie Hong
Browning of white adipose tissue has been proven to be a potential target to fight against obesity and its metabolic commodities, making the exploration of molecules involved in browning process important. Among those browning agents reported recently, FGF21 play as a quite promising candidate for treating obesity for its obvious enhancement of thermogenic capacity in adipocyte and significant improvement of metabolic disorders in both mice and human. However, whether other members of fibroblast growth factor (FGF) family play roles in adipose thermogenesis and obese development is still an open question. Here, we examined the mRNA expression of all FGF family members in three adipose tissues of male C57BL/6 mice and found that FGF9 is highly expressed in adipose tissue and decreased under cold stress. Furthermore, FGF9 treatment inhibited thermogenic genes in the process of beige adipocytes differentiation from stromal vascular fraction (SVF) in a dose-dependent manner. Similar results were obtained with FGF9 overexpression. Consistently, knockdown of FGF9 in SVF cells by using lentiviral shRNA increased thermogenic genes in differentiated beige adipocytes. RNA sequencing analysis revealed a significant increment of hypoxia-inducible factor (HIF) pathway in the early stage of beige adipocytes differentiation under FGF9 treatment, which was validated by real-time PCR. FGF9 expression was increased in subcutaneous WAT of obese human and mice. This study shows that adipose-derived FGF9 play as an inhibitory role in the browning of white adipocytes. Activation of hypoxia signaling at early stage of adipose browning process may contribute to this anti-thermogenic effect of FGF9.
O Verlaeten, C Casery, S Cavagna, D Naville, P Giraudon, M F Belin, M Begeot and A Bernard
Obesity results from disturbances of tightly regulated interactions between the nervous, endocrine, and metabolic systems that can be caused by external factors, such as viral infections. A mouse model of obesity induced by brain infection with a morbillivirus, canine distemper virus, allowed us to identify obesity-related genes. Using a subtractive library for the hypothalamus, the main brain structure regulating energy homeostasis, we identified a new gene on mouse chromosome 19 which we named upregulated obese product (Urop) 11 and, which has no homology with any known mRNA. A step-by-step molecular approach allowed us to isolate the full-length mRNA, predict the protein sequence, and identify consensus sites. Urop11 was mainly detected in the hypothalamus and adipocytes, and was dramatically upregulated in these central and peripheral structures in obese mice. Urop11 was also expressed in human neural and lymphoid samples and its expression seemed to be regulated by the state of lymphocyte activation. Interestingly, Urop11 expression was strongly upregulated both in vivo in mouse hypothalamus and in vitro in mouse neural cell lines, after leptin treatment. Taken together, our data show that Urop11 is a target of leptin, the satiety factor produced by adipocytes, in physiological and pathological conditions, including obesity. This new gene can be considered a key molecule in the hypothalamic integration pathway and demonstrates the importance of Urop11 as a target of leptin action.
S Viengchareun, H Bouzinba-Segard, J-P Laigneau, M-C Zennaro, P A Kelly, A Bado, M Lombès and N Binart
The pituitary hormone prolactin (PRL) exerts pleiotropic effects, which are mediated by a membrane receptor (PRLR) present in numerous cell types including adipocytes. Brown adipose tissue (BAT) expresses uncoupling proteins (UCPs), involved in thermogenesis, but also secretes leptin, a key hormone involved in the control of body weight. To investigate PRL effects on BAT, we used the T37i brown adipose cell line, and demonstrated that PRLRs are expressed as a function of cell differentiation. Addition of PRL leads to activation of the JAK/STAT and MAP kinase signaling pathways, demonstrating that PRLRs are functional in these cells. Basal and catecholamine-induced UCP1 expression were not affected by PRL. However, PRL combined with insulin significantly increases leptin expression and release, indicating that PRL potentiates the stimulatory effect of insulin as revealed by the recruitment of insulin receptor substrates and the activation of phosphatidylinositol 3-kinase. To explore the in vivo physiological relevance of PRL action in BAT, we showed that leptin content was significantly increased in BAT of PRLR-null mice compared with wild-type mice, highlighting the involvement of PRL in the leptin secretion process. This study provides the first evidence for a functional link between PRL and energy balance via a cross-talk between insulin and PRL signaling pathways in brown adipocytes.
Susan M van den Berg, Andrea D van Dam, Pascal J H Kusters, Linda Beckers, Myrthe den Toom, Saskia van der Velden, Jan Van den Bossche, Irma van Die, Mariëtte R Boon, Patrick C N Rensen, Esther Lutgens and Menno P J de Winther
Brown adipose tissue (BAT) activation and white adipose tissue (WAT) beiging can increase energy expenditure and have the potential to reduce obesity and associated diseases. The immune system is a potential target in mediating brown and beige adipocyte activation. Type 2 and anti-inflammatory immune cells contribute to metabolic homeostasis within lean WAT, with a prominent role for eosinophils and interleukin (IL)-4-induced anti-inflammatory macrophages. We determined eosinophil numbers in epididymal WAT (EpAT), subcutaneous WAT (ScAT) and BAT after 1 day, 3 days or 1 week of high-fat diet (HFD) feeding in C57Bl/6 mice. One day of HFD resulted in a rapid drop in eosinophil numbers in EpAT and BAT, and after 3 days, in ScAT. In an attempt to restore this HFD-induced drop in adipose tissue eosinophils, we treated 1-week HFD-fed mice with helminth antigens from Schistosoma mansoni or Trichuris suis and evaluated whether the well-known protective metabolic effects of helminth antigens involves BAT activation or beiging. Indeed, antigens of both helminth species induced high numbers of eosinophils in EpAT, but failed to induce beiging. In ScAT, Schistosoma mansoni antigens induced mild eosinophilia, which was accompanied by slightly more beiging. No effects were observed in BAT. To study type 2 responses on brown adipocytes directly, T37i cells were stimulated with IL-4. This increased Ucp1 expression and strongly induced the production of eosinophil chemoattractant CCL11 (+26-fold), revealing that brown adipocytes themselves can attract eosinophils. Our findings indicate that helminth antigen-induced eosinophilia fails to induce profound beiging of white adipocytes.
Lingyun Zhang, Takashi Sugiyama, Nao Murabayashi, Takashi Umekawa, Ning Ma, Yuki Kamimoto, Yoshihiro Ogawa and Norimasa Sagawa
The infiltration of classically activated macrophages (M1) and alternatively activated macrophages (M2) in subcutaneous adipose tissue (SAT) and parametrial adipose tissue (PAT) was analyzed to investigate whether local inflammatory change in adipose tissue occurs in late pregnancy. C57B L /6N female mice at 6 weeks of age were fed a normal chow diet for 4 weeks prior to mating at 10 weeks of age and were sampled on day 17 of pregnancy. The serum levels of adipokines and biochemical markers were measured using ELISA and enzymatic methods. The identification of M1 and M2 was analyzed by double immunofluorescence with anti-F4/80 and anti-CD11c antibodies. The gene expression of adipokines in adipose tissues was analyzed by quantitative RT-PCR. The pregnant group showed adipocyte hypertrophy, higher macrophage infiltration, and higher M1/M2 in both SAT and PAT compared with the non-pregnant (NP) group. Serum levels of free fatty acids, tumor necrosis factor α (TNFα), interleukin 6 (IL6), and IL10 were higher, and serum levels of adiponectin were lower in the pregnant group than those in the NP group. The gene expressions of CD68, Itgax, CCR2, TNF α, and PAI1 in SAT during pregnancy were significantly higher than those in the NP group, as were the gene expressions of CD68, Emrl, Itgax, MCP1, TNF α , IL6, PAI1, adiponectin, and IL10 in PAT. These results suggest that the low-grade inflammation of adipose tissue indicated by increased macrophage infiltration occurs in late normal pregnancy.
Raquel Martinez-deMena and Maria-Jesus Obregón
Type II 5′ deiodinase (D2) activity produces triiodothyronine (T3) from thyroxine (T4) and is induced by cold and norepinephrine (NE) in brown adipose tissue. T3 is required for and amplifies the adrenergic stimulation of D2 activity and mRNA in cultured brown adipocytes. D2 is upregulated by insulin and decrease in fasting. We now study the regulation by insulin of the adrenergically induced D2 activity and mRNA in primary cultures of rat brown adipocytes. Insulin alone does not increase D2 activity or mRNA. Insulin-depleted cells show a reduction in the adrenergically induced D2 activity, which is proportional to the length of insulin depletion and is restored after insulin addition. IGFs mimic this effect at higher doses. ERK 1/2 MAPK activity (p44/p42), stimulated by insulin, serum and NE, is an absolute requirement for the adrenergic stimulation of D2 activity and mRNA. PI3K is stimulated by insulin and serum, and NE increases the effect of insulin. The action of insulin on D2 is not due to changes in D2 half-life or in the proteasome-mediated degradation of D2, but it seems to modulate the transcriptional induction mediated by NE. D2 mRNA expression, induced by NE plus T3, is reduced when insulin is withdrawn at early differentiation stages. Insulin or IGF-I promotes increases in D2 mRNA. Insulin is required for the induction of D2 mRNA by T3. In conclusion, MAPK signaling is required for the adrenergic stimulation of D2 activity and mRNA, and insulin stimulates D2 activity via MAPK and PI3K and enhances the adrenergic pathways.