Leptin Expression In Adipocytes Research Articles

Regulation of adipocyte leptin expression by signaling metabolite

Regulation of adipocyte leptin expression by signaling metabolite

Breast cancer cell-derived exosome-delivered microRNA-155 targets UBQLN1 in adipocytes and facilitates cancer cachexia-related fat loss.

Cachexia occurrence and development are associated with loss of white adipose tissues, which may be involved with cancer-derived exosomes. This study attempted to characterize the functional mechanisms of bc cell-derived exosomes-loaded microRNA (miR)-155 in cancer cachexia-related fat loss. Exosomes were incubated with preadipocytes and cellular lipid droplet accumulation was observed using oil red O staining. Western blots evaluated the cellular levels of lipogenesis marker peroxisome proliferator activated receptor gamma (PPARγ) and adiponectin, C1Q and collagen domain containing (AdipoQ). Differentiated adipocytes were incubated with exosomes, and phosphate hormone sensitive lipase (P-HSL), adipose triglyceride lipase (ATGL), and glycerol were detected in adipocytes, in addition to uncoupling protein 1 (UCP1) and leptin levels. A mouse model of cancer cachexia was established where cancer exosomes were injected intravenously. The changes in body weight and tumor-free body weights were recorded and serum glycerol levels and lipid accumulation in adipose tissues were determined. Also, the relationship between miR-155 and UBQLN1 was predicted and verified. bc exosome treatment reduced PPARγ and AdipoQ protein levels, promoted the levels of P-HSL and ATGL proteins, facilitated glycerol release, increased UCP1 expression, and lowered leptin expression in adipocytes. Exosomal miR-155 inhibited lipogenesis in preadipocytes and boosted the browning of white adipose tissues. miR-155 downregulation alleviated cancer exosome-induced browning of white adipose tissues and fat loss. Mechanistically, miR-155 targeted UBQLN1, and UBQLN1 upregulation reversed the impacts of cancer exosomes. miR-155 loaded by bc cell-derived exosomes significantly affects white adipose browning and inhibition of cancer-derived exosomes.

Metformin alleviates hyperuricaemia-induced serum FFA elevation and insulin resistance by inhibiting adipocyte hypertrophy and reversing suppressed white adipose tissue beiging.

Hyperuricaemia (HUA) significantly increases the risk of metabolic syndrome and is strongly associated with the increased prevalence of high serum free fatty acids (FFAs) and insulin resistance. However, the underlying mechanisms are not well established, especially the effect of uric acid (UA) on adipose tissue, a vital organ in regulating whole-body energy and FFA homeostasis. In the present study, we noticed that adipocytes from the white adipose tissue of patients with HUA were hypertrophied and had decreased UCP1 expression. To test the effects of UA on adipose tissue, we built both in vitro and in vivo HUA models and elucidated that a high level of UA could induce hypertrophy of adipocytes, inhibit their hyperplasia and reduce their beige-like characteristics. According to mRNA-sequencing analysis, UA significantly decreased the expression of leptin in adipocytes, which was closely related to fatty acid metabolism and the AMPK signalling pathway, as indicated by KEGG pathway analysis. Moreover, lowering UA using benzbromarone (a uricosuric agent) or metformin-induced activation of AMPK expression significantly attenuated UA-induced FFA metabolism impairment and adipose beiging suppression, which subsequently alleviated serum FFA elevation and insulin resistance in HUA mice. Taken together, these observations confirm that UA is involved in the aetiology of metabolic abnormalities in adipose tissue by regulating leptin-AMPK pathway, and metformin could lessen HUA-induced serum FFA elevation and insulin resistance by improving adipose tissue function via AMPK activation. Therefore, metformin could represent a novel treatment strategy for HUA-related metabolic disorders.

Acute effect of concurrent exercise on serum leptin and resistance insulin response in sedentary men

Aim: This study aimed to determine the delayed effect of one session of concurrent exercise on serum leptin and resistance insulin levels of sedentary men. Materials and Methods: Fifteen healthy young men with a mean age of 22.9 ± 1.7 years and a body mass index of 23.3 ± 1 kg/m2 voluntarily participated in this experimental research. They participated in one session of concurrent exercise including 20 min of aerobic running on a treadmill at 60%–70% maximum oxygen uptake plus a resistance exercise at the intensity of 70% of 1-repetition maximum with ten repetitions per set to second round. Blood serum leptin, glucose, insulin, and insulin resistance index were assessed before, 24, 48, and 72 h after the exercise program.Results: The results showed that leptin level did not change statistically significantly immediately and 72 h after the exercise termination (P > 0.05) but did decrease statistically significantly 24 and 48 h after the exercise program (P ≤ 0.05). The result also showed that insulin and insulin resistance levels decreased statistically significantly immediately after the exercise and lasted for up to 48 h postexercise (P ≤ 0.05); however, it returned to its initial value after 72 h of recovery (P > 0.05). Conclusions: It was concluded that energy use in one session of concurrent exercise might reduce leptin levels up to 48 h of recovery. In addition, a decrease in insulin, a known inducer of leptin expression in adipocytes, occurs before the decrease in leptin. This change may mediate the decrease of leptin concentration.

A structure-function approach identifies L-PGDS as a mediator responsible for glucocorticoid-induced leptin expression in adipocytes

Leptin is an adipokine predominantly secreted by adipocytes and has many physiological roles, including in energy homeostasis. We identified that AM630, a cannabinoid receptor 2 (CB2) antagonist, down-regulated leptin expression in mature adipocytes differentiated from either stromal vascular fractions isolated from inguinal fat pads of C57BL/6J mice or 3T3-L1 preadipocytes. However, the leptin-suppressive effects of AM630 preserved in CB2-deficient adipocytes indicated the off-target activity of AM630 in leptin expression. Pharmacological and genetic studies, cheminformatics, and docking simulation were applied to identify the potential protein target of AM630 that modulates leptin expression in differentiated primary preadipocytes. Screening of the reported off-targets of AM630 identified a synthetic cannabinoid WIN55212-2 exerting the same function. Target deconvolution and docking simulation suggested that AM630 and WIN55212-2 were both inhibitors of lipocalin-type prostaglandin D2 synthase (L-PGDS). Further studies showed that L-PGDS positively regulates leptin expression. Although glucocorticoid and aldosterone were previously reported to induce expression of both L-PGDS and leptin, our data demonstrated that L-PGDS mediates only glucocorticoid-induced leptin expression in differentiated primary preadipocytes. No effect was observed after aldosterone treatment. This newly discovered glucocorticoid – L-PGDS – leptin pathway may provide insights into current clinical use of glucocorticoid and management of their undesired effects such as obesity.

SHORT CHAIN FATTY ACIDS UPREGULATE ADIPOKINE PRODUCTION IN TYPE 2 DIABETES-DERIVED HUMAN ADIPOCYTES.

Short chain fatty acids (SCFAs) play a major regulatory role in adipocyte function and metabolism. The aim of this study was to investigate the effects of SCFAs on adiponectin and leptin expression in adipocytes, and also to determine whether the effects of SCFA treatment in visceral adipocytes obtained from healthy subjects are different relative to the effects in adipocytes from patients with type 2 diabetes. Human pericardiac preadipocytes and human pericardiac preadipocytes type 2 diabetes were differentiated into adipocytes for 21 days in 48-well plates. After differentiation, two kinds of mature adipocytes, human pericardiac adipocytes (HPAd) and human pericardiac adipocytes-type 2 diabetes (HPAd-T2D) were incubated with or without 1 mM of acetic acid (AA), butyrate acid (BA), and propionic acid (PA). After 48 hours of incubation, intracellular lipid accumulation was measured using oil red staining. In addition, mRNA levels of adiponectin, leptin and Peroxisome Proliferator-Activated Receptor γ (PPARγ) were determined by Real-Time PCR system. In HPAd, SCFA supplementation did not inhibit lipid accumulation. By contrast, both AA (p<0.01) and PA (p<0.01) significantly inhibited lipid accumulation in HPAd-T2D. Regarding mRNA levels of adiponectin, no significant changes were found in HPAd, while all three types of SCFAs significantly increased (p<0.05) adiponectin expression in HPAd-T2D. Leptin mRNA expression levels were significantly increased by treatment with all three types of SCFAs in both HPAd (p<0.05) and HPAd-T2D (p<0.05). SCFAs inhibited lipid droplet accumulation and increased mRNA expression of adiponectin and leptin in T2D-derived adipocytes.

Leptin Function and Regulation.

We summarize the biological impact of leptin signaling as well as the molecular and cellular characteristics of leptin action. Our focus is principally in the central nervous system and we describe the properties of the neuronal networks that are mediators of leptin's effects on ingestive behavior, energy balance, and the reproductive system. The molecular targets of leptin's effects are also responsible for the attenuation and termination of the intracellular signal transduction pathway for leptin, providing a clear understanding of the mechanisms leading to leptin resistance or insensitivity. Using the tools of comparative biology, we explore the potential functions of leptin in fish and birds. Based on the highly variable expression of leptin in multiple tissues, a clear lack of expression of leptin in adipocytes in numerous species of fish and birds and an absence of changes of leptin concentrations in blood that are correlated with changes in nutritional status, it is clear that leptin is unlikely to function as a signal for triglyceride stores in nonmammalian species. This comparative survey serves to highlight the unique function of leptin in mammalian biology as a modulator of energy balance, sexual development, and fertility. © 2018 American Physiological Society. Compr Physiol 8:351-369, 2018.

Interrelationship between lymphocytes and leptin in fat depots of obese mice revealed by changes in nutritional status.

The mechanisms underlying the relationships between nutritional status and immunity remain to be fully characterized. The present study was undertaken to analyze by flow cytometry, in the context of diet-induced obesity, the status of immune cells in subcutaneous, and epididymal fat depots in wild-type and immunodeficient Rag2-/- mice submitted to nutritional challenge, i.e., 48-h fasting and 1-week refeeding. In parallel, the responsiveness of mature adipocytes and immune cells in bone marrow, lymph node, and liver were also analyzed. The results show that fasting in obese wild-type mice induces a prominent lipolysis in epididymal AT and immunosuppression restricted to both subcutaneous and epididymal AT, characterized by reduced number of CD4+ T and B lymphocytes and M1/M2 macrophages associated with reduced leptin and increased FGF21 expression in mature adipocytes. One-week refeeding was sufficient to reverse the fasting-induced effects. Obese immunodeficient mice under nutritional challenge exhibited no changes in adipocyte leptin expression and no marked trafficking of AT macrophages or NK cells, while the fasted-induced upregulation of FGF21 expression was maintained as well as the lipolytic responses. The present results demonstrate that, in a context of diet-induced obesity, fasting-induced immunosuppression is restricted to fat depots in immunocompetent mice. Lack of adipocyte leptin regulation and fasting-induced immunosuppression in obese immunodeficient mice strongly suggests that lymphocytes are involved in the modulation of adipocyte leptin expression on one hand and on the other that leptin is involved in the immune changes in AT according to nutritional status.

Effects of nutritional status on plasma leptin levels and in vitro regulation of adipocyte leptin expression and secretion in rainbow trout

As leptin has a key role on appetite, knowledge about leptin regulation is important in order to understand the control of energy balance. We aimed to explore the modulatory effects of adiposity on plasma leptin levels in vivo and the role of potential regulators on leptin expression and secretion in rainbow trout adipocytes in vitro. Fish were fed a regular diet twice daily ad libitum or a high-energy diet once daily at two ration levels; satiation (SA group) or restricted (RE group) to 25% of satiation, for 8weeks. RE fish had significantly reduced growth (p<0.001) and adipose tissue weight (p<0.001), and higher plasma leptin levels (p=0.022) compared with SA fish. Moreover, plasma leptin levels negatively correlated with mesenteric fat index (p=0.009). Adipocytes isolated from the different fish were treated with insulin, ghrelin, leucine, eicosapentaenoic acid or left untreated (control). In adipocytes from fish fed regular diet, insulin and ghrelin increased leptin secretion dose-dependently (p=0.002; p=0.033, respectively). Leptin secretion in control adipocytes was significantly higher in RE than in SA fish (p=0.022) in agreement with the in vivo findings, indicating that adipose tissue may contribute to the circulating leptin levels. No treatment effects were observed in adipocytes from the high-energy diet groups, neither in leptin expression nor secretion, except that leptin secretion was significantly reduced by leucine in RE fish adipocytes (p=0.025). Overall, these data show that the regulation of leptin in rainbow trout adipocytes by hormones and nutrients seems to be on secretion, rather than at the transcriptional level.

Abstract 512: p16INK4A down-regulation activates breast stromal adipocytes.

Abstract Obesity, a disease linked to increased number of adipocytes in various tissues, is now recognized as a risk factor for the development of breast cancer. Importantly, obesity has been reported to be associated with the occurrence of larger, more advanced tumors and aggressive cancer pathological features, including lymph node metastasis, advanced tumor stage, and high grade. Cancer-associated adipocytes (CAAs), the most abundant cellular component of breast cancer-associated stroma, promote carcinogenesis through paracrine effects. However, the molecular basis of adipocytes implication in breast carcinogenesis remains elusive. To shed light on this important phenomenon, we established and characterized normal adipocytes from post-plastic surgery of breast tissues. We have shown that these cells express various adipocyte biomarkers, including Leptin, TNF-α and FABP4. Furthermore, we investigated the role of the tumor suppressor p16 INK4A protein in adipocytes activation. We have found that specific down-regulation of p16INK4A by shRNA increased the expression/secretion levels of various adipokines including leptin, activated breast adipocyte and enhanced their migration/invasion abilities. Consequently, media conditioned with these cells stimulated the proliferation and the migration/invasion of breast cancer cells and enhanced endothelial cell differentiation into capillary-like structures. In addition, we have also shown that media conditioned with breast cancer cells decrease the expression of p16INK4A and increase the expression of leptin in adipocytes. These results provide the first indication that p16INK4A down-regulation in breast stromal adipocytes is an important step toward their activation. Citation Format: Huda H. Alkhalaf, Abdelilah Aboussekhra. p16INK4A down-regulation activates breast stromal adipocytes. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 512. doi:10.1158/1538-7445.AM2013-512

Fenretinide Treatment Prevents Diet-Induced Obesity in Association With Major Alterations in Retinoid Homeostatic Gene Expression in Adipose, Liver, and Hypothalamus

The synthetic retinoid, Fenretinide (FEN), inhibits obesity and insulin resistance in mice and is in early clinical trials for treatment of insulin resistance in obese humans. We aimed to determine whether alterations in retinoic acid (RA)-responsive genes contribute to the beneficial effects of FEN. We examined the effect of FEN on 3T3-L1 adipocyte differentiation and alterations in gene expression in C57Bl/6 and retinaldehyde dehydrogenase (RALDH) 1 knockout (KO) mice fed a high-fat (HF) diet. FEN completely inhibited adipocyte differentiation by blocking CCAAT/enhancer-binding protein (C/EBP) α/peroxisome proliferator–activated receptor (PPAR) γ−mediated induction of downstream genes and upregulating RA-responsive genes like cellular retinol-binding protein-1. In mice fed an HF diet, RA-responsive genes were markedly increased in adipose, liver, and hypothalamus, with short-term and long-term FEN treatment. In adipose, FEN inhibited the downregulation of PPARγ and improved insulin sensitivity and the levels of adiponectin, resistin, and serum RBP (RBP4). FEN inhibited hyperleptinemia in vivo and leptin expression in adipocytes. Surprisingly, hypothalamic neuropeptide Y expression was completely suppressed, suggesting a central effect of FEN to normalize hyperglycemia. Moreover, FEN induced RA-responsive genes in RALDH1 KO mice, demonstrating that FEN can augment RA signaling when RA synthesis is impaired. We show that FEN-mediated beneficial effects are through alterations in retinoid homeostasis genes, and these are strong candidates as therapeutic targets for the treatment of obesity and insulin resistance.

Dopamine D2 receptors regulate the expression of leptin in adipocytes

Leptin is secreted by adipose tissue, regulates food intake, and increases secretion of pro‐inflammatory cytokines. Mouse adipocytes expressed dopamine D2 receptors (D2R). Therefore, we aimed to determine the role of the D2Rs on the regulation of the expression of leptin, adiponectin, and other pro‐inflammatory cytokines in adipocytes. For this experiments mouse 3T3‐L1 cells were cultured to 100% confluency, differentiated to adipocytes for 3 days, and studied 8 days after differentiation. Stimulation of D2Rs with quinpirole (1ìM, 24h) increased the expression of leptin both in cells (23±8%, P&lt;0.05; western blot) and in the media (59±4pg/ml vs. 45±3pg/ml, P&lt;0.05, ELISA), as well as the expression of IL‐6 (49±7%, P&lt;0.05, western blot), but did not modify that of adiponectin. The effects were prevented by the D2R selective antagonist (L741,626). D2R stimulation also increased gene expression (qRT‐PCR) of leptin (1.50±0.03 fold, P&lt;0.05), IL‐6 (2.44±0.08 fold, P&lt;0.05), TNF alpha (2.23±0.06 fold, P&lt;0.05), MCP1 (1.82±0.04 fold, P&lt;0.05), MCP2 (2.43±0.06 fold, P&lt;0.05) and NFkB p50 (1.47±0.02 fold, P&lt;0.05). Adipocyte D2R positively regulates the expression of leptin and pro‐inflammatory cytokines and chemokines in 3T3‐L1. In contrast renal D2R inhibits the their expression. We suggest that the effect of D2R is tissue‐specific but the mechanism involved is undetermined.

FOSL2 promotes leptin gene expression in human and mouse adipocytes

The adipocyte-derived hormone leptin is a critical regulator of many physiological functions, ranging from satiety to immunity. Surprisingly, very little is known about the transcriptional pathways that regulate adipocyte-specific expression of leptin. Here, we report studies in which we pursued a strategy integrating BAC transgenic reporter mice, reporter assays, and chromatin state mapping to locate an adipocyte-specific cis-element upstream of the leptin (LEP) gene in human fat cells. Quantitative proteomics with affinity enrichment of protein-DNA complexes identified the transcription factor FOS-like antigen 2 (FOSL2) as binding specifically to the identified region, a result that was confirmed by ChIP. Knockdown of FOSL2 in human adipocytes decreased LEP expression, and overexpression of Fosl2 increased Lep expression in mouse adipocytes. Moreover, the elevated LEP expression observed in obesity correlated well with increased FOSL2 levels in mice and humans, and adipocyte-specific genetic deletion of Fosl2 in mice reduced Lep expression. Taken together, these data identify FOSL2 as a critical regulator of leptin expression in adipocytes.

Mechanism of the inhibitory effect of atorvastatin on leptin expression induced by angiotensin II in cultured human coronary artery smooth muscle cells

Leptin contributes to the pathogenesis of atherosclerosis. Ang II (angiotensin II), a proatherogenic cytokine, increases leptin synthesis in cultured adipocytes. Statin suppresses leptin expression in adipocytes and human coronary artery endothelial cells. However, the effect of Ang II and statin on leptin expression in VSMCs (vascular smooth muscle cells), the major cell typesin atheroma, is poorly understood. Thus the aim of the present study was to investigate the molecular mechanism of atorvastatin for reducing leptin expression after Ang II stimulation in VSMCs. VSMCs from human coronary artery were cultured. Ang II stimulation increased leptin protein and mRNA and phospho-JNK (c-Jun N-terminal kinase) expression. Exogenous addition of Dp44mT (2,2'-dipyridyl-N,N-dimethylsemicarbazone) and mevalonate increased leptin protein expression similarly to Ang II. Atorvastatin, SP600125, JNK siRNA (small interfering RNA) and NAC (N-acetylcysteine) completely attenuated the leptin and phospho-JNK protein expression induced by Ang II. Ang II significantly increased ROS (reactive oxygen species) formation in human VSMCs. Addition of atorvastatin and NAC significantly attenuated the formation of ROS induced by Ang II. Addition of atorvastatin and SP600125 inhibited the phosphorylation of Rac1 induced by Ang II. The gel shift and promoter activity assay showed that Ang II increased AP-1 (activator protein-1)-binding activity and leptin promoter activity, while SP600125, NAC and atorvastatin inhibited the AP-1-binding activity and leptin promoter activity induced by Ang II. Ang II significantly increased the migration and proliferation of cultured VSMCs, while addition of atorvastatin, SP600125, NAC and leptin siRNA before Ang II stimulation significantly inhibited the migration and proliferation of VSMCs induced by Ang II. Ang II significantly increased secretion of leptin from human VSMCs, and addition of SP600125, atorvastatin and NAC before Ang II stimulation almost completely inhibited the leptin secretion induced by Ang II. In conclusion, Ang II induces leptin expression in human VSMCs, and atorvastatin could inhibit the leptin expression induced by Ang II. The inhibitory effect of atorvastatin on Ang II-induced leptin expression was mediated by Rac, ROS and JNK pathways.

Leptin derived from adipocytes in injured peripheral nerves facilitates development of neuropathic pain via macrophage stimulation

Nerve injury may result in neuropathic pain, characterized by allodynia and hyperalgesia. Accumulating evidence suggests the existence of a molecular substrate for neuropathic pain produced by neurons, glia, and immune cells. Here, we show that leptin, an adipokine exclusively produced by adipocytes, is critical for the development of tactile allodynia through macrophage activation in mice with partial sciatic nerve ligation (PSL). PSL increased leptin expression in adipocytes distributed at the epineurium of the injured sciatic nerve (SCN). Leptin-deficient animals, ob/ob mice, showed an absence of PSL-induced tactile allodynia, which was reversed by the administration of leptin to the injured SCN. Perineural injection of a neutralizing antibody against leptin reproduced this attenuation. Macrophages recruited to the perineurium of the SCN expressed the leptin receptor and phosphorylated signal transducer and activator of transcription 3 (pSTAT3), a transcription factor downstream of leptin. PSL also up-regulated the accepted mediators of neuropathic pain--namely, cyclooxygenase-2, inducible nitric oxide synthase, and matrix metalloprotease-9--in the injured SCN, with transcriptional activation of their gene promoters by pSTAT3. This up-regulation was partly reproduced in a macrophage cell line treated with leptin. Administration of peritoneal macrophages treated with leptin to the injured SCN reversed the failure of ob/ob mice to develop PSL-induced tactile allodynia. We suggest that leptin induces recruited macrophages to produce pronociceptive mediators for the development of tactile allodynia. This report shows that adipocytes associated with primary afferent neurons may be involved in the development of neuropathic pain through adipokine secretion.

Agouti/Melanocortin Interactions with Leptin Pathways in Obesity

The cloning of mouse obesity genes and their human homologues provides unique opportunities to identify novel cellular targets for therapeutic intervention. The first of these to be cloned, agouti, antagonizes central nervous system melanocortin receptor (MCR) binding, resulting in hyperphagia and an obesity/hyperinsulinemia syndrome. There appears to be significant cross-talk between the agouti and leptin signaling systems. Agouti antagonism of central nervous system (CNS) MCR binding inhibits the anorexic effects of leptin, whereas agouti up-regulates adipocyte leptin expression, serving to limit the magnitude of agouti-induced obesity. The effects of agouti and leptin mutations on obesity, however, are independent and additive. Agouti also regulates adipocyte lipid metabolism, functioning both to increase the expression and activity of lipogenic genes and to inhibit lipolysis. Both of these actions occur via a Ca(2+)-dependent mechanism, suggesting that modulation of adipocyte Ca2+ transport may be a key target for further investigation.

Glycolaldehyde‐Modified Bovine Serum Albumin Downregulates Leptin Expression in Mouse Adipocytes via a CD36‐Mediated Pathway

Previous observations by us have clarified that proteins modified by advanced glycation end products (AGEs) are recognized as effective ligands by CD36-overexpressed CHO cells and undergo receptor-mediated endocytosis. CD36, a member of the class B scavenger receptor family, also acts as a fatty acid transporter in adipocytes. Oxidized low-density lipoprotein (Ox-LDL), a ligand for CD36, is known to upregulate CD36 by activating peroxisome proliferator-activated receptor gamma (PPAR-gamma) in macrophages, whereas PPAR-gamma ligands such as troglitazone and 15-deoxy-delta12,14-prostaglandin J2 decrease leptin secretion from adipocytes. The purpose of this study was to examine effects of AGE ligands on leptin expression in adipocytes. Glycolaldehyde-modified bovine serum albumin (GA-BSA) decreased leptin expression at both the protein and mRNA levels in 3T3-L1 adipocytes and mouse epididymal adipocytes. The binding to and subsequent endocytic degradation of GA-BSA by 3T3-L1 adipocytes were effectively inhibited by a neutralizing anti-CD36 antibody. These results indicate that the ligand interaction of GA-BSA with CD36 leads to downregulation of leptin expression in 3T3-L1 adipocytes, suggesting that AGE-induced leptin downregulation is linked to reduction of the insulin sensitivity in metabolic syndrome.

Advanced glycation end products-modified proteins and oxidized LDL mediate down-regulation of leptin in mouse adipocytes via CD36

Advanced glycation end products (AGE)-modified proteins as well as oxidized-LDL (Ox-LDL) undergo receptor-mediated endocytosis by CHO cells overexpressing CD36, a member of class B scavenger receptor family. The purpose of the present study was to examine the effects of glycolaldehyde-modified BSA (GA-BSA) as an AGE-ligand and Ox-LDL on leptin expression in adipocytes. GA-BSA decreased leptin expression at both protein and mRNA levels in 3T3-L1 adipocytes and mouse epididymal adipocytes. Ox-LDL showed a similar inhibitory effect on leptin expression in 3T3-L1 adipocytes, which effect was protected by N-acetylcysteine, a reactive oxygen species (ROS) inhibitor. Binding of 125I-GA-BSA or 125I-Ox-LDL to 3T3-L1 adipocytes and subsequent endocytic degradation were inhibited by a neutralizing anti-CD36 antibody. Furthermore, this antibody also suppressed Ox-LDL-induced leptin down-regulation. These results clarify that the interaction of GA-BSA and Ox-LDL with CD36 leads to down-regulation of leptin expression via ROS system(s) in 3T3-L1 adipocytes, suggesting that a potential link of AGE- and/or Ox-LDL-induced leptin down-regulation might be linked to insulin-sensitivity in metabolic syndrome.

Tissue-specific regulation of leptin expression and secretion by all-trans retinoic acid.

In addition to hormones and the sympathetic nervous system, specific nutrients may regulate leptin mRNA expression and adipose tissue metabolism. However, little is known regarding the effect of nutrients on leptin mRNA expression. Retinoic acid (RA) is a ligand of some nuclear receptors and previous reports have demonstrated contradictory effects on plasma leptin levels. Thus, we examined the effect of RA on expression of leptin in adipocytes of murine and human origin. After 48 h incubation of murine 3T3-L1 adipocytes with 1 and 10 microM all-trans RA, the expression of leptin mRNA was reduced by 56% and 65%, respectively, whereas the secretion of leptin was reduced by 38% and 77%, respectively. In human adipose tissue explants, 1 microM all-trans RA reduced leptin mRNA expression levels by 55% and leptin secretion by 25% after 24 h incubation. We observed an increased mRNA expression level of the transcription factors peroxisomal proliferator activated receptor gamma (PPAR gamma), retinoid X receptor alpha (RXR alpha), and RA receptor alpha (RAR alpha) in 3T3-L1 cells, whereas the mRNA level of these transcription factors was unchanged in human adipose tissue explants after incubation with RA. In two other leptin-expressing cell systems, the human placental trophoblast cell line BeWo and normal human primary osteoblasts, there was no effect of RA on leptin mRNA expression, but leptin secretion was reduced by 64% after 24 h incubation with 10 microM all-trans RA in BeWo cells. In conclusion, all-trans RA reduced both expression and secretion of leptin in human and rodent adipose tissue. In human BeWo cells or primary osteoblasts, leptin mRNA expression levels was not changed by all-trans RA, indicating a tissue-specific regulation of leptin mRNA expression by all-trans RA.

Activation of leptin expression by an inhibitor of carnitine palmitoyltransferase-1

Leptin may regulate peripheral fatty acid oxidation and invoke a feedback mechanism that affects leptin expression in adipocytes. The objective of this study, therefore, was to determine whether inhibiting systemic fatty acid oxidation at the level of carnitine palmitoyltransferase-1 (CPT1) affects leptin expression. To accomplish this objective, fed or overnight fasted rats were treated with 2-tetradecylglycidic acid (TDGA), a specific, irreversible CPT1 inhibitor, and acute changes in rat epididymal leptin expression and serum leptin content were measured using Northern, RT-PCR, and radioimmunoassay analyses. Overnight fasting decreased both epididymal leptin mRNA content and serum leptin. Treating overnight fasted rats with TDGA increased both their epididymal leptin mRNA and their serum leptin significantly in a time- and concentration-dependent manner. TDGA affected neither epididymal leptin mRNA nor serum leptin in fed rats where systemic fatty acid oxidation is low. These results support the conclusion that CPT1-linked fatty acid oxidation is a key modulator of leptin expression in fasting rats.