AMPK and ACC phosphorylation: effect of leptin, muscle fibre type and obesity

Correlation of Leptin in Patients With Type 2 Diabetes Mellitus

The exponential increase in diabetes mellitus (DM) poses serious public health concerns. In this review, we focus on the role of leptin in type 2 DM. The peripheral actions of leptin consist of upregulating proinflammatory cytokines which play an important role in the pathogenesis of type 2 DM and insulin resistance. Moreover, leptin is known to inhibit insulin secretion and plays a significant role in insulin resistance in obesity and type 2 DM. A literature search was conducted on Medline, Cochrane, Embase, and Google Scholar for relevant articles published until December 2023. The following search strings and Medical Subject Headings (MeSH terms) were used: "Diabetes Mellitus," "Leptin," "NPY," and "Biomarker." This article aims to discuss the physiology of leptin in type 2 DM, its glucoregulatory actions, its relationship with appetite, the impact that various lifestyle modifications can have on leptin levels, and, finally, explore leptin as a potential target for various treatment strategies.

Anti‑adipogenic effect and underlying mechanism of lignan‑enriched nutmeg extract on 3T3‑L1 preadipocytes

Nutmeg is the seed derived from Myristica fragrans. Nutmeg seeds contain alkylbenzene derivatives such as myristicin, which are toxic to the human organism, and lignan compounds such as nectandrin B, which possess anti-aging and anti-diabetic properties. However, the anti-adipogenic, prolipolytic and anti-inflammatory effects of lignan-enriched nutmeg extract (LNX) on preadipocytes remain unclear. In the present study, the effects of LNX on lipid accumulation, glycerol release and inflammatory cyclooxygenase-2 (COX-2) expression in differentiated 3T3-L1 preadipocytes were investigated. Oil red O staining demonstrated that treatment with LNX resulted in a concentration-dependent reduction in lipid accumulation in differentiating 3T3-L1 preadipocytes without affecting cell growth. Mechanistically, LNX treatment at 6 µg/ml led to a reduction in phosphorylation levels of signal transducer and activator of transcription 3 (STAT3), whereas it did not influence the peroxisome proliferator-activated receptor gamma (PPAR-γ) and CCAAT enhancer binding protein alpha (C/EBP-α) expression levels during 3T3-L1 preadipocyte differentiation. In addition, LNX treatment at 6 µg/ml led to a decrease in fatty acid synthase (FAS) expression levels on day (D) 2, but not D5 and D8, during preadipocyte differentiation. Treatment with LNX at 6 µg/ml did not affect the expression levels of perilipin A during preadipocyte differentiation. In differentiated 3T3-L1 adipocytes, LNX treatment at 6 µg/ml did not stimulate glycerol release and hormone-sensitive lipase phosphorylation, which are known lipolysis hallmarks. Furthermore, LNX treatment at the doses tested had no effect on tumor necrosis factor alpha-induced COX-2 expression in 3T3-L1 preadipocytes. Collectively, these results demonstrated that LNX has an anti-adipogenic effect on differentiating 3T3-L1 preadipocytes, which is mediated by the downregulation of STAT3 phosphorylation and FAS expression.

AMPK and the Endocrine Control of Metabolism

Complex multicellular organisms require a coordinated response from multiple tissues to maintain whole-body homeostasis in the face of energetic stressors such as fasting, cold, and exercise. It is also essential that energy is stored efficiently with feeding and the chronic nutrient surplus that occurs with obesity. Mammals have adapted several endocrine signals that regulate metabolism in response to changes in nutrient availability and energy demand. These include hormones altered by fasting and refeeding including insulin, glucagon, glucagon-like peptide-1, catecholamines, ghrelin, and fibroblast growth factor 21; adipokines such as leptin and adiponectin; cell stress-induced cytokines like tumor necrosis factor alpha and growth differentiating factor 15, and lastly exerkines such as interleukin-6 and irisin. Over the last 2 decades, it has become apparent that many of these endocrine factors control metabolism by regulating the activity of the AMPK (adenosine monophosphate-activated protein kinase). AMPK is a master regulator of nutrient homeostasis, phosphorylating over 100 distinct substrates that are critical for controlling autophagy, carbohydrate, fatty acid, cholesterol, and protein metabolism. In this review, we discuss how AMPK integrates endocrine signals to maintain energy balance in response to diverse homeostatic challenges. We also present some considerations with respect to experimental design which should enhance reproducibility and the fidelity of the conclusions.

The Receptor Tyrosine Kinase c-Met Promotes Lipid Accumulation in 3T3-L1 Adipocytes

The receptor tyrosine kinase c-Met is elaborated in embryogenesis, morphogenesis, metabolism, cell growth, and differentiation. JNJ38877605 (JNJ) is an inhibitor of c-Met with anti-tumor activity. The c-Met expression and its role in adipocyte differentiation are unknown. Here, we investigated the c-Met expression and phosphorylation, knockdown (KD) effects, and pharmacological inhibition of c-Met by JNJ on fat accumulation in murine preadipocyte 3T3-L1 cells. During 3T3-L1 preadipocyte differentiation, strikingly, c-Met expression at the protein and mRNA levels and the protein phosphorylation on Y1234/1235 and Y1349 is crucial for inducing its kinase catalytic activity and activating a docking site for signal transducers were increased in a time-dependent manner. Of note, JNJ treatment at 20 μM that strongly inhibits c-Met phosphorylation without altering its total expression resulted in less lipid accumulation and triglyceride (TG) content with no cytotoxicity. JNJ further reduced the expression of adipogenic regulators, including CCAAT/enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), fatty acid synthase (FAS), acetyl CoA carboxylase (ACC), and perilipin A. Moreover, JNJ treatment increased cAMP-activated protein kinase (AMPK) and liver kinase B-1 (LKB-1) phosphorylation but decreased ATP levels. Significantly, KD of c-Met suppressed fat accumulation and triglyceride (TG) quantity and reduced the expression of C/EBP-α, PPAR-γ, FAS, ACC, and perilipin A. Collectively, the present results demonstrate that c-Met is a novel, highly conserved mediator of adipogenesis regulating lipid accumulation in murine adipocytes.

Xiaoyao San, a Chinese herbal formula, ameliorates depression-like behavior in mice through the AdipoR1/AMPK/ACC pathway in hypothalamus

OBJECTIVE

Depression and metabolic disorders have overlapping psychosocial and pathophysiological causes. Current research is focused on the possible role of adiponectin in regulating common biological mechanisms. Xiaoyao San (XYS), a classic Chinese medicine compound, has been widely used in the treatment of depression and can alleviate metabolic disorders such as lipid or glucose metabolism disorders. However, the ability of XYS to ameliorate depression-like behavior as well as metabolic dysfunction in mice and the underlying mechanisms are unclear.

METHODS

An in vivo animal model of depression was established by chronic social defeat stress (CSDS). XYS and fluoxetine were administered by gavage to the drug intervention group. Depression-like behaviors were analyzed by the social interaction test, open field test, forced swim test, and elevated plus maze test. Glucose levels were measured using the oral glucose tolerance test. The involvement of certain molecules was validated by immunofluorescence, histopathology, and Western blotting. In vitro, hypothalamic primary neurons were exposed to high glucose to induce neuronal damage, and the neuroprotective effect of XYS was evaluated by cell counting kit-8 assay. Immunofluorescence and Western blotting were used to evaluate the influences of XYS on adiponectin receptor 1 (AdipoR1), adenosine 5'-monophosphate-activated protein kinase (AMPK), acetyl-coenzyme A carboxylase (ACC) and other related proteins.

RESULTS

XYS ameliorated CSDS-induced depression-like behaviors and glucose tolerance impairment in mice and increased the level of serum adiponectin. XYS also restored Nissl bodies in hypothalamic neurons in mice that exhibited depression-like behaviors and decreased the degree of neuronal morphological damage. In vivo and in vitro studies indicated that XYS increased the expression of AdipoR1 in hypothalamic neurons.

CONCLUSION

Adiponectin may be a key regulator linking depression and metabolic disorders; regulation of the hypothalamic AdipoR1/AMPK/ACC pathway plays an important role in treatment of depression by XYS.

Balanced branched-chain amino acids modulate meat quality by adjusting muscle fiber type conversion and intramuscular fat deposition in finishing pigs

BACKGROUND

Pork is an important food for humans and improving the quality of pork is closely related to human health. This study was designed to investigate the effects of balanced branched-chain amino acid (BCAA)-supplemented protein-restricted diets on meat quality, muscle fiber types, and intramuscular fat (IMF) in finishing pigs.

RESULTS

The results showed that, compared with the normal protein diet (160 g kg-1 crude protein), the reduced-protein diet (120 g kg-1 crude protein) supplemented with BCAAs to the ratio of 2:1:2 not only had higher average daily gain (P < 0.05) and carcass weight (P < 0.05) but also improved meat tenderness and juiciness by decreasing shear force (P < 0.05) and increasing water-holding capacity (P < 0.05). In particular, this treatment showed higher (P < 0.05) levels of phospho-acetyl-CoA carboxylase (P-ACC) and peroxisome proliferation-activated receptor-γ (PPARγ), and lower (P < 0.05) levels of P-adenosine 5'-monophosphate (AMP)-activated protein kinase (P-AMPK), increasing the composition of IMF and MyHC I (P < 0.05) in the longissimus dorsi muscle (LDM). In terms of health, this group increased eicosapentaenoic acid (EPA) (P < 0.01) and desirable hypocholesterolemic fatty acids (DHFA) (P < 0.05), and decreased atherogenicity (AI) (P < 0.01) and hypercholesterolemic saturated fatty acids (HSFA) (P < 0.05).

CONCLUSION

Our findings suggest a novel role for a balanced BCAA-supplemented restricted protein (RP) diet in the epigenetic regulation of more tender and healthier pork by increasing IMF deposition and fiber type conversion, providing a cross-regulatory molecular basis for revealing the nutritional regulation network of meat quality. © 2021 Society of Chemical Industry.

Anti-adipogenic and Pro-lipolytic Effects on 3T3-L1 Preadipocytes by CX-4945, an Inhibitor of Casein Kinase 2

Casein kinase 2 (CK2) is a ubiquitously expressed serine/threonine kinase and is upregulated in human obesity. CX-4945 (Silmitasertib) is a CK2 inhibitor with anti-cancerous and anti-adipogenic activities. However, the anti-adipogenic and pro-lipolytic effects and the mode of action of CX-4945 in (pre)adipocytes remain elusive. Here, we explored the effects of CX-4945 on adipogenesis and lipolysis in differentiating and differentiated 3T3-L1 cells, a murine preadipocyte cell line. CX-4945 at 15 μM strongly reduced lipid droplet (LD) accumulation and triglyceride (TG) content in differentiating 3T3-L1 cells, indicating the drug’s anti-adipogenic effect. Mechanistically, CX-4945 reduced the expression levels of CCAAT/enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), and perilipin A in differentiating 3T3-L1 cells. Strikingly, CX-4945 further increased the phosphorylation levels of cAMP-activated protein kinase (AMPK) and liver kinase B-1 (LKB-1) while decreasing the intracellular ATP content in differentiating 3T3-L1 cells. In differentiated 3T3-L1 cells, CX-4945 had abilities to stimulate glycerol release and elevate the phosphorylation levels of hormone-sensitive lipase (HSL), pointing to the drug’s pro-lipolytic effect. In addition, CX-4945 induced the activation of extracellular signal-regulated kinase-1/2 (ERK-1/2), and PD98059, an inhibitor of ERK-1/2, attenuated the CX4945-induced glycerol release and HSL phosphorylation in differentiated 3T3-L1 cells, indicating the drug’s ERK-1/2-dependent lipolysis. In summary, this investigation shows that CX-4945 has strong anti-adipogenic and pro-lipolytic effects on differentiating and differentiated 3T3-L1 cells, mediated by control of the expression and phosphorylation levels of CK2, C/EBP-α, PPAR-γ, FAS, ACC, perilipin A, AMPK, LKB-1, ERK-1/2, and HSL.

Effects of age on subcutaneous adipose tissue proteins in Chinese indigenous Ningxiang pig by TMT-labeled quantitative proteomics

Adipose tissue not only affects meat quality and animal productivity, but also participates in inflammation and immunity. Ningxiang pig is famous for their excellent meat quality, disease resistance and tolerance of roughage. It is not yet well known how proteins in adipose tissue is dynamically regulated during the growth of Ningxiang pig. This report studies the proteomic changes in subcutaneous adipose tissue in Ningxiang pigs to gain a better understanding of the molecular mechanism of fat development during the growth period. By TMT-labeled quantitative proteomic analysis of subcutaneous adipose tissue of 9 purebred Ningxiang pigs of different ages, we identified 2533 unique proteins and 716 differentially abundant proteins (DAPs), of which more than half of the DAPs were concentrated in the 90d-210d period. Retrograde endocannabinoid signaling was only significantly enriched in DAPs of N90d vs N30d, Alcoholism and Graft-versus-host disease were only significantly enriched in DAPs of N210d vs N90d. Proteins related to dilated cardiomyopathy was found to be an important pathway in fat development and lipid metabolism. A variety of novel DAPs involved in maintaining mitochondrial function and cell viability, such as NDUFS6, SDHB, COX5A, ATP5D and TNNT1, which play a role in controlling the prediction networks, may indirectly regulate the development and functional maintenance of adipocytes. SIGNIFICANCE: These age-dependent DAPs discovered in this study may help expand the understanding of the molecular mechanisms of the development, function maintenance and transformation of adipose tissue in Ningxiang pig for developing new strategies for improving meat quality and pig breeding in the future.

LIPOSA pharmacopuncture, a new herbal formula, affects localized adiposity by regulating lipid metabolism in vivo

Localized adiposity is a serious aesthetic problem and a well-known health risk factor. There is a growing interest in minimally invasive treatment options for excessive fat accumulation, such as pharmacopuncture. LIPOSA is a newly developed pharmacopuncture formula from three natural herbs: The tuber of Pinellia ternata (Thunb.) Breitenb., the whole plant of Taraxacum platycarpum Dahlst. and the root of Astragalus membranaceus Bunge. The present study investigated the effects of pharmacopuncture treatment with LIPOSA on localized adiposity. Male C57BL/6J mice were fed high fat diet for 8 weeks to induce obesity. Then, 100 µl LIPOSA was injected into the left-side inguinal fat pad at various concentrations, including 13.35, 26.7 and 53.4 mg/ml. Normal saline was injected into the right-side inguinal fat pad of each mouse as a control. The treatment was performed three times per week for 2 weeks. The weight and histological changes were analyzed in the inguinal fat pad of the obese mice. The expression levels of adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), autophagy-related gene (ATG)5, ATG7 and LC3-II, as lipophagy-related factors, were evaluated to confirm the lipid-catabolic effects of LIPOSA. LIPOSA pharmacopuncture markedly decreased the weight of the fat tissue and the size of the adipocytes in the inguinal region of the mouse models of obesity in a dose-dependent manner. The expression levels of ATGL, HSL, ATG5, ATG7 and LC3-II were significantly increased by the LIPOSA treatments. In addition, LIPOSA pharmacopuncture was found to decrease the expression levels of ACC, PPAR-γ and PEPCK. The results indicated that subcutaneous injection of LIPOSA can degrade local fat and induce lipophagic and lipase activation effects. In addition, lipid metabolism related to fat accumulation was regulated by the LIPOSA treatment. The present study suggests that LIPOSA pharmacopuncture can be a non-surgical alternative in the treatment of localized adiposity.

The influence of thyroid state on hypothalamic AMP-activated protein kinase pathways in broilers

To investigate whether there are important interactions in play in broilers between thyroid hormones and the central regulation of energy homeostasis through AMP-activated protein kinase (AMPK), we induced a functional hyperthyroid and hypothyroid state in broiler chicks, and quantified systemic and hypothalamic AMPK related gene expression and related protein. Thyroid state was manipulated through dietary supplementation of triiodothyronine (T₃) or methimazole (MMI) for 7 days. A hypothalamic AMPK suppressor, 0.1% α-lipoic acid (α-LA) was used to assess the effects of the T₃ and MMI feed formulations on the AMPK pathways. Feed intake and body weight were reduced in both hypothyroid and hyperthyroid conditions. In hyperthyroid conditions (T₃ supplementation) expression of the AMPKα1 subunit increased, while in hypothyroid conditions (MMI supplementation) active phosphorylated AMPK levels in the hypothalamus dropped, but gene expression of the AMPKα1 and α2 subunit increased. For FAS and ACC (involved in fatty acid metabolism), and CRH, TRH and CNR1 (anorexigenic neuropeptides stimulating energy expenditure) there were indications that their regulation in response to thyroid state might be modulated through AMPK pathways. Our results indicate that the expression of hypothalamic AMPK as well as that of several other genes from AMPK pathways are involved in thyroid-hormone-induced changes in appetite, albeit differently according to thyroid state.

Different Proportions of Branched-Chain Amino Acids Modulate Lipid Metabolism in a Finishing Pig Model

This study aimed to investigate the effect of the supplementation of branched-chain amino acids (BCAAs) at different ratios in protein restriction diets on lipid metabolism in a finishing pig model. The BCAA supplementation (leucine/isoleucine/valine = 2:1:1 and 2:1:2) ameliorated the poor growth performance and carcass characteristics, particularly high fat mass caused by a protein-restricted diet. Serum adiponectin increased while leptin decreased in BCAA diets in comparison to the 12% CP group. BCAA supplementation also increased the low-protein expression of AMPK and SIRT1 caused by protein restriction. The mRNA and protein levels of peroxisome proliferation-activated receptor-γ (PPARγ) and acetyl-CoA carboxylase (ACC) were highest in the protein-restricted group and lowered in the 2:1:1 or 2:1:2 group. In conclusion, BCAAs supplemented in an adequate ratio range of 2:1:1 to 2:1:2 (2:1:2 is recommended) in reduced protein diets could modulate lipid metabolism by accelerating the secretion of adipokines and fatty acid oxidation.

Tissue-Specific Effects of Leptin on Glucose and Lipid Metabolism

The discovery of leptin was intrinsically associated with its ability to regulate body weight. However, the effects of leptin are more far-reaching and include profound glucose-lowering and anti-lipogenic effects, independent of leptin's regulation of body weight. Regulation of glucose metabolism by leptin is mediated both centrally and via peripheral tissues and is influenced by the activation status of insulin signaling pathways. Ectopic fat accumulation is diminished by both central and peripheral leptin, an effect that is beneficial in obesity-associated disorders. The magnitude of leptin action depends upon the tissue, sex, and context being examined. Peripheral tissues that are of particular relevance include the endocrine pancreas, liver, skeletal muscle, adipose tissues, immune cells, and the cardiovascular system. As a result of its potent metabolic activity, leptin is used to control hyperglycemia in patients with lipodystrophy and is being explored as an adjunct to insulin in patients with type 1 diabetes. To fully understand the role of leptin in physiology and to maximize its therapeutic potential, the mechanisms of leptin action in these tissues needs to be further explored.

Dietary dihydromyricetin supplementation enhances antioxidant capacity and improves lipid metabolism in finishing pigs

Nowadays, chronic diseases have become a potential danger to human health and are highly concerning. Given that pigs are a suitable animal model for human nutrition and metabolism for its similar anatomical and physiological properties to those of humans, this study has used 24 castrated male Duroc × Landrace × Yorkshire (DLY) pigs as experimental subjects to explore the effects of dietary dihydromyricetin (DHM) supplementation on the antioxidant capacity and lipid metabolism. Results showed that dietary 300 and 500 mg DHM kg-1 diet supplementation increased the serum total superoxide dismutase (T-SOD) level, serum and liver reduced glutathione (GSH), muscle catalase (CAT) level and serum high-density lipoprotein cholesterol (HDL-C) level, and reduced the liver malondialdehyde (MDA) level and muscle triglyceride (TG) level in finishing pigs. Western blot analysis showed that dietary DHM supplementation activated the nuclear-related factor 2 (Nrf2) and AMP-activated protein kinase (AMPK)/acetyl-CoA carboxylase (ACC) signals. Real-time quantitative PCR analysis showed that dietary DHM supplementation upregulated the mRNA levels of lipolysis and fatty acid oxidation-related genes, and down-regulated the mRNA expression of lipogenesis-related genes in finishing pigs. Together, we provide evidence that dietary DHM supplementation improved the antioxidant capacity and lipid metabolism in finishing pigs.

SIRT6 cooperates with SIRT5 to regulate bovine preadipocyte differentiation and lipid metabolism via the AMPKα signaling pathway

Preadipocyte differentiation and lipid synthesis are critical steps for intramuscular fat (IMF) deposition and lipid metabolism homeostasis. IMF content of beef not only determines the ratio of muscle to adipose, but also determines the beef quality, flavor, and sensory characteristics. Maintaining lipid metabolism homeostasis is the key means of preventing and treating diabetes, obesity, and other metabolic diseases. SIRT6, which is an ADP-ribosyltransferase and NAD⁺-dependent deacetylase of acetyl and long-chain fatty acyl groups, playing central roles in lipid and glucose metabolism, is closely related to the occurrence of diabetes and obesity caused by overnutrition and aging. This study was based on bovine preadipocyte differentiation and an obese mice model, and comprehensively used transcriptome sequencing (RNA-seq) and morphological identification methods to explore the effects of inhibition of SIRT6 on differentiation and lipid synthesis, and related molecular mechanisms. Additionally, the feedback synergistic regulation of SIRT5 and SIRT6 on differentiation and lipid deposition was analyzed. The results showed that in the differentiation process of bovine preadipocytes, inhibition of SIRT5 significantly promoted SIRT6 expression. In addition, SIRT6 inhibited bovine preadipocyte differentiation and lipid synthesis, cooperating with SIRT5 to decrease lipid deposition, and repressed cell cycle arrest of preadipocytes. Moreover, in vivo verification experiments also obtained consistent results. Furthermore, SIRT6 inhibited preadipocyte differentiation and lipid deposition by activating the adenosine monophosphate activated protein kinase alpha (AMPKα) pathway. The above results provided a novel approach for understanding the functions of SIRT6 in regulating bovine adipocyte differentiation and lipid metabolism, as well as a new target for the treatment of diabetes and obesity in a clinical setting.

Antihyperlipidemic Activity of Ligularia fischeri Extract in Mice Fed a High-Carbohydrate Diet

Ligularia fischeri, indigenous to eastern Asia, has been used as a traditional herbal medicine. Ligularia fischeri reportedly possesses a number of biological activities such as antimutagenic, antioxidant, antigenotoxic, and anti-inflammation. This study demonstrated the effects of ethanol extracts of Ligularia fischeri (ELF) on a high-carbohydrate diet (HCD)-induced hyperlipidemia in C57BL/6 mice. The mice were divided into six groups (n = 7/group) as follows: normal diet, HCD, or HCD+ELF (100, 200, 400, and 800 mg/kg/day), which were orally administered daily for 12 weeks. Various lipid parameters and histological changes in liver and fat tissue were compared among the treatment and control groups. ELF remarkably reduced body weight gain and attenuated hyperlipidemia by improving the plasma levels of total cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, atherogenic index, and cardiac risk factor. Moreover, ELF decreased the HCD-induced hepatic accumulation of lipid droplets and adipocyte hypertrophy. These regulatory effects of ELF appeared to be mediated through the phosphorylation of AMP-activated protein kinase, acetyl-CoA carboxylase, sterol regulatory element-binding protein-1c, and expression of fatty acid synthase. Taken together, these findings indicate a functional role for ELF in the regulation of HCD-induced obesity and hyperlipidemia.

Lycopene attenuates western-diet-induced cognitive deficits via improving glycolipid metabolism dysfunction and inflammatory responses in gut-liver-brain axis

BACKGROUND/OBJECTIVES

The aim of the current study was to investigate the inhibitory effect of lycopene (LYC), a major carotenoid present in tomato, on high-fat and high-fructose western diet (HFFD)-induced cognitive impairments and the protective effects on HFFD-elicited insulin resistance, lipid metabolism dysfunction and inflammatory responses in the gut-liver-brain axis.

SUBJECTS/METHODS

We randomly assigned 3-month-old C57BL/6 J mice to three groups with different diets: the control group, HFFD group and HFFD + LYC group (LYC, 0.03% w/w, mixed into high-fat diet) for 10 weeks.

RESULTS

The results of the Y-maze task and Morris water maze tests demonstrated that LYC attenuated HFFD-induced memory loss. Moreover, LYC suppressed HFFD-elicited synaptic dysfunction and increased the expressions of SNAP-25 and PSD-95. Furthermore, LYC ameliorated insulin resistance, lipid metabolism dysfunction and inflammatory responses in the mouse brain and liver. LYC also prevente.d intestinal barrier integrity damages and decreased the level of circulating LPS.

CONCLUSIONS

These results demonstrated that LYC ameliorated HFFD-induced cognitive impairments in a mouse model by improving insulin resistance, lipid metabolism dysfunction and inflammatory responses in the gut-liver-brain axis. These findings indicate that LYC might be a nutritional strategy for western diet-induced dysfunction of the central nervous system.

Lactobacillus acidophilus NS1 attenuates diet-induced obesity and fatty liver

Obesity is a major threat to public health, and it is strongly associated with insulin resistance and fatty liver disease. Here, we demonstrated that administration of Lactobacillus acidophilus NS1 (LNS1) significantly reduced obesity and hepatic lipid accumulation, with a concomitant improvement in insulin sensitivity, in high-fat diet (HFD)-fed mice. Furthermore, administration of LNS1 inhibited the effect of HFD feeding on the SREBP-1c and PPARα signaling pathways and reduced lipogenesis with an increase in fatty acid oxidation in ex vivo livers from HFD-fed mice. These LNS1 effects were confirmed in HepG2 cells and ex vivo livers by treatment with LNS1 culture supernatant (LNS1-CS). Interestingly, AMPK phosphorylation and activity in the liver of HFD-fed mice were increased by administration of LNS1. Consistently, chemical inhibition of AMPK with compound C, a specific inhibitor of AMPK, dramatically reduced the effect of LNS1-CS on lipid metabolism in HepG2 cells and ex vivo livers by modulating the SREBP-1c and PPARα signaling pathways. Furthermore, administration of LNS1 to HFD-fed mice significantly improved insulin resistance and increased Akt phosphorylation in the liver, white adipose tissue and skeletal muscle. Together, these data suggest that LNS1 may prevent diet-induced obesity and related metabolic disorders by improving lipid metabolism and insulin sensitivity through an AMPK→SREBP-1c/PPARα signaling pathway.

AZD1208, a pan-Pim kinase inhibitor, inhibits adipogenesis and induces lipolysis in 3T3-L1 adipocytes

The proviral integration moloney murine leukaemia virus (Pim) kinases, consisting of Pim-1, Pim-2 and Pim-3, are involved in the control of cell growth, metabolism and differentiation. Pim kinases are emerging as important mediators of adipocyte differentiation. AZD1208 is a pan-Pim kinase inhibitor and is known for its anti-cancer activity. In this study, we investigated the effect of AZD1208 on adipogenesis and lipolysis in 3T3-L1 cells, a murine preadipocyte cell line. AZD1208 markedly suppressed lipid accumulation and reduced triglyceride contents in differentiating 3T3-L1 cells, suggesting the drug's anti-adipogenic effect. On mechanistic levels, AZD1208 reduced not only the expressions of CCAAT/enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC) and perilipin A but also the phosphorylation of signal transducer and activator of transcription-3 (STAT-3) in differentiating 3T3-L1 cells. Remarkably, AZD1208 increased cAMP-activated protein kinase (AMPK) and LKB-1 phosphorylation while decreased intracellular ATP contents in differentiating 3T3-L1 cells. Furthermore, in differentiated 3T3-L1 adipocytes, AZD1208 also partially promoted lipolysis and enhanced the phosphorylation of hormone-sensitive lipase (HSL), a key lipolytic enzyme, indicating the drug's HSL-dependent lipolysis. In summary, the findings show that AZD1208 has anti-adipogenic and lipolytic effects on 3T3-L1 adipocytes. These effects are mediated by the expression and/or phosphorylation levels of C/EBP-α, PPAR-γ, FAS, ACC, perilipin A, STAT-3, AMPK and HSL.

Maternal Overweight Disrupts the Sexual Maturation of the Offspring

The aims of the present work were to study the effect of maternal overweight and obesity on the ovarian reserve, follicular development, and ovulation of the offspring and to assess whether this maternal condition alters oocyte integrity. To this end, female offspring from rats fed standard (OSD) or cafeteria (OCD) diet were used. Body weight, vaginal opening, and estrous cycle were recorded and ovaries were obtained on the day of the second estrus. In addition, ovarian weight, ovulation rate (measured by the number of oocytes within oviducts), follicular development (determined by histology), and oocyte integrity were examined. The OCD were divided into 2 groups: offspring from rats with 17% and 28% of overweight (OCD17 and OCD28, respectively). Both OCD groups showed higher body weight, but OCD28 also exhibited early vaginal opening and higher ovarian weight and glycemia at euthanasia compared with OSD. Both OCD17 and OCD28 had lower number of primordial and primary follicles, and only OCD28 exhibited lower number of antral follicles, all compared with OSD rats. In addition, both OCD17 and OCD28 had higher ovulation rate than controls, and OCD28 had lower number of healthy oocytes, which, in turn, exhibited morphological alterations such as larger perivitelline space and zona pellucida than those of control animals. These results suggest that maternal overweight may severely affect the reproductive ability of the offspring, likely as a result of altering the organogenesis.

Targeting AMPK for cancer prevention and treatment

AMP-activated protein kinase (AMPK) is an important mediator in maintaining cellular energy homeostasis. AMPK is activated in response to a shortage of energy. Once activated, AMPK can promote ATP production and regulate metabolic energy. AMPK is a known target for treating metabolic syndrome and type-2 diabetes; however, recently AMPK is emerging as a possible metabolic tumor suppressor and target for cancer prevention and treatment. Recent epidemiological studies indicate that treatment with metformin, an AMPK activator reduces the incidence of cancer. In this article we review the role of AMPK in regulating inflammation, metabolism, and other regulatory processes with an emphasis on cancer, as well as, discuss the potential for targeting AMPK to treat various types of cancer. Activation of AMPK has been found to oppose tumor progression in several cancer types and offers a promising cancer therapy. This review evaluates the evidence linking AMPK with tumor suppressor function and analyzes the molecular mechanisms involved. AMPK activity opposes tumor development and progression in part by regulating inflammation and metabolism.

Leptin regulates energy metabolism in MCF-7 breast cancer cells

Obesity is known to be a poorer prognosis factor for breast cancer in postmenopausal women. Among the diverse endocrine factors associated to obesity, leptin has received special attention since it promotes breast cancer cell growth and invasiveness, processes which force cells to adapt their metabolism to satisfy the increased demands of energy and biosynthetic intermediates. Taking this into account, our aim was to explore the effects of leptin in the metabolism of MCF-7 breast cancer cells. Polarographic analysis revealed that leptin increased oxygen consumption rate and cellular ATP levels were more dependent on mitochondrial oxidative metabolism in leptin-treated cells compared to the more glycolytic control cells. Experiments with selective inhibitors of glycolysis (2-DG), fatty acid oxidation (etomoxir) or aminoacid deprivation showed that ATP levels were more reliant on fatty acid oxidation. In agreement, levels of key proteins involved in lipid catabolism (FAT/CD36, CPT1, PPARα) and phosphorylation of the energy sensor AMPK were increased by leptin. Regarding glucose, cellular uptake was not affected by leptin, but lactate release was deeply repressed. Analysis of pyruvate dehydrogenase (PDH), lactate dehydrogenase (LDH) and pyruvate carboxylase (PC) together with the pentose-phosphate pathway enzyme glucose-6 phosphate dehydrogenase (G6PDH) revealed that leptin favors the use of glucose for biosynthesis. These results point towards a role of leptin in metabolic reprogramming, consisting of an enhanced use of glucose for biosynthesis and lipids for energy production. This metabolic adaptations induced by leptin may provide benefits for MCF-7 growth and give support to the reverse Warburg effect described in breast cancer.

Combination of deep sea water and Sesamum indicum leaf extract prevents high-fat diet-induced obesity through AMPK activation in visceral adipose tissue

The aim of the present study was to evaluate the protective effects of a combination of deep sea water (DSW) and Sesamum indicum leaf extract (SIE) against high-fat diet (HFD)-induced obesity and investigate its molecular mechanisms in adipose tissue. ICR mice were randomly divided into three groups: HFD control (HFC), DSW and DSW + 125 mg/kg SIE (DSS) groups. The mice in the HFC group had free access to drinking water while those in the DSW and DSS groups had free access to DSW. The mice in the DSS group were treated with SIE once per day for 8 weeks. The mice in all three groups were allowed to freely access a HFD. Compared with the HFC group, the DSS group showed lower body weight gain and serum levels of glucose, triglycerides and leptin. Histological analyses of the epididymal white, retroperitoneal white and scapular brown adipose tissue of mice in the DSS group revealed that the adipocytes were markedly decreased in size compared with those in the HFC group. Moreover, DSS significantly increased the levels of phosphorylated adenosine monophosphate-activated protein kinase (AMPK) and its substrate, acetyl-CoA carboxylase (ACC) in mice epididymal adipose tissues. Furthermore, DSS upregulated the expression levels of lipolysis-associated mRNA, specifically peroxisome proliferator-activated receptor-α (PPAR-α) and cluster of differentiation 36 (CD36), and energy expenditure-associated mRNA, namely uncoupling protein 2 (UCP2) and carnitine palmitoyltransferase-1 (CPT1) in the epididymal adipose tissues. By contrast, DSS suppressed the expression of the lipogenesis-related gene sterol regulatory element-binding protein-1 (SREBP1) at the mRNA level. These results suggest that DSS is effective for suppressing body weight gain and enhancing the lipid profile.

Obesity and cancer progression: is there a role of fatty acid metabolism?

Currently, there is renewed interest in elucidating the metabolic characteristics of cancer and how these characteristics may be exploited as therapeutic targets. Much attention has centered on glucose, glutamine and de novo lipogenesis, yet the metabolism of fatty acids that arise from extracellular, as well as intracellular, stores as triacylglycerol has received much less attention. This review focuses on the key pathways of fatty acid metabolism, including uptake, esterification, lipolysis, and mitochondrial oxidation, and how the regulators of these pathways are altered in cancer. Additionally, we discuss the potential link that fatty acid metabolism may serve between obesity and changes in cancer progression.

Dietary enrichment with fish oil prevents high fat-induced metabolic dysfunction in skeletal muscle in mice

High saturated fat (HF-S) diets increase intramyocellular lipid, an effect ameliorated by omega-3 fatty acids in vitro and in vivo, though little is known about sex- and muscle fiber type-specific effects. We compared effects of standard chow, HF-S, and 7.5% HF-S replaced with fish oil (HF-FO) diets on the metabolic profile and lipid metabolism gene and protein content in red (soleus) and white (extensor digitorum longus) muscles of male and female C57BL/6 mice (n = 9-12/group). Weight gain was similar in HF-S- and HF-FO-fed groups. HF-S feeding increased mesenteric fat mass and lipid marker, Oil Red O, in red and mixed muscle; HF-FO increased interscapular brown fat mass. Compared to chow, HF-S and HF-FO increased expression of genes regulating triacylglycerol synthesis and fatty acid transport, HF-S suppressed genes and proteins regulating fatty acid oxidation, whereas HF-FO increased oxidative genes, proteins and enzymes and lipolytic gene content, whilst suppressing lipogenic genes. In comparison to HF-S, HF-FO further increased fat transporters, markers of fatty acid oxidation and mitochondrial content, and reduced lipogenic genes. No diet-by-sex interactions were observed. Neither diet influenced fiber type composition. However, some interactions between muscle type and diet were observed. HF-S induced changes in triacylglycerol synthesis and lipogenic genes in red, but not white, muscle, and mitochondrial biogenesis and oxidative genes were suppressed by HF-S and increased by HF-FO in red muscle only. In conclusion, HF-S feeding promotes lipid storage in red muscle, an effect abrogated by the fish oil, which increases mediators of lipolysis, oxidation and thermogenesis while inhibiting lipogenic genes. Greater storage and synthesis, and lower oxidative genes in red, but not white, muscle likely contribute to lipid accretion encountered in red muscle. Despite several gender-dimorphic genes, both sexes exhibited a similar HF-S-induced metabolic and gene expression profile; likewise fish oil was similarly protective in both sexes.

Counterregulation of insulin by leptin as key component of autonomic regulation of body weight

A re-examination of the mechanism controlling eating, locomotion, and metabolism prompts formulation of a new explanatory model containing five features: a coordinating joint role of the (1) autonomic nervous system (ANS); (2) the suprachiasmatic (SCN) master clock in counterbalancing parasympathetic digestive and absorptive functions and feeding with sympathetic locomotor and thermogenic energy expenditure within a circadian framework; (3) interaction of the ANS/SCN command with brain substrates of reward encompassing dopaminergic projections to ventral striatum and limbic and cortical forebrain. These drive the nonhomeostatic feeding and locomotor motivated behaviors in interaction with circulating ghrelin and lateral hypothalamic neurons signaling through melanin concentrating hormone and orexin-hypocretin peptides; (4) counterregulation of insulin by leptin of both gastric and adipose tissue origin through: potentiation by leptin of cholecystokinin-mediated satiation, inhibition of insulin secretion, suppression of insulin lipogenesis by leptin lipolysis, and modulation of peripheral tissue and brain sensitivity to insulin action. Thus weight-loss induced hypoleptimia raises insulin sensitivity and promotes its parasympathetic anabolic actions while obesity-induced hyperleptinemia supresses insulin lipogenic action; and (5) inhibition by leptin of bone mineral accrual suggesting that leptin may contribute to the maintenance of stability of skeletal, lean-body, as well as adipose tissue masses.

Genistein stimulates fatty acid oxidation in a leptin receptor-independent manner through the JAK2-mediated phosphorylation and activation of AMPK in skeletal muscle

Obesity is a public health problem that contributes to the development of insulin resistance, which is associated with an excessive accumulation of lipids in skeletal muscle tissue. There is evidence that soy protein can decrease the ectopic accumulation of lipids and improves insulin sensitivity; however, it is unknown whether soy isoflavones, particularly genistein, can stimulate fatty acid oxidation in the skeletal muscle. Thus, we studied the mechanism by which genistein stimulates fatty acid oxidation in the skeletal muscle. We showed that genistein induced the expression of genes of fatty acid oxidation in the skeletal muscle of Zucker fa/fa rats and in leptin receptor (ObR)-silenced C2C12 myotubes through AMPK phosphorylation. Furthermore, the genistein-mediated AMPK phosphorylation occurred via JAK2, which was possibly activated through a mechanism that involved cAMP. Additionally, the genistein-mediated induction of fatty acid oxidation genes involved PGC1α and PPARδ. As a result, we observed that genistein increased fatty acid oxidation in both the control and silenced C2C12 myotubes, as well as a decrease in the RER in mice, suggesting that genistein can be used in strategies to decrease lipid accumulation in the skeletal muscle.

Effect of leptin treatment on mitochondrial function in obese leptin-deficient ob/ob mice

OBJECTIVE

Leptin stimulates peripheral lipid oxidation, but the influence on mitochondrial function is partly unknown. We investigated tissue-specific mitochondrial function in leptin-deficient obese C57BL/6J-ob/ob mice compared to lean littermates following leptin treatment.

MATERIALS AND METHODS

Lean and obese ob/ob mice were treated with saline or leptin for 5 days. At day six, liver, extensor digitorum longus (EDL) and soleus muscle were dissected and mitochondrial respiration analyzed in freshly dissected tissues. Expression of key proteins in the regulation of mitochondrial function was determined.

RESULTS

In liver, mitochondrial respiration was reduced in ob/ob mice compared to lean mice. Expression of mitochondrial transcription factor A (TFAM) was decreased in ob/ob mice, but increased with leptin treatment. In glycolytic EDL muscle, mitochondrial respiration was increased in ob/ob mice. Protein markers of complex II, IV and ATP synthase were increased in EDL muscle from both saline- and leptin-treated ob/ob mice. TFAM protein abundance was decreased, while dynamin-1-like protein was increased in EDL muscle from saline-treated ob/ob mice and restored by leptin treatment. In oxidative soleus muscle, mitochondrial respiration and electron transport system protein abundance were unchanged, while TFAM was reduced in ob/ob mice.

CONCLUSIONS

In conclusion, leptin-deficient ob/ob mice display tissue-specific mitochondrial adaptations under basal conditions and in response to leptin treatment. Mitochondrial respiration was decreased in liver, increased in glycolytic muscle and unaltered in oxidative muscle from ob/ob mice. Insight into the tissue-specific regulation of mitochondrial function in response to energy supply and demand may provide new opportunities for the treatment of insulin resistance.

Shizukaol D isolated from Chloranthus japonicas inhibits AMPK-dependent lipid content in hepatic cells by inducing mitochondrial dysfunction

This study is the first to demonstrate that shizukaol D, a natural compound isolated from Chloranthusjaponicus, can activate AMP- activated protein kinase (AMPK), a key sensor and regulator of intracellular energy metabolism, leading to a decrease in triglyceride and cholesterol levels in HepG2 cells. Furthermore, we found that shizukaol D induces mitochondrial dysfunction by depolarizing the mitochondrial membrane and suppressing energy production, which may result in AMPK activation. Our results provide a possible link between mitochondrial dysfunction and AMPK activation and suggest that shizukaol D might be used to treat metabolic syndrome.

Differential regulation of adipokines may influence migratory behavior in the white-throated sparrow (Zonotrichia albicollis)

White-throated sparrows increase fat deposits during pre-migratory periods and rely on these fat stores to fuel migration. Adipose tissue produces hormones and signaling factors in a rhythmic fashion and may be controlled by a clock in adipose tissue or driven by a master clock in the brain. The master clock may convey photoperiodic information from the environment to adipose tissue to facilitate pre-migratory fattening, and adipose tissue may, in turn, release adipokines to indicate the extent of fat energy stores. Here, we present evidence that a change in signal from the adipokines adiponectin and visfatin may act to indicate body condition, thereby influencing an individual's decision to commence migratory flight, or to delay until adequate fat stores are acquired. We quantified plasma adiponectin and visfatin levels across the day in captive birds held under constant photoperiod. The circadian profiles of plasma adiponectin in non-migrating birds were approximately inverse the profiles from migrating birds. Adiponectin levels were positively correlated to body fat, and body fat was inversely related to the appearance of nocturnal migratory restlessness. Visfatin levels were constant across the day and did not correlate with fat deposits; however, a reduction in plasma visfatin concentration occurred during the migratory period. The data suggest that a significant change in the biological control of adipokine expression exists between the two migratory conditions and we propose a role for adiponectin, visfatin and adipose clocks in the regulation of migratory behaviors.

Postprandial heat production in skeletal muscle is associated with altered mitochondrial function and altered futile calcium cycling

This study aimed to determine whether postprandial temperature excursions in skeletal muscle are consistent with thermogenesis or altered blood flow. Temperature probes were implanted into the vastus lateralis muscle of ovariectomized ewes, and blood flow was assessed using laser-Doppler flowmetry (tissue flow) and transit-time ultrasound flowmetry (femoral artery flow). The animals were program-fed between 1100 and 1600, and temperature and blood flow were measured during intravenous administration of either isoprenaline or phenylephrine and during feeding and meal anticipation. In addition, muscle biopsies were collected prefeeding and postfeeding to measure uncoupling protein (UCP) expression and mitochondrial function, as well as indices of calcium cycling (ryanodine 1 receptor: RyR1 and sarcoendoplasmic calcium-dependent ATPases SERCA1/ SERCA2a). Isoprenaline increased femoral artery blood flow, whereas phenylephrine reduced blood flow. At high doses only, isoprenaline treatment increased heat production in muscle. Phenylephrine treatment did not alter muscle temperature. Meal anticipation was evoked in fasted animals (previously program-fed) that were housed beside animals that were fed. Increases in muscle temperature were elicited by feeding and meal anticipation, without changes in blood flow during either paradigm. Analyses of respiration in isolated mitochondria indicated that the postprandial increase in heat production was associated with an increase in state 4 respiration, without increased UCP1, UCP2, or UCP3 expression. Feeding increased the expression of RyR1 and SERCA2a. We conclude that excursions in muscle temperature may occur independent of blood flow, suggesting that postprandial heat production is driven by altered mitochondrial function and changes in calcium cycling.

Central leptin activates mitochondrial function and increases heat production in skeletal muscle

Leptin acts on the brain to increase postprandial heat production in skeletal muscle of sheep. To determine a mechanism for this effect, we examined the role of mitochondrial uncoupling and AMP-activated protein kinase (AMPK). Ovariectomized ewes (n=4/group) received infusion lines into the lateral cerebral ventricle, and leptin (10 μg/h) was infused to increase heat production in skeletal muscle. In animals that were program fed (1100-1600 h), skeletal muscle biopsies were taken after either central infusion of leptin or vehicle to measure the expression of uncoupling protein (UCP) mRNA and the phosphorylation status of AMPK. Respiratory function was also quantified in mitochondria isolated from skeletal muscle. Leptin infusion increased the expression of UCP2 and UCP3 mRNA as well as UCP3 protein but not UCP1 mRNA in muscle. Leptin also increased substrate-driven, coupled (ADP-driven), and uncoupled (oligomycin) respiration but had no effect on the total respiratory capacity. The respiratory control ratio was lower in leptin-treated (vs. vehicle-treated) animals, indicating a predominant effect on uncoupled respiration. There was no effect of central leptin treatment on AMPK phosphorylation. We then infused 5-aminoimidazole-4-carboxamide-1β-riboside (AICAR) (10 mg/h for 6 h) directly into the femoral artery and measured skeletal muscle temperature; muscle was also collected for isolated mitochondria studies. AICAR had no effect on heat production or substrate-driven, uncoupled, or total respiratory states in skeletal muscle mitochondria. However, AICAR increased ADP-driven (coupled) respiration in mitochondria. In conclusion, leptin acts at the brain to increase heat production in muscle through altered mitochondrial function, indicative of adaptive thermogenesis.

Restoration of skeletal muscle leptin response does not precede the exercise-induced recovery of insulin-stimulated glucose uptake in high-fat-fed rats

Leptin administration increases fatty acid (FA) oxidation rates and decreases lipid storage in oxidative skeletal muscle, thereby improving insulin response. We have previously shown high-fat (HF) diets to rapidly induce skeletal muscle leptin resistance, prior to the disruption of normal muscle FA metabolism (increase in FA transport; accumulation of triacylglycerol, diacylglycerol, ceramide) that occurs in advance of impaired insulin signaling and glucose transport. All of this occurs within a 4-wk period. Conversely, exercise can rapidly improve insulin response, in as little as one exercise bout. Thus, if the early development of leptin resistance is a contributor to HF diet-induced insulin resistance (IR) in skeletal muscle, then it is logical to predict that the rapid restoration of insulin response by exercise training would be preceded by the recovery of leptin response. In the current study, we sought to determine 1) whether 1, 2, or 4 wk of exercise training was sufficient to restore leptin response in isolated soleus muscle of rats already consuming a HF diet (60% kcal), and 2) whether this preceded the training-induced corrections in FA metabolism and improved insulin-stimulated glucose transport. In the low-fat (LF)-fed control group, insulin increased glucose transport by 153% and leptin increased AMPK and ACC phosphorylation and the rate of palmitate oxidation (+73%). These responses to insulin and leptin were either severely blunted or absent following 4 wk of HF feeding. Exercise intervention decreased muscle ceramide content (-28%) and restored insulin-stimulated glucose transport to control levels within 1 wk; muscle leptin response (AMPK and ACC phosphorylation, FA oxidation) was also restored, but not until the 2-wk time point. In conclusion, endurance exercise training is able to restore leptin response, but this does not appear to be a necessary precursor for the restoration of insulin response.

Adiponectin activation of AMPK disrupts leptin-mediated hepatic fibrosis via suppressors of cytokine signaling (SOCS-3)

Adiponectin is an adipocytokine that was recently shown to be anti-fibrogenic in hepatic fibrosis. Leptin, on the other hand, promotes hepatic fibrosis. The purpose of the present study was to elucidate a mechanism (or mechanisms) whereby adiponectin dampens leptin signaling in activated hepatic stellate cells (HSCs), and prevents excess extracellular matrix production. Activated HSCs, between passages 2 and 5, were cultured and exposed to recombinant human adiponectin and recombinant leptin. Immunoblot analysis for SOCS-3, TIMP-1, and the phosphorylated species of Stat3 and adenosine monophosphate-activated protein kinase (AMPK) were conducted. We also examined MMP-1 activity by immunosorbant fluorimetric analysis. In HSCs, adiponectin-induced phosphorylation of AMPK, and subsequently suppressed leptin-mediated Stat3 phosphorylation and SOCS-3 induction. Adiponectin also blocked leptin-stimulated secretion of TIMP-1, and significantly increased MMP-1 activity, in vitro. To extend this study, we treated adiponectin knockout mice (Ad-/-) daily with 5 mg/kg recombinant leptin and/or carbon tetrachloride (2 ml/kg) for 6 weeks. Post-necropsy analysis was performed to examine for inflammation, and histological changes in the Ad-/- and wild-type mice. There was no significant difference in inflammation, or aminotransferases, between mice receiving carbon tetrachloride and leptin versus carbon tetrachloride alone. As anticipated, the combination of leptin and CCl(4) enhanced hepatic fibrosis in both wild-type and Ad-/- mice, as estimated by amount of collagen in injured livers, but wild-type mice had significantly higher levels of SOCS-3 and significantly lower levels of TIMP-1 mRNA and protein than did adiponectin KO mice exposed to both CCl(4) and leptin. We therefore conclude that the protective effects of adiponectin against liver fibrosis require AMPK activation, and may occur through inhibition of the Jak-Stat signal transduction pathway.

Regulation of lipid metabolism by energy availability: a role for the central nervous system

The central nervous system (CNS) is crucial in the regulation of energy homeostasis. Many neuroanatomical studies have shown that the white adipose tissue (WAT) is innervated by the sympathetic nervous system, which plays a critical role in adipocyte lipid metabolism. Therefore, there are currently numerous reports indicating that signals from the CNS control the amount of fat by modulating the storage or oxidation of fatty acids. Importantly, some CNS pathways regulate adipocyte metabolism independently of food intake, suggesting that some signals possess alternative mechanisms to regulate energy homeostasis. In this review, we mainly focus on how neuronal circuits within the hypothalamus, such as leptin- ghrelin-and resistin-responsive neurons, as well as melanocortins, neuropeptide Y, and the cannabinoid system exert their actions on lipid metabolism in peripheral tissues such as WAT, liver or muscle. Dissecting the complicated interactions between peripheral signals and neuronal circuits regulating lipid metabolism might open new avenues for the development of new therapies preventing and treating obesity and its associated cardiometabolic sequelae.

Positive regulatory control loop between gut leptin and intestinal GLUT2/GLUT5 transporters links to hepatic metabolic functions in rodents

Background and Aims

The small intestine is the major site of absorption of dietary sugars. The rate at which they enter and exit the intestine has a major effect on blood glucose homeostasis. In this study, we determine the effects of luminal leptin on activity/expression of GLUT2 and GLUT5 transporters in response to sugars intake and analyse their physiological consequences.

Methodology

Wistar rats, wild type and AMPKα₂^−/− mice were used. In vitro and in vivo isolated jejunal loops were used to quantify transport of fructose and galactose in the absence and the presence of leptin. The effects of fructose and galactose on gastric leptin release were determined. The effects of leptin given orally without or with fructose were determined on the expression of GLUT2/5, on some gluconeogenesis and lipogenic enzymes in the intestine and the liver.

Principal Findings

First, in vitro luminal leptin activating its receptors coupled to PKCβII and AMPKα, increased insertion of GLUT2/5 into the brush-border membrane leading to enhanced galactose and fructose transport. Second in vivo, oral fructose but not galactose induced in mice a rapid and potent release of gastric leptin in gastric juice without significant changes in plasma leptin levels. Moreover, leptin given orally at a dose reproducing comparable levels to those induced by fructose, stimulated GLUT5-fructose transport, and potentiated fructose-induced: i) increase in blood glucose and mRNA levels of key gluconeogenesis enzymes; ii) increase in blood triglycerides and reduction of mRNA levels of intestinal and hepatic Fasting-induced adipocyte factor (Fiaf) and iii) increase in SREBP-1c, ACC-1, FAS mRNA levels and dephosphorylation/activation of ACC-1 in liver.

Conclusion/Significance

These data identify for the first time a positive regulatory control loop between gut leptin and fructose in which fructose triggers release of gastric leptin which, in turn, up-regulates GLUT5 and concurrently modulates metabolic functions in the liver. This loop appears to be a new mechanism (possibly pathogenic) by which fructose consumption rapidly becomes highly lipogenic and deleterious.

Fatty acid metabolism: target for metabolic syndrome

Fatty acids are a major energy source and important constituents of membrane lipids, and they serve as cellular signaling molecules that play an important role in the etiology of the metabolic syndrome. Acetyl-CoA carboxylases 1 and 2 (ACC1 and ACC2) catalyze the synthesis of malonyl-CoA, the substrate for fatty acid synthesis and the regulator of fatty acid oxidation. They are highly regulated and play important roles in the energy metabolism of fatty acids in animals, including humans. They are presently considered as an attractive target to regulate the human diseases of obesity, diabetes, cancer, and cardiovascular complications. In this review we discuss the role of fatty acid metabolism and its key players, ACC1 and ACC2, in animal evolution and physiology, as related to health and disease.