Diet-induced obesity regulates the galanin-mediated signaling cascade in the adipose tissue of mice

Role of Spexin in White Adipose Tissue Thermogenesis under Basal and Cold-Stimulated Conditions

Spexin (SPX) is a novel adipokine that plays an emerging role in metabolic diseases due to its involvement in carbohydrate homeostasis, weight loss, appetite control, and gastrointestinal movement, among others. In obese patients, SPX plasma levels are reduced. Little is known about the relationship between SPX and white adipose tissue (WAT) thermogenesis. Therefore, the aim of the present study was to evaluate the role of SPX in this process. C57BL/6J male mice were treated or not with SPX for ten days. On day 3, mice were randomly divided into two groups: one kept at room temperature and the other kept at cold temperature (4 °C). Caloric intake and body weight were recorded daily. At the end of the protocol, plasma, abdominal (epididymal), subcutaneous (inguinal), and brown AT (EAT, IAT, and BAT, respectively) depots were collected for measurements. We found that SPX treatment reduced Uncoupling protein 1 levels in WAT under both basal and cold conditions. SPX also reduced cox8b and pgc1α mRNA levels and mitochondrial DNA, principally in IAT. SPX did not modulate the number of beige precursors. SPX decreased spx levels in IAT depots and galr2 in WAT depots. No differences were observed in the BAT depots. In conclusion, we showed, for the first time, that SPX treatment in vivo reduced the thermogenic process in subcutaneous and abdominal AT, being more evident under cold stimulation.

Exogenous GalR2-specific peptide agonist as a tool for treating myocardial ischemia/reperfusion injury

OBJECTIVES

The aim of this work was to elucidate the role of GalR2 receptor activation in protecting the rat heart in vivo from ischemia/reperfusion (I/R) damage by a pharmacological peptide agonist WTLNSAGYLLGPβAH-OH (G1) and full-length rat galanin GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2 (G2) using M871, a selective inhibitor of GalR2.

METHODS

The peptides were prepared by the automatic solid-phase synthesis using the Fmoc-strategy and purified by high-performance liquid chromatography (HPLC). A 40-min left anterior descending (LAD) coronary artery occlusion followed by a 60-min reperfusion was performed. The criteria for damage/protection of the heart were the infarct size (IS) and plasma activity of creatine kinase-MB (CK-MB) at the end of reperfusion.

RESULTS

Intravenous injection of G1 or G2 at an optimal dose of 1 mg/kg at the fifth minute of reperfusion significantly reduced the IS (by 35% and 32%, respectively) and activity of CK-MB at the end of reperfusion (by 43% and 38%, respectively) compared with the control. Administration of M871 (8 mg/kg) 5 min before the onset of reperfusion abolished the effects of G1 on IS and CK-MB activity, returning them to control values. Co-administration of M871 (8 mg/kg) with G2 attenuated protective effect of G2 on both IS and plasma СK-MB activity. However, differences in these parameters between the M871+G2 and G2 groups did not reach statistical significance (P = 0.139 and P = 0.121, respectively).

CONCLUSION

Thus, GalR2 is the principal receptor subtype that transduces the protective effects of galanin and ligand G1 in myocardial I/R injury. This suggests that GalR2-specific peptide agonists could be used as drug candidates for treating ischemic heart disease.

Spexin role in human granulosa cells physiology and PCOS: expression and negative impact on steroidogenesis and proliferation†

Spexin (SPX) is a novel neuropeptide and adipokine negatively correlated with obesity and insulin resistance. A recent study investigated expression and regulatory function of SPX in the hypothalamus and pituitary; however, the effect on ovarian function is still unknown. The aim of this study was to characterize the expression of SPX and its receptors, galanin receptors 2 and 3 (GALR2/3), in the human ovary and to study its in vitro effect on granulosa cells (GC) function. Follicular fluid (FF) and GC were obtained from normal weight and obese healthy and diagnosed with polycystic ovarian syndrome (PCOS) women. Expression of SPX and GALR2/3 in the ovary was studied by qPCR, western blot, and immunohistochemistry. The level of SPX in FF was assessed by enzyme-linked immunosorbent assay. The in vitro effect of recombinant human SPX on GC proliferation, steroidogenesis, and signaling pathways (MAP3/1, STAT3, AKT, PKA) was analyzed. Moreover, GC proliferation and estradiol (E2) secretion were measured with and without an siRNA against GALR2/3 and pharmacological inhibition of the above kinases. The results showed that both the SPX concentration in FF and its gene expression were decreased in GC of obese and PCOS women, while the protein expression of GALR2/3 was increased. We noted that SPX reduced GC proliferation and steroidogenesis; these effects were mediated by GALR2/3 and kinases MAP3/1, AKT, and STAT3 for proliferation or kinases MAP3/1 and PKA for E2 secretion. The obtained data clearly documented that SPX is a novel regulator of human ovarian physiology and possibly plays a role in PCOS pathogenesis.

Spexin-based galanin receptor 2 agonist improves renal injury in mice with type 2 diabetes

The spexin-based GALR2 agonist (NS200) is a novel drug, which has shown antidepressant and anxiolytic action in a recent experimental study. In this study, we investigated the effects of NS200 on renal injury in an animal model of type 2 diabetes. Eight-week-old diabetic db/db mice were administered NS200 for 12 weeks. NS200 was intraperitoneally administered at a dose of 1.0 mg/kg/day. Metabolic parameters and structural and molecular changes in the kidneys were compared among the three groups: non-diabetic db/m control, db/db mice, and NS200-treated db/db mice. In db/db mice, NS200 administration did not impact the body weight, food and water intake, urinary volume, fasting blood glucose level, or HbA1c levels. Insulin and glucose tolerance were also unaffected by NS200 treatment. However, NS200 improved urinary albumin excretion and glomerulosclerosis in diabetic kidneys. Activation of TGFβ1 and insulin signaling pathways, such as PI3 K /AKT/ERK, were inhibited by NS200. In conclusion, a spexin-based GALR2 agonist attenuated diabetic nephropathy by alleviating renal fibrosis in mice with type 2 diabetes. Spexin-based GALR2 agonists have considerable potential as novel treatment agents in diabetic nephropathy.

Neuroendocrine and neuroimmune mechanisms underlying comorbidity of pain and obesity

Pain and obesity, as well as their associated impairments, are major health concerns. Understanding the relationship between the two is the focus of a growing body of research. However, early researches attribute increased mechanical stress from excessive weight as the main factor of obesity-related pain, which not only over-simplify the association, but also fail to explain some controversial outcomes arising from clinical investigations. This review focuses on neuroendocrine and neuroimmune modulators importantly involved in both pain and obesity, analyzing nociceptive and anti-nociceptive mechanisms based on neuroendocrine pathways including galanin, ghrelin, leptin and their interactions with other neuropeptides and hormone systems which have been reported to play roles in pain and obesity. Mechanisms of immune activities and metabolic alterations are also discussed, due to their intense interactions with neuroendocrine system and crucial roles in the development and maintenance of inflammatory and neuropathic pain. These findings have implications for health given rising rates of obesity and pain-related diagnoses, by providing novel weight-control and analgesic therapies targeted on specific pathways.

Genome-wide association studies for additive and dominance effects for body composition traits in commercial crossbred Piétrain pigs

Fat depth (FD) and muscle depth (MD) are economically important traits and used to estimate carcass lean content (LMP), which is one of the main breeding objectives in pig breeding programmes. We assessed the genetic architectures of body composition traits for additive and dominance effects in commercial crossbred Piétrain pigs using both 50 K array and sequence genotypes. We first performed a genome-wide association study (GWAS) using single-marker association analysis with a false discovery rate of 0.1. Then, we estimated the additive and dominance effects of the most significant variant in the quantitative trait loci (QTL) regions. It was investigated whether the use of whole-genome sequence (WGS) will improve the QTL detection (both additive and dominance) with a higher power compared with lower density SNP arrays. Our results showed that more QTL regions were detected by WGS compared with 50 K array (n = 54 vs. n = 17). Of the novel associated regions associated with FD and LMP and detected by WGS, the most pronounced peak was on SSC13, situated at ~116-118, 121-127 and 129-134 Mbp. Additionally, we found that only additive effects contributed to the genetic architecture of the analysed traits and no significant dominance effects were found for the tested SNPs at QTL regions, regardless of panel density. The associated SNPs are located in or near several relevant candidate genes. Of these genes, GABRR2, GALR1, RNGTT, CDH20 and MC4R have been previously reported as being associated with fat deposition traits. However, the genes on SSC1 (ZNF292, ORC3, CNR1, SRSF12, MDN1, TSHZ1, RELCH and RNF152) and SSC18 (TTC26 and KIAA1549) have not been reported previously to our best knowledge. Our current findings provide insights into the genomic regions influencing composition traits in Piétrain pigs.

Spexin modulates molecular thermogenic profile of adipose tissue and thermoregulatory behaviors in female C57BL/6 mice

Thermoregulation is the physiological process by which an animal regulates body temperature in response to its environment. It is known that galanin, a neuropeptide widely distributed throughout the central nervous system and secreted by the gut, plays a role in thermoregulatory behaviors and metabolism. We tested the ability of the novel neuropeptide spexin, which shares sequence homology to galanin, to regulate these functions in female mice. Supraphysiological levels of spexin in C57BL/6 mice did not lead to weight loss after 50 days of treatment. Behavioral analysis of long-term spexin treatment showed it decreased anxiety and increased thermoregulatory nest building, which was not observed when mice were housed at thermoneutral temperatures. Treatment also disrupted the thermogenic profile of brown and white adipose tissue, decreasing mRNA expression of Ucp1 in BAT and immunodetection of β3-adrenergic receptors in gWAT. Our results reveal novel functions for spexin as a modulator of thermoregulatory behaviors and adipose tissue metabolism.

Neuropeptidergic Control of Feeding: Focus on the Galanin Family of Peptides

Obesity/overweight are important health problems due to metabolic complications. Dysregulation of peptides exerting orexigenic/anorexigenic effects must be investigated in-depth to understand the mechanisms involved in feeding behaviour. One of the most important and studied orexigenic peptides is galanin (GAL). The aim of this review is to update the mechanisms of action and physiological roles played by the GAL family of peptides (GAL, GAL-like peptide, GAL message-associated peptide, alarin) in the control of food intake and to review the involvement of these peptides in metabolic diseases and food intake disorders in experimental animal models and humans. The interaction between GAL and NPY in feeding and energy metabolism, the relationships between GAL and other substances involved in food intake mechanisms, the potential pharmacological strategies to treat food intake disorders and obesity and the possible clinical applications will be mentioned and discussed. Some research lines are suggested to be developed in the future, such as studies focused on GAL receptor/neuropeptide Y Y₁ receptor interactions in hypothalamic and extra-hypothalamic nuclei and sexual differences regarding the expression of GAL in feeding behaviour. It is also important to study the possible GAL resistance in obese individuals to better understand the molecular mechanisms by which GAL regulates insulin/glucose metabolism. GAL does not exert a pivotal role in weight regulation and food intake, but this role is crucial in fat intake and also exerts an important action by regulating the activity of other key compounds under conditions of stress/altered diet.

An assembly of galanin-galanin receptor signaling network

The galanin receptor family of proteins is present throughout the central nervous system and endocrine system. It comprises of three subtypes-GalR1, GalR2, and GalR3; all of which are G-protein-coupled receptors. Galanin predominantly acts as an inhibitory, hyper-polarizing neuromodulator, which has several physiological as well as pathological functions. Galanin has a role in mediating food intake, memory, sexual behavior, nociception and is also associated with diseases such as Alzheimer's disease, epilepsy, diabetes mellitus, and chronic pain. However, the understanding of signaling mechanisms of the galanin family of neuropeptides is limited and an organized pathway map is not yet available. Therefore, a detailed literature mining of the publicly available articles pertaining to the galanin receptor was followed by manual curation of the reactions and their integration into a map. This resulted in the cataloging of molecular reactions involving 64 molecules into five categories such as molecular association, activation/inhibition, catalysis, transport, and gene regulation. For enabling easy access of biomedical researchers, the galanin-galanin receptor signaling pathway data was uploaded to WikiPathways ( https://www.wikipathways.org/index.php/Pathway:WP4970 ), a freely available database of biological pathways.

Identification of strong candidate genes for backfat and intramuscular fatty acid composition in three crosses based on the Iberian pig

Meat quality has an important genetic component and can be modified by the fatty acid (FA) composition and the amount of fat contained in adipose tissue and muscle. The present study aimed to find genomic regions associated with the FA composition in backfat and muscle (longissimus dorsi) in 439 pigs with three different genetic backgrounds but having the Iberian breed in common. Genome-wide association studies (GWAS) were performed between 38,424 single-nucleotide polymorphisms (SNPs) covering the pig genome and 60 phenotypic traits related to backfat and muscle FA composition. Nine significant associated regions were found in backfat on the Sus scrofa chromosomes (SSC): SSC1, SSC2, SSC4, SSC6, SSC8, SSC10, SSC12, and SSC16. For the intramuscular fat, six significant associated regions were identified on SSC4, SSC13, SSC14, and SSC17. A total of 52 candidate genes were proposed to explain the variation in backfat and muscle FA composition traits. GWAS were also reanalysed including SNPs on five candidate genes (ELOVL6, ELOVL7, FADS2, FASN, and SCD). Regions and molecular markers described in our study may be useful for meat quality selection of commercial pig breeds, although several polymorphisms were breed-specific, and further analysis would be needed to evaluate possible causal mutations.

"Spexin improves adipose tissue inflammation and macrophage recruitment in obese mice"

Spexin (SPX) is a novel adipokine related to many metabolic effects, such as gastrointestinal movements, insulin and glucose homeostasis, lipid metabolism and energy balance. This study evaluates the role of SPX in the improvement of the metabolic and inflammatory profile in fructose-rich-diet obese mice. Adult Swiss mice were supplemented or not with fructose (20% in tap water, FRD and CTR, respectively) for 10 weeks. The last ten days, mice were treated or not with SPX (ip. 29 μg/Kg/day, FRD-SPX and CTR-SPX, respectively). A positive correlation was observed between body weight prior to treatment and weight loss after SPX challenge. Moreover, plasma and liver triglycerides and adipose tissue (AT) features (mass, adipocyte hypertrophy, mRNA of leptin) were improved. SPX also induced a reduction in epididymal AT (EAT) expression of TNFα, IL1β and IL6 and an improvement in IL10 and CD206. M1 macrophages in EAT, principally the Ly6C^- populations (M1a and M1b), were decreased. Adipocytes from FRD-SPX mice induced less macrophage activation (IL6, mRNA and secretion) than FRD after overnight co-culture with the monocyte cell line (RAW264.7) in stimulated conditions (M1 activation, LPS 100 ng/mL). Finally, in vitro, monocytes pre-incubated with SPX and stimulated with LPS showed decreased inflammatory mRNA markers compared to monocytes with LPS alone. In conclusion, SPX decreased body weight and improved the metabolic profile and adipocyte hypertrophy. Inflammatory Ly6C^- macrophages decreased, together with inflammatory marker expression. In vitro studies demonstrate that SPX induced a decrease in M1 macrophage polarization directly or through mature adipocytes.

Galanin receptors activation modulates myocardial metabolic and antioxidant responses to ischaemia/reperfusion stress

The mechanisms of protective action of the neuropeptide galanin and its N-terminal fragments against myocardial ischaemia/reperfusion (I/R) injury remain obscure. The aim of this work was to study effects of a novel peptide agonist of galanin receptors [βAla14, His15]-galanin (2-15) (G1) and the full-length galanin (G2) on energy and antioxidant status of the heart with acute infarction. The peptides were synthesized by the automatic solid phase method using Fmoc technology. Their structure was identified by ¹ H-NMR spectroscopy and MALDI-TOF mass spectrometry. Experiments were performed on anaesthetized open-chest rats subjected to myocardial regional ischaemia and reperfusion. Intravenous (iv) administration of optimal doses of peptides G1 and G2 (1.0 and 0.5 mg/kg, respectively, at the onset of reperfusion significantly reduced infarct size (on average by 40% compared with control) and the plasma activity of creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH). These effects were associated with augmented preservation of aerobic energy metabolism, increased activity of Cu,Zn superoxide dismutase (Cu,Zn-SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) and decreased lipid peroxidation in the area at risk (AAR) at the end of reperfusion. Peptide G1 showed more efficient recovery of the majority of metabolic and antioxidant parameters. The results provide evidence that the galaninergic system can be considered a promising target to reduce energy dysregulation and oxidative damage in myocardial I/R injury.

Protective Effects of a Novel Agonist of Galanin Receptors Against Doxorubicin-Induced Cardiotoxicity in Rats

The clinical use of antineoplastic agent doxorubicin (DOX) is limited due to its cardiotoxic action. [βAla14, His15]-galanine (2-15) (G) is a novel synthetic agonist of galanin receptors GalR1-3 having cardioprotective properties in animal models in vivo. The aim of the present study was to explore effects of G on DOX-induced cardiotoxicity. Wistar rats were divided into four groups and treated with DOX (D group), DOX and G (D + G group), G (G group), and saline (control). Before treatment and at the end of the study, concentration of thiobarbituric acid reactive substances (TBARS) and activity of creatine kinase-MB (CK-MB) were determined in blood plasma, the animals were weighed, and cardiac function was evaluated by echocardiography. At the end of experiments, the hearts were used to determine energy metabolites and mitochondrial respiration in permeabilized fibers. After an 8-week study, D group exhibited a pronounced cardiac failure, the absence of weight gain, an increased plasma TBARS concentration, and CK-MB activity. These disorders were accompanied by a reduced myocardial content of high-energy phosphates and mitochondrial respiratory parameters. Co-administration of G with DOX significantly decreased plasma TBARS level and prevented an increase in plasma CK-MB activity. In D + G group, myocardial contents of ATP, PCr, total adenine nucleotides, and total creatine as well as myocardial PCr/ATP ratio and the respiratory control index were higher than in D group at the end of the experiments. Peptide G significantly improved parameters of left ventricular (LV) function and caused weight gain in animals of D + G group. These results suggest that peptide G may be a potential pharmacological agent that attenuates the cardiotoxic effects of DOX.

Galanin and its N-terminal fragments reduce acute myocardial infarction in rats

Agonists and antagonists for galanin receptor subtypes GalR1-3 can be used as putative therapeutics targets for the treatment of various human diseases. However, effects of galanin and its N-terminal fragments on myocardial ischemia/reperfusion injury remain unclear. This study was designed to assess the ability of the full-length galanin (GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2, G1), the natural fragments WTLNSAGYLL-NH2 (G2) and WTLNSAGYLLGPHA (G3), and their modified analogs WTLNAAGYLL (G4) and WTLNSAGYLLGPβAH (G5) to limit acute myocardial infarction in rats in vivo. The peptides G2-5 were synthesized by the automatic solid phase method using Fmoc technology, purified by preparative HPLC and identified by 1H NMR spectroscopy and MALDI -TOF mass spectrometry. The peptides G1-5 were administered by i.v. bolus injection at the onset of reperfusion at doses of 0.25, 0.50, 1.0, 2.0 or 3.0 mg/kg. The optimal doses of the peptides G1-5 significantly reduced the infarction area and decreased the activity of CK-MB and LDH in blood plasma at the end of reperfusion compared with the control. Among the peptides studied, G5 showed high efficacy in reducing the infarct size and the activity of necrosis markers in blood plasma with no significant effect on hemodynamic parameters. The results suggest that a novel agonist for galanin receptors G5 may be a promising tool for the treatment of myocardial ischemia/reperfusion (I/R) injury. Further studies are warranted to explore the stability of this peptide in blood plasma and mechanisms that contribute to its cardioprotective effects.

Galanin/GalR1-3 system: A promising therapeutic target for myocardial ischemia/reperfusion injury

N-terminal fragments of galanin (2-11) and (2-15) are critical for binding to GalR1-3 receptors, members of the G-protein-coupled receptor superfamily, and are involved in myocardial protection against ischemia/reperfusion (I/R) injury. This study was designed to synthesize novel GalR1-3 agonists with improved properties and evaluate their efficiency as cardioprotective agents. Peptide agonists were synthesized by the automatic solid phase method using Fmoc technology and purified by preparative HPLC. Their chemical structure was identified by ¹H-NMR spectroscopy and MALDI-TOF mass spectrometry. Novel ligands of galanin receptors have greater solubility in water than natural galanin fragments. Cardiac function indices, myocardial infarct size and plasma activity of creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) were measured to assess the peptide bioactivity. Infusion of optimal concentrations of the peptides (210-240 μM) after global ischemia enhanced functional recovery of isolated rat heart during reperfusion. Intravenous administration of the peptides in a dose range of 1-2 mg/kg at the onset of reperfusion significantly reduced infarct size and plasma levels of CK-MB and LDH in rats in vivo. The chimeric ligand [βAla14, His15]-galanin (2-15) exhibited the most beneficial effect on both models of I/R injury. The results suggest that pharmacological agonists of GalR1-3 receptors can be a rational basis for drug developments in the field of cardiovascular diseases.

Cardioprotective properties of N-terminal galanin fragment (2-15) in experimental ischemia/reperfusion injury

Background and purpose

Galanin is an endogenous peptide involved in diverse physiological functions in the central nervous system including central cardiovascular regulation. The present study was designed to evaluate the potential effects of the short N-terminal galanin fragment 2-15 (G) on cardiac ischemia/reperfusion (I/R) injury.

Experimental Approach

Peptide G was synthesized by the automatic solid phase method and identified by 1H-NMR spectroscopy and mass spectrometry. Experiments were performed on cultured rat cardiomyoblast (H9C2) cells, isolated perfused working rat hearts and anaesthetized open-chest rats.

Key Results

Cell viability increased significantly after treatment with 10 and 50 nM of G peptide. In hypoxia and reoxygenation conditions, exposure of H9C2 cells to G peptide decreased cell apoptosis and mitochondrial reactive oxygen species (ROS) production. Postischemic infusion of G peptide reduced cell membrane damage and improved functional recovery in isolated hearts during reperfusion. These effects were accompanied by enhanced restoration of myocardial metabolic state. Treatment with G peptide at the onset of reperfusion induced minor changes in hemodynamic variables but significantly reduced infarct size and plasma levels of necrosis markers.

Conclusion and implications

These findings suggest that G peptide is effective in mitigating cardiac I/R injury, thereby providing a rationale for promising tool for the treatment of cardiovascular diseases.

Adipose tissue dysfunction as a central mechanism leading to dysmetabolic obesity triggered by chronic exposure to p,p'-DDE

Endocrine-disrupting chemicals such as p,p’-dichlorodiphenyldichloroethylene (p,p’-DDE), are bioaccumulated in the adipose tissue (AT) and have been implicated in the obesity and diabetes epidemic. Thus, it is hypothesized that p,p’-DDE exposure could aggravate the harm of an obesogenic context. We explored the effects of 12 weeks exposure in male Wistar rats’ metabolism and AT biology, assessing a range of metabolic, biochemical and histological parameters. p,p’-DDE -treatment exacerbated several of the metabolic syndrome-accompanying features induced by high-fat diet (HF), such as dyslipidaemia, glucose intolerance and hypertension. A transcriptome analysis comparing mesenteric visceral AT (vAT) of HF and HF/DDE groups revealed a decrease in expression of nervous system and tissue development-related genes, with special relevance for the neuropeptide galanin that also revealed DNA methylation changes at its promoter region. Additionally, we observed an increase in transcription of dipeptidylpeptidase 4, as well as a plasmatic increase of the pro-inflammatory cytokine IL-1β. Our results suggest that p,p’-DDE impairs vAT normal function and effectively decreases the dynamic response to energy surplus. We conclude that p,p’-DDE does not merely accumulate in fat, but may contribute significantly to the development of metabolic dysfunction and inflammation. Our findings reinforce their recognition as metabolism disrupting chemicals, even in non-obesogenic contexts.

Gene expression modulation of lipid and central energetic metabolism related genes by high-fat diet intake in the main homeostatic tissues

HF diet feeding affects the energy balance by transcriptional metabolic adaptations, based in direct gene expression modulation, perinatal programing and transcriptional factor regulation, which could be affected by the animal model, gender or period of dietary treatment.

Influencing Factors of Thermogenic Adipose Tissue Activity

Obesity is an escalating public health challenge and contributes tremendously to the disease burden globally. New therapeutic strategies are required to alleviate the health impact of obesity-related metabolic dysfunction. Brown adipose tissue (BAT) is specialized for dissipating chemical energy for thermogenesis as a defense against cold environment. Intriguingly, the brown-fat like adipocytes that dispersed throughout white adipose tissue (WAT) in rodents and humans, called "brite" or "beige" adipocytes, share similar thermogenic characteristics to brown adipocytes. Recently, researchers have focused on cognition of these thermogenic adipose tissues. Some factors have been identified to regulate the development and function of thermogenic adipose tissues. Cold exposure, pharmacological conditions, and lifestyle can enhance non-shivering thermogenesis and metabolism via some mechanisms. However, environmental pollutants, such as ambient fine particulates and ozone, may impair the function of these thermogenic adipose tissues and thereby induce metabolic dysfunction. In this review, the origin, function and influencing factors of thermogenic adipose tissues were summarized and it will provide insights into identifying new therapeutic strategies for the treatment of obesity and obesity-related diseases.

Central Administration of Galanin Receptor 1 Agonist Boosted Insulin Sensitivity in Adipose Cells of Diabetic Rats

Our previous studies testified the beneficial effect of central galanin on insulin sensitivity of type 2 diabetic rats. The aim of the study was further to investigate whether central M617, a galanin receptor 1 agonist, can benefit insulin sensitivity. The effects of intracerebroventricular administration of M617 on insulin sensitivity and insulin signaling were evaluated in adipose tissues of type 2 diabetic rats. The results showed that central injection of M617 significantly increased plasma adiponectin contents, glucose infusion rates in hyperinsulinemic-euglycemic clamp tests, GLUT4 mRNA expression levels, GLUT4 contents in plasma membranes, and total cell membranes of the adipose cells but reduced the plasma C-reactive protein concentration in nondiabetic and diabetic rats. The ratios of GLUT4 contents were higher in plasma membranes to total cell membranes in both nondiabetic and diabetic M617 groups than each control. In addition, the central administration of M617 enhanced the ratios of pAkt/Akt and pAS160/AS160, but not phosphorylative cAMP response element-binding protein (pCREB)/CREB in the adipose cells of nondiabetic and diabetic rats. These results suggest that excitation of central galanin receptor 1 facilitates insulin sensitivity via activation of the Akt/AS160 signaling pathway in the fat cells of type 2 diabetic rats.

The generation of knock-in mice expressing fluorescently tagged galanin receptors 1 and 2

The neuropeptide galanin has diverse roles in the central and peripheral nervous systems, by activating the G protein-coupled receptors Gal1, Gal2 and the less studied Gal3 (GalR1-3 gene products). There is a wealth of data on expression of Gal1-3 at the mRNA level, but not at the protein level due to the lack of specificity of currently available antibodies. Here we report the generation of knock-in mice expressing Gal1 or Gal2 receptor fluorescently tagged at the C-terminus with, respectively, mCherry or hrGFP (humanized Renilla green fluorescent protein). In dorsal root ganglia (DRG) neurons expressing the highest levels of Gal1-mCherry, localization to the somatic cell membrane was detected by live-cell fluorescence and immunohistochemistry, and that fluorescence decreased upon addition of galanin. In spinal cord, abundant Gal1-mCherry immunoreactive processes were detected in the superficial layers of the dorsal horn, and highly expressing intrinsic neurons of the lamina III/IV border showed both somatic cell membrane localization and outward transport of receptor from the cell body, detected as puncta within cell processes. In brain, high levels of Gal1-mCherry immunofluorescence were detected within thalamus, hypothalamus and amygdala, with a high density of nerve endings in the external zone of the median eminence, and regions with lesser immunoreactivity included the dorsal raphe nucleus. Gal2-hrGFP mRNA was detected in DRG, but live-cell fluorescence was at the limits of detection, drawing attention to both the much lower mRNA expression than to Gal1 in mice and the previously unrecognized potential for translational control by upstream open reading frames (uORFs).

The regulative effect of galanin family members on link of energy metabolism and reproduction

It is essential for the species survival that an efficient coordination between energy storage and reproduction through endocrine regulation. The neuropeptide galanin, one of the endocrine hormones, can potently coordinate energy metabolism and the activities of hypothalamic-pituitary-gonadal reproductive axis to adjust synthesis and release of metabolic and reproductive hormones in animals and humans. However, few papers have summarized the regulative effect of the galanin family members on the link of energy storage and reproduction as yet. To address this issue, this review attempts to summarize the current information available about the regulative effect of galanin, galanin-like peptide and alarin on the metabolic and reproductive events, with special emphasis on the interactions between galanin and hypothalamic gonadotropin-releasing hormone, pituitary luteinizing hormone and ovarian hormones. This research line will further deepen our understanding of the physiological roles of the galanin family in regulating the link of energy metabolism and reproduction.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.

Oleuropein attenuates visceral adiposity in high-fat diet-induced obese mice through the modulation of WNT10b- and galanin-mediated signalings

SCOPE

The aim of the present study was to investigate the antiobesity effect of oleuropein on high-fat diet (HFD) induced body weight gain and visceral adiposity in mice, and to explore the underlying mechanisms involved.

METHODS AND RESULTS

C57BL/6N mice were fed with a normal diet, HFD (40% fat of total energy), and HFD-supplemented with 0.03% oleuropein for 10 wk. Oleuropein significantly reduced HFD-induced body weight gain and visceral adiposity. Oleuropein also significantly reversed the HFD-induced elevations of adipogenic related gene expression involved in WNT10b- and galanin-mediated signalings in adipose tissue of mice. Consistent with in vivo findings, oleuropein dose-dependently suppressed lipid accumulation in 3T3-L1 cells during preadipocyte differentiation. Additionally, exposure of the 3T3-L1 preadipocytes to oleuropein resulted in a marked attenuation of the secreted frizzled-related protein 2 (WNT inhibitor) or galnon (galanin receptor agonist) induced cellular lipid accumulation.

CONCLUSION

This study demonstrated the oleuropein-reduced body weight gain and visceral adiposity in HFD-fed mice. The protective effect of oleuropein against HFD-induced adiposity in mice appeared to be mediated through the upregulation of genes involved in WNT10b-mediated signaling and downregulation of genes involved in galanin-mediated signaling cascades.

Decaffeinated green coffee bean extract attenuates diet-induced obesity and insulin resistance in mice

This study investigated whether decaffeinated green coffee bean extract prevents obesity and improves insulin resistance and elucidated its mechanism of action. Male C57BL/6N mice (N = 48) were divided into six dietary groups: chow diet, HFD, HFD-supplemented with 0.1%, 0.3%, and 0.9% decaffeinated green coffee bean extract, and 0.15% 5-caffeoylquinic acid. Based on the reduction in HFD-induced body weight gain and increments in plasma lipids, glucose, and insulin levels, the minimum effective dose of green coffee bean extract appears to be 0.3%. Green coffee bean extract resulted in downregulation of genes involved in WNT10b- and galanin-mediated adipogenesis and TLR4-mediated proinflammatory pathway and stimulation of GLUT4 translocation to the plasma membrane in white adipose tissue. Taken together, decaffeinated green coffee bean extract appeared to reverse HFD-induced fat accumulation and insulin resistance by downregulating the genes involved in adipogenesis and inflammation in visceral adipose tissue.

Olive leaf extract attenuates obesity in high-fat diet-fed mice by modulating the expression of molecules involved in adipogenesis and thermogenesis

The present study aimed to investigate whether olive leaf extract (OLE) prevents high-fat diet (HFD)-induced obesity in mice and to explore the underlying mechanisms. Mice were randomly divided into groups that received a chow diet (CD), HFD, or 0.15% OLE-supplemented diet (OLD) for 8 weeks. OLD-fed mice showed significantly reduced body weight gain, visceral fat-pad weights, and plasma lipid levels as compared with HFD-fed mice. OLE significantly reversed the HFD-induced upregulation of WNT10b- and galanin-mediated signaling molecules and key adipogenic genes (PPAR γ , C/EBP α , CD36, FAS, and leptin) in the epididymal adipose tissue of HFD-fed mice. Furthermore, the HFD-induced downregulation of thermogenic genes involved in uncoupled respiration (SIRT1, PGC1 α , and UCP1) and mitochondrial biogenesis (TFAM, NRF-1, and COX2) was also significantly reversed by OLE. These results suggest that OLE exerts beneficial effects against obesity by regulating the expression of genes involved in adipogenesis and thermogenesis in the visceral adipose tissue of HFD-fed mice.

Galanin receptors possibly modulate the obesity-induced change in pain threshold

Pain threshold may be up-regulated or down-regulated according to gender, age, race/ethnic and psychological state. Previous studies indicated that obesity may change pain threshold, both nociceptive and antinociceptive, which resulted from obesity-reduced variation of neuroendocrine. However there is a limited understanding of its molecular mechanism underlying this variation. A lot of evidence supports that galanin increases food intake and body weight to induce obesity in animals. This peptide may also modulate nociceptive susceptibility via central galanin receptor 1 and peripheral galanin receptor 2 in dorsal root ganglion. Whereas injury and obesity may up-regulate the galanin expression and stimulate its secretion to elevate the plasma levels of subjects. Pain may increase the risk of obesity through reduced physical activity. In this review, we highlighted the multiple bilateral interrelation between obesity and pain sensitivity, between galanin and obesity and between galanin and injure-induced pain. In view of the above, we reasoned that galanin receptors possibly participated in the modulation of the obesity-induced change in pain threshold, which need further direct evidence to support as yet. This review is helpful to explore the mechanism that galanin receptors regulate the obesity-induced change of pain sensitivity and to contribute to our understanding of the relation among galanin, obesity and pain threshold.

A genome wide association study for backfat thickness in Italian Large White pigs highlights new regions affecting fat deposition including neuronal genes

Background

Carcass fatness is an important trait in most pig breeding programs. Following market requests, breeding plans for fresh pork consumption are usually designed to reduce carcass fat content and increase lean meat deposition. However, the Italian pig industry is mainly devoted to the production of Protected Designation of Origin dry cured hams: pigs are slaughtered at around 160 kg of live weight and the breeding goal aims at maintaining fat coverage, measured as backfat thickness to avoid excessive desiccation of the hams. This objective has shaped the genetic pool of Italian heavy pig breeds for a few decades. In this study we applied a selective genotyping approach within a population of ~ 12,000 performance tested Italian Large White pigs. Within this population, we selectively genotyped 304 pigs with extreme and divergent backfat thickness estimated breeding value by the Illumina PorcineSNP60 BeadChip and performed a genome wide association study to identify loci associated to this trait.

Results

We identified 4 single nucleotide polymorphisms with P≤5.0E-07 and additional 119 ones with 5.0E-07<P≤5.0E-05. These markers were located throughout all chromosomes. The largest numbers were found on porcine chromosomes 6 and 9 (n=15), 4 (n=13), and 7 (n=12) while the most significant marker was located on chromosome 18. Twenty-two single nucleotide polymorphisms were in intronic regions of genes already recognized by the Pre-Ensembl Sscrofa10.2 assembly. Gene Ontology analysis indicated an enrichment of Gene Ontology terms associated with nervous system development and regulation in concordance with results of large genome wide association studies for human obesity.

Conclusions

Further investigations are needed to evaluate the effects of the identified single nucleotide polymorphisms associated with backfat thickness on other traits as a pre-requisite for practical applications in breeding programs. Reported results could improve our understanding of the biology of fat metabolism and deposition that could also be relevant for other mammalian species including humans, confirming the role of neuronal genes on obesity.

Galanin peptide family as a modulating target for contribution to metabolic syndrome

Metabolic syndrome (MetS) is defined as abdominal central obesity, atherogenic dyslipidemia, insulin resistance, glucose intolerance and hypertension. The rapid increasing prevalence of MetS and the consequent diseases, such as type 2 diabetes mellitus and cardiovascular disorder, are becoming a global epidemic health problem. Despite considerable research into the etiology of this complex disease, the precise mechanism underlying MetS and the association of this complex disease with the development of type 2 diabetes mellitus and increased cardiovascular disease remains elusive. Therefore, researchers continue to actively search for new MetS treatments. Recent animal studies have indicated that the galanin peptide family of peptides may increase food intake, glucose intolerance, fat preference and the risk for obesity and dyslipidemia while decreasing insulin resistance and blood pressure, which diminishes the probability of type 2 diabetes mellitus and hypertension. To date, however, few papers have summarized the role of the galanin peptide family in modulating MetS. Through a summary of available papers and our recent studies, this study reviews the updated evidences of the effect that the galanin peptide family has on the clustering of MetS components, including obesity, dyslipidemia, insulin resistance and hypertension. This line of research will further deepen our understanding of the relationship between the galanin peptide family and the mechanisms underlying MetS, which will help develop new therapeutic strategies for this complex disease.

Galanin and its receptors: a novel strategy for appetite control and obesity therapy

The rapid increase in the prevalence of overweight and obesity is becoming an important health problem. Overweight and obesity may cause several metabolic complications, including type 2 diabetes mellitus, hyperlipidemia, high cholesterol, coronary artery disease as well as hypertension. Prevention and treatment of obesity will benefit the treatment of these related diseases. Current strategies for treatment of obesity are not adequately effective and are frequently companied with many side effects. Thus, new ways to treat obesity are urgently needed. Galanin is undoubtedly involved in the regulation of food intake and body weight. The aim of this review is to provide up-to-date knowledge concerning the roles of central and peripheral galanin as well as its receptors in the regulation of metabolism, obesity and appetite. We also highlight the mechanisms of galanin and its receptors in experimental obesity, trying to establish a novel anti-obesity strategy.

Cinchonine Prevents High-Fat-Diet-Induced Obesity through Downregulation of Adipogenesis and Adipose Inflammation

Cinchonine (C₁₉H₂₂N₂O) is a natural compound of Cinchona bark. Although cinchonine's antiplatelet effect has been reported in the previous study, antiobesity effect of cinchonine has never been studied. The main objective of this study was to investigate whether cinchonine reduces high-fat-diet- (HFD-) induced adipogenesis and inflammation in the epididymal fat tissues of mice and to explore the underlying mechanisms involved in these reductions. HFD-fed mice treated with 0.05% dietary cinchonine for 10 weeks had reduced body weight gain (−38%), visceral fat-pad weights (−26%), and plasma levels of triglyceride, free fatty acids, total cholesterol, and glucose compared with mice fed with the HFD. Moreover, cinchonine significantly reversed HFD-induced downregulations of WNT10b and galanin-mediated signaling molecules and key adipogenic genes in the epididymal adipose tissues of mice. Cinchonine also attenuated the HFD-induced upregulation of proinflammatory cytokines by inhibiting toll-like-receptor-2- (TLR2-) and TLR4-mediated signaling cascades in the adipose tissue of mice. Our findings suggest that dietary cinchonine with its effects on adipogenesis and inflammation may have a potential benefit in preventing obesity.

Ablation of the transcriptional regulator Id1 enhances energy expenditure, increases insulin sensitivity, and protects against age and diet induced insulin resistance, and hepatosteatosis

Obesity is a major health concern that contributes to the development of diabetes, hyperlipidemia, coronary artery disease, and cancer. Id proteins are helix-loop-helix transcription factors that regulate the proliferation and differentiation of cells from multiple tissues, including adipocytes. We screened mouse tissues for the expression of Id1 and found that Id1 protein is highly expressed in brown adipose tissue (BAT) and white adipose tissue (WAT), suggesting a role for Id1 in adipogenesis and cell metabolism. Id1(-/-) mice are viable but show a significant reduction in fat mass (P<0.005) over the life of the animal that was not due to decreased number of adipocytes. Analysis of Id1(-/-) mice revealed higher energy expenditure, increased lipolysis, and fatty acid oxidation, resulting in reduced triglyceride accumulation in WAT compared to Id1(+/+) mice. Serum levels of triglycerides (193.9±32.2 vs. 86.5±33.8, P<0.0005), cholesterol (189.4±33.8 vs. 110.6±8.23, P<0.0005) and leptin (1263±835 vs. 222±260, P<0.005) were significantly lower in aged Id1(-/-) mice compared to Id1(+/+) mice. Id1-deficient mice have higher resting (P<0.005) and total (P<0.05) O(2) consumption and lower respiratory exchange ratio (P<0.005), confirming that Id1(-/-) mice use a higher proportion of lipid as an energy source for the increased energy expenditure. The expression of PGC1α and UCP1 were 2- to 3-fold up-regulated in Id1(-/-) BAT, suggesting that loss of Id1 increases thermogenesis. As a consequence of higher energy expenditure and reduced fat mass, Id1(-/-) mice displayed enhanced insulin sensitivity. Id1 deficiency protected mice against age- and high-fat-diet-induced adiposity, insulin resistance, and hepatosteatosis. Our findings suggest that Id1 plays a critical role in the regulation of energy homeostasis and could be a potential target in the treatment of insulin resistance and fatty liver disease.

Resveratrol exerts anti-obesity effects via mechanisms involving down-regulation of adipogenic and inflammatory processes in mice

Resveratrol is a natural polyphenolic stilbene derivative found in a variety of edible fruits, including nuts, berries, and grape skin. Although resveratrol has been suggested to improve thermogenesis in the brown adipose tissues of obese animals, there have been no reports on the anti-adipogenic and anti-inflammatory effects of resveratrol in the white adipose tissues of obese animals. The primary aim of this study was to investigate whether resveratrol attenuates high-fat diet (HFD)-induced adipogenesis and inflammation in the epididymal fat tissues of mice and to explore the underlying mechanisms involved in this attenuation. In comparison with HFD-fed mice, mice fed with a 0.4% resveratrol-supplemented diet (RSD) showed significantly lower body weight gain (-48%), visceral fat-pad weights (-58%), and plasma levels of triglyceride, FFA, total cholesterol, glucose, tumor necrosis factor (TNF) α, and monocyte chemoattractant protein-1 (MCP1). Resveratrol significantly reversed the HFD-induced up-regulation of galanin-mediated signaling molecules (GalR1/2, PKCδ, Cyc-D, E2F1, and p-ERK) and key adipogenic genes (PPARγ2, C/EBPα, SREBP-1c, FAS, LPL, aP2, and leptin) in the epididymal adipose tissues of mice. Furthermore, resveratrol significantly attenuated the HFD-induced up-regulation of pro-inflammatory cytokines (TNFα, IFNα, IFNβ, and IL-6) and their upstream signaling molecules (TLR2/4, MyD88, Tirap, TRIF, TRAF6, IRF5, p-IRF3, and NF-κB) in the adipose tissues of mice. The results of this study suggest that resveratrol inhibits visceral adipogenesis by suppressing the galanin-mediated adipogenesis signaling cascade. It may also attenuate cytokine production in the adipose tissue by repressing the TLR2- and TLR4-mediated pro-inflammatory signaling cascades in HFD-fed mice.

Uncoupling protein 1 expression and high-fat diets

Uncoupling protein 1 (Ucp1) is the key component of β-adrenergically controlled nonshivering thermogenesis in brown adipocytes. This process combusts stored and nutrient energy as heat. Cold exposure not only activates Ucp1-mediated thermogenesis to maintain normothermia but also results in adaptive thermogenesis, i.e., the recruitment of thermogenic capacity in brown adipose tissue. As a hallmark of adaptive thermogenesis, Ucp1 synthesis is increased proportionally to temperature and duration of exposure. Beyond this classical thermoregulatory function, it has been suggested that Ucp1-mediated thermogenesis can also be employed for metabolic thermogenesis to prevent the development of obesity. Accordingly, in times of excess caloric intake, one may expect a positive regulation of Ucp1. The general impression from an overview of the present literature is, indeed, an increased brown adipose tissue Ucp1 mRNA and protein content after feeding a high-fat diet (HFD) to mice and rats. The reported increases are very variable in magnitude, and the effect size seems to be independent of dietary fat content and duration of the feeding trial. In white adipose tissue depots Ucp1 mRNA is generally downregulated by HFD, indicating a decline in the number of interspersed brown adipocytes.