Reduced serotonin reuptake transporter (SERT) function causes insulin resistance and hepatic steatosis independent of food intake. PLoS One. 2012;7:e32511. [PMID: 22412882 PMCID: PMC3297606 DOI: 10.1371/journal.pone.0032511]

The Role of Solute Carrier Family Transporters in Hepatic Steatosis and Hepatic Fibrosis

Solute carrier (SLC) family transporters are crucial transmembrane proteins responsible for transporting various molecules, including amino acids, electrolytes, fatty acids, and nucleotides. To date, more than fifty SLC transporter subfamilies have been identified, many of which are linked to the progression of hepatic steatosis and fibrosis. These conditions are often caused by factors such as non-alcoholic fatty liver disease and non-alcoholic steatohepatitis, which are major contributors to the global liver disease burden. The activity of SLC members regulates the transport of substrates across biological membranes, playing key roles in lipid synthesis and metabolism, mitochondrial function, and ferroptosis. These processes, in turn, influence the function of hepatocytes, hepatic stellate cells, and macrophages, thereby contributing to the development of hepatic steatosis and fibrosis. Additionally, some SLC transporters are involved in drug transport, acting as critical regulators of drug-induced hepatic steatosis. Beyond substrate transport, certain SLC members also exhibit additional functions. Given the pivotal role of the SLC family in hepatic steatosis and fibrosis, this review aimed to summarize the molecular mechanisms through which SLC transporters influence these conditions.

Gut microbiota and its metabolites regulate insulin resistance: traditional Chinese medicine insights for T2DM

The gut microbiota is closely associated with the onset and development of type 2 diabetes mellitus (T2DM), characterized by insulin resistance (IR) and chronic low-grade inflammation. However, despite the widespread use of first-line antidiabetic drugs, IR in diabetes and its complications continue to rise. The gut microbiota and its metabolic products may promote the development of T2DM by exacerbating IR. Therefore, regulating the gut microbiota has become a promising therapeutic strategy, with particular attention given to probiotics, prebiotics, synbiotics, and fecal microbiota transplantation. This review first examines the relationship between gut microbiota and IR in T2DM, summarizing the research progress of microbiota-based therapies in modulating IR. We then delve into how gut microbiota-related metabolic products contribute to IR. Finally, we summarize the research findings on the role of traditional Chinese medicine in regulating the gut microbiota and its metabolic products to improve IR. In conclusion, the gut microbiota and its metabolic products play a crucial role in the pathophysiological process of T2DM by modulating IR, offering new insights into potential therapeutic strategies for T2DM.

SERT-Deficient Mice Fed Western Diet Reveal Altered Metabolic and Pro-Inflammatory Responses of the Liver: A Link to Abnormal Behaviors

BACKGROUND

The inheritance of the short SLC6A4 allele, encoding the serotonin transporter (SERT) in humans, increases susceptibility to neuropsychiatric and metabolic disorders, with aging and female sex further exacerbating these conditions. Both central and peripheral mechanisms of the compromised serotonin (5-HT) system play crucial roles in this context. Previous studies on SERT-deficient (Sert-/-) mice, which model human SERT deficiency, have demonstrated emotional and metabolic disturbances, exacerbated by exposure to a high-fat Western diet (WD). Growing evidence suggests the significance of hepatic regulatory mechanisms in the neurobiology of central nervous system disorders, supporting the 'liver-brain' concept. However, the relationship between aberrant behavior and hepatic alterations under conditions of SERT deficiency remains poorly investigated.

METHODS

One-year-old female Sert-/- mice and their wild-type (WT) littermates were subjected to a control diet (CD) or the WD for a duration of three weeks. The WD had a higher caloric content and was characterized by an elevated saturated fat content (21%) compared to the CD (4.5%) and contained 0.2% cholesterol. Mice were evaluated for anxiety-like behavior, exploration and locomotor activity in the open field test, as well as glucose tolerance and histological indicators of hepatic steatosis. Hepatic pro-inflammatory and metabolism-related gene expression and markers of nitrosative stress, were analyzed utilizing real-time polymerase chain reaction (RT-PCR) and correlated with behavioral and histological outcomes.

RESULTS

In comparison to unchallenged mice, Sert-/-/WD mutants, but not the WT/WD group, had increased locomotion and anxiety-like behavior, increased hepatic steatosis, and elevated expression of insulin receptor B and pro-inflammatory cytokines interleukin-1β (Il-1β) and Tnf, as well as decreased expression of leptin receptor B. The two genotypes displayed distinct gene expression patterns of nitric oxide (NO)-related molecules inducible NO synthase (iNos) and arginase (Arg2), insulin receptor-related signaling factors: cluster of differentiation 36 (Cd36), ecto-nucleotide pyrophosphatase/phosphodiesterase (Enpp), protein tyrosine phosphatase N1 (Ptpn1), cytochrome P450 omega-hydroxylase 4A14 (Cyp4a14), acyl-CoA synthetase 1 (Acsl1) and phosphatase and tensin homolog (Pten). Furthermore, there were profound differences in correlations between molecular, histological, and behavioral measurements across the two genotypes.

CONCLUSIONS

Our findings suggest that the genetic deficiency of SERT results in abnormal hepatic pro-inflammatory and metabolic adaptations in response to WD. The significant correlations observed between behavioral measures and pro-inflammatory and metabolic alterations in WD-fed mice suggest the importance of liver-brain interactions and their role in the aberrant behaviors exhibited by Sert-/- mutants. This study presents the first evidence that altered liver functions are associated with pathological behaviors arising from genetic SERT deficiency.

Evaluation of lavender and rose aromatherapies on the success of inferior alveolar nerve block in symptomatic irreversible pulpitis: A randomized clinical trial

Trial design

This is a prospective, block-randomized, blinded, multiple arm and parallel-group superiority clinical trial.

Methods

Seventy-eight patients satisfying the recruitment standards, were randomly allocated into three groups as follows: Group I (n = 26) - Inferior alveolar nerve block (IANB) devoid of aromatherapy (AT); Group II (n = 26) - IANB with lavender AT and Group III - IANB with rose AT (n = 26) with the help of the ultrasonic aroma diffuser (with respective oils)for 20 min/2 h in operatories 1,2 and 3 respectively. For AT, 3-4 drops of lavender and rose-conditioned oils were added from a 100 ml solution containing 100 mg of these medicinal plants. The pre-operative (PRO) and access opening (AO) pain as well as the anxiety of patients were recorded using the Visual Analog Scale (VAS) and Modified Dental Anxiety Scale (MDAS) respectively. Data thus obtained was entered into the Excel sheet and subjected to statistical tests (analysis of variance and paired t-test). The p-value less than 0.05 was considered statistically significant.

Results

Group I showed non-significant disparity between PRO and AO for both VAS as well as MDAS (p = 0.62, p = 0.71). However, group II (p = 0.04, p = 0.02) and group III (p = 0.03, p = 0.01) revealed significant differences between PO - AO VAS and MDAS. MDAS and VAS intergroup comparison revealed a significant difference among groups I and II (p = 0.03, p = 0.04), and groups I and III (p = 0.02, p = 0.03). However non-significant disparity was observed among groups II and III (p = 0.85, 0.34). Moreover, there was a statistically significant reduction in anxiety levels in females compared to males after rose AT (p = 0.02). Nevertheless, groups I and II did not show any gender predilection for anxiety as well as pain.

Conclusion

Alleviation of dental anxiety as well as reduction in pain during AO of teeth with SIP can be achieved using Lavender and rose AT. In female patients, rose AT can be preferred over lavender AT.

Impact of Serotonin Transporter Absence on Brain Insulin Receptor Expression, Plasma Metabolome Changes, and ADHD-like Behavior in Mice fed a Western Diet

The impaired function of the serotonin transporter (SERT) in humans has been linked to a higher risk of obesity and type 2 diabetes, especially as people age. Consuming a "Western diet" (WD), which is high in saturated fats, cholesterol, and sugars, can induce metabolic syndrome. Previous research indicated that mice carrying a targeted inactivation of the Sert gene (knockout, KO) and fed a WD display significant metabolic disturbances and behaviors reminiscent of ADHD. These abnormalities might be mediated via a dysfunction in insulin receptor (IR) signaling, which is also associated with adult ADHD. However, the impact of Sert deficiency on IR signaling and systemic metabolic changes has not been thoroughly explored. In this study, we conducted a detailed analysis of locomotor behavior in wild-type (WT) and KO mice fed a WD or control diet. We investigated changes in the blood metabolome and examined, via PCR, the expression of insulin receptor A and B isoforms and key regulators of their function in the brain. Twelve-month-old KO mice and their WT littermates were fed a WD for three weeks. Nuclear magnetic resonance spectroscopy analysis of plasma samples showed that KO mice on a WD had higher levels of lipids and lipoproteins and lower levels of glucose, lactate, alanine, valine, and isoleucine compared to other groups. SERT-KO mice on the control diet exhibited increased brain levels of both IR A and B isoforms, accompanied by a modest increase in the negative regulator ENPP. The KO mice also displayed anxiety-like behavior and reduced exploratory activity in an open field test. However, when the KO animals were fed a WD, the aberrant expression levels of IR isoforms in the KO mice and locomotor behavior were ameliorated indicating a complex interaction between genetic and dietary factors that might contribute to ADHD-like symptoms. Overall, our findings suggest that the lack of Sert leads to a unique metabolic phenotype in aged mice, characterized by dysregulated IR-related pathways. These changes are exacerbated by WD in the blood metabolome and are associated with behavioral abnormalities.

Butyrate acts as a positive allosteric modulator of the 5-HT transporter to decrease availability of 5-HT in the ileum

BACKGROUND AND PURPOSE

Radiation therapy-induced gastrointestinal distress is partly associated with the elimination of gut microbiota. The effectiveness of 5-HT receptor antagonists to treat radiation therapy-induced emesis implies a pathophysiological role of 5-HT. Peripheral 5-HT is derived from intestinal epithelium. We have investigated the role of gut microbiota in regulating intestinal 5-HT availability.

EXPERIMENTAL APPROACH

A radiation therapy murine model accompanied by faecal microbiota transplantation from donors fed different diets was investigated, and mouse ileal organoids were used for mechanistic studies. The clinical relevance was validated by a small-scale human study.

KEY RESULTS

Short-term high-fat diet (HFD) induced gut bacteria to produce butyrate. Irradiated mice receiving HFD-induced microbiome had the lowest ileal levels of 5-HT, compared with other recipients. Treatment with butyrate increased 5-HT uptake in mouse ileal organoids, assayed by the real-time tracking of a fluorescent substrate for monoamine transporters. Silencing the 5-HT transporter (SERT) in the organoids abolished butyrate-stimulated 5-HT uptake. The competitive tests using different types of selective 5-HT reuptake inhibitors suggested that butyrate acted as a positive allosteric modulator of SERT. In human gut microbiota, butyrate production was associated with the interconversion between acetate and butyrate. Faecal contents of both acetate and butyrate were negatively associated with serum 5-HT, but only butyrate was positively correlated with body mass index in humans.

CONCLUSION AND IMPLICATIONS

Short-term HFD may be beneficial for alleviating gastrointestinal reactions by increasing butyrate to suppress local 5-HT levels and providing energy to cancer patients given radiation therapy.

Serotonin Transporter Deficiency Induces Metabolic Alterations in the Ileal Mucosa

Serotonin transporter (SERT) deficiency has been implicated in metabolic syndrome, intestinal inflammation, and microbial dysbiosis. Interestingly, changes in microbiome metabolic capacity and several alterations in host gene expression, including lipid metabolism, were previously observed in SERT-/- mice ileal mucosa. However, the precise host or microbial metabolites altered by SERT deficiency that may contribute to the pleiotropic phenotype of SERT KO mice are not yet understood. This study investigated the hypothesis that SERT deficiency impacts lipid and microbial metabolite abundances in the ileal mucosa, where SERT is highly expressed. Ileal mucosal metabolomics was performed by Metabolon on wild-type (WT) and homozygous SERT knockout (KO) mice. Fluorescent-activated cell sorting (FACS) was utilized to measure immune cell populations in ileal lamina propria to assess immunomodulatory effects caused by SERT deficiency. SERT KO mice exhibited a unique ileal mucosal metabolomic signature, with the most differentially altered metabolites being lipids. Such changes included increased diacylglycerols and decreased monoacylglycerols in the ileal mucosa of SERT KO mice compared to WT mice. Further, the ileal mucosa of SERT KO mice exhibited several changes in microbial-related metabolites known to play roles in intestinal inflammation and insulin resistance. SERT KO mice also had a significant reduction in the abundance of ileal group 3 innate lymphoid cells (ILC3). In conclusion, SERT deficiency induces complex alterations in the ileal mucosal environment, indicating potential links between serotonergic signaling, gut microbiota, mucosal immunity, intestinal inflammation, and metabolic syndrome.

Serotonin reuptake transporter deficiency promotes liver steatosis and impairs intestinal barrier function in obese mice fed a Western-style diet

BACKGROUND

Intestinal barrier dysfunctions have been associated with liver steatosis and metabolic diseases. Besides nutritional factors, like a Western-style diet (WSD), serotonin has been linked with leaky gut. Therefore, we aimed to evaluate the role of serotonin in the pathogenesis of intestinal barrier dysfunctions and liver steatosis in mice fed high-fat and high-sugar diets.

METHODS

6-8 weeks old male serotonin reuptake transporter knockout mice (SERT-/- ) and wild-type controls (SERT+/+ ) were fed either a WSD or a control diet (CD) ad libitum with or without fructose 30% (F) added to the drinking water for 12 weeks. Markers of liver steatosis and intestinal barrier function were assessed.

KEY RESULTS

SERT-/- mice showed increased weight gain compared with SERT+/+ mice when fed a WSD ± F for 12 weeks (p < 0.05), whereby SERT-/- mice exhibited reduced energy (-21%) intake. Furthermore, SERT knockout resulted in a more pronounced liver steatosis (p < 0.05), enhanced levels of endotoxin in portal vein plasma (p < 0.05), and increased liver expression of Tnf and Myd88 (p < 0.05), when mice were fed a WSD ± F. Finally, SERT-/- mice, when compared with SERT+/+ mice, had a decreased mRNA expression of Muc2 (p < 0.01), Ocln (p < 0.05), Cldn5 (p = 0.054) and 7 (p < 0.01), Defa5 (p < 0.05) and other antimicrobial peptides in the ileum. On the protein level, ZO-1 (p < 0.01) and DEFA5 protein (p < 0.0001) were decreased.

CONCLUSION AND INFERENCES

Our data demonstrate that SERT knockout causes weight gain, liver steatosis, and leaky gut, especially in mice fed a WSD. Therefore, SERT induction could be a novel therapeutic approach to improve metabolic diseases associated with intestinal barrier dysfunction.

Unraveling the serotonin saga: from discovery to weight regulation and beyond - a comprehensive scientific review

The prevalence of obesity is rapidly increasing worldwide, while the development of effective obesity therapies lags behind. Although new therapeutic targets to alleviate obesity are identified every day, and drug efficacy is improving, adverse side effects and increased health risks remain serious issues facing the weight-loss industry. Serotonin, also known as 5-HT, has been extensively studied in relation to appetite reduction and weight loss. As a result, dozens of upstream and downstream neural targets of 5-HT have been identified, revealing a multitude of neural circuits involved in mediating the anorexigenic effect of 5-HT. Despite the rise and fall of several 5-HT therapeutics in recent decades, the future of 5-HT as a therapeutic target for weight-loss therapy looks promising. This review focuses on the history of serotonin, the state of current central serotonin research, previous serotonergic therapies, and the future of serotonin for treating individuals with obesity.

The serotonin transporter sustains human brown adipose tissue thermogenesis

Activation of brown adipose tissue (BAT) in humans is a strategy to treat obesity and metabolic disease. Here we show that the serotonin transporter (SERT), encoded by SLC6A4, prevents serotonin-mediated suppression of human BAT function. RNA sequencing of human primary brown and white adipocytes shows that SLC6A4 is highly expressed in human, but not murine, brown adipocytes and BAT. Serotonin decreases uncoupled respiration and reduces uncoupling protein 1 via the 5-HT2B receptor. SERT inhibition by the selective serotonin reuptake inhibitor (SSRI) sertraline prevents uptake of extracellular serotonin, thereby potentiating serotonin's suppressive effect on brown adipocytes. Furthermore, we see that sertraline reduces BAT activation in healthy volunteers, and SSRI-treated patients demonstrate no 18F-fluorodeoxyglucose uptake by BAT at room temperature, unlike matched controls. Inhibition of BAT thermogenesis may contribute to SSRI-induced weight gain and metabolic dysfunction, and reducing peripheral serotonin action may be an approach to treat obesity and metabolic disease.

Serotonin transporter-deficient mice display enhanced adipose tissue inflammation after chronic high-fat diet feeding

Introduction

Serotonin is involved in leukocyte recruitment during inflammation. Deficiency of the serotonin transporter (SERT) is associated with metabolic changes in humans and mice. A possible link and interaction between the inflammatory effects of serotonin and metabolic derangements in SERT-deficient mice has not been investigated so far.

Methods

SERT-deficient (Sert -/-) and wild type (WT) mice were fed a high-fat diet, starting at 8 weeks of age. Metabolic phenotyping (metabolic caging, glucose and insulin tolerance testing, body and organ weight measurements, qPCR, histology) and assessment of adipose tissue inflammation (flow cytometry, histology, qPCR) were carried out at the end of the 19-week high-fat diet feeding period. In parallel, Sert -/- and WT mice received a control diet and were analyzed either at the time point equivalent to high-fat diet feeding or as early as 8-11 weeks of age for baseline characterization.

Results

After 19 weeks of high-fat diet, Sert -/- and WT mice displayed similar whole-body and fat pad weights despite increased relative weight gain due to lower starting body weight in Sert -/-. In obese Sert -/- animals insulin resistance and liver steatosis were enhanced as compared to WT animals. Leukocyte accumulation and mRNA expression of cytokine signaling mediators were increased in epididymal adipose tissue of obese Sert -/- mice. These effects were associated with higher adipose tissue mRNA expression of the chemokine monocyte chemoattractant protein 1 and presence of monocytosis in blood with an increased proportion of pro-inflammatory Ly6C+ monocytes. By contrast, Sert -/- mice fed a control diet did not display adipose tissue inflammation.

Discussion

Our observations suggest that SERT deficiency in mice is associated with inflammatory processes that manifest as increased adipose tissue inflammation upon chronic high-fat diet feeding due to enhanced leukocyte recruitment.

New Insight into Selective Serotonin Receptor Agonists in the Central Nervous System, Studied with WAY163909 in Obese and Diabetic Wistar Rats

Background and aims: We investigated the effect of WAY-163909, a novel 5-hydroxytryptamine selective 2C receptor agonist on body weight, blood glucose levels, and insulin resistance in obese and diabetic Wistar rats. Materials and methods: We used twenty male Wistar rats with obesity and obesity-induced diabetes and twenty healthy Wistar rats as a control group. Each of these groups was separated into two subgroups: one with a daily intraperitoneal application of WAY-163909 (1 mg/kg) and one without. During the study, body weight, blood glucose levels, and immunoreactive insulin were tracked. Results: A reduction of 5.5% (p < 0.05) in body weight was registered in the rat group with diabetes and obesity and 2.56% in the control group with a daily application of WAY-163909 (1 mg/kg) at the end of the study. Decreases of 35.4% in blood glucose levels at week four in the diabetic and obese rat group with a daily application of WAY-163909 (1 mg/kg) were registered. A reduction of insulin levels of 4.1% (p < 0.05) in the diabetic and obese rats group using WAY-163909 was also observed. Conclusion: In our study, using WAY-163909 (1 mg/kg) led to a reduction of blood glucose levels, immunoreactive insulin, and body weight.

Orexin, serotonin, and energy balance

The lateral hypothalamus is critical for the control of ingestive behavior and spontaneous physical activity (SPA), as lesion or stimulation of this region alters these behaviors. Evidence points to lateral hypothalamic orexin neurons as modulators of feeding and SPA. These neurons affect a broad range of systems, and project to multiple brain regions such as the dorsal raphe nucleus, which contains serotoninergic neurons (DRN) important to energy homeostasis. Physical activity is comprised of intentional exercise and SPA. These are opposite ends of a continuum of physical activity intensity and structure. Non‐goal‐oriented behaviors, such as fidgeting, standing, and ambulating, constitute SPA in humans, and reflect a propensity for activity separate from intentional activity, such as high‐intensity voluntary exercise. In animals, SPA is activity not influenced by rewards such as food or a running wheel. Spontaneous physical activity in humans and animals burns calories and could theoretically be manipulated pharmacologically to expend calories and protect against obesity. The DRN neurons receive orexin inputs, and project heavily onto cortical and subcortical areas involved in movement, feeding and energy expenditure (EE). This review discusses the function of hypothalamic orexin in energy‐homeostasis, the interaction with DRN serotonin neurons, and the role of this orexin‐serotonin axis in regulating food intake, SPA, and EE. In addition, we discuss possible brain areas involved in orexin–serotonin cross‐talk; the role of serotonin receptors, transporters and uptake‐inhibitors in the pathogenesis and treatment of obesity; animal models of obesity with impaired serotonin‐function; single‐nucleotide polymorphisms in the serotonin system and obesity; and future directions in the orexin–serotonin field.

This article is categorized under:

Metabolic Diseases > Molecular and Cellular Physiology

Imipramine Accelerates Nonalcoholic Fatty Liver Disease, Renal Impairment, Diabetic Retinopathy, Insulin Resistance, and Urinary Chromium Loss in Obese Mice

Imipramine is a tricyclic antidepressant that has been approved for treating depression and anxiety in patients and animals and that has relatively mild side effects. However, the mechanisms of imipramine-associated disruption to metabolism and negative hepatic, renal, and retinal effects are not well defined. In this study, we evaluated C57BL6/J mice subjected to a high-fat diet (HFD) to study imipramine's influences on obesity, fatty liver scores, glucose homeostasis, hepatic damage, distribution of chromium, and retinal/renal impairments. Obese mice receiving imipramine treatment had higher body, epididymal fat pad, and liver weights; higher serum triglyceride, aspartate and alanine aminotransferase, creatinine, blood urea nitrogen, renal antioxidant enzyme, and hepatic triglyceride levels; higher daily food efficiency; and higher expression levels of a marker of fatty acid regulation in the liver compared with the controls also fed an HFD. Furthermore, the obese mice that received imipramine treatment exhibited insulin resistance, worse glucose intolerance, decreased glucose transporter 4 expression and Akt phosphorylation levels, and increased chromium loss through urine. In addition, the treatment group exhibited considerably greater liver damage and higher fatty liver scores, paralleling the increases in patatin-like phospholipid domain containing protein 3 and the mRNA levels of sterol regulatory element-binding protein 1 and fatty acid-binding protein 4. Retinal injury worsened in imipramine-treated mice; decreases in retinal cell layer organization and retinal thickness and increases in nuclear factor κB and inducible nitric oxide synthase levels were observed. We conclude that administration of imipramine may result in the exacerbation of nonalcoholic fatty liver disease, diabetes, diabetic retinopathy, and kidney injury.

High-Throughput Screening of Mouse Gene Knockouts Identifies Established and Novel High Body Fat Phenotypes

PURPOSE

Obesity is a major public health problem. Understanding which genes contribute to obesity may better predict individual risk and allow development of new therapies. Because obesity of a mouse gene knockout (KO) line predicts an association of the orthologous human gene with obesity, we reviewed data from the Lexicon Genome5000TM high throughput phenotypic screen (HTS) of mouse gene KOs to identify KO lines with high body fat.

MATERIALS AND METHODS

KO lines were generated using homologous recombination or gene trapping technologies. HTS body composition analyses were performed on adult wild-type and homozygous KO littermate mice from 3758 druggable mouse genes having a human ortholog. Body composition was measured by either DXA or QMR on chow-fed cohorts from all 3758 KO lines and was measured by QMR on independent high fat diet-fed cohorts from 2488 of these KO lines. Where possible, comparisons were made to HTS data from the International Mouse Phenotyping Consortium (IMPC).

RESULTS

Body fat data are presented for 75 KO lines. Of 46 KO lines where independent external published and/or IMPC KO lines are reported as obese, 43 had increased body fat. For the remaining 29 novel high body fat KO lines, Ksr2 and G2e3 are supported by data from additional independent KO cohorts, 6 (Asnsd1, Srpk2, Dpp8, Cxxc4, Tenm3 and Kiss1) are supported by data from additional internal cohorts, and the remaining 21 including Tle4, Ak5, Ntm, Tusc3, Ankk1, Mfap3l, Prok2 and Prokr2 were studied with HTS cohorts only.

CONCLUSION

These data support the finding of high body fat in 43 independent external published and/or IMPC KO lines. A novel obese phenotype was identified in 29 additional KO lines, with 27 still lacking the external confirmation now provided for Ksr2 and G2e3 KO mice. Undoubtedly, many mammalian obesity genes remain to be identified and characterized.

Single or combined ablation of peripheral serotonin and p21 limit adipose tissue expansion and metabolic alterations in early adulthood in mice fed a normocaloric diet

Identifying the fundamental molecular factors that drive weight gain even in the absence of hypercaloric food intake, is crucial to enable development of novel treatments for the global pandemic of obesity. Here we investigated both adipose tissue-specific and systemic events that underlie the physiological weight gain occurring during early adulthood in mice fed a normocaloric diet. In addition, we used three different genetic models to identify molecular factors that promote physiological weight gain during normocaloric and hypercaloric diets. We demonstrated that normal physiological weight gain was accompanied by an increase in adipose tissue mass and the presence of cellular and metabolic signatures typically found during obesity, including adipocyte hypertrophy, macrophage recruitment into visceral fat and perturbed glucose metabolism. At the molecular level, this was associated with an increase in adipose tissue tryptophan hydroxylase 1 (Tph1) transcripts, the key enzyme responsible for the synthesis of peripheral serotonin. Genetic inactivation of Tph1 was sufficient to limit adipose tissue expansion and associated metabolic alterations. Mechanistically, we discovered that Tph1 inactivation resulted in down-regulation of cyclin-dependent kinase inhibitor p21Waf1/Cip1 expression. Single or double ablation of Tph1 and p21 were equally effective in preventing adipocyte expansion and systemic perturbation of glucose metabolism, upon both normocaloric and hypercaloric diets. Our results suggest that serotonin and p21 act as a central molecular determinant of weight gain and associated metabolic alterations, and highlights the potential of targeting these molecules as a pharmacologic approach to prevent the development of obesity.

Serotonin system genes contribute to the susceptibility to obesity in Black adolescents

OBJECTIVE

The importance of the central and peripheral serotonin systems in regulating energy balance and obesity development has been highlighted in animal models. Yet, the role of both serotonin systems has not been systematically assessed in humans. The purpose of this study was to investigate the association of genes within both serotonin systems with obesity outcomes in black adolescents.

METHODS

African-American adolescents (n = 1052) whose mothers participated the Memphis New Mother's Study were assessed. In total, 110 polymorphisms mapped to 10 serotonin genes were examined for their associations with standardized body mass index (BMI-z) scores and waist circumferences using generalized estimating equation models.

RESULTS

Over 39% of adolescents were overweight or had obesity. Three single nucleotide polymorphisms (SNPs) within TPH2, HTR3B, and SLC6A4, were significantly associated with BMI-z scores (p < 1.7 × 10-3). Two SNPs in TPH2 were nominally associated with waist circumferences. One SNP in HTR2C was associated with BMI-z scores (p = 0.001) and waist circumferences (p = 0.005) only in girls. Tissue-specific expression indicates that three identified genes are predominantly expressed in the brain.

CONCLUSION

The central serotonin system may play a key role in obesity development in black adolescents. Future studies are warranted to explore additional serotonin system genes and their potential obesogenic mechanisms in humans.

5-HTT Deficiency in Male Mice Affects Healing and Behavior after Myocardial Infarction

Anxiety disorders and depression are common comorbidities in cardiac patients. Mice lacking the serotonin transporter (5-HTT) exhibit increased anxiety-like behavior. However, the role of 5-HTT deficiency on cardiac aging, and on healing and remodeling processes after myocardial infarction (MI), remains unclear. Cardiological evaluation of experimentally naïve male mice revealed a mild cardiac dysfunction in ≥4-month-old 5-HTT knockout (−/−) animals. Following induction of chronic cardiac dysfunction (CCD) by MI vs. sham operation 5-HTT−/− mice with infarct sizes >30% experienced 100% mortality, while 50% of 5-HTT+/− and 37% of 5-HTT+/+ animals with large MI survived the 8-week observation period. Surviving (sham and MI < 30%) 5-HTT−/− mutants displayed reduced exploratory activity and increased anxiety-like behavior in different approach-avoidance tasks. However, CCD failed to provoke a depressive-like behavioral response in either 5-Htt genotype. Mechanistic analyses were performed on mice 3 days post-MI. Electrocardiography, histology and FACS of inflammatory cells revealed no abnormalities. However, gene expression of inflammation-related cytokines (TGF-β, TNF-α, IL-6) and MMP-2, a protein involved in the breakdown of extracellular matrix, was significantly increased in 5-HTT−/− mice after MI. This study shows that 5-HTT deficiency leads to age-dependent cardiac dysfunction and disrupted early healing after MI probably due to alterations of inflammatory processes in mice.

Metabolic Disturbances in Rat Sublines with Constitutionally Altered Serotonin Homeostasis

Central and peripheral serotonin (5HT) have opposing functions in the regulation of energy homeostasis. Both increasing 5HT signaling in the brain and decreasing 5HT signaling in the periphery have been proposed as potential treatments for obesity. This study investigates the relationship between constitutionally high or low 5HT activity and systemic net energy balance. Two sublines of rats with high and low whole-body 5HT tone, obtained by selective breeding for platelet 5HT parameters, were examined for fat accumulation in different white adipose tissue (WAT) depots, glucose/insulin tolerance, blood metabolic parameters, and expression of various metabolic genes. High-5HT animals, unlike their low-5HT counterparts, developed widespread intra-abdominal obesity associated with glucose and insulin intolerance, which worsened with age. They also had elevated blood glucose and lipid parameters but showed no significant changes in circulating leptin, resistin, and adipsin levels. Surprisingly, adiponectin levels were increased in plasma but reduced in the WAT of high-5HT rats. A limited number of metabolic genes belonging to different functional classes showed differential expression in WAT of high-5HT compared to low-5HT rats. Overall, a constitutive increase in 5HT tone is associated with a positive energy balance acting through subtle dysregulation of a broad spectrum of metabolic pathways.

BDNF Overexpression in the Ventral Hippocampus Promotes Antidepressant- and Anxiolytic-Like Activity in Serotonin Transporter Knockout Rats

BDNF plays a pivotal role in neuroplasticity events, vulnerability and resilience to stress-related disorders, being decreased in depressive patients and increased after antidepressant treatment. BDNF was found to be reduced in patients carrying the human polymorphism in the serotonin transporter promoter region (5-HTTLPR). The serotonin knockout rat (SERT^-/-) is one of the animal models used to investigate the underlying molecular mechanisms of depression in humans. They present decreased BDNF levels, and anxiety- and depression-like behavior. To investigate whether upregulating BDNF would ameliorate the phenotype of SERT^-/- rats, we overexpressed BDNF locally into the ventral hippocampus and submitted the animals to behavioral testing. The results showed that BDNF overexpression in the vHIP of SERT^-/- rats promoted higher sucrose preference and sucrose intake; on the first day of the sucrose consumption test it decreased immobility time in the forced swim test and increased the time spent in the center of a novel environment. Furthermore, BDNF overexpression altered social behavior in SERT^-/- rats, which presented increased passive contact with test partner and decreased solitary behavior. Finally, it promoted decrease in plasma corticosterone levels 60 min after restraint stress. In conclusion, modulation of BDNF IV levels in the vHIP of SERT^-/- rats led to a positive behavioral outcome placing BDNF upregulation in the vHIP as a potential target to new therapeutic approaches to improve depressive symptoms.

Hypocretinergic interactions with the serotonergic system regulate REM sleep and cataplexy

Loss of muscle tone triggered by emotions is called cataplexy and is the pathognomonic symptom of narcolepsy, which is caused by hypocretin deficiency. Cataplexy is classically considered to be an abnormal manifestation of REM sleep and is treated by selective serotonin (5HT) reuptake inhibitors. Here we show that deleting the 5HT transporter in hypocretin knockout mice suppressed cataplexy while dramatically increasing REM sleep. Additionally, double knockout mice showed a significant deficit in the buildup of sleep need. Deleting one allele of the 5HT transporter in hypocretin knockout mice strongly increased EEG theta power during REM sleep and theta and gamma powers during wakefulness. Deleting hypocretin receptors in the dorsal raphe neurons of adult mice did not induce cataplexy but consolidated REM sleep. Our results indicate that cataplexy and REM sleep are regulated by different mechanisms and both states and sleep need are regulated by the hypocretinergic input into 5HT neurons.

Narcolepsy is characterized by a sudden loss of muscle tone (cataplexy) similar to REM sleep and is caused by hypocretin deficiency. Here, the authors show that deleting the serotonin transporter gene in hypocretin knockout mice suppresses cataplexy while dramatically increasing REM sleep, indicating that these are two different states but are both regulated by hypocretinergic input to serotonergic neurons.

Role of Serotonin Transporter in Eye Development of Drosophila melanogaster

Serotonin transporter (SerT) in the brain is an important neurotransmitter transporter involved in mental health. However, its role in peripheral organs is poorly understood. In this study, we investigated the function of SerT in the development of the compound eye in Drosophila melanogaster. We found that SerT knockdown led to excessive cell death and an increased number of cells in S-phase in the posterior eye imaginal disc. Furthermore, the knockdown of SerT in the eye disc suppressed the activation of Akt, and the introduction of PI3K effectively rescued this phenotype. These results suggested that SerT plays a role in the healthy eye development of D.melanogaster by controlling cell death through the regulation of the PI3K/Akt pathway.

One-Carbon Metabolism in Fatty Liver Disease and Fibrosis: One-Carbon to Rule Them All

Nonalcoholic fatty liver disease (NAFLD) is a term used to characterize a range of disease states that involve the accumulation of fat in the liver but are not associated with excessive alcohol consumption. NAFLD is a prevalent disease that can progress to organ damage like liver cirrhosis and hepatocellular carcinoma. Many animal models have demonstrated that one-carbon metabolism is strongly associated with NAFLD. Phosphatidylcholine is an important phospholipid that affects hepatic lipid homeostasis and de novo synthesis of this phospholipid is associated with NAFLD. However, one-carbon metabolism serves to support all cellular methylation reactions and catabolism of methionine, serine, glycine, choline, betaine, tryptophan, and histidine. Several different pathways within one-carbon metabolism that play important roles in regulating energy metabolism and immune function have received less attention in the study of fatty liver disease and fibrosis. This review examines what we have learned about hepatic lipid metabolism and liver damage from the study of one-carbon metabolism thus far and highlights unexplored opportunities for future research.

Metabolic, Molecular, and Behavioral Effects of Western Diet in Serotonin Transporter-Deficient Mice: Rescue by Heterozygosity?

Reduced function of the serotonin transporter (SERT) is associated with increased susceptibility to anxiety and depression and with type-2 diabetes, which is especially true in older women. Preference for a "Western diet" (WD), enriched with saturated fat, cholesterol, and sugars, may aggravate these conditions. In previous studies, decreased glucose tolerance, central and peripheral inflammation, dyslipidemia, emotional, cognitive, and social abnormalities were reported in WD-fed young female mice. We investigated the metabolic, molecular, and behavioral changes associated with a 3-week-long dietary regime of either the WD or control diet in 12-month-old female mice with three different Sert genotypes: homozygous (Slc6a4) gene knockout (Sert ^-/-: KO), heterozygous (Sert ^+/-: HET), or wild-type mice (Sert ^+/+: WT). In the WT-WD and KO-WD groups, but not in HET-WD-fed mice, most of changes induced by the WD paralleled those found in the younger mice, including brain overexpression of inflammatory marker Toll-like receptor 4 (Tlr4) and impaired hippocampus-dependent performance in the marble test. However, the 12-month-old female mice became obese. Control diet KO mice exhibited impaired hippocampal-dependent behaviors, increased brain expression of the serotonin receptors Htr2c and Htr1b, as well as increased Tlr4 and mitochondrial regulator, peroxisome proliferator-activated receptor gamma-coactivator-1a (Ppargc1a). Paradoxically, these, and other changes, were reversed in KO-WD mutants, suggesting a complex interplay between Sert deficiency and metabolic factors as well as potential compensatory molecular mechanisms that might be disrupted by the WD exposure. Most, but not all, of the changes in gene expression in the brain and liver of KO mice were not exhibited by the HET mice fed with either diet. Some of the WD-induced changes were similar in the KO-WD and HET-WD-fed mice, but the latter displayed a "rescued" phenotype in terms of diet-induced abnormalities in glucose tolerance, neuroinflammation, and hippocampus-dependent performance. Thus, complete versus partial Sert inactivation in aged mice results in distinct metabolic, molecular, and behavioral consequences in response to the WD. Our findings show that Sert ^+/- mice are resilient to certain environmental challenges and support the concept of heterosis as evolutionary adaptive mechanism.

Effect of Pregnancy on Paroxetine-Induced Adiposity and Glucose Intolerance in Mice

Long-term use of selective serotonin reuptake inhibitors (SSRIs) targeting the serotonin transporter (SERT) has been suggested to be associated with an increased risk for obesity and type 2 diabetes. Previously, using a murine knockout model of SERT, we showed that estrogen suppression is involved in SERT deficiency-induced obesity and glucose intolerance in nonpregnant mice. The present study investigated the effects of chronic paroxetine treatment on adiposity and glucose tolerance in mice before and during pregnancy. Chronic paroxetine treatment in nonpregnant mice resulted in visceral adiposity and glucose intolerance accompanied by reduced circulating 17β-estradiol levels and ovarian expression of the aromatase (CYP19a1). Remarkably, pregnancy significantly reduced adiposity and improved glucose tolerance in paroxetine-treated mice by rebooting ovarian CYP19a1 expression and 17β-estradiol production. These effects appear to be reversible as ovarian CYP19a1 expression and circulating 17β-estradiol returned to prepregnancy levels soon after parturition. As in pregnant mice, 17β-estradiol replacement treatment in nonpregnant mice reduced paroxetine-induced adiposity. Our findings further suggested that modulation of estrogen synthesis underlies the observed metabolic adverse effects of SSRIs. Although our data revealed a transient reversal effect of pregnancy on SSRI-induced metabolic abnormalities, these observations are experimental and limited to mice. The use of SSRIs during human pregnancy should be cautioned because of potential adverse effects to the fetuses.

Emerging Roles for Serotonin in Regulating Metabolism: New Implications for an Ancient Molecule

Serotonin is a phylogenetically ancient biogenic amine that has played an integral role in maintaining energy homeostasis for billions of years. In mammals, serotonin produced within the central nervous system regulates behavior, suppresses appetite, and promotes energy expenditure by increasing sympathetic drive to brown adipose tissue. In addition to these central circuits, emerging evidence also suggests an important role for peripheral serotonin as a factor that enhances nutrient absorption and storage. Specifically, glucose and fatty acids stimulate the release of serotonin from the duodenum, promoting gut peristalsis and nutrient absorption. Serotonin also enters the bloodstream and interacts with multiple organs, priming the body for energy storage by promoting insulin secretion and de novo lipogenesis in the liver and white adipose tissue, while reducing lipolysis and the metabolic activity of brown and beige adipose tissue. Collectively, peripheral serotonin acts as an endocrine factor to promote the efficient storage of energy by upregulating lipid anabolism. Pharmacological inhibition of serotonin synthesis or signaling in key metabolic tissues are potential drug targets for obesity, type 2 diabetes, and nonalcoholic fatty liver disease (NAFLD).

Alterations in serotonin transporter and body image-related cognition in anorexia nervosa

The serotonin system has been implicated in the pathophysiology of anorexia nervosa (AN). A recent report proposed that body image distortion (BID), a core symptom of AN, may relate to abnormalities of the serotonin system, especially the serotonin transporter (5HTT). Positron emission tomography (PET) studies of underweight patients with active AN reported alterations in serotonin receptors, but not 5HTT. Here, we aimed to disclose the clinicopathophysiology of AN by focusing on 5HTT and cognitive functions, including BID, in groups with active AN. Twenty-two underweight female patients with AN (12 restricting-type AN (ANR); 10 binge-eating/purging-type AN (ANBP)) and 20 age-matched healthy female subjects underwent PET with a 5HTT radioligand [¹¹C]DASB. The binding potential (BP_ND) of [¹¹C]DASB was estimated semiquantitatively, and clinical data from Raven's colored progressive matrices for general intelligence, the Stroop test for focused attention, the Iowa gambling task for decision making and a dot-probe task designed for BID were compared with the levels of BP_ND in different groups. [¹¹C]DASB BP_ND was significantly decreased in the medial parietal cortex in patients with AN and in the dorsal raphe in patients with ANR compared with healthy subjects (p < .05 corrected). Patients with ANR showed a significantly negative correlation between [¹¹C]DASB BP_ND in the dorsal raphe and performance on the dot-probe task (p < .05 corrected). While reduced 5HTT in the medial parietal cortex (the somatosensory association area) is pathophysiologically important in AN in general, additional 5HTT reduction in the dorsal raphe as seen in ANR is implicated for the clinicopathophysiological relevance.

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5HTT decreased in the parietal cortex in patients with AN.

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5HTT decreased in the parietal cortex in patients with ANBP.

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5HTT decreased in the parietal cortex and the dorsal raphe in patients with ANR.

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Patients with AN were poor at responding to the test for body image distortion (BID).

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5HTT in the dorsal raphe was associated with cognitive performance of BID.

Hirsutanol A Attenuates Lipopolysaccharide-Mediated Matrix Metalloproteinase 9 Expression and Cytokines Production and Improves Endotoxemia-Induced Acute Sickness Behavior and Acute Lung Injury

Activated human monocytes/macrophages, which increase the levels of matrix metalloproteinases (MMPs) and pro-inflammatory cytokines, are the essential mechanisms for the progression of sepsis. In the present study, we determined the functions and mechanisms of hirsutanolA (HA), which is isolated from the red alga-derived marine fungus Chondrostereum sp. NTOU4196, on the production of pro-inflammatory mediators produced from lipopolysaccharide (LPS)-treated THP-1 cells. Our results showed that HA suppressed LPS-triggered MMP-9-mediated gelatinolysis and expression of protein and mRNA in a concentration-dependent manner without effects on TIMP-1 activity. Also, HA significantly attenuated the levels of TNF-α, IL-6, and IL-1β from LPS-treated THP-1 cells. Moreover, HA significantly inhibited LPS-mediated STAT3 (Tyr705) phosphorylation, IκBα degradation and ERK1/2 activation in THP-1 cells. In an LPS-induced endotoxemia mouse model, studies indicated that HA pretreatment improved endotoxemia-induced acute sickness behavior, including acute motor deficits and anxiety-like behavior. HA also attenuated LPS-induced phospho-STAT3 and pro-MMP-9 activity in the hippocampus. Notably, HA reduced pathologic lung injury features, including interstitial tissue edema, infiltration of inflammatory cells and alveolar collapse. Likewise, HA suppressed the induction of phospho-STAT3 and pro-MMP-9 in lung tissues. In conclusion, our results provide pharmacological evidence that HA could be a useful agent for treating inflammatory diseases, including sepsis.

Potentiation of serotonin signaling leads to increased carbohydrate and lipid absorption in the murine small intestine

BACKGROUND

Enteric serotonin influences intestinal homeostasis and functions as a mucosal growth factor. Previously, we demonstrated increased mucosal surface area and enhanced crypt cell proliferation in serotonin reuptake transporter (SERT)-deficient mice. Therefore, we hypothesized that serotonin-mediated mucosal growth would also result in enhanced carbohydrate and lipid absorption.

MATERIAL AND METHODS

Wild-type C57Bl/6 (WT) and SERT-knockout (SERTKO) mice were fasted then gavaged with D-xylose or boron-dipyrromethene (BODIPY) FL-C12 medium-chain fatty acid analog. Serum D-xylose and BODIPY concentrations were serially measured from blood drawn at 30 to 360 min post-gavage. Small intestine was harvested from both groups for comparison of morphometric parameters. Area under the curve of plotted graphs was calculated, and means were compared with Student's t-test to a significance of p < 0.05.

RESULTS

Villus height and crypt depth were significantly greater in the middle and distal small intestine of SERTKO animals compared to WT. Overall absorption of D-xylose and BODIPY was greater in SERTKO animals compared to WT animals. Absorption of D-xylose was persistently elevated in SERTKO animals, while there was an initial delay in BODIPY absorption followed by a sustained and significantly greater absorption in SERTKO animals at 60-360 min after gavage.

CONCLUSION

Potentiation of serotonin signaling in SERTKO mice results in small intestinal mucosal growth and enhanced carbohydrate and fat absorption in vivo. These functional increases support the concept of targeting the serotonin signaling system to augment intestinal adaptation in the setting of intestinal failure.

Differential SLC6A4 methylation: a predictive epigenetic marker of adiposity from birth to adulthood

BACKGROUND

The early life environment may influence susceptibility to obesity and metabolic disease in later life through epigenetic processes. SLC6A4 is an important mediator of serotonin bioavailability, and has a key role in energy balance. We tested the hypothesis that methylation of the SLC6A4 gene predicts adiposity across the life course.

METHODS

DNA methylation at 5 CpGs within the SLC6A4 gene identified from a previous methyl binding domain array was measured by pyrosequencing. We measured DNA methylation in umbilical cord (UC) from children in the Southampton Women's Survey cohort (n = 680), in peripheral blood from adolescents in the Western Australian Pregnancy Cohort Study (n = 812), and in adipose tissue from lean and obese adults from the UK BIOCLAIMS cohort (n = 81). Real-time PCR was performed to assess whether there were corresponding alterations in gene expression in the adipose tissue.

RESULTS

Lower UC methylation of CpG5 was associated with higher total fat mass at 4 years (p = 0.031), total fat mass at 6-7 years (p = 0.0001) and % fat mass at 6-7 years (p = 0.004). Lower UC methylation of CpG5 was also associated with higher triceps skinfold thickness at birth (p = 0.013), 6 months (p = 0.038), 12 months (p = 0.062), 2 years (p = 0.0003), 3 years (p = 0.00004) and 6-7 years (p = 0.013). Higher maternal pregnancy weight gain (p = 0.046) and lower parity (p = 0.029) were both associated with lower SLC6A4 CpG5 methylation. In adolescents, lower methylation of CpG5 in peripheral blood was associated with greater concurrent measures of adiposity including BMI (p ≤ 0.001), waist circumference (p = 0.011), subcutaneous fat (p ≤ 0.001) and subscapular, abdominal and suprailiac skinfold thicknesses (p = 0.002, p = 0.008, p = 0.004, respectively). In adipose tissue, methylation of both SLC6A4 CpG5 (p = 0.019) and expression of SLC6A4 (p = 0.008) was lower in obese compared with lean adults.

CONCLUSIONS

These data suggest that altered methylation of CpG loci within SLC6A4 may provide a robust marker of adiposity across the life course.

Serotonin Transporter Deficiency is Associated with Dysbiosis and Changes in Metabolic Function of the Mouse Intestinal Microbiome

Serotonin transporter (SERT) plays a critical role in regulating extracellular availability of serotonin (5-HT) in the gut and brain. Mice with deletion of SERT develop metabolic syndrome as they age. Changes in the gut microbiota are being increasingly implicated in Metabolic Syndrome and Diabetes. To investigate the relationship between the gut microbiome and SERT, this study assessed the fecal and cecal microbiome profile of 11 to 12 week-old SERT+/+ and SERT-/- mice. Microbial DNA was isolated, processed for metagenomics shotgun sequencing, and taxonomic and functional profiles were assessed. 34 differentially abundant bacterial species were identified between SERT+/+ and SERT-/-. SERT-/- mice displayed higher abundances of Bacilli species including genera Lactobacillus, Streptococcus, Enterococcus, and Listeria. Furthermore, SERT-/- mice exhibited significantly lower abundances of Bifidobacterium species and Akkermansia muciniphilia. Bacterial community structure was altered in SERT-/- mice. Differential abundance of bacteria was correlated with changes in host gene expression. Bifidobacterium and Bacilli species exhibited significant associations with host genes involved in lipid metabolism pathways. Our results show that SERT deletion is associated with dysbiosis similar to that observed in obesity. This study contributes to the understanding as to how changes in gut microbiota are associated with metabolic phenotype seen in SERT deficiency.

Association with serotonin transporter enables the phosphorylation of insulin receptor in placenta

Upon binding to insulin, the β-subunit of insulin receptor (IR) is phosphorylated and instantly activates intracellular signaling. A defect in this process causes the development of several metabolic disorders including non-insulin-dependent diabetes, such as type 2 and gestational diabetes mellitus (GDM). Under diabetic conditions the phosphorylation of IR in placenta, but not in platelets, is impaired. Interestingly the cellular distribution of the serotonin transporter (SERT), which utilizes the insulin signaling for posttranslational modification, shows tissue-type-dependent variation: SERT function is impaired in GDM-associated placenta, but not in platelets. In order to understand the correlation between IR, SERT and their tissue-type-dependent features, we tested an association between SERT and IR and whether this association affects the phosphorylation of IR. Using various approaches, we demonstrated a physical association between the Carboxyl terminal of SERT and the β-subunit of IR. This association was found on the plasma membrane of the placenta and the platelets. Next, the contribution of the SERT-IR association to the phosphorylation of IR was analyzed in heterologous and endogenous expression systems following insulin-treatment. The in vivo impact of SERT-IR association on the phosphorylation of IR was explored in placenta and platelets of SERT gene knockout (KO) mice. The IR phosphorylation was significantly downregulated only in the placenta, but not in platelets of SERT-KO mice. These findings are supported by time course experiments, which demonstrate that the phosphorylation of IR occurs vis-a-vis IR-SERT association, and at least one of the IR binding domains is identified as the carboxyl-terminus of SERT. These findings suggest an important role for IR-SERT association in maintaining the phosphorylation of IR and regulating the insulin signaling in placenta.

Serotonin induced hepatic steatosis is associated with modulation of autophagy and notch signaling pathway

Background

Besides its neurotransmitter and vasoconstriction functions, serotonin is an important mediator of numerous biological processes in peripheral tissues including cell proliferation, steatosis, and fibrogenesis. Recent reports indicate that serotonin may promote tumor growth in liver cancer, however, the molecular mechanisms remain elusive. n this study, we investigated the role and molecular signaling mechanisms mediated by serotonin in liver cancer cell survival, drug resistance, and steatosis.

Methods

Effect of serotonin on modulation of cell survival/proliferation was determined by MTT/WST1 assay. Effect of serotonin on the regulation of autophagy biomarkers and lipid/fatty acid proteins expression, AKT/mTOR and Notch signaling was evaluated by immunoblotting. The role of serotonin in normal human hepatocytes and liver cancer cell steatosis was analyzed by Oil Red O staining. The mRNA expression levels of lipid/fatty acid proteins and serotonin receptors were validated by qRT-PCR. The important roles of autophagy, Notch signaling, serotonin receptors and serotonin re-uptake proteins on serotonin-mediated cell steatosis were investigated by using selective inhibitors or antagonists. The association of peripheral serotonin, autophagy, and hepatic steatosis was also investigated using chronic EtOH fed mouse model.

Results

Exposure of liver cancer cells to serotonin induced Notch signaling and autophagy, independent of AKT/mTOR pathway. Also, serotonin enhanced cancer cell proliferation/survival and drug resistance. Furthermore, serotonin treatment up-regulated the expression of lipogenic proteins and increased steatosis in liver cancer cells. Inhibition of autophagy or Notch signaling reduced serotonin-mediated cell steatosis. Treatment with serotonin receptor antagonists 5-HTr1B and 5-HTr2B reduced serotonin-mediated cell steatosis; in contrast, treatment with selective serotonin reuptake inhibitors (SSRIs) increased steatosis. In addition, mice fed with chronic EtOH resulted in increased serum serotonin levels which were associated with the induction of hepatic steatosis and autophagy.

Conclusions

Serotonin regulates liver cancer cell steatosis, cells survival, and may promote liver carcinogenesis by activation of Notch signaling and autophagy.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0282-6) contains supplementary material, which is available to authorized users.

Aptamer-field-effect transistors overcome Debye length limitations for small-molecule sensing

Detection of analytes by means of field-effect transistors bearing ligand-specific receptors is fundamentally limited by the shielding created by the electrical double layer (the "Debye length" limitation). We detected small molecules under physiological high-ionic strength conditions by modifying printed ultrathin metal-oxide field-effect transistor arrays with deoxyribonucleotide aptamers selected to bind their targets adaptively. Target-induced conformational changes of negatively charged aptamer phosphodiester backbones in close proximity to semiconductor channels gated conductance in physiological buffers, resulting in highly sensitive detection. Sensing of charged and electroneutral targets (serotonin, dopamine, glucose, and sphingosine-1-phosphate) was enabled by specifically isolated aptameric stem-loop receptors.

Maternal Western diet during gestation and lactation modifies adult offspring's cognitive and hedonic brain processes, behavior, and metabolism in Yucatan minipigs

This study explores the long-term effects of exposure to a maternal Western diet (WD) vs. standard diet (SD) in the Yucatan minipig, on the adult progeny at lean status ( n = 32), and then overweight status. We investigated eating behavior, cognitive abilities, brain basal glucose metabolism, dopamine transporter availability, microbiota activity, blood lipids, and glucose tolerance. Although both groups demonstrated similar cognitive abilities in a holeboard test, WD pigs expressed a higher stress level than did SD pigs (immobility, P < 0.05) and lower performance in an alley maze ( P = 0.06). WD pigs demonstrated lower dopamine transporter binding potential in the hippocampus and parahippocampal cortex ( P < 0.05 for both), as well as a trend in putamen ( P = 0.07), associated with lower basal brain activity in the prefrontal cortex and nucleus accumbens ( P < 0.05) compared with lean SD pigs. Lean WD pigs demonstrated a lower glucose tolerance than did SD animals (higher glucose peak, P < 0.05) and a tendency to a higher incremental area under the curve of insulin from 0 to 30 minutes after intravenous glucose injection ( P < 0.1). Both groups developed glucose intolerance with overweight, but WD animals were less impacted than SD animals. These results demonstrate that maternal diet shaped the offspring's brain functions and cognitive responses long term, even after being fed a balanced diet from weaning, but behavioral effects were only revealed in WD pigs under anxiogenic situation; however, WD animals seemed to cope better with the obesogenic diet from a metabolic standpoint.-Gautier, Y., Luneau, I., Coquery, N., Meurice, P., Malbert, C.-H., Guerin, S., Kemp, B., Bolhuis, J. E., Clouard, C., Le Huërou-Luron, I., Blat, S., Val-Laillet, D. Maternal Western diet during gestation and lactation modifies adult offspring's cognitive and hedonic brain processes, behavior, and metabolism in Yucatan minipigs.

Inhibition of Serotonin Synthesis Induces Negative Hepatic Lipid Balance

BACKGROUND

Hepatic steatosis is caused by metabolic stress associated with a positive lipid balance, such as insulin resistance and obesity. Previously we have shown the anti-obesity effects of inhibiting serotonin synthesis, which eventually improved insulin sensitivity and hepatic steatosis. However, it is not clear whether serotonin has direct effect on hepatic lipid accumulation. Here, we showed the possibility of direct action of serotonin on hepatic steatosis.

METHODS

Mice were treated with para-chlorophenylalanine (PCPA) or LP-533401 to inhibit serotonin synthesis and fed with high fat diet (HFD) or high carbohydrate diet (HCD) to induce hepatic steatosis. Hepatic triglyceride content and gene expression profiles were analyzed.

RESULTS

Pharmacological and genetic inhibition of serotonin synthesis reduced HFD-induced hepatic lipid accumulation. Furthermore, short-term PCPA treatment prevented HCD-induced hepatic steatosis without affecting glucose tolerance and browning of subcutaneous adipose tissue. Gene expression analysis revealed that the expressions of genes involved in de novo lipogenesis and triacylglycerol synthesis were downregulated by short-term PCPA treatment as well as long-term PCPA treatment.

CONCLUSION

Short-term inhibition of serotonin synthesis prevented hepatic lipid accumulation without affecting systemic insulin sensitivity and energy expenditure, suggesting the direct steatogenic effect of serotonin in liver.

Autonomic nervous system network and liver regeneration

To date, various signal transducers, cytokines, growth factors, and hormones have been reported to play an important role in homeostasis of various organs. Various cells and organs are involved in the hepatic regeneration process, which proceeds as a result of the coordination of many factors. While these factors are well known to be involved in the liver regeneration after the liver injury, however, as the details of such mechanisms have not been sufficiently elucidated, the practical applicability of hepatic regeneration based on the action of these and cytokines growth factors is still unclear. In terms of the involvement of the autonomic nervous system in hepatic regeneration, cell proliferation resulting from direct signal transduction to the liver has also been reported and recent studies focusing on the inter-organ communication via neural network opened a novel aspect of this field for therapeutic applicability. Therefore, the appropriate understanding of the relationship between autonomic neural network and liver regeneration through various organs including brain, afferent nerve, efferent nerve, etc. is essential. This mini-review explains the principle of neural system involved in the inter-organ communication and its contribution on the liver regeneration upon the liver injury reviewing recent progress in this field.

Effect of a neural relay on liver regeneration in mice: activation of serotonin release from the gastrointestinal tract

The development of therapeutic options to promote hepatic regeneration following severe liver injury is essential. While humoral factors have been reported as mechanisms of liver regeneration, the contributions of interorgan communication to liver regeneration have not been reported. In this study, we examined the effect of a neural relay on liver regeneration via activation of serotonin release from the gastrointestinal (GI) tract. Our results demonstrated that the afferent visceral nerve from the liver activates the efferent vagus nerve from the brain, leading to activation of serotonin release from the GI tract and contributing to liver regeneration. While it is difficult to apply these results directly to human health, we believe that this study may represent a step toward developing essential therapeutics to promote liver regeneration.

SLC6A4 5HTTLPR Polymorphism Affects Insulin Secretion in Patients with Polycystic Ovary Syndrome

PURPOSE

To investigate in a pilot study of genetic polymorphisms in serotonin system influencing basal- and glucose-stimulated insulin secretion in women with polycystic ovary syndrome (PCOS).

METHODS

A cross-sectional study included 65 female patients with PCOS followed up at the endocrine outpatient clinic of the University Medical Center Ljubljana and a control group of 94 young healthy female blood donors. Oral glucose tolerance test was performed only in PCOS patients and basal- and glucose-stimulated blood glucose and insulin levels were measured. All the subjects were genotyped for 5HTR1A rs6295, 5HTR1B rs13212041, and SLC6A4 5HTTLPR polymorphisms in the serotonin system.

RESULTS

Genotype distributions were in accordance with the Hardy-Weinberg equilibrium (HWE), except for 5HTR1A rs6295 in healthy controls and 5HTR1B rs13212041 in PCOS patients that were not consistent with HWE. SLC6A4 5HTTLPR polymorphism was significantly associated with insulin secretion (p = 0.030) and with the area under the curve of insulin blood levels during OGTT (p = 0.021). None of the investigated polymorphisms was significantly associated with basal- or glucose-stimulated blood glucose levels at any point in time during OGTT or with the basal insulin concentration.

CONCLUSIONS

Serotonin system may play a role in glucose-stimulated insulin secretion in patients with insulin resistance (IR) and decreased insulin sensitivity. Further studies are needed to conclude whether the observed effect is characteristic for PCOS-related metabolic disturbances or for the identified mutation in different high metabolic risk populations.

Serotonin transporter deficiency drives estrogen-dependent obesity and glucose intolerance

Depression and use of antidepressant medications are both associated with increased risk of obesity, potentially attributed to a reduced serotonin transporter (SERT) function. However, how SERT deficiency promotes obesity is unknown. Here, we demonstrated that SERT^−/− mice display abnormal fat accumulation in both white and brown adipose tissues, glucose intolerance and insulin resistance while exhibiting suppressed aromatase (Cyp19a1) expression and reduced circulating 17β-estradiol levels. 17β-estradiol replacement in SERT^−/− mice reversed the obesity and glucose intolerance, supporting a role for estrogen in SERT deficiency-associated obesity and glucose intolerance. Treatment of wild type mice with paroxetine, a chemical inhibitor of SERT, also resulted in Cyp19a1 suppression, decreased circulating 17β-estradiol levels, abnormal fat accumulation, and glucose intolerance. Such effects were not observed in paroxetine-treated SERT^−/− mice. Conversely, pregnant SERT^−/− mice displayed normalized estrogen levels, markedly reduced fat accumulation, and improved glucose tolerance, which can be eliminated by an antagonist of estrogen receptor α (ERα). Together, these findings support that estrogen suppression is involved in SERT deficiency-induced obesity and glucose intolerance, and suggest approaches to restore 17β-estradiol levels as a novel treatment option for SERT deficiency associated obesity and metabolic abnormalities.

Serotonin transporter protects the placental cells against apoptosis in caspase 3-independent pathway

Serotonin (5-HT) and its specific transporter, SERT play important roles in pregnancy. Using placentas dissected from 18d gestational SERT-knock out (KO), peripheral 5-HT (TPH1)-KO, and wild-type (WT) mice, we explored the role of 5-HT and SERT in placental functions in detail. An abnormal thick band of fibrosis and necrosis under the giant cell layer in SERT-KO placentas appeared only moderately in TPH1-KO and minimally present in WT placentas. The majority of the changes were located at the junctional zone of the placentas in SERT. The etiology of these findings was tested with TUNEL assays. The placentas from SERT-KO and TPH1-KO showed 49- and 8-fold increase in TUNEL-positive cells without a concurrent change in the DNA repair or cell proliferation compared to WT placentas. While the proliferation rate in the embryos of TPH1-KO mice was 16-fold lower than the rate in gestational age matched embryos of WT or SERT-KO mice. These findings highlight an important role of continuous 5-HT signaling on trophoblast cell viability. SERT may contribute to protecting trophoblast cells against cell death via terminating the 5-HT signaling which changes cell death ratio in trophoblast as well as proliferation rate in embryos. However, the cell death in SERT-KO placentas is in caspase 3-independent pathway.

He-Wei granules inhibit chemotherapy-induced vomiting (CINV) in rats by reducing oxidative stress and regulating 5-HT, substance P, ghrelin and obestatin

As a common side effect of a variety of chemotherapy drugs, CINV severely limits the clinical use of chemotherapy drugs.

Serotonin Transporter Binding in the Diencephalon Is Reduced in Insulin-Resistant Obese Humans

BACKGROUND

Altered brain dopaminergic and serotonergic pathways have been shown in obese rodents and humans, but it is unknown whether this is related to obesity per se or to the metabolic derangements associated with obesity.

METHODS

We performed a case-control study in insulin-sensitive obese (ISO) and insulin-resistant obese (IRO) subjects (n = 12) and age-matched lean controls (n = 8) and measured serotonin transporter (SERT) binding in the whole diencephalon and specifically in the hypothalamus, as well as dopamine transporter (DAT) binding in the striatum using 123I- FP-CIT single-photon emission computed tomography. We assessed insulin sensitivity using the homeostatic model assessment of insulin resistance.

RESULTS

BMI did not differ between the IRO and ISO subjects. SERT binding in the diencephalon was significantly lower in IRO than in ISO subjects, but was not different between lean and obese subjects. SERT binding in the hypothalamus tended to be reduced in obese versus lean subjects, but was not different between IRO and ISO subjects. Striatal DAT binding was similar between lean and obese subjects as well as between ISO and IRO subjects.

CONCLUSIONS

We conclude that SERT binding in the diencephalon is reduced in insulin-resistant subjects independently of body weight, while hypothalamic SERT binding tends to be lower in obesity, with no difference between insulin-resistant and insulin-sensitive subjects. This suggests that the metabolic perturbations associated with obesity independently affect SERT binding within the diencephalon.

The emerging roles of human trace amines and human trace amine-associated receptors (hTAARs) in central nervous system

Human trace amines (TAs) are endogenous compounds, previously almost ignored in human pathology for many reasons (difficulty of their measurement in biological fluids, unknown receptors for elusive amines), are now considered to play a significant role in synaptic transmission within the central nervous system (CNS) acting as neuromodulators. The recent discovery of a novel family of G-protein-coupled receptors (GPCRs) that includes individual members that are highly specific for TAs indicates a potential role for TAs as vertebrate neurotransmitters or neuromodulators, although the majority of these GPCRs so far have not been demonstrated to be activated by TAs. Human trace amine receptors (including TAAR1 TAAR2 TAAR5 TAAR6 TAAR8 TAAR9) are expressed in the brain and play significant physiological and neuropathological roles by activation of trace amines. We herein discuss the recent findings that provide insights into the functional roles of human trace amines (including P-Octopamine, β phenylethylamine, Tryptamine, Tyramine, Synephrine, 3-Iodothyronamine, 3-Methoxytyramine, N-Methyltyramine, N-Methylphenethylamine) in brain. Furthermore, we discuss the known functions of human trace amine receptors in brain.

Sleep restriction acutely impairs glucose tolerance in rats

Chronic sleep curtailment in humans has been related to impairment of glucose metabolism. To better understand the underlying mechanisms, the purpose of the present study was to investigate the effect of acute sleep deprivation on glucose tolerance in rats. A group of rats was challenged by 4-h sleep deprivation in the early rest period, leading to prolonged (16 h) wakefulness. Another group of rats was allowed to sleep during the first 4 h of the light period and sleep deprived in the next 4 h. During treatment, food was withdrawn to avoid a postmeal rise in plasma glucose. An intravenous glucose tolerance test (IVGTT) was performed immediately after the sleep deprivation period. Sleep deprivation at both times of the day similarly impaired glucose tolerance and reduced the early-phase insulin responses to a glucose challenge. Basal concentrations of plasma glucose, insulin, and corticosterone remained unchanged after sleep deprivation. Throughout IVGTTs, plasma corticosterone concentrations were not different between the control and sleep-deprived group. Together, these results demonstrate that independent of time of day and sleep pressure, short sleep deprivation during the resting phase favors glucose intolerance in rats by attenuating the first-phase insulin response to a glucose load. In conclusion, this study highlights the acute adverse effects of only a short sleep restriction on glucose homeostasis.

Association of DRD3, COMT, and SLC6A4 Gene Polymorphisms with Type 2 Diabetes in Southern Chinese: A Hospital-Based Case-Control Study

AIM

The aim of this study was to assess the associations of six single nucleotide polymorphisms (SNPs) of three genes (DRD3, COMT, and SCL6A4) with type 2 diabetes mellitus (T2DM) in Southern Chinese.

SUBJECTS AND METHODS

Five hundred ninety-five cases with T2DM and 725 healthy controls of Han origin were recruited from six hospitals in Guangdong Province, Southern China. Fasting serum concentrations of markers of interest (total cholesterol, triglyceride, plasma glucose, etc.) were measured in hospitals. SNP genotyping was performed using a custom-by-design 2-×48-Plex SNPscan™ kit (Genesky Biotechnologies Inc., Shanghai, China). Single-point SNP analysis, haplotype analysis, and SNP-SNP interactions were carried out.

RESULTS

SNP rs4646312 in COMT achieved statistical significance in both allelic association and genotypic association and even after adjusting covariates (odds ratio [OR]=1.26; 95% confidence interval [CI], 1.04-1.53; P=0.021). Two haplotypes consisting of rs4646312 and rs4680 were also significantly associated with T2DM, of which C-G was a protective haplotype for T2DM (OR=0.83; 95% CI, 0.70-0.98; P=0.029), whereas T-A was a risk one (OR=1.23, 95% CI, 1.03-1.46; P=0.022). Interaction analysis identified a significant epistatic effect between rs4680 in COMT and rs2066713 in SCL6A4 after adjusting for covariates (OR=3.59, 95% CI, 1.72-7.48; P=0.001 for dominant-dominant model). However, only the interaction between rs4680 and rs2066713 was significant, and haplotype T-A showed a marginally increased risk after Bonferroni correction.

CONCLUSIONS

The genetic polymorphisms in COMT and SCL6A4 confer significant effects in joint actions to T2DM in Southern Chinese.

Serotonin, a possible intermediate between disturbed circadian rhythms and metabolic disease

It is evident that eating in misalignment with the biological clock (such as in shift work, eating late at night and skipping breakfast) is associated with increased risk for obesity and diabetes. The biological clock located in the suprachiasmatic nucleus dictates energy balance including feeding behavior and glucose metabolism. Besides eating and sleeping patterns, glucose metabolism also exhibits clear diurnal variations with higher blood glucose concentrations, glucose tolerance and insulin sensitivity prior to waking up. The daily variation in plasma glucose concentrations in rats, is independent of the rhythm in feeding behavior. On the other hand, feeding itself has profound effects on glucose metabolism, but differential effects occur depending on the time of the day. We here review data showing that a disturbed diurnal eating pattern results in alterations in glucose metabolism induced by a disrupted circadian clock. We first describe the role of central serotonin on feeding behavior and glucose metabolism and subsequently describe the effects of central serotonin on the circadian system. We next explore the interaction between the serotonergic system and the circadian clock in conditions of disrupted diurnal rhythms in feeding and how this might be involved in the metabolic dysregulation that occurs with chronodisruption.

Which demographic variables are necessary to correct in neuroimaging studies of serotonin transporter availability? A SPECT study with [¹²³I]ADAM

Previous studies have shown that many demographic variables influence serotonin transporter (SERT) availability as assessed by single photon emission computed tomography (SPECT). The aim of this study was to explore which demographic variables influenced the SERT availability most in a SPECT study with [(123)I]ADAM. Ninety-five healthy volunteers were recruited. Age, sex, smoking, alcohol intake, educational level, body mass index, seasonal change, and SERT availability were recorded and then analyzed by multivariate linear regression. Age was the only variable that was significantly associated with SERT availability (calculate: (midbrain-cerebellum)/cerebellum). Furthermore, the inverse correlation of age and SERT availability may be present only before the age of 47. Age should be a covariate in SERT-related neuroimaging analyses, particularly in participants under the age of 47 years.