Role of the neurotrophin network in eating disorders' subphenotypes: body mass index and age at onset of the disease

Risk factors for eating disorders: findings from a rapid review

BACKGROUND

Risk factors represent a range of complex variables associated with the onset, development, and course of eating disorders. Understanding these risk factors is vital for the refinement of aetiological models, which may inform the development of targeted, evidence-based prevention, early intervention, and treatment programs. This Rapid Review aimed to identify and summarise research studies conducted within the last 12 years, focusing on risk factors associated with eating disorders.

METHODS

The current review forms part of a series of Rapid Reviews to be published in a special issue in the Journal of Eating Disorders, funded by the Australian Government to inform the development of the National Eating Disorder Research and Translation Strategy 2021-2031. Three databases were searched for studies published between 2009 and 2021, published in English, and comprising high-level evidence studies (meta-analyses, systematic reviews, moderately sized randomised controlled studies, moderately sized controlled-cohort studies, or population studies). Data pertaining to risk factors for eating disorders were synthesised and outlined in the current paper.

RESULTS

A total of 284 studies were included. The findings were divided into nine main categories: (1) genetics, (2) gastrointestinal microbiota and autoimmune reactions, (3) childhood and early adolescent exposures, (4) personality traits and comorbid mental health conditions, (5) gender, (6) socio-economic status, (7) ethnic minority, (8) body image and social influence, and (9) elite sports. A substantial amount of research exists supporting the role of inherited genetic risk in the development of eating disorders, with biological risk factors, such as the role of gut microbiota in dysregulation of appetite, an area of emerging evidence. Abuse, trauma and childhood obesity are strongly linked to eating disorders, however less conclusive evidence exists regarding developmental factors such as role of in-utero exposure to hormones. Comorbidities between eating disorders and mental health disorders, including personality and mood disorders, have been found to increase the severity of eating disorder symptomatology. Higher education attainment, body image-related factors, and use of appearance-focused social media are also associated with increased risk of eating disorder symptoms.

CONCLUSION

Eating disorders are associated with multiple risk factors. An extensive amount of research has been conducted in the field; however, further studies are required to assess the causal nature of the risk factors identified in the current review. This will assist in understanding the sequelae of eating disorder development and in turn allow for enhancement of existing interventions and ultimately improved outcomes for individuals.

Underlying Mechanisms Involved in Gambling Disorder Severity: A Pathway Analysis Considering Genetic, Psychosocial, and Clinical Variables

Gambling Disorder (GD) has a complex etiology that involves biological and environmental aspects. From a genetic perspective, neurotrophic factors (NTFs) polymorphisms have been associated with the risk of developing GD. The aim of this study was to assess the underlying mechanisms implicated in GD severity by considering the direct and mediational relationship between different variables including genetic, psychological, socio-demographic, and clinical factors. To do so, we used genetic variants that were significantly associated with an increased risk for GD and evaluated its relationship with GD severity through pathway analysis. We found that the interaction between these genetic variants and other different biopsychological features predicted a higher severity of GD. On the one hand, the presence of haplotype block 2, interrelated with haplotype block 3, was linked to a more dysfunctional personality profile and a worse psychopathological state, which, in turn, had a direct link with GD severity. On the other hand, having rs3763614 predicted higher general psychopathology and therefore, higher GD severity. The current study described the presence of complex interactions between biopsychosocial variables previously associated with the etiopathogenesis and severity of GD, while also supporting the involvement of genetic variants from the NTF family.

The role of neurotrophin genes involved in the vulnerability to gambling disorder

Evidence about the involvement of genetic factors in the development of gambling disorder (GD) has been assessed. Among studies assessing heritability and biological vulnerability for GD, neurotrophin (NTF) genes have emerged as promising targets, since a growing literature showed a possible link between NTF and addiction-related disorders. Thus, we aimed to explore the role of NTF genes and GD with the hypothesis that some NTF gene polymorphisms could constitute biological risk factors. The sample included 166 patients with GD and 191 healthy controls. 36 single nucleotide polymorphisms (SNPs) from NTFs (NGF, NGFR, NTRK1, BDNF, NTRK2, NTF3, NTRK3, NTF4, CNTF and CNTFR) were selected and genotyped. Linkage disequilibrium (LD) and haplotype constructions were analyzed, in relationship with the presence of GD. Finally, regulatory elements overlapping the identified SNPs variants associated with GD were searched. The between groups comparisons of allele frequencies indicated that 6 SNPs were potentially associated with GD. Single and multiple-marker analyses showed a strong association between both NTF3 and NTRK2 genes, and GD. The present study supports the involvement of the NTF family in the aetiopathogenesis of GD. An altered cross-regulation of different NTF members signalling pathways might be considered as a biological vulnerability factor for GD.

Low-molecular mimetics of nerve growth factor and brain-derived neurotrophic factor: Design and pharmacological properties

To overcome the limitations of the clinical use of neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), scientists have been trying to create their low-molecular-weight mimetics having improved pharmacokinetic properties and lacking side effects of full-sized proteins since the 90s of the last century. The efforts of various research groups have led to the production of peptide and nonpeptide mimetics, being agonists or modulators of the corresponding Trk or p75 receptors that reproduced the therapeutic effects of full-sized proteins. This review discusses different strategies and approaches to the design of such compounds. The relationship between the structure of the mimetics obtained and their action mechanisms and pharmacological properties are analyzed. Special attention is paid to the dipeptide mimetics of individual NGF and BDNF loops having different patterns of activation of Trk receptors signal transduction pathways, phosphoinositide 3-kinase/protein kinase B and mitogen-activated protein kinase/extracellular signal-regulated kinase, which allowed to evaluate the contribution of each pathway to different pharmacological effects. In conclusion, data on therapeutically promising compounds being at different stages of preclinical and clinical studies are summarized.

[Not Available]

Eating disorders (EDs) are complex and multifactorial psychiatric illnesses that induce significant and sustained pathological disruption of food intake. The Diagnostic and Statistical Manual of Mental Illnesses (DSM-5) describes the clinical criteria of major disorders including anorexia nervosa (AN), bulimia nervosa (BN) and binge eating disorder (BED). The neurobiological basis of food intake is well characterized. Epidemiological studies reported a heritability about 70% in AN and 60% in BN, suggesting that genetic factors are involved in the vulnerability to EDs. The analysis of genetic regions and candidate genes identified several genes associated with AN, including the BDNF gene, encoding a neurotrophic factor and the ESR1 gene, encoding the α-receptor to estrogens. Recent genome-wide association studies (GWAS), carried out on several thousand patients versus controls, identify new candidate genes. Preliminary analyses of methylation levels, for candidate genes or on the whole methylome, suggest that epigenetic signatures are associated with EDs.

Harm avoidance involved in mediating the association between nerve growth factor (NGF) gene polymorphisms and antidepressant efficacy in patients with major depressive disorder

BACKGROUND

Antidepressants have variable efficacies in subjects with major depressive disorder (MDD). Nerve growth factor (NGF) has been suggested to play an important role in the pathogenesis of depressive symptoms and the response to antidepressant therapy. The aim of this study was to examine whether NGF gene polymorphisms are associated with the antidepressant therapeutic efficacy in subjects with MDD.

METHODS

A naturalistic follow-up study was carried out on 557 subjects with MDD. Of the enrolled patients, 304 completed the 8-week open-label antidepressant treatment. Seven single-nucleotide polymorphisms (SNPs) of the NGF gene were genotyped. The 21-item Hamilton Depression Rating Scale was used to assess depressive severity from baseline to endpoint. Tridimensional Personality Questionnaire was used to assess baseline personality traits. Single marker and haplotype analyses were conducted. Binary logistic regression was used to calculate odds ratios of remission. Structural equation modeling was used to analyze the predicted mediation effect.

RESULTS

A significant difference in genotype frequencies between remitters and non-remitters was observed in three NGF SNPs (rs12760036, rs7523654, and rs17033692). The haplotype analysis revealed that the CCC haplotype (rs2254527-rs6678788-rs12760036) was associated with a higher remission rate, while the CCA haplotype was associated with a lower remission rate. The harm avoidance psychological factor partially mediated the effect of NGF variants on antidepressant efficacy.

LIMITATIONS

The selected SNPs may not cover whole NGF gene.

CONCLUSIONS

NGF variants are associated with remission rates after 8-week antidepressant treatment, and harm avoidance partially mediated the effect of NGF variants on treatment outcomes.

A genome-wide scan for signatures of directional selection in domesticated pigs

Background

Animal domestication involved drastic phenotypic changes driven by strong artificial selection and also resulted in new populations of breeds, established by humans. This study aims to identify genes that show evidence of recent artificial selection during pig domestication.

Results

Whole-genome resequencing of 30 individual pigs from domesticated breeds, Landrace and Yorkshire, and 10 Asian wild boars at ~16-fold coverage was performed resulting in over 4.3 million SNPs for 19,990 genes. We constructed a comprehensive genome map of directional selection by detecting selective sweeps using an F_ST-based approach that detects directional selection in lineages leading to the domesticated breeds and using a haplotype-based test that detects ongoing selective sweeps within the breeds. We show that candidate genes under selection are significantly enriched for loci implicated in quantitative traits important to pig reproduction and production. The candidate gene with the strongest signals of directional selection belongs to group III of the metabolomics glutamate receptors, known to affect brain functions associated with eating behavior, suggesting that loci under strong selection include loci involved in behaviorial traits in domesticated pigs including tameness.

Conclusions

We show that a significant proportion of selection signatures coincide with loci that were previously inferred to affect phenotypic variation in pigs. We further identify functional enrichment related to behavior, such as signal transduction and neuronal activities, for those targets of selection during domestication in pigs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1330-x) contains supplementary material, which is available to authorized users.

The anorexigenic cytokine ciliary neurotrophic factor stimulates POMC gene expression via receptors localized in the nucleus of arcuate neurons

Ciliary neurotrophic factor (CNTF) is a neural cytokine that reduces appetite and body weight when administrated to rodents or humans. We have demonstrated recently that the level of CNTF in the arcuate nucleus (ARC), a key hypothalamic region involved in food intake regulation, is positively correlated with protection against diet-induced obesity. However, the comprehension of the physiological significance of neural CNTF action was still incomplete because CNTF lacks a signal peptide and thus may not be secreted by the classical exocytosis pathways. Knowing that CNTF distribution shares similarities with that of its receptor subunits in the rat ARC, we hypothesized that CNTF could exert a direct intracrine effect in ARC cells. Here, we demonstrate that CNTF, together with its receptor subunits, translocates to the cell nucleus of anorexigenic POMC neurons in the rat ARC. Furthermore, the stimulation of hypothalamic nuclear fractions with CNTF induces the phosphorylation of several signaling proteins, including Akt, as well as the transcription of the POMC gene. These data strongly suggest that intracellular CNTF may directly modulate POMC gene expression via the activation of receptors localized in the cell nucleus, providing a novel plausible mechanism of CNTF action in regulating energy homeostasis.