TUB gene expression in hypothalamus and adipose tissue and its association with obesity in humans

The Tip of the Iceberg: Genotype of Puerto Rican Pediatric Obesity

Childhood obesity is a significant public health concern, particularly among Hispanic populations. This study aimed to elucidate the genetic predisposition to obesity in Puerto Rican children of Hispanic descent, addressing a notable gap in existing research. A cohort of 103 children with obesity and hyperphagia underwent genetic screening for rare obesity-related variants. Clinical assessments and family history evaluations were conducted to characterize the demographic and clinical characteristics of the cohort. Genetic testing revealed a high prevalence of variants, with 73% of subjects having at least one reported variant. Pathogenic variants, predominantly associated with obesity-related ciliopathies, were identified in 7% of cases. Additionally, 90% of cases had variants of uncertain significance, highlighting the complexity of genetic contributions to obesity. This study emphasizes the critical need for further investigation into the genetic foundations of obesity, particularly within Hispanic communities. The findings emphasize the importance of early medical evaluation, vigilant monitoring for hyperphagia onset, and targeted interventions tailored to the unique genetic landscape of Puerto Rican children. This research provides a foundational framework for future studies to mitigate the impact of genetic obesity within this population.

DNA Hypomethylation-Mediated Transcription Dysregulation Participates in Pathogenesis of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a highly heterogeneous and genetically complex endocrine disorder. Although the etiology remains mostly elusive, growing evidence suggested abnormal changes of DNA methylation correlate well with systemic and tissue-specific dysfunctions in PCOS. A dehydroepiandrosterone-induced PCOS-like mouse model was generated, which has a similar metabolic and reproductive phenotype as human patients with PCOS, and was used to experimentally validate the potential role of aberrant DNA methylation in PCOS in this study. Integrated DNA methylation and transcriptome analysis revealed the potential role of genomic DNA hypomethylation in transcription regulation of PCOS and identified several key candidate genes, including BMP4, Adcy7, Tnfaip3, and Fas, which were regulated by aberrant DNA hypomethylation. Moreover, i.p. injection of S-adenosylmethionine increased the overall DNA methylation level of PCOS-like mice and restored expression of the candidate genes to similar levels as the control, alleviating reproductive and metabolic abnormalities in PCOS-like mice. These findings provided direct evidence showing the importance of normal DNA methylation in epigenetic regulation of PCOS and potential targets for diagnosis and treatment of the disease.

Arcuate Nucleus of the Hypothalamus: Anatomy, Physiology, and Diseases

The hypothalamus is part of the diencephalon and has several nuclei, one of which is the arcuate nucleus. The arcuate nucleus of hypothalamus (ARH) consists of neuroendocrine neurons and centrally-projecting neurons. The ARH is the center where the homeostasis of nutrition/metabolism and reproduction are maintained. As such, dysfunction of the ARH can lead to disorders of nutrition/metabolism and reproduction. Here, we review various types of neurons in the ARH and several genetic disorders caused by mutations in the ARH.

Biallelic Inactivating TUB Variants Cause Retinal Ciliopathy Impairing Biogenesis and the Structure of the Primary Cilium

Inherited retinal degeneration (IRD) represents a clinically variable and genetically heterogeneous group of disorders characterized by photoreceptor dysfunction. These diseases typically present with progressive severe vision loss and variable onset, ranging from birth to adulthood. Genomic sequencing has allowed to identify novel IRD-related genes, most of which encode proteins contributing to photoreceptor-cilia biogenesis and/or function. Despite these insights, knowledge gaps hamper a molecular diagnosis in one-third of IRD cases. By exome sequencing in a cohort of molecularly unsolved individuals with IRD, we identified a homozygous splice site variant affecting the transcript processing of TUB, encoding the first member of the Tubby family of bipartite transcription factors, in a sporadic case with retinal dystrophy. A truncating homozygous variant in this gene had previously been reported in a single family with three subjects sharing retinal dystrophy and obesity. The clinical assessment of the present patient documented a slightly increased body mass index and no changes in metabolic markers of obesity, but confirmed the occurrence of retinal detachment. In vitro studies using patient-derived fibroblasts showed the accelerated degradation of the encoded protein and aberrant cilium morphology and biogenesis. These findings definitely link impaired TUB function to retinal dystrophy and provide new data on the clinical characterization of this ultra-rare retinal ciliopathy.

Acute exercise reduces feeding by activating IL-6/Tubby axis in the mouse hypothalamus

Background: Acute exercise contributes to decreased feeding through leptin and interleukin/Janus kinase 2/signal transducers and activators of transcription 3 (IL-6/JAK2/STAT3) signaling. Considering the pleiotropic use of substrates by JAK2 and that JAK2 can phosphorylate the Tubby protein (TUB) in CHO-IR cells, we speculated that acute exercise can activate the IL-6/JAK2/TUB pathway to decrease food intake.

Aims: We investigated whether acute exercise induced tyrosine phosphorylation and the association of TUB and JAK2 in the hypothalamus and if IL-6 is involved in this response, whether acute exercise increases the IL-6/TUB axis to regulate feeding, and if leptin has an additive effect over this mechanism.

Methods: We applied a combination of genetic, pharmacological, and molecular approaches.

Key findings: The in vivo experiments showed that acute exercise increased the tyrosine phosphorylation and association of JAK2/TUB in the hypothalamus, which reduced feeding. This response was dependent on IL-6. Leptin had no additive effect on this mechanism.

Significance: The results of this study suggest a novel hypothalamic pathway by which IL-6 released by exercise regulates feeding and reinforces the beneficial effects of exercise.

Reviewed and updated Algorithm for Genetic Characterization of Syndromic Obesity Phenotypes

Background: Individuals with a phenotype of early-onset severe obesity associated with intellectual disability can have molecular diagnoses ranging from monogenic to complex genetic traits. Severe overweight is the major sign of a syndromic physical appearance and predicting the influence of a single gene and/or polygenic risk profile is extremely complicated among the majority of the cases. At present, considering rare monogenic bases as the principal etiology for the majority of obesity cases associated with intellectual disability is scientifically poor. The diversity of the molecular bases responsible for the two entities makes the appliance of the current routinely powerful genomics diagnostic tools essential. Objective: Clinical investigation of these difficult-to-diagnose patients requires pediatricians and neurologists to use optimized descriptions of signs and symptoms to improve genotype correlations. Methods: The use of modern integrated bioinformatics strategies which are conducted by experienced multidisciplinary clinical teams. Evaluation of the phenotype of the patient's family is also of importance. Results: The next step involves discarding the monogenic canonical obesity syndromes and considering infrequent unique molecular cases, and/or then polygenic bases. Adequate management of the application of the new technique and its diagnostic phases is essential for achieving good cost/efficiency balances. Conclusion: With the current clinical management, it is necessary to consider the potential coincidence of risk mutations for obesity in patients with genetic alterations that induce intellectual disability. In this review, we describe an updated algorithm for the molecular characterization and diagnosis of patients with a syndromic obesity phenotype.

Mechanisms of Weight Control by Primary Cilia

A primary cilium, a hair-like protrusion of the plasma membrane, is a pivotal organelle for sensing external environmental signals and transducing intracellular signaling. An interesting linkage between cilia and obesity has been revealed by studies of the human genetic ciliopathies Bardet-Biedl syndrome and Alström syndrome, in which obesity is a principal manifestation. Mouse models of cell type-specific cilia dysgenesis have subsequently demonstrated that ciliary defects restricted to specific hypothalamic neurons are sufficient to induce obesity and hyperphagia. A potential mechanism underlying hypothalamic neuron cilia-related obesity is impaired ciliary localization of G protein-coupled receptors involved in the regulation of appetite and energy metabolism. A well-studied example of this is melanocortin 4 receptor (MC4R), mutations in which are the most common cause of human monogenic obesity. In the paraventricular hypothalamus neurons, a blockade of ciliary trafficking of MC4R as well as its downstream ciliary signaling leads to hyperphagia and weight gain. Another potential mechanism is reduced leptin signaling in hypothalamic neurons with defective cilia. Leptin receptors traffic to the periciliary area upon leptin stimulation. Moreover, defects in cilia formation hamper leptin signaling and actions in both developing and differentiated hypothalamic neurons. The list of obesity-linked ciliary proteins is expending and this supports a tight association between cilia and obesity. This article provides a brief review on the mechanism of how ciliary defects in hypothalamic neurons facilitate obesity.

Gene expression atlas of energy balance brain regions

Energy balance is controlled by interconnected brain regions in the hypothalamus, brainstem, cortex, and limbic system. Gene expression signatures of these regions can help elucidate the pathophysiology underlying obesity. RNA sequencing was conducted on P56 C57BL/6NTac male mice and E14.5 C57BL/6NTac embryo punch biopsies in 16 obesity-relevant brain regions. The expression of 190 known obesity-associated genes (monogenic, rare, and low-frequency coding variants; GWAS; syndromic) was analyzed in each anatomical region. Genes associated with these genetic categories of obesity had localized expression patterns across brain regions. Known monogenic obesity causal genes were highly enriched in the arcuate nucleus of the hypothalamus and developing hypothalamus. The obesity-associated genes clustered into distinct “modules” of similar expression profile, and these were distinct from expression modules formed by similar analysis with genes known to be associated with other disease phenotypes (type 1 and type 2 diabetes, autism, breast cancer) in the same energy balance–relevant brain regions.

Common genetic variants associated with obesity in an African-American and Hispanic/Latino population

INTRODUCTION

Over 35% of all adults in the world are currently obese and risk of obesity in racial or ethnic minority groups exist in the US, but the causes of these differences are not all known. As obesity is a leading cause of cardiovascular disease, an improved understanding of risk factors across racial and ethnic groups may improve outcomes.

OBJECTIVE

The objective of this study was to determine if susceptibility to obesity is associated with genetic variation in candidate single nucleotide polymorphisms (SNPs) in African Americans and Hispanic/Latinos.

MATERIALS AND METHODS

We examined data from 534 African Americans and 557 Hispanic/Latinos participants from the UIC Cohort of Patients, Family and Friends. Participants were genotyped for the top 26 obesity-associated SNPs within FTO, MC4R, TUB, APOA2, APOA5, ADIPOQ, ARL15, CDH13, KNG1, LEPR, leptin, and SCG3 genes.

RESULTS

The mean (SD) age of participants was 49±13 years, 55% were female, and mean body mass index (BMI) was 31±7.5 kg/m2. After adjusting for age and sex, we found that rs8050136 in FTO (odds ratio [OR] 1.40, 95% confidence interval [CI] 1.1-1.8; P = 0.01) among African Americans and rs2272383 in TUB (OR 1.34, 95% CI 1.04-1.71; P = 0.02) among Hispanic/Latinos were associated with obesity. However, none of the SNPs in multivariable analysis of either AA or H/L cohorts were significant when adjusted for multiple correction.

CONCLUSIONS

We show that candidate SNPs in the FTO and TUB genes are associated with obesity in African Americans and Hispanic/Latinos individuals respectively. While the underlying pathophysiological mechanisms by which common genetic variants cause obesity remain unclear, we have identified novel therapeutic targets across racial and ethnic groups.

Kahweol Reduces Food Intake of Caenorhabditis elegans

The coffee diterpene kahweol may contribute to the anti-obesity effects of coffee but its physiological effects have yet to be elucidated. Caenorhabditis elegans is used as an animal model in obesity research because its lipid metabolism is conserved in humans. The goal was to investigate kahweol's effects on lipid metabolism in C. elegans. Kahweol at 120 μM reduced fat accumulation by 17% compared to the control, which was associated with a reduced food intake. Kahweol did not reduce fat in eat-2 mutants, which have a disrupted pharynx contraction rate, suggesting that the fat-lowering effects of kahweol were dependent on food intake. Lipid metabolism-related gene homologues of tubby protein (tub-1), enoyl-CoA hydratase (ech-1.1), adipose triglyceride lipase (atgl-1), insulin/insulin-like growth receptor (daf-2), and forkhead box O transcription factor (daf-16) were also associated with changes in food intake by kahweol. Therefore, kahweol's fat-lowering effects are due to a reduction of food intake in C. elegans.

Butein inhibits lipogenesis in Caenorhabditis elegans

Butein, a flavonoid found in annatto seeds and lacquer trees, may be used for many health benefits, including the prevention of obesity. However, its anti-obesity effects are not completely understood; in particular, the effects of butein on the regulation of lipid metabolism have not been explained. Thus, the goal of the current study was to determine the effects of butein on lipid metabolism in Caenorhabditis elegans, which is a multi-organ nematode used as an animal model in obesity research. Butein at 70 μM reduced triglyceride content by 27% compared to the control without altering food intake and energy expenditure. The reduced triglyceride content by butein was associated with the downregulation of sbp-1, fasn-1, and fat-7, the lipogenesis-related homologs of sterol regulatory element-binding proteins, fatty acid synthase and stearoyl-CoA desaturase, respectively. Furthermore, fat-7 and skn-1, a homolog of nuclear respiratory factors, were identified as genetic requirements for butein's effects on triglyceride content in C. elegans. The effects of butein on sbp-1 and fasn-1 were dependent on skn-1, but the downregulation of fat-7 was independent of skn-1. These results suggest that the inhibitory effects of butein on lipogenesis are via SKN-1- and FAT-7-dependent pathways in C. elegans.