Disruption of the SH2-B gene causes age-dependent insulin resistance and glucose intolerance

SH2B1 Defends Against Energy Imbalance, Obesity, and Metabolic Disease via a Paraventricular Hypothalamus→Dorsal Raphe Nucleus Neurocircuit

SH2B1 mutations are associated with obesity, type 2 diabetes, and metabolic dysfunction-associated steatotic liver disease (MASLD) in humans. Global deletion of Sh2b1 results in severe obesity, type 2 diabetes, and MASLD in mice. Neuron-specific restoration of SH2B1 rescues the obesity phenotype of Sh2b1-null mice, indicating that the brain is a main SH2B1 target. However, SH2B1 neurocircuits remain elusive. SH2B1-expressing neurons in the paraventricular hypothalamus (PVHSH2B1) and a PVHSH2B1→dorsal raphe nucleus (DRN) neurocircuit are identified here. PVHSH2B1 axons monosynaptically innervate DRN neurons. Optogenetic stimulation of PVHSH2B1 axonal fibers in the DRN suppresses food intake. Chronic inhibition of PVHSH2B1 neurons causes obesity. In male and female mice, either embryonic-onset or adult-onset deletion of Sh2b1 in PVH neurons causes energy imbalance, obesity, insulin resistance, glucose intolerance, and MASLD. Ablation of Sh2b1 in the DRN-projecting PVHSH2B1 subpopulation also causes energy imbalance, obesity, and metabolic disorders. Conversely, SH2B1 overexpression in either total or DRN-projecting PVHSH2B1 neurons protects against diet-induced obesity. SH2B1 binds to TrkB and enhances brain-derived neurotrophic factor (BDNF) signaling. Ablation of Sh2b1 in PVHSH2B1 neurons induces BDNF resistance in the PVH, contributing to obesity. In conclusion, these results unveil a previously unrecognized PVHSH2B1→DRN neurocircuit through which SH2B1 defends against obesity by enhancing BDNF/TrkB signaling.

Control of germinal center B cell survival and IgE production by an adaptor molecule containing PH and SH2 domains, Aps/Sh2b2

The germinal centers (GCs) are structure found within secondary lymphoid organs and are important for the antibody-producing response against foreign antigens. In GCs, antigen-specific B cells proliferate intensely, inducing immunoglobulin class switching. Recent studies have shown that GCs are also an important site for class switching to IgE, which is implicated in allergy. However, the mechanisms by which IgE production is regulated in GCs remain unclear. Here, we found impairment in IgE-specific production and a reduction of GC B cells after immunization in mice deficient in the Aps/Sh2b2 gene encoding the Lnk/Sh2b family adaptor protein Aps. GC B cells express higher levels of the Aps gene than non-GC B cells, and cell death of Aps-/- GC B cells is enhanced compared to wild-type GC B cells. An in vitro culture system with purified Aps-/- B cells induced the same level of IgE production and frequencies of IgE+ B cells as wild-type B cells. We found that Aps deficiency in B cells resulted in augmented depletion of IgE+ blasts by B cell receptor crosslinking with anti-CD79b antibodies compared to wild-type IgE+ cells. These results suggest that Aps regulates IgE production by controlling the survival of GC B cells and IgE+ plasma cells and may serve as a potential therapeutic target to control IgE production.

STAP-2 facilitates insulin signaling through binding to CAP/c-Cbl and regulates adipocyte differentiation

Signal-transducing adaptor protein-2 (STAP-2) is an adaptor molecule involved in several cellular signaling cascades. Here, we attempted to identify novel STAP-2 interacting molecules, and identified c-Cbl associated protein (CAP) as a binding protein through the C-terminal proline-rich region of STAP-2. Expression of STAP-2 increased the interaction between CAP and c-Cbl, suggesting that STAP-2 bridges these proteins and enhances complex formation. CAP/c-Cbl complex is known to regulate GLUT4 translocation in insulin signaling. STAP-2 overexpressed human hepatocyte Hep3B cells showed enhanced GLUT4 translocation after insulin treatment. Elevated levels of Stap2 mRNA have been observed in 3T3-L1 cells and mouse embryonic fibroblasts (MEFs) during adipocyte differentiation. The differentiation of 3T3-L1 cells into adipocytes was highly promoted by retroviral overexpression of STAP-2. In contrast, STAP-2 knockout (KO) MEFs exhibited suppressed adipogenesis. The increase in body weight with high-fat diet feeding was significantly decreased in STAP-2 KO mice compared to WT animals. These data suggest that the expression of STAP-2 correlates with adipogenesis. Thus, STAP-2 is a novel regulatory molecule that controls insulin signal transduction by forming a c-Cbl/STAP-2/CAP ternary complex.

Chromosomal deletions on 16p11.2 encompassing SH2B1 are associated with accelerated metabolic disease

New approaches are needed to treat people whose obesity and type 2 diabetes (T2D) are driven by specific mechanisms. We investigate a deletion on chromosome 16p11.2 (breakpoint 2-3 [BP2-3]) encompassing SH2B1, a mediator of leptin and insulin signaling. Phenome-wide association scans in the UK (N = 502,399) and Estonian (N = 208,360) biobanks show that deletion carriers have increased body mass index (BMI; p = 1.3 × 10-10) and increased rates of T2D. Compared with BMI-matched controls, deletion carriers have an earlier onset of T2D, with poorer glycemic control despite higher medication usage. Cystatin C, a biomarker of kidney function, is significantly elevated in deletion carriers, suggesting increased risk of renal impairment. In a Mendelian randomization study, decreased SH2B1 expression increases T2D risk (p = 8.1 × 10-6). We conclude that people with 16p11.2 BP2-3 deletions have early, complex obesity and T2D and may benefit from therapies that enhance leptin and insulin signaling.

Role of the Beta and Gamma Isoforms of the Adapter Protein SH2B1 in Regulating Energy Balance

Human variants of the adapter protein SH2B1 are associated with severe childhood obesity, hyperphagia, and insulin resistance-phenotypes mimicked by mice lacking Sh2b1. SH2B1β and γ isoforms are expressed ubiquitously, whereas SH2B1α and δ isoforms are expressed primarily in the brain. Restoring SH2B1β driven by the neuron-specific enolase promoter largely reverses the metabolic phenotype of Sh2b1-null mice, suggesting crucial roles for neuronal SH2B1β in energy balance control. Here we test this hypothesis by using CRISPR/Cas9 gene editing to delete the β and γ isoforms from the neurons of mice (SH2B1βγ neuron-specific knockout [NKO] mice) or throughout the body (SH2B1βγ knockout [KO] mice). While parameters of energy balance were normal in both male and female SH2B1βγ NKO mice, food intake, body weight, and adiposity were increased in male (but not female) SH2B1βγ KO mice. Analysis of long-read single-cell RNA seq data from wild-type mouse brain revealed that neurons express almost exclusively the α and δ isoforms, whereas neuroglial cells express almost exclusively the β and γ isoforms. Our work suggests that neuronal SH2B1β and γ are not primary regulators of energy balance. Rather, non-neuronal SH2B1β and γ in combination with neuronal SH2B1α and δ suffice for body weight maintenance. While SH2B1β/γ and SH2B1α/δ share some functionality, SH2B1β/γ appears to play a larger role in promoting leanness.

SH2B1 variants as potential causes of non-syndromic monogenic obesity in a Brazilian cohort

PURPOSE

SH2B1 gene encodes an important adaptor protein to receptor tyrosine kinases or cytokine receptors associated with Janus kinases. This gene has been associated with the structural and functional modulation of neurons and other cells, and impacts on energy and glucose homeostasis. Several studies suggested that alterations in this gene are strong candidates for the development of obesity. However, only a few studies have screened SH2B1 point variants in individuals with obesity. Therefore, the aim of this study was to investigate the prevalence of SH2B1 variants in a Brazilian cohort of patients with severe obesity and candidates to bariatric surgery.

METHODS

The cohort comprised 122 individuals with severe obesity, who developed this phenotype during childhood. As controls, 100 normal-weight individuals were included. The coding region of SH2B1 gene was screened by Sanger sequencing.

RESULTS

A total of eight variants were identified in SH2B1, of which p.(Val345Met) and p.(Arg630Gln) variants were rare and predicted as potentially pathogenic by the in the silico algorithms used in this study. The p.(Val345Met) was not found in either the control group or in publicly available databases. This variant was identified in a female patient with severe obesity, metabolic syndrome and hyperglycemia. The p.(Arg630Gln) was also absent in our control group, but it was reported in gnomAD with an extremely low frequency. This variant was observed in a female patient with morbid obesity, metabolic syndrome, hypertension and severe binge-eating disorder.

CONCLUSION

Our study reported for the first time two rare and potentially pathogenic variants in Brazilian patients with severe obesity. Further functional studies will be necessary to confirm and elucidate the impact of these variants on SH2B1 protein function and stability, and their impact on energetic metabolism.

LEVEL OF EVIDENCE

Level V, cross-sectional descriptive study.

Genetic Obesity in Children: Overview of Possible Diagnoses with a Focus on SH2B1 Deletion

INTRODUCTION

Genetic obesity is rare and quite challenging for pediatricians in terms of early identification. Src-homology-2 (SH2) B adapter protein 1 (SH2B1) is an important component in the leptin-melanocortin pathway and is found to play an important role in leptin and insulin signaling and therefore in the pathogenesis of obesity and diabetes. Microdeletions in chromosome 16p11.2, encompassing the SH2B1 gene, are known to be associated with obesity, insulin resistance, hyperphagia, and developmental delay. The aim of our study is to report on a case series of young individuals with 16p11.2 microdeletions, including the SH2B1 gene, and provide detailed information on body mass index (BMI) development and obesity-associated comorbidities. In this way, we want to raise awareness of this syndromic form of obesity as a differential diagnosis of genetic obesity.

METHODS

We describe the phenotype of 7 children (3 male; age range: 2.8-18.0 years) with 16p11.2 microdeletions, encompassing the SH2B1 gene, and present their BMI trajectories from birth onward. Screening for obesity-associated comorbidities was performed at the time of genetic diagnosis.

RESULTS

All children presented with severe, early-onset obesity already at the age of 5 years combined with variable developmental delay. Five patients presented with elevated fasting insulin levels, 1 patient developed diabetes mellitus type 2, 4 patients had dyslipidemia, and 4 developed nonalcoholic fatty-liver disease.

DISCUSSION/CONCLUSION

Chromosomal microdeletions in 16p11.2, including the SH2B1 gene, in children are associated with severe, early-onset obesity and comorbidities associated with insulin resistance. Early genetic testing in suspicious patients and early screening for comorbidities are recommended.

Deleted genes associated with obesity in Mexican patients diagnosed with nonalcoholic fatty liver disease

AIM

Nonalcoholic fatty liver disease (NAFLD) is a complex metabolic condition in which both lifestyle and genetic factors have a pathogenic role. The LEP gene encodes leptin, which regulates appetite, body weight, and several metabolic functions. Proopiomelanocortin (POMC), regulates food intake and energy balance. The aim of the study was to determine partial or complete deletions of genes associated with obesity in patients diagnosed with NAFLD.

MATERIAL AND METHODS

Blood samples and DNA from 43 individuals diagnosed with NAFLD by ultrasonographic technique (Fibroscan) were obtained. The partial or complete deletions of genes were determined by MLPA (Multiplex Ligation-dependent Probe Amplification) using the SALSA probemix P220-B2 Obesity only on 43 individuals. Fifty blood samples from healthy individuals were included.

RESULTS

Eleven out of 43 individuals analyzed by MLPA presented some deletion of the genes analyzed: six were female and five were male. The partial or complete deletion of the LEPR and POMC genes was observed in eight patients (18.6%), SIM1 in six patients (13.9%), GRIK2 and SH2B1 in two patients (4.7%), SEZGL2 in four patients (9.3%), and MCR4 in one patient (2.3%).

CONCLUSION

Partial deletion was observed in LEPR, POMC, SIM1, GRIK2, SH2B1, SEZGL2, and MCR4 genes in 26% of the cases, and we suggest that these alterations probably has a potential relationship for the development of NAFLD.

The nucleolar δ isoform of adapter protein SH2B1 enhances morphological complexity and function of cultured neurons

The adapter protein SH2B1 is recruited to neurotrophin receptors, including TrkB (also known as NTRK2), the receptor for brain-derived neurotrophic factor (BDNF). Herein, we demonstrate that the four alternatively spliced isoforms of SH2B1 (SH2B1α-SH2B1δ) are important determinants of neuronal architecture and neurotrophin-induced gene expression. Primary hippocampal neurons from Sh2b1-/- [knockout (KO)] mice exhibit decreased neurite complexity and length, and BDNF-induced expression of the synapse-related immediate early genes Egr1 and Arc. Reintroduction of each SH2B1 isoform into KO neurons increases neurite complexity; the brain-specific δ isoform also increases total neurite length. Human obesity-associated variants, when expressed in SH2B1δ, alter neurite complexity, suggesting that a decrease or increase in neurite branching may have deleterious effects that contribute to the severe childhood obesity and neurobehavioral abnormalities associated with these variants. Surprisingly, in contrast to SH2B1α, SH2B1β and SH2B1γ, which localize primarily in the cytoplasm and plasma membrane, SH2B1δ resides primarily in nucleoli. Some SH2B1δ is also present in the plasma membrane and nucleus. Nucleolar localization, driven by two highly basic regions unique to SH2B1δ, is required for SH2B1δ to maximally increase neurite complexity and BDNF-induced expression of Egr1, Arc and FosL1.

Genes and Longevity of Lifespan

Aging is a complex process indicated by low energy levels, declined physiological activity, stress induced loss of homeostasis leading to the risk of diseases and mortality. Recent developments in medical sciences and an increased availability of nutritional requirements has significantly increased the average human lifespan worldwide. Several environmental and physiological factors contribute to the aging process. However, about 40% human life expectancy is inherited among generations, many lifespan associated genes, genetic mechanisms and pathways have been demonstrated during last decades. In the present review, we have evaluated many human genes and their non-human orthologs established for their role in the regulation of lifespan. The study has included more than fifty genes reported in the literature for their contributions to the longevity of life. Intact genomic DNA is essential for the life activities at the level of cell, tissue, and organ. Nucleic acids are vulnerable to oxidative stress, chemotherapies, and exposure to radiations. Efficient DNA repair mechanisms are essential for the maintenance of genomic integrity, damaged DNA is not replicated and transferred to next generations rather the presence of deleterious DNA initiates signaling cascades leading to the cell cycle arrest or apoptosis. DNA modifications, DNA methylation, histone methylation, histone acetylation and DNA damage can eventually lead towards apoptosis. The importance of calorie restriction therapy in the extension of lifespan has also been discussed. The role of pathways involved in the regulation of lifespan such as DAF-16/FOXO (forkhead box protein O1), TOR and JNK pathways has also been particularized. The study provides an updated account of genetic factors associated with the extended lifespan and their interactive contributory role with cellular pathways.

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.

Three case reports of patients indicating the diversity of molecular and clinical features of 16p11.2 microdeletion anomaly

BACKGROUND

16p11.2 microdeletion is a known chromosomal anomaly associated mainly with neurocognitive developmental delay, predisposition to obesity, and variable dysmorphism. Although this deletion is relatively rare among the general population, it is one of the serious known genetic aetiologies of obesity and autism spectrum disorder.

CASE PRESENTATION

This study presents three cases of deletions within the 16p11.2 region. Every child had mild variable craniofacial abnormalities, hand or foot anomalies and developmental and language delays. The first proband had obesity, epilepsy, moderate intellectual disability, aphasia, motor delay, hyperinsulinism, and café au lait spots. The second proband suffered from cardiac, pulmonary, and haematological problems. The third proband had motor and language delays, bronchial asthma, and umbilical hernia. Although each patient presented some features of the syndrome, the children differed in terms of their clinical pictures. Genetic diagnosis of 16p11.2 microdeletion syndrome was made in children at different ages based on multiplex ligation probe-dependent amplification analysis and/or microarray methods.

CONCLUSIONS

Our reports allow us to analyse and better understand the biology of 16p11.2 microdeletion throughout development. However, the variability of presented cases supports the alternate conclusion to this presented in available literature regarding 16p11.2 deletion, as we observed no direct cause-and-effect genotype/phenotype relationships. The reported cases indicate the key role of the interdisciplinary approach in 16p11.2 deletion diagnostics. The care of patients with this anomaly is based on regular health assessment and adjustment of nervous system development therapy.

Deletion of the Brain-Specific α and δ Isoforms of Adapter Protein SH2B1 Protects Mice From Obesity

Mice lacking SH2B1 and humans with variants of SH2B1 display severe obesity and insulin resistance. SH2B1 is an adapter protein that is recruited to the receptors of multiple hormones and neurotrophic factors. Of the four known alternatively spliced SH2B1 isoforms, SH2B1β and SH2B1γ exhibit ubiquitous expression, whereas SH2B1α and SH2B1δ are essentially restricted to the brain. To understand the roles for SH2B1α and SH2B1δ in energy balance and glucose metabolism, we generated mice lacking these brain-specific isoforms (αδ knockout [αδKO] mice). αδKO mice exhibit decreased food intake, protection from weight gain on standard and high-fat diets, and an adiposity-dependent improvement in glucose homeostasis. SH2B1 has been suggested to impact energy balance via the modulation of leptin action. However, αδKO mice exhibit leptin sensitivity that is similar to that of wild-type mice by multiple measures. Thus, decreasing the abundance of SH2B1α and/or SH2B1δ relative to the other SH2B1 isoforms likely shifts energy balance toward a lean phenotype via a primarily leptin-independent mechanism. Our findings suggest that the different alternatively spliced isoforms of SH2B1 perform different functions in vivo.

Genetics of Obesity in East Asians

Obesity has become a public health problem worldwide. Compared with Europe, people in Asia tend to suffer from type 2 diabetes with a lower body mass index (BMI). Genome-wide association studies (GWASs) have identified over 750 loci associated with obesity. Although the majority of GWAS results were conducted in individuals of European ancestry, a recent GWAS in individuals of Asian ancestry has made a significant contribution to the identification of obesity susceptibility loci. Indeed, owing to the multifactorial character of obesity with a strong environmental component, the revealed loci may have distinct contributions in different ancestral genetic backgrounds and in different environments as presented through diet and exercise among other factors. Uncovering novel, yet unrevealed genes in non-European ancestries may further contribute to explaining the missing heritability for BMI. In this review, we aimed to summarize recent advances in obesity genetics in individuals of Asian ancestry. We therefore compared proposed mechanisms underlying susceptibility loci for obesity associated with individuals of European and Asian ancestries and discussed whether known genetic variants might explain ethnic differences in obesity risk. We further acknowledged that GWAS implemented in individuals of Asian ancestries have not only validated the potential role of previously specified obesity susceptibility loci but also exposed novel ones, which have been missed in the initial genetic studies in individuals of European ancestries. Thus, multi-ethnic studies have a great potential not only to contribute to a better understanding of the complex etiology of human obesity but also potentially of ethnic differences in the prevalence of obesity, which may ultimately pave new avenues in more targeted and personalized obesity treatments.

The central melanocortin system and human obesity

The prevalence of obesity and the associated comorbidities highlight the importance of understanding the regulation of energy homeostasis. The central melanocortin system plays a critical role in controlling body weight balance. Melanocortin neurons sense and integrate the neuronal and hormonal signals, and then send regulatory projections, releasing anorexigenic or orexigenic melanocortin neuropeptides, to downstream neurons to regulate the food intake and energy expenditure. This review summarizes the latest progress in our understanding of the role of the melanocortin pathway in energy homeostasis. We also review the advances in the identification of human genetic variants that cause obesity via mechanisms that affect the central melanocortin system, which have provided rational targets for treatment of genetically susceptible patients.

LNK deficiency decreases obesity-induced insulin resistance by regulating GLUT4 through the PI3K-Akt-AS160 pathway in adipose tissue

In recent years, LNK, an adapter protein, has been found to be associated with metabolic diseases, including hypertension and diabetes. We found that the expression of LNK in human adipose tissue was positively correlated with serum glucose and insulin in obese people. We examined the role of LNK in insulin resistance and systemic energy metabolism using LNK-deficient mice (LNK^-/-). With consumption of a high-fat diet, wild type (WT) mice accumulated more intrahepatic triglyceride, higher serum triglyceride (TG), free fatty acid (FFA) and high sensitivity C-reactive protein (hsCRP) compared with LNK^-/- mice. However, there was no significant difference between LNK^-/- and WT mice under normal chow diet. Meanwhile, glucose transporter 4 (GLUT4) expression in adipose tissue and insulin-stimulated glucose uptake in adipocytes were increased in LNK^-/- mice. LNK^-/- adipose tissue showed activated reactivity for IRS1/PI3K/Akt/AS160 signaling, and administration of a PI3K inhibitor impaired glucose uptake. In conclusion, LNK plays a pivotal role in adipose glucose transport by regulating insulin-mediated IRS1/PI3K/Akt/AS160 signaling.

Leptin receptor-expressing neuron Sh2b1 supports sympathetic nervous system and protects against obesity and metabolic disease

Leptin stimulates the sympathetic nervous system (SNS), energy expenditure, and weight loss; however, the underlying molecular mechanism remains elusive. Here, we uncover Sh2b1 in leptin receptor (LepR) neurons as a critical component of a SNS/brown adipose tissue (BAT)/thermogenesis axis. LepR neuron-specific deletion of Sh2b1 abrogates leptin-stimulated sympathetic nerve activation and impairs BAT thermogenic programs, leading to reduced core body temperature and cold intolerance. The adipose SNS degenerates progressively in mutant mice after 8 weeks of age. Adult-onset ablation of Sh2b1 in the mediobasal hypothalamus also impairs the SNS/BAT/thermogenesis axis; conversely, hypothalamic overexpression of human SH2B1 has the opposite effects. Mice with either LepR neuron-specific or adult-onset, hypothalamus-specific ablation of Sh2b1 develop obesity, insulin resistance, and liver steatosis. In contrast, hypothalamic overexpression of SH2B1 protects against high fat diet-induced obesity and metabolic syndromes. Our results unravel an unrecognized LepR neuron Sh2b1/SNS/BAT/thermogenesis axis that combats obesity and metabolic disease.

Obesity of G2e3 Knockout Mice Suggests That Obesity-Associated Variants Near Human G2E3 Decrease G2E3 Activity

PURPOSE

In humans, single nucleotide polymorphisms (SNPs) near the adjacent protein kinase D1 (PRKD1) and G2/M-phase-specific E3 ubiquitin protein ligase (G2E3) genes on chromosome 14 are associated with obesity. To date, no published evidence links inactivation of either gene to changes in body fat. These two genes are also adjacent on mouse chromosome 12. Because obesity genes are highly conserved between humans and mice, we analyzed body fat in adult G2e3 and Prkd1 knockout (KO) mice to determine whether inactivating either gene leads to obesity in mice and, by inference, probably in humans.

METHODS

The G2e3 and Prkd1 KO lines were generated by gene trapping and by homologous recombination methodologies, respectively. Body fat was measured by DEXA in adult mice fed chow from weaning and by QMR in a separate cohort of mice fed high-fat diet (HFD) from weaning. Glucose homeostasis was evaluated with oral glucose tolerance tests (OGTTs) performed on adult mice fed HFD from weaning.

RESULTS

Body fat was increased in multiple cohorts of G2e3 KO mice relative to their wild-type (WT) littermates. When data from all G2e3 KO (n=32) and WT (n=31) mice were compared, KO mice showed increases of 11% in body weight (P<0.01), 65% in body fat (P<0.001), 48% in % body fat (P<0.001), and an insignificant 3% decrease in lean body mass. G2e3 KO mice were also glucose intolerant during an OGTT (P<0.05). In contrast, Prkd1 KO and WT mice had comparable body fat levels and glucose tolerance.

CONCLUSION

Significant obesity and glucose intolerance were observed in G2e3, but not Prkd1, KO mice. The conservation of obesity genes between mice and humans strongly suggests that the obesity-associated SNPs located near the human G2E3 and PRKD1 genes are linked to variants that decrease the amount of functional human G2E3.

New perspective on SH2B1: An accelerator of cancer progression

SH2B1 is well-known as an adaptor protein, and deletion of SH2B1 results in severe obesity and both leptin and insulin resistance. Some studies have revealed that SH2B1 is involved in the progression of lung cancer, esophageal cancer, gastric cancer, oropharyngeal cancer, and so on. Biological function experiments have proven that SH2B1 can regulate cellular morphology, motility and adhesion by modifying the actin cytoskeletal reorganization, and it can promote cell mitogenesis, transformation, survival and differentiation via different signal pathways by enhancing the kinase activity of several receptor tyrosine kinases. In addition, SH2B1 is an obesity-related gene, and epidemiological surveys suggest a complex relationship between obesity and cancer. Therefore, what is the relationship between SH2B1 and cancer? Herein, we attempt to provide a mini overview of the roles of SH2B1 in cancer.

Crucial Role of the SH2B1 PH Domain for the Control of Energy Balance

Disruption of the adaptor protein SH2B1 (SH2-B, PSM) is associated with severe obesity, insulin resistance, and neurobehavioral abnormalities in mice and humans. Here, we identify 15 SH2B1 variants in severely obese children. Four obesity-associated human SH2B1 variants lie in the Pleckstrin homology (PH) domain, suggesting that the PH domain is essential for SH2B1's function. We generated a mouse model of a human variant in this domain (P322S). P322S/P322S mice exhibited substantial prenatal lethality. Examination of the P322S/+ metabolic phenotype revealed late-onset glucose intolerance. To circumvent P322S/P322S lethality, mice containing a two-amino acid deletion within the SH2B1 PH domain (ΔP317, R318 [ΔPR]) were studied. Mice homozygous for ΔPR were born at the expected Mendelian ratio and exhibited obesity plus insulin resistance and glucose intolerance beyond that attributable to their increased adiposity. These studies demonstrate that the PH domain plays a crucial role in how SH2B1 controls energy balance and glucose homeostasis.

Insulin/IGF signaling and discoidin domain receptors: An emerging functional connection

The insulin/insulin-like growth factor system (IIGFs) plays a fundamental role in the regulation of prenatal and postnatal growth, metabolism and homeostasis. As a consequence, dysregulation of this axis is associated with growth disturbance, type 2 diabetes, chronic inflammation and tumor progression. A functional crosstalk between IIGFs and discoidin domain receptors (DDRs) has been recently discovered. DDRs are non-integrin collagen receptors that canonically undergo slow and long-lasting autophosphorylation after binding to fibrillar collagen. While both DDR1 and DDR2 functionally interact with IIGFs, the crosstalk with DDR1 is so far better characterized. Notably, the IIGFs-DDR1 crosstalk presents a feed-forward mechanism, which does not require collagen binding, thus identifying novel non-canonical action of DDR1. Further studies are needed to fully explore the role of this IIGFs-DDRs functional loop as potential target in the treatment of inflammatory and neoplastic disorders.

Insulin-Like Growth Factor I Regulation and Its Actions in Skeletal Muscle

The insulin-like growth factor (IGF) pathway is essential for promoting growth and survival of virtually all tissues. It bears high homology to its related protein insulin, and as such, there is an interplay between these molecules with regard to their anabolic and metabolic functions. Skeletal muscle produces a significant proportion of IGF-1, and is highly responsive to its actions, including increased muscle mass and improved regenerative capacity. In this overview, the regulation of IGF-1 production, stability, and activity in skeletal muscle will be described. Second, the physiological significance of the forms of IGF-1 produced will be discussed. Last, the interaction of IGF-1 with other pathways will be addressed. © 2019 American Physiological Society. Compr Physiol 9:413-438, 2019.

Scaffold Proteins: From Coordinating Signaling Pathways to Metabolic Regulation

Among their pleiotropic functions, scaffold proteins are required for the accurate coordination of signaling pathways. It has only been within the past 10 years that their roles in glucose homeostasis and metabolism have emerged. It is well appreciated that changes in the expression or function of signaling effectors, such as receptors or kinases, can influence the development of chronic diseases such as diabetes and obesity. However, little is known regarding whether scaffolds have similar roles in the pathogenesis of metabolic diseases. In general, scaffolds are often underappreciated in the context of metabolism or metabolic diseases. In the present review, we discuss various scaffold proteins and their involvement in signaling pathways related to metabolism and metabolic diseases. The aims of the present review were to highlight the importance of scaffold proteins and to raise awareness of their physiological contributions. A thorough understanding of how scaffolds influence metabolism could aid in the discovery of novel therapeutic approaches to treat chronic conditions, such as diabetes, obesity, and cardiovascular disease, for which the incidence of all continue to increase at alarming rates.

Overexpression of miR-142-3p improves mitochondrial function in cardiac hypertrophy

BACKGROUND AND PURPOSE

Our previous studies have shown that Src homology 2 (SH2) B adaptor protein 1 (SH2B1) plays an important role in cardiac hypertrophy, but the specific mechanism remains to be studied. Through bioinformatics and related research, it is found that miR-14 2-3 p is closely related to SH2B1. Exploring the relationship between miR-14 2-3 p and gene SH2B1 expression is beneficial for the treatment of cardiac hypertrophy. SH2B1 is a key factor regulating energy metabolism, mitochondria are the main organelles of energy metabolism and cardiac hypertrophy are closely related to mitochondrial dysfunction. So it is particularly important to explore the relationship between miR-14 2-3 p and SH2B1 and myocardial mitochondrial function. In this study, we investigated whether overexpression of miR-14 2-3 p can inhibit the expression of gene SH2B1, ameliorate cardiac mitochondrial dysfunction and cardiac hypertrophy.

METHODS

We first constructed a pressure overload myocardial hypertrophy model by ligation of the abdominal aorta(AB) of rats. After 4 weeks of modeling, echocardiographic examination showed that the heart volume of the model group became larger, and Hematoxylin and Eosin Staining Kit (HE) staining showed that the cross-sectional area of the heart tissue became larger. The expression of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), β-Myosin Heavy Chain (β-MHC) messenger RNA (mRNA) increased by real‑time polymerase chain reaction (PCR), which proved that the model of cardiac hypertrophy was successfully constructed. Then, miR-14 2-3 p agomir was injected into the tail vein of rats 2 weeks and 4 weeks respectively. The expression of miR-4 2-3 p mRNA was increased by PCR, suggesting that the miR-14 2-3 p plasmid was successfully transfected. At 4 weeks of pressure overload myocardial hypertrophy model, echocardiography was used to detect cardiac function. HE staining of heart tissue and the expression of ANP, BNP, β-MHC mRNA were used to detect cardiac hypertrophy. Flow cytometry was used to detect changes in mitochondrial membrane potential. Secondly, we observed the effect of miR-14 2-3 p on cardiomyocyte hypertrophy and mitochondrial function in vitro by culture neonatal rat cardiomyocytes. Afterwards, using angiotensin (Ang)II-, miRNA mimic- and miRNA mimic nc- treated cardiomyocytes for a given time. α-actin staining found that the myocardial cells became larger, The expression of ANP, BNP, β-MHC mRNA increased by PCR, which proved that AngII-induced cardiac hypertrophy was successfully constructed. Then, the mitochondrial density was measured using mitochondrial Mito-Red staining by Confocal microscope, the mitochondrial membrane potential was evaluated using flow cytometry, Mitochondrial respiration oxygen consumption rate (OCR) was measured by a Seahorse Extracellular Flux Analyzer XF96, and the expression levels of miR-14 2-3 p, ANP, BNP, β-MHC mRNA, SH2B1 in the cardiomyocytes of different groups were measured by RT-PCR and Western blotting. Finally, we used luciferase assay and transfected miR-14 2-3 p agomir in rats, transfected miR-14 2-3 p mimic in Cardiomyocytes, it is found that myocardial SH2B1 mRNA and protein expression both were reduced.

RESULTS

When the pressure overload myocardial hypertrophy model was constructed for four weeks, echocardiography revealed that the heart volume, Left ventricular end diastolic diameter(LVIDd), Left ventricular end systolic diameter (LVIDs), Left ventricular posterior wall thickness (LVPWd), Systolic left ventricular posterior wall (LVPWs), Left ventricle (LV) Mass increased, Ejection fraction (EF) % decreased of AB group increased, but transfected with miR-14 2-3 p agomir of AB, these increase was not significant, EF% reduction was not obvious. HE staining showed that the myocardial cross-sectional area of AB group increased significantly, but the miR-14 2-3 p agomir treatment of AB group did not increase significantly. PCR analysis showed that the expression of ANP, BNP,β-MHC mRNA was significantly increased in AB group, but the miR-14 2-3 p agomir treatment of AB group was not significantly increased. Flow cytometry showed that the mitochondrial membrane potential of AB group was significantly reduced, and the miR-14 2-3 p agomir treatment of AB group was not significantly decreased. During AngII-induced cardiomyocyte hypertrophy, ANP, BNP,β-MHC mRNA expression was increased, while these factors was not significantly increased in miR-14 2-3 p mimic treatment group; mitochondrial membrane potential, mitochondrial density and OCR was significantly decreased in AngII treated group, and these were not significantly reduced in miR-14 2-3 p mimic treatment group; CONCLUSIONS: miR-14 2-3 p not only mitigate cardiac hypertrophy by directly inhibit the expression of gene SH2B1, but also can protect mitochondrial function in cardiac hypertrophy of vitro and vivo.

SH2B1 promotes NSCLC cell proliferation through PI3K/Akt/mTOR signaling cascade

Background

Non-small cell lung cancer (NSCLC), the most prevalent type of human lung cancer, is characterized by many molecular abnormalities. SH2B1, a member of the SH2-domain containing family, have recently been shown to act as tumor activators in multiple cancers. The objective of this study was to investigate the role SH2B1 and the underlying molecular mechanism in NSCLC.

Methods

Cell functional analysis and cell line-derived xenograft model were performed to determine SH2B1 potential roles on NSCLC cell proliferation in vitro and in vivo. In vitro assays were performed to identify signal molecular mechanisms. Subsequently, 104 patients with NSCLC undergoing primary surgical resection were recruited to evaluated expression of SH2B1 and Akt/mTOR signaling markers by immunohistochemical staining to determine their clinicopathologic significance.

Results

Modulation of SH2B1 expression levels had distinct effects on cell proliferation, cell cycle and apoptosis in the NSCLC cell lines A549 and H1299. At the molecular level, overexpression of SH2B1 resulted in the upregulation of the Akt/mTOR markers, p-Akt and p-mTOR, and downregulation of PTEN to promote NSCLC cell proliferation, while silencing SH2B1 had the opposite effect. In human NSCLC specimens, SH2B1 expression levels were positively associated with Akt/mTOR signaling pathway markers.

Conclusions

The SH2B1/Akt/mTOR/PTEN axis is required for regulating NSCLC cell proliferation and might prove to be a promising strategy for restraining tumor progression in NSCLC patients.

Electronic supplementary material

The online version of this article (10.1186/s12935-018-0632-x) contains supplementary material, which is available to authorized users.

Clinical, molecular genetics and therapeutic aspects of syndromic obesity

Obesity has become a major health problem worldwide. To date, more than 25 different syndromic forms of obesity are known in which one (monogenic) or multiple (polygenic) genes are involved. This review gives an overview of these forms and focuses more in detail on 6 syndromes: Prader Willi Syndrome and Prader Willi like phenotype, Bardet Biedl Syndrome, Alström Syndrome, Wilms tumor, Aniridia, Genitourinary malformations and mental Retardation syndrome and 16p11.2 (micro)deletions. Years of research provided plenty of information on the molecular genetics of these disorders and the obesity phenotype leading to a more individualized treatment of the symptoms, however, many questions still remain unanswered. As these obesity syndromes have different signs and symptoms in common, it makes it difficult to accurately diagnose patients which may result in inappropriate treatment of the disease. Therefore, the big challenge for clinicians and scientists is to more clearly differentiate all syndromic forms of obesity to provide conclusive genetic explanations and eventually deliver accurate genetic counseling and treatment. In addition, further delineation of the (functions of the) underlying genes with the use of array- or next-generation sequencing-based technology will be helpful to unravel the mechanisms of energy metabolism in the general population.

Recent advances of adapter proteins in the regulation of heart diseases

Heart diseases are major causes of mortality. Cardiac hypertrophy, myocardial infarction (MI), viral cardiomyopathy, ischemic and reperfusion (I/R) heart injury finally lead to heart failure and death. Insulin and IGF1 signal pathways play key roles in normal cardiomyocyte growth and physiological cardiac hypertrophy while inflammatory signal pathway is associated with pathological cardiac hypertrophy, MI, viral cardiomyopathy, I/R heart injury, and heart failure. Adapter proteins are the major family proteins, which transduce signals from insulin, IGF1, or cytokine receptors to the downstream pathways and have been shown to regulate variety of heart diseases. Here, we summarized the recent advances in understanding the physiological and pathological roles of adapter proteins in heart failure.

Phosphorylation of the Unique C-Terminal Tail of the Alpha Isoform of the Scaffold Protein SH2B1 Controls the Ability of SH2B1α To Enhance Nerve Growth Factor Function

The scaffold protein SH2B1, a major regulator of body weight, is recruited to the receptors of multiple cytokines and growth factors, including nerve growth factor (NGF). The β isoform but not the α isoform of SH2B1 greatly enhances NGF-dependent neurite outgrowth of PC12 cells. Here, we asked how the unique C-terminal tails of the α and β isoforms modulate SH2B1 function. We compared the actions of SH2B1α and SH2B1β to those of the N-terminal 631 amino acids shared by both isoforms. In contrast to the β tail, the α tail inhibited the ability of SH2B1 to both cycle through the nucleus and enhance NGF-mediated neurite outgrowth, gene expression, phosphorylation of Akt and phospholipase C-gamma (PLC-γ), and autophosphorylation of the NGF receptor TrkA. These functions were restored when Tyr753 in the α tail was mutated to phenylalanine. We provide evidence that TrkA phosphorylates Tyr753 in SH2B1α, as well as tyrosines 439 and 55 in both SH2B1α and SH2B1β. Finally, coexpression of SH2B1α but not SH2B1α with a mutation of Y to F at position 753 (Y753F) inhibited the ability of SH2B1β to enhance neurite outgrowth. These results suggest that the C-terminal tails of SH2B1 isoforms are key determinants of the cellular role of SH2B1. Furthermore, the function of SH2B1α is regulated by phosphorylation of the α tail.

SH2B1 promotes epithelial-mesenchymal transition through the IRS1/β-catenin signaling axis in lung adenocarcinoma

Lung adenocarcinoma (LADC), the most prevalent type of human lung cancer, is characterized by many molecular abnormalities. SH2B1, a member of the SH2‐domain containing family, have recently been shown to act as tumor activators in multiple cancers, including LADC. However, the mechanisms underlying SH2B1 overexpression are not completely understood. Here, we reported that SH2B1 expression levels were significantly upregulated and positively associated with EMT markers and poor patient survival in LADC specimens. Modulation of SH2B1 levels had distinct effects on cell proliferation, cell cycle, migration, invasion, and morphology in A549 and H1299 cells in vitro and in vivo. At the molecular level, overexpression of SH2B1 resulted in the upregulation of the EMT markers, especially induced β‐catenin accumulation and activated β‐catenin signaling to promote LADC cell proliferation and metastasis, while silencing SH2B1 had the opposite effect. Furthermore, ectopic expression of SH2B1 in H1299 cells increased IRS1 expression level. Reduced expression of IRS1 considerably inhibited H1299 cell proliferation, migration, and invasion which were driven by SH2B1 overexpression. Collectively, these results provide unequivocal evidence to establish that SH2B1‐IRS1‐β‐catenin axis is required for promoting EMT, and might prove to be a promising strategy for restraining tumor progression in LADC patients.

The Effect of SH2B1 Variants on Expression of Leptin- and Insulin-Induced Pathways in Murine Hypothalamus

OBJECTIVE

We aimed to determine the effect of human SH2B1 variants on leptin and insulin signaling, major regulators of energy homeostasis, on the RNA level.

METHODS

We analyzed the expression of infrequent alleles of seven SH2B1 variants (Arg67Cys, Lys150Arg, Thr175Ala, Thr343Met, Thr484Ala, Ser616Pro and Pro689Leu) in response to insulin or leptin cell stimulation. Two of these were identified in own mutation screens, the others were predicted to be deleterious or to serve as controls. The variants were analyzed in a homologous system of mouse hypothalamic cells. Changes in expression of downstream genes were measured. Student’s t-test for independent samples was applied and effect sizes using Cohen’s d were calculated.

RESULTS

In 34 of 54 analyzed genes involved in leptin (JAK/STAT or AKT) signaling, variants nominally changed expression. The expression of three genes was considerably increased (p values ≤ 0.001: Gbp2b (67Cys; d = 25.11), Irf9 (689Leu; d = 44.65) and Isg15 (150Arg; d = 20.35)). Of 32 analyzed genes in the insulin signaling pathway, the expression of 10 genes nominally changed (p ≤ 0.05), three resulted in p values ≤ 0.01 ( Cap1 (150Arg; d = 7.48), Mapk1 (343Met; d = –6.80) and Sorbs1 (689Leu; d = 7.82)).

CONCLUSION

The increased expression of genes in leptin (JAK/STAT or AKT) signaling implies that the main mode of action for human SH2B1 mutations might affect leptin signaling rather than insulin signaling.

Changes in circulating miRNAs in healthy overweight and obese subjects: Effect of diet composition and weight loss

BACKGROUND

MicroRNAs (miRNAs) are small non-coding RNA molecules that can play an important role in several chronic metabolic conditions, including obesity. However, to date little is known about how they are regulated. Weight loss induced by surgical procedures has been effective at modulating specific circulating miRNAs, but the effect of energy-restricted diets with different macronutrient compositions on circulating miRNAs is not well understood. The objective of the present analysis was to explore the effect of three energy-restricted diets of different macronutrient composition and carbohydrate quality on plasma miRNA levels.

METHODS

The GLYNDIET study is a 6-month, parallel, randomized clinical trial conducted on overweight and obese subjects who were randomized to one of three different dietary intervention groups: i) a moderate-carbohydrate and low glycemic index diet (LGI), ii) a moderate-carbohydrate and high glycemic index diet (HGI), and iii) a low-fat and high glycemic index diet (LF). We assessed the genome-wide circulating miRNA profile in a subsample of eight randomly selected participants. A total of 8 miRNAs (miR-411, miR-432, miR-99b, miR-340, miR-423, miR-361, let-7c) were differently quantified according to diet intervention, and were therefore longitudinally validated in 103 participants before and after the energy-restricted diets.

RESULTS

Circulating miR-361 levels were lower in the LGI group than in the HGI group, even after adjusting for differences in weight loss. The intra-group analyses demonstrated a significant down-regulation of all miRNAs screened in our study subjects after the LGI intervention. Similarly, miR-139 and miR-340 were down-regulated after the HGI intervention, while miR-139, miR-432 and miR-423 were down-regulated after the low-fat diet. Changes in circulating miR-139 and let-7c were significantly associated with changes in lipid profile and insulin resistance.

CONCLUSION

An energy-restricted low-glycemic index diet down-regulates circulating miRNA-361 more than an energy-restricted high-glycemic index, regardless of the magnitude of the weight loss.

Evidence for Association between SH2B1 Gene Variants and Glycated Hemoglobin in Nondiabetic European American Young Adults: The Add Health Study

Glycated hemoglobin (HbA1c) is used to classify glycaemia and type 2 diabetes (T2D). Body mass index (BMI) is a predictor of HbA1c levels and T2D. We tested 43 established BMI and obesity loci for association with HbA1c in a nationally representative multiethnic sample of young adults from the National Longitudinal Study of Adolescent to Adult Health [Add Health: age 24-34 years; n = 5641 European Americans (EA); 1740 African Americans (AA); 1444 Hispanic Americans (HA)] without T2D, using two levels of covariate adjustment (Model 1: age, sex, smoking, and geographic region; Model 2: Model 1 covariates plus BMI). Bonferroni adjustment was made for 43 SNPs and we considered P < 0.0011 statistically significant. Means (SD) for HbA1c were 5.4% (0.3) in EA, 5.7% (0.4) in AA, and 5.5% (0.3) in HA. We observed significant evidence for association with HbA1c for two variants near SH2B1 in EA (rs4788102, P = 2.2 × 10(-4) ; rs7359397, P = 9.8 × 10(-4) ) for Model 1. Both results were attenuated after adjustment for BMI (rs4788102, P = 1.7 × 10(-3) ; rs7359397, P = 4.6 × 10(-3) ). No variant reached Bonferroni-corrected significance in AA or HA. These results suggest that SH2B1 polymorphisms are associated with HbA1c, largely independent of BMI, in EA young adults.

Lyn mediates FIP1L1-PDGFRA signal pathway facilitating IL-5RA intracellular signal through FIP1L1-PDGFRA/JAK2/Lyn/Akt network complex in CEL

The Fip1-like1 (FIP1L1)–platelet-derived growth factor receptor alpha (PDGFRA) (F/P) oncogene can cause chronic eosinophilic leukemia (CEL), but requires IL-5 cytokine participation. In this study, we investigate the mechanism of F/P in collaboration with IL-5 in CEL. The results showed that Lyn, a key effector in the IL-5-motivated eosinophil production, is extensively activated in F/P-positive CEL cells. Lyn can associate and phosphorylate IL-5 receptor α (IL-5RA) in F/P-positive cells. Moreover, the activation of Lyn and IL-5R kinase were strengthened when the cells were stimulated by IL-5. Lyn inhibition in F/P-positive CEL cells attenuated cellular proliferation, induced apoptosis, and blocked cell migration and major basic protein (MBP) release. We identified the FIP1L1-PDGFRA/JAK2/Lyn/Akt complex in the F/P-expressing cells which can be disrupted by dual inhibition of JAK2 and Lyn, repressing cell proliferation in both EOL-1(F/P-positive human eosinophilic cell line) and imatinib-resistance (IR) cells. Altogether, our data demonstrate that Lyn is a vital downstream kinase activated by F/P converged with IL-5 signals in CEL cells. Lyn activate and expand IL-5RA intracellular signaling through FIP1L1-PDGFRA/JAK2/Lyn/Akt network complex, provoking eosinophils proliferation and exaggerated activation manifested as CEL.

Genetic and structural variation in the SH2B1 gene in the Belgian population

OBJECTIVE

Animal studies, genome-wide association and genomic structural variation studies have identified the SH2B1 gene as a candidate gene for obesity. Therefore, we have designed an extensive mutation and copy number variation (CNV) analysis investigating the prevalence of genetic and structural variations in SH2B1 in the Belgian population.

DESIGN AND METHODS

In the first part of this study, we performed a mutation screen for variants in the SH2B1 coding region in 581 obese children and adolescents and 433 healthy, lean individuals with high-resolution melting curve analysis followed by direct sequencing. In the second part of this study, Multiplex Amplicon Quantification (MAQ) analysis was used to identify CNVs in the distal SH2B1-containing chr.16p11.2 region in 421 obese children and adolescents with no developmental delay or behavioral phenotype.

RESULTS

Mutation analysis resulted in the identification of fifteen rare non-synonymous heterozygous variants. Several of these were found both in lean and obese subjects, suggesting that these are neutral polymorphisms. However, six private, heterozygous, non-synonymous variations were present in obese children only. Furthermore, we also identified six missense variants solely in lean individuals. CNV analysis could not identify carriers of the distal 16p11.2 deletion in our population.

CONCLUSION

Our mutation analysis has demonstrated that variation in the SH2B1 gene is frequent in both lean and obese groups, with distinctive variations being present on either side of the weight spectrum. Although the equal variation frequency does not immediately support disease causality, it cannot be excluded that some variations are weight-increasing or -decreasing. Further functional testing of the variants will be necessary to fully understand the impact of these variants on SH2B1. We were not able to detect carriers of the distal 16p11.2 deletion in our study population. As we excluded patients with developmental or behavioral problems, we suggest that in addition to obesity, the distal deletion might predispose for these traits. Further characterization of the phenotype is therefore necessary to clearly identify the phenotype of the distal 16p11.2 microdeletion syndrome.

SH2B1 is critical for the regulation of cardiac remodelling in response to pressure overload

AIMS

Src homology 2 (SH2) B adaptor protein 1 (SH2B1) is expressed in various tissues, including the heart. Previous studies have demonstrated that SH2B1 is involved in a variety of biological process, such as maintaining neuronal differentiation, regulating energy and glucose homeostasis, and promoting cell proliferation and motility. However, the role of SH2B1 in cardiac hypertrophy remains unclear. This study aimed at identifying the effects and the underlying mechanisms of SH2B1 in cardiac hypertrophy.

METHODS AND RESULTS

We performed gain- and loss-of-function studies using genetic approaches, and cardiac hypertrophy was evaluated through pathological, echocardiographic, haemodynamic, and molecular analyses. We found that SH2B1 expression was significantly increased in both failing human hearts and hypertrophic murine hearts. Mice overexpressing SH2B1 specifically in the heart displayed increased aortic banding (AB)-induced cardiac hypertrophy, fibrosis, ventricular dilation, and dysfunction compared with controls, whereas loss of SH2B1 produced the opposite phenotype. Consistently, similar results were observed in a global SH2B1-knockout rat model. Mechanistically, the pro-hypertrophic effects elicited by SH2B1 were associated with activation of the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signalling cascade. Furthermore, rescue experiments revealed that pharmacological inactivation of JAK2 rescued pressure overload-induced cardiac abnormalities in transgenic mice with cardiac-specific SH2B1 overexpression.

CONCLUSION

Taken together, our data demonstrate, for the first time, that SH2B1 is a key positive mediator of pathological cardiac hypertrophy, and that it primarily acts by regulating JAK2/STAT3 signalling.

Energy metabolism in the liver

The liver is an essential metabolic organ, and its metabolic function is controlled by insulin and other metabolic hormones. Glucose is converted into pyruvate through glycolysis in the cytoplasm, and pyruvate is subsequently oxidized in the mitochondria to generate ATP through the TCA cycle and oxidative phosphorylation. In the fed state, glycolytic products are used to synthesize fatty acids through de novo lipogenesis. Long-chain fatty acids are incorporated into triacylglycerol, phospholipids, and/or cholesterol esters in hepatocytes. These complex lipids are stored in lipid droplets and membrane structures, or secreted into the circulation as very low-density lipoprotein particles. In the fasted state, the liver secretes glucose through both glycogenolysis and gluconeogenesis. During pronged fasting, hepatic gluconeogenesis is the primary source for endogenous glucose production. Fasting also promotes lipolysis in adipose tissue, resulting in release of nonesterified fatty acids which are converted into ketone bodies in hepatic mitochondria though β-oxidation and ketogenesis. Ketone bodies provide a metabolic fuel for extrahepatic tissues. Liver energy metabolism is tightly regulated by neuronal and hormonal signals. The sympathetic system stimulates, whereas the parasympathetic system suppresses, hepatic gluconeogenesis. Insulin stimulates glycolysis and lipogenesis but suppresses gluconeogenesis, and glucagon counteracts insulin action. Numerous transcription factors and coactivators, including CREB, FOXO1, ChREBP, SREBP, PGC-1α, and CRTC2, control the expression of the enzymes which catalyze key steps of metabolic pathways, thus controlling liver energy metabolism. Aberrant energy metabolism in the liver promotes insulin resistance, diabetes, and nonalcoholic fatty liver diseases.

Functional characterization of obesity-associated variants involving the α and β isoforms of human SH2B1

We have previously reported rare variants in sarcoma (Src) homology 2 (SH2) B adaptor protein 1 (SH2B1) in individuals with obesity, insulin resistance, and maladaptive behavior. Here, we identify 4 additional SH2B1 variants by sequencing 500 individuals with severe early-onset obesity. SH2B1 has 4 alternatively spliced isoforms. One variant (T546A) lies within the N-terminal region common to all isoforms. As shown for past variants in this region, T546A impairs SH2B1β enhancement of nerve growth factor-induced neurite outgrowth, and the individual with the T546A variant exhibits mild developmental delay. The other 3 variants (A663V, V695M, and A723V) lie in the C-terminal tail of SH2B1α. SH2B1α variant carriers were hyperinsulinemic but did not exhibit the behavioral phenotype observed in individuals with SH2B1 variants that disrupt all isoforms. In in vitro assays, SH2B1α, like SH2B1β, enhances insulin- and leptin-induced insulin receptor substrate 2 (IRS2) phosphorylation and GH-induced cell motility. None of the variants affect SH2B1α enhancement of insulin- and leptin-induced IRS2 phosphorylation. However, T546A, A663V, and A723V all impair the ability of SH2B1α to enhance GH-induced cell motility. In contrast to SH2B1β, SH2B1α does not enhance nerve growth factor-induced neurite outgrowth. These studies suggest that genetic variants that disrupt isoforms other than SH2B1β may be functionally significant. Further studies are needed to understand the mechanism by which the individual isoforms regulate energy homeostasis and behavior.

SH2B1 regulation of energy balance, body weight, and glucose metabolism

The Src homology 2B (SH2B) family members (SH2B1, SH2B2 and SH2B3) are adaptor signaling proteins containing characteristic SH2 and PH domains. SH2B1 (also called SH2-B and PSM) and SH2B2 (also called APS) are able to form homo- or hetero-dimers via their N-terminal dimerization domains. Their C-terminal SH2 domains bind to tyrosyl phosphorylated proteins, including Janus kinase 2 (JAK2), TrkA, insulin receptors, insulin-like growth factor-1 receptors, insulin receptor substrate-1 (IRS1), and IRS2. SH2B1 enhances leptin signaling by both stimulating JAK2 activity and assembling a JAK2/IRS1/2 signaling complex. SH2B1 promotes insulin signaling by both enhancing insulin receptor catalytic activity and protecting against dephosphorylation of IRS proteins. Accordingly, genetic deletion of SH2B1 results in severe leptin resistance, insulin resistance, hyperphagia, obesity, and type 2 diabetes in mice. Neuron-specific overexpression of SH2B1β transgenes protects against diet-induced obesity and insulin resistance. SH2B1 in pancreatic β cells promotes β cell expansion and insulin secretion to counteract insulin resistance in obesity. Moreover, numerous SH2B1 mutations are genetically linked to leptin resistance, insulin resistance, obesity, and type 2 diabetes in humans. Unlike SH2B1, SH2B2 and SH2B3 are not required for the maintenance of normal energy and glucose homeostasis. The metabolic function of the SH2B family is conserved from insects to humans.

SH2B1 in β-cells promotes insulin expression and glucose metabolism in mice

Insulin deficiency drives the progression of both type 1 and type 2 diabetes. Pancreatic β-cell insulin expression and secretion are tightly regulated by nutrients and hormones; however, intracellular signaling proteins that mediate nutrient and hormonal regulation of insulin synthesis and secretion are not fully understood. SH2B1 is an SH2 domain-containing adaptor protein. It enhances the activation of the Janus tyrosine kinase 2 (JAK2)/signal transducer and activator of transcription and the phosphatidylinositol 3-kinase pathways in response to a verity of hormones, growth factors, and cytokines. Here we identify SH2B1 as a new regulator of insulin expression. In rat INS-1 832/13 β-cells, SH2B1 knockdown decreased, whereas SH2B1 overexpression increased, both insulin expression and glucose-stimulated insulin secretion. SH2B1-deficent islets also had reduced insulin expression, insulin content, and glucose-stimulated insulin secretion. Heterozygous deletion of SH2B1 decreased pancreatic insulin content and plasma insulin levels in leptin-deficient ob/ob mice, thus exacerbating hyperglycemia and glucose intolerance. In addition, overexpression of JAK2 increased insulin promoter activity, and SH2B1 enhanced the ability of JAK2 to activate the insulin promoter. Overexpression of SH2B1 also increased the expression of Pdx1 and the recruitment of Pdx1 to the insulin promoter in INS-1 832/13 cells, whereas silencing of SH2B1 had the opposite effects. Consistently, Pdx1 expression was lower in SH2B1-deficient islets. These data suggest that the SH2B1 in β-cells promotes insulin synthesis and secretion at least in part by enhancing activation of JAK2 and/or Pdx1 pathways in response to hormonal and nutritional signals.

SH2B1 in β-cells regulates glucose metabolism by promoting β-cell survival and islet expansion

IGF-1 and insulin promote β-cell expansion by inhibiting β-cell death and stimulating β-cell proliferation, and the phosphatidylinositol (PI) 3-kinase/Akt pathway mediates insulin and IGF-1 action. Impaired β-cell expansion is a risk factor for type 2 diabetes. Here, we identified SH2B1, which is highly expressed in β-cells, as a novel regulator of β-cell expansion. Silencing of SH2B1 in INS-1 832/13 β-cells attenuated insulin- and IGF-1-stimulated activation of the PI 3-kinase/Akt pathway and increased streptozotocin (STZ)-induced apoptosis; conversely, overexpression of SH2B1 had the opposite effects. Activation of the PI 3-kinase/Akt pathway in β-cells was impaired in pancreas-specific SH2B1 knockout (PKO) mice fed a high-fat diet (HFD). HFD-fed PKO mice also had increased β-cell apoptosis, decreased β-cell proliferation, decreased β-cell mass, decreased pancreatic insulin content, impaired insulin secretion, and exacerbated glucose intolerance. Furthermore, PKO mice were more susceptible to STZ-induced β-cell destruction, insulin deficiency, and hyperglycemia. These data indicate that SH2B1 in β-cells is an important prosurvival and proproliferative protein and promotes compensatory β-cell expansion in the insulin-resistant state and in response to β-cell stress.

Hepatic SH2B1 and SH2B2 regulate liver lipid metabolism and VLDL secretion in mice

SH2B1 is an SH2 and PH domain-containing adaptor protein. Genetic deletion of SH2B1 results in obesity, type 2 diabetes, and fatty liver diseases in mice. Mutations in SH2B1 are linked to obesity in humans. SH2B1 in the brain controls energy balance and body weight at least in part by enhancing leptin sensitivity in the hypothalamus. SH2B1 in peripheral tissues also regulates glucose and lipid metabolism, presumably by enhancing insulin sensitivity in peripheral metabolically-active tissues. However, the function of SH2B1 in individual peripheral tissues is unknown. Here we generated and metabolically characterized hepatocyte-specific SH2B1 knockout (HKO) mice. Blood glucose and plasma insulin levels, glucose tolerance, and insulin tolerance were similar between HKO, albumin-Cre, and SH2B1^f/f mice fed either a normal chow diet or a high fat diet (HFD). Adult-onset deletion of SH2B1 in the liver either alone or in combination with whole body SH2B2 knockout also did not exacerbate HFD-induced insulin resistance and glucose intolerance. Adult-onset, but not embryonic, deletion of SH2B1 in the liver attenuated HFD-induced hepatic steatosis. In agreement, adult-onset deletion of hepatic SH2B1 decreased the expression of diacylglycerol acyltransferase-2 (DGAT2) and increased the expression of adipose triglyceride lipase (ATGL). Furthermore, deletion of liver SH2B1 in SH2B2 null mice attenuated very low-density lipoprotein (VLDL) secretion. These data indicate that hepatic SH2B1 is not required for the maintenance of normal insulin sensitivity and glucose metabolism; however, it regulates liver triacylglycerol synthesis, lipolysis, and VLDL secretion.

New function of the adaptor protein SH2B1 in brain-derived neurotrophic factor-induced neurite outgrowth

Neurite outgrowth is an essential process for the establishment of the nervous system. Brain-derived neurotrophic factor (BDNF) binds to its receptor TrkB and regulates axonal and dendritic morphology of neurons through signal transduction and gene expression. SH2B1 is a signaling adaptor protein that regulates cellular signaling in various physiological processes. The purpose of this study is to investigate the role of SH2B1 in the development of the central nervous system. In this study, we show that knocking down SH2B1 reduces neurite formation of cortical neurons whereas overexpression of SH2B1β promotes the development of hippocampal neurons. We further demonstrate that SH2B1β promotes BDNF-induced neurite outgrowth and signaling using the established PC12 cells stably expressing TrkB, SH2B1β or SH2B1β mutants. Our data indicate that overexpressing SH2B1β enhances BDNF-induced MEK-ERK1/2, and PI3K-AKT signaling pathways. Inhibition of MEK-ERK1/2 and PI3K-AKT pathways by specific inhibitors suggest that these two pathways are required for SH2B1β-promoted BDNF-induced neurite outgrowth. Moreover, SH2B1β enhances BDNF-stimulated phosphorylation of signal transducer and activator of transcription 3 at serine 727. Finally, our data indicate that the SH2 domain and tyrosine phosphorylation of SH2B1β contribute to BDNF-induced signaling pathways and neurite outgrowth. Taken together, these findings demonstrate that SH2B1β promotes BDNF-induced neurite outgrowth through enhancing pathways involved MEK-ERK1/2 and PI3K-AKT.

Melatonin improves insulin sensitivity independently of weight loss in old obese rats

In aged rats, insulin signaling pathway (ISP) is impaired in tissues that play a pivotal role in glucose homeostasis, such as liver, skeletal muscle, and adipose tissue. Moreover, the aging process is also associated with obesity and reduction in melatonin synthesis from the pineal gland and other organs. The aim of the present work was to evaluate, in male old obese Wistar rats, the effect of melatonin supplementation in the ISP, analyzing the total protein amount and the phosphorylated status (immunoprecipitation and immunoblotting) of the insulin cascade components in the rat hypothalamus, liver, skeletal muscle, and periepididymal adipose tissue. Melatonin was administered in the drinking water for 8- and 12 wk during the night period. Food and water intake and fasting blood glucose remained unchanged. The insulin sensitivity presented a 2.1-fold increase both after 8- and 12 wk of melatonin supplementation. Animals supplemented with melatonin for 12 wk also presented a reduction in body mass. The acute insulin-induced phosphorylation of the analyzed ISP proteins increased 1.3- and 2.3-fold after 8- and 12 wk of melatonin supplementation. The total protein content of the insulin receptor (IR) and the IR substrates (IRS-1, 2) remained unchanged in all investigated tissues, except for the 2-fold increase in the total amount of IRS-1 in the periepididymal adipose tissue. Therefore, the known age-related melatonin synthesis reduction may also be involved in the development of insulin resistance and the adequate supplementation could be an important alternative for the prevention of insulin signaling impairment in aged organisms.

Molecular characterization of mutant mouse strains generated from the EUCOMM/KOMP-CSD ES cell resource

The Sanger Mouse Genetics Project generates knockout mice strains using the EUCOMM/KOMP-CSD embryonic stem (ES) cell collection and characterizes the consequences of the mutations using a high-throughput primary phenotyping screen. Upon achieving germline transmission, new strains are subject to a panel of quality control (QC) PCR- and qPCR-based assays to confirm the correct targeting, cassette structure, and the presence of the 3' LoxP site (required for the potential conditionality of the allele). We report that over 86 % of the 731 strains studied showed the correct targeting and cassette structure, of which 97 % retained the 3' LoxP site. We discuss the characteristics of the lines that failed QC and postulate that the majority of these may be due to mixed ES cell populations which were not detectable with the original screening techniques employed when creating the ES cell resource.

Screening for coding variants in FTO and SH2B1 genes in Chinese patients with obesity

Objective

To investigate potential functional variants in FTO and SH2B1 genes among Chinese children with obesity.

Methods

Sanger sequencing of PCR products of all FTO and SH2B1 exons and their flanking regions were performed in 338 Chinese Han children with obesity and 221 age- and sex-matched lean controls.

Results

A total of seven and five rare non-synonymous variants were identified in FTO and SH2B1, respectively. The overall frequencies of FTO and SH2B1 rare non-synonymous variants were similar in obese and lean children (2.37% and 0.90% vs. 1.81% and 1.36%, P>0.05). However, four out of the seven variants in FTO were novel and all were unique to obese children (p>0.05). None of the novel variants was consistently being predicted to be deleterious. Four out of five variants in SH2B1 were novel and one was unique to obese children (p>0.05). One variant (L293R) that was consistently being predicted as deleterious in SH2B1 gene was unique to lean control. While rare missense mutations were more frequently detected in girls from obesity as well as lean control than boys, the difference was not statistically significant. In addition, it's shown that the prevalence of rare missense mutations of FTO as well as SH2B1 was similar across different ethnic groups.

Conclusion

The rare missense mutations of FTO and SH2B1 did not confer risks of obesity in Chinese Han children in our cohort.

Functional relevance of genes implicated by obesity genome-wide association study signals for human adipocyte biology

AIMS/HYPOTHESIS

Genome-wide association studies (GWAS) have identified numerous single-nucleotide polymorphisms associated with obesity, consequently implying a role in adipocyte biology for many closely residing genes. We investigated the functional relevance of such genes in human adipocytes.

METHODS

We selected eight genes (BDNF, MAF, MTCH2, NEGR1, NPC1, PTER, SH2B1 and TMEM18) from obesity GWAS and analysed their effect in human adipogenesis using small interfering (si)RNA-mediated knockdown, their regulation by metabolic agents in adipocytes and pre-adipocytes, and gene expression in paired samples of human fat biopsies (68 non-obese, 165 obese) by quantitative real-time PCR.

RESULTS

We show a two- to threefold upregulation of MAF, MTCH2 and NEGR1 and a two- to fourfold downregulation of BDNF and PTER during adipogenesis. Knockdown of BDNF (mean ± SEM; 83.8 ± 4.7% of control; p = 0.0002), MTCH2 (72.7 ± 9.5%; p = 0.0006), NEGR1 (70.2 ± 5.7%; p < 0.0001) and TMEM18 (70.8 ± 6.1%; p < 0.0001) significantly inhibited adipocyte maturation, while knockdown of the other proteins had no effect. Insulin slightly induced MAF (1.65-fold; p = 0.0009) and MTCH2 (1.72-fold; p < 0.0001), while it suppressed BDNF (59.6%; p = 0.0009), NEGR1 (58.0%; p = 0.0085) and TMEM18 (69.3%; p = 0.0377) in adipocytes. The synthetic glucocorticoid dexamethasone suppressed MAF (45.7%; p = 0.0022), BDNF (66.6%; p = 0.0012) and TMEM18 (63.5%; p = 0.0181), but induced NEGR1 (3.2-fold; p = 0.0117) expression. Furthermore, MTCH2, NEGR1 and TMEM18 were differentially expressed in subcutaneous and visceral adipose tissue. TMEM18 expression was decreased in the adipose tissue of obese patients, and negatively correlated with anthropometric variables and adipocyte size.

CONCLUSIONS/INTERPRETATION

Our results imply a regulatory role for TMEM18, BDNF, MTCH2 and NEGR1 in adipocyte differentiation and biology. In addition, we show a variation of MAF expression during adipogenesis, while NPC1, PTER and SH2B1 were not regulated.

Regulation of insulin and type 1 insulin-like growth factor signaling and action by the Grb10/14 and SH2B1/B2 adaptor proteins

The effects of insulin and type 1 insulin-like growth factor (IGF-1) on metabolism, growth and survival are mediated by their association with specific receptor tyrosine kinases, which results in both receptor and substrate phosphorylation. Phosphotyrosine residues on receptors and substrates provide docking sites for signaling proteins containing SH2 (Src homology 2) domains, including molecular adaptors. This review focuses on the regulation of insulin/IGF-1 signaling and action by two adaptor families with a similar domain organization: the growth factor receptor-bound proteins Grb7/10/14 and the SH2B proteins. Both Grb10/14 and SH2B1/B2 associate with the activation loop of insulin/IGF-1 receptors through their SH2 domains, but association of Grb10/14 also involves their unique BPS domain. Consistent with Grb14 binding as a pseudosubstrate to the kinase active site, insulin/IGF-induced activation of receptors and downstream signaling pathways in cultured cells is inhibited by Grb10/14 adaptors, but is potentiated by SH2B1/B2 adaptors. Accordingly, Grb10 and Grb14 knockout mice show improved insulin/IGF sensitivity in vivo, and, for Grb10, overgrowth and increased skeketal muscle and pancreatic β-cell mass. Conversely, SH2B1-depleted mice display insulin and IGF-1 resistance, with peripheral depletion leading to reduced adiposity and neuronal depletion leading to obesity through associated leptin resistance. Grb10/14 and SH2B1 adaptors also modulate insulin/IGF-1 action by interacting with signaling components downstream of receptors and exert several tissue-specific effects. The identification of Grb10/14 and SH2B1 as physiological regulators of insulin signaling and action, together with observations that variants at their gene loci are associated with obesity and/or insulin resistance, highlight them as potential therapeutic targets for these conditions.

The Lnk adaptor protein: a key regulator of normal and pathological hematopoiesis

The development and function of blood cells are regulated by specific growth factors/cytokines and their receptors' signaling pathways. In this way, these factors influence cell survival, proliferation and differentiation of hematopoietic cells. Central to this positive and/or negative control are the adaptor proteins. Since their identification 10 years ago, members of the Lnk adaptor protein family have proved to be important activators and/or inhibitors in the hematopoietic, immune and vascular system. In particular, the generation of animal and cellular models for the Lnk and APS proteins has helped establish the physiological role of these molecules through the identification of their specific signaling pathways and the characterization of their binding partners. Moreover, the recent identification of mutations in the LNK gene in myeloproliferative disorders, as well as the correlation of a single nucleotide polymorphism on LNK with hematological, immune and vascular diseases have suggested its involvement in the pathophysiology of these malignancies. The latter findings have thus raised the possibility of addressing Lnk signaling for the treatment of certain human diseases. This review therefore describes the pathophysiological role of this adaptor protein in hematological malignancies and the potential benefits of Lnk therapeutic targeting.