Changhong Li

Identification of Genetic and Environmental Factors Predicting Metabolically Healthy Obesity in Children: Data From the BCAMS Study

CONTEXT Available data related to the metabolically healthy obesity (MHO) phenotype are mainly derived from studies in adults because studies during childhood are very limited to date. OBJECTIVE The objective of the study was to determine the prevalence of MHO in Chinese children and to investigate environmental and genetic factors impacting on MHO status. DESIGN This was a cross-sectional study. PARTICIPANTS A total of 1213 children with a body mass index at the 95th percentile or greater aged 6–18 years were included in this study. Participants were classified as MHO or of metabolically unhealthy obesity based on insulin resistance (IR) or cardiometabolic risk (CR) factors (blood pressure, lipids, and glucose). Twenty-two genetic variants previously reported from genome-wide association studies of obesity and diabetes plus the environmental factors of lifestyle, socioeconomic status, and birth weight was assessed. RESULTS The prevalence of MHO-IR and MHO-CR were 27.1% and 37.2%, respectively. Waist circumference was an independent predictor of MHO, regardless of definitions, whereas walking to school and KCNQ1-rs2237897 were independent predictors of MHO-CR. Acanthosis nigricans, birth weight, the frequency of soft drink consumption, the mothers education status, and KCNQ1-rs2237892 were independent predictors of MHO-IR. Multiplicative interaction effects were found between KCNQ1-rs2237897 and walking to school on MHO-CR (odds ratio 1.31 [95% confidence interval 1.05–1.63]) and between rs2237892 and consumption of soft drinks on MHO-IR (odds ratio 0.80 [95% confidence interval 0.68–0.94]). CONCLUSIONS Approximately one-third of Chinese obese children can be classified as MHO. Both genetic predisposition and environment factors and their interaction contribute to the prediction of MHO status. This study provides novel insights into the heterogeneity of obesity and has the potential to impact the optimization of the intervention options and regimens in the management of pediatric obesity.

A severe case of hyperinsulinism due to hemizygous activating mutation of glutamate dehydrogenase

Activating mutations in the GLUD1 gene, which encodes glutamate dehydrogenase (GDH), result in the hyperinsulinism‐hyperammonemia syndrome. GDH is an allosterically regulated enzyme responsible for amino acid‐mediated insulin secretion via the oxidative deamination of glutamate to 2‐oxoglutarate, leading to ATP production and insulin release. This study characterizes a novel combination of mutations in GLUD1 found in a neonate who presented on the first day of life with severe hypoglycemia, hyperammonemia, and seizures. Mutation analysis revealed a novel frameshift mutation (c.37delC) inherited from the asymptomatic mother that results in a truncated protein and a de novo activating mutation (p.S445L) close to the GTP binding site that has previously been reported. GTP inhibition of GDH enzyme activity in 293T cells expressing the p.S445L or wild‐type GDH showed that the half‐maximal inhibitory concentration (IC50) for GTP was approximately 800 times higher for p.S445L compared to wild type. GTP inhibition of GDH activity in lymphoblasts from the patient, from a heterozygote for the p.S445L mutation, and in wild‐type lymphoblasts showed that the IC50 for GTP of the patient was approximately 200 times that of wild type and 7 times that of heterozygote. However, while the patient had a loss of GTP inhibition of GDH that was more severe than that of heterozygotes, the patients clinical phenotype is similar to typical heterozygous mutations of GDH. This is the first time we have observed a functionally homozygous activating mutation of GDH in a human.

Sleep Duration and Cardiometabolic Risk Among Chinese School-aged Children: Do Adipokines Play a Mediating Role?

Study Objectives To assess the associations between sleep duration and cardiometabolic risk factors in Chinese school-aged children and to explore the possible mediating role of adipokines. Methods Sleep duration was collected in 3166 children from the Beijing Child and Adolescent Metabolic Syndrome study. Glucose homeostasis and other cardiometabolic risk factors were assessed. Serum adipokines including leptin, total and high-molecular-weight (HMW) adiponectin, resistin, fibroblast growth factor 21 (FGF21), and retinol binding protein 4 (RBP4) were determined. Results Among the 6- to 12-year-old children, after adjusting for covariates including puberty, short sleep duration was associated with increased body mass index (BMI), waist circumference, fasting glucose, insulin and homeostasis model assessment of insulin resistance (all p < .0001), higher triglyceride and lower high-density lipoprotein cholesterol (p < .05), along with increased leptin (p < .0001), FGF21 (p < .05) and decreased HMW-adiponectin (p ≤ .01); the association with leptin remained significant after further adjustment for BMI. However, these associations, except for glucose (p < .0001), disappeared after further adjusted for leptin. For the 13-18 years old group, short sleep duration was associated with higher BMI, waist circumference, and RBP4 (all p < .05), but the association with RBP4 was attenuated after adjusting for BMI (p = .067). Conclusions Short sleep duration is strongly associated with obesity and hyperglycemia (in 6-12 years old), along with adverse adipokine secretion patterns among Chinese children. The associations with cardiometabolic risk factors appear to be more pronounced in younger children, and could be explained, at least partially, by leptin levels.

Ezh2 phosphorylation state determines its capacity to maintain CD8 + T memory precursors for antitumor immunity

Memory T cells sustain effector T-cell production while self-renewing in reaction to persistent antigen; yet, excessive expansion reduces memory potential and impairs antitumor immunity. Epigenetic mechanisms are thought to be important for balancing effector and memory differentiation; however, the epigenetic regulator(s) underpinning this process remains unknown. Herein, we show that the histone methyltransferase Ezh2 controls CD8+ T memory precursor formation and antitumor activity. Ezh2 activates Id3 while silencing Id2, Prdm1 and Eomes, promoting the expansion of memory precursor cells and their differentiation into functional memory cells. Akt activation phosphorylates Ezh2 and decreases its control of these transcriptional programs, causing enhanced effector differentiation at the expense of T memory precursors. Engineering T cells with an Akt-insensitive Ezh2 mutant markedly improves their memory potential and capability of controlling tumor growth compared to transiently inhibiting Akt. These findings establish Akt-mediated phosphorylation of Ezh2 as a critical target to potentiate antitumor immunotherapeutic strategies.During an immune response naive CD8+ T cells can differentiate into either effector or memory T cells. Here the authors show that Akt-mediated phosphorylation of the epigenetic regulator Ezh2 is critical for the generation of an anti-tumor CD8 T cell response and promotes the expansion of memory-precursors.

Hsp90 inhibition destabilizes Ezh2 protein in alloreactive T cells and reduces graft-versus-host disease in mice

Modulating T-cell alloreactivity has been a main strategy to reduce graft-versus-host disease (GVHD), a life-threatening complication after allogeneic hematopoietic stem-cell transplantation (HSCT). Genetic deletion of T-cell Ezh2, which catalyzes trimethylation of histone H3 at lysine 27 (H3K27me3), inhibits GVHD. Therefore, reducing Ezh2-mediated H3K27me3 is thought to be essential for inhibiting GVHD. We tested this hypothesis in mouse GVHD models. Unexpectedly, administration of the Ezh2 inhibitor GSK126, which specifically decreases H3K27me3 without affecting Ezh2 protein, failed to prevent the disease. In contrast, destabilizing T-cell Ezh2 protein by inhibiting Hsp90 using its specific inhibitor AUY922 reduced GVHD in mice undergoing allogeneic HSCT. In vivo administration of AUY922 selectively induced apoptosis of activated T cells and decreased the production of effector cells producing interferon γ and tumor necrosis factor α, similar to genetic deletion of Ezh2. Introduction of Ezh2 into alloreactive T cells restored their expansion and production of effector cytokines upon AUY922 treatment, suggesting that impaired T-cell alloreactivity by inhibiting Hsp90 is achieved mainly through depleting Ezh2. Mechanistic analysis revealed that the enzymatic SET domain of Ezh2 directly interacted with Hsp90 to prevent Ezh2 from rapid degradation in activated T cells. Importantly, pharmacological inhibition of Hsp90 preserved antileukemia activity of donor T cells, leading to improved overall survival of recipient mice after allogeneic HSCT. Our findings identify the Ezh2-Hsp90 interaction as a previously unrecognized mechanism essential for T-cell responses and an effective target for controlling GVHD.

Nutrient sensing in pancreatic islets: lessons from congenital hyperinsulinism and monogenic diabetes

Pancreatic beta cells sense changes in nutrients during the cycles of fasting and feeding and release insulin accordingly to maintain glucose homeostasis. Abnormal beta cell nutrient sensing resulting from gene mutations leads to hypoglycemia or diabetes. Glucokinase (GCK) plays a key role in beta cell glucose sensing. As one form of congenital hyperinsulinism (CHI), activating mutations of GCK result in a decreased threshold for glucose‐stimulated insulin secretion and hypoglycemia. In contrast, inactivating mutations of GCK result in diabetes, including a mild form (MODY2) and a severe form (permanent neonatal diabetes mellitus (PNDM)). Mutations of beta cell ion channels involved in insulin secretion regulation also alter glucose sensing. Activating or inactivating mutations of ATP‐dependent potassium (KATP) channel genes result in severe but completely opposite clinical phenotypes, including PNDM and CHI. Mutations of the other ion channels, including voltage‐gated potassium channels (Kv7.1) and voltage‐gated calcium channels, also lead to abnormal glucose sensing and CHI. Furthermore, amino acids can stimulate insulin secretion in a glucose‐independent manner in some forms of CHI, including activating mutations of the glutamate dehydrogenase gene, HDAH deficiency, and inactivating mutations of KATP channel genes. These genetic defects have provided insight into a better understanding of the complicated nature of beta cell fuel‐sensing mechanisms.

Leptin-adiponectin imbalance as a marker of metabolic syndrome among Chinese children and adolescents: The BCAMS study

Purpose Leptin and adiponectin have opposite effects on subclinical inflammation and insulin resistance, both involved in the development of metabolic syndrome (MS). We aimed to investigate whether leptin/adiponectin ratio (L/A), as a marker of these two adipokines imbalance, may improve diagnosis of MS in children and adolescents, and determined its cut-off value in the diagnosis of MS. Methods A total of 3,428 subjects aged 6–18 years were selected from Beijing Child and Adolescent Metabolic Syndrome study. Adipokine leptin and adiponectin were measured using enzyme-linked immunosorbent assay. Odds ratio of MS per 1 z-score of adipokine was examined using logistic regression. Diagnosis accuracy was assessed using c-statistics (AUC) and net reclassification index. Results The levels of leptin and L/A increased with number of positive MS components, while the levels of adiponectin declined in both boys and girls (all P <0.001). AUCs for diagnosis of MS in girls were 0.793, 0.773, and 0.689 using L/A, leptin and adiponectin, respectively; and AUCs in boys were 0.822, 0.798, and 0.697 for L/A, leptin and adiponectin, respectively. Notably, L/A outperformed individual leptin or adiponectin in discriminating a diagnosis of MS (all P < 0.02 in AUC comparisons). In addition, the optimal cut-offs of L/A by ROC curve differed by genders and pubertal stages, which were 1.63, 1.28, 1.95 and 1.53 ng/ug for total, pre-, mid- and postpubertal boys, respectively and 2.19, 0.87,1.48 and 2.27 ng/ug for total, pre-, mid- and postpubertal girls, respectively, yielding high sensitivity and moderate specificity for a screening test. Conclusions In this pediatric population, leptin-adiponectin imbalance, as reflected by an increase in L/A level, was found to be a better diagnostic biomarker for MS than leptin or adiponectin alone. Future longitudinal studies are needed to further validate the gender-specific cutoff values.

Glutamate Dehydrogenase, a Complex Enzyme at a Crucial Metabolic Branch Point

In-vitro, glutamate dehydrogenase (GDH) catalyzes the reversible oxidative deamination of glutamate to α-ketoglutarate (α-KG). GDH is found in all organisms, but in animals is allosterically regulated by a wide array of metabolites. For many years, it was not at all clear why animals required such complex control. Further, in both standard textbooks and some research publications, there has been some controversy as to the directionality of the reaction. Here we review recent work demonstrating that GDH operates mainly in the catabolic direction in-vivo and that the finely tuned network of allosteric regulators allows GDH to meet the varied needs in a wide range of tissues in animals. Finally, we review the progress in using pharmacological agents to activate or inhibit GDH that could impact a wide range of pathologies from insulin disorders to tumor growth.

Inhibition of cholinergic potentiation of insulin secretion from pancreatic islets by chronic elevation of glucose and fatty acids: Protection by casein kinase 2 inhibitor

Objectives Chronic hyperlipidemia and hyperglycemia are characteristic features of type 2 diabetes (T2DM) that are thought to cause or contribute to β-cell dysfunction by “glucolipotoxicity.” Previously we have shown that acute treatment of pancreatic islets with fatty acids (FA) decreases acetylcholine-potentiated insulin secretion. This acetylcholine response is mediated by M3 muscarinic receptors, which play a key role in regulating β-cell function. Here we examine whether chronic FA exposure also inhibits acetylcholine-potentiated insulin secretion using mouse and human islets. Methods Islets were cultured for 3 or 4 days at different glucose concentration with 0.5 mM palmitic acid (PA) or a 2:1 mixture of PA and oleic acid (OA) at 1% albumin (PA/BSA molar ratio 3.3). Afterwards, the response to glucose and acetylcholine were studied in perifusion experiments. Results FA-induced impairment of insulin secretion and Ca2+ signaling depended strongly on the glucose concentrations of the culture medium. PA and OA in combination reduced acetylcholine potentiation of insulin secretion more than PA alone, both in mouse and human islets, with no evidence of a protective role of OA. In contrast, lipotoxicity was not observed with islets cultured for 3 days in medium containing less than 1 mM glucose and a mixture of glutamine and leucine (7 mM each). High glucose and FAs reduced endoplasmic reticulum (ER) Ca2+ storage capacity; however, preserving ER Ca2+ by blocking the IP3 receptor with xestospongin C did not protect islets from glucolipotoxic effects on insulin secretion. In contrast, an inhibitor of casein kinase 2 (CK2) protected the glucose dependent acetylcholine potentiation of insulin secretion in mouse and human islets against glucolipotoxicity. Conclusions These results show that chronic FA treatment decreases acetylcholine potentiation of insulin secretion and that this effect is strictly glucose dependent and might involve CK2 phosphorylation of β-cell M3 muscarinic receptors.

Data from: Birthweight and type 2 diabetes risk factors in children: the mediating role of adipose tissue

Supplementary information for manuscript: Birthweight and type 2 diabetes risk factors in children: the mediating role of adipose tissue