Effects of flora deficiency on the structure and function of the large intestine.

The significant anatomical changes in large intestine of germ-free (GF) mice provide excellent material for understanding microbe-host crosstalk. We observed significant differences of GF mice in anatomical and physiological involving in enlarged cecum, thinned mucosal layer and enriched water in cecal content. Furthermore, integration analysis of multi-omics data revealed the associations between the structure of large intestinal mesenchymal cells and the thinning of the mucosal layer. Increased Aqp8 expression in GF mice may contribute to enhanced water secretion or altered hydrodynamics in the cecum. In addition, the proportion of epithelial cells, nutrient absorption capacity, immune function and the metabolome of cecum contents of large intestine were also significantly altered. Together, this is the first systematic study of the transcriptome and metabolome of the cecum and colon of GF mice, and these findings contribute to our understanding of the intricate interactions between microbes and the large intestine.

Bacteroides methylmalonyl-CoA mutase produces propionate that promotes intestinal goblet cell differentiation and homeostasis.

Propionate is a short-chain fatty acid that is generated upon microbiome-mediated fiber fermentation in the intestine. By modulating immune and metabolic pathways, propionate exerts many health benefits. Key bacterial species, such as Bacteroides thetaiotaomicron, generate propionate, but the biochemical pathways and specific functions remain undetermined. We identified a gene operon-encoding methylmalonyl-CoA mutase (MCM) that contributes to propionate biosynthesis in B. thetaiotaomicron. Colonization of germ-free mice with wild-type or MCM-deficient strains as well as in vitro examination demonstrated that MCM-mediated propionate production promotes goblet cell differentiation and mucus-related gene expression. Intestinal organoids lacking the propionate receptor, GPR41, showed reduced goblet cell differentiation upon MCM-mediated propionate production. Furthermore, although wild-type B. thetaiotaomicron alleviated DSS-induced intestinal inflammation, this effect was abolished in mice receiving the MCM-deficient strain but restored upon propionate supplementation. These data emphasize the critical role of MCM-mediated propionate biosynthesis in goblet cell differentiation, offering potential pathways to ameliorate colitis.

Gut microbiota regulates postprandial GLP-1 response via ileal bile acid-TGR5 signaling.

The gut microbiota interacts with intestinal epithelial cells through microbial metabolites to regulate the release of gut hormones. We investigated whether the gut microbiota affects the postprandial glucagon-like peptide-1 (GLP-1) response using antibiotic-treated mice and germ-free mice. Gut microbiome depletion completely abolished postprandial GLP-1 response in the circulation and ileum in a lipid tolerance test. Microbiome depletion did not influence the GLP-1 secretory function of primary ileal cells in response to stimulators in vitro, but dramatically changed the postprandial dynamics of endogenous bile acids, particularly ω-muricholic acid (ωMCA) and hyocholic acid (HCA). The bile acid receptor Takeda G protein-coupled receptor 5 (TGR5) but not farnesoid X receptor (FXR), participated in the regulation of postprandial GLP-1 response in the circulation and ileum, and ωMCA or HCA stimulated GLP-1 secretion via TGR5. Finally, fecal microbiota transplantation or ωMCA and HCA supplementation restored postprandial GLP-1 response. In conclusion, gut microbiota is indispensable for maintaining the postprandial GLP-1 response specifically in the ileum, and bile acid (ωMCA and HCA)-TGR5 signaling is involved in this process. This study helps to understand the essential interplay between the gut microbiota and host in regulating postprandial GLP-1 response and opens the foundation for new therapeutic targets.

The rs1421085 variant within FTO promotes brown fat thermogenesis.

One lead genetic risk signal of obesity-the rs1421085 T>C variant within the FTO gene-is reported to be functional in vitro but lacks evidence at an organism level. Here we recapitulate the homologous human variant in mice with global and brown adipocyte-specific variant knock-in and reveal that mice carrying the C-allele show increased brown fat thermogenic capacity and resistance to high-fat diet-induced adiposity, whereas the obesity-related phenotypic changes are blunted at thermoneutrality. Both in vivo and in vitro data reveal that the C-allele in brown adipocytes enhances the transcription of the Fto gene, which is associated with stronger chromatin looping linking the enhancer region and Fto promoter. Moreover, FTO knockdown or inhibition effectively eliminates the increased thermogenic ability of brown adipocytes carrying the C-allele. Taken together, these findings identify rs1421085 T>C as a functional variant promoting brown fat thermogenesis.

Human RSPO1 Mutation Represses Beige Adipocyte Thermogenesis and Contributes to Diet-Induced Adiposity.

Recent genetic evidence has linked WNT downstream mutations to fat distribution. However, the roles of WNTs in human obesity remain unclear. Here, the authors screen all Wnt-related paracrine factors in 1994 obese cases and 2161 controls using whole-exome sequencing (WES) and identify that 12 obese patients harbor the same mutations in RSPO1 (p.R219W/Q) predisposing to human obesity. RSPO1 is predominantly expressed in visceral fat, primarily in the fibroblast cluster, and is increased with adiposity. Mice overexpressing human RSPO1 in adipose tissues develop obesity under a high-fat diet (HFD) due to reduced brown/beige fat thermogenesis. In contrast, Rspo1 ablation resists HFD-induced adiposity by increasing thermogenesis. Mechanistically, RSPO1 overexpression or administration significantly inhibits adipocyte mitochondrial respiration and thermogenesis via LGR4-Wnt/ß-catenin signaling pathway. Importantly, humanized knockin mice carrying the hotspot mutation (p.R219W) display suppressed thermogenesis and recapitulate the adiposity feature of obese carriers. The mutation disrupts RSPO1's electrostatic interaction with the extracellular matrix, leading to excessive RSPO1 release that activates LGR4-Wnt/ß-catenin signaling and attenuates thermogenic capacity in differentiated beige adipocytes. Therefore, these findings identify that gain-of-function mutations and excessive expression of RSPO1, acting as a paracrine Wnt activator, suppress fat thermogenesis and contribute to obesity in humans.

Fasting and refeeding triggers specific changes in bile acid profiles and gut microbiota.

BACKGROUND: Bile acids (BAs) are closely related to nutrient supply and modified by gut microbiota. Gut microbiota perturbations shape BA composition, which further affects host metabolism. METHODS: We investigated BA profiles in plasma, feces, and liver of mice fed ad libitum, fasted for 24 h, fasted for 24 h and then refed for 24 h using ultraperformance liquid chromatography coupled to tandem mass spectrometry. Gut microbiota was measured by 16S rRNA gene sequencing. Expressions of BA biosynthesis-related genes in the liver and BA reabsorption-related genes in the ileum were analyzed. FINDINGS: Compared with the controls, unconjugated primary BAs (PBAs) and unconjugated secondary BAs (SBAs) in plasma were decreased whereas conjugated SBAs in plasma, unconjugated PBAs, unconjugated SBAs and conjugated SBAs in feces, and unconjugated SBAs in liver were increased in the fasting mice. The expression of BA biosynthesis-related genes in the liver and BA reabsorption-related genes in the ileum were decreased in the fasting mice compared with the controls. Compared with the controls, Akkermansia, Parabacteroides, Muribaculum, Eubacterium_coprostanoligenes and Muribaculaceae were increased in the fasting mice whereas Lactobacillus and Bifidobacterium were decreased. All these changes in BAs and gut microbiota were recovered under refeeding. Akkermansia was negatively correlated with plasma levels of unconjugated PBAs, unconjugated SBAs and glucose, whereas it was positively correlated with plasma conjugated SBAs, fecal unconjugated PBAs, and fecal unconjugated SBAs. CONCLUSIONS: We characterized the BA profiles, gut microbiota, and gene expression responsible for BA biosynthesis and intestinal reabsorption to explore their rapid changes in response to food availability. Our study highlighted the rapid effect of nutrient supply on BAs and gut microbiota.

GREM2 is associated with human central obesity and inhibits visceral preadipocyte browning.

BACKGROUND: Some circulating proteins are linked to central adiposity. Gremlin 2 (GREM2) functions as a secreted factor involved in osteogenesis and adipogenesis. Here, we investigated the association of blood GREM2 levels and central adiposity, and the biological roles of GREM2 in the browning program of visceral preadipocytes. METHODS: Three independent cohorts were applied to detect circulating GREM2 levels. Recombinant Grem2 protein, Grem2 overexpression and knockout mouse models, and preadipocyte-specific Bmpr2 knockout mice were used to assess the roles of Grem2 in the browning program. FINDINGS: We detected the presence of GREM2 protein in human serum using an ELISA approach. We revealed elevated GREM2 levels in severely obese subjects and validated this finding in a large-scale community population involving 10,327 subjects. Notably, serum GREM2 was positively associated with visceral fat volume, as quantified by 3D reconstruction methods. In mice, Grem2 was highly expressed in visceral fat and liver tissues, while surgical removal of visceral fat lowered circulating Grem2 levels. Visceral fat secreted more Grem2 in obese mice. Grem2-overexpressed mice exhibited a reduced browning ability of visceral fat, whereas Grem2 ablation enhanced the browning capacity and reduced visceral fat content. Mechanistically, Grem2 attenuated the browning program of visceral preadipocytes partially by antagonizing BMP4/7-SMAD1/5/8 signaling pathway. Further, genetic deletion of Bmpr2 in Pdgfrα+ preadipocytes abolished the antagonistic effect of Grem2. INTERPRETATION: These findings indicate that GREM2 might function as a circulating protein factor associated with human visceral adiposity, and Grem2 inhibits the browning capacity of visceral preadipocytes partially by BMP4/7-BMPR2 signaling pathway. FUNDING: The complete list of funders can be found in the Acknowledgement section.

Sexual dimorphism in glucose metabolism is shaped by androgen-driven gut microbiome.

Males are generally more susceptible to impaired glucose metabolism and type 2 diabetes (T2D) than females. However, the underlying mechanisms remain to be determined. Here, we revealed that gut microbiome depletion abolished sexual dimorphism in glucose metabolism. The transfer of male donor microbiota into antibiotics-treated female mice led the recipients to be more insulin resistant. Depleting androgen via castration changed the gut microbiome of male mice to be more similar to that of females and improved glucose metabolism, while reintroducing dihydrotestosterone (DHT) reversed these alterations. More importantly, the effects of androgen on glucose metabolism were largely abolished when the gut microbiome was depleted. Next, we demonstrated that androgen modulated circulating glutamine and glutamine/glutamate (Gln/Glu) ratio partially depending on the gut microbiome, and glutamine supplementation increases insulin sensitivity in vitro. Our study identifies the effects of androgen in deteriorating glucose homeostasis partially by modulating the gut microbiome and circulating glutamine and Gln/Glu ratio, thereby contributing to the difference in glucose metabolism between the two sexes.

Deciphering CT texture features of human visceral fat to evaluate metabolic disorders and surgery-induced weight loss effects.

BACKGROUND: Metabolic syndrome (MetS) is highly related to the excessive accumulation of visceral adipose tissue (VAT). Quantitative measurements of VAT are commonly applied in clinical practice for measurement of metabolic risks; however, it remains largely unknown whether the texture of VAT can evaluate visceral adiposity, stratify MetS and predict surgery-induced weight loss effects. METHODS: 675 Chinese adult volunteers and 63 obese patients (with bariatric surgery) were enrolled. Texture features were extracted from VATs of the computed tomography (CT) scans and machine learning was applied to identify significant imaging biomarkers associated with metabolic-related traits. FINDINGS: Combined with sex, ten VAT texture features achieved areas under the curve (AUCs) of 0.872, 0.888, 0.961, and 0.947 for predicting the prevalence of insulin resistance, MetS, central obesity, and visceral obesity, respectively. A novel imaging biomarker, RunEntropy, was identified to be significantly associated with major metabolic outcomes and a 3.5-year follow-up in 338 volunteers demonstrated its long-term effectiveness. More importantly, the preoperative imaging biomarkers yielded high AUCs and accuracies for estimation of surgery responses, including the percentage of excess weight loss (%EWL) (0.867 and 74.6%), postoperative BMI group (0.930 and 76.1%), postoperative insulin resistance (0.947 and 88.9%), and excess visceral fat loss (the proportion of visceral fat reduced over 50%; 0.928 and 84.1%). INTERPRETATION: This study shows that the texture features of VAT have significant clinical implications in evaluating metabolic disorders and predicting surgery-induced weight loss effects. FUNDING: The complete list of funders can be found in the Acknowledgement section.

Missense Variants in PAX4 Are Associated with Early-Onset Diabetes in Chinese.

INTRODUCTION: East Asians are more susceptible to early-onset diabetes than Europeans and exhibit reduced insulin secretion at earlier stages. PAX4 plays a critical role in the development of ß-cells. The dysfunction-missense variants PAX4 R192H and PAX4 R192S are common in East Asians but rare in Europeans. Therefore, we aim to investigate the diabetes-associated genes, including PAX4 R192H/S, in East Asians with early-onset diabetes. METHODS: Exome variants of 80 Chinese early-onset diabetes patients (onset age < 35 years) after the exclusion of type 1 diabetes (T1D) were detected by a customized gene panel covering 32 known diabetes-associated genes. Then, 229 subjects with early-onset diabetes (T1D excluded) and 1679 controls from the Chinese population were genotyped to validate the association of PAX4 R192H/S with early-onset diabetes and related phenotypes. RESULTS: The gene panel detected 11 monogenic diabetes patients with five novel mutations among the 80 early-onset diabetes patients. Asian-specifically enriched PAX4 R192H and R192S were associated with early-onset diabetes (R192H: OR 1.88, 95% CI 1.37-2.60, P = 8.41 × 10-5; R192S: OR 1.71, 95% CI 1.17-2.51, P = 0.005). In early-onset diabetes patients, PAX4 R192H carriers had higher haemoglobin A1c (HbA1c) levels (P = 0.030) and lower 2 h C-peptide levels in the oral glucose tolerance test (OGTT) (P = 0.040); R192S carriers had lower fasting C-peptide (FCP) (P = 0.011) and 2 h C-peptide levels (P = 0.033) in OGTT than non-variant carriers. CONCLUSIONS: The ethnic-specific enrichment of PAX4 R192H/S predisposing East Asians to early-onset diabetes with decreased C-peptide levels may be one explanation of the discrepancy of diabetes between East Asians and Europeans. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov (NCT01938365).

Prognosis for residual islet ß-cell secretion function in young patients with newly diagnosed type 1 diabetes.

BACKGROUND: This study investigated possible predictors of residual islet ß-cell function (RBF) in young patients with newly diagnosed type 1 diabetes (T1D). METHODS: After analyzing RBF in 443 patients with T1D according to age at diagnosis and disease duration, 110 were followed-up over 18-60 months. A nomogram was developed by logistic regression to explore factors associated with long-term RBF. RESULTS: Of the 443 T1D patients (mean [±SD] age 20.28 ± 5.50 years; mean [±SD] diabetes duration 28.5 ± 14.6 months), RBF was preserved in 64.3%. Independent predictors for poor RBF outcome among the 110 patients in the follow-up cohort were age at onset (odds ratio [OR] 0.82; 95% confidence interval [CI] 0.73-0.92; P < 0.001), high-risk human leukocyte antigen (HLA) status (OR 4.73; CI 1.28-17.52; P = 0.020), female sex (OR 3.39; CI 1.03-11.22; P = 0.045), and a history of diabetic ketoacidosis (DKA; OR 8.71; CI 2.31-32.83; P < 0.001). Baseline glutamic acid decarboxylase (GAD) antibody, family history of diabetes, body mass index, insulin dosage, and C-peptide and HbA1c levels were not associated with poor RBF outcome. Intensive glycemic control after T1D diagnosis may improve RBF within a mean (±SD) follow-up of 35.1 ± 13.8 months. The calibration plot for the probability of 2-, 3-, and 4-year RBF showed optimal agreement between nomogram-predicted and actual observed probabilities. CONCLUSIONS: Younger age of onset, female sex, higher HLA risk status, and a history of DKA were the main factors predicting long-term poor preserved ß-cell function. Glycemic control could improve RBF during the course of diabetes. The nomogram provides an individualized risk estimate of RBF in patients with newly diagnosed T1D within Chinese Han populations.

IRX3 Promotes the Browning of White Adipocytes and Its Rare Variants are Associated with Human Obesity Risk.

BACKGROUND: IRX3 was recently reported as the effector of the FTO variants. We aimed to test IRX3's roles in the browning program and to evaluate the association between the genetic variants in IRX3 and human obesity. METHODS: IRX3 expression was examined in beige adipocytes in human and mouse models, and further validated in induced beige adipocytes. The browning capacity of primary preadipocytes was assessed with IRX3 knockdown. Luciferase reporter analysis and ChIP assay were applied to investigate IRX3's effects on UCP1 transcriptional activity. Moreover, genetic analysis of IRX3 was performed in 861 young obese subjects and 916 controls. RESULTS: IRX3 expression was induced in the browning process and was positively correlated with the browning markers. IRX3 knockdown remarkably inhibited UCP1 expression in induced mouse and human beige adipocytes, and also repressed the uncoupled oxygen consumption rate. Further, IRX3 directly bound to UCP1 promoter and increased its transcriptional activity. Moreover, 17 rare heterozygous missense/frameshift IRX3 variants were identified, with a significant enrichment in obese subjects (P=0.038, OR=2.27; 95% CI, 1.02-5.05). CONCLUSIONS: IRX3 deficiency repressed the browning program of white adipocytes partially by regulating UCP1 transcriptional activity. Rare variants of IRX3 were associated with human obesity.

The Influence of Dihydrotestosterone on the Development of Graves' Disease in Female BALB/c Mice.

BACKGROUND: Graves' disease (GD) is a common organ-specific autoimmune disease characterized by hyperthyroidism that has significant sex differences in prevalence and clinical expressions. Abnormal cytokine production and T cell activation may result in various manifestations of GD. Studies have shown that androgen treatment can provide protection against autoimmune diseases, but the effects of androgen treatment on GD are still unknown. Therefore, this study investigated whether a potent bioactive androgen, 5α-dihydrotestosterone (DHT), could be of benefit in a BALB/c mouse model of GD. The aims of this study were to investigate (i) whether DHT pretreatment inhibits autoimmune responses, and (ii) the mechanism of immune protection of DHT in GD. METHODS: Female BALB/c mice were immunized three times with an adenovirus expressing the human thyrotropin receptor (TSHR) A-subunit (Ad-TSHR289). Three doses (1.5, 5, and 15 mg) of DHT or a matching placebo were implanted a week before the first immunization. Four weeks after the third immunization, mice were sacrificed, and blood, the spleen, and the thyroid were removed for further analysis. RESULTS: After DHT treatment, thyroid hormones were dramatically reduced compared with placebo. In addition, a remarkable reduction in interferon-γ and interleukin-2 production was observed in DHT-pretreated mice. CONCLUSIONS: DHT can alleviate the severity of GD by downregulating pro-autoimmune T helper 1 cells in female BALB/c mice. The protective influence was more noticeable with 5 mg and 15 mg doses of DHT.

A second course of antithyroid drug therapy for recurrent Graves' disease: an experience in endocrine practice.

OBJECTIVE: There are scarce reports regarding the prognosis of a second course of antithyroid drug (ATD) therapy on recurrent Graves' disease (GD). The aim of this study was to assess the long-term remission rate after a second ATD therapy and verify significant clinical predictors of a remission. DESIGN: A prospective randomized clinical trial with long-term follow-up was conducted to evaluate the effects of a second course of ATD therapy. METHODS: A total of 128 recurrent GD patients who had finished a first regular ATD therapy were enrolled in this study, and prescribed methimazole (MMI) treatment with titration regimen. The patients were randomly assigned to two groups when the drug doses were reduced to 2.5 mg daily (qd). Group 1 was discontinued with 2.5 mg qd after about 5 months. Group 2 was continuously reduced to 2.5 mg every other day (qod) after 5 months and then discontinued with 2.5 mg qod after about a further 5 months. The patients were followed for 48 months after drug withdrawal. RESULTS: Of the total number of patients, 97 cases (75.78%) achieved permanent remission at the end of follow-up, with the recurrence of 31 cases (24.22%). The remission rate of group 2 (84.62%) was significantly higher than that of group 1 (66.67%) (P=0.024). Cox regression showed that the hazard ratio for recurrence decreased under a high or high normal TSH level at drug withdrawal. CONCLUSION: A second course of ATD therapy can bring about a satisfying long-term remission on recurrent GD. The drug dose of 2.5 mg qod and a high or high normal TSH level at drug withdrawal may increase the likelihood of permanent remission.

Assessment of molecular testing in fine-needle aspiration biopsy samples: an experience in a Chinese population.

Fine-needle aspiration biopsy remains the mainstay for preoperative examination of thyroid nodules; however, it does not provide a definite diagnosis in up to 25% of nodules. Considerable studies have been performed to identify molecular markers to resolve this diagnostic dilemma. The aim of this study was to establish the distribution and frequency of common genetic alterations in a comprehensive set of benign and malignant thyroid nodules, and to determine the feasibility and role of testing for a panel of genetic alterations in improving the accuracy of cytology diagnosis in a Chinese population. This study was conducted in 314 thyroid nodules comprising 104 papillary thyroid carcinomas, 13 suspicious nodules, 52 indeterminate nodules, and 145 benign nodules. Point mutations and RET/PTC rearrangements, were evaluated by pyrosequencing and TaqMan real-time PCR, respectively. After surgery, 115 nodules were confirmed as conventional papillary thyroid carcinoma and 102 (88.70%) of these nodules harbored either the BRAF(V600E) mutation (76.52%) or RET/PTC rearrangements (12.17%). RAS mutation was found in 1 (33.33%) follicular thyroid carcinoma, 1 (14.29%) follicular thyroid adenoma and 4 (10%) goiter nodules. With cytology and molecular testing, the diagnostic accuracy was further increased to 98.82% in papillary thyroid carcinoma diagnosis, and was preoperatively increased to 76.92% and 84.00%, respectively, in nodules with suspicious and indeterminate cytology. In conclusion, molecular testing of a panel of genetic alterations in fine-needle aspiration biopsy can be effectively performed in clinical practice. It enhances the accuracy of cytology and is of particular value for indeterminate nodules in the Chinese population.