The Diabetes Gene and Wnt Pathway Effector TCF7L2 Regulates Adipocyte Development and Function

The role of transcription factor 7-like 2 in metabolic disorders

Transcription factor 7-like 2 (TCF7L2), a member of the T cell factor/lymphoid enhancer factor family, generally forms a complex with β-catenin to regulate the downstream target genes as an effector of the canonical Wnt signalling pathway. TCF7L2 plays a vital role in various biological processes and functions in many organs and tissues, including the liver, islet and adipose tissues. Further, TCF7L2 down-regulates hepatic gluconeogenesis and promotes lipid accumulation. In islets, TCF7L2 not only affects the insulin secretion of the β-cells but also has an impact on other cells. In addition, TCF7L2 influences adipogenesis in adipose tissues. Thus, an out-of-control TCF7L2 expression can result in metabolic disorders. The TCF7L2 gene is composed of 17 exons, generating 13 different transcripts, and has many single-nucleotide polymorphisms (SNPs). The discovery that these SNPs have an impact on the risk of type 2 diabetes (T2D) has attracted thorough investigations in the study of TCF7L2. Apart from T2D, TCF7L2 SNPs are also associated with type 1, posttransplant and other types of diabetes. Furthermore, TCF7L2 variants affect the progression of other disorders, such as obesity, cancers, metabolic syndrome and heart diseases. Finally, the interaction between TCF7L2 variants and diet also needs to be investigated.

Running Against the Wnt: How Wnt/β-Catenin Suppresses Adipogenesis

Mesenchymal stem cells (MSCs) give rise to adipocytes, osteocytes, and chondrocytes and reside in various tissues, including bone marrow and adipose tissue. The differentiation choices of MSCs are controlled by several signaling pathways, including the Wnt/β-catenin signaling. When MSCs undergo adipogenesis, they first differentiate into preadipocytes, a proliferative adipocyte precursor cell, after which they undergo terminal differentiation into mature adipocytes. These two steps are controlled by the Wnt/β-catenin pathway, in such a way that when signaling is abrogated, the next step in adipocyte differentiation can start. This sequence suggests that the main role of Wnt/β-catenin signaling is to suppress differentiation while increasing MSC and preadipocytes cell mass. During later steps of MSC differentiation, however, active Wnt signaling can promote osteogenesis instead of keeping the MSCs undifferentiated and proliferative. The exact mechanisms behind the various functions of Wnt signaling remain elusive, although recent research has revealed that during lineage commitment of MSCs into preadipocytes, Wnt signaling is inactivated by endogenous Wnt inhibitors. In part, this process is regulated by histone-modifying enzymes, which can lead to increased or decreased Wnt gene expression. The role of Wnt in adipogenesis, as well as in osteogenesis, has implications for metabolic diseases since Wnt signaling may serve as a therapeutic target.

Chronic D-ribose and D-mannose overload induce depressive/anxiety-like behavior and spatial memory impairment in mice

The effects of different forms of monosaccharides on the brain remain unclear, though neuropsychiatric disorders undergo changes in glucose metabolism. This study assessed cell viability responses to five commonly consumed monosaccharides-D-ribose (RIB), D-glucose, D-mannose (MAN), D-xylose and L-arabinose-in cultured neuro-2a cells. Markedly decreased cell viability was observed in cells treated with RIB and MAN. We then showed that high-dose administration of RIB induced depressive- and anxiety-like behavior as well as spatial memory impairment in mice, while high-dose administration of MAN induced anxiety-like behavior and spatial memory impairment only. Moreover, significant pathological changes were observed in the hippocampus of high-dose RIB-treated mice by hematoxylin-eosin staining. Association analysis of the metabolome and transcriptome suggested that the anxiety-like behavior and spatial memory impairment induced by RIB and MAN may be attributed to the changes in four metabolites and 81 genes in the hippocampus, which is involved in amino acid metabolism and serotonin transport. In addition, combined with previous genome-wide association studies on depression, a correlation was found between the levels of Tnni3k and Tbx1 in the hippocampus and RIB induced depressive-like behavior. Finally, metabolite-gene network, qRT-PCR and western blot analysis showed that the insulin-POMC-MEK-TCF7L2 and MAPK-CREB-GRIN2A-CaMKII signaling pathways were respectively associated with RIB and MAN induced depressive/anxiety-like behavior and spatial memory impairment. Our findings clarified our understanding of the biological mechanisms underlying RIB and MAN induced depressive/anxiety-like behavior and spatial memory impairment in mice and highlighted the deleterious effects of high-dose RIB and MAN as long-term energy sources.

Identification and co-expression analysis of long noncoding RNAs and mRNAs involved in the deposition of intramuscular fat in Aohan fine-wool sheep

BACKGROUND

Intramuscular fat (IMF) content has become one of the most important indicators for measuring meat quality, and levels of IMF are affected by various genes. Long non-coding RNAs (lncRNAs) are widely expressed non-coding RNAs that play an important regulatory role in a variety of biological processes; however, research on the lncRNAs involved in sheep IMF deposition is still in its infancy. Aohan fine-wool sheep (AFWS), one of China's most important meat-hair, dual-purpose sheep breed, provides a great model for studying the role of lncRNAs in the regulation of IMF deposition. We identified lncRNAs by RNA sequencing in Longissimus thoracis et lumborum (LTL) samples of sheep at two ages: 2 months (Mth-2) and 12 months (Mth-12).

RESULTS

We identified a total of 26,247 genes and 6935 novel lncRNAs in LTL samples of sheep. Among these, 199 mRNAs and 61 lncRNAs were differentially expressed. We then compared the structural characteristics of lncRNAs and mRNAs. We obtained target genes of differentially expressed lncRNAs (DELs) and performed enrichment analyses using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG). We found that target mRNAs were enriched in metabolic processes and developmental pathways. One pathway was significantly enriched, namely tight junction. Based on the analysis of critical target genes, we obtained seven candidate lncRNAs that potentially regulated lipid deposition and constructed a lncRNA-mRNA co-expression network that included MSTRG.4051.3-FZD4, MSTRG.16157.3-ULK1, MSTRG.21053.3-PAQR3, MSTRG.19941.2-TPI1, MSTRG.12864.1-FHL1, MSTRG.2469.2-EXOC6 and MSTRG.21381.1-NCOA1. We speculated that these candidate lncRNAs might play a role by regulating the expression of target genes. We randomly selected five mRNAs and five lncRNAs to verify the accuracy of the sequencing data by qRT-PCR.

CONCLUSIONS

Our study identified the differentially expressed mRNAs and lncRNAs during intramuscular lipid deposition in Aohan fine-wool sheep. The work may widen the knowledge about the annotation of the sheep genome and provide a working basis for investigating intramuscular fat deposition in sheep.

The Wnt Effector TCF7l2 Promotes Oligodendroglial Differentiation by Repressing Autocrine BMP4-Mediated Signaling

Promoting oligodendrocyte (OL) differentiation represents a promising option for remyelination therapy for treating the demyelinating disease multiple sclerosis (MS). The Wnt effector transcription factor 7-like 2 (TCF7l2) was upregulated in MS lesions and had been proposed to inhibit OL differentiation. Recent data suggest the opposite yet underlying mechanisms remain elusive. Here, we unravel a previously unappreciated function of TCF7l2 in controlling autocrine bone morphogenetic protein (BMP)4-mediated signaling. Disrupting TCF7l2 in mice of both sexes results in oligodendroglial-specific BMP4 upregulation and canonical BMP4 signaling activation in vivo Mechanistically, TCF7l2 binds to Bmp4 gene regulatory element and directly represses its transcriptional activity. Functionally, enforced TCF7l2 expression promotes OL differentiation by reducing autocrine BMP4 secretion and dampening BMP4 signaling. Importantly, compound genetic disruption demonstrates that oligodendroglial-specific BMP4 deletion rescues arrested OL differentiation elicited by TCF7l2 disruption in vivo Collectively, our study reveals a novel connection between TCF7l2 and BMP4 in oligodendroglial lineage and provides new insights into augmenting TCF7l2 for promoting remyelination in demyelinating disorders such as MS.SIGNIFICANCE STATEMENT Incomplete or failed myelin repairs, primarily resulting from the arrested differentiation of myelin-forming oligodendrocytes (OLs) from oligodendroglial progenitor cells, is one of the major reasons for neurologic progression in people affected by multiple sclerosis (MS). Using in vitro culture systems and in vivo animal models, this study unraveled a previously unrecognized autocrine regulation of bone morphogenetic protein (BMP)4-mediated signaling by the Wnt effector transcription factor 7-like 2 (TCF7l2). We showed for the first time that TCF7l2 promotes oligodendroglial differentiation by repressing BMP4-mediated activity, which is dysregulated in MS lesions. Our study suggests that elevating TCF7l2 expression may be possible in overcoming arrested oligodendroglial differentiation as observed in MS patients.

Adipocyte-specific deletion of Tcf7l2 induces dysregulated lipid metabolism and impairs glucose tolerance in mice

AIMS/HYPOTHESIS

Transcription factor 7-like 2 (TCF7L2) is a downstream effector of the Wnt/β-catenin signalling pathway implicated in type 2 diabetes risk through genome-wide association studies. Although its expression is critical for adipocyte development, the potential roles of changes in adipose tissue TCF7L2 levels in diabetes risk are poorly defined. Here, we investigated whether forced changes in Tcf7l2 expression in adipocytes affect whole body glucose or lipid metabolism and crosstalk between disease-relevant tissues.

METHODS

Tcf7l2 was selectively ablated in mature adipocytes in C57BL/6J mice using Cre recombinase under Adipoq promoter control to recombine Tcf7l2 alleles floxed at exon 1 (referred to as aTCF7L2 mice). aTCF7L2 mice were fed normal chow or a high-fat diet for 12 weeks. Glucose and insulin sensitivity, as well as beta cell function, were assessed in vivo and in vitro. Levels of circulating NEFA, selected hormones and adipokines were measured using standard assays.

RESULTS

Reduced TCF7L2 expression in adipocytes altered glucose tolerance and insulin secretion in male but not in female mice. Thus, on a normal chow diet, male heterozygote knockout mice (aTCF7L2het) exhibited impaired glucose tolerance at 16 weeks (p = 0.03) and increased fat mass (1.4 ± 0.1-fold, p = 0.007) but no changes in insulin secretion. In contrast, male homozygote knockout (aTCF7L2hom) mice displayed normal body weight but impaired oral glucose tolerance at 16 weeks (p = 0.0001). These changes were mechanistically associated with impaired in vitro glucose-stimulated insulin secretion (decreased 0.5 ± 0.1-fold vs control mice, p = 0.02) and decreased levels of the incretins glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide (0.6 ± 0.1-fold and 0.4 ± 0.1-fold vs control mice, p = 0.04 and p < 0.0001, respectively). Circulating levels of plasma NEFA and fatty acid binding protein 4 were increased by 1.3 ± 0.1-fold and 1.8 ± 0.3-fold vs control mice (p = 0.03 and p = 0.05, respectively). Following exposure to a high-fat diet for 12 weeks, male aTCF7L2hom mice exhibited reduced in vivo glucose-stimulated insulin secretion (0.5 ± 0.1-fold vs control mice, p = 0.02).

CONCLUSIONS/INTERPRETATION

Loss of Tcf7l2 gene expression selectively in adipocytes leads to a sexually dimorphic phenotype, with impairments not only in adipocytes, but also in pancreatic islet and enteroendocrine cells in male mice only. Our findings suggest novel roles for adipokines and incretins in the effects of diabetes-associated variants in TCF7L2, and further illuminate the roles of TCF7L2 in glucose homeostasis and diabetes risk. Graphical abstract.

MiR-34a-5p and miR-452-5p: The Novel Regulators of Pancreatic Endocrine Dysfunction in Diabetic Zucker Rats?

Objective: The pancreatic endocrinal system dominates the regulation of blood glucose levels in vivo, and the dysfunction of pancreatic endocrine β-cells is a major cause of the occurrence and development of Type 2 diabetes (T2D). Although microRNA (miRNA) have been found to be key regulators of pancreatic β-cells proliferation, differentiation and apoptosis, the underlying mechanism remains enigmatic. The aim of this study was to identify several novel miRNAs which might be involved in the etiopathogenesis of diabetic β-cells dysfunction. Methods: The miRNA expression profiles in the pancreas of high-fat diet (HFD) fed Zucker diabetic fatty (ZDF) rats and Zucker lean (ZL) rats feed with normal-fat diet (NFD) were detected by using miRNA microarray chip, and individually verified the most significant factors by quantitative real-time polymerase chain reaction (qRT-PCR) assay. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to predict the target genes related to each of the identified miRNAs and the functions of these target genes in different metabolic signaling pathways. Results: Compared with the ZL rats, a total of 24 differentially expressed miRNAs were detected in ZDF rats. Among which miR-34a-5p and miR-452-5p were the most significantly up-regulated and down-regulated respectively. These miRNAs have not been reported in rats' pancreas before. By GO and KEGG enrichment analyses, we found that miR-34a-5p could negatively regulate pancreatic β-cell proliferation through the involvement of Wnt signaling pathway. In addition, it was also found to regulate insulin secretion through the insulin signaling pathway to modulate blood glucose levels. At the same time, miR-452-5p was found to positively regulate the activity of the key rate-limiting enzyme branched-chain α-keto acid dehydrogenase-β (BCKDHB) in the catabolism of branched chain amino acids (BCAA), leading to mitochondrial dysfunction in pancreatic β-cells. Conclusions: miR-34a-5p and miR-452-5p were identified as the novel regulators of pancreatic endocrine dysfunction. These miRNAs might have the potential to be utilized as the new predictive biomarkers for the diagnosis of the occurrence and development of T2D, as well as the therapeutic targets for T2D treatment.

Association of TCF7L2 rs7903146 Gene Polymorphism with the Risk of NAFLD and CAD in the Chinese Han Population

Background and Aims: Coronary artery disease (CAD) is a major cause of morbidity and mortality in patients with non-alcoholic fatty liver disease (NAFLD). Previous studies have suggested that TCF7L2 rs7903146 was related to the risk of developing NAFLD but the conclusions are not consistent and no related study has been conducted in Chinese populations. The aim of this study was to investigate the association between TCF7L2 rs7903146 and the risk of developing NAFLD and CAD in a Chinese Han population. Methods: TCF7L2 rs7903146 genotypes were measured by the MALDI-TOF-MS from 143 NAFLD patients, 159 CAD patients, 131 NAFLD + CAD patients, and 212 healthy controls. The demographic data and serum lipid profiles of all subjects were collected. The distributions of genotype and allele frequency in each group were also tested. Logistic regression was used to investigate the risk of TCF7L2 rs7903146 with NAFLD and CAD. All statistical analyses were conducted using SPSS 23.0. Results: There were no significant differences in the distributions of TCF7L2 rs7903146 genotype and allele frequency in each of the two groups, and the TCF7L2 rs7903146 CT + TT genotype did not increase the risk of developing NAFLD, CAD, and NAFLD + CAD. Except for body mass index in the control group, the differences of clinical parameters between the TCF7L2 rs7903146 T allele carriers and non-carriers in each group were not significant. In the non-obese group, the TCF7L2 rs7903146 CT + TT genotype was a protective factor for the development of NAFLD in the non-obese subjects (odds ratio=0.359, 95% confidence interval: 0.134-0.961, p = 0.041). Conclusions: TCF7L2 rs7903146 was not associated with the risk of developing NAFLD, CAD, and NAFLD + CAD in the Chinese Han population. In the non-obese population, the TCF7L2 rs7903146 CT + TT genotype was a protective factor against the development of NAFLD.

A Multi-omic Integrative Scheme Characterizes Tissues of Action at Loci Associated with Type 2 Diabetes

Resolving the molecular processes that mediate genetic risk remains a challenge because most disease-associated variants are non-coding and functional characterization of these signals requires knowledge of the specific tissues and cell-types in which they operate. To address this challenge, we developed a framework for integrating tissue-specific gene expression and epigenomic maps to obtain "tissue-of-action" (TOA) scores for each association signal by systematically partitioning posterior probabilities from Bayesian fine-mapping. We applied this scheme to credible set variants for 380 association signals from a recent GWAS meta-analysis of type 2 diabetes (T2D) in Europeans. The resulting tissue profiles underscored a predominant role for pancreatic islets and, to a lesser extent, adipose and liver, particularly among signals with greater fine-mapping resolution. We incorporated resulting TOA scores into a rule-based classifier and validated the tissue assignments through comparison with data from cis-eQTL enrichment, functional fine-mapping, RNA co-expression, and patterns of physiological association. In addition to implicating signals with a single TOA, we found evidence for signals with shared effects in multiple tissues as well as distinct tissue profiles between independent signals within heterogeneous loci. Lastly, we demonstrated that TOA scores can be directly coupled with eQTL colocalization to further resolve effector transcripts at T2D signals. This framework guides mechanistic inference by directing functional validation studies to the most relevant tissues and can gain power as fine-mapping resolution and cell-specific annotations become richer. This method is generalizable to all complex traits with relevant annotation data and is made available as an R package.

Genetic landscape and autoimmunity of monocytes in developing Vogt-Koyanagi-Harada disease

Vogt-Koyanagi-Harada (VKH) disease is a systemic autoimmune disorder affecting multiple organs, including eyes, skin, and central nervous system. It is known that monocytes significantly contribute to the development of autoimmune disease. However, the subset heterogeneity with unique functions and signatures in human circulating monocytes and the identity of disease-specific monocytic populations remain largely unknown. Here, we employed an advanced single-cell RNA sequencing technology to systematically analyze 11,259 human circulating monocytes and genetically defined their subpopulations. We constructed a precise atlas of human blood monocytes, identified six subpopulations-including S100A12, HLA, CD16, proinflammatory, megakaryocyte-like, and NK-like monocyte subsets-and uncovered two previously unidentified subsets: HLA and megakaryocyte-like monocyte subsets. Relative to healthy individuals, cellular composition, gene expression signatures, and activation states were markedly alternated in VKH patients utilizing cell type-specific programs, especially the CD16 and proinflammatory monocyte subpopulations. Notably, we discovered a disease-relevant subgroup, proinflammatory monocytes, which showed a discriminative gene expression signature indicative of inflammation, antiviral activity, and pathologic activation, and converted into a pathologic activation state implicating the active inflammation during VKH disease. Additionally, we found the cell type-specific transcriptional signature of proinflammatory monocytes, ISG15, whose production might reflect the treatment response. Taken together, in this study, we present discoveries on accurate classification, molecular markers, and signaling pathways for VKH disease-associated monocytes. Therapeutically targeting this proinflammatory monocyte subpopulation would provide an attractive approach for treating VKH, as well as other autoimmune diseases.

GWA-based pleiotropic analysis identified potential SNPs and genes related to type 2 diabetes and obesity

Metabolic syndrome is a cluster of symptoms including excessive body fat and insulin resistance which may lead to obesity and type 2 diabetes (T2D). The physiological and pathological cross-talk between T2D and obesity is crucial and complex, meanwhile, the genetic connection between T2D and obesity is largely unknown. The purpose of this study is to identify pleiotropic SNPs and genes between these two associated conditions by applying genetic analysis incorporating pleiotropy and annotation (GPA) on two large genome-wide association studies (GWAS) data sets: a body mass index (BMI) data set containing 339,224 subjects and a T2D data set containing 110,452 subjects. In all, 5182 SNPs showed pleiotropy in both T2D and obesity. After further prioritization based on suggested local false discovery rates (FDR) by the GPA model, 2146 SNPs corresponding to 217 unique genes are significantly associated with both traits (FDR < 0.2), among which 187 are newly identified pleiotropic genes compare with original GWAS in individual traits. Subsequently, gene enrichment and pathway analyses highlighted several pleiotropic SNPs including rs849135 (FDR = 0.0002), rs2119812 (FDR = 0.0018), rs4506565 (FDR = 1.23E-08), rs1558902 (7.23E-10) and corresponding genes JAZF1, SYN2, TCF7L2, FTO which may play crucial rol5es in the etiology of both T2D and obesity. Additional evidences from expression data analysis of pleiotropic genes strongly supports that the pleiotropic genes including JAZF1 (p = 1.39E-05 and p = 2.13E-05), SYN2 (p = 5.49E-03 and p = 5.27E-04), CDKN2C (p = 1.99E-12 and p = 6.27E-11), RABGAP1 (p = 3.08E-03 and p = 7.46E-03), and UBE2E2 (p = 1.83E-04 and p = 8.22E-03) play crucial roles in both obesity and T2D pathogenesis. Pleiotropic analysis integrated with functional network identified several novel and causal SNPs and genes involved in both BMI and T2D which may be ignored in single GWAS.

EV-transported microRNAs of Schistosoma mansoni and Fasciola hepatica: Potential targets in definitive hosts

Trematodes are widespread parasitic flatworms that significantly affect mankind either directly as human parasites, or indirectly via the infection of livestock and the related economic damage. The two most important trematode taxa are the blood flukes Schistosoma and the liver flukes Fasciola, but detection and differentiation of these parasites remains a challenge. Recently, microRNAs (miRNAs) were described from extracellular vesicles (EV) for both parasites secreted into respective hosts. These molecules have been proposed as mediators of parasite-host communication, and potential biomarkers for the detection of parasitic infections from host blood. Our aim here was to study similarities and differences in the miRNA complements of Schistosoma mansoni and Fasciola hepatica, EV-load in particular, to predict their targets and potential functions in the parasite-host interaction. We reanalyzed the known miRNA complements of S. mansoni and F. hepatica and found 16 and 4 previously overlooked, but deeply conserved miRNAs, respectively, further moving their complements closer together. We found distinct miRNA enrichment patterns in EVs both showing high levels of flatworm miRNAs with potential for the detection of an infection from blood. Two miRNAs of the protostome specific MIR-71 and MIR-277 families were highly expressed in EVs and could, therefore, have potential as biomarkers for trematode infection. Curiously, we identified nucleotide differences in the sequence of Mir-277-P2 between S. mansoni and F. hepatica that hold great promise for the distinction of both parasites. To test whether the EV-miRNAs of S. mansoni and F. hepatica could be modulating the expression of host genes, we predicted miRNA targets in 321 human and cattle messenger RNAs that overlapped between both hosts. Of several predicted targets, wnt signaling pathway genes stood out and their suppression likely leads to changes in the glucose concentration in host blood and the reduction of inflammatory and immune responses.

Wntless regulates lipogenic gene expression in adipocytes and protects against diet-induced metabolic dysfunction

OBJECTIVE

Obesity is a key risk factor for many secondary chronic illnesses, including type 2 diabetes and cardiovascular disease. Canonical Wnt/β-catenin signaling is established as an important endogenous inhibitor of adipogenesis. This pathway is operative in mature adipocytes; however, its roles in this context remain unclear due to complexities of Wnt signaling and differences in experimental models. In this study, we used novel cultured cell and mouse models to investigate functional roles of Wnts secreted from adipocytes.

METHODS

We generated adipocyte-specific Wntless (Wls) knockout mice and cultured cell models to investigate molecular and metabolic consequences of disrupting Wnt secretion from mature adipocytes. To characterize Wls-deficient cultured adipocytes, we evaluated the expression of Wnt target and lipogenic genes and the downstream functional effects on carbohydrate and lipid metabolism. We also investigated the impact of adipocyte-specific Wls deletion on adipose tissues and global glucose metabolism in mice fed normal chow or high-fat diets.

RESULTS

Many aspects of the Wnt signaling apparatus are expressed and operative in mature adipocytes, including the Wnt chaperone Wntless. Deletion of Wntless in cultured adipocytes results in the inhibition of de novo lipogenesis and lipid monounsaturation, likely through repression of Srebf1 (SREBP1c) and Mlxipl (ChREBP) and impaired cleavage of immature SREBP1c into its active form. Adipocyte-specific Wls knockout mice (Wls-/-) have lipogenic gene expression in adipose tissues and isolated adipocytes similar to that of controls when fed a normal chow diet. However, closer investigation reveals that a subset of Wnts and downstream signaling targets are upregulated within stromal-vascular cells of Wls-/- mice, suggesting that adipose tissues defend loss of Wnt secretion from adipocytes. Interestingly, this compensation is lost with long-term high-fat diet challenges. Thus, after six months of a high-fat diet, Wls-/- mice are characterized by decreased adipocyte lipogenic gene expression, reduced visceral adiposity, and improved glucose homeostasis.

CONCLUSIONS

Taken together, these studies demonstrate that adipocyte-derived Wnts regulate de novo lipogenesis and lipid desaturation and coordinate the expression of lipogenic genes in adipose tissues. In addition, we report that Wnt signaling within adipose tissues is defended, such that a loss of Wnt secretion from adipocytes is sensed and compensated for by neighboring stromal-vascular cells. With chronic overnutrition, this compensatory mechanism is lost, revealing that Wls-/- mice are resistant to diet-induced obesity, adipocyte hypertrophy, and metabolic dysfunction.

New Insights into the Genetics of Latent Autoimmune Diabetes in Adults

PURPOSE OF REVIEW

Diabetes is a spectrum of clinical manifestations, including latent autoimmune diabetes in adults (LADA). However, it has been questioned whether LADA exists or simply is a group of misclassified type 1 diabetes (T1D) and type 2 diabetes (T2D) patients. This review will provide an updated overview of the genetics of LADA, highlight what genetics tell us about LADA as a diabetes subtype, and point to future directions in the study of LADA.

RECENT FINDINGS

Recent studies have verified the genetic overlap between LADA and both T1D and T2D and have contributed identification of a novel LADA-specific locus, namely, PFKFB3, and subtype-specific signatures in the HLA region. Genetic risk scores comprising T1D-risk variants have been shown to be a promising tool for discriminating diabetes subtypes and identifying patients rapidly progressing to insulin dependence. Genetic data support the existence of LADA, but further studies are needed to fully determine the place of LADA in the diabetes spectrum.

Histone demethylase KDM4A regulates adipogenic and osteogenic differentiation via epigenetic regulation of C/EBPα and canonical Wnt signaling

Epigenetic modifications play a central role in cell differentiation and development. In the current study, we have recognized lysine demethylase 4A (KDM4A) as a novel epigenetic regulator of osteoblast and adipocyte differentiation. Kdm4a expression was upregulated during osteogenesis and adipogenesis of primary marrow stromal cells and established stromal ST2 line. Overexpression of wild-type Kdm4a promoted adipogenic differentiation and blocked osteogenic differentiation of the progenitor cells. This effect was largely alleviated when the catalytically dead mutation was made. Conversely, depletion or inactivation of Kdm4a in undifferentiated progenitor cells inhibited the formation of adipocytes and promoted the differentiation of osteoblasts. Mechanism explorations showed that overexpression of Kdm4a upregulated the expression of secreted frizzled-related protein 4 (Sfrp4) and CCAAT/enhancer-binding protein α (C/ebpα). Chromatin immunoprecipitation assay demonstrated that KDM4A directly bound the promoters of Sfrp4 and C/ebpα, removed the histone methylation mark H3K9me3, and reduced DNA methylation levels of CpG in promoter regions of C/ebpα and Sfrp4. Furthermore, overexpression of Kdm4a inactivated canonical Wnt signaling. Moreover, activation of canonical Wnt signaling through silencing of Sfrp4 in ST2 attenuated the inhibition of osteogenic differentiation and the enhancement of adipogenic differentiation by KDM4A. These data have identified KDM4A as a novel regulator of osteoblast and adipocyte differentiation and suggest KDM4A inhibition as a potential therapeutic target for treating metabolic disorders such as osteoporosis.

Circulating miR-330-3p in Late Pregnancy is Associated with Pregnancy Outcomes Among Lean Women with GDM

Gestational Diabetes Mellitus (GDM) is characterised by insulin resistance accompanied by reduced beta-cell compensation to increased insulin demand, typically observed in the second and third trimester and associated with adverse pregnancy outcomes. There is a need for a biomarker that can accurately monitor status and predict outcome in GDM, reducing foetal-maternal morbidity and mortality risks. To this end, circulating microRNAs (miRNAs) present themselves as promising candidates, stably expressed in serum and known to play crucial roles in regulation of glucose metabolism. We analysed circulating miRNA profiles in a cohort of GDM patients (n = 31) and nondiabetic controls (n = 29) during the third trimester for miRNA associated with insulin-secretory defects and glucose homeostasis. We identified miR-330-3p as being significantly upregulated in lean women with GDM compared to nondiabetic controls. Furthermore, increased levels of miR-330-3p were associated with better response to treatment (diet vs. insulin), with lower levels associated with exogenous insulin requirement. We observed miR-330-3p to be significantly related to the percentage of caesarean deliveries, with miR-330-3p expression significantly higher in spontaneously delivered GDM patients. We report this strong novel association of circulating miR-330-3p with risk of primary caesarean delivery as a pregnancy outcome linked with poor maternal glycaemic control, strengthening the growing body of evidence for roles of diabetes-associated miRNAs in glucose homeostasis and adaptation to the complex changes related to pregnancy.

TGF-β-driven downregulation of the Wnt/β-Catenin transcription factor TCF7L2/TCF4 in PDGFRα+ fibroblasts

Mesenchymal stromal/stem cells (MSCs) are multipotent progenitors essential for organogenesis, tissue homeostasis, regeneration, and scar formation. Tissue injury upregulates TGF-β signaling, which modulates myofibroblast fate, extracellular matrix remodeling, and fibrosis. However, the molecular determinants of MSCs differentiation and survival remain poorly understood. The canonical Wnt Tcf/Lef transcription factors regulate development and stemness, but the mechanisms by which injury-induced cues modulate their expression remain underexplored. Here, we studied the cell-specific gene expression of Tcf/Lef and, more specifically, we investigated whether damage-induced TGF-β impairs the expression and function of TCF7L2, using several models of MSCs, including skeletal muscle fibro-adipogenic progenitors. We show that Tcf/Lefs are differentially expressed and that TGF-β reduces the expression of TCF7L2 in MSCs but not in myoblasts. We also found that the ubiquitin-proteasome system regulates TCF7L2 proteostasis and participates in TGF-β-mediated TCF7L2 protein downregulation. Finally, we show that TGF-β requires HDACs activity to repress the expression of TCF7L2. Thus, our work found a novel interplay between TGF-β and Wnt canonical signaling cascades in PDGFRα+ fibroblasts and suggests that this mechanism could be targeted in tissue repair and regeneration.

Revealing the Interactions Between Diabetes, Diabetes-Related Diseases, and Cancers Based on the Network Connectivity of Their Related Genes

Diabetes-related diseases (DRDs), especially cancers pose a big threat to public health. Although people have explored pathological pathways of a few common DRDs, there is a lack of systematic studies on important biological processes (BPs) connecting diabetes and its related diseases/cancers. We have proposed and compared 10 protein-protein interaction (PPI)-based computational methods to study the connections between diabetes and 254 diseases, among which a method called DIconnectivity_eDMN performs the best in the sense that it infers a disease rank (according to its relation with diabetes) most consistent with that by literature mining. DIconnectivity_eDMN takes diabetes-related genes, other disease-related genes, a PPI network, and genes in BPs as input. It first maps genes in a BP into the PPI network to construct a BP-related subnetwork, which is expanded (in the whole PPI network) by a random walk with restart (RWR) process to generate a so-called expanded modularized network (eMN). Since the numbers of known disease genes are not high, an RWR process is also performed to generate an expanded disease-related gene list. For each eMN and disease, the expanded diabetes-related genes and disease-related genes are mapped onto the eMN. The association between diabetes and the disease is measured by the reachability of their genes on all eMNs, in which the reachability is estimated by a method similar to the Kolmogorov-Smirnov (KS) test. DIconnectivity_eDMN achieves an area under receiver operating characteristic curve (AUC) of 0.71 for predicting both Type 1 DRDs and Type 2 DRDs. In addition, DIconnectivity_eDMN reveals important BPs connecting diabetes and DRDs. For example, "respiratory system development" and "regulation of mRNA metabolic process" are critical in associating Type 1 diabetes (T1D) and many Type 1 DRDs. It is also found that the average proportion of diabetes-related genes interacting with DRDs is higher than that of non-DRDs.

Modelling the gene expression and the DNA-binding in the 3T3-L1 differentiating adipocytes

The 3T3-L1 pre-adipocyte cell line is widely used to study the fat cell differentiation in vitro. Researchers also use this cell model to study obesity and insulin resistance. We surveyed the literature, the gene expression omnibus and the sequence read archive for RNA-Seq and ChIP-Seq datasets of MDI-induced 3T3-L1 differentiating cells sampled at one or more time points. The metadata of the relevant datasets were manually curated using unified language across the original studies. The raw reads were collected and pre-processed using a reproducible state-of-the-art pipeline. The final datasets are presented as reads count in genes for the RNA-Seq and reads count in peaks for the ChIP-Seq dataset. The curated datasets are available as two Bioconductor experimental data packages curatedAdipoRNA and curatedAdipoChIP. In addition, the packages document the source code of the data collection and the pre-processing pipelines. Here, we provide a descriptive analysis of the datasets with context and technical validation.

TCF7L2 polymorphisms are associated with amygdalar volume in elderly individuals with Type 2 Diabetes

The association between several Single Nucleotide Polymorphisms (SNPs) within the transcription factor 7-like 2 (TCF7L2) gene and Type 2 Diabetes (T2D) as well as additional T2D-related traits is well established. Since alteration in total and regional brain volumes are consistent findings among T2D individuals, we studied the association of four T2D susceptibility SNPS within TCF7L2 (rs7901695, rs7903146, rs11196205, and rs12255372) with volumes of white matter hyperintensities (WMH), gray matter, and regional volumes of amygdala and hippocampus obtained from structural MRI among 191 T2D elderly Jewish individuals. Under recessive genetic model (controlling for age, sex and intracranial volume), we found that for all four SNPs, carriers of two copies of the T2D risk allele (homozygous genotype) had significantly smaller amygdalar volume: rs7901695- CC genotype vs. CT + TT genotypes, p = 0.002; rs7903146-TT vs. TC + CC, p = 0.003; rs11196205- CC vs. CG + GG, p = 0.0003; and rs12255372- TT vs. TG + GG, p = 0.003. Adjusting also for T2D-related covariates, body mass index (BMI), and ancestry did not change the results substantively (rs7901695, p = 0.003; rs7903146, p = 0.005; rs11196205, p = 0.001; and rs12255372, p = 0.005). Conditional analysis demonstrated that only rs11196205 was independently associated with amygdalar volume at a significant level. Separate analysis of left and right amygdala revealed stronger results for left amygdalar volume. Taken together, we report association of TCF7L2 SNPs with amygdalar volume among T2D elderly Jewish patients. Further studies in other populations are required to support these findings and reach more definitive conclusions.

TCF7L2 Expression Is Regulated by Cell Differentiation and Overfeeding in Human Adipose Tissue

Aim: The TCF7L2 gene variant rs7903146 has the largest effect on type 2 diabetes risk reported in genome-wide association studies, however its role in adipose tissue development and function is unknown. We investigate the association between gene variant rs7903146 and metabolic parameters and examine in vitro and ex vivo gene expression of TCF7L2 in human adipose tissue and progenitor cells from two independent populations of young healthy men with increased risk of type 2 diabetes due to low birth weight (LBW). Design: Adipose tissue biopsies were excised from 40 healthy young men with low and normal birth weights (NBW) after a control and 5-day high-fat overfeeding diet. In another cohort including 13 LBW and 13 NBW men, adipocyte progenitor cells were isolated and cultivated. Transcriptome-wide expression was performed on RNA extracted from biopsies or cell cultures. Results: Diet-induced peripheral insulin resistance is more pronounced in carriers of the T-risk allele rs7903146, whereas no association with hepatic insulin resistance was shown. TCF7L2 expression increased during adipogenesis in isolated preadipocytes from both LBW and NBW men (p < 0.001) and correlated positively with markers of progenitor cell proliferation and maturation capacity. In the mature adipose tissue, LBW men had lower expression of TCF7L2 compared to NBW men at baseline (p = 0.03) and TCF7L2 expression was suppressed by short-term overfeeding in NBW men (p = 0.005). Conclusions: The results suggest a regulation of TCF7L2 expression during adipogenesis and in mature adipose tissue upon overfeeding, and further that young men exposed to an adverse intrauterine environment have reduced mature adipose tissue TCF7L2 expression.

Association of common type 1 and type 2 diabetes gene variants with latent autoimmune diabetes in adults: A meta-analysis

BACKGROUND

The aim of this meta-analysis was to determine the association of common type 1 diabetes (T1D) and type 2 diabetes (T2D) gene variants (protein tyrosine phosphatase non-receptor 22 [PTPN22] rs2476601C/T, insulin [INS] rs689A/T and transcription factor 7-like 2 [TCF7L2] rs7903146C/T) with latent autoimmune diabetes in adults (LADA).

METHODS

A systematic search of electronic databases was conducted up to 2017 and data from 16 independent case-control studies for three gene variants were pooled. The pooled allele and genotype frequencies for each T1D and T2D gene variant were used to calculate odds ratios (ORs) with 95% confidence intervals (CIs) to assess the strength of the association. Heterogeneity tests and evaluation of publication bias were performed for all studies.

RESULTS

In all, 8869 cases and 20 829 controls pooled from 16 case-control studies were included in the analysis. For rs2476601, a significant association was found for homozygote TT (OR 2.67; 95% CI 1.92-3.70; P < 0.0001), heterozygote CT (OR 1.61; 95% CI 1.44-1.79; P < 0.0001), and the T allele (OR 1.62; 95% CI 1.48-1.78; P < 0.0001). Overall, a significant inverse association was observed for rs689 in the TT genotype (OR 0.43; 95% CI 0.30-0.64; P < 0.0001), AT genotype (OR 0.53; 95% CI 0.45-0.62; P < 0.0001), and T allele (OR 0.61; 95% CI 0.52-0.71; P < 0.0001). For the rs7903146 polymorphism, the T allele (OR 1.19; 95% CI 1.00-1.40; P = 0.04) may be associated with the risk of LADA.

CONCLUSION

The rs2476601C/T, rs689A/T, and rs7903146C/T polymorphisms were found to be associated with the risk of LADA, thereby indicating that, genetically, LADA could be an admixture of both T1D and T2D.

Assessment of TCF7L2 expression after bariatric surgery

Objective

To assess the influence of bariatric surgery on transcription factor 7-like 2 (TCF7L2) expression and its association with body mass index (BMI) and Type 2 diabetes mellitus (T2DM).

Methods

Prospective study performed between 2016 and 2018, where 26 obese patients undergoing bariatric surgery were divided into two subgroups: diabetics and non-diabetics. The RNAs were extracted from peripheral blood samples that were obtained from each patient in two different moments: before surgery and after 12 months of follow-up. The relative expression of TCF7L2 was determined according to the delta-Ct method.

Results

The linear regression model of BMI x delta-Ct showed a positive correlation (p = 0.037). In the subgroups, an inversely proportional relationship was found between delta-Ct and BMI in the diabetic group and a directly proportional relationship in the non-diabetic group (p>0.05 in both). In the postoperative period, the regression model was similar to the preoperative, except when analyzing the subgroups, where diabetic patients showed a directly proportional relationship (p>0.05). The relative expression of TCF7L2 showed an average of 1.16 ± 0.91, CI-95% 0.79–1.53. There was an increase in relative expression of 48% in the non-diabetic group (p = 0.021), and a decrease of 27% in the T2DM group (p>0.05) in the postoperative. There was a positive correlation between a greater decrease in BMI and increased relative expression (p = 0.027).

Conclusion

Our results showed that generally, the TCF7L2 expression increase with a decrease in BMI, however, for patients with T2DM, it exhibits an inverse pattern, which is normalized one year after bariatric surgery.

Targeted deletion of Tcf7l2 in adipocytes promotes adipocyte hypertrophy and impaired glucose metabolism

OBJECTIVE

Activation of the Wnt-signaling pathway is known to inhibit differentiation in adipocytes. However, there is a gap in our understanding of the transcriptional network regulated by components of the Wnt-signaling pathway during adipogenesis and in adipocytes during postnatal life. The key intracellular effectors of the Wnt-signaling pathway occur through TCF transcription factors such as TCF7L2 (transcription factor-7-like 2). Several genetic variants in proximity to TCF7L2 have been linked to type 2 diabetes through genome-wide association studies in various human populations. Our work aims to functionally characterize the adipocyte specific gene program regulated by TCF7L2 and understand how this program regulates metabolism.

METHODS

We generated Tcf7l2^F/F mice and assessed TCF7L2 function in isolated adipocytes and adipose specific knockout mice. ChIP-sequencing and RNA-sequencing was performed on the isolated adipocytes with control and TCF7L2 knockout cells. Adipose specific TCF7L2 knockout mice were challenged with high fat diet and assessed for body weight, glucose tolerance, and lipolysis.

RESULTS

Here we report that TCF7L2 regulates adipocyte size, endocrine function, and glucose metabolism. Tcf7l2 is highly expressed in white adipose tissue, and its expression is suppressed in genetic and diet-induced models of obesity. Genome-wide distribution of TCF7L2 binding and gene expression analysis in adipocytes suggests that TCF7L2 directly regulates genes implicated in cellular metabolism and cell cycle control. When challenged with a high-fat diet, conditional deletion of TCF7L2 in adipocytes led to impaired glucose tolerance, impaired insulin sensitivity, promoted weight gain, and increased adipose tissue mass. This was accompanied by reduced expression of triglyceride hydrolase, reduced fasting-induced free fatty acid release, and adipocyte hypertrophy in subcutaneous adipose tissue.

CONCLUSIONS

Together our studies support that TCF7L2 is a central transcriptional regulator of the adipocyte metabolic program by directly regulating the expression of genes involved in lipid and glucose metabolism.

Pygo2 Regulates Adiposity and Glucose Homeostasis via β-Catenin-Axin2-GSK3β Signaling Pathway

Wnt/β-catenin signaling plays a key role in regulating adipogenesis through indirectly inhibiting the expression of C/EBPα and peroxisome proliferator-activated receptor γ (PPARγ); however, the detailed molecular mechanism remains poorly understood. Moreover, the factor(s) that determines the Wnt/β-catenin output level during adipogenesis is also not completely defined. In this study, we showed that Pygo2 exhibited a declined expression pattern during adipocyte differentiation, resulting in an attenuated Wnt/β-catenin output level. The mechanism study indicated that Pygo2 inhibition led to the downregulation of Axin2, a constitutive Wnt target, in the cytoplasm. Consequently, Axin2-bound GSK3β was released and translocated into the nucleus to phosphorylate C/EBPβ and Snail, resulting in an increase in the DNA binding activity of C/EBPβ and decreased protein stability of Snail, which subsequently activated the expression of C/EBPα and PPARγ. Consistent with this, embryonic fibroblasts from Pygo2^-/- mice exhibited spontaneous adipocyte differentiation, and adipocyte precursor-specific Pygo2-deficient mice exhibited increased adiposity with decreased energy expenditure. We further showed impaired glucose tolerance and decreased systemic insulin sensitivity in Pygo2-deficient mice. Our study revealed an association between Pygo2 function and obesity or diabetes.

The diabetes pandemic and associated infections: suggestions for clinical microbiology

There are 425 million people with diabetes mellitus in the world. By 2045, this figure will grow to over 600 million. Diabetes mellitus is classified among noncommunicable diseases. Evidence points to a key role of microbes in diabetes mellitus, both as infectious agents associated with the diabetic status and as possible causative factors of diabetes mellitus. This review takes into account the different forms of diabetes mellitus, the genetic determinants that predispose to type 1 and type 2 diabetes mellitus (especially those with possible immunologic impact), the immune dysfunctions that have been documented in diabetes mellitus. Common infections occurring more frequently in diabetic vs. nondiabetic individuals are reviewed. Infectious agents that are suspected of playing an etiologic/triggering role in diabetes mellitus are presented, with emphasis on enteroviruses, the hygiene hypothesis, and the environment. Among biological agents possibly linked to diabetes mellitus, the gut microbiome, hepatitis C virus, and prion-like protein aggregates are discussed. Finally, preventive vaccines recommended in the management of diabetic patients are considered, including the bacillus calmette-Guerin vaccine that is being tested for type 1 diabetes mellitus. Evidence supports the notion that attenuation of immune defenses (both congenital and secondary to metabolic disturbances as well as to microangiopathy and neuropathy) makes diabetic people more prone to certain infections. Attentive microbiologic monitoring of diabetic patients is thus recommendable. As genetic predisposition cannot be changed, research needs to identify the biological agents that may have an etiologic role in diabetes mellitus, and to envisage curative and preventive ways to limit the diabetes pandemic.

Transcription factor 7-like 2 controls matrix degradation through nuclear factor κB signaling and is repressed by microRNA-155 in nucleus pulposus cells

AIM

TCF7L2, a key transcription factor in the canonical Wnt pathway, plays a vital role in the matrix degradation of chondrocytes. However, it is unknown whether TCF7L2 is important in the matrix metabolism of inner gel-like nucleus pulposus (NP) cells; thus, the aim of this study was to explore the effect and mechanism of TCF7L2 in this process.

METHODS

Western blotting and immunofluorescence analyses were used to observe TCF7L2 expression in rat and human NP tissues. Real-time PCR and western blotting were performed to detect the expression of TCF7L2 stimulated by inflammatory cytokines. Dual luciferase reporter assay, real-time PCR, western blotting and knockdown experiments were performed to demonstrate the role of NF-κB signaling in matrix regulation by TCF7L2 and the regulation of TCF7L2 by miR-155 in intervertebral disc degeneration.

KEY FINDINGS

TCF7L2 is present in rat and human NP tissues and is expressed in the nucleus of NP cells. TCF7L2 is refractory to stimulation of rat and human NP cells with the inflammatory cytokines TNF-α and IL-1β, in contrast to the results in other cell types. Loss-of-function experiments using TCF7L2 siRNA or lentiviral shTCF7L2 showed that TCF7L2 knockdown suppresses matrix degradation through p65/NF-κB signaling in the absence and presence of TNF-α. In addition, TCF7L2 expression is repressed by miR-155 overexpression and promoted by miR-155 inhibition.

SIGNIFICANCE

Overall, these results demonstrate that the suppression of TCF7L2, which is modulated by miR-155, inhibits matrix degradation through p65/NF-κB signaling. TCF7L2 suppression may have therapeutic potential in intervertebral disc degeneration.

Wnt/β-Catenin Signaling and Obesity

Obesity has become epidemic worldwide, which triggers several obesity-associated complications. Obesity is characterized by excess fat storage mainly in the visceral white adipose tissue (vWAT), subcutaneous WAT (sWAT), and other tissues. Myriad studies have demonstrated the crucial role of canonical Wnt/β-catenin cascade in the development of organs and physiological homeostasis, whereas recent studies show that genetic variations/mutations in the Wnt/β-catenin pathway are associated with human metabolic diseases. In this review, we highlight the regulation of updated Wnt/β-catenin signaling in obesity, especially the distinctly depot-specific roles between subcutaneous and visceral adipose tissue under high-fed diet stimulation and WAT browning process.