Identification of C2CD4A as a human diabetes susceptibility gene with a role in β cell insulin secretion

FOXO1 regulates expression of Neurod4 in the pituitary gland

Pituitary gland function is regulated by the activity of various transcription factors that control cell fate decisions leading to cellular differentiation and hormone production. FOXO1 is necessary for normal somatotrope differentiation and function. Recent in vivo data implicate FOXO1 in the regulation of genes important for somatotrope differentiation including Gh1, Neurod4, and Pou1f1. In the current study, the somatotrope-like cell line GH3 was treated with a FOXO1 inhibitor, resulting in significant reduction in Neurod4 and Gh1 expression. Consistent with these findings, CRISPR/Cas9-mediated deletion of Foxo1 in GH3 cells significantly reduced expression of Gh1 and Neurod4. Chromatin immunoprecipitation sequencing identifies novel FOXO1 binding sites associated with the Neurod4, Gh1, and Pou1f1 genes. The FOXO1 binding site in the Neurod4 gene exhibits enhancer activity in somatotrope-like cells but not in gonadotrope-like cells. These data strongly suggest FOXO1 directly contributes to the transcriptional control of genes important for somatotrope differentiation.

Cyb5r3 activation rescues secondary failure to sulfonylurea but not β-cell dedifferentiation

Diabetes mellitus is characterized by insulin resistance and β-cell failure. The latter involves impaired insulin secretion and β-cell dedifferentiation. Sulfonylurea (SU) is used to improve insulin secretion in diabetes, but it suffers from secondary failure. The relationship between SU secondary failure and β-cell dedifferentiation has not been examined. Using a model of SU secondary failure, we have previously shown that functional loss of oxidoreductase Cyb5r3 mediates effects of SU failure through interactions with glucokinase. Here we demonstrate that SU failure is associated with partial β-cell dedifferentiation. Cyb5r3 knockout mice show more pronounced β-cell dedifferentiation and glucose intolerance after chronic SU administration, high-fat diet feeding, and during aging. A Cyb5r3 activator improves impaired insulin secretion caused by chronic SU treatment, but not β-cell dedifferentiation. We conclude that chronic SU administration affects progression of β-cell dedifferentiation and that Cyb5r3 activation reverses secondary failure to SU without restoring β-cell dedifferentiation.

Unraveling the mysteries of hepatic insulin signaling: deconvoluting the nuclear targets of insulin

Over 100 years have passed since insulin was first administered to a diabetic patient. Since then great strides have been made in diabetes research. It has determined where insulin is secreted from, which organs it acts on, how it is transferred into the cell and is delivered to the nucleus, how it orchestrates the expression pattern of the genes, and how it works with each organ to maintain systemic metabolism. Any breakdown in this system leads to diabetes. Thanks to the numerous researchers who have dedicated their lives to cure diabetes, we now know that there are three major organs where insulin acts to maintain glucose/lipid metabolism: the liver, muscles, and fat. The failure of insulin action on these organs, such as insulin resistance, result in hyperglycemia and/or dyslipidemia. The primary trigger of this condition and its association among these tissues still remain to be uncovered. Among the major organs, the liver finely tunes the glucose/lipid metabolism to maintain metabolic flexibility, and plays a crucial role in glucose/lipid abnormality due to insulin resistance. Insulin resistance disrupts this tuning, and selective insulin resistance arises. The glucose metabolism loses its sensitivity to insulin, while the lipid metabolism maintains it. The clarification of its mechanism is warranted to reverse the metabolic abnormalities due to insulin resistance. This review will provide a brief historical review for the progress of the pathophysiology of diabetes since the discovery of insulin, followed by a review of the current research clarifying our understanding of selective insulin resistance.

Genomic Characterization and Initial Insight into Mastitis-Associated SNP Profiles of Local Latvian Bos taurus Breeds

Latvia has two local Bos taurus breeds-Latvian Brown (LBG) and Latvian Blue (LZG)-characterized by a good adaptation to the local climate, longevity, and high fat and protein contents in milk. Since these are desired traits in the dairy industry, this study investigated the genetic background of the LBG and LZG breeds and identified the genetic factors associated with mastitis. Blood and semen samples were acquired, and whole genome sequencing was then performed to acquire a genomic sequence with at least 35× or 10× coverage. The heterozygosity, nucleotide diversity, and LD analysis indicated that LBG and LZG cows have similar levels of genetic diversity compared to those of other breeds. An analysis of the population structure revealed that each breed clustered together, but the overall differentiation between the breeds was small. The highest genetic variance was observed in the LZG breed compared with the LBG breed. Our results show that SNP rs721295390 is associated with mastitis in the LBG breed, and SNPs rs383806754, chr29:43998719CG>C, and rs462030680 are associated with mastitis in the LZG breed. This study shows that local Latvian LBG and LZG breeds have a pronounced genetic differentiation, with each one suggesting its own mastitis-associated SNP profile.

Genome-wide association study and functional characterization identifies candidate genes for insulin-stimulated glucose uptake

Distinct tissue-specific mechanisms mediate insulin action in fasting and postprandial states. Previous genetic studies have largely focused on insulin resistance in the fasting state, where hepatic insulin action dominates. Here we studied genetic variants influencing insulin levels measured 2 h after a glucose challenge in >55,000 participants from three ancestry groups. We identified ten new loci (P < 5 × 10-8) not previously associated with postchallenge insulin resistance, eight of which were shown to share their genetic architecture with type 2 diabetes in colocalization analyses. We investigated candidate genes at a subset of associated loci in cultured cells and identified nine candidate genes newly implicated in the expression or trafficking of GLUT4, the key glucose transporter in postprandial glucose uptake in muscle and fat. By focusing on postprandial insulin resistance, we highlighted the mechanisms of action at type 2 diabetes loci that are not adequately captured by studies of fasting glycemic traits.

Nutrient regulation of the islet epigenome controls adaptive insulin secretion

Adaptation of the islet β cell insulin-secretory response to changing insulin demand is critical for blood glucose homeostasis, yet the mechanisms underlying this adaptation are unknown. Here, we have shown that nutrient-stimulated histone acetylation plays a key role in adapting insulin secretion through regulation of genes involved in β cell nutrient sensing and metabolism. Nutrient regulation of the epigenome occurred at sites occupied by the chromatin-modifying enzyme lysine-specific demethylase 1 (Lsd1) in islets. β Cell-specific deletion of Lsd1 led to insulin hypersecretion, aberrant expression of nutrient-response genes, and histone hyperacetylation. Islets from mice adapted to chronically increased insulin demand exhibited shared epigenetic and transcriptional changes. Moreover, we found that genetic variants associated with type 2 diabetes were enriched at LSD1-bound sites in human islets, suggesting that interpretation of nutrient signals is genetically determined and clinically relevant. Overall, these studies revealed that adaptive insulin secretion involves Lsd1-mediated coupling of nutrient state to regulation of the islet epigenome.

Methylation of histone H3 lysine 4 is required for maintenance of beta cell function in adult mice

AIMS/HYPOTHESIS

Beta cells control glucose homeostasis via regulated production and secretion of insulin. This function arises from a highly specialised gene expression programme that is established during development and then sustained, with limited flexibility, in terminally differentiated cells. Dysregulation of this programme is seen in type 2 diabetes but mechanisms that preserve gene expression or underlie its dysregulation in mature cells are not well resolved. This study investigated whether methylation of histone H3 lysine 4 (H3K4), a marker of gene promoters with unresolved functional importance, is necessary for the maintenance of mature beta cell function.

METHODS

Beta cell function, gene expression and chromatin modifications were analysed in conditional Dpy30 knockout mice, in which H3K4 methyltransferase activity is impaired, and in a mouse model of diabetes.

RESULTS

H3K4 methylation maintains expression of genes that are important for insulin biosynthesis and glucose responsiveness. Deficient methylation of H3K4 leads to a less active and more repressed epigenome profile that locally correlates with gene expression deficits but does not globally reduce gene expression. Instead, developmentally regulated genes and genes in weakly active or suppressed states particularly rely on H3K4 methylation. We further show that H3K4 trimethylation (H3K4me3) is reorganised in islets from the Lepr^db/db mouse model of diabetes in favour of weakly active and disallowed genes at the expense of terminal beta cell markers with broad H3K4me3 peaks.

CONCLUSIONS/INTERPRETATION

Sustained methylation of H3K4 is critical for the maintenance of beta cell function. Redistribution of H3K4me3 is linked to gene expression changes that are implicated in diabetes pathology.

Calorie Restriction activates a gastric Notch-FOXO1 pathway to expand Ghrelin cells

Calorie restriction increases lifespan. While some tissue-specific protective effects of calorie restriction have been described, the impact of calorie restriction on the gastrointestinal tract remains unclear. We found increased abundance of chromogranin A+, including orexigenic ghrelin+, endocrine cells in the stomach of calorie-restricted mice. This effect coincided with increased Notch target Hes1 and Notch ligand Jag1 and was reversed when Notch signaling was blocked using the γ-secretase inhibitor DAPT. Using primary cultures and genetically-modified reporter mice, we determined that increased endocrine cell abundance was due to altered stem and progenitor proliferation. Different from the intestine, calorie restriction decreased gastric Lgr5+ stem cells, while increasing a FOXO1/Neurog3+ subpopulation of endocrine progenitors in a Notch-dependent manner. Further, calorie restriction triggered nuclear localization of FOXO1, which was sufficient to promote endocrine cell differentiation. Taken together, the data indicate that calorie restriction promotes gastric endocrine cell differentiation triggered by active Notch signaling and regulated by FOXO1.

Integrative single-cell characterization of frugivory adaptations in the bat kidney and pancreas

Frugivory evolved multiple times in mammals, including bats. However, the cellular and molecular components driving it remain largely unknown. Here, we used integrative single-cell sequencing on insectivorous and frugivorous bat kidneys and pancreases and identified key cell population, gene expression and regulatory element differences associated with frugivorous adaptation that also relate to human disease, particularly diabetes. We found an increase in collecting duct cells and differentially active genes and regulatory elements involved in fluid and electrolyte balance in the frugivore kidney. In the frugivorous pancreas, we observed an increase in endocrine and a decrease in exocrine cells and differences in genes and regulatory elements involved in insulin regulation. Combined, our work provides novel insights into frugivorous adaptation that also could be leveraged for therapeutic purposes.

Cyb5r3-based mechanism and reversal of secondary failure to sulfonylurea in diabetes

Sulfonylureas (SUs) are effective and affordable antidiabetic drugs. However, chronic use leads to secondary failure, limiting their utilization. Here, we identify cytochrome b5 reductase 3 (Cyb5r3) down-regulation as a mechanism of secondary SU failure and successfully reverse it. Chronic exposure to SU lowered Cyb5r3 abundance and reduced islet glucose utilization in mice in vivo and in ex vivo murine islets. Cyb5r3 β cell-specific knockout mice phenocopied SU failure. Cyb5r3 engaged in a glucose-dependent interaction that stabilizes glucokinase (Gck) to maintain glucose utilization. Hence, Gck activators can circumvent Cyb5r3-dependent SU failure. A Cyb5r3 activator rescued secondary SU failure in mice in vivo and restored insulin secretion in ex vivo human islets. We conclude that Cyb5r3 is a key factor in the secondary failure to SU and a potential target for its prevention, which might rehabilitate SU use in diabetes.

Reflections on the state of diabetes research and prospects for treatment

Research on the etiology and treatment of diabetes has made substantial progress. As a result, several new classes of anti-diabetic drugs have been introduced in clinical practice. Nonetheless, the number of patients achieving glycemic control targets has not increased for the past 20 years. Two areas of unmet medical need are the restoration of insulin sensitivity and the reversal of pancreatic beta cell failure. In this review, we integrate research advances in transcriptional regulation of insulin action and pathophysiology of beta cell dedifferentiation with their potential impact on prospects of a durable "cure" for patients suffering from type 2 diabetes.

C2CD4A/B variants in the predisposition of lung cancer in the Chinese Han population

BACKGROUND

The mRNA levels of C2CD4A and C2CD4B were dysregulation in lung cancer (LC). We aimed to evaluate the role of C2CD4A/B variants in LC susceptibility.

METHODS

There were 710 cases with LC and 710 healthy controls enrolled in the study. The genotyping of twelve variants in C2CD4A/B was carried out by Agena MassARRAY system. Odds ratios (ORs) were calculated by logistic regression analysis to assess the relationship between these variants and LC predisposition.

RESULTS

Rs8037894 (OR = 0.81, p = 0.005), rs7172432 (OR = 0.83, p = 0.013), rs11856307 (OR = 0.86, p = 0.043), and rs1436953 (OR = 0.79, p = 0.002) were related to the reduced risk of LC. Besides, the relation of rs7172432 with LC risk in subjects aged > 60 years was observed. Rs4502156 conferred to the increased LC risk, while rs1436953 was associated with the lower susceptibility to LC among males. Rs731820, rs4502156, rs11071657, rs7172432, and rs11856307 contributed to the predisposition of LC among subjects with BMI > 24 kg/m², while rs7495253 was associated with an increased risk of LC in subjects with BMI ≤ 24 kg/m². The increased LC risk was found in rs4502156, while the protective risk effect of rs8037894, rs7172432, rs11856307, and rs1436953 on the occurrence of LC was observed in smokers and non-drinkers. Moreover, rs7495253 and rs7495931 had a higher risk of lymphatic metastasis. Rs1436953 was related to the reduced risk of lung adenocarcinoma, while rs4502156, rs8037894, rs7172432, rs11856307, and rs1436953 were related to the risk of small cell carcinoma.

CONCLUSIONS

Our results first display that C2CD4A/B polymorphisms served as protective factors for LC predisposition in a Chinese Han population. These findings could provide new biological insight into the understanding of C2CD4A/B genes on LC pathogenesis.

FOXO1 Is Present in Stomach Epithelium and Determines Gastric Cell Distribution

BACKGROUND AND AIMS

Stomach cells can be converted to insulin-producing cells by Neurog3, MafA, and Pdxl over-expression. Enteroendocrine cells can be similarly made to produce insulin by the deletion of FOXO1. Characteristics and functional properties of FOXO1-expressing stomach cells are not known.

METHODS

Using mice bearing a FOXO1-GFP knock-in allele and primary cell cultures, we examined the identity of FOXO1-expressing stomach cells and analyzed their features through loss-of-function studies with red-to-green fluorescent reporters.

RESULTS

FOXO1 localizes to a subset of Neurog3 and parietal cells. FOXO1 deletion ex vivo or in vivo using Neurog3-cre or Atp4b-cre increased numbers of parietal cells, generated insulin- and C-peptide-immunoreactive cells, and raised Neurog3 messenger RNA. Gene expression and ChIP- seq experiments identified the cell cycle regulator cyclin E1 (CCNE1) as a FOXO1 target.

CONCLUSION

FOXO1 is expressed in a subset of stomach cells. Its ablation increases parietal cells and yields insulin-immunoreactive cells, consistent with a role in lineage determination.

Loss of Human Beta Cell Identity in a Reconstructed Omental Stromal Cell Environment

In human type 2 diabetes, adipose tissue plays an important role in disturbing glucose homeostasis by secreting factors that affect the function of cells and tissues throughout the body, including insulin-producing pancreatic beta cells. We aimed here at studying the paracrine effect of stromal cells isolated from subcutaneous and omental adipose tissue on human beta cells. We developed an in vitro model wherein the functional human beta cell line EndoC-βH1 was treated with conditioned media from human adipose tissues. By using RNA-sequencing and western blotting, we determined that a conditioned medium derived from omental stromal cells stimulates several pathways, such as STAT, SMAD and RELA, in EndoC-βH1 cells. We also observed that upon treatment, the expression of beta cell markers decreased while dedifferentiation markers increased. Loss-of-function experiments that efficiently blocked specific signaling pathways did not reverse dedifferentiation, suggesting the implication of more than one pathway in this regulatory process. Taken together, we demonstrate that soluble factors derived from stromal cells isolated from human omental adipose tissue signal human beta cells and modulate their identity.

Stem Cell-Derived β Cells: A Versatile Research Platform to Interrogate the Genetic Basis of β Cell Dysfunction

Pancreatic β cell dysfunction is a central component of diabetes progression. During the last decades, the genetic basis of several monogenic forms of diabetes has been recognized. Genome-wide association studies (GWAS) have also facilitated the identification of common genetic variants associated with an increased risk of diabetes. These studies highlight the importance of impaired β cell function in all forms of diabetes. However, how most of these risk variants confer disease risk, remains unanswered. Understanding the specific contribution of genetic variants and the precise role of their molecular effectors is the next step toward developing treatments that target β cell dysfunction in the era of personalized medicine. Protocols that allow derivation of β cells from pluripotent stem cells, represent a powerful research tool that allows modeling of human development and versatile experimental designs that can be used to shed some light on diabetes pathophysiology. This article reviews different models to study the genetic basis of β cell dysfunction, focusing on the recent advances made possible by stem cell applications in the field of diabetes research.

Time-restricted feeding prevents deleterious metabolic effects of circadian disruption through epigenetic control of β cell function

Circadian rhythm disruption (CD) is associated with impaired glucose homeostasis and type 2 diabetes mellitus (T2DM). While the link between CD and T2DM remains unclear, there is accumulating evidence that disruption of fasting/feeding cycles mediates metabolic dysfunction. Here, we used an approach encompassing analysis of behavioral, physiological, transcriptomic, and epigenomic effects of CD and consequences of restoring fasting/feeding cycles through time-restricted feeding (tRF) in mice. Results show that CD perturbs glucose homeostasis through disruption of pancreatic β cell function and loss of circadian transcriptional and epigenetic identity. In contrast, restoration of fasting/feeding cycle prevented CD-mediated dysfunction by reestablishing circadian regulation of glucose tolerance, β cell function, transcriptional profile, and reestablishment of proline and acidic amino acid–rich basic leucine zipper (PAR bZIP) transcription factor DBP expression/activity. This study provides mechanistic insights into circadian regulation of β cell function and corresponding beneficial effects of tRF in prevention of T2DM.

Increased glycolysis affects β-cell function and identity in aging and diabetes

Objective

Age is a risk factor for type 2 diabetes (T2D). We aimed to elucidate whether β-cell glucose metabolism is altered with aging and contributes to T2D.

Methods

We used senescence-accelerated mice (SAM), C57BL/6J (B6) mice, and ob/ob mice as aging models. As a diabetes model, we used db/db mice. The glucose responsiveness of insulin secretion and the [U-¹³C]-glucose metabolic flux were examined in isolated islets. We analyzed the expression of β-cell-specific genes in isolated islets and pancreatic sections as molecular signatures of β-cell identity. β cells defective in the malate-aspartate (MA) shuttle were previously generated from MIN6-K8 cells by the knockout of Got1, a component of the shuttle. We analyzed Got1 KO β cells as a model of increased glycolysis.

Results

We identified hyperresponsiveness to glucose and compromised cellular identity as dysfunctional phenotypes shared in common between aged and diabetic mouse β cells. We also observed a metabolic commonality between aged and diabetic β cells: hyperactive glycolysis through the increased expression of nicotinamide mononucleotide adenylyl transferase 2 (Nmnat2), a cytosolic nicotinamide adenine dinucleotide (NAD)-synthesizing enzyme. Got1 KO β cells showed increased glycolysis, β-cell dysfunction, and impaired cellular identity, phenocopying aging and diabetes. Using Got1 KO β cells, we show that attenuation of glycolysis or Nmnat2 activity can restore β-cell function and identity.

Conclusions

Our study demonstrates that hyperactive glycolysis is a metabolic signature of aged and diabetic β cells, which may underlie age-related β-cell dysfunction and loss of cellular identity. We suggest Nmnat2 suppression as an approach to counteract age-related T2D.

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Glucose hypersensitivity and impaired identity are common features of aged and diabetic β cells.

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Metabolic tracing reveals increased glycolysis and altered NAD production in aged and diabetic β cells.

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Increased glycolysis induces β-cell dysfunction and loss of identity.

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NAD production by Nmnat2 can be targeted to restore β-cell phenotypes.

Aldo-ketoreductase 1c19 ablation does not affect insulin secretion in murine islets

Beta cell failure is a critical feature of diabetes. It includes defects of insulin production, secretion, and altered numbers of hormone-producing cells. In previous work, we have shown that beta cell failure is mechanistically linked to loss of Foxo1 function. This loss of function likely results from increased Foxo1 protein degradation, due to hyperacetylation of Foxo1 from increased nutrient turnover. To understand the mechanisms of Foxo1-related beta cell failure, we performed genome-wide analyses of its target genes, and identified putative mediators of sub-phenotypes of cellular dysfunction. Chromatin immunoprecipitation analyses demonstrated a striking pattern of Foxo1 binding to the promoters of a cluster of aldo-ketoreductases on chromosome 13: Akr1c12, Akr1c13, Akr1c19. Of these, Akr1c19 has been reported as a marker of Pdx1-positive endodermal progenitor cells. Here we show that Akr1c19 expression is dramatically decreased in db/db islets. Thus, we investigated whether Akr1c19 is involved in beta cell function. We performed gain- and loss-of-function experiments in cultured beta cells and generated Akr1c19 knockout mice. We show that Foxo1 and HNF1a cooperatively regulate Akr1c19 expression. Nonetheless, functional characterization of Akr1c19 both using islets and knockout mice did not reveal abnormalities on glucose homeostasis. We conclude that reduced expression of Akr1c19 is not sufficient to affect islet function.

An integrative transcriptional logic model of hepatic insulin resistance

Abnormalities of lipid/lipoprotein and glucose metabolism are hallmarks of hepatic insulin resistance in type 2 diabetes. The former antedate the latter, but the latter become progressively refractory to treatment and contribute to therapeutic failures. It's unclear whether the two processes share a common pathogenesis and what underlies their progressive nature. In this study, we investigated the hypothesis that genes in the lipid/lipoprotein pathway and those in the glucose metabolic pathway are governed by different transcriptional regulatory logics that affect their response to physiologic (fasting/refeeding) as well as pathophysiologic cues (insulin resistance and hyperglycemia). To this end, we obtained genomic and transcriptomic maps of the key insulin-regulated transcription factor, FoxO1, and integrated them with those of CREB, PPAR-α, and glucocorticoid receptor. We found that glucose metabolic genes are primarily regulated by promoter and intergenic enhancers in a fasting-dependent manner, while lipid genes are regulated through fasting-dependent intron enhancers and fasting-independent enhancerless introns. Glucose genes also showed a remarkable transcriptional resiliency (i.e., the ability to compensate following constitutive FoxO1 ablation through an enrichment of active marks at shared PPAR-α/FoxO1 regulatory elements). Unexpectedly, insulin resistance and hyperglycemia were associated with a "spreading" of FoxO1 binding to enhancers and the emergence of unique target sites. We surmise that this unusual pattern correlates with the progressively intractable nature of hepatic insulin resistance. This transcriptional logic provides an integrated model to interpret the combined lipid and glucose abnormalities of type 2 diabetes.

Antagonistic epistasis of Hnf4α and FoxO1 metabolic networks through enhancer interactions in β-cell function

OBJECTIVE

Genetic and acquired abnormalities contribute to pancreatic β-cell failure in diabetes. Transcription factors Hnf4α (MODY1) and FoxO1 are respective examples of these two components and act through β-cell-specific enhancers. However, their relationship is unclear.

METHODS

In this report, we show by genome-wide interrogation of chromatin modifications that ablation of FoxO1 in mature β-cells enriches active Hnf4α enhancers according to a HOMER analysis.

RESULTS

To model the functional significance of this predicted unusual enhancer utilization, we generated single and compound knockouts of FoxO1 and Hnf4α in β-cells. Single knockout of either gene impaired insulin secretion in mechanistically distinct fashions as indicated by their responses to sulfonylurea and calcium fluxes. Surprisingly, the defective β-cell secretory function of either single mutant in hyperglycemic clamps and isolated islets treated with various secretagogues was completely reversed in double mutants lacking FoxO1 and Hnf4α. Gene expression analyses revealed distinct epistatic modalities by which the two transcription factors regulate networks associated with reversal of β-cell dysfunction. An antagonistic network regulating glycolysis, including β-cell "disallowed" genes, and a synergistic network regulating protocadherins emerged as likely mediators of the functional restoration of insulin secretion.

CONCLUSIONS

The findings provide evidence of antagonistic epistasis as a model of gene/environment interactions in the pathogenesis of β-cell dysfunction.

The novel circSLC6A6/miR-1265/C2CD4A axis promotes colorectal cancer growth by suppressing p53 signaling pathway

Background

Colorectal cancer (CRC) is one of the most frequent malignancy and a leading cause of cancer-related deaths. Therefore, further researches are required to identify novel and more effective diagnoses and to identify molecular targets in treatment of CRC.

Methods

C2CD4A expression in CRC tissues and cell lines was detected by qRT-PCR and western blot. The biological functions of C2CD4A were performed both in vitro and in vivo. Western blot, cDNA array, IP-MS, Co-immunoprecipitation assay, and Ubiquitination assay were used to analyze the interaction between C2CD4A and p53. Bioinformatics analysis, FISH, RNA sequencing, luciferase reporter assay, RNA immunoprecipitation, RNA pull-down and rescue experiments, were deployed to detect upstream regulation mechanism of C2CD4A.

Results

C2CD4A was elevated in CRC tissues compared with adjacent normal colorectal tissues. C2CD4A knockdown significantly promoted cell apoptosis and with inhibited proliferation in vitro, and tumorigenicity in vivo, whereas C2CD4A overexpression led to opposite effects. Moreover, circSLC6A6 was upregulated and shown to positively regulate C2CD4A expression via sponging miR-1265. Fundamentally, C2CD4A inhibited p53 signaling pathway through interacting with p53 and increasing its ubiquitination and degradation.

Conclusion

Our results identified that circSLC6A6/miR-1265/C2CD4A axis, which was involved in CRC via the p53 signaling pathway, may serve as a therapeutic target for CRC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02126-y.

An inhibitor-mediated beta-cell dedifferentiation model reveals distinct roles for FoxO1 in glucagon repression and insulin maturation

OBJECTIVE

The loss of forkhead box protein O1 (FoxO1) signaling in response to metabolic stress contributes to the etiology of type II diabetes, causing the dedifferentiation of pancreatic beta cells to a cell type reminiscent of endocrine progenitors. Lack of methods to easily model this process in vitro, however, have hindered progress into the identification of key downstream targets and potential inhibitors. We therefore aimed to establish such an in vitro cellular dedifferentiation model and apply it to identify novel agents involved in the maintenance of beta-cell identity.

METHODS

The murine beta-cell line, Min6, was used for primary experiments and high-content screening. Screens encompassed a library of small-molecule drugs representing the chemical and target space of all FDA-approved small molecules with an automated immunofluorescence readout. Validation experiments were performed in a murine alpha-cell line as well as in primary murine and human diabetic islets. Developmental effects were studied in zebrafish and C. elegans models, while diabetic db/db mouse models were used to elucidate global glucose metabolism outcomes.

RESULTS

We show that short-term pharmacological FoxO1 inhibition can model beta-cell dedifferentiation by downregulating beta-cell-specific transcription factors, resulting in the aberrant expression of progenitor genes and the alpha-cell marker glucagon. From a high-content screen, we identified loperamide as a small molecule that can prevent FoxO inhibitor-induced glucagon expression and further stimulate insulin protein processing and secretion by altering calcium levels, intracellular pH, and FoxO1 localization.

CONCLUSIONS

Our study provides novel models, molecular targets, and drug candidates for studying and preventing beta-cell dedifferentiation.

Transcriptional mechanisms of pancreatic β-cell maturation and functional adaptation

Pancreatic β-cells secrete insulin commensurate to circulating nutrient levels to maintain normoglycemia. The ability of β-cells to couple insulin secretion to nutrient stimuli is acquired during a postnatal maturation process. In mature β-cells the insulin secretory response adapts to changes in nutrient state. Both β-cell maturation and functional adaptation rely on the interplay between extracellular cues and cell type-specific transcriptional programs. Here we review emerging evidence that developmental and homeostatic regulation of β-cell function involves collaboration between lineage-determining and signal-dependent transcription factors (LDTFs and SDTFs, respectively). A deeper understanding of β-cell SDTFs and their cognate signals would delineate mechanisms of β-cell maturation and functional adaptation, which has direct implications for diabetes therapies and for generating mature β-cells from stem cells.

Low-Density Lipoprotein Cholesterol Is Associated With Insulin Secretion

CONTEXT

Pharmacological lowering of low-density lipoprotein (LDL) cholesterol potently reduces cardiovascular risk while concurrently increasing type 2 diabetes risk.

OBJECTIVE

The aim of this study was to investigate the relationship between LDL cholesterol concentrations and insulin secretion and glucagon levels.

METHODS

A total of 3039 individuals without cholesterol-lowering therapy, but with increased risk for diabetes, underwent routine blood tests and a 5-point oral glucose tolerance test (OGTT). Glucagon concentrations, insulin secretion, and insulin clearance indices were derived from the OGTT.

RESULTS

There was no association between LDL cholesterol and fasting glucagon (P = .7, β = -.01) or post-glucose load glucagon levels (P = .7, β = -.07), but we detected significant positive associations of LDL cholesterol and C-peptide-based indices of insulin secretion (area under the curve [AUC]C-Peptide(0-30min)/AUCGlucose(0-30min): P < .001, β = .06; AUCC-Peptide(0-120min) /AUCGlucose(0-120min): P < .001, β = -.08). In contrast, we found a negative association of insulin-based insulin secretion indices with LDL concentrations (insulinogenic index: P = .01, β = -.04; disposition index: P < .001, β = -.06). LDL cholesterol levels, however, were positively associated with insulin clearance assessed from C-peptide and insulin concentrations, both in the fasting state and post-glucose load (P < .001, β = .09 and P < .001, β = .06, respectively).

CONCLUSION

As C-peptide based indices reflect insulin secretion independent of hepatic clearance, our results indicate lower insulin secretion in case of lesser LDL cholesterol. This could explain deteriorating glycemic control in response to cholesterol-lowering drugs.

Sexually dimorphic roles for the type 2 diabetes-associated C2cd4b gene in murine glucose homeostasis

AIMS/HYPOTHESIS

Variants close to the VPS13C/C2CD4A/C2CD4B locus are associated with altered risk of type 2 diabetes in genome-wide association studies. While previous functional work has suggested roles for VPS13C and C2CD4A in disease development, none has explored the role of C2CD4B.

METHODS

CRISPR/Cas9-induced global C2cd4b-knockout mice and zebrafish larvae with c2cd4a deletion were used to study the role of this gene in glucose homeostasis. C2 calcium dependent domain containing protein (C2CD)4A and C2CD4B constructs tagged with FLAG or green fluorescent protein were generated to investigate subcellular dynamics using confocal or near-field microscopy and to identify interacting partners by mass spectrometry.

RESULTS

Systemic inactivation of C2cd4b in mice led to marked, but highly sexually dimorphic changes in body weight and glucose homeostasis. Female C2cd4b mice displayed unchanged body weight compared with control littermates, but abnormal glucose tolerance (AUC, p = 0.01) and defective in vivo, but not in vitro, insulin secretion (p = 0.02). This was associated with a marked decrease in follicle-stimulating hormone levels as compared with wild-type (WT) littermates (p = 0.003). In sharp contrast, male C2cd4b null mice displayed essentially normal glucose tolerance but an increase in body weight (p < 0.001) and fasting blood glucose (p = 0.003) after maintenance on a high-fat and -sucrose diet vs WT littermates. No metabolic disturbances were observed after global inactivation of C2cd4a in mice, or in pancreatic beta cell function at larval stages in C2cd4a null zebrafish. Fasting blood glucose levels were also unaltered in adult C2cd4a-null fish. C2CD4B and C2CD4A were partially localised to the plasma membrane, with the latter under the control of intracellular Ca2+. Binding partners for both included secretory-granule-localised PTPRN2/phogrin.

CONCLUSIONS/INTERPRETATION

Our studies suggest that C2cd4b may act centrally in the pituitary to influence sex-dependent circuits that control pancreatic beta cell function and glucose tolerance in rodents. However, the absence of sexual dimorphism in the impact of diabetes risk variants argues for additional roles for C2CD4A or VPS13C in the control of glucose homeostasis in humans.

DATA AVAILABILITY

The datasets generated and/or analysed during the current study are available in the Biorxiv repository ( www.biorxiv.org/content/10.1101/2020.05.18.099200v1 ). RNA-Seq (GSE152576) and proteomics (PXD021597) data have been deposited to GEO ( www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE152576 ) and ProteomeXchange ( www.ebi.ac.uk/pride/archive/projects/PXD021597 ) repositories, respectively.

Functional Genomics in Pancreatic β Cells: Recent Advances in Gene Deletion and Genome Editing Technologies for Diabetes Research

The inheritance of variants that lead to coding changes in, or the mis-expression of, genes critical to pancreatic beta cell function can lead to alterations in insulin secretion and increase the risk of both type 1 and type 2 diabetes. Recently developed clustered regularly interspaced short palindromic repeats (CRISPR/Cas9) gene editing tools provide a powerful means of understanding the impact of identified variants on cell function, growth, and survival and might ultimately provide a means, most likely after the transplantation of genetically "corrected" cells, of treating the disease. Here, we review some of the disease-associated genes and variants whose roles have been probed up to now. Next, we survey recent exciting developments in CRISPR/Cas9 technology and their possible exploitation for β cell functional genomics. Finally, we will provide a perspective as to how CRISPR/Cas9 technology may find clinical application in patients with diabetes.

Metabolism as a central regulator of β-cell chromatin state

Pancreatic β-cells are critical mediators of glucose homeostasis in the body, and proper cellular nutrient metabolism is critical to β-cell function. Several interacting signaling networks that uniquely control β-cell metabolism produce essential substrates and co-factors for catalytic reactions, including reactions that modify chromatin. Chromatin modifications, in turn, regulate gene expression. The reactions that modify chromatin are therefore well-positioned to adjust gene expression programs according to nutrient availability. It follows that dysregulation of nutrient metabolism in β-cells may impact chromatin state and gene expression through altering the availability of these substrates and co-factors. Metabolic disorders such as type 2 diabetes (T2D) can significantly alter metabolite levels in cells. This suggests that a driver of β-cell dysfunction during T2D may be the altered availability of substrates or co-factors necessary to maintain β-cell chromatin state. Induced changes in the β-cell chromatin modifications may then lead to dysregulation of gene expression, in turn contributing to the downward cascade of events that leads to the loss of functional β-cell mass, and loss of glucose homeostasis, that occurs in T2D.

Cyb5r3 links FoxO1-dependent mitochondrial dysfunction with β-cell failure

OBJECTIVE

Diabetes is characterized by pancreatic β-cell dedifferentiation. Dedifferentiating β cells inappropriately metabolize lipids over carbohydrates and exhibit impaired mitochondrial oxidative phosphorylation. However, the mechanism linking the β-cell's response to an adverse metabolic environment with impaired mitochondrial function remains unclear.

METHODS

Here we report that the oxidoreductase cytochrome b5 reductase 3 (Cyb5r3) links FoxO1 signaling to β-cell stimulus/secretion coupling by regulating mitochondrial function, reactive oxygen species generation, and nicotinamide actin dysfunction (NAD)/reduced nicotinamide actin dysfunction (NADH) ratios.

RESULTS

The expression of Cyb5r3 is decreased in FoxO1-deficient β cells. Mice with β-cell-specific deletion of Cyb5r3 have impaired insulin secretion, resulting in glucose intolerance and diet-induced hyperglycemia. Cyb5r3-deficient β cells have a blunted respiratory response to glucose and display extensive mitochondrial and secretory granule abnormalities, consistent with altered differentiation. Moreover, FoxO1 is unable to maintain expression of key differentiation markers in Cyb5r3-deficient β cells, suggesting that Cyb5r3 is required for FoxO1-dependent lineage stability.

CONCLUSIONS

The findings highlight a pathway linking FoxO1 to mitochondrial dysfunction that can mediate β-cell failure.