Serum preadipocyte factor 1 concentrations and risk of developing diabetes: a nested case-control study

Advancements in the study of DLK1 in the pathogenesis of diabetes

DLK1, as a membrane-bound protein, has been extensively studied in the field of cancer research. As a ligand downstream of the Notch pathway, it broadly influences developmental and metabolic processes in the body. With deeper research, it has been found that DLK1 can induce the synthesis and secretion of insulin through the ERK and AKT pathways, playing a crucial role in the development of metabolic diseases. Diabetes mellitus (DM) is a chronic metabolic disorder characterized by insufficient insulin production by the pancreas or inadequate utilization of insulin by the body. This article aims to review the relationship between DLK1 and diabetes, recent research advancements, and to discuss future research directions and challenges.

Association of DLK1 SNPs with body mass index and plasma lipid levels in children

BACKGROUND

The DLK1 human gene encodes for the transmembrane EGF-like repeat-containing protein DLK1, which acts as a modulator of adipogenesis. A role for DLK1 in energy metabolism and lipid homeostasis has been suggested and DLK1 gene variants have been related to pubertal development.

OBJECTIVE

The aim of this study was to uncover DLK1 SNPs in a cohort of children and analyze their relationship with anthropometric and biochemical variables.

METHODS

Our population-based sample comprises 1237 healthy 6-to-8-year-old Caucasian children. The presence of five DLK1 SNPs (rs1802710, rs876374, rs7155375, rs57098752, and rs7149242) was analyzed by Real-Time PCR, using predesigned TaqMan™ Genotyping Assays.

RESULTS

We observed that the SNPs rs1802710 and rs876374 were associated with BMI, and the prevalence of these two SNPs was different in normal-weight children compared to children with obesity. Related to biochemical variables, we found a significant association of the SNPs rs1802710, rs876374, and rs57098752 and their combination with Apo-B plasma concentrations after adjusting by BMI and sex. The SNPs rs1802710 and rs57098752 were also significantly associated with plasma levels of LDL-C and HDL-C, respectively.

CONCLUSION

Our study reveals that DLK1 gene variants may influence both body weight and lipid homeostasis, affecting particularly to the Apo-B biology, in children.

IMPACT

DLK1 polymorphisms are associated with BMI and with lipid levels, independently of BMI, early in life. Our data add to the existing literature the evidence that DLK1 gene variants impact on lipid metabolism. The confirmation at the population level that DLK1 genetic variants are associated with anthropometric and lipid variables sustains the role of DLK1 in obesity and related disorders and should lead to further studies aimed at clarifying this effect.

Genetic variants in epoxyeicosatrienoic acid processing and degradation pathways are associated with gestational diabetes mellitus

AIM

To explore the genetic effects of CYP2C8, CYP2C9, CYP2J2, and EPHX2, the key genes involved in epoxyeicosatrienoic acid processing and degradation pathways in gestational diabetes mellitus (GDM) and metabolic traits in Chinese pregnant women.

METHODS

A total of 2548 unrelated pregnant women were included, of which 938 had GDM and 1610 were considered as controls. Common variants were genotyped using the Infinium Asian Screening Array. Association studies of single nucleotide polymorphisms (SNPs) with GDM and related traits were performed using logistic regression and multivariable linear regression analyses. A genetic risk score (GRS) model based on 12 independent target SNPs associated with GDM was constructed. Logistic regression was used to estimate odds ratios and 95% confidence intervals, adjusting for potential confounders including age, pre-pregnancy body mass index, history of polycystic ovarian syndrome, history of GDM, and family history of diabetes, with GRS entered both as a continuous variable and categorized groups. The relationship between GRS and quantitative traits was also evaluated.

RESULTS

The 12 SNPs in CYP2C8, CYP2C9, CYP2J2, and EPHX2 were significantly associated with GDM after adjusting for covariates (all P < 0.05). The GRS generated from these SNPs significantly correlated with GDM. Furthermore, a significant interaction between CYP2J2 and CYP2C8 in GDM (P_Interaction = 0.014, OR_Interaction= 0.61, 95%CI 0.41-0.90) was observed.

CONCLUSION

We found significant associations between GDM susceptibility and 12 SNPs of the four genes involved in epoxyeicosatrienoic acid processing and degradation pathways in a Chinese population. Subjects with a higher GRS showed higher GDM susceptibility with higher fasting plasma glucose and area under the curve of glucose and poorer β-cell function.

Common single-nucleotide polymorphisms combined with a genetic risk score provide new insights regarding the etiology of gestational diabetes mellitus

AIMS

Few studies have constructed a genetic risk score (GRS) to predict the risk of gestaional diabetes mellitus (GDM). We tested the hypothesis that single-nucleotide polymorphisms (SNPs) confirmed for diabetes and obesity and the GRS are associated with GDM.

METHODS

We conducted a case-control study comprising 971 GDM cases and 1682 controls from the University of Hong Kong Shenzhen Hospital. A total of 1448 SNPs reported with type 2 diabetes (T2D), type 1 diabetes (T1D), and obesity were selected and the GRS based on SNPs associated with GDM was created.

RESULTS

We confirmed that rs10830963 (OR = 1.41,95% CI = 1.25, 1.59) in MTNR1B and rs2206734 (OR = 1.38, 95% CI = 1.22, 1.55) in CDKAL1 were strongly associated with the risk of GDM. Compared with participants with GRS based on T2D SNPs in the low tertile, the ORs of GDM across increasing GRS tertiles were 1.63 (95% CI 1.29, 2.06) and 2.72 (95% CI 2.18, 3.38) in the middle and high tertile, respectively. The positive associations between the GRS and the risk of GDM were also observed in GRS based on obesity/waist-to-hip ratio (WHR)/body mass index (BMI) SNPs. The resulting GRS for each allele increase was significantly associated with higher glycemic indices and lower HOMA-B values for GRS based on T2D SNPs, but not for GRS based on T1D SNPs and GRS based on obesity/WHR/BMI SNPs.

CONCLUSION

These findings indicate that GDM may share a common genetic background with T2D and obesity and that SNPs associated with insulin secretion defects have a vital role in the development of GDM.

Circulating levels of DLK1 and glucose homeostasis in girls with obesity: A pilot study

INTRODUCTION

DLK1 gene is considered a molecular gatekeeper of adipogenesis. DLK1 mutations have been reported as a cause of central precocious puberty associated with obesity and metabolic syndrome with undetectable DLK1 serum levels. We investigated the association between DLK1 circulating levels with clinical and biochemical parameters in obese adolescents and healthy controls.

METHODS

Sixty-five obese adolescents and 40 controls were enrolled and underwent a complete clinical examination and biochemical assessment for glucose homeostasis and DLK1 plasma levels.

RESULTS

We observed lower DLK1 levels in cases compared to controls. Moreover, we found a negative correlation between DLK1 and HOMA-IR and a direct correlation with insulin-sensitivity index.

DISCUSSION

Our findings suggest that DLK1 might be involved in metabolic derangement in obese children.

Imprinted Genes Impact Upon Beta Cell Function in the Current (and Potentially Next) Generation

Beta cell failure lies at the centre of the aetiology and pathogenesis of type 2 diabetes and the epigenetic control of the expression of critical beta cell genes appears to play a major role in this decline. One such group of epigenetically-controlled genes, termed 'imprinted' genes, are characterised by transgenerational monoallelic expression due to differential allelic DNA methylation and play key functional roles within beta cells. Here, we review the evidence for this functional importance of imprinted genes in beta cells as well as their nutritional regulation by the diet and their altered methylation and/or expression in rodent models of diabetes and in type 2 diabetic islets. We also discuss imprinted genes in the context of the next generation, where dietary overnutrition in the parents can lead to their deregulation in the offspring, alongside beta cell dysfunction and defective glucose handling. Both the modulation of imprinted gene expression and the likelihood of developing type 2 diabetes in adulthood are susceptible to the impact of nutritional status in early life. Imprinted loci, therefore, represent an excellent opportunity with which to assess epigenomic changes in beta cells due to the diet in both the current and next generation.

Preadipocyte factor 1 regulates adipose tissue browning via TNF-α-converting enzyme-mediated cleavage

BACKGROUND

Increasing adaptive thermogenesis in adipose tissue may be a potential therapeutic target for overcoming obesity and obesity-related disorders. Preadipocyte factor 1 (Pref-1), a preadipocyte secreted protein, plays an inhibitory role in adipogenic differentiation. However, the role of Pref-1 in adipose tissue browning remains unknown. We investigated whether Pref-1 regulates thermogenic program and beige fat biogenesis.

METHODS

Pref-1 expression levels were examined in inguinal white adipose tissue (iWAT) and differentiated 3T3-L1 adipocytes in thermogenic conditions induced by cold exposure or a beta-adrenergic stimulus (CL316,243). Overexpression and knockdown studies were performed both in vivo and in vitro to clarify the role of Pref-1 in iWAT browning.

RESULTS

Cold exposure or CL316,243 induced a thermogenic program in adipose tissue of C57BL/6N mice and in 3T3-L1 adipocytes. Notably, Pref-1 levels were down-regulated in iWAT and adipocytes under these conditions. Overexpressing Pref-1 showed reduced thermogenic gene expressions in response to CL316,243 treatment, whereas depletion of Pref-1 augmented thermogenic program in 3T3-L1 adipocytes. Correspondingly, treating C57BL/6N mice with Pref-1 resulted in reduced expression of thermogenic and beige fat markers, a reduced rate of oxygen consumption, blunting of UCP1 expression and beige fat formation in iWAT in response to cold exposure or CL316,243 injection compared to the untreated mice. The opposite phenotype was observed in mice with inducible fat-specific knock-out of Pref-1. Mechanistically, these effects were regulated by modulation of TNF-α-converting enzyme activity and Pref-1 cleavage.

CONCLUSION

Our findings establish a novel role of Pref-1 that regulates adaptive thermogenesis. This offers a unique target for improving energy homeostasis and treating obesity.

The imprinted gene Delta like non-canonical notch ligand 1 (Dlk1) associates with obesity and triggers insulin resistance through inhibition of skeletal muscle glucose uptake

BACKGROUND

The imprinted gene Delta like non-canonical Notch ligand 1 (Dlk1) is considered an inhibitor of adipogenesis, but its in vivo impact on fat mass indeed remains elusive and controversial.

METHODS

Fat deposits were assessed by MRI and DXA scanning in two cohorts of non-diabetic men, whereas glucose disposal rate (GDR) was determined during euglycemic hyperinsulinemic clamp. Blood analyte measurements were used for correlation and mediation analysis to investigate how age, BMI, and fat percentage affect the relation between DLK1 and GDR. Confirmatory animal studies performed in normal (NC) and high fat diet (HFD) fed Dlk1^+/+ and Dlk1^-/- mice included DXA scanning, glucose tolerance tests (GTTs), blood measurements, and skeletal muscle glucose uptake studies by positron emission tomography (PET), histology, qRT-PCR, and in vitro cell studies.

FINDINGS

Overall, DLK1 is positively correlated with fat amounts, which is consistent with a negative linear relationship between DLK1 and GDR. This relationship is not mediated by age, BMI, or fat percentage. In support, DLK1 also correlates positively with HOMA-IR and ADIPO-IR in these humans, but has no linear relationship with the early diabetic inflammation marker MCP-1. In Dlk1^-/- mice, the increase in fat percentage and adipocyte size induced by HFD is attenuated, and these animals are protected against insulin resistance. These Dlk1 effects seem independent of gluconeogenesis, but at least partly relies on increased in vivo glucose uptake in skeletal muscles by Dlk1 regulating the major glucose transporter Glut4 in vivo as well as in two independent cell lines.

INTERPRETATION

Thus, instead of an adipogenic inhibitor, Dlk1 should be regarded as a factor causally linked to obesity and insulin resistance, and may be used to predict development of type 2 diabetes. FUND: The Danish Diabetes Academy supported by the Novo Nordisk Foundation, The Danish National Research Council (#09-073648), The Lundbeck Foundation, University of Southern Denmark, and Dep. Of Clinical Biochemistry and Pharmacology/Odense University Hospital, the Swedish Research Council, the Swedish Diabetes Foundation, the Strategic Research Program in Diabetes at Karolinska Institute and an EFSD/Lilly grant.

Serum Betatrophin Concentrations and the Risk of Incident Diabetes: A Nested Case-Control Study from Chungju Metabolic Disease Cohort

BACKGROUND

Betatrophin is a newly identified hormone derived from the liver and adipose tissue, which has been suggested to regulate glucose and lipid metabolism. Circulating levels of betatrophin are altered in various metabolic diseases, although the results are inconsistent. We aimed to examine whether betatrophin is a useful biomarker in predicting the development of diabetes.

METHODS

A nested case-control study was performed using a prospective Chungju Metabolic disease Cohort Study. During a 4-year follow-up period, we analyzed 167 individuals who converted to diabetes and 167 non-converters, who were matched by age, sex, and body mass index. Serum betatrophin levels were measured by an ELISA (enzyme-linked immunosorbent assay).

RESULTS

Baseline serum betatrophin levels were significantly higher in the converter group compared to the non-converter group (1,315±598 pg/mL vs. 1,072±446 pg/mL, P<0.001). After adjusting for age, sex, body mass index, fasting plasma glucose, systolic blood pressure, total cholesterol, and family history of diabetes, the risk of developing diabetes showed a stepwise increase across the betatrophin quartile groups. Subjects in the highest baseline quartile of betatrophin levels had more than a threefold higher risk of incident diabetes than the subjects in the lowest quartile (relative risk, 3.275; 95% confidence interval, 1.574 to 6.814; P=0.010). However, no significant relationships were observed between serum betatrophin levels and indices of insulin resistance or β-cell function.

CONCLUSION

Circulating levels of betatrophin could be a potential biomarker for predicting new-onset diabetes. Further studies are needed to understand the underlying mechanism of this association.

Preadipocyte factor 1 induces pancreatic ductal cell differentiation into insulin-producing cells

The preadipocyte factor 1 (Pref-1) is involved in the proliferation and differentiation of various precursor cells. However, the intracellular signaling pathways that control these processes and the role of Pref-1 in the pancreas remain poorly understood. Here, we showed that Pref-1 induces insulin synthesis and secretion via two independent pathways. The overexpression of Pref-1 activated MAPK signaling, which induced nucleocytoplasmic translocation of FOXO1 and PDX1 and led to the differentiation of human pancreatic ductal cells into β-like cells and an increase in insulin synthesis. Concurrently, Pref-1 activated Akt signaling and facilitated insulin secretion. A proteomics analysis identified the Rab43 GTPase-activating protein as a downstream target of Akt. A serial activation of both proteins induced various granular protein syntheses which led to enhanced glucose-stimulated insulin secretion. In a pancreatectomised diabetic animal model, exogenous Pref-1 improved glucose homeostasis by accelerating pancreatic ductal and β-cell regeneration after injury. These data establish a novel role for Pref-1, opening the possibility of applying this molecule to the treatment of diabetes.