DLK1/PREF1 regulates nutrient metabolism and protects from steatosis

Enrichment of trimethyl histone 3 lysine 4 in the Dlk1 and Grb10 genes affects pregnancy outcomes due to dietary manipulation of excess folic acid and low vitamin B12

The aberrant expression of placental imprinted genes due to epigenetic alterations during pregnancy can impact fetal development. We investigated the impact of dietary modification of low vitamin B12 with varying doses of folic acid on the epigenetic control of imprinted genes and fetal development using a transgenerational model of C57BL/6J mice. The animals were kept on four distinct dietary combinations based on low vitamin B12 levels and modulated folic acid, mated in the F0 generation within each group. In the F1 generation, each group of mice is split into two subgroups; the sustained group was kept on the same diet, while the transient group was fed a regular control diet. After mating, maternal placenta (F1) and fetal tissues (F2) were isolated on day 20 of gestation. We observed a generation-wise opposite promoter CpG methylation and gene expression trend of the two developmental genes Dlk1 and Grb10, with enhanced gene expression in both the sustained and transient experimental groups in F1 placentae. When fetal development characteristics and gene expression were correlated, there was a substantial negative association between placental weight and Dlk1 expression (r = - 0.49, p < 0.05) and between crown-rump length and Grb10 expression (r = - 0.501, p < 0.05) in fetuses of the F2 generation. Consistent with these results, we also found that H3K4me3 at the promoter level of these genes is negatively associated with all fetal growth parameters. Overall, our findings suggest that balancing vitamin B12 and folic acid levels is important for maintaining the transcriptional status of imprinted genes and fetal development.

The long non-coding RNA Meg3 mediates imprinted gene expression during stem cell differentiation

The imprinted Dlk1-Dio3 domain comprises the developmental genes Dlk1 and Rtl1, which are silenced on the maternal chromosome in different cell types. On this parental chromosome, the domain's imprinting control region activates a polycistron that produces the lncRNA Meg3 and many miRNAs (Mirg) and C/D-box snoRNAs (Rian). Although Meg3 lncRNA is nuclear and associates with the maternal chromosome, it is unknown whether it controls gene repression in cis. We created mouse embryonic stem cells (mESCs) that carry an ectopic poly(A) signal, reducing RNA levels along the polycistron, and generated Rian-/- mESCs as well. Upon ESC differentiation, we found that Meg3 lncRNA (but not Rian) is required for Dlk1 repression on the maternal chromosome. Biallelic Meg3 expression acquired through CRISPR-mediated demethylation of the paternal Meg3 promoter led to biallelic Dlk1 repression, and to loss of Rtl1 expression. lncRNA expression also correlated with DNA hypomethylation and CTCF binding at the 5'-side of Meg3. Using Capture Hi-C, we found that this creates a Topologically Associating Domain (TAD) organization that brings Meg3 close to Dlk1 on the maternal chromosome. The requirement of Meg3 for gene repression and TAD structure may explain how aberrant MEG3 expression at the human DLK1-DIO3 locus associates with imprinting disorders.

Metabolic liability for weight gain in early adulthood

While weight gain is associated with a host of chronic illnesses, efforts in obesity have relied on single "snapshots" of body mass index (BMI) to guide genetic and molecular discovery. Here, we study >2,000 young adults with metabolomics and proteomics to identify a metabolic liability to weight gain in early adulthood. Using longitudinal regression and penalized regression, we identify a metabolic signature for weight liability, associated with a 2.6% (2.0%-3.2%, p = 7.5 × 10-19) gain in BMI over ≈20 years per SD higher score, after comprehensive adjustment. Identified molecules specified mechanisms of weight gain, including hunger and appetite regulation, energy expenditure, gut microbial metabolism, and host interaction with external exposure. Integration of longitudinal and concurrent measures in regression with Mendelian randomization highlights the complexity of metabolic regulation of weight gain, suggesting caution in interpretation of epidemiologic or genetic effect estimates traditionally used in metabolic research.

DLK1: A Novel Biomarker of Placental Insufficiency in Stillbirth and Live Birth

OBJECTIVE

Delta-like homolog 1 (DLK1) is a growth factor that is reduced in maternal sera in pregnancies with small for gestational age neonates. We sought to determine if DLK1 is associated with stillbirth (SB), with and without placental insufficiency.

STUDY DESIGN

A nested case-control study was performed using maternal sera from a multicenter case-control study of SB and live birth (LB). SB and LB were stratified as placental insufficiency cases (small for gestational age <5% or circulatory lesions on placental histopathology) or normal placenta controls (appropriate for gestational age and no circulatory lesions). Enzyme-linked immunosorbent assay (ELISA) was used to measure DLK1. The mean difference in DLK1 was compared on the log scale in an adjusted linear regression model with pairwise differences, stratified by term/preterm deliveries among DLK1 results in the quantifiable range. In exploratory analysis, geometric means were compared among all data and the proportion of "low DLK1" (less than the median value for gestational age) was compared between groups and modeled using linear and logistic regression, respectively.

RESULTS

Overall, 234 SB and 234 LB were analyzed; 246 DLK1 values were quantifiable within the standard curve. Pairwise comparisons of case and control DLK1 geometric means showed no significant differences between groups. In exploratory analysis of all data, adjusted analysis revealed a significant difference for the LB comparison only (SB: 71.9 vs. 99.1 pg/mL, p = 0.097; LB: 37.6 vs. 98.1 pg/mL, p = 0.005). In exploratory analysis of "low DLK1," there was a significant difference between the odds ratio of having "low DLK1" between preterm cases and controls for both SB and LB. There were no significant differences in geometric means nor "low DLK1" between SB and LB.

CONCLUSION

In exploratory analysis, more placental insufficiency cases in preterm SB and LB had "low DLK1." However, low DLK1 levels were not associated with SB.

KEY POINTS

· Maternally circulating DLK1 is correlated with placental insufficiency.. · Maternally circulating DLK1 is not correlated with SB.. · DLK1 is a promising marker for placental insufficiency..

Evaluation of preadipocyte factor-1 (Pref-1) level in cord blood of newborns born by mothers with gestational diabetes mellitus (GDM)

BACKGROUND

Gestational diabetes mellitus (GDM) is the most common metabolic complication, which leads to short and long-term consequences in both mother and fetus exposed to hyperglycemia. The aetiology of this condition is proposed to be based on the dysfunction of the adipose tissue, which is characterised by the aberrant generation of adipokines. One of them is preadipocyte factor-1 (Pref-1), which could mediate controlling the adaptation of the maternal metabolism to pregnancy.

AIMS

The study aims to examine the level of Pref-1 in the cord blood of healthy pregnant women's neonates and fetuses born to mothers with GDM.

MATERIALS AND METHODS

Cord blood samples were collected from 30 newborns of mothers with GDM and 40 newborns of healthy pregnant women. Pref-1 concentrations were measured with an ELISA kit.

RESULTS

Fetal Pref-1 concentrations were significantly lower in newborns of mothers with GDM compared to the normal pregnancy group children (5.32 ± 0.29 vs. 7.38 ± 0.53; p < 0.001). Mothers with GDM had a significantly higher index of BMI before pregnancy, maternal gestational weight gain, and maternal fasting glucose. In-depth analysis through multiple variant linear regression revealed a significant association between fetal serum Pref-1 levels, exposure to GDM, and gestational age.

CONCLUSION

These findings contribute valuable insights into maternal-fetal health and pave the way for more targeted and effective clinical interventions.

Preconceptional and in utero exposure of sheep to a real-life environmental chemical mixture disrupts key markers of energy metabolism in male offspring

Over recent decades, an extensive array of anthropogenic chemicals have entered the environment and have been implicated in the increased incidence of an array of diseases, including metabolic syndrome. The ubiquitous presence of these environmental chemicals (ECs) necessitates the use of real-life exposure models to the assess cumulative risk burden to metabolic health. Sheep that graze on biosolids-treated pastures are exposed to a real-life mixture of ECs such as phthalates, per- and polyfluoroalkyl substances, heavy metals, pharmaceuticals, pesticides, and metabolites thereof, and this EC exposure can result in metabolic disorders in their offspring. Using this model, we evaluated the effects of gestational exposure to a complex EC mixture on plasma triglyceride (TG) concentrations and metabolic and epigenetic regulatory genes in tissues key to energy regulation and storage, including the hypothalamus, liver, and adipose depots of 11-month-old male offspring. Our results demonstrated a binary effect of EC exposure on gene expression particularly in the hypothalamus. Principal component analysis revealed two subsets (B-S1 [n = 6] and B-S2 [n = 4]) within the biosolids group (B, n = 10), relative to the controls (C, n = 11). Changes in body weight, TG levels, and in gene expression in the hypothalamus, and visceral and subcutaneous fat were apparent between biosolid and control and the two subgroups of biosolids animals. These findings demonstrate that gestational exposure to an EC mixture results in differential regulation of metabolic processes in adult male offspring. Binary effects on hypothalamic gene expression and altered expression of lipid metabolism genes in visceral and subcutaneous fat, coupled with phenotypic outcomes, point to differences in individual susceptibility to EC exposure that could predispose vulnerable individuals to later metabolic dysfunction.

Familial central precocious puberty due to DLK1 deficiency: novel genetic findings and relevance of serum DLK1 levels

BACKGROUND

Several rare loss-of-function mutations of delta-like noncanonical notch ligand 1 (DLK1) have been described in non-syndromic children with familial central precocious puberty (CPP).

OBJECTIVE

We investigated genetic abnormalities of DLK1 gene in a French cohort of children with idiopathic CPP. Additionally, we explored the pattern of DLK1 serum levels in patients with CPP and in healthy children at puberty, as well as in wild-type female mice.

PATIENTS AND METHODS

Genomic DNA was obtained from 121 French index cases with CPP. Automated sequencing of the coding region of the DLK1 gene was performed in all cases. Serum DLK1 levels were measured by enzyme linked immunosorbent assay (ELISA) in 209 individuals, including 191 with normal pubertal development and in female mice during postnatal pubertal maturation.

RESULTS

We identified 2 rare pathogenic DLK1 allelic variants: A stop gain variant (c.372C>A; p.Cys124X) and a start loss variant (c.2T>G; p.Met1?, or p.0) in 2 French girls with CPP. Mean serum DLK1 levels were similar between healthy children and idiopathic CPP children. In healthy individuals, DLK1 levels correlated with pubertal stage: In girls, DLK1 decreased between Tanner stages III and V, whereas in boys, DLK1 decreased between Tanner stages II and V (P = .008 and .016, respectively). Serum levels of Dlk1 also decreased in wild-type female mice.

CONCLUSIONS

Novel loss-of-function mutations in DLK1 gene were identified in 2 French girls with CPP. Additionally, we demonstrated a pattern of dynamic changes in circulating DLK1 serum levels in humans and mice during pubertal stages, reinforcing the role of this factor in pubertal timing.

Imprinted Dlk1 dosage as a size determinant of the mammalian pituitary gland

Co-regulated genes of the Imprinted Gene Network are involved in the control of growth and body size, and imprinted gene dysfunction underlies human paediatric disorders involving the endocrine system. Imprinted genes are highly expressed in the pituitary gland, among them, Dlk1, a paternally expressed gene whose membrane-bound and secreted protein products can regulate proliferation and differentiation of multiple stem cell populations. Dosage of circulating DLK1 has been previously implicated in the control of growth through unknown molecular mechanisms. Here we generate a series of mouse genetic models to modify levels of Dlk1 expression in the pituitary gland and demonstrate that the dosage of DLK1 modulates the process of stem cell commitment with lifelong impact on pituitary gland size. We establish that stem cells are a critical source of DLK1, where embryonic disruption alters proliferation in the anterior pituitary, leading to long-lasting consequences on growth hormone secretion later in life.

The development of blood protein profiles in extremely preterm infants follows a stereotypic evolution pattern

BACKGROUND

Preterm birth is the leading cause of neonatal mortality and morbidity. Early diagnosis and interventions are critical to improving the clinical outcomes of extremely premature infants. Blood protein profiling during the first months of life in preterm infants can shed light on the role of early extrauterine development and provide an increased understanding of maturation after extremely preterm birth and the underlying mechanisms of prematurity-related disorders.

METHODS

We have investigated the blood protein profiles during the first months of life in preterm infants on the role of early extrauterine development. The blood protein levels were analyzed using next generation blood profiling on 1335 serum samples, collected longitudinally at nine time points from birth to full-term from 182 extremely preterm infants.

RESULTS

The protein analysis reveals evident predestined serum evolution patterns common for all included infants. The majority of the variations in blood protein expression are associated with the postnatal age of the preterm infants rather than any other factors. There is a uniform protein pattern on postnatal day 1 and after 30 weeks postmenstrual age (PMA), independent of gestational age (GA). However, during the first month of life, GA had a significant impact on protein variability.

CONCLUSIONS

The unified pattern of protein development for all included infants suggests an age-dependent stereotypic development of blood proteins after birth. This knowledge should be considered in neonatal settings and might alter the clinical approach within neonatology, where PMA is today the most dominant age variable.

A pref-1-controlled non-inflammatory mechanism of insulin resistance

While insulin resistance (IR) is associated with inflammation in white adipose tissue, we report a non-inflammatory adipose mechanism of high fat-induced IR mediated by loss of Pref-1. Pref-1, released from adipose Pref-1+ cells with characteristics of M2 macrophages, endothelial cells or progenitors, inhibits MIF release from both Pref-1+ cells and adipocytes by binding with integrin β1 and inhibiting the mobilization of p115. High palmitic acid induces PAR2 expression in Pref-1+ cells, downregulating Pref-1 expression and release in an AMPK-dependent manner. The loss of Pref-1 increases adipose MIF secretion contributing to non-inflammatory IR in obesity. Treatment with Pref-1 blunts the increase in circulating plasma MIF levels and subsequent IR induced by a high palmitic acid diet. Thus, high levels of fatty acids suppress Pref-1 expression and secretion, through increased activation of PAR2, resulting in an increase in MIF secretion and a non-inflammatory adipose mechanism of IR.

The Congenital and Acquired Mechanisms Implicated in the Etiology of Central Precocious Puberty

The etiology of central precocious puberty (CPP) is multiple and heterogeneous, including congenital and acquired causes that can be associated with structural or functional brain alterations. All causes of CPP culminate in the premature pulsatile secretion of hypothalamic GnRH and, consequently, in the premature reactivation of hypothalamic-pituitary-gonadal axis. The activation of excitatory factors or suppression of inhibitory factors during childhood represent the 2 major mechanisms of CPP, revealing a delicate balance of these opposing neuronal pathways. Hypothalamic hamartoma (HH) is the most well-known congenital cause of CPP with central nervous system abnormalities. Several mechanisms by which hamartoma causes CPP have been proposed, including an anatomical connection to the anterior hypothalamus, autonomous neuroendocrine activity in GnRH neurons, trophic factors secreted by HH, and mechanical pressure applied to the hypothalamus. The importance of genetic and/or epigenetic factors in the underlying mechanisms of CPP has grown significantly in the last decade, as demonstrated by the evidence of genetic abnormalities in hypothalamic structural lesions (eg, hamartomas, gliomas), syndromic disorders associated with CPP (Temple, Prader-Willi, Silver-Russell, and Rett syndromes), and isolated CPP from monogenic defects (MKRN3 and DLK1 loss-of-function mutations). Genetic and epigenetic discoveries involving the etiology of CPP have had influence on the diagnosis and familial counseling providing bases for potential prevention of premature sexual development and new treatment targets in the future. Global preventive actions inducing healthy lifestyle habits and less exposure to endocrine-disrupting chemicals during the lifespan are desirable because they are potentially associated with CPP.

Vitamin A: A Key Inhibitor of Adipocyte Differentiation

Inhibiting adipocyte differentiation, the conversion of preadipocytes to mature functional adipocytes, might represent a new approach to treating obesity and related metabolic disorders. Peroxisome proliferator-activated receptor γ and CCAAT-enhancer-binding protein α are two master coregulators controlling adipogenesis both in culture and in vivo. Many recent studies have confirmed the relationship between retinoic acid (RA) and the conversion of embryonic stem cells into adipocytes; however, these studies have shown that RA potently blocks the differentiation of preadipocytes into mature adipocytes. Nevertheless, the functional role of RA in early tissue development and stem cell differentiation, including in adipose tissue, remains unclear. This study highlights transcription factors that block adipocyte differentiation and maintain preadipocyte status, focusing on those controlled by RA. However, some of these novel adipogenesis inhibitors have not been validated in vivo, and their mechanisms of action require further clarification.

Paternal dietary ratio of n-6: n-3 polyunsaturated fatty acids programs offspring leptin expression and gene imprinting in mice

Background

This study determined the effects of the paternal dietary ratio of n-6: n-3 polyunsaturated fatty acids (PUFAs) on leptin expression in the offspring and associated gene imprinting in a mouse model.

Methods

Three- to four-week-old male C57BL/6J mice (F0) were fed an n-3 PUFA-deficient (n-3 D) diet, a diet with normal n-3 PUFA content (n-3 N; n-6: n-3 = 4.3:1), or a diet with a high n-3 PUFA content (n-3 H; n-6: n-3 = 1.5:1) for 8 weeks. Two subsequent generations were generated by mating F0 and F1 male mice with 10-week-old virgin female C57 BL/6J mice, to produce F1 and F2 offspring.

Results

Compared to the paternal n-3 D diet, paternal n-3 N and n-3 H diets reduced adipose mRNA expression of leptin (Lep) and its plasma concentrations in juvenile F1 male and female offspring, and adult F1 male and F2 female offspring, with upregulated Lep receptor mRNA expression in the hypothalamus. Meanwhile, paternal n-3 N and n-3 H diets altered the expression of the imprinted genes H19, Igf2, Igf2r, Plagl1, Cdkn1c, Kcnq1ot1, Peg3, and Grb10 in the adipose tissue of juvenile and adult F1 males, with almost no effects on F1 females, while more effects were observed in the adult F2 females than F2 males. Principal component analysis verified that Plagl1, Cdkn1c, and Kcnq1ot1 contributed the most to variation in adipose tissue expression in all offspring. Some of these genes (Plagl1, Cdkn1c, Kcnq1ot1, Peg3, and Grb10) were altered by the paternal n-3 N and n-3 H diets in the F1 and F2 generation testes as well. Furthermore, adipose Lep expression was positively correlated with expressions of H19, Igf2r, Plagl1, and Kcnq1ot1 in juvenile F1 males and females, negatively correlated with the Kcnq1ot1 expression in adult F1 males, and positively correlated with the Plagl1 expression in adult F2 females.

Conclusion

These data imply that paternal Plagl1, Cdkn1c, and Kcnq1ot1 might be part of the pathways involved in offspring leptin programming. Therefore, a lower ratio of n-6: n-3 PUFAs, with higher intake of n-3 PUFAs in paternal pre-conception, may help maintain the offspring's optimal leptin pattern in a sex-specific manner through multiple generations, and thereby, be beneficial for the offspring's long-term health.

Systematic investigation of imprinted gene expression and enrichment in the mouse brain explored at single-cell resolution

BACKGROUND

Although a number of imprinted genes are known to be highly expressed in the brain, and in certain brain regions in particular, whether they are truly over-represented in the brain has never been formally tested. Using thirteen single-cell RNA sequencing datasets we systematically investigated imprinted gene over-representation at the organ, brain region, and cell-specific levels.

RESULTS

We established that imprinted genes are indeed over-represented in the adult brain, and in neurons particularly compared to other brain cell-types. We then examined brain-wide datasets to test enrichment within distinct brain regions and neuron subpopulations and demonstrated over-representation of imprinted genes in the hypothalamus, ventral midbrain, pons and medulla. Finally, using datasets focusing on these regions of enrichment, we identified hypothalamic neuroendocrine populations and the monoaminergic hindbrain neurons as specific hotspots of imprinted gene expression.

CONCLUSIONS

These analyses provide the first robust assessment of the neural systems on which imprinted genes converge. Moreover, the unbiased approach, with each analysis informed by the findings of the previous level, permits highly informed inferences about the functions on which imprinted gene expression converges. Our findings indicate the neuronal regulation of motivated behaviours such as feeding and sleep, alongside the regulation of pituitary function, as functional hotspots for imprinting. This adds statistical rigour to prior assumptions and provides testable predictions for novel neural and behavioural phenotypes associated with specific genes and imprinted gene networks. In turn, this work sheds further light on the potential evolutionary drivers of genomic imprinting in the brain.

Comparative transcriptome analysis of longissimus dorsi tissues with different intramuscular fat contents from Guangling donkeys

Background

Donkey meat has low fat and high protein contents and is rich in various unsaturated fatty acids and trace elements that are beneficial to human digestion and absorption. IMF (intramuscular fat), also known as marbling, is an important indicator of the lean meat to fat ratio, which directly affects the tenderness and juiciness of the meat. At present, the underlying molecular variations affecting IMF content among donkey breeds are unclear. The Guangling donkey is an indigenous species in China. This study explored candidate regulatory genes that affect IMF content in Guangling donkeys. The IMF content of the longissimus dorsi muscle in 30 Guangling donkeys was measured. Six donkeys of similar age were selected according to age factors and divided into two groups, the high (H) and low (L) fat groups, according to their IMF content.

Results

RNA-seq technology was used to compare the muscle transcriptome between the two groups. More than 75.0% of alternative splicing (AS) events were of the skipped exon (SE) type. A total of 887 novel genes were identified; only 386 novel genes were aligned to the annotation information of various databases. Transcriptomics analysis revealed 167 differentially expressed genes (DEGs), of which 64 were upregulated and 103 were downregulated between the H and L groups. Gene ontology analysis showed that the DEGs were enriched in multiple biological processes and pathways that are related to adipocyte differentiation, lipid synthesis, and neutral lipid metabolism. KEGG pathway analysis suggested that arachidonic acid metabolism, the HIF-1 signalling pathway, fructose and mannose metabolism, glycerophospholipid metabolism, and the AMPK signalling pathway were involved in lipid deposition. In addition, a gene–gene interaction network was constructed that revealed that the DEGs, including SCD, LEPR, CIDEA, DLK1, DGAT2, ITGAL, HMOX1, WNT10B, and DGKA, had significant roles in adipocyte differentiation and adipogenesis. The selected DEGs were further validated by qRT–PCR.

Conclusion

This study improves the in-depth understanding of gene regulation and protein expression regarding IMF deposition and lays a basis for subsequent molecular breeding studies in Guangling donkeys.

Pituitary Tumor-Transforming Gene 1/Delta like Non-Canonical Notch Ligand 1 Signaling in Chronic Liver Diseases

The management of chronic liver diseases (CLDs) remains a challenge, and identifying effective treatments is a major unmet medical need. In the current review we focus on the pituitary tumor transforming gene (PTTG1)/delta like non-canonical notch ligand 1 (DLK1) axis as a potential therapeutic target to attenuate the progression of these pathological conditions. PTTG1 is a proto-oncogene involved in proliferation and metabolism. PTTG1 expression has been related to inflammation, angiogenesis, and fibrogenesis in cancer and experimental fibrosis. On the other hand, DLK1 has been identified as one of the most abundantly expressed PTTG1 targets in adipose tissue and has shown to contribute to hepatic fibrosis by promoting the activation of hepatic stellate cells. Here, we extensively analyze the increasing amount of information pointing to the PTTG1/DLK1 signaling pathway as an important player in the regulation of these disturbances. These data prompted us to hypothesize that activation of the PTTG1/DLK1 axis is a key factor upregulating the tissue remodeling mechanisms characteristic of CLDs. Therefore, disruption of this signaling pathway could be useful in the therapeutic management of CLDs.

Maternal Serum Delta-Like 1 and Nesfatin-1 Levels in Gestational Diabetes Mellitus: A Prospective Case-Control Study

Objective

Delta-like 1 (DLK1) and nesfatin-1 are adipokines that have been shown to affect glucose metabolism. We aimed to search serum DLK1 and nesfatin-1 concentrations at 24-28 weeks of pregnancy in women newly defined with gestational diabetes mellitus (GDM) and investigate the relationship of these adipokines with various metabolic parameters.

Methods

Serum levels of DLK1 and nesfatin-1 were evaluated in 44 women with GDM, and in 40 healthy pregnant women by enzyme-linked immunosorbent assay (ELISA) kits. While performing oral glucose tolerance test (OGTT) for GDM diagnosis at 24-28 weeks of pregnancy, homeostasis model assessment of insulin resistance (HOMA-IR), lipid profiles, glycosylated hemoglobin (HbA1c) were also measured.

Results

Maternal serum DLK1 and nesfatin-1 concentrations were found lower in pregnant women with GDM compared with healthy pregnant women (418.4±282.6 vs. 586.7±303 ng/L, p=0.002; 12.2±7.6 vs. 26.7±16.4 ng/ml, p<0.001, respectively). Maternal serum DLK1 levels correlated positively with HOMA-IR and fasting insulin (r=0.395, p=0.008; r=0.374, p=0.012, respectively).

Conclusion

We determined that DLK1 and nesfatin-1 levels were lower in GDM. Based on this study, it may be considered that DLK1 could be culpable for metabolic disorders in GDM.

Lack of miR-379/miR-544 Cluster Resists High-Fat Diet-Induced Obesity and Prevents Hepatic Triglyceride Accumulation in Mice

Non-alcoholic fatty liver disease (NAFLD) affects obesity-associated metabolic syndrome, which exhibits hepatic steatosis, insulin insensitivity and glucose intolerance. Emerging evidence suggests that microRNAs (miRNAs) are essential for the metabolic homeostasis of liver tissues. Many hepatic miRNAs located in the miR-379/miR-544 cluster were significantly increased in leptin-receptor-deficient type 2 mice (db/db), a mouse model of diabetes. However, the function of the miR-379/miR-544 cluster in the process of hepatic steatosis remains unclear. Here, we report that the novel function of miR-379/miR-544 cluster in regulating obesity-mediated metabolic dysfunction. Genetical mutation of miR-379/miR-544 cluster in mice displayed resistance to high-fat diet (HFD)-induced obesity with moderate hepatic steatosis and hypertriglyceridemia. In vitro studies revealed that silencing of miR-379 in human hepatocellular carcinoma (HepG2) cells ameliorated palmitic acid-induced elevation of cellular triglycerides, and overexpression of miR-379 had the opposite effect. Moreover, Igf1r (Insulin-like growth factor 1 receptor) and Dlk1 (Delta-like homolog 1) were directly targeted by miR-379 and miR-329, respectively, and elevated in the livers of the miR-379/miR-544 cluster knockout mice fed on HFD. Further transcriptome analyses revealed that the hepatic gene expressions are dysregulated in miR-379/miR-544 knockout mice fed with HFD. Collectively, our findings identify the miR-379/miR-544 cluster as integral components of a regulatory circuit that functions under conditions of metabolic stress to control hepatic steatosis. Thus, this miRNA cluster provides potential targets for pharmacologic intervention in obesity and NAFLD.

Screening of patients born small for gestational age with the Silver-Russell syndrome phenotype for DLK1 variants

Silver-Russell syndrome (SRS) is a rare imprinting disorder associated with prenatal and postnatal growth retardation. Loss of methylation (LOM) on chromosome 11p15 is observed in 40 to 60% of patients and maternal uniparental disomy (mUPD) for chromosome 7 (upd(7)mat) in ~5 to 10%. Patients with LOM or mUPD 14q32 can present clinically as SRS. Delta like non-canonical Notch ligand 1 (DLK1) is one of the imprinted genes expressed from chromosome 14q32. Dlk1-null mice display fetal growth restriction (FGR) but no genetic defects of DLK1 have been described in human patients born small for gestational age (SGA). We screened a cohort of SGA patients with a SRS phenotype for DLK1 variants using a next-generation sequencing (NGS) approach to search for new molecular defects responsible for SRS. Patients born SGA with a clinical suspicion of SRS and normal methylation by molecular testing at the 11p15 or 14q32 loci and upd(7)mat were screened for DLK1 variants using targeted NGS. Among 132 patients, only two rare variants of DLK1 were identified (NM_003836.6:c.103 G > C (p.(Gly35Arg) and NM_003836.6: c.194 A > G p.(His65Arg)). Both variants were inherited from the mother of the patients, which does not favor a role in pathogenicity, as the mono-allelic expression of DLK1 is from the paternal-inherited allele. We did not identify any pathogenic variants in DLK1 in a large cohort of SGA patients with a SRS phenotype. DLK1 variants are not a common cause of SGA.

Pregnancy Serum DLK1 Concentrations Are Associated With Indices of Insulin Resistance and Secretion

CONTEXT

Delta like noncanonical notch ligand 1 (DLK1) is a paternally expressed imprinted gene that encodes an epidermal growth factor repeat-containing transmembrane protein. A bioactive, truncated DLK1 protein is present in the circulation and has roles in development and metabolism.

OBJECTIVE

We sought to investigate links between maternal pregnancy circulating DLK1 concentrations and: (1) maternal and fetal DLK1 genotypes, (2) maternal insulin resistance and secretion, and (3) offspring size at birth.

PATIENTS, DESIGN, AND SETTING

We measured third-trimester maternal serum DLK1 concentrations and examined their associations with parentally transmitted fetal and maternal DLK1 genotypes, indices of maternal insulin resistance and secretion derived from 75-g oral glucose tolerance tests performed around week 28 of pregnancy, and offspring size at birth in 613 pregnancies from the Cambridge Baby Growth Study.

RESULTS

Maternal DLK1 concentrations were associated with the paternally transmitted fetal DLK1 rs12147008 allele (P = 7.8 × 10-3) but not with maternal rs12147008 genotype (P = 0.4). Maternal DLK1 concentrations were positively associated with maternal prepregnancy body mass index (P = 3.5 × 10-6), and (after adjustment for maternal body mass index) with both maternal fasting insulin resistance (Homeostatic Model Assessment of Insulin Resistance: P = 0.01) and measures of maternal insulin secretion in response to oral glucose (insulinogenic index: P = 1.2 × 10-3; insulin disposition index: P = 0.049). Further positive associations were found with offspring weight (P = 0.02) and head circumference at birth (P = 0.04).

CONCLUSION

These results are consistent with a partial paternal or placental origin for the maternal circulating DLK1 which may lead to increased maternal circulating DLK1 concentrations, stimulation of maternal insulin resistance and compensatory hyperinsulinemia during pregnancy, and the promotion of fetal growth.

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.

Functional characterization of DLK1/MEG3 locus on chromosome 14q32.2 reveals the differentiation of pituitary neuroendocrine tumors

Pituitary neuroendocrine tumors (PitNETs) represent the neoplastic proliferation of the anterior pituitary gland. Transcription factors play a key role in the differentiation of PitNETs. However, for a substantial proportion of PitNETs, the etiology is poorly understood. According to the transcription data of 172 patients, we found the imprinting disorders of the 14q32.2 region and DLK1/MEG3 locus associated with the differentiation of PitNETs. DLK1/MEG3 locus promoted somatotroph differentiation and inhibited tumor proliferation in PIT1(+) patients, furthermore, the level of DLK1 played a critical role in the trend of somatotroph or lactotroph differentiation. Anti-DLK1 monoclonal antibody blockade or siMEG3 both indicated that the DLK1/MEG3 significantly promoted the synthesis and secretion of GH/IGF-1 and inhibited cell proliferation. In addition, loss of DLK1 activated the mTOR signaling pathway in high DLK1-expressing and PIT1(+) GH3 cell lines, a mild effect in the low DLK1-expressing and PIT1(+) MMQ cell lines and no effect in the PIT1(-) ATT20 cell line. These findings emphasize that expression at the DLK1/MEG3 locus plays a key role in the differentiation of PitNETs, especially somatotroph adenomas, and provide potential molecular target data for patient stratification and treatment in the future.

DLK1 Expressed in Mouse Orexin Neurons Modulates Anxio-Depressive Behavior but Not Energy Balance

Lateral hypothalamic area (LHA) neurons expressing the neuropeptide orexin (OX) are implicated in obesity and anxio-depression. However, these neurons release OX as well as a host of other proteins that might contribute to normal physiology and disease states. We hypothesized that delta-like homolog 1 (DLK1), a protein reported to be co-expressed by all OX neurons, contributes to the regulation of energy balance and/or anxio-depression. Consistent with previous reports, we found that all rat OX neurons co-express DLK1. Yet, in mice and humans only a subset of OX neurons co-expressed DLK1. Since human OX-DLK1 distribution is more similar to mice than rats, mice are a comparable model to assess the human physiologic role of DLK1. We therefore used a viral lesion strategy to selectively delete DLK1 within the LHA of adult mice (DLK1^Null) to reveal its role in body weight and behavior. Adult-onset DLK1 deletion had no impact on body weight or ingestive behavior. However, DLK1^Null mice engaged in more locomotor activity than control mice and had decreased anxiety and depression measured via the elevated plus maze and forced swim tests. These data suggest that DLK1 expression via DLK1-expressing OX neurons primarily contributes to anxio-depression behaviors without impacting body weight.

NOTCH Receptors and DLK Proteins Enhance Brown Adipogenesis in Mesenchymal C3H10T1/2 Cells

The NOTCH family of receptors and ligands is involved in numerous cell differentiation processes, including adipogenesis. We recently showed that overexpression of each of the four NOTCH receptors in 3T3-L1 preadipocytes enhances adipogenesis and modulates the acquisition of the mature adipocyte phenotype. We also revealed that DLK proteins modulate the adipogenesis of 3T3-L1 preadipocytes and mesenchymal C3H10T1/2 cells in an opposite way, despite their function as non-canonical inhibitory ligands of NOTCH receptors. In this work, we used multipotent C3H10T1/2 cells as an adipogenic model. We used standard adipogenic procedures and analyzed different parameters by using quantitative-polymerase chain reaction (qPCR), quantitative reverse transcription-polymerase chain reaction (qRT-PCR), luciferase, Western blot, and metabolic assays. We revealed that C3H10T1/2 multipotent cells show higher levels of NOTCH receptors expression and activity and lower Dlk gene expression levels than 3T3-L1 preadipocytes. We found that the overexpression of NOTCH receptors enhanced C3H10T1/2 adipogenesis levels, and the overexpression of NOTCH receptors and DLK (DELTA-like homolog) proteins modulated the conversion of cells towards a brown-like adipocyte phenotype. These and our prior results with 3T3-L1 preadipocytes strengthen the idea that, depending on the cellular context, a precise and highly regulated level of global NOTCH signaling is necessary to allow adipogenesis and determine the mature adipocyte phenotype.

The Role of Pref-1 during Adipogenic Differentiation: An Overview of Suggested Mechanisms

Obesity contributes significantly to the global health burden. A better understanding of adipogenesis, the process of fat formation, may lead to the discovery of novel treatment strategies. However, it is of concern that the regulation of adipocyte differentiation has predominantly been studied using the murine 3T3-L1 preadipocyte cell line and murine experimental animal models. Translation of these findings to the human setting requires confirmation using experimental models of human origin. The ability of mesenchymal stromal/stem cells (MSCs) to differentiate into adipocytes is an attractive model to study adipogenesis in vitro. Differences in the ability of MSCs isolated from different sources to undergo adipogenic differentiation, may be useful in investigating elements responsible for regulating adipogenic differentiation potential. Genes involved may be divided into three broad categories: early, intermediate and late-stage regulators. Preadipocyte factor-1 (Pref-1) is an early negative regulator of adipogenic differentiation. In this review, we briefly discuss the adipogenic differentiation potential of MSCs derived from two different sources, namely adipose-derived stromal/stem cells (ASCs) and Wharton’s Jelly derived stromal/stem cells (WJSCs). We then discuss the function and suggested mechanisms of action of Pref-1 in regulating adipogenesis, as well as current findings regarding Pref-1’s role in human adipogenesis.

Analysis of the Bovine DLK1 Gene Polymorphism and Its Relation to Lipid Metabolism in Chinese Simmental

In this study, we precisely constructed and transfected the overexpression and interference vectors in BFFs to evaluate the role of DLK1 gene on lipid metabolism in vitro. The expression of of DLK1 in the mRNA and protein level tended to reduce, and TGs were significantly increased in the pGPU6-shDLK1 group compared to the control group (p < 0.05). The expression of DLK1 in the mRNA and protein level were increased in the pBI-CMV3-DLK1 group compared to the control group, and the TGs content showed a significant decrease in the pBI-CMV3-DLK1 group (p < 0.05). Meanwhile, we used the restriction fragment length polymorphism (RFLP-PCR) detection method to screen SNPs further to explore and analyze the relationship between the gene and the economic traits of 28-month-old Chinese Simmental and the fatty acids composition of cattle longissimus muscle. The result showed that two SNPs, IVS3 + 478 C>T and IVS3 + 609 T>G, were identified as being significantly associated with carcass and meat quality traits in Chinese Simmental, such as the carcass fat coverage rate, loin eye muscle area, and fat color score. In summary, our results indicated that DLK1 can affect lipid metabolism in bovine and these two SNPs might be applied as genetic markers of meat quality traits for beef cattle breeding.

Genomic imprinting and its effects on postnatal growth and adult metabolism

Imprinted genes display parent-of-origin-specific expression with this epigenetic system of regulation found exclusively in therian mammals. Historically, defined imprinted gene functions were almost solely focused on pregnancy and the influence on the growth parameters of the developing embryo and placenta. More recently, a number of postnatal functions have been identified which converge on resource allocation, both for animals in the nest and in adults. While many of the prenatal functions of imprinted genes that have so far been described adhere to the "parental conflict" hypothesis, no clear picture has yet emerged on the functional role of imprints on postnatal metabolism. As these roles are uncovered, interest in the potential for these genes to influence postnatal metabolism and associated adult-onset disease outcomes when dysregulated has gathered pace. Here, we review the published data on imprinted genes and their influence on postnatal metabolism, starting in the nest, and then progressing through to adulthood. When observing the functional effects of these genes on adult metabolism, we must always be careful to acknowledge the influence both of direct expression in the relevant metabolic tissue, but also indirect metabolic programming effects caused by their modulation of both in utero and postnatal growth trajectories.

Meg3 Non-coding RNA Expression Controls Imprinting by Preventing Transcriptional Upregulation in cis

Although many long non-coding RNAs (lncRNAs) are imprinted, their roles often remain unknown. The Dlk1-Dio3 domain expresses the lncRNA Meg3 and multiple microRNAs and small nucleolar RNAs (snoRNAs) on the maternal chromosome and constitutes an epigenetic model for development. The domain's Dlk1 (Delta-like-1) gene encodes a ligand that inhibits Notch1 signaling and regulates diverse developmental processes. Using a hybrid embryonic stem cell (ESC) system, we find that Dlk1 becomes imprinted during neural differentiation and that this involves transcriptional upregulation on the paternal chromosome. The maternal Dlk1 gene remains poised. Its protection against activation is controlled in cis by Meg3 expression and also requires the H3-Lys-27 methyltransferase Ezh2. Maternal Meg3 expression additionally protects against de novo DNA methylation at its promoter. We find that Meg3 lncRNA is partially retained in cis and overlaps the maternal Dlk1 in embryonic cells. Combined, our data evoke an imprinting model in which allelic lncRNA expression prevents gene activation in cis.

Pioneering studies on monogenic central precocious puberty

Pubertal timing in humans is determined by complex interactions including hormonal, metabolic, environmental, ethnic, and genetic factors. Central precocious puberty (CPP) is defined as the premature reactivation of the hypothalamic-pituitary-gonadal axis, starting before the ages of 8 and 9 years in girls and boys, respectively; familial CPP is defined by the occurrence of CPP in two or more family members. Pioneering studies have evidenced the participation of genetic factors in pubertal timing, mainly identifying genetic causes of CPP in sporadic and familial cases. In this context, rare activating mutations were identified in genes of the kisspeptin excitatory pathway (KISS1R and KISS1 mutations). More recently, loss-of-function mutations in two imprinted genes (MKRN3 and DLK1) have been identified as important causes of familial CPP, describing novel players in the modulation of the hypothalamic-pituitary-gonadal axis in physiological and pathological conditions. MKRN3 mutations are the most common cause of familial CPP, and patients with MKRN3 mutations present clinical features indistinguishable from idiopathic CPP. Meanwhile, adult patients with DLK1 mutations present high frequency of metabolic alterations (overweight/obesity, early onset type 2 diabetes and hyperlipidemia), indicating that DLK1 may be a novel link between reproduction and metabolism. Arch Endocrinol Metab. 2019;63(4):438-44.

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.

DLK1, Notch Signaling and the Timing of Puberty

The factors that trigger human puberty are among the central mysteries of reproductive biology. Several approaches, including mutational analysis of candidate genes, large-scale genome-wide association studies, whole exome sequencing, and whole genome sequencing have been performed in attempts to identify novel genetic factors that modulate the human hypothalamic-pituitary-gonadal axis to result in premature sexual development. Genetic abnormalities involving excitatory and inhibitory pathways regulating gonadotropin-releasing hormone secretion, represented by the kisspeptin (KISS1 and KISS1R) and makorin ring finger 3 (MKRN3) systems, respectively, have been associated with sporadic and familial cases of central precocious puberty (CPP). More recently, paternally inherited genetic defects of DLK1 were identified in four families with nonsyndromic CPP and a metabolic phenotype. DLK1 encodes a transmembrane protein that is important for adipose tissue homeostasis and neurogenesis and is located in the imprinted chromosome 14q32 region associated with Temple syndrome. In this review, we highlight the clinical and genetic features of patients with CPP caused by DLK1 mutations and explore the involvement of Notch signaling and DLK1 in the control of pubertal onset.

Genomic Imprinting and Physiological Processes in Mammals

Complex multicellular organisms, such as mammals, express two complete sets of chromosomes per nucleus, combining the genetic material of both parents. However, epigenetic studies have demonstrated violations to this rule that are necessary for mammalian physiology; the most notable parental allele expression phenomenon is genomic imprinting. With the identification of endogenous imprinted genes, genomic imprinting became well-established as an epigenetic mechanism in which the expression pattern of a parental allele influences phenotypic expression. The expanding study of genomic imprinting is revealing a significant impact on brain functions and associated diseases. Here, we review key milestones in the field of imprinting and discuss mechanisms and systems in which imprinted genes exert a significant role.

Placental Delta-Like 1 Gene DNA Methylation Levels Are Related to Mothers' Blood Glucose Concentration

PURPOSE

We aim to identify the methylation status of delta-like 1 (DLK1) in the placenta and the correlation between DLK1 methylation and maternal serum glucose level and fetal birth weight.

METHODS

We analyzed the gene expression of DLK1 gene in both maternal and fetal sides of the placenta in a GDM group (n = 15) and a control group (n = 15) using real-time polymerase chain reaction. With MethylTargetTM technique, we detected the methylation status of DLK1 promotor in the placenta. Furthermore, Pearson's correlation was used to confirm the association of methylation alteration of DLK1 promoter and maternal 2 h OGTT glucose level and fetal birth weight.

RESULTS

In our study, we found that DLK1 expression in both maternal and fetal sides of the placenta decreased significantly in GDM group compared with control group, and it was caused by hypermethylation of DLK1 promoter region. Additionally, the methylation status of DLK1 gene in the maternal side of the placenta highly correlated with maternal 2 h OGTT glucose level (coefficient = 0.7968, P < 0.0001), while the methylation status in the fetal side of the placenta was closely related to fetal birth weight (coefficient = 0.6233, P < 0.0001).

CONCLUSIONS

Our results demonstrated that altered expression of DLK1 was caused by the hypermethylation of DLK1 promoter region in the placenta, and intrauterine exposure to GDM has long-lasting effects on the epigenome of the offspring.

DLK proteins modulate NOTCH signaling to influence a brown or white 3T3-L1 adipocyte fate

The role of NOTCH signaling in adipogenesis is highly controversial, with data indicating null, positive or negative effects on this differentiation process. We hypothesize that these contradictory results could be due to the different global NOTCH signaling levels obtained in different experimental settings, because of a specific modulation of NOTCH receptors’ activity by their ligands. We have previously demonstrated that DLK1 and DLK2, two non-canonical NOTCH1 ligands that inhibit NOTCH1 signaling in a dose-dependent manner, modulate the adipogenesis process of 3T3-L1 preadipocytes. In this work, we show that over-expression of any of the four NOTCH receptors enhanced adipogenesis of 3T3-L1 preadipocytes. We also determine that DLK proteins inhibit not only the activity of NOTCH1, but also the activity of NOTCH2, 3 and 4 receptors to different degrees. Interestingly, we have observed, by different approaches, that NOTCH1 over-expression seems to stimulate the differentiation of 3T3-L1 cells towards a brown-like adipocyte phenotype, whereas cells over-expressing NOTCH2, 3 or 4 receptors or DLK proteins would rather differentiate towards a white-like adipocyte phenotype. Finally, our data also demonstrate a complex feed-back mechanism involving Notch and Dlk genes in the regulation of their expression, which suggest that a precise level of global NOTCH expression and NOTCH-dependent transcriptional activity of specific targets could be necessary to determine the final phenotype of 3T3-L1 adipocytes.

Effects of maternal feed intake restriction during pregnancy on the expression of growth regulation, imprinting and epigenetic transcription-related genes in foetal goats

Maternal nutrition during gestation is a leading factor of modifying the foetal epigenome and phenotype for mammals. Imprinting genes have important roles in regulating foetal growth, programming and development. There, however, are limited data available on the effects of feed intake restriction on the expression of imprinting genes in pregnant goats. The present study, therefore, was conducted to assess the effects of maternal feed intake restriction on the relative abundance of mRNA for growth imprinting, DNA methyltransferase (DNMT) and epigenetic transcription-related genes in the liver and heart of foetal goats during gestation. A total of 24 Liuyang black goats (2.0±0.3 yr) with similar body weight (BW, 31.22±8.09 kg) and parity (2) were allocated equally to either a control group (CG) or a restriction group (RG) during both early (from 26 to 65 days) and late (from 96 to 135 days) gestation. All goats were fed a mixed diet and had free access to fresh water. The feed of the RG was 40% less than that of the CG. The early and late gestation goats were weighed, bled and slaughtered on days 65 and 135 of gestation, respectively. In early gestation, the foetal weight, body length, the weight of foetal heart and liver were greater (P <  0.05) in the RG. The CpG methylation of genomic DNA in the foetal heart was less (P =  0.0001) in the RG. The relative abundance of mRNA of methyl-CpG-binding domain protein 2 (MBD2) and methyl-CpG-binding domain protein 3 (MBD3) genes in the foetal liver were greater (P <  0.05) in the RG. During the late gestation, the foetal weight, heart weight and liver weight were less (P <  0.05) in the RG. The relative abundance of mRNA for the MBD2 gene (P =  0.043) in the foetal heart, and the ten-eleven translocation protein 1 (TET1) gene (P <  0.05) in both the foetal heart and liver were greater in the RG. These results indicate feed intake restriction during gestation influenced foetal development and regulated the relative abundance of mRNA for epigenetic transcription-related genes.

Genomic imprinting, growth and maternal–fetal interactions

In the 1980s, mouse nuclear transplantation experiments revealed that both male and female parental genomes are required for successful development to term (McGrath and Solter, 1983; Surani and Barton, 1983). This non-equivalence of parental genomes is because imprinted genes are predominantly expressed from only one parental chromosome. Uniparental inheritance of these genomic regions causes paediatric growth disorders such as Beckwith–Wiedemann and Silver–Russell syndromes (reviewed in Peters, 2014). More than 100 imprinted genes have now been discovered and the functions of many of these genes have been assessed in murine models. The first such genes described were the fetal growth factor insulin-like growth factor 2 (Igf2) and its inhibitor Igf2 receptor (Igf2r) (DeChiara et al., 1991; Lau et al., 1994; Wang et al., 1994). Since then, it has emerged that most imprinted genes modulate fetal growth and resource acquisition in a variety of ways. First, imprinted genes are required for the development of a functional placenta, the organ that mediates the exchange of nutrients between mother and fetus. Second, these genes act in an embryo-autonomous manner to affect the growth rate and organogenesis. Finally, imprinted genes can signal the nutritional status between mother and fetus, and can modulate levels of maternal care. Importantly, many imprinted genes have been shown to affect postnatal growth and energy homeostasis. Given that abnormal birthweight correlates with adverse adult metabolic health, including obesity and cardiovascular disease, it is crucial to understand how the modulation of this dosage-sensitive, epigenetically regulated class of genes can contribute to fetal and postnatal growth, with implications for lifelong health and disease.

Soluble delta-like 1 homolog (DLK1) stimulates angiogenesis through Notch1/Akt/eNOS signaling in endothelial cells

AIM

Delta-like 1 homolog (DLK1) is a non-canonical ligand of Notch signaling, which plays a pivotal role in vascular development and tumor angiogenesis. This study aimed to elucidate the function and mechanism of DLK1 in angiogenesis.

METHODS AND RESULTS

By using in situ hybridization and immunohistochemical studies, expression analysis revealed a unique vascular tropism of DLK1 in vasculature of neuroblastoma and vascular tumors. Thus, it was hypothesized that DLK1 may be cleaved and then bound to endothelial cells, thereby regulating the endothelial function. To test such hypothesis, soluble DLK1 encompassing DLK1 extracellular domain (DLK1-EC) was generated and validated by its inhibitory function in adipogenesis assay. Recombinant DLK1-EC exhibited the preferential binding capability toward endothelial cells and stimulated the microvessels sprouting in aorta rings. Above all, implantation of DLK1-EC dose-dependently elicited the cornea neovascularization in rats. By using various angiogenesis assays, it was delineated that DLK1-EC stimulated the angiogenesis by promoting the proliferation, motility and tube formation of endothelial cells. By immunoblot and luciferase analysis, it was elucidated that DLK1-EC enhanced the expression and activities of Notch1/Akt/eNOS/Hes-1 signaling in dose- and time-dependent manners. Pharmaceutical blockage of Notch signaling using γ-secretase inhibitor DAPT abrogated the DLK1-EC-induced endothelial migration and Hes-1-driven luciferase activities. Furthermore, Notch1 inactivation by neutralizing antibodies or RNA interference reversed the DLK1-EC-induced angiogenesis.

CONCLUSIONS

The present study unveils the pro-angiogenic function and mechanism of soluble DLK1 through activation of Notch1 signaling in endothelial cells.

Overexpression of microRNAs from the Gtl2-Rian locus contributes to postnatal death in mice

The Dlk1-Dio3 imprinted domain functions in embryonic development but the roles of noncoding RNAs expressed from this domain remain unclear. We addressed this question by generating transgenic (TG) mice harbouring a BAC carrying IG-DMR (intergenic-differentially methylated region), Gtl2-DMR, Gtl2, Rtl1/Rtl1as, and part of Rian. High postnatal lethality (>85%) of the BAC-TG pups was observed in the maternally transmitted individuals (MAT-TG), but not following paternal transmission (PAT-TG). The DNA methylation status of IG-DMR and Gtl2-DMR in the BAC-allele was paternally imprinted similar to the genomic allele. The mRNA-Seq and miRNA-Seq analysis revealed marked expression changes in the MAT-TG, with 1,500 upregulated and 2,131 downregulated genes. The long noncoding RNAs and 12 miRNAs containing the BAC locus were markedly enhanced in the MAT-TG. We identified the 24 target genes of the overexpressed miRNAs and confirmed the downregulation in the MAT-TG. Notably, overexpression of mir770, mir493, and mir665 from Gtl2 in the MAT-TG embryos led to decreased expression of the 3 target genes, Col5a1, Pcgf2, and Clip2. Our results suggest that decreased expression of the 3 target genes concomitant with overexpression of the miRNAs within Gtl2 may be involved in the postnatal death in the MAT-TG. Because this imprinted domain is well conserved between mice and humans, the results of genetic and molecular analysis in mice hold important implications for related human disorders such as Temple syndrome.

Fetus-derived DLK1 is required for maternal metabolic adaptations to pregnancy and is associated with fetal growth restriction

Pregnancy is a state of high metabolic demand. Fasting diverts metabolism to fatty acid oxidation, and the fasted response occurs much more rapidly in pregnant women than in non-pregnant women. The product of the imprinted DLK1 gene (delta-like homolog 1) is an endocrine signaling molecule that reaches a high concentration in the maternal circulation during late pregnancy. By using mouse models with deleted Dlk1, we show that the fetus is the source of maternal circulating DLK1. In the absence of fetally derived DLK1, the maternal fasting response is impaired. Furthermore, we found that maternal circulating DLK1 levels predict embryonic mass in mice and can differentiate healthy small-for-gestational-age (SGA) infants from pathologically small infants in a human cohort. Therefore, measurement of DLK1 concentration in maternal blood may be a valuable method for diagnosing human disorders associated with impaired DLK1 expression and to predict poor intrauterine growth and complications of pregnancy.

Sex-determining region Y-box 9 acts downstream of NADPH oxidase to influence the effect of leptin on PPARγ1 expression in hepatic stellate cells

Leptin, an adipocyte-derived hormone, promotes liver fibrogenesis and inhibits the expression of peroxisome-proliferator activated receptor γ (PPARγ), a key transcription factor in inhibition of hepatic stellate cell (HSC) activation, in HSCs. This research aimed to further investigate the mechanisms underlying leptin regulation of PPARγ1 in HSCs in vivo and in vitro. Results demonstrated that sex-determining region Y-box 9 (Sox9) could bind to a site around -2275 within leptin response region of PPARγ1 promoter and inhibited PPARγ1 expression. Sox9 upregulated the expressions of α1(I)collagen and alpha-smooth muscle actin in HSCs. Leptin stimulated Sox9 expression and Sox9 binding to PPARγ1 promoter. The signaling pathways of NADPH oxidase, β-catenin, and delta-like homolog1 (DLK1) mediated leptin upregulation of Sox9 expression. Moreover, there existed crosstalk between NADPH oxidase pathway and β-catenin or DLK1 signaling pathway. Human liver specimens of cirrhosis were shown to be of a large number of the positive HSCs for p47phox (playing a central role in NADPH oxidase activity), 4-hydroxynonenal (a lipid peroxidation product), Sox9, and α-smooth muscle actin whereas PPARγ-positive HSCs were rarely detected. These results might deepen understanding of the molecular mechanisms for leptin inhibition of PPARγ1 expression in HSCs and for the liver fibrosis associated with leptin.

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

AIM

To determine whether preadipocyte factor 1 could be a predictive marker for the development of diabetes in people without diabetes at baseline.

METHODS

We conducted a population-based, nested case-control study of individuals who progressed to diabetes (n = 43) or prediabetes (n = 345) and control participants matched on age, sex and fasting plasma glucose concentration, who maintained normal glucose tolerance (n = 389) during a 4-year follow-up using data from the Chungju Metabolic disease Cohort Study. Circulating levels of preadipocyte factor 1 were measured using an enzyme-linked immunosorbent assay.

RESULTS

Baseline serum preadipocyte factor 1 levels showed a stepwise decrease across the glucose tolerance status groups at follow-up (normal glucose tolerance: 10.02 ± 3.02 ng/ml; prediabetes: 9.48 ± 3.35 ng/ml; diabetes: 8.66 ± 3.29 ng/ml; P for trend, 0.0151). Individuals whose fasting plasma glucose level had increased or whose homeostasis model assessment of β-cell function had decreased at follow-up showed significantly lower levels of preadipocyte factor 1 compared with their control group counterparts. After adjusting for age, BMI, fasting plasma glucose, serum insulin levels, systolic blood pressure and triglycerides, the incidence of diabetes was nearly threefold higher in the lowest vs. the upper three quartiles of circulating preadipocyte factor 1 (relative risk 2.794; 95% CI 1.188-6.571; P = 0.0185). Notably, these findings were significant in women but not in men.

CONCLUSIONS

Levels of circulating preadipocyte factor 1 may be a useful biomarker for identifying women at high risk of developing diabetes.

IVF affects embryonic development in a sex-biased manner in mice

Increasing evidence indicates that IVF (IVF includes in vitro fertilization and culture) embryos and babies are associated with a series of health complications, and some of them show sex-dimorphic patterns. Therefore, we hypothesized that IVF procedures have sex-biased or even sex-specific effects on embryonic and fetal development. Here, we demonstrate that IVF-induced side effects show significant sexual dimorphic patterns from the pre-implantation to the prenatal stage. During the pre-implantation stage, female IVF embryos appear to be more vulnerable to IVF-induced effects, including an increased percentage of apoptosis (7.22±1.94 vs 0.71±0.76, P<0.01), and dysregulated expression of representative sex-dimorphic genes (Xist, Hprt, Pgk1 and Hsp70). During the mid-gestation stage, IVF males had a higher survival rate than IVF females at E13.5 (male:female=1.33:1), accompanied with a female-biased pregnancy loss. In addition, while both IVF males and females had reduced placental vasculogenesis/angiogenesis, the compensatory placental overgrowth was more evident in IVF males. During the late-gestation period, IVF fetuses had a higher sex ratio (male:female=1.48:1) at E19.5, and both male and female IVF placentas showed overgrowth. After birth, IVF males grew faster than their in vivo (IVO) counterparts, while IVF females showed a similar growth pattern with IVO females. The present study provides a new insight into understanding IVF-induced health complications during embryonic and fetal development. By understanding and minimizing these sex-biased effects of the IVF process, the health of IVF-conceived babies may be improved in the future.

Exogenous administration of DLK1 ameliorates hepatic steatosis and regulates gluconeogenesis via activation of AMPK

BACKGROUND/OBJECTIVES

Activation of Notch signaling pathologically enhances lipogenesis and gluconeogenesis in the liver causing non-alcoholic fatty liver disease (NAFLD) and diabetes. Delta-like 1 homolog (DLK1), an imprinted gene that can modulate adipogenesis and muscle development in mice, was found as an inhibitory regulator of Notch signaling. Therefore, we investigated the metabolic effect of exogenous DLK1 in vitro and in vivo.

SUBJECTS/METHODS

A soluble DLK1 peptide was generated with fusion between a human Fc fragment and extracellular domain of DLK1. Male db/db mice were randomly assigned to two groups: vehicle treated and DLK1-treated group (25 mg kg(-1), intraperitoneal injection, twice a week for 4 weeks). Primary mice hepatocytes and HepG2 cells were used for in vitro experiments.

RESULTS

After 4 weeks of DLK1 administration, hepatic triglyceride content and lipid droplets in liver tissues, as well as serum levels of liver enzymes, were markedly decreased in db/db mice. DLK1 treatment induced phosphorylation of AMPK and ACC and suppressed nuclear expression of SREBP-1c in the mouse liver or hepatocytes, indicating regulation of fatty acid oxidation and synthesis pathways. Furthermore, DLK1-treated mice showed significantly lower levels of fasting and random glucose, with improved glucose and insulin tolerance compared with the vehicle-treated group. Macrophage infiltration and proinflammatory cytokine levels in the epididymal fat were decreased in DLK1-treated db/db mice. Moreover, DLK1 suppressed glucose production from hepatocytes, which was blocked after co-administration of an AMPK inhibitor, compound C. DLK1-treated hepatocytes and mouse liver tissues showed lower PEPCK and G6Pase expression. DLK1 triggered AKT phosphorylation followed by cytosolic translocation of FOXO1 from the nucleus in hepatocytes.

CONCLUSIONS

The present study demonstrated that exogenous administration of DLK1 reduced hepatic steatosis and hyperglycemia via AMPK activation in the liver. This result suggests that DLK1 may be a novel therapeutic approach for treating NAFLD and diabetes.

Assisted reproduction causes placental maldevelopment and dysfunction linked to reduced fetal weight in mice

Compelling evidence indicates that stress in utero, as manifested by low birth weight (LBW), increases the risk of metabolic syndrome in adulthood. Singletons conceived by assisted reproductive technology (ART) display a significant increase in LBW risk and ART offspring have a different metabolic profile starting at birth. Here, used mouse as a model, we found that ART resulted in reduced fetal weight and placental overgrowth at embryonic day 18.5 (E18.5). The ART placentae exhibited histomorphological alterations with defects in placental layer segregation and glycogen cells migration at E18.5. Further, ART treatments resulted in downregulation of a majority of placental nutrient transporters and reduction in placental efficiency. Moreover, the ART placentae were associated with increased methylation levels at imprinting control regions of H19, KvDMR1 and disrupted expression of a majority of imprinted genes important for placental development and function at E18.5. Our results from the mouse model show the first piece of evidence that ART treatment could affect fetal growth by disrupting placental development and function, suggests that perturbation of genomic imprinting resulted from embryo manipulation may contribute to these problems.

Molecular basis of imprinting disorders affecting chromosome 14: lessons from murine models

Uniparental inheritance of chromosome 14q32 causes developmental failure during gestation and early postnatal development due to mis-expression of a cluster of imprinted genes under common epigenetic control. Two syndromes associated with chromosome 14q32 abnormalities have been described, Kagami–Ogata and Temple syndromes. Both of these syndromes are characterised by specific impairments of intrauterine development, placentation and early postnatal survival. Such abnormalities arise because the processes of intrauterine growth and postnatal adaptation are critically modulated by the dosage of imprinted genes in the chromosome 14q32 cluster. Much of our understanding of how the imprinted genes in this cluster are regulated, as well as their individual functions in the molecular pathways controlling growth and postnatal adaptation, has come from murine models. Mouse chromosome 12qF1 contains an imprinted region syntenic to human chromosome 14q32, collectively referred to as the Dlk1–Dio3 cluster. In this review, we will summarise the wealth of information derived from animal models of chromosome 12 imprinted gene mis-regulation, and explore the relationship between the functions of individual genes and the phenotypic result of their mis-expression. As there is often a considerable overlap between the functions of genes in the Dlk1–Dio3 cluster, we propose that the expression dosage of these genes is controlled by common regulatory mechanisms to co-ordinate the timing of growth and postnatal adaptation. While the diseases associated with mis-regulated chromosome 14 imprinting are rare, studies carried out in mice on the functions of the affected genes as well as their normal regulatory mechanisms have revealed new mechanistic pathways for the control of growth and survival in early life.

Genetic Regulation of Puberty Timing in Humans

Understanding the regulation of puberty timing has relevance to developmental and human biology and to the pathogenesis of various diseases. Recent large-scale genome-wide association studies on puberty timing and adult height, body mass index (BMI) and central body shape provide evidence for shared biological mechanisms that regulate these traits. There is a substantial genetic overlap between age at menarche in women and BMI, with almost invariable directional consistency with the epidemiological associations between earlier menarche and higher BMI. By contrast, the genetic loci identified for age at menarche are largely distinct from those identified for central body shape, while alleles that confer earlier menarche can be associated with taller or shorter adult height. The findings of population-based studies on age at menarche show increasing relevance for other studies of rare monogenic disorders and enrich our understanding of the mechanisms that regulate the timing of puberty and reproductive function.