Diet-induced adipose tissue expansion is mitigated in mice with a targeted inactivation of mesoderm specific transcript (Mest)

Interindividual differences of dietary fat-inducible Mest in white adipose tissue of C57BL/6J mice are not heritable

OBJECTIVE

Differences in white adipose tissue (WAT) expression of mesoderm-specific transcript (Mest) in C57BL6/J mice fed a high-fat diet (HFD) are concomitant with and predictive for the development of obesity. However, the basis for differences in WAT Mest among mice is unknown. This study investigated whether HFD-inducible WAT Mest, as well as susceptibility to obesity, is transmissible from parents to offspring.

METHODS

WAT biopsies of mice fed an HFD for 2 weeks identified parents with low and high WAT Mest for breeding. Obesity phenotypes, WAT Mest, hepatic gene expression, and serum metabolites were determined in offspring fed an HFD for 2 weeks.

RESULTS

Offspring showed no heritability of obesity or WAT Mest phenotypes from parents but did show hepatic and serum metabolite changes consistent with their WAT Mest. Importantly, retired male breeders showed WAT Mest expression congruent with initial WAT biopsies even though HFD exposure occurred early in life.

CONCLUSIONS

Disparity of HFD-induced Mest in mice is not heritable but, rather, is reestablished during each generation and remains fixed from an early age to adulthood. Short-term HFD feeding reveals variation of WAT Mest expression within isogenic mice that is positively associated with the development of obesity.

Endothelial IL17RD promotes Western diet-induced aortic myeloid cell infiltration

The Interleukin-17 (IL17) family is a group of cytokines implicated in the etiology of several inflammatory diseases. Interleukin-17 receptor D (IL17RD), also known as Sef (similar expression to fibroblast growth factor) belonging to the family of IL17 receptors, has been shown to modulate IL17A-associated inflammatory phenotypes. The objective of this study was to test the hypothesis that IL17RD promotes endothelial cell activation and consequent leukocyte adhesion. We utilized primary human aortic endothelial cells and demonstrated that RNAi targeting of IL17RD suppressed transcript levels by 83 % compared to non-targeted controls. Further, RNAi knockdown of IL17RD decreased the adhesion of THP-1 monocytic cells onto a monolayer of aortic endothelial cells in response to IL17A. Additionally, we determined that IL17A did not significantly enhance the activation of canonical MAPK and NFκB pathways in endothelial cells, and further did not significantly affect the expression of VCAM-1 and ICAM-1 in aortic endothelial cells, which is contrary to previous findings. We also determined the functional relevance of our findings in vivo by comparing the expression of endothelial VCAM-1 and ICAM-1 and leukocyte infiltration in the aorta in Western diet-fed Il17rd null versus wild-type mice. Our results showed that although Il17rd null mice do not have significant alteration in aortic expression of VCAM-1 and ICAM-1 in endothelial cells, they exhibit decreased accumulation of proinflammatory monocytes and neutrophils, suggesting that endothelial IL17RD induced in vivo myeloid cell accumulation is not dependent on upregulation of VCAM-1 and ICAM-1 expression. We further performed proteomics analysis to identify potential molecular mediators of the IL17A/IL17RD signaling axis. Collectively, our results underscore a critical role for Il17rd in the regulation of aortic myeloid cell infiltration in the context of Western diet feeding.

Paternal developmental thyrotoxicosis disrupts neonatal leptin leading to increased adiposity and altered physiology of the melanocortin system

Background

The genetic code does not fully explain individual variability and inheritance of susceptibility to endocrine conditions, suggesting the contribution of epigenetic factors acting across generations.

Methods

We used a mouse model of developmental thyrotoxicosis (Dio3-/- mouse) to analyze endocrine outcomes in the adult offspring of Dio3-/- males using standard methods for body composition, and baseline and fasting hormonal and gene expression determinations in serum and tissues of relevance to the control of energy balance.

Results

Compared to controls, adult females with an exposed father (EF females) exhibited higher body weight and fat mass, but not lean mass, a phenotype that was much milder in EF males. After fasting, both EF females and males exhibited a more pronounced decrease in body weight than controls. EF females also showed markedly elevated serum leptin, increased white adipose tissue mRNA expression of leptin and mesoderm-specific transcript but decreased expression of type 2 deiodinase. EF females exhibited decreased serum ghrelin, which showed more pronounced post-fasting changes in EF females than in control females. EF female hypothalami also revealed significant decreases in the expression of pro-opiomelanocortin, agouti-related peptide, neuropeptide Y and melanocortin receptor 4. These markers also showed larger changes in response to fasting in EF females than in control females. Adult EF females showed no abnormalities in serum thyroid hormones, but pituitary expression of thyrotropin-releasing hormone receptor 1 and thyroid gland expression of thyroid-stimulating hormone receptor, thyroid peroxidase and iodotyrosine deiodinase were increased at baseline and showed differential regulation after fasting, with no increase in Trhr1 expression and more pronounced reductions in Tshr, Tpo and Iyd. In EF males, these abnormalities were generally milder. In addition, postnatal day 14 (P14) serum leptin was markedly reduced in EF pups.

Discussion

A paternal excess of thyroid hormone during development modifies the endocrine programming and energy balance in the offspring in a sexually dimorphic manner, with baseline and dynamic range alterations in the leptin-melanocortin system and thyroid gland, and consequences for adiposity phenotypes. We conclude that thyroid hormone overexposure may have important implications for the non-genetic, inherited etiology of endocrine and metabolic pathologies.

Integrative genomic analyses in adipocytes implicate DNA methylation in human obesity and diabetes

DNA methylation variations are prevalent in human obesity but evidence of a causative role in disease pathogenesis is limited. Here, we combine epigenome-wide association and integrative genomics to investigate the impact of adipocyte DNA methylation variations in human obesity. We discover extensive DNA methylation changes that are robustly associated with obesity (N = 190 samples, 691 loci in subcutaneous and 173 loci in visceral adipocytes, P < 1 × 10-7). We connect obesity-associated methylation variations to transcriptomic changes at >500 target genes, and identify putative methylation-transcription factor interactions. Through Mendelian Randomisation, we infer causal effects of methylation on obesity and obesity-induced metabolic disturbances at 59 independent loci. Targeted methylation sequencing, CRISPR-activation and gene silencing in adipocytes, further identifies regional methylation variations, underlying regulatory elements and novel cellular metabolic effects. Our results indicate DNA methylation is an important determinant of human obesity and its metabolic complications, and reveal mechanisms through which altered methylation may impact adipocyte functions.

Rapamycin/metformin co-treatment normalizes insulin sensitivity and reduces complications of metabolic syndrome in type 2 diabetic mice

Rapamycin treatment has positive and negative effects on progression of type 2 diabetes (T2D) in a recombinant inbred polygenic mouse model, male NONcNZO10/LtJ (NcZ10). Here, we show that combination treatment with metformin ameliorates negative effects of rapamycin while maintaining its benefits. From 12 to 30 weeks of age, NcZ10 males were fed a control diet or diets supplemented with rapamycin, metformin, or a combination of both. Rapamycin alone reduced weight gain, adiposity, HOMA-IR, and inflammation, and prevented hyperinsulinemia and pre-steatotic hepatic lipidosis, but exacerbated hyperglycemia, hypertriglyceridemia, and pancreatic islet degranulation. Metformin alone reduced hyperinsulinemia and circulating c-reactive protein, but exacerbated nephropathy. Combination treatment retained the benefits of both while preventing many of the deleterious effects. Importantly, the combination treatment reversed effects of rapamycin on markers of hepatic insulin resistance and normalized systemic insulin sensitivity in this inherently insulin-resistant model. In adipose tissue, rapamycin attenuated the expression of genes associated with adipose tissue expansion (Mest, Gpam), inflammation (Itgam, Itgax, Hmox1, Lbp), and cell senescence (Serpine1). In liver, the addition of metformin counteracted rapamycin-induced alterations of G6pc, Ppara, and Ldlr expressions that promote hyperglycemia and hypertriglyceridemia. Both rapamycin and metformin treatment reduced hepatic Fasn expression, potentially preventing lipidosis. These results delineate a state of "insulin signaling restriction" that withdraws endocrine support for further adipogenesis, progression of the metabolic syndrome, and the development of its comorbidities. Our results are relevant for the treatment of T2D, the optimization of current rapamycin-based treatments for posttransplant rejection and various cancers, and for the development of treatments for healthy aging.

Social and maternal behavior in mesoderm specific transcript (Mest)-deficient mice

Mesoderm specific transcript (Mest)/paternally expressed gene-1 (Peg1) is an imprinted gene expressed predominantly from the paternal allele. Aberrations in maternal behavior were previously reported in a Mest global knockout mouse (Mest^tm1Masu). In this study, we performed in-depth social and maternal behavioral testing in a mouse model of Mest inactivation developed in our laboratory (Mest^tm1.2Rkz). Mice with paternal allele inactivation (Mest^pKO) did not show anxiety after testing in the elevated plus maze, open field trial, and marble burying; nor depression-like behaviors in the tail suspension test. Mest^pKO showed normal social behaviors and memory/cognition in the three-chamber box test and the novel object recognition test, respectively. Primiparous Mest^pKO and Mest^gKO (biallelic Mest inactivation) female mice exhibited normal nest building and maternal behavior; and, virgin Mest^pKO and Mest^gKO female mice showed normal maternal instinct. Analyses of gene expression in adult hypothalamus, embryonic day 14.5 whole brain and adult whole brain demonstrated full abrogation of Mest mRNA in Mest^pKO and Mest^gKO mice with no effect on miR-335 expression. Our data indicates no discernible impairments in object recognition memory, social behavior or maternal behavior resulting from loss of Mest. The basis for the differences in maternal phenotypic behaviors between Mest^tm1Masu and Mest^tm1.2Rkz is not known.

Mouse mesoderm-specific transcript inhibits adipogenic differentiation and induces trans-differentiation into hepatocyte-like cells in 3T3-L1 preadiocytes

OBJECTIVE

The mesoderm-specific transcript (Mest) is an imprinted gene that is transcribed from the paternal allele. It is a marker of adipose tissue expansion; however, it is uncertain whether Mest expression promotes or suppresses adipogenic differentiation. To elucidate the effects of Mest expression on adipogenic differentiation, we transfected an expression vector or siRNA for mouse Mest into 3T3-L1 mouse preadipocyte cell line.

RESULTS

In differentiated 3T3-L1 adipocytes, Mest overexpression decreased lipid accumulation. Conversely, gene silencing of Mest increased the accumulation of lipid droplets in adipocytes. These results demonstrate that Mest negatively regulates adipocyte differentiation. Further, Mest induced trans-differentiation of 3T3-L1 cells into hepatocytes, and its overexpression induced the expression of hepatocyte marker genes, including albumin and α-fetoprotein. In the presence of dexamethasone, the forced expression of the Mest caused morphological changes in 3T3-L1 cells. Cells were flat and polygonal shapes, with an increased accumulation of intracellular glycogen and other features that are typical of hepatocytes. Therefore, Mest inhibits adipogenic differentiation of 3T3-L1 preadipocytes by inducing hepatocyte trans-differentiation.

Histone Deacetylase 3 Regulates Adipocyte Phenotype at Early Stages of Differentiation

Obesity is a condition characterized by uncontrolled expansion of adipose tissue mass resulting in pathological weight gain. Histone deacetylases (HDACs) have emerged as crucial players in epigenetic regulation of adipocyte metabolism. Previously, we demonstrated that selective inhibition of class I HDACs improves white adipocyte functionality and promotes the browning phenotype of murine mesenchymal stem cells (MSCs) C3H/10T1/2 differentiated to adipocytes. These effects were also observed in db/db and diet induced obesity mouse models and in mice with adipose-selective inactivation of HDAC3, a member of class I HDACs. The molecular basis of class I HDACs action in adipose tissue is not deeply characterized and it is not known whether the effects of their inhibition are exerted on adipocyte precursors or mature adipocytes. Therefore, the aim of the present work was to explore the molecular mechanism of class I HDAC action in adipocytes by evaluating the effects of HDAC3-specific silencing at different stages of differentiation. HDAC3 was silenced in C3H/10T1/2 MSCs at different stages of differentiation to adipocytes. shRNA targeting HDAC3 was used to generate the knock-down model. Proper HDAC3 silencing was assessed by measuring both mRNA and protein levels of mouse HDAC3 via qPCR and western blot, respectively. Mitochondrial DNA content and gene expression were quantified via qPCR. HDAC3 silencing at the beginning of differentiation enhanced adipocyte functionality by amplifying the expression of genes regulating differentiation, oxidative metabolism, browning and mitochondrial activity, starting from 72 h after induction of differentiation and silencing. Insulin signaling was enhanced as demonstrated by increased AKT phosphorylation following HDAC3 silencing. Mitochondrial content/density did not change, while the increased expression of the transcriptional co-activator Ppargc1b suggests the observed phenotype was related to enhanced mitochondrial activity, which was confirmed by increased maximal respiration and proton leak linked to reduced coupling efficiency. Moreover, the expression of pro-inflammatory markers increased with HDAC3 early silencing. To the contrary, no differences in terms of gene expression were found when HDAC3 silencing occurred in terminally differentiated adipocyte. Our data demonstrated that early epigenetic events mediated by class I HDAC inhibition/silencing are crucial to commit adipocyte precursors towards the above-mentioned metabolic phenotype. Moreover, our data suggest that these effects are exerted on adipocyte precursors.

Cajanolactone A, a stilbenoid from Cajanus cajan, inhibits energy intake and lipid synthesis/storage, and promotes energy expenditure in ovariectomized mice

BACKGROUND

We had reported that cajanolactone A (CLA) from Cajanus cajan dose-dependently inhibited ovariectomy-induced obesity and liver steatosis in mice, showing potential to prevent postmenopausal obesity and fatty liver. In this study, the role of CLA in the regulation of energy and lipid homeostasis was investigated.

METHODS

Ovariectomized mice treated with CLA or vehicle for 12 weeks were performed a 48 h monitoring for energy metabolism and food uptake. After that, hypothalami, perigonadal (pWATs), inguinal (iWATs) and brown (BATs) adipose tissues, livers, sera, and fecal and cecal contents were collected and analyzed.

FINDINGS

In CLA-treated mice, we observed reduced food uptake; increased energy expenditure; inhibited expression of orexigenic genes (ORX, ORXR2, pMCH and Gal) in the hypothalami, of lipogenic genes (CD36, SREBP-1c, ChREBP, PPARγ) in the livers, and of lipid storage proteins in the WATs (FSP27, MEST and caveolin-1) and livers (FSP27, Plin2 and Plin5); stimulated expression of metabolism-related proteins (pATGL and Echs1) in the adipose tissues and of thermogenic protein (UCP1) in the inguinal WATs; increased BAT content; increased mitochondria in the pWATs and livers; inhibited angiogenesis in the pWATs; and altered gut microbiome diversity with an increased abundance of Bacteroides.

INTERPRETATION

CLA prevents ovariectomy-induced obesity and liver steatosis via regulating energy intake and lipid synthesis/storage, promoting UCP1-dependent heat production, and protecting the mitochondrial function of hepatocytes and adipocytes. The improved gut microecology and inhibited angiogenesis may also contribute to the anti-obese activity of CLA.

Mesoderm-specific transcript localization in the ER and ER-lipid droplet interface supports a role in adipocyte hypertrophy

Highly variable expression of mesoderm-specific transcript (Mest) in adipose tissue among genetically homogeneous mice fed an obesogenic diet, and its positive association with fat mass expansion, suggests that Mest is an epigenetic determinant for the development of obesity. Although the mechanisms by which MEST augments fat accumulation in adipocytes have not been elucidated, it has sequence homology and catalytic peptide motifs which suggests that it functions as an epoxide hydrolase or as a glycerol- or acylglycerol-3-phosphate acyltransferase. To better understand MEST function, detailed studies were performed to precisely define the intracellular organelle localization of MEST using immunofluorescence confocal microscopy. Lentiviral-mediated expression of a C-terminus Myc-DDK-tagged MEST fusion protein expressed in 3T3-L1 preadipocytes/adipocytes, and ear-derived mesenchymal stem cells (EMSC) from mice was observed in the endoplasmic reticulum (ER) membranes and is consistent with previous studies showing endogenous MEST in the membrane fraction of adipose tissue. MEST was not associated with the Golgi apparatus or mitochondria; however, frequent contacts were observed between MEST-positive ER and mitochondria. MEST-positive domains were also shown on the plasma membrane (PM) of non-permeabilized cells but they did not co-localize with ER-PM bridges. Post-adipogenic differentiated 3T3-L1 adipocytes and EMSC showed significant co-localization of MEST with the lipid droplet surface marker perilipin at contact points between the ER and lipid droplet. Identification of MEST as an ER-specific protein that co-localizes with lipid droplets in cells undergoing adipogenic differentiation supports a function for MEST in the facilitation of lipid accumulation and storage in adipocytes.