Insulin-stimulated lipogenesis gets an epigenetic makeover.

Hepatic de novo lipogenesis is a major contributor to nonalcoholic fatty liver disease (NAFLD). In this issue of the JCI, Liu and Lin et al. identified Slug as an epigenetic regulator of lipogenesis. Their findings suggest that Slug is stabilized by insulin signaling, and that it promotes lipogenesis by recruiting the histone demethylase Lsd1 to the fatty acid synthase gene promoter. On the other hand, genetic deletion or acute depletion of Slug, or Lsd1 inhibition, reduced lipogenesis and protected against obesity-associated NAFLD and insulin resistance in mice. This study advances our understanding of how lipogenesis is regulated downstream of insulin signaling in health and disease.

N-Acetylcysteine Resolves Placental Inflammatory-Vasculopathic Changes in Mice Consuming a High-Fat Diet.

The mechanism by which poor maternal nutrition can affect the long-term health of offspring is poorly understood. In mice, we previously found that maternal high-fat diet (HFD) exposure results in reduced fetal growth regardless of maternal genotype. We tested our hypothesis that maternal HFD-induced inflammation contributes to metabolic disease susceptibility of the offspring via alterations in the placenta. The effect of maternal genotype, diet, and treatment with the anti-inflammatory compound N-acetylcysteine (NAC) on placental morphologic features was investigated. Placentas from wild-type dams maintained on a HFD but not those heterozygous (+/-) for Glut4 (Slc2a4) on the same diet had an increase in decidual inflammation and vasculopathy occurring together. NAC administration resulted in amelioration of HFD-induced decidual vasculopathy independent of offspring genotype and sex. Consistent with these morphologic improvements, placentas from HFD dams treated with NAC had decreased mRNA and immunostaining of IL-1ß and monocyte chemoattractant protein-1, decreased mRNA of inflammatory genes, and increased mRNA of Vegfa. These results strongly suggest consumption of an HFD results in vascular changes in placenta reflected by alterations in expression of pivotal vascular developmental markers and inflammatory genes all of which are ameliorated by NAC. These placental changes play a key role in the increased programed metabolic disease of HFD-exposed offspring.

Increased apolipoprotein C3 drives cardiovascular risk in type 1 diabetes.

Type 1 diabetes mellitus (T1DM) increases the risk of atherosclerotic cardiovascular disease (CVD) in humans by poorly understood mechanisms. Using mouse models of T1DM-accelerated atherosclerosis, we found that relative insulin deficiency rather than hyperglycemia elevated levels of apolipoprotein C3 (APOC3), an apolipoprotein that prevents clearance of triglyceride-rich lipoproteins (TRLs) and their remnants. We then showed that serum APOC3 levels predict incident CVD events in subjects with T1DM in the Coronary Artery Calcification in Type 1 Diabetes (CACTI) study. To explore underlying mechanisms, we investigated the impact of Apoc3 antisense oligonucleotides (ASOs) on lipoprotein metabolism and atherosclerosis in a mouse model of T1DM. Apoc3 ASO treatment abolished the increased hepatic Apoc3 expression in diabetic mice - resulting in lower levels of TRLs - without improving glycemic control. APOC3 suppression also prevented arterial accumulation of APOC3-containing lipoprotein particles, macrophage foam cell formation, and the accelerated atherosclerosis in diabetic mice. Our observations demonstrate that relative insulin deficiency increases APOC3 and that this results in elevated levels of TRLs and accelerated atherosclerosis in a mouse model of T1DM. Because serum levels of APOC3 predicted incident CVD events in the CACTI study, inhibiting APOC3 might reduce CVD risk in T1DM patients.

Immune tolerance attenuates gut dysbiosis, dysregulated uterine gene expression and high-fat diet potentiated preterm birth in mice.

BACKGROUND: Preterm delivery accounts for 85% of perinatal morbidity and mortality. Although the consumption of a high-fat diet leads to exaggerated proinflammatory responses and, in pregnant women, increased rates of spontaneous preterm birth, the underlying mechanisms remain unclear. OBJECTIVE: We sought to elucidate the mechanisms by which maternal consumption of a high-fat diet leads to a dysregulated immune response and, subsequently, spontaneous preterm birth. STUDY DESIGN: We performed 16S ribosomal RNA sequencing of DNA extracted and amplified from stool samples and compared the gut microbiomes of lipopolysaccharide-induced pregnant mice that were maintained on a high-fat diet compared to a normal control diet. Next, we sequenced the uterine transcriptomes of the mice. To test the effect of dampening of the immune response on the microbiome, transcriptome, and risk of spontaneous preterm birth, we induced immune tolerance with repetitive subclinical doses (0.2 mg/kg/week for 8 weeks) of endotoxin and performed 16S ribosomal RNA and uterine transcriptome sequencing on these immunotolerized mice. RESULTS: High-fat diet potentiates lipopolysaccharide-induced preterm birth by affecting the maternal gut microbiome and uterine transcriptome and reduces antioxidant capacity in a murine model. High-fat diet consumption also increases the colonization of the gut by 5 immunogenic bacteria and decreases colonization by Lachnospiraceae_NK4A136_group. Uteri from high-fat diet mice had increased expression of genes that stimulate the inflammatory-oxidative stress axis, autophagy/apoptosis, and smooth muscle contraction. Repetitive endotoxin priming protects high-fat diet dams from spontaneous preterm birth, increases colonization of the gut by Lachnospiraceae_NK4A136_group, decreases levels of immunogenic bacteria in the gut microbiome, and reduces the number of dysregulated genes after high-fat diet consumption from 994 to 74. CONCLUSION: High-fat diet-potentiated spontaneous preterm birth is mediated by increased inflammation, oxidative stress, and gut dysbiosis. The induction of immune tolerance via endotoxin priming reverses these effects and protects high-fat diet dams from spontaneous preterm birth. Based on this work, the role of immunomodulation as a novel therapeutic approach to prevent preterm birth among women who consume high-fat diets should be explored.

Saturated and unsaturated fatty acids differentially regulate in vitro and ex vivo placental antioxidant capacity.

PROBLEM: Complications from prematurity are the leading cause of death among children under 5 years of age. Although clinical studies have shown a positive correlation between maternal high-fat diet (HFD) and preterm birth (PTB), the underlying mechanisms remain to be elucidated. Furthermore, it remains unclear how fatty acid type influences the effects of bacterial endotoxins. METHOD OF STUDY: HTR-8/SVneo trophoblasts were cultured in either 0.5 mmol L-1 palmitic acid (PA) or linoleic acid (LA) in the absence or presence of 100 µg mL-1 of lipopolysaccharide (LPS) or lipoteichoic acid (LTA). Murine placental explants were cultured in either 2 mmol L-1 PA or LA, and cell viability, total antioxidant capacity (TAC), lipid peroxidation, H2 O2 , heme oxygenase-1 (HO-1), and nuclear erythroid 2-related factor 2 (Nrf-2) and nuclear factor-kappa light-chain enhancer of activated B cells (NF-κB) transcription factor activity assays were assessed. RESULTS: Palmitic acid significantly (i) increased cell death, (ii) decreased TAC, and (iii) increased lipid peroxidation; but did not significantly increase HO-1. In contrast, LA maintained cell viability and significantly increased TAC and HO-1. In addition, incubating placental explants with PA significantly increased NF-κB activity. Co-incubating cells with PA and LPS or LTA significantly potentiated H2 O2 production and increased lipid peroxidation. Co-incubating cells with PA and LTA synergistically impaired TAC, and LTA decreased TAC more so than LPS. Co-incubation with PA/LA and LPS/LTA decreased HO-1 levels compared to treatment with either fatty acid alone. CONCLUSION: Our findings suggest that saturated and unsaturated fats differentially regulate placental viability, antioxidant capacity, and inflammation and the actions of gram-positive and gram-negative endotoxins.

Discrepancies in Animal Models of Preterm Birth.

BACKGROUND: Preterm birth (PTB) is a multifactorial syndrome occurring before the 37th week of fullterm pregnancy [1]. Babies delivered preterm experience short-term and long-term complications affecting multiple organ systems, and serious maternal complications include hemorrhage and infection. Each year, an estimated 15 million babies are born preterm, and complications from prematurity are the leading cause of death among children up to 5 years of age [2]. With another increase in PTB rates over the last several years, the United States continues to have the highest incidence of any industrialized country [3]. Makena (a progesterone analog) is the only FDA approved medication available in the United States to reduce the risk of PTB. Its use is only indicated in women who are currently pregnant with one fetus and have unexpectedly delivered a baby preterm in the past [4]. Furthermore, Makena is very expensive and not used in mothers with multiple gestations or other risk factors, such as infection, preeclampsia and obesity. Consequently, physicians commonly prescribe supportive therapies, such as magnesium sulfate, to slow uterine contractions, and glucocorticoids to stimulate fetal lung maturity. METHODS: In this article, we review the full spectrum of in vivo models that investigators have developed to study PTB, including rodent, ruminant and non-human primate models. We evaluate the discrepancies among various models, the shortcomings of individual models and how well these models reflect various causes of PTB in humans. RESULTS: Recent studies reveal that infection is unessential in reproductive disorders linked to inflammation, and that infection and inflammation are two of many triggers of PTB [1, 5-6]. Despite such findings, many investigators continue recycling infectious- (using bacterium) and non-infectious-based models (using products of bacteria or individual cytokines). These models are inconsistent across laboratories, and produce variable degrees of maternal morbidity (inconsistent with human PTB). CONCLUSION: The aim of this review is to encourage the reproductive science community to rethink the design of non-infectious PTB animal studies. While these models have strengthened our understanding of the mediators and triggers of PTB, we must develop improved models that are more consistent with the various factors associated with human PTB (Fig. 1). If we continue viewing PTB through one lens or dimension, Makena will remain the only FDA approved medication. In vivo PTB research requires multi-model, multifactorial approaches that account for the complexity of living animals within and between species.