The Signal Transducer and Activator of Transcription 1 (STAT1) Inhibits Mitochondrial Biogenesis in Liver and Fatty Acid Oxidation in Adipocytes

The transcription factor STAT1 plays a central role in orchestrating responses to various pathogens by activating the transcription of nuclear-encoded genes that mediate the antiviral, the antigrowth, and immune surveillance effects of interferons and other cytokines. In addition to regulating gene expression, we report that STAT1-/- mice display increased energy expenditure and paradoxically decreased release of triglycerides from white adipose tissue (WAT). Liver mitochondria from STAT1-/- mice show both defects in coupling of the electron transport chain (ETC) and increased numbers of mitochondria. Consistent with elevated numbers of mitochondria, STAT1-/- mice expressed increased amounts of PGC1α, a master regulator of mitochondrial biogenesis. STAT1 binds to the PGC1α promoter in fed mice but not in fasted animals, suggesting that STAT1 inhibited transcription of PGC1α. Since STAT1-/-mice utilized more lipids we examined white adipose tissue (WAT) stores. Contrary to expectations, fasted STAT1-/- mice did not lose lipid from WAT. β-adrenergic stimulation of glycerol release from isolated STAT1-/- WAT was decreased, while activation of hormone sensitive lipase was not changed. These findings suggest that STAT1-/- adipose tissue does not release glycerol and that free fatty acids (FFA) re-esterify back to triglycerides, thus maintaining fat mass in fasted STAT1-/- mice

Comparison of Hepatic-like Cell Production from Human Embryonic Stem Cells and Adult Liver Progenitor Cells: CAR Transduction Activates a Battery of Detoxification Genes

In vitro production of human hepatocytes is of primary importance in basic research, pharmacotoxicology and biotherapy of liver diseases. We have developed a protocol of differentiation of human embryonic stem cells (ES) towards hepatocyte-like cells (ES-Hep). Using a set of human adult markers including CAAT/enhancer binding protein (C/EBPalpha), hepatocyte nuclear factor 4/7 ratio (HNF4alpha1/HNF4alpha7), cytochrome P450 7A1 (CYP7A1), CYP3A4 and constitutive androstane receptor (CAR), and fetal markers including alpha-fetoprotein, CYP3A7 and glutathione S-transferase P1, we analyzed the expression of a panel of 41 genes in ES-Hep comparatively with human adult primary hepatocytes, adult and fetal liver. The data revealed that after 21 days of differentiation, ES-Hep are representative of fetal hepatocytes at less than 20 weeks of gestation. The glucocorticoid receptor pathway was functional in ES-Hep. Extending protocols of differentiation to 4 weeks did not improve cell maturation. When compared with hepatocyte-like cells derived from adult liver non parenchymal epithelial (NPE) cells (NPE-Hep), ES-Hep expressed several adult and fetal liver makers at much greater levels (at least one order of magnitude), consistent with greater expression of liver-enriched transcription factors Forkhead box A2, C/EBPalpha, HNF4alpha and HNF6. It therefore seems that ES-Hep reach a better level of differentiation than NPE-Hep and that these cells use different lineage pathways towards the hepatic phenotype. Finally we showed that lentivirus-mediated expression of xenoreceptor CAR in ES-Hep induced the expression of several detoxification genes including CYP2B6, CYP2C9, CYP3A4, UDP-glycosyltransferase 1A1, solute carriers 21A6, as well as biotransformation of midazolam, a CYP3A4-specific substrate

Complement component 3 (C3) expression in the hippocampus after excitotoxic injury: role of C/EBPβ

[Background] The CCAAT/enhancer-binding protein β (C/EBPβ) is a transcription factor implicated in the control of proliferation, differentiation, and inflammatory processes mainly in adipose tissue and liver; although more recent results have revealed an important role for this transcription factor in the brain. Previous studies from our laboratory indicated that CCAAT/enhancer-binding protein β is implicated in inflammatory process and brain injury, since mice lacking this gene were less susceptible to kainic acid-induced injury. More recently, we have shown that the complement component 3 gene (C3) is a downstream target of CCAAT/enhancer-binding protein β and it could be a mediator of the proinflammatory effects of this transcription factor in neural cells.[Methods] Adult male Wistar rats (8–12 weeks old) were used throughout the study. C/EBPβ+/+ and C/EBPβ–/– mice were generated from heterozygous breeding pairs. Animals were injected or not with kainic acid, brains removed, and brain slices containing the hippocampus analyzed for the expression of both CCAAT/enhancer-binding protein β and C3.[Results] In the present work, we have further extended these studies and show that CCAAT/enhancer-binding protein β and C3 co-express in the CA1 and CA3 regions of the hippocampus after an excitotoxic injury. Studies using CCAAT/enhancer-binding protein β knockout mice demonstrate a marked reduction in C3 expression after kainic acid injection in these animals, suggesting that indeed this protein is regulated by C/EBPβ in the hippocampus in vivo.[Conclusions] Altogether these results suggest that CCAAT/enhancer-binding protein β could regulate brain disorders, in which excitotoxic and inflammatory processes are involved, at least in part through the direct regulation of C3.This work was supported by MINECO, Grant SAF2014-52940-R and partially financed with FEDER funds. CIBERNED is funded by the Instituto de Salud Carlos III. JAM-G was supported by CIBERNED. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe

Mol Cell Biol

Vitamin A is secreted from cellular stores and circulates in blood bound to retinol-binding protein (RBP). In turn, holo-RBP associates in plasma with transthyretin (TTR) to form a ternary RBP-retinol-TTR complex. It is believed that binding to TTR prevents the loss of RBP by filtration in the kidney. At target cells, holo-RBP is recognized by STRA6, a plasma membrane protein that serves a dual role: it mediates uptake of retinol from extracellular RBP into cells, and it functions as a cytokine receptor that, upon binding holo-RBP, triggers a JAK/STAT signaling cascade. We previously showed that STRA6-mediated signaling underlies the ability of RBP to induce insulin resistance. However, the role that TTR, the binding partner of holo-RBP in blood, plays in STRA6-mediated activities remained unknown. Here we show that TTR blocks the ability of holo-RBP to associate with STRA6 and thereby effectively suppresses both STRA6-mediated retinol uptake and STRA6-initiated cell signaling. Consequently, TTR protects mice from RBP-induced insulin resistance, reflected by reduced phosphorylation of insulin receptor and glucose tolerance tests. The data indicate that STRA6 functions only under circumstances where the plasma RBP level exceeds that of TTR and demonstrate that, in addition to preventing the loss of RBP, TTR plays a central role in regulating holo-RBP/STRA6 signaling

Resistance to diet-induced obesity in mice with a single substituted chromosome

Obesity and its comorbidities are taking an increasing toll on human health. Key pathways that were identified with single gene variants in humans and model organisms have led to improved understanding and treatment of rare cases of human obesity. However, similar progress remains elusive for the more common multifactorial cases of metabolic dysfunction and disease. A survey of mouse chromosome substitution strains (CSSs) provided insight into the complex genetic control of diet-induced obesity and related conditions. We now report a survey of 60 traits related to obesity and metabolic syndrome in mice with a single substituted chromosome as well as selected traits measured in congenic strains derived from the substituted strain. We found that each strain that was resistant to diet-induced obesity had a distinct phenotype that uniquely modeled different combinations of traits related to metabolic disease. For example, the chromosome 6 CSS remained insulin resistant in the absence of obesity, demonstrating an atypical relationship between body weight and insulin resistance. These results provide insights into the genetic control of constant components of this mouse model of diet-induced metabolic disease as well as phenotypes that vary depending on genetic background. A better understanding of these genotype-phenotype relationships may enable a more individualized diagnosis and treatment of obesity and the metabolic syndrome