Enhanced Microbial Bile Acid Deconjugation and Impaired Ileal Uptake in Pregnancy Repress Intestinal Regulation of Bile Acid Synthesis.

Pregnancy is associated with progressive hypercholanemia, hypercholesterolemia, and hypertriglyceridemia, which can result in metabolic disease in susceptible women. Gut signals modify hepatic homeostatic pathways, linking intestinal content to metabolic activity. We sought to identify whether enteric endocrine signals contribute to raised serum bile acids observed in human and murine pregnancies, by measuring fibroblast growth factor (FGF) 19/15 protein and mRNA levels, and 7α-hydroxy-4-cholesten-3-one. Terminal ileal farnesoid X receptor (FXR)-mediated gene expression and apical sodium bile acid transporter (ASBT) protein concentration were measured by qPCR and western blotting. Shotgun whole-genome sequencing and ultra-performance liquid chromatography tandem mass spectrometry were used to determine the cecal microbiome and metabonome. Targeted and untargeted pathway analyses were performed to predict the systemic effects of the altered metagenome and metabolite profiles. Dietary CA supplementation was used to determine whether the observed alterations could be overcome by intestinal bile acids functioning as FXR agonists. Human and murine pregnancy were associated with reduced intestinal FXR signaling, with lower FGF19/15 and resultant increased hepatic bile acid synthesis. Terminal ileal ASBT protein was reduced in murine pregnancy. Cecal bile acid conjugation was reduced in pregnancy because of elevated bile salt hydrolase-producing Bacteroidetes. CA supplementation induced intestinal FXR signaling, which was not abrogated by pregnancy, with strikingly similar changes to the microbiota and metabonome as identified in pregnancy. Conclusion: The altered intestinal microbiota of pregnancy enhance bile acid deconjugation, reducing ileal bile acid uptake and lowering FXR induction in enterocytes. This exacerbates the effects mediated by reduced bile acid uptake transporters in pregnancy. Thus, in pregnant women and mice, there is reduced FGF19/15-mediated hepatic repression of hepatic bile acid synthesis, resulting in hypercholanemia.

Obeticholic acid ameliorates dyslipidemia but not glucose tolerance in mouse model of gestational diabetes.

Metabolism alters markedly with advancing gestation, characterized by progressive insulin resistance, dyslipidemia, and raised serum bile acids. The nuclear receptor farnesoid X receptor (FXR) has an integral role in bile acid homeostasis and modulates glucose and lipid metabolism. FXR is known to be functionally suppressed in pregnancy. The FXR agonist, obeticholic acid (OCA), improves insulin sensitivity in patients with type 2 diabetes with nonalcoholic fatty liver disease. We therefore hypothesized that OCA treatment during pregnancy could improve disease severity in a mouse model of gestational diabetes mellitus (GDM). C57BL/6J mice were fed a high-fat diet (HFD; 60% kcal from fat) for 4 wk before and throughout pregnancy to induce GDM. The impact of the diet supplemented with 0.03% OCA throughout pregnancy was studied. Pregnant HFD-fed mice displayed insulin resistance and dyslipidemia. OCA significantly reduced plasma cholesterol concentrations in nonpregnant and pregnant HFD-fed mice (by 22.4%, P < 0.05 and 36.4%, P < 0.001, respectively) and reduced the impact of pregnancy on insulin resistance but did not change glucose tolerance. In nonpregnant HFD-fed mice, OCA ameliorated weight gain, reduced mRNA expression of inflammatory markers in white adipose tissue, and reduced plasma glucagon-like peptide 1 concentrations (by 62.7%, P < 0.01). However, these effects were not evident in pregnant mice. OCA administration can normalize plasma cholesterol levels in a mouse model of GDM. However, the absence of several of the effects of OCA in pregnant mice indicates that the agonistic action of OCA is not sufficient to overcome many metabolic consequences of the pregnancy-associated reduction in FXR activity.

Hepatic peroxisome proliferator-activated receptor γ coactivator 1ß drives mitochondrial and anabolic signatures that contribute to hepatocellular carcinoma progression in mice.

The peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1ß (PGC-1 ß) is a master regulator of mitochondrial biogenesis and oxidative metabolism as well as of antioxidant defense. Specifically, in the liver, PGC-1ß also promotes de novo lipogenesis, thus sustaining cellular anabolic processes. Given the relevant pathogenic role of mitochondrial and fatty acid metabolism in hepatocarcinoma (HCC), here we pointed to PGC-1ß as a putative novel transcriptional player in the development and progression of HCC. For this purpose, we generated both hepatic-specific PGC-1ß-overexpressing (LivPGC-1ß) and PGC-1ß knockout (LivPGC-1ßKO) mice, and we challenged them with both chemical and genetic models of hepatic carcinogenesis. Our results demonstrate a pivotal role of PGC-1ß in driving liver tumor development. Indeed, whereas mice overexpressing PGC-1ß show greater tumor susceptibility, PGC-1ß knockout mice are protected from carcinogenesis. High levels of PGC-1ß are able to boost reactive oxygen species (ROS) scavenger expression, therefore limiting the detrimental ROS accumulation and, consequently, apoptosis. Moreover, it supports tumor anabolism, enhancing the expression of genes involved in fatty acid and triglyceride synthesis. Accordingly, the specific hepatic ablation of PGC-1ß promotes the accumulation of ROS-driven macromolecule damage, finally limiting tumor growth. CONCLUSION: The present data elect hepatic PGC-1ß as a transcriptional gatekeeper of mitochondrial function and redox status in HCC, orchestrating different metabolic programs that allow tumor progression. (Hepatology 2018;67:884-898).

Hepatic microRNA Expression by PGC-1α and PGC-1ß in the Mouse.

The fine-tuning of liver metabolism is essential to maintain the whole-body homeostasis and to prevent the onset of diseases. The peroxisome proliferator-activated receptor-γ coactivators (PGC-1s) are transcriptional key players of liver metabolism, able to regulate mitochondrial function, gluconeogenesis and lipid metabolism. Their activity is accurately modulated by post-translational modifications. Here, we showed that specific PGC-1s expression can lead to the upregulation of different microRNAs widely implicated in liver physiology and diseases development and progression, thus offering a new layer of complexity in the control of hepatic metabolism.

Lipid zonation and phospholipid remodeling in nonalcoholic fatty liver disease.

Nonalcoholic fatty liver disease (NAFLD) can progress from simple steatosis (i.e., nonalcoholic fatty liver [NAFL]) to nonalcoholic steatohepatitis (NASH), cirrhosis, and cancer. Currently, the driver for this progression is not fully understood; in particular, it is not known how NAFLD and its early progression affects the distribution of lipids in the liver, producing lipotoxicity and inflammation. In this study, we used dietary and genetic mouse models of NAFL and NASH and translated the results to humans by correlating the spatial distribution of lipids in liver tissue with disease progression using advanced mass spectrometry imaging technology. We identified several lipids with distinct zonal distributions in control and NAFL samples and observed partial to complete loss of lipid zonation in NASH. In addition, we found increased hepatic expression of genes associated with remodeling the phospholipid membrane, release of arachidonic acid (AA) from the membrane, and production of eicosanoid species that promote inflammation and cell injury. The results of our immunohistochemistry analyses suggest that the zonal location of remodeling enzyme LPCAT2 plays a role in the change in spatial distribution for AA-containing lipids. This results in a cycle of AA-enrichment in pericentral hepatocytes, membrane release of AA, and generation of proinflammatory eicosanoids and may account for increased oxidative damage in pericentral regions in NASH. CONCLUSION: NAFLD is associated not only with lipid enrichment, but also with zonal changes of specific lipids and their associated metabolic pathways. This may play a role in the heterogeneous development of NAFLD. (Hepatology 2017;65:1165-1180).

Changes in LXR signaling influence early-pregnancy lipogenesis and protect against dysregulated fetoplacental lipid homeostasis.

Human pregnancy is associated with enhanced de novo lipogenesis in the early stages followed by hyperlipidemia during advanced gestation. Liver X receptors (LXRs) are oxysterol-activated nuclear receptors that stimulate de novo lipogenesis and also promote the efflux of cholesterol from extrahepatic tissues followed by its transport back to the liver for biliary excretion. Although LXR is recognized as a master regulator of triglyceride and cholesterol homeostasis, it is unknown whether it facilitates the gestational adaptations in lipid metabolism. To address this question, biochemical profiling, protein quantification, and gene expression studies were used, and gestational metabolic changes in T0901317-treated wild-type mice and Lxrab-/- mutants were investigated. Here, we show that altered LXR signaling contributes to the enhanced lipogenesis in early pregnancy by increasing the expression of hepatic Fas and stearoyl-CoA desaturase 1 (Scd1). Both the pharmacological activation of LXR with T0901317 and the genetic ablation of its two isoforms disrupted the increase in hepatic fatty acid biosynthesis and the development of hypertriglyceridemia during early gestation. We also demonstrate that absence of LXR enhances maternal white adipose tissue lipolysis, causing abnormal accumulation of triglycerides, cholesterol, and free fatty acids in the fetal liver. Together, these data identify LXR as an important factor in early-pregnancy lipogenesis that is also necessary to protect against abnormalities in fetoplacental lipid homeostasis.

PGC-1ß promotes enterocyte lifespan and tumorigenesis in the intestine.

The mucosa of the small intestine is renewed completely every 3-5 d throughout the entire lifetime by small populations of adult stem cells that are believed to reside in the bottom of the crypts and to migrate and differentiate into all the different populations of intestinal cells. When the cells reach the apex of the villi and are fully differentiated, they undergo cell death and are shed into the lumen. Reactive oxygen species (ROS) production is proportional to the electron transfer activity of the mitochondrial respiration chain. ROS homeostasis is maintained to control cell death and is finely tuned by an inducible antioxidant program. Here we show that peroxisome proliferator-activated receptor-γ coactivator-1ß (PGC-1ß) is highly expressed in the intestinal epithelium and possesses dual activity, stimulating mitochondrial biogenesis and oxygen consumption while inducing antioxidant enzymes. To study the role of PGC-1ß gain and loss of function in the gut, we generated both intestinal-specific PGC-1ß transgenic and PGC-1ß knockout mice. Mice overexpressing PGC-1ß present a peculiar intestinal morphology with very long villi resulting from increased enterocyte lifespan and also demonstrate greater tumor susceptibility, with increased tumor number and size when exposed to carcinogens. PGC-1ß knockout mice are protected from carcinogenesis. We show that PGC-1ß triggers mitochondrial respiration while protecting enterocytes from ROS-driven macromolecule damage and consequent apoptosis in both normal and dysplastic mucosa. Therefore, PGC-1ß in the gut acts as an adaptive self-point regulator, capable of providing a balance between enhanced mitochondrial activity and protection from increased ROS production.

Hepatic-specific activation of peroxisome proliferator-activated receptor γ coactivator-1ß protects against steatohepatitis.

Development of hepatic steatosis and its progression to steatohepatitis may be the consequence of dysfunction of several metabolic pathways, such as triglyceride synthesis, very low-density lipoprotein (VLDL) secretion, and fatty acid ß-oxidation. Peroxisome proliferator-activated receptor γ coactivator-1ß (PGC-1ß) is a master regulator of mitochondrial biogenesis and oxidative metabolism, lipogenesis, and triglyceride (TG) secretion. Here we generated a novel mouse model with constitutive hepatic activation of PGC-1ß and studied the role of this transcriptional coactivator in dietary-induced steatosis and steatohepatitis. Selective activation of PGC-1ß within hepatocytes is able to protect the liver from lipid overload and from progression to fibrosis. The protective function exerted by PGC-1ß is due to its ability to induce mitochondrial oxidative phosphorylation, fatty acid ß-oxidation, and citrate cycle, as well as to decrease oxidative stress and promote TG secretion in the blood stream. These findings bolster the concept that a combined hepatic specific action of PGC-1ß on lipid synthesis and secretion, as well as on mitochondrial biogenesis and function, could protect against steatohepatitis.

Selective activation of nuclear bile acid receptor FXR in the intestine protects mice against cholestasis.

BACKGROUND & AIMS: Cholestasis is a liver disorder characterized by impaired bile flow, reduction of bile acids (BAs) in the intestine, and retention of BAs in the liver. The farnesoid X receptor (FXR) is the transcriptional regulator of BA homeostasis. Activation of FXR by BAs reduces circulating BA levels in a feedback mechanism, repressing hepatic cholesterol 7α-hydroxylase (Cyp7a1), the rate-limiting enzyme for the conversion of cholesterol to BAs. This mechanism involves the hepatic nuclear receptor small heterodimer partner and the intestinal fibroblast growth factor (FGF) 19 and 15. We investigated the role of activation of intestine-specific FXR in reducing hepatic levels of BAs and protecting the liver from cholestasis in mice. METHODS: We generated transgenic mice that express a constitutively active FXR in the intestine. Using FXR gain- and loss-of-function models, we studied the roles of intestinal FXR in mice with intrahepatic and extrahepatic cholestasis. RESULTS: Selective activation of intestinal FXR induced FGF15 and repressed hepatic Cyp7a1, reducing the pool size of BAs and changing the BA pool composition. Activation of intestinal FXR protected mice from obstructive extrahepatic cholestasis after bile duct ligation or administration of α-naphthylisothiocyanate. In Mdr2(-/-) mice, transgenic expression of activated FXR in the intestine protected against liver damage, whereas absence of FXR promoted progression of liver disease. CONCLUSIONS: Activation of FXR transcription in the intestine protects the liver from cholestasis in mice by inducing FGF15 expression and reducing the hepatic pool of BA; this approach might be developed to reverse cholestasis in patients.

Sulfated Progesterone Metabolites That Enhance Insulin Secretion via TRPM3 Are Reduced in Serum From Women With Gestational Diabetes Mellitus.

Serum progesterone sulfates were evaluated in the etiology of gestational diabetes mellitus (GDM). Serum progesterone sulfates were measured using ultra-performance liquid chromatography-tandem mass spectrometry in four patient cohorts: 1) the Hyperglycemia and Adverse Pregnancy Outcomes study; 2) London-based women of mixed ancestry and 3) U.K.-based women of European ancestry with or without GDM; and 4) 11-13 weeks pregnant women with BMI ≤25 or BMI ≥35 kg/m2 with subsequent uncomplicated pregnancies or GDM. Glucose-stimulated insulin secretion (GSIS) was evaluated in response to progesterone sulfates in mouse islets and human islets. Calcium fluorescence was measured in HEK293 cells expressing transient receptor potential cation channel subfamily M member 3 (TRPM3). Computer modeling using Molecular Operating Environment generated three-dimensional structures of TRPM3. Epiallopregnanolone sulfate (PM5S) concentrations were reduced in GDM (P < 0.05), in women with higher fasting plasma glucose (P < 0.010), and in early pregnancy samples from women who subsequently developed GDM with BMI ≥35 kg/m2 (P < 0.05). In islets, 50 µmol/L PM5S increased GSIS by at least twofold (P < 0.001); isosakuranetin (TRPM3 inhibitor) abolished this effect. PM5S increased calcium influx in TRPM3-expressing HEK293 cells. Computer modeling and docking showed identical positioning of PM5S to the natural ligand in TRPM3. PM5S increases GSIS and is reduced in GDM serum. The activation of GSIS by PM5S is mediated by TRPM3 in both mouse and human islets.

Maternal glucose homeostasis is impaired in mouse models of gestational cholestasis.

Women with intrahepatic cholestasis of pregnancy (ICP), a disorder characterised by raised serum bile acids, are at increased risk of developing gestational diabetes mellitus and have impaired glucose tolerance whilst cholestatic. FXR and TGR5 are modulators of glucose metabolism, and FXR activity is reduced in normal pregnancy, and further in ICP. We aimed to investigate the role of raised serum bile acids, FXR and TGR5 in gestational glucose metabolism using mouse models. Cholic acid feeding resulted in reduced pancreatic ß-cell proliferation and increased apoptosis in pregnancy, without altering insulin sensitivity, suggesting that raised bile acids affect ß-cell mass but are insufficient to impair glucose tolerance. Conversely, pregnant Fxr-/- and Tgr5-/- mice are glucose intolerant and have reduced insulin secretion in response to glucose challenge, and Fxr-/- mice are also insulin resistant. Furthermore, fecal bile acids are reduced in pregnant Fxr-/- mice. Lithocholic acid and deoxycholic acid, the principal ligands for TGR5, are decreased in particular. Therefore, we propose that raised serum bile acids and reduced FXR and TGR5 activity contribute to the altered glucose metabolism observed in ICP.

PGC-1ß Induces Susceptibility To Acetaminophen-Driven Acute Liver Failure.

Acetaminophen (APAP) is a worldwide commonly used painkiller drug. However, high doses of APAP can lead to acute hepatic failure and, in some cases, death. Previous studies indicated that different factors, including life-style and metabolic diseases, could predispose to the risk of APAP-induced liver failure. However, the molecular process that could favor APAP hepatotoxicity remains understood. Here, we reported that a short-term high fat-enriched diet worsens APAP-induced liver damage, by promoting liver accumulation of lipids that induces the activation of peroxisome proliferator-activated receptor gamma coactivator 1-beta (PGC-1ß). Therefore, we challenged mice with hepatic-specific PGC-1ß overexpression on a chow diet with a subtoxic dose of APAP and we found that PGC-1ß overexpression renders the liver more sensitive to APAP damage, mainly due to intense oxidative stress, finally ending up with liver necrosis and mice death. Overall, our results indicated that during high fat feeding, PGC-1ß adversely influences the ability of the liver to overcome APAP toxicity by orchestrating different metabolic pathways that finally lead to fatal outcome.

Biliary Phospholipids Sustain Enterocyte Proliferation and Intestinal Tumor Progression via Nuclear Receptor Lrh1 in mice.

The proliferative-crypt compartment of the intestinal epithelium is enriched in phospholipids and accumulation of phospholipids has been described in colorectal tumors. Here we hypothesize that biliary phospholipid flow could directly contribute to the proliferative power of normal and dysplastic enterocytes. We used Abcb4-/- mice which lack biliary phospholipid secretion. We first show that Abcb4-/- mice are protected against intestinal tumorigenesis. At the molecular level, the transcriptional activity of the nuclear receptor Liver Receptor Homolog-1 (Lrh1) is reduced in Abcb4-/- mice and its re-activation re-establishes a tumor burden comparable to control mice. Feeding Abcb4-/- mice a diet supplemented with phospholipids completely overcomes the intestinal tumor protective phenotype, thus corroborating the hypothesis that the absence of biliary phospholipids and not lack of Abcb4 gene per se is responsible for the protection. In turn, phospholipids cannot re-establish intestinal tumorigenesis in Abcb4-/- mice crossed with mice with intestinal specific ablation of Lrh1, a nuclear hormone receptor that is activates by phospholipids. Our data identify the key role of biliary phospholipids in sustaining intestinal mucosa proliferation and tumor progression through the activation of nuclear receptor Lrh1.

Master regulation of bile acid and xenobiotic metabolism via the FXR, PXR and CAR trio.

Recent discoveries highlighted intriguing molecular pathways that regulate synthesis, uptake, metabolism and excretion of bile acids and xenobiotics. The knowledge of factors that control these homeostatic processes is of clinical relevance to better understand the drug-drug interacting scenario as well as to control cholesterol detoxification, cholestasis and other conditions. Here we present evidences for the existence of a gut-liver safety network whereby activation of the nuclear receptor FXR, PXR, CAR trio provides protection against accumulation of exogenous and metabolic noxae.