Epigenomic regulation of bile acid metabolism: emerging role of transcriptional cofactors

Exploration of the intestinal flora to reveal the important contribution of Radix Astragali to Huangqi Jianzhong Tang in treating chronic atrophic gastritis rats

Radix Astragali (Huangqi in Chinese, HQ) is a commonly used Chinese herbal medicine for thousands of years. In this study, A classic prescription Huangqi Jianzhong tang (HQJZ) was selected to evaluate the important effect of HQ on rats with chronic atrophic gastritis (CAG) from the perspective of intestinal flora in cecal contents samples. Traditional pharmacological indicators, including weight change, pathological examination and biochemical indicators showed that HQ exerted favorable contribution to HQJZ against CAG, where the efficiencies of HQ and HQJZ were better than HY (HQJZ prepared without HQ). An accurate strategy was adopted to screen out the differential metabolites in the metabolomis analysis of intestinal flora in cecal contents samples based on the optimal screening factors, including VIP (importance of variables in projection), FC (fold change), AUROC (area under the receiver operating characteristic curve) and -ln(p-value), which were evaluated based on their interpreting, grouping, and predicting abilities of the performed orthogonal partial least-squares-discriminate analysis (OPLS-DA) models. Ten altered differential metabolites were obtained and associated with the intestinal flora, which HQ exerted the important metabolic contributions to HQJZ. The efficacy on the diversity of intestinal flora and their correlations with the altered metabolites further showed the important role of HQ in HQJZ composition. This work provided valuable approach for looking for potential biomarkers associated with metabolomics research with more accuracy, and provided new insights into the mechanisms to explain the efficacy of HQ contributing to HQJZ formula.

Antibiotic-Induced Gut Microbiota Dysbiosis Modulates Host Transcriptome and m6A Epitranscriptome via Bile Acid Metabolism

Gut microbiota can influence host gene expression and physiology through metabolites. Besides, the presence or absence of gut microbiome can reprogram host transcriptome and epitranscriptome as represented by N6-methyladenosine (m6A), the most abundant mammalian mRNA modification. However, which and how gut microbiota-derived metabolites reprogram host transcriptome and m6A epitranscriptome remain poorly understood. Here, investigation is conducted into how gut microbiota-derived metabolites impact host transcriptome and m6A epitranscriptome using multiple mouse models and multi-omics approaches. Various antibiotics-induced dysbiotic mice are established, followed by fecal microbiota transplantation (FMT) into germ-free mice, and the results show that bile acid metabolism is significantly altered along with the abundance change in bile acid-producing microbiota. Unbalanced gut microbiota and bile acids drastically change the host transcriptome and the m6A epitranscriptome in multiple tissues. Mechanistically, the expression of m6A writer proteins is regulated in animals treated with antibiotics and in cultured cells treated with bile acids, indicating a direct link between bile acid metabolism and m6A biology. Collectively, these results demonstrate that antibiotic-induced gut dysbiosis regulates the landscape of host transcriptome and m6A epitranscriptome via bile acid metabolism pathway. This work provides novel insights into the interplay between microbial metabolites and host gene expression.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

Bile Acids and Biliary Fibrosis

Biliary fibrosis is the driving pathological process in cholangiopathies such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). Cholangiopathies are also associated with cholestasis, which is the retention of biliary components, including bile acids, in the liver and blood. Cholestasis may worsen with biliary fibrosis. Furthermore, bile acid levels, composition and homeostasis are dysregulated in PBC and PSC. In fact, mounting data from animal models and human cholangiopathies suggest that bile acids play a crucial role in the pathogenesis and progression of biliary fibrosis. The identification of bile acid receptors has advanced our understanding of various signaling pathways involved in regulating cholangiocyte functions and the potential impact on biliary fibrosis. We will also briefly review recent findings linking these receptors with epigenetic regulatory mechanisms. Further detailed understanding of bile acid signaling in the pathogenesis of biliary fibrosis will uncover additional therapeutic avenues for cholangiopathies.

Regulation of cholesterol homeostasis in health and diseases: from mechanisms to targeted therapeutics

Disturbed cholesterol homeostasis plays critical roles in the development of multiple diseases, such as cardiovascular diseases (CVD), neurodegenerative diseases and cancers, particularly the CVD in which the accumulation of lipids (mainly the cholesteryl esters) within macrophage/foam cells underneath the endothelial layer drives the formation of atherosclerotic lesions eventually. More and more studies have shown that lowering cholesterol level, especially low-density lipoprotein cholesterol level, protects cardiovascular system and prevents cardiovascular events effectively. Maintaining cholesterol homeostasis is determined by cholesterol biosynthesis, uptake, efflux, transport, storage, utilization, and/or excretion. All the processes should be precisely controlled by the multiple regulatory pathways. Based on the regulation of cholesterol homeostasis, many interventions have been developed to lower cholesterol by inhibiting cholesterol biosynthesis and uptake or enhancing cholesterol utilization and excretion. Herein, we summarize the historical review and research events, the current understandings of the molecular pathways playing key roles in regulating cholesterol homeostasis, and the cholesterol-lowering interventions in clinics or in preclinical studies as well as new cholesterol-lowering targets and their clinical advances. More importantly, we review and discuss the benefits of those interventions for the treatment of multiple diseases including atherosclerotic cardiovascular diseases, obesity, diabetes, nonalcoholic fatty liver disease, cancer, neurodegenerative diseases, osteoporosis and virus infection.

The Role of Bile Acids in the Human Body and in the Development of Diseases

Bile acids are specific and quantitatively important organic components of bile, which are synthesized by hepatocytes from cholesterol and are involved in the osmotic process that ensures the outflow of bile. Bile acids include many varieties of amphipathic acid steroids. These are molecules that play a major role in the digestion of fats and the intestinal absorption of hydrophobic compounds and are also involved in the regulation of many functions of the liver, cholangiocytes, and extrahepatic tissues, acting essentially as hormones. The biological effects are realized through variable membrane or nuclear receptors. Hepatic synthesis, intestinal modifications, intestinal peristalsis and permeability, and receptor activity can affect the quantitative and qualitative bile acids composition significantly leading to extrahepatic pathologies. The complexity of bile acids receptors and the effects of cross-activations makes interpretation of the results of the studies rather difficult. In spite, this is a very perspective direction for pharmacology.

Long noncoding RNAs-a new dimension in the molecular architecture of the bile acid/FXR pathway

Bile acids, regarded as the body's detergent for digesting lipids, also function as critical signaling molecules that regulate cholesterol and triglyceride levels in the body. Bile acids are the natural ligands of the nuclear receptor, FXR, which controls an intricate network of cellular pathways to maintain metabolic homeostasis. In recent years, growing evidence supports that many cellular actions of the bile acid/FXR pathway are mediated by long non-coding RNAs (lncRNAs), and lncRNAs are in turn powerful regulators of bile acid levels and FXR activities. In this review, we highlight the substantial progress made in the understanding of the functional and mechanistic role of lncRNAs in bile acid metabolism and how lncRNAs connect bile acid activity to additional metabolic processes. We also discuss the potential of lncRNA studies in elucidating novel molecular mechanisms of the bile acid/FXR pathway and the promise of lncRNAs as potential diagnostic markers and therapeutic targets for diseases associated with altered bile acid metabolism.

Biomarkers of cholestasis

Cholestasis is a major pathological manifestation, often resulting in detrimental liver conditions, which occurs in a variety of indications collectively termed cholestatic liver diseases. The frequent asymptomatic character and complexity of cholestasis, together with the lack of a straightforward biomarker, hampers early detection and treatment of the condition. The 'omics' era, however, has resulted in a plethora of cholestatic indicators, yet a single clinically applicable biomarker for a given cholestatic disease remains missing. The criteria to fulfil as an ideal biomarker as well as the challenging molecular pathways in cholestatic liver diseases advocate for a scenario in which multiple biomarkers, originating from different domains, will be assessed concomitantly. This review gives an overview of classical clinical and novel molecular biomarkers in cholestasis, focusing on their benefits and drawbacks.

25-Hydroxycholesterol 3-sulfate is an endogenous ligand of DNA methyltransferases in hepatocytes

The oxysterol sulfate, 25-hydroxycholesterol 3-sulfate (25HC3S), has been shown to play an important role in lipid metabolism, inflammatory response, and cell survival. However, the mechanism(s) of its function in global regulation is unknown. The current study investigates the molecular mechanism by which 25HC3S functions as an endogenous epigenetic regulator. To study the effects of oxysterols/sterol sulfates on epigenetic modulators, 12 recombinant epigenetic enzymes were used to determine whether 25HC3S acts as their endogenous ligand. The enzyme kinetic study demonstrated that 25HC3S specifically inhibited DNA methyltransferases (DNMTs), DNMT1, DNMT3a, and DNMT3b with IC₅₀ of 4.04, 3.03, and 9.05 × 10^-6 M, respectively. In human hepatocytes, high glucose induces lipid accumulation by increasing promoter CpG methylation of key genes involved in development of nonalcoholic fatty liver diseases. Using this model, whole genome bisulfate sequencing analysis demonstrated that 25HC3S converts the ^5mCpG to CpG in the promoter regions of 1,074 genes. In addition, we observed increased expression of the demethylated genes, which are involved in the master signaling pathways, including MAPK-ERK, calcium-AMP-activated protein kinase, and type II diabetes mellitus pathways. mRNA array analysis showed that the upregulated genes encoded for key elements of cell survival; conversely, downregulated genes encoded for key enzymes that decrease lipid biosynthesis. Taken together, our results indicate that the expression of these key elements and enzymes are regulated by the demethylated signaling pathways. We summarized that 25HC3S DNA demethylation of ^5mCpG in promoter regions is a potent regulatory mechanism.

American eels produce and release bile acid profiles that vary across life stage

The American eel (Anguilla rostrata) is an imperilled fish hypothesized to use conspecific cues, in part, to coordinate long-distance migration during their multistage life history. Here, holding water and tissue from multiple American eel life stages was collected and analysed for the presence, profile and concentration of bile acids. Distinct bile acid profiles were identified in glass, elver, yellow eel and silver eel holding waters using ultraperformance liquid chromatography high-resolution mass spectrometry and principal component analysis. Taurochenodeoxycholic acid, taurodeoxycholic acid, cholic acid, deoxycholic acid, taurolithocholic acid and taurocholic acid were detected in whole tissue of American glass eels and elvers, and in liver, intestine and gallbladder samples of late-stage yellow eels. Bile acids were not a major component of silver eel washings or tissue. This study is novel because little was previously known about bile acids produced and emitted into the environment by American eels. Future behavioural studies could evaluate whether any bile acids produced by American eels influence conspecific migratory behaviour.

Enhancer deletion and allelic effects define a regulatory molecular mechanism at the VLDLR cholesterol GWAS locus

Total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) are heritable risk factors for cardiovascular disease, yet the molecular mechanisms underlying the majority of blood lipid-associated genome-wide association studies signals remain elusive. One association signal is located in intron 3 of VLDLR; rs3780181-A is a risk allele associated (P ≤ 2 × 10-9) with increased TC and LDL-C. We investigated variants, genes and mechanisms underlying this association signal. We used a functional genetic approach to show that the intronic region spanning rs3780181 exhibited 1.6-7.6-fold enhancer activity in human HepG2 hepatocyte, THP-1 monocyte and Simpson-Golabi-Behmel Syndrome (SGBS) preadipocyte cells and that the rs3780181-A risk allele showed significantly less enhancer activity compared with the G allele, consistent with the direction of an expression quantitative trait locus in liver. In addition, rs3780181 alleles showed differential binding to multiple nuclear proteins, including stronger IRF2 binding to the rs3780181 G allele. We used a CRISPR-cas9 approach to delete 475 and 663 bp of the putative enhancer element in HEK293T kidney cells; compared to expression of mock-edited cell lines, the homozygous enhancer deletion cell lines showed 1.2-fold significantly (P < 0.04) decreased expression of VLDLR, as well as 1.5-fold decreased expression of SMARCA2, located 388 kb away. Together, these results identify an enhancer of VLDLR expression and suggest that altered binding of one or more factors bound to rs3780181 alleles decreases enhancer activity and reduces at least VLDLR expression, leading to increased TC and LDL-C.

Bile Acids and Cancer: Direct and Environmental-Dependent Effects

Bile acids (BAs) regulate the absorption of fat-soluble vitamins, cholesterol and lipids but have also a key role as singalling molecules and in the modulation of epithelial cell proliferation, gene expression and metabolism. These homeostatic pathways, when disrupted, are able to promote local inflammation, systemic metabolic disorders and, ultimately, cancer. The effect of hydrophobic BAs, in particular, can be linked with cancer in several digestive (mainly oesophagus, stomach, liver, pancreas, biliary tract, colon) and extra-digestive organs (i.e. prostate, breast) through a complex series of mechanisms including direct oxidative stress with DNA damage, apoptosis, epigenetic factors regulating gene expression, reduced/increased expression of nuclear receptors (mainly farnesoid X receptor, FXR) and altered composition of gut microbiota, also acting as a common interface between environmental factors (including diet, lifestyle, exposure to toxics) and the molecular events promoting cancerogenesis. Primary prevention strategies (i.e. changes in dietary habits and lifestyle, reduced exposure to environmental toxics) mainly able to modulate gut microbiota and the epigenome, and the therapeutic use of hydrophilic BAs to counterbalance the negative effects of the more hydrophobic BAs might be, in the near future, part of useful tools for cancer prevention and management.

Bile acids as global regulators of hepatic nutrient metabolism

Bile acids (BA) are synthesized from cholesterol in the liver. They are essential for promotion of the absorption of lipids, cholesterol, and lipid-soluble vitamins from the intestines. BAs are hormones that regulate nutrient metabolism by activating nuclear receptors (farnesoid X receptor (FXR), pregnane X receptor, vitamin D) and G protein-coupled receptors (e.g., TGR5, sphingosine-1-phosphate receptor 2 (S1PR2)) in the liver and intestines. In the liver, S1PR2 activation by conjugated BAs activates the extracellular signal-regulated kinase 1/2 and AKT signaling pathways, and nuclear sphingosine kinase 2. The latter produces sphingosine-1-phosphate (S1P), an inhibitor of histone deacetylases 1/2, which allows for the differential up-regulation of expression of genes involved in the metabolism of sterols and lipids. We discuss here the emerging concepts of the interactions of BAs, FXR, insulin, S1P signaling and nutrient metabolism.

A postprandial FGF19-SHP-LSD1 regulatory axis mediates epigenetic repression of hepatic autophagy

Lysosome-mediated autophagy is essential for cellular survival and homeostasis upon nutrient deprivation, but is repressed after feeding. Despite the emerging importance of transcriptional regulation of autophagy by nutrient-sensing factors, the role for epigenetic control is largely unexplored. Here, we show that Small Heterodimer Partner (SHP) mediates postprandial epigenetic repression of hepatic autophagy by recruiting histone demethylase LSD1 in response to a late fed-state hormone, FGF19 (hFGF19, mFGF15). FGF19 treatment or feeding inhibits macroautophagy, including lipophagy, but these effects are blunted in SHP-null mice or LSD1-depleted mice. In addition, feeding-mediated autophagy inhibition is attenuated in FGF15-null mice. Upon FGF19 treatment or feeding, SHP recruits LSD1 to CREB-bound autophagy genes, including Tfeb, resulting in dissociation of CRTC2, LSD1-mediated demethylation of gene-activation histone marks H3K4-me2/3, and subsequent accumulation of repressive histone modifications. Both FXR and SHP inhibit hepatic autophagy interdependently, but while FXR acts early, SHP acts relatively late after feeding, which effectively sustains postprandial inhibition of autophagy. This study demonstrates that the FGF19-SHP-LSD1 axis maintains homeostasis by suppressing unnecessary autophagic breakdown of cellular components, including lipids, under nutrient-rich postprandial conditions.

The role of bile acids in metabolic regulation

Bile acids (BA), long believed to only have lipid-digestive functions, have emerged as novel metabolic modulators. They have important endocrine effects through multiple cytoplasmic as well as nuclear receptors in various organs and tissues. BA affect multiple functions to control energy homeostasis, as well as glucose and lipid metabolism, predominantly by activating the nuclear farnesoid X receptor and the cytoplasmic G protein-coupled BA receptor TGR5 in a variety of tissues. However, BA also are aimed at many other cellular targets in a wide array of organs and cell compartments. Their role in the pathogenesis of diabetes, obesity and other 'diseases of civilization' becomes even more clear. They also interact with the gut microbiome, with important clinical implications, further extending the complexity of their biological functions. Therefore, it is not surprising that BA metabolism is substantially modulated by bariatric surgery, a phenomenon contributing favorably to the therapeutic effects of these surgical procedures. Based on these data, several therapeutic approaches to ameliorate obesity and diabetes have been proposed to affect the cellular targets of BA.

A shift in paradigm towards human biology-based systems for cholestatic-liver diseases

Cholestatic-liver diseases (CLDs) arise from diverse causes ranging from genetic factors to drug-induced cholestasis. The so-called diseases of civilization (obesity, diabetes, metabolic disorders, non-alcoholic liver disease, cardiovascular diseases, etc.) are intricately implicated in liver and gall bladder diseases. Although CLDs have been extensively studied, there seem to be important gaps in the understanding of human disease. Despite the fact that many animal models exist and substantial clinical data are available, translation of this knowledge towards therapy has been disappointingly limited. Recent advances in liver cell culture such as in vivo-like 3D cultivation of human primary hepatic cells, human induced pluripotent stem cell-derived hepatocytes; and cutting-edge analytical techniques such as 'omics' technologies and high-content screenings could play a decisive role in deeper mechanistic understanding of CLDs. This Topical Review proposes a roadmap to human biology-based research using omics technologies providing quantitative information on mechanisms in an adverse outcome/disease pathway framework. With modern sensitive tools, a shift in paradigm in human disease research seems timely and even inevitable to overcome species barriers in translation.

Farnesoid X receptor-induced lysine-specific histone demethylase reduces hepatic bile acid levels and protects the liver against bile acid toxicity

Bile acids (BAs) function as endocrine signaling molecules that activate multiple nuclear and membrane receptor signaling pathways to control fed-state metabolism. Since the detergent-like property of BAs causes liver damage at high concentrations, hepatic BA levels must be tightly regulated. Bile acid homeostasis is regulated largely at the level of transcription by nuclear receptors, particularly the primary BA receptor, farnesoid X receptor, and small heterodimer partner, which inhibits BA synthesis by recruiting repressive histone-modifying enzymes. Although histone modifiers have been shown to regulate BA-responsive genes, their in vivo functions remain unclear. Here, we show that lysine-specific histone demethylase1 (LSD1) is directly induced by BA-activated farnesoid X receptor, is recruited to the BA synthetic genes Cyp7a1 and Cyp8b1 and the BA uptake transporter gene Ntcp, and removes a gene-activation marker, trimethylated histone H3 lysine-4, leading to gene repression. Recruitment of LSD1 was dependent on small heterodimer partner, and LSD1-mediated demethylation of trimethylated histone H3 lysine-4 was required for additional repressive histone modifications, acetylated histone 3 on lysine 9 and 14 deacetylation, and acetylated histone 3 on lysine 9 methylation. A BA overload, feeding 0.5% cholic acid chow for 6 days, resulted in adaptive responses of altered expression of hepatic genes involved in BA synthesis, transport, and detoxification/conjugation. In contrast, adenovirus-mediated downregulation of hepatic LSD1 blunted these responses, which led to substantial increases in liver and serum BA levels, serum alanine aminotransferase and aspartate aminotransferase levels, and hepatic inflammation.

CONCLUSION

This study identifies LSD1 as a novel histone-modifying enzyme in the orchestrated regulation mediated by the farnesoid X receptor and small heterodimer partner that reduces hepatic BA levels and protects the liver against BA toxicity.

Thyroid-stimulating hormone regulates hepatic bile acid homeostasis via SREBP-2/HNF-4α/CYP7A1 axis

BACKGROUND & AIMS

Bile acids (BAs) play a crucial role in dietary fat digestion and in the regulation of lipid, glucose, and energy metabolism. Thyroid-stimulating hormone (TSH) is a hormone produced by the anterior pituitary gland that directly regulates several metabolic pathways. However, the impact of TSH on BA homeostasis remains largely unknown.

METHODS

We analyzed serum BA and TSH levels in healthy volunteers under strict control of caloric intake. Thyroidectomized rats were administered thyroxine and injected with different doses of TSH. Tshr(-/-) mice were supplemented with thyroxine, and C57BL/6 mice were injected with Tshr-siRNA via the tail vein. The serum BA levels, BA pool size, and fecal BA excretion rate were measured. The regulation of SREBP-2, HNF-4α, and CYP7A1 by TSH were analyzed using luciferase reporter, RNAi, EMSA, and CHIP assays.

RESULTS

A negative correlation was observed between the serum levels of TSH and the serum BA levels in healthy volunteers. TSH administration led to a decrease in BA content and CYP7A1 activity in thyroidectomized rats supplemented with thyroxine. When Tshr was silenced in mice, the BA pool size, fecal BA excretion rate, and serum BA levels all increased. Additionally, we found that HNF-4α acts as a critical molecule through which TSH represses CYP7A1 activity. We further confirmed that the accumulation of mature SREBP-2 protein could impair the capacity of nuclear HNF-4α to bind to the CYP7A1 promoter, a mechanism that appears to mediate the effects of TSH.

CONCLUSIONS

TSH represses hepatic BA synthesis via a SREBP-2/HNF-4α/CYP7A1 signaling pathway. This finding strongly supports the notion that TSH is an important pathophysiological regulator of liver BA homeostasis independently of thyroid hormones.

Conjugated bile acid-activated S1P receptor 2 is a key regulator of sphingosine kinase 2 and hepatic gene expression

Bile acids are important hormones during the feed/fast cycle, allowing the liver to coordinately regulate nutrient metabolism. How they accomplish this has not been fully elucidated. Conjugated bile acids activate both the ERK1/2 and AKT signaling pathways via sphingosine 1-phosphate receptor 2 (S1PR2) in rodent hepatocytes and in vivo. Here, we report that feeding mice a high-fat diet, infusion of taurocholate into the chronic bile fistula rat, or overexpression of the gene encoding S1PR2 in mouse hepatocytes significantly upregulated hepatic sphingosine kinase 2 (SphK2) but not SphK1. Key genes encoding nuclear receptors/enzymes involved in nutrient metabolism were significantly downregulated in livers of S1PR2(-/-) and SphK2(-/-) mice. In contrast, overexpression of the gene encoding S1PR2 in primary mouse hepatocytes differentially increased SphK2, but not SphK1, and mRNA levels of key genes involved in nutrient metabolism. Nuclear levels of sphingosine-1-phosphate, an endogenous inhibitor of histone deacetylases 1 and 2, as well as the acetylation of histones H3K9, H4K5, and H2BK12 were significantly decreased in hepatocytes prepared from S1PR2(-/-) and SphK2(-/-) mice.

CONCLUSION

Both S1PR2(-/-) and SphK2(-/-) mice rapidly developed fatty livers on a high-fat diet, suggesting the importance of conjugated bile acids, S1PR2, and SphK2 in regulating hepatic lipid metabolism.

Bile acid signaling through farnesoid X and TGR5 receptors in hepatobiliary and intestinal diseases

BACKGROUND

The well-known functions of bile acids (BAs) are the emulsification and absorption of lipophilic xenobiotics. However, the emerging evidences in the past decade showed that BAs act as signaling molecules that not only autoregulate their own metabolism and enterohepatic recirculation, but also as important regulators of integrative metabolism by activating nuclear and membrane-bound G protein-coupled receptors. The present review was to get insight into the role of maintenance of BA homeostasis and BA signaling pathways in development and management of hepatobiliary and intestinal diseases.

DATA SOURCES

Detailed and comprehensive search of PubMed and Scopus databases was carried out for original and review articles.

RESULTS

Disturbances in BA homeostasis contribute to the development of several hepatobiliary and intestinal disorders, such as non-alcoholic fatty liver disease, liver cirrhosis, cholesterol gallstone disease, intestinal diseases and both hepatocellular and colorectal carcinoma.

CONCLUSION

Further efforts made in order to advance the understanding of sophisticated BA signaling network may be promising in developing novel therapeutic strategies related not only to hepatobiliary and gastrointestinal but also systemic diseases.

Epigenetic regulation of cholesterol homeostasis

Although best known as a risk factor for cardiovascular disease, cholesterol is a vital component of all mammalian cells. In addition to key structural roles, cholesterol is a vital biochemical precursor for numerous biologically important compounds including oxysterols and bile acids, as well as acting as an activator of critical morphogenic systems (e.g., the Hedgehog system). A variety of sophisticated regulatory mechanisms interact to coordinate the overall level of cholesterol in cells, tissues and the entire organism. Accumulating evidence indicates that in additional to the more “traditional” regulatory schemes, cholesterol homeostasis is also under the control of epigenetic mechanisms such as histone acetylation and DNA methylation. The available evidence supporting a role for these mechanisms in the control of cholesterol synthesis, elimination, transport and storage are the focus of this review.

Differential abundance of IGF1, bile acids, and the genes involved in their signaling in the dominant follicle microenvironment of lactating cows and nulliparous heifers

It is well documented that incidence of fertility problems is high in lactating cows but not in heifers of the same genetic merit. Understanding the metabolic and molecular differences between fertile heifers and relatively infertile lactating cows will help us understand the pathogenesis of infertility in dairy cows. Follicular waves in lactating cows (30-50 days in milk; n = 12) and heifers (n = 10) were synchronized by ultrasound-guided follicle ablation. Follicular fluid and granulosa cells of the dominant follicle were collected by ultrasound-guided aspiration along with blood sampling on Day 6 after synchronization. Dominant and subordinate follicles were larger in lactating cows than in heifers. Metabolic stress in lactating cows was evidenced by lower glucose and higher ß-hydroxy butyric acid compared with heifers. Insulin-like growth factor 1 signaling was reduced in the dominant follicle in lactating cows through reduced insulin-like growth factor 1 concentrations in plasma and follicular fluid of the dominant follicle, and reduced expression of pregnancy-associated plasma protein A (PAPPA) in their granulosa cells. We also found increased levels of total bile acids in the follicular fluid of the dominant follicle of lactating cows compared with heifers. Granulosa cells of the dominant follicle had higher expression of SLC10A2 and GPBAR1 (bile acid transporter and receptor, respectively) in lactating cows. These novel data are indicative of increased bile acid signaling within the dominant follicles of lactating cows compared with heifers. Overall, we demonstrate in the present study the metabolic, endocrine, and molecular differences within the microenvironment of the dominant follicles in lactating cows and heifers. These differences in follicular microenvironment may contribute toward abnormal ovarian function in lactating dairy cows.

Bile acid signal-induced phosphorylation of small heterodimer partner by protein kinase Cζ is critical for epigenomic regulation of liver metabolic genes

Bile acids (BAs) are recently recognized key signaling molecules that control integrative metabolism and energy expenditure. BAs activate multiple signaling pathways, including those of nuclear receptors, primarily farnesoid X receptor (FXR), membrane BA receptors, and FXR-induced FGF19 to regulate the fed-state metabolism. Small heterodimer partner (SHP) has been implicated as a key mediator of these BA signaling pathways by recruitment of chromatin modifying proteins, but the key question of how SHP transduces BA signaling into repressive histone modifications at liver metabolic genes remains unknown. Here we show that protein kinase Cζ (PKCζ) is activated by BA or FGF19 and phosphorylates SHP at Thr-55 and that Thr-55 phosphorylation is critical for the epigenomic coordinator functions of SHP. PKCζ is coimmunopreciptitated with SHP and both are recruited to SHP target genes after bile acid or FGF19 treatment. Activated phosphorylated PKCζ and phosphorylated SHP are predominantly located in the nucleus after FGF19 treatment. Phosphorylation at Thr-55 is required for subsequent methylation at Arg-57, a naturally occurring mutation site in metabolic syndrome patients. Thr-55 phosphorylation increases interaction of SHP with chromatin modifiers and their occupancy at selective BA-responsive genes. This molecular cascade leads to repressive modifications of histones at metabolic target genes, and consequently, decreased BA pools and hepatic triglyceride levels. Remarkably, mutation of Thr-55 attenuates these SHP-mediated epigenomic and metabolic effects. This study identifies PKCζ as a novel key upstream regulator of BA-regulated SHP function, revealing the role of Thr-55 phosphorylation in epigenomic regulation of liver metabolism.