Biological Age, PNPLA3, and Risk of Metabolic Dysfunction-associated Steatotic Liver Disease.
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Journal Article↗
Biomedical subjects
Anna Mae Diehl
Publications and source records attributed to Anna Mae Diehl.
PPARgamma agonists prevent TGFbeta1/Smad3-signaling in human hepatic stellate cells.
PPARgamma agonists inhibit liver fibrosis, but the mechanisms involved are uncertain. We hypothesized that PPARgamma agonists inhibit transforming growth factor (TGF)beta1-activation of TGFbeta receptor (TGFbetaR)-1 signaling in quiescent stellate cells, thereby abrogating Smad3-dependent induction of extracellular matrix (ECM) genes, such as PAI-1 and collagen-1alphaI. To test this, human HSC were cultured to induce a quiescent phenotype, characterized by lipid accumulation and PPARgamma expression and transcriptional activity. These adipocytic HSC were then treated with TGFbeta1+/-a TGFbetaR-1 kinase inhibitor (SB431542) or a PPARgamma agonist (GW7845). TGFbeta1 caused dose- and time-dependent increases in Smad3 phosphorylation, followed by induction of collagen and PAI-1 expression. Like the TGFbetaR-1 kinase inhibitor, the PPARgamma agonist caused dose-dependent inhibition of all of these responses without effecting HSC proliferation or viability. Thus, the anti-fibrotic actions of PPARgamma agonists reflect their ability to inhibit TGFbeta1-TGFbetaR1 signaling that initiates ECM gene expression in quiescent HSC.
Activin Receptors, Type I↗
Interleukin-15 increases hepatic regenerative activity.
BACKGROUND/AIMS: Interleukin-15 (IL-15) is expressed in many organs. It generally inhibits apoptosis and increases cellular proliferation and differentiation. However, IL-15's roles in liver are unknown. We aimed to determine if IL-15 influences hepatic integrity and regenerative activity. METHODS: Expression of IL-15 and its receptors was evaluated in several liver injury models, primary hepatocytes, and two liver cell lines. Effects of IL-15 on viability, proliferation, and apoptosis were assessed in cultured liver cells, and also in the livers of healthy mice. RESULTS: IL-15 and its receptors are expressed constitutively in healthy livers, and ligand expression is induced in injured livers. Cultured primary hepatocytes and liver cell lines express IL-15 and its receptors. Administration of IL-15 has minimal effects on cultured liver cells, but significantly up-regulates oval cell accumulation, cyclin mRNA expression, and mature hepatocyte replication in healthy mice. These effects are associated with focal hepatic inflammation and increased expression of TNF-alpha and IFN-gamma, but not with increased cell death or aminotransferase release. CONCLUSIONS: IL-15 expression increases during liver injury and IL-15 treatment induces a wound healing-type response in healthy adult mice. These findings suggest that IL-15 may contribute to regenerative activity in damaged liver.
Animals↗
Evidence for epithelial-mesenchymal transitions in adult liver cells.
Both myofibroblastic hepatic stellate cells (HSC) and hepatic epithelial progenitors accumulate in damaged livers. In some injured organs, the ability to distinguish between fibroblastic and epithelial cells is sometimes difficult because cells undergo epithelial-mesenchymal transitions (EMT). During EMT, cells coexpress epithelial and mesenchymal cell markers. To determine whether EMT occurs in adult liver cells, we analyzed the expression profile of primary HSC, two HSC lines, and hepatic epithelial progenitors. As expected, all HSC expressed HSC markers. Surprisingly, these markers were also expressed by epithelial progenitors. In addition, one HSC line expressed typical epithelial progenitor mRNAs, and these epithelial markers were inducible in the second HSC line. In normal and damaged livers, small ductular-type cells stained positive for an HSC marker. In conclusion, HSC and hepatic epithelial progenitors both coexpress epithelial and mesenchymal markers, providing evidence that EMT occurs in adult liver cells.
Animals↗
Nonalcoholic steatohepatitis and nonalcoholic Fatty liver disease in young women with polycystic ovary syndrome.
CONTEXT: Nonalcoholic fatty liver disease and polycystic ovary syndrome (PCOS) are both associated with insulin resistance. Thus, women with PCOS may have an increased prevalence of nonalcoholic fatty liver disease, including nonalcoholic steatohepatitis (NASH). OBJECTIVE: The objective of the study was to determine the prevalence and characteristics of NASH and abnormal aminotransferase activity in women with PCOS. DESIGN: The study is a retrospective chart review. SETTING: The setting is an academic endocrinology clinic. PATIENTS: Patients were 200 women with PCOS, defined as irregular menses and hyperandrogenism. MAIN OUTCOME MEASURES: Biopsy-documented NASH and aminotransferase levels were the main outcome measures. RESULTS: Fifteen percent (29 of 200) had aspartate aminotransferase and/or alanine aminotransferase more than 60 U/liter. Women with aminotransferase elevations had lower high-density lipoprotein (HDL) (41 vs. 50 mg/dl, P = 0.006), higher triglycerides (174 vs. 129 mg/dl, P = 0.024), and higher fasting insulin (21 vs. 12 microIU/ml, P = 0.036) compared with women with normal aminotransferases. Six women (mean age 29 yr) with persistent aminotransferase elevations underwent liver biopsy. All six had NASH with fibrosis. Compared with the 194 of 200 PCOS women who did not undergo biopsy, women with biopsy-documented NASH had lower HDL (median 34 vs. 50 mg/dl, P < 0.001), and higher triglycerides (245 vs. 132 mg/dl, P = 0.025), fasting insulin (26 vs. 13 microIU/ml, P = 0.038), aspartate aminotransferase (144 vs. 22 U/liter, P < 0.001), and alanine aminotransferase (143 vs. 28 U/liter, P < 0.001). CONCLUSION: Abnormal aminotransferase activity is common in women with PCOS. Low HDL, high triglycerides, and high fasting insulin were associated with abnormal aminotransferase activity. Some women already had evidence of NASH with fibrosis. Further studies are needed to evaluate whether to screen PCOS women for liver disease at an earlier age than is currently recommended for the general population.
Adolescent↗
What impact does a specialized center for transplantation and heptobiliary disease have on post-graduate resident training of gastroenterologists and surgeons?
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Accreditation↗
Sustained activation of Rac1 in hepatic stellate cells promotes liver injury and fibrosis in mice.
Rac, a small, GTP-binding protein in the Rho family, regulates several cellular functions, including the activation of NADPH oxidase, a major intracellular producer of reactive oxygen species (ROS). Hepatic stellate cells (HSCs) isolated from mice that are genetically deficient in NADPH oxidase produce less ROS, and their activation during chronic liver injury is abrogated, resulting in decreased liver fibrosis. Therefore, we hypothesized that HSC ROS production and activation would be enhanced, and fibrosis worsened, by increasing Rac expression in HSCs. To achieve this, we used transgenic mice that express constitutively active human Rac1 under the control of the alpha-smooth muscle actin (alpha-sma) promoter, because alpha-sma expression is induced spontaneously during HSC activation. Transgene expression was upregulated progressively during culture of primary Rac-transgenic HSCs, and this increased HSC ROS production as well as expression of activation markers and collagen. Similarly, Rac mice treated with carbon tetrachloride (CCl(4)) accumulated greater numbers of activated HSCs and had more liver damage, hepatocyte apoptosis, and liver fibrosis-as well as higher mortality-than CCl(4)-treated wild-type mice. In conclusion, sustained activation of Rac in HSCs perpetuates their activation and exacerbates toxin-induced liver injury and fibrosis, prompting speculation that Rac may be a therapeutic target in patients with cirrhosis.
Actins↗
Dysregulation of the Hedgehog pathway in human hepatocarcinogenesis.
Hedgehog (Hh) pathway activation promotes tumors in several endodermally derived tissues, but its role in the pathogenesis of hepatocellular carcinoma (HCC) is unknown. Although normal hepatocytes lack Hh signaling, activation of the Hh pathway in endodermal progenitors is required for liver development. Thus, we hypothesized that hepatocarcinogenesis may involve regulation of Hh signaling. This pathway is activated when Hh ligand binds to its receptor, Patched (PTC). In an unoccupied state, PTC normally functions as a tumor suppressor that inhibits Smoothened (SMO), a proto-oncoprotein, from activating downstream components and transcription of target genes. Here we show that in HCCs, overexpression of the Smo proto-oncogene, as well as an increase in the stoichiometric ratio of Smo to Ptc mRNA levels, correlated with tumor size, a prognostic indicator in HCC biology. In one tumor we identified a novel Smo mutation in an evolutionarily conserved residue. We also demonstrated that HCC cell lines (HepG2 and Hep3B) expressed Hh pathway components and activated Hh transcriptional targets. In Hep3B cells, cyclopamine, an inhibitor of wild-type SMO, had no effect, but KAAD-cyclopamine, a blocker of oncogenic SMO, inhibited Hh signaling activity by 50%, decreased expression of the hepatocarcinogenic oncogene, c-myc, by 8-fold, and inhibited the growth rate of Hep3B cells by 94%. These data support our hypothesis that Hh signaling is dysregulated in human hepatocarcinogenesis. We demonstrate that overexpression and/or tumorigenic activation of the Smo proto-oncogene mediates c-myc overexpression which plays a critical role in hepatocarcinogenesis and suggests that Smo is a prognostic factor in HCC tumorigenesis.
Animals↗
Hedgehog signaling maintains resident hepatic progenitors throughout life.
Hedgehog signaling through its receptor, Patched, activates transcription of genes, including Patched, that regulate the fate of various progenitors. Although Hedgehog signaling is required for endodermal commitment and hepatogenesis, the possibility that it regulates liver turnover in adults had not been considered because mature liver epithelial cells lack Hedgehog signaling. Herein, we show that this pathway is essential throughout life for maintaining hepatic progenitors. Patched-expressing cells have been identified among endodermally lineage-restricted, murine embryonic stem cells as well as in livers of fetal and adult Ptc-lacZ mice. An adult-derived, murine hepatic progenitor cell line expresses Patched, and Hedgehog-responsive cells exist in stem cell compartments of fetal and adult human livers. In both species, manipulation of Hedgehog activity influences hepatic progenitor cell survival. Therefore, Hedgehog signaling is conserved in hepatic progenitors from fetal development through adulthood and may be a new therapeutic target in patients with liver damage.
Animals↗
Lessons from animal models of NASH.
Studies of animals with obesity-related liver disease have taught us much about the mechanisms that mediate this pathology. Our work with genetically obese, insulin-resistant ob/ob mice demonstrates that hepatocytes become steatotic and die at increased rates. Thus, ob/ob mice develop non-alcoholic steatohepatitis (NASH) spontaneously. NASH is intimately related to the insulin resistance (i.e., metabolic) syndrome, a constellation of disorders that result from abnormal production of hormones and cytokines that regulate inflammatory responses. Like humans with the metabolic syndrome, ob/ob mice exhibit increased tumor necrosis factor (TNF) but relatively low levels of adiponectin. Because TNF and adiponectin typically antagonize each other, the combination of increased TNF and decreased adiponectin promotes a state of high TNF activity. Consequently, hepatocytes generate excessive reactive oxygen species (ROS), have altered viability, accumulate lipid and are resistant to insulin. Treatments that inhibit TNF activity or that increase adiponectin improve NASH in ob/ob mice, other mice and humans with NASH. Hence, there is no doubt that cytokine and hormonal imbalances play a key role in the pathogenesis of NASH. However, the fundamental cellular events involved are still poorly understood. Even within very small areas of livers with NASH, most hepatocytes are merely steatotic, while others are ballooned (pre-necrotic), and still others have succumbed to apoptosis. This observation suggests cell-to-cell variability in the response to chronic inflammatory stress. In NASH, most steatotic hepatocytes survive by inducing adaptive, cytoprotective factors. However, such cells respond to super-imposed toxic and mitogenic stimuli differently than (3)naïve(2) (un-adapted) hepatocytes. Fatty hepatocytes tend to be more vulnerable to ATP depletion and less proliferative, perpetuating chronic liver injury while encouraging the expansion of liver progenitor populations that may become neoplastic. Finally, like other causes of chronic injury, NASH increases the risk for cirrhosis. Studies of ob/ob mice demonstrate that progression to cirrhosis is potentiated by leptin. Leptin probably acts at multiple levels to promote hepatic fibrosis, including direct activation of stellate cells via leptin receptors, regulation of pro- and anti-fibrogenic cytokine production by innate immune cells, and modulation of other neuronal factors that regulate stellate cell activation. The latter two mechanisms seem to dominate because stellate cell activation, fibrogenic cytokine production, collagen gene expression and fibrosis can all be induced by manipulating cytokines and neuronal factors in ob/ob mice (that are genetically deficient in leptin). Thus, studies in mice have uncovered several basic mechanisms that explain the dysfunction that occurs in different types of liver cells during the metabolic syndrome. This has important therapeutic implications for human NASH.
Journal Article↗
Dietary factors alter hepatic innate immune system in mice with nonalcoholic fatty liver disease.
Dietary factors promote obesity and obesity-related disorders, such as fatty liver disease. Natural killer T (NKT) cells are components of the innate immune system that regulate proinflammatory (Th-1) and anti-inflammatory (Th-2) immune responses. Previously, we noted that NKT cells are selectively reduced in the fatty livers of obese, leptin-deficient ob/ob mice and demonstrated that this promotes proinflammatory polarization of hepatic cytokine production, exacerbating lipopolysaccharide (LPS) liver injury in these animals. In the current study, we show that hepatic NKT cells are also depleted by diets that induce obesity and fatty livers in wild-type mice, promoting Th-1 polarization of hepatic cytokine production and sensitization to LPS liver injury despite persistent leptin. Adult male C57BL6 mice fed diets containing high amounts of either fat or sucrose, or combined high-fat, high-sucrose, develop increased hepatic NKT cell apoptosis and reduced liver NKT cells. The hepatic lymphocytes are more Th-1 polarized with increased intracellular interferon gamma and tumor necrosis factor alpha. Mice fed high-fat diets also exhibit more liver injury, reflected by 2-fold greater serum alanine aminotransferase (ALT) than control animals after receiving LPS. In conclusion, when otherwise normal mice are fed with high-fat or sucrose diet, they become obese, develop fatty livers, and acquire hepatic innate immune system abnormalities, including increased NKT cell apoptosis. The latter reduces liver NKT cell populations and promotes excessive hepatic production of Th-1 cytokines that promote hepatic inflammation. These diet-induced alterations in the hepatic innate immune system may contribute to obesity-related liver disease.
Animals↗
Hepatic complications of obesity.
Obesity increases the risk and severity of liver disease. The most common form of liver disease that occurs in obesity is NAFLD. A better understanding of the basic disease mechanisms and natural histories ofNAFLD is needed to guide management and treatment of obese patients and others with this disorder. Large, prospective, randomized, controlled treatment trials also are needed. Ideally, such studies will focus on well-defined patient subsets and monitor the impact of therapy on clinically relevant endpoints, such as liver-related morbidity and mortality.
Biopsy, Needle↗
Hepatic angiomyolipoma and hepatic stellate cells share a similar gene expression profile.
BACKGROUND AND AIMS: Angiomyolipomas (AMLs) of the liver are rare neoplasms composed of large epithelioid cells with intermixed fat and blood vessels. Hepatic AMLs have no clear normal-cell counterpart in the liver. However, AMLs and stellate cells both are positive for neural crest-derived markers including HMB-45 antigen. METHODS: To further explore the similarities between hepatic AMLs and stellate cells, gene expression of a hepatic AML was studied by cDNA microarray. Real-time polymerase chain reaction was used to confirm gene expression. Hepatic stellate cells can be quiescent, activated, or have a myofibroblastic phenotype depending on their state of activation. Expression of known markers of activated stellate cells was compared between the AML, activated primary mouse stellate cells, and stellate cell lines with activated and myofibroblastic phenotypes. Next, 5 novel genes from the AML were selected because they were not previously known to be markers of stellate cells and mRNA expression measured in the activated mouse stellate cells and in myofibroblastic stellate cell lines. Finally, expression levels of 10 novel genes were determined in 5 cirrhotic and 5 noncirrhotic human livers. RESULTS: Overexpression of known markers of activated stellate cells including transforming growth factor beta (TGF- beta ), smooth muscle actin, and collagen was found in the hepatic AML. Three of 5 novel markers that were identified in the AML, RRAD (Ras-related associated with diabetes), CTSK (cathepsin K), and NIBAN were also found to be overexpressed in activated stellate cells compared with quiescent or myofibroblastic stellate cells. In addition, 9 of 10 novel genes overexpressed in AML were also overexpressed in cirrhotic human livers versus noncirrhotic livers. CONCLUSIONS: Hepatic AMLs share a similar gene expression profile and may differentiate toward activated stellate cells.
Angiomyolipoma↗
Role for hedgehog signaling in hepatic stellate cell activation and viability.
Hepatic stellate cells (HSC) have a complex phenotype that includes both neural and myofibroblastic features. The Hedgehog (Hh) pathway has been shown to direct the fate of neural and myofibroblastic cells during embryogenesis and during tissue remodeling in adults. Therefore, we hypothesized that Hh signaling may regulate the fate of HSC in adults. In this study, we find that freshly isolated stellate cells from adult Patched-lacZ transgenic mice exhibit beta-galactosidase activity, indicating Hh pathway activity. Transcripts of Hh ligands, the Hh pathway receptor, and Hh-regulated transcription factors are expressed by stellate cells from mice, rats, and humans. Transfection experiments in a cell line using a Hh-inducible luciferase reporter demonstrate constitutive Hh pathway activity. Moreover, neutralizing antibodies to Hh increase apoptosis, while viability is restored by treatment with Hh ligand. In vitro treatment of primary stellate cells with cyclopamine (Cyc), a pharmacologic inhibitor of the Hh pathway, inhibits activation and slightly decreases cell survival, while a single injection of Cyc into healthy adult mice reduces activation of HSC by more than 50% without producing obvious liver damage. Our findings reveal a novel mechanism, namely the Hh pathway, that regulates the activation and viability of HSC.
Animals↗
Should nonalcoholic fatty liver disease be treated differently in elderly patients?
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Age Factors↗
Roux-en-Y gastric bypass improves liver histology in patients with non-alcoholic fatty liver disease.
OBJECTIVES: Non-alcoholic fatty liver disease (NAFLD) is the most common cause of liver disease in the United States and is prevalent in morbidly obese patients. While weight loss and treatment of risk factors are recommended, the reported effects of bariatric surgery on NAFLD are mixed. RESEARCH METHODS AND PROCEDURES: We examined liver histology at the time of Roux-en-Y gastric bypass surgery and at elective incisional hernia repair after weight loss for 16 patients at one center. Slides were read by one pathologist, blinded to clinical data, using the Brunt criteria. Clinical and laboratory data were extracted from chart review. Alcohol use was ascertained by two interviews. RESULTS: At baseline, the mean age was 44 years, 50% were women, 88% were white, and the mean BMI was 51 kg/m2. None had significant alcohol use. On initial biopsy, all patients showed steatosis, 94% had inflammation, 88% had ballooning degeneration, 88% had perisinusoidal fibrosis, and 81% had portal fibrosis. The mean time between the two biopsies was 305 +/- 131 (SD) days. The mean weight loss was 118 +/- 29 lb. Steatosis improved in 15 of 16 patients, with resolution in 13. Twelve of 15 patients with inflammation at baseline showed improvement, and 12 of 14 showed less ballooning. Six of 14 patients with perisinusoidal fibrosis and 6 of 13 with portal fibrosis showed improvement. No patient had worsening of steatosis, inflammation, ballooning, or fibrosis. DISCUSSION: Our study shows improvement in all of the histological features of NAFLD after Roux-en-Y gastric bypass surgery-induced weight loss, despite significant histopathology at baseline and substantial weight loss.
Adult↗
Role of inflammation in nonalcoholic steatohepatitis.
PURPOSE OF REVIEW: Products of hepatic macrophages and lymphocytes are acknowledged regulators of liver injury and repair. Recent studies have identified inflammatory modulators from sources within and outside the liver that are critical to the pathogenesis and progression of chronic liver diseases, including nonalcoholic fatty liver disease. This review will focus on these developments to clarify how inflammatory mediators from adipose tissue and the liver interact to mediate the pathogenesis of nonalcoholic fatty liver disease. RECENT FINDINGS: Hepatic steatosis and steatohepatitis are extremely prevalent in obese individuals with the metabolic syndrome. The metabolic syndrome results from abnormal production of various adipose-derived and liver-derived factors that modulate energy substrate flux to coordinate tissue anabolism and catabolism. Individuals with the metabolic syndrome produce a relative excess of proinflammatory factors. Some factors inhibit hepatic fat disposal and promote lipid accumulation within hepatocytes. The latter induces sustained hepatic generation of proinflammatory cytokines, particularly when the hepatic innate immune system becomes Th-1 polarized. Although chronic inflammation induces production of various profibrogenic factors, progression to latter stages of nonalcoholic fatty liver disease is relatively unusual in individuals with the metabolic syndrome. This may reflect requirements for additional factors that become abundant only in individuals who have additional defects in hepatic innate immunity. SUMMARY: Obesity and the metabolic syndrome represent chronic inflammatory states and are associated with nonalcoholic fatty liver disease. Liver injury that ensues is dictated by metabolic and immunomodulatory factors that are produced by adipose tissue and within the liver.
Adipose Tissue↗
Hepatic 31P magnetic resonance spectroscopy: a hepatologist's user guide.
Hepatic phosphorus magnetic resonance spectroscopy (31P MRS) offers the exciting potential of studying metabolic processes in the human liver in vivo. Many investigators have utilized 31P MRS to research a broad range of metabolic questions, and there is outstanding potential for this imaging modality in the future. However, at times it is difficult to appreciate this potential because most published series have been small, and comparisons between studies are difficult. Indeed, the published literature contains significant variation in data acquisition and data analysis techniques and, perhaps most importantly, the interpretation of the data itself. As MR technology continues to evolve and more studies are being performed, perhaps a greater consensus of study techniques and endpoints will emerge. This review summarizes the present literature on human hepatic 31P MRS.
Gastroenterology↗