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Nonalcoholic Fatty Liver Disease in Children: Where Are We?

Combined alcoholic and non-alcoholic steatohepatitis.

Lean Fatty Liver Disease: Through Thick and Thin

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease in the United States and, indeed, worldwide. It has become a global public health issue. In the United States, the prevalence in the general population is estimated at approximately 20%, while that in the morbidly obese population at approximately 75-92% and in the pediatric population at approximately 13-14%. The progressive form of NAFLD, nonalcoholic steatohepatitis, is estimated at approximately 3-5%, with approximately 3-5% of these having progressed to cirrhosis. Thus, the numbers of individuals at risk for end-stage liver disease and development of primary liver cancer is large. NAFLD is an independent risk factor for cardiovascular disease, leads to increased all-cause mortality, and to increased liver-related mortality. This review focuses on recent advances in our understanding of the NAFLD disease spectrum, including etiology, diagnosis, treatment, and genetic and environmental risk factors and suggests future directions for research in this important area.

Non-alcoholic steatohepatitis: The role of oxidized low-density lipoproteins

Despite years of effort, exact pathogenesis of nonalcoholic fatty liver disease (NAFLD) remains obscure. To gain an insight into the regulatory roles of microRNAs (miRNAs) in aberrant energy metabolic status and pathogenesis of NAFLD, we analyzed the expression of miRNAs in livers of ob/ob mice, streptozotocin (STZ)-induced type 1 diabetic mice, and normal C57BL/6 mice by miRNA microarray. Compared with normal C57BL/6 mice, ob/ob mice showed upregulation of eight miRNAs and downregulation of four miRNAs in fatty livers. Upregulation of miR-34a and downregulation of miR-122 was found in livers of STZ-induced diabetic mice. These results demonstrate that distinct miRNAs are strongly dysregulated in NAFLD and hyperglycemia. Comparison between miRNA expressions in livers of ob/ob mice and STZ-administered mice further revealed upregulation of four miRNAs and downregulation of two miRNAs in livers of ob/ob mice, indicating that these miRNAs may represent a molecular signature of NAFLD. A distinctive miRNA expression pattern was identified in ob/ob mouse liver, and hierarchical clustering of this pattern could clearly discriminate ob/ob mice from either normal C57BL/6 mice or STZ-administered mice. These findings suggest an important role of miRNAs in hepatic energy metabolism and implicate the participation of miRNAs in the pathophysiological processes of NAFLD.

In addition to the well-recognized transport function of lipoproteins, a large body of evidence has demonstrated that lipoproteins also play an important role in host defense as part of the innate immune system (for review, see Ref. 1). One of the key defensive functions is the ability of HDL and other lipoproteins to bind endotoxin (lipopolysaccharide, LPS) and other bacterial products and neutralize their toxic effects. In this issue of the Journal of Lipid Research, Wang et al. (2) provide insights into the structural requirements for LPS neutralization by apolipoprotein A-I. The helical structure of apolipoprotein A-I is based on eight similar 22 amino acid and two 11 amino acid tandem repeats, but the areas required for HDL formation and function can now be attributed to specific regions based on studies of specific mutations (3). The central region (amino acids 144–186) activates LCAT and contributes to HDL maturation and stability. The N(44–65) and C(220–241) terminal repeats are necessary to initiate lipid binding, form nascent HDL, and remove cholesterol from macrophages. A larger portion of the C-terminal region (190–243) is critical for phospholipid binding and promoting cholesterol efflux. Naturally occurring mutations of cysteines in apolipoprotein A-I, such as A-IMilano and A-IParis, are associated with protection against atherosclerosis even when HDL cholesterol levels are decreased (4). The paper by Wang et al. (2) addresses what regions of apolipoprotein A-I are required for neutralization of LPS by substituting other amino acids for specific cysteine residues. Serine substitution of one cysteine (228) in the C-terminal domain dramatically reduced the ability of HDL to neutralize LPS, while another C-terminal substitution (cysteine 195), proximal to the last 22 residue repeat, had little effect. Midregion substitutions (cysteines 107, 129, and 173) also had little effect. On the other hand, substitution in the first N-terminal repeat (cysteine 52) and especially the next region (cysteine 74) formed HDL that was more effective at neutralizing LPS and protecting from LPS induced lung injury. Thus, Wang et al. (2) have shown that, as with cholesterol and phospholipid metabolism, specific regions of apolipoprotein A-I are essential for LPS neutralization. Furthermore, the regions involved in LPS neutralization are different than those involved in cholesterol and phospholipid metabolism. For example, these authors have previously shown (5) that substitution for cysteine residues 129 and 195 impaired lipid binding, while substitutions at 173 and 195 impaired the ability of HDL to promote cholesterol efflux. In contrast, a substitution at 107 had an increased capacity to promote cholesterol efflux. As noted above, the substitutions at 52 and 74 enhanced the ability of HDL to neutralize LPS, yet these substitutions had no effect on HDL structure or the ability of HDL to remove cholesterol from macrophages. Consequently, the increase in protection from LPS makes the 52 and 74 substitutions “super” apolipoproteins A-Is for host defense, with little downside in adversely affecting reverse cholesterol transport and increasing the risk of atherosclerosis. It remains to be seen whether similar naturally occurring mutations occur in humans and whether such mutations in apolipoprotein A-I will have a beneficial effect during gram-negative infections. Additionally, studies should examine whether similar modifications of apolipoprotein A-I will also enhance the neutralization of other toxic bacterial products, such as lipoteichoic acid. Infections activate Toll-like receptors stimulating the secretion of cytokines, which have profound effects on lipid and lipoprotein metabolism (for review, see Ref. 1). The changes in lipid and lipoprotein metabolism are part of the acute phase response (APR), a pattern best known for increases in serum proteins (6). Positive APR proteins are those whose circulating levels increase during the APR while negative APR proteins decrease. Two positive APR proteins, C-reactive protein and serum amyloid A, bind to lipoproteins and hence can be considered to be apolipoproteins. The increases in serum proteins during the APR are transcriptionally mediated and usually driven by activation of transcription at NF-kB and NF-IL-6 response elements (6). However, many of the changes in lipid and lipoprotein metabolism are part of the negative

Nonalcoholic steatohepatitis (NASH) is a leading cause of chronic liver disease worldwide and is characterized by steatosis, inflammation, and fibrosis. The molecular mechanisms underlying NASH development remain obscure. The nuclear receptor small heterodimer partner (Shp) plays a complex role in lipid metabolism and inflammation. Here, we sought to determine SHP's role in regulating steatosis and inflammation in NASH. Shp deletion in murine hepatocytes (ShpHep−/−) resulted in massive infiltration of macrophages and CD4+ T cells in the liver. ShpHep−/− mice developed reduced steatosis, but surprisingly increased hepatic inflammation and fibrosis after being fed a high-fat, -cholesterol, and -fructose (HFCF) diet. RNA-Seq analysis revealed that pathways involved in inflammation and fibrosis are significantly activated in the liver of ShpHep−/− mice fed a chow diet. After having been fed the HFCF diet, WT mice displayed up-regulated peroxisome proliferator-activated receptor γ (Pparg) signaling in the liver; however, this response was completely abolished in the ShpHep−/− mice. In contrast, livers of ShpHep−/− mice had consistent NF-κB activation. To further characterize the role of Shp specifically in the transition of steatosis to NASH, mice were fed the HFCF diet for 4 weeks, followed by Shp deletion. Surprisingly, Shp deletion after steatosis development exacerbated hepatic inflammation and fibrosis without affecting liver steatosis. Together, our results indicate that, depending on NASH stage, hepatic Shp plays an opposing role in steatosis and inflammation. Mechanistically, Shp deletion in hepatocytes activated NF-κB and impaired Pparg activation, leading to the dissociation of steatosis, inflammation, and fibrosis in NASH development. Nonalcoholic steatohepatitis (NASH) is a leading cause of chronic liver disease worldwide and is characterized by steatosis, inflammation, and fibrosis. The molecular mechanisms underlying NASH development remain obscure. The nuclear receptor small heterodimer partner (Shp) plays a complex role in lipid metabolism and inflammation. Here, we sought to determine SHP's role in regulating steatosis and inflammation in NASH. Shp deletion in murine hepatocytes (ShpHep−/−) resulted in massive infiltration of macrophages and CD4+ T cells in the liver. ShpHep−/− mice developed reduced steatosis, but surprisingly increased hepatic inflammation and fibrosis after being fed a high-fat, -cholesterol, and -fructose (HFCF) diet. RNA-Seq analysis revealed that pathways involved in inflammation and fibrosis are significantly activated in the liver of ShpHep−/− mice fed a chow diet. After having been fed the HFCF diet, WT mice displayed up-regulated peroxisome proliferator-activated receptor γ (Pparg) signaling in the liver; however, this response was completely abolished in the ShpHep−/− mice. In contrast, livers of ShpHep−/− mice had consistent NF-κB activation. To further characterize the role of Shp specifically in the transition of steatosis to NASH, mice were fed the HFCF diet for 4 weeks, followed by Shp deletion. Surprisingly, Shp deletion after steatosis development exacerbated hepatic inflammation and fibrosis without affecting liver steatosis. Together, our results indicate that, depending on NASH stage, hepatic Shp plays an opposing role in steatosis and inflammation. Mechanistically, Shp deletion in hepatocytes activated NF-κB and impaired Pparg activation, leading to the dissociation of steatosis, inflammation, and fibrosis in NASH development.

Contribution of metabolic factors to alanine aminotransferase activity in persons with other causes of liver disease

The immunobiology of hepatocellular carcinoma in humans and mice: Basic concepts and therapeutic implications

We have reconstituted human mitochondrial transcription in vitro on DNA oligonucleotide templates representing the light strand and heavy strand-1 promoters using protein components (RNA polymerase and transcription factors A and B2) isolated from Escherichia coli. We show that 1 eq of each transcription factor and polymerase relative to the promoter is required to assemble a functional initiation complex. The light strand promoter is at least 2-fold more efficient than the heavy strand-1 promoter, but this difference cannot be explained solely by the differences in the interaction of the transcription machinery with the different promoters. In both cases, the rate-limiting step for production of the first phosphodiester bond is open complex formation. Open complex formation requires both transcription factors; however, steps immediately thereafter only require transcription factor B2. The concentration of nucleotide required for production of the first dinucleotide product is substantially higher than that required for subsequent cycles of nucleotide addition. In vitro, promoter-specific differences in post-initiation control of transcription exist, as well as a second rate-limiting step that controls conversion of the transcription initiation complex into a transcription elongation complex. Rate-limiting steps of the biochemical pathways are often those that are targeted for regulation. Like the more complex multisubunit transcription systems, multiple steps may exist for control of transcription in human mitochondria. The tools and mechanistic framework presented here will facilitate not only the discovery of mechanisms regulating human mitochondrial transcription but also interrogation of the structure, function, and mechanism of the complexes that are regulated during human mitochondrial transcription.

Reply to: Correspondence on “EASL Clinical Practice Guidelines on non-invasive tests for evaluation of liver disease severity and prognosis – 2021 update”

Electrocardiographic features of patients with COVID-19: One year of unexpected manifestations

Rod outer segments (ROSs) are specialized light-sensitive organelles in vertebrate photoreceptor cells. Lipids in ROS are of considerable importance, not only in providing an adequate environment for efficient phototransduction, but also in originating the second messengers involved in signal transduction. ROSs have the ability to adapt the sensitivity and speed of their responses to ever-changing conditions of ambient illumination. A major contributor to this adaptation is the light-driven translocation of key signaling proteins into and out of ROS. The present review shows how generation of the second lipid messengers from phosphatidylcholine, phosphatidic acid, and diacylglycerol is modulated by the different illumination states in the vertebrate retina. Findings suggest that the light-induced translocation of phototransduction proteins influences the enzymatic activities of phospholipase D, lipid phosphate phosphatase, diacylglyceride lipase, and diacylglyceride kinase, all of which are responsible for the generation of the second messenger molecules.

Non-alcoholic fatty liver disease: Not time for an obituary just yet!