Liver X receptor α induces 17β-hydroxysteroid dehydrogenase-13 expression through SREBP-1c

Zearalenone exacerbates lipid metabolism disorders by promoting liver lipid droplet formation and disrupting gut microbiota

Zearalenone (ZEA), produced by Fusarium, is a fungal toxin commonly found in maize, wheat, and other cereals. ZEA has the ability to bind to estrogen receptors of humans and animals and is an environmental endocrine disruptor that may interfere with glucose homeostasis and lipid metabolism. In this study, we first investigated the effects of chronic exposure to low doses of ZEA with a high-fat-diet (HFD) in obese C57BL/6 J mice. In the absence of significant toxicity and without affecting glucose tolerance, 50 and 100 μg/kg b. w. ZEA was found to significantly exacerbate lipid synthesis, accumulation and alter the overall transcriptional profile of the liver in mice synergistically with HFD. Validation in combination with AML-12 cells revealed that ZEA promoted lipid synthesis and increased hepatic lipid droplet accumulation via the HNF1β/PPARγ and SREBP1c-HSD17B13/PLINs signal pathways. Further, by analyzing the changes in the intestinal flora of mice and their relationship with lipid metabolism genes, it was found that ZEA decreased the relative abundance of Lactobacillus and increased the relative abundance of Ileococcus, E. faecalis, and Ricardia. These changes were significantly correlated with the expression of Pparg and Srebf1, etc. ZEA may contribute to the abnormality of lipid metabolism by influencing the intestinal microbiota. This study highlights the synergistic effects of long-term low-dose ZEA and excess lipids, providing a theoretical basis for elucidating the mechanism of chronic toxicity of ZEA and its negative impact on metabolic diseases.

Lipid droplet-associated proteins in alcohol-associated fatty liver disease: A proteomic approach

BACKGROUND

The earliest manifestation of alcohol-associated liver disease (ALD) is steatosis characterized by deposition of fat in specialized organelles called lipid droplets (LDs). While alcohol administration causes a rise in LD numbers in the hepatocytes, little is known regarding their characteristics that allow their accumulation and size to increase. The aim of the present study is to gain insights into underlying pathophysiological mechanisms by investigating the ethanol-induced changes in hepatic LD proteome as a function of LD size.

METHODS

Adult male Wistar rats (180-200 g BW) were fed with ethanol liquid diet for 6 weeks. At sacrifice, large-, medium-, and small-sized hepatic LD subpopulations (LD1, LD2, and LD3, respectively) were isolated and subjected to morphological and proteomic analyses.

RESULTS

Morphological analysis of LD1-LD3 fractions of ethanol-fed rats clearly demonstrated that LD1 contained larger LDs compared with LD2 and LD3 fractions. Our preliminary results from principal component analysis showed that the proteome of different-sized hepatic LD fractions was distinctly different. Proteomic data analysis identified over 2000 proteins in each LD fraction with significant alterations in protein abundance among the three LD fractions. Among the altered proteins, several were related to fat metabolism, including synthesis, incorporation of fatty acid, and lipolysis. Ingenuity pathway analysis revealed increased fatty acid synthesis, fatty acid incorporation, LD fusion, and reduced lipolysis in LD1 compared to LD3. Overall, the proteomic findings indicate that the increased level of protein that facilitates fusion of LDs combined with an increased association of negative regulators of lipolysis dictates the generation of large-sized LDs during the development of alcohol-associated hepatic steatosis.

CONCLUSION

Several significantly altered proteins were identified in different-sized LDs isolated from livers of ethanol-fed rats. Ethanol-induced increases in specific proteins that hinder LD lipid metabolism led to the accumulation and persistence of large-sized LDs in the liver.

Dynamics simulation and in vitro studies of betulinic acid derivative with liver X receptor

Molecular dynamics simulation of the dominant conformational conjugate was performed for 40 ns and 100 ns via Amber software based on molecular docking by Sybyl software. Because the RMSD and RMSF of 100 ns MD simulation were higher than that of 40 ns MD simulation, the 40 ns was reasonable and credible for MD simulation. The binding free energy and decomposition free energy of the two systems of betulinic acid, com3 with liver X receptor was calculated by the MM_GBSA and MM_PBSA methods, respectively. The results showed that the two systems reached equilibrium and convergence at 20 ns, both stable at about 2 Å, and exhibited low volatility in the range of amino acid 270 to 370 (RMSF <1 Å). The binding energy of com3 (ΔGbind = -68.02 kcal/mol by the MM_GBSA method or -55.50 kcal/mol by the MM_PBSA method) with the liver X receptor was lower than that of betulinic acid (ΔGbind = -55.70 kcal/mol or -42.73 kcal/mol) respectively, and van der Waals force was the most important main driving force, which was consistent with molecular docking and previous experiments. Hydrophobic groups and aromatic rings can be introduced appropriately in structure optimization to increase the van der Waals force and π-π accumulation effect of betulinic acid and liver X receptor, which is conducive to binding and thereby increasing antitumor activity. The clone formation assay and results of western blotting indicated that BA derivative com3 exposure inhibited cell proliferation may relate to the regulation of the AKT/mTOR pathway in 7721 cells. This study clarifies the dynamic interaction mode and potential mechanism of betulinic acid and its derivatives with the liver X receptor, which provides a new idea for the rapid screening of liver X receptor agonists from traditional Chinese medicines.Communicated by Ramaswamy H. Sarma.

Unraveling the pathogenesis of non-alcoholic fatty liver diseases through genome-wide association studies

Non-alcoholic fatty liver disease (NAFLD) is a significant health burden around the world, affecting approximately 25% of the population. Recent advances in human genetic databases have allowed for the identification of various single nucleotide polymorphisms associated with NAFLD-related traits. Investigating the functions of these genetic factors provides insight into the pathogenesis of NAFLD and potentially identifies novel therapeutic targets for NAFLD. In this review, we summarized current research on genes with NAFLD-associated mutations, highlighting phospholipid remodeling and spatially clustered loci as common pathological and genetic features of these mutations. These features suggest a complex yet intriguing mechanism of dissociated steatosis and insulin resistance, which is observed in a subset of patients and may lead to more precise therapy against NAFLD in the future.

Review article: the role of HSD17B13 on global epidemiology, natural history, pathogenesis and treatment of NAFLD

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) occurs in around a quarter of the global population and is one of the leading causes of chronic liver disease. The phenotypic manifestation and the severity of NAFLD are influenced by an interplay of environmental and genetic factors. Recently, several inactivating variants in the novel 17-Beta hydroxysteroid dehydrogenase 13 (HSD17B13) gene have been found to be associated with a reduced risk of chronic liver diseases, including NAFLD.

AIMS

To review the existing literature on the epidemiology of HSD17B13 and discuss its role in the natural history, disease pathogenesis and treatment of NAFLD.

METHODS

We extensively searched relevant literature in PubMed, Google Scholar, clinicaltrials.gov and the reference list of articles included in the review.

RESULTS

HSD17B13 is a liver-specific, lipid droplet (LD)-associated protein that has enzymatic pathways involving steroids, pro-inflammatory lipid mediators and retinol. The estimated prevalence of the best characterised HSD17B13 variant (rs72613567) ranges from 5% in Africa to 34% in East Asia. Loss-of-function variants in HSD17B13 are protective against the progression of NAFLD from simple steatosis to non-alcoholic steatohepatitis (NASH), liver fibrosis, cirrhosis and hepatocellular carcinoma. Emerging data from mechanistic and preclinical studies with RNA interference (RNAi) and small molecule agents indicate that inhibiting HSD17B13 activity may prevent NAFLD progression.

CONCLUSIONS

The loss-of-function polymorphisms of the newly identified HSD17B13 gene mitigate the progression of NAFLD. It is important to understand the exact mechanism by which these variants exert a protective effect and implement the gathered knowledge in the treatment of NAFLD.

Letrozole ameliorates liver fibrosis through the inhibition of the CTGF pathway and 17β-hydroxysteroid dehydrogenase 13 expression

BACKGROUND

To establish a treatment option for liver fibrosis, the possibility of the drug repurposing theory was investigated, with a focus on the off-target effects of active pharmaceutical ingredients.

METHODS

First, several active pharmaceutical ingredients were screened for their effects on the gene expression in the hepatocytes using chimeric mice with humanized hepatocytes. As per the gene expression-based screening assay for 36 medications, we assessed the mechanism of the antifibrotic effect of letrozole, a third-generation aromatase inhibitor, in mouse models of liver fibrosis induced by carbon tetrachloride (CCl₄) and a methionine choline-deficient (MCD) diet. We assessed liver histology, serum biochemical markers, and fibrosis-related gene and protein expressions in the hepatocytes.

RESULTS

A gene expression-based screening assay revealed that letrozole had a modifying effect on fibrosis-related gene expression in the hepatocytes, including YAP, CTGF, TGF-β, and CYP26A1. Letrozole was administered to mouse models of CCl4- and MCD-induced liver fibrosis and it ameliorated the liver fibrosis. The mechanisms involved the inhibition of the Yap-Ctgf profibrotic pathway following a decrease in retinoic acid levels in the hepatocytes caused by suppression of the hepatic retinol dehydrogenase, Hsd17b13 and activation of the retinoic acid hydrogenase, Cyp26a1.

CONCLUSIONS

Letrozole slowed the progression of liver fibrosis by inhibiting the Yap-Ctgf pathway. The mechanisms involved the modification of the Hsd17b13 and Cyp26a1 expressions led to the suppression of retinoic acid in the hepatocytes, which contributed to the activation of Yap-Ctgf pathway. Because of its off-target effect, letrozole could be repurposed for the treatment of liver fibrosis. The third-generation aromatase inhibitor letrozole ameliorated liver fibrosis by suppressing the Yap-Ctgf pathway by partially modifying the Hsd17b13 and Cyp26a1 expressions, which reduced the retinoic acid level in the hepatocytes. The gene expression analysis using chimeric mice with humanized liver revealed that the mechanisms are letrozole specific and, therefore, may be repurposed for the treatment of liver fibrosis.

Phosphorylation of 17β-hydroxysteroid dehydrogenase 13 at serine 33 attenuates nonalcoholic fatty liver disease in mice

17β-hydroxysteroid dehydrogenase-13 is a hepatocyte-specific, lipid droplet-associated protein. A common loss-of-function variant of HSD17B13 (rs72613567: TA) protects patients against non-alcoholic fatty liver disease with underlying mechanism incompletely understood. In the present study, we identify the serine 33 of 17β-HSD13 as an evolutionally conserved PKA target site and its phosphorylation facilitates lipolysis by promoting its interaction with ATGL on lipid droplets. Targeted mutation of Ser33 to Ala (S33A) decreases ATGL-dependent lipolysis in cultured hepatocytes by reducing CGI-58-mediated ATGL activation. Importantly, a transgenic knock-in mouse strain carrying the HSD17B13 S33A mutation (HSD17B13^33A/A) spontaneously develops hepatic steatosis with reduced lipolysis and increased inflammation. Moreover, Hsd17B13^33A/A mice are more susceptible to high-fat diet-induced nonalcoholic steatohepatitis. Finally, we find reproterol, a potential 17β-HSD13 modulator and FDA-approved drug, confers a protection against nonalcoholic steatohepatitis via PKA-mediated Ser33 phosphorylation of 17β-HSD13. Therefore, targeting the Ser33 phosphorylation site could represent a potential approach to treat NASH.

Down-Regulating the High Level of 17-Beta-Hydroxysteroid Dehydrogenase 13 Plays a Therapeutic Role for Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide, and there is no specific drug to treat it. Recent results showed that 17-beta-hydroxysteroid dehydrogenase type 13 (HSD17B13) is associated with liver diseases, but these conclusions are controversial. Here, we showed that HSD17B13 was more highly expressed in the livers of NAFLD patients, and high expression was induced in the livers of murine NAFLD models and cultural hepatocytes treated using various etiologies. The high HSD17B13 expression in the hepatocytes facilitated the progression of NAFLD by directly stabilizing the intracellular lipid drops and by indirectly activating hepatic stellate cells. When HSD17B13 was overexpressed in the liver, it aggravated liver steatosis and fibrosis in mice fed with a high-fat diet, while down-regulated the high expression of HSD17B13 by short hairpin RNAs produced a therapeutic effect in the NAFLD mice. We concluded that high HSD17B13 expression is a good target for the development of drugs to treat NAFLD.

SIRT6 regulates SREBP1c-induced glucolipid metabolism in liver and pancreas via the AMPKα-mTORC1 pathway

The aim of this study was to determine the mechanism by which SIRT6 regulates glucolipid metabolism disorders. We detected histological and molecular changes in Sprague-Dawley rats as well as in BRL 3A and INS-1 cell lines subjected to overnutrition and starvation. SIRT6, SREBP1c, and glucolipid metabolism biomarkers were identified by fluorescence co-localization, real-time PCR, and western blotting. Gene silencing studies were performed. Recombinant SIRT6, AMPK agonist (AICAR), mTOR inhibitor (rapamycin), and liver X receptor (LXR) agonist (T0901317) were used to pre-treated in BRL 3A and INS-1 cells. Real-time PCR and western blotting were used to detect related proteins, and cell counting was utilized to detect proliferation. We obtained conflicting results; SIRT6 and SREBP1c appeared in both the liver and pancreas of high-fat and hungry rats. Recombinant SIRT6 alleviated the decrease in AMPKα and increase in mTORC1 (complex of mTOR, Raptor, and Rheb) caused by overnutrition. SIRT6 siRNA reversed the glucolipid metabolic disorders caused by the AMPK agonist and mTOR inhibitor but not by the LXR agonist. Taken together, our results demonstrate that SIRT6 regulates glycolipid metabolism through AMPKα-mTORC1 regulating SREBP1c in the liver and pancreas induced by overnutrition and starvation, independent of LXR.

Lipid Metabolism: Immune Regulation and Therapeutic Prospectives in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a heterogeneous disease characterized by the production of abnormal autoantibodies and immune complexes that can affect the organ and organ systems, particularly the kidneys and the cardiovascular system. Emerging evidence suggests that dysregulated lipid metabolism, especially in key effector cells, such as T cells, B cells, and innate immune cells, exerts complex effects on the pathogenesis and progression of SLE. Beyond their important roles as membrane components and energy storage, different lipids can also modulate different cellular processes, such as proliferation, differentiation, and survival. In this review, we summarize altered lipid metabolism and the associated mechanisms involved in the pathogenesis and progression of SLE. Furthermore, we discuss the recent progress in the role of lipid metabolism as a potential therapeutic target in SLE.

HSD17B13: A Potential Therapeutic Target for NAFLD

Nonalcoholic fatty liver disease (NAFLD), especially in its inflammatory form (steatohepatitis, NASH), is closely related to the pathogenesis of chronic liver disease. Despite substantial advances in the management of NAFLD/NASH in recent years, there are currently no efficacious therapies for its treatment. The biogenesis and expansion of lipid droplets (LDs) are critical pathophysiological processes in the development of NAFLD/NASH. In the past decade, increasing evidence has demonstrated that lipid droplet-associated proteins may represent potential therapeutic targets for the treatment of NAFLD/NASH given the critical role they play in regulating the biogenesis and metabolism of lipid droplets. Recently, HSD17B13, a newly identified liver-enriched, hepatocyte-specific, lipid droplet-associated protein, has been reported to be strongly associated with the development and progression of NAFLD/NASH in both mice and humans. Notably, human genetic studies have repeatedly reported a robust association of HSD17B13 single nucleotide polymorphisms (SNPs) with the occurrence and severity of NAFLD/NASH and other chronic liver diseases (CLDs). Here we briefly overview the discovery, tissue distribution, and subcellular localization of HSD17B13 and highlight its important role in promoting the pathogenesis of NAFLD/NASH in both experimental animal models and patients. We also discuss the potential of HSD17B13 as a promising target for the development of novel therapeutic agents for NAFLD/NASH.

Lipid droplet - mitochondria coupling: A novel lipid metabolism regulatory hub in diabetic nephropathy

Diabetic nephropathy (DN) involves serious lipid metabolism disorder, and renal ectopic lipid deposition aggravates DN progression. However, the molecular mechanism of renal lipid deposition in DN remains unclear. Lipid droplets (LDs) are lipid pools in cells that change dynamically in response to the cellular energy needs. The LDs and mitochondria are connected through a part of the mitochondria known as the peridroplet mitochondria (PDM). In this review, we summarize the definition, detection methods, and function of the PDM. Finally, we discuss the research status of PDM in DN and the possibility of its use as a therapeutic target.

Lipid Droplet-Associated Factors, PNPLA3, TM6SF2, and HSD17B Proteins in Hepatopancreatobiliary Cancer

Simple Summary

Aberrant lipid synthesis and reprogrammed lipid metabolism are both associated with the development and progression of pancreatic and liver cancer. Most cells store fatty acids in the form of triacylglycerols in lipid droplets. Lipid droplets are intracellular organelles that not only store neutral lipids, but also play roles as molecular messengers and signaling factors. Some cancer cells accumulate massive amount of lipid droplets. Lipid droplets and lipid droplet-associated factors are further implicated to mediate proliferation, invasion, metastasis, as well as chemotherapy resistance in several types of cancer. This review dissected recent findings on the role of several lipid droplet-associated factors, patatin-like phospholipase domain-containing 3 (PNPLA3), Transmembrane 6 superfamily member 2 (TM6SF2), and 17β-hydroxysteroid dehydrogenase (HSD17B) 11 and 13 as well as their genetic variations in hepatopancreatobiliary diseases, especially cancer.

Abstract

Pancreatic and liver cancer are leading causes of cancer deaths, and by 2030, they are projected to become the second and the third deadliest cancer respectively. Cancer metabolism, especially lipid metabolism, plays an important role in progression and metastasis of many types of cancer, including pancreatic and liver cancer. Lipid droplets are intracellular organelles that store neutral lipids, but also act as molecular messengers, and signaling factors. It is becoming increasingly evident that alterations in the regulation of lipid droplets and their associated factors influence the risk of developing not only metabolic disease but also fibrosis and cancer. In the current review article, we summarized recent findings concerning the roles of lipid droplet-associated factors, patatin-like phospholipase domain-containing 3, Transmembrane 6 superfamily member 2, and 17β-hydroxysteroid dehydrogenase 11 and 13 as well as genetic variants in pancreatic and hepatic diseases. A better understanding of cancer type- and cell type-specific roles of lipid droplet-associated factors is important for establishing new therapeutic options in the future.

Is HSD17B13 Genetic Variant a Protector for Liver Dysfunction? Future Perspective as a Potential Therapeutic Target

As diet and lifestyle have changed, fatty liver disease (FLD) has become more and more prevalent. Many genetic risk factors, such as variants of PNPLA3, TM6SF2, GCKR, and MBOAT7, have previously been uncovered via genome wide association studies (GWAS) to be associated with FLD. In 2018, a genetic variant (rs72613567, T > TA) of hydroxysteroid 17-β dehydrogenase family 13 (HSD17B13) was first associated with a lower risk of developing alcoholic liver disease and non-alcoholic fatty liver disease (NAFLD) in minor allele carriers. Other HSD17B13 variants were also later linked with either lower inflammation scores among NAFLD patients or protection against NAFLD (rs6834314, A > G and rs9992651, G > A) respectively. HSD17B13 is a lipid droplet-associated protein, but its function is still ambiguous. Compared to the other genetic variants that increase risk for FLD, HSD17B13 variants serve a protective role, making this gene a potential therapeutic target. However, the mechanism by which these variants reduce the risk of developing FLD is still unclear. Because studies in cell lines and mouse models have produced conflicting results, human liver tissue modeling using induced pluripotent stem cells may be the best way to move forward and solve this mystery.

Lipid droplets and their interactions with other organelles in liver diseases

Lipid droplets are cellular organelles used for lipid storage with a hydrophobic core of neutral lipids enclosed by a phospholipid monolayer. Besides presenting as giant single organelles in fat tissue, lipid droplets are also widely present as a multitude of small structures in hepatocytes, where they play key roles in health and disease of the liver. In addition to lipid storage, lipid droplets are also directly involved in lipid metabolism, membrane biosynthesis, cell signaling, inflammation, pathogen-host interaction and cancer development. In addition, they interact with other cellular organelles to regulate cellular biology. It is fair to say that the exact functions of lipid droplets in cellular physiology remain largely obscure. Thus prompted, here we aim to analyze the corpus of contemporary biomedical literature to create a framework as to how the role of lipid droplets in hepatocyte physiology and pathophysiology should be understood. The resulting framework should help understanding the interaction of lipid droplets with other organelles in important liver diseases, including fatty liver disease, viral hepatitis and liver cancer and direct further research directions.

Pathophysiological mechanisms underlying MAFLD

BACKGROUND AND AIMS

The pathophysiology underlying metabolic associated fatty liver disease (MAFLD) involves a multitude of interlinked processes, including insulin resistance (IR) underlying the metabolic syndrome, lipotoxicity attributable to the accumulation of toxic lipid species, infiltration of proinflammatory cells causing hepatic injury and ultimately leading to hepatic stellate cell (HSC) activation and fibrogenesis. The proximal processes, such as IR, lipid overload and lipotoxicity are relatively well established, but the downstream molecular mechanisms, such as inflammatory processes, hepatocyte lipoapoptosis, and fibrogenesis are incompletely understood.

METHODS

A literature search was performed with Medline (PubMed), Scopus and Google Scholar electronic databases till June 2020, using relevant keywords (nonalcoholic fatty liver disease; metabolic associated fatty liver disease; nonalcoholic steatohepatitis; NASH pathogenesis) to extract relevant studies describing pathogenesis of MAFLD/MASH.

RESULTS

Several studies have reported new concepts underlying pathophysiology of MAFLD. Activation of HSCs is the common final pathway for diverse signals from damaged hepatocytes and proinflammatory cells. Activated HSCs then secrete excess extracellular matrix (ECM) which accumulates and impairs structure and function of the liver. TAZ (a transcriptional regulator), hedgehog (HH) ligands, transforming growth factor-β (TGF-β), bone morphogenetic protein 8B (BMP8B) and osteopontin play important roles in activating these HSCs. Dysfunctional gut microbiome, dysregulated bile acid metabolism, endogenous alcohol production, and intestinal fructose handling, modify individual susceptibility to MASH.

CONCLUSIONS

Newer concepts of pathophysiology underlying MASH, such as TAZ/Ihh pathway, extracellular vesicles, microRNA, dysfunctional gut microbiome and intestinal fructose handling present promising targets for the development of therapeutic agents.

Genetic Variation in HSD17B13 Reduces the Risk of Developing Cirrhosis and Hepatocellular Carcinoma in Alcohol Misusers

BACKGROUND AND AIMS

Carriage of rs738409:G in patatin-like phospholipase domain containing 3 (PNPLA3) is associated with an increased risk for developing alcohol-related cirrhosis and hepatocellular carcinoma (HCC). Recently, rs72613567:TA in hydroxysteroid 17-beta dehydrogenase 13 (HSD17B13) was shown to be associated with a reduced risk for developing alcohol-related liver disease and to attenuate the risk associated with carriage of PNPLA3 rs738409:G. This study explores the risk associations between these two genetic variants and the development of alcohol-related cirrhosis and HCC.

APPROACH AND RESULTS

Variants in HSD17B13 and PNPLA3 were genotyped in 6,171 participants, including 1,031 with alcohol-related cirrhosis and HCC, 1,653 with alcohol-related cirrhosis without HCC, 2,588 alcohol misusers with no liver disease, and 899 healthy controls. Genetic associations with the risks for developing alcohol-related cirrhosis and HCC were determined using logistic regression analysis. Carriage of HSD17B13 rs72613567:TA was associated with a lower risk for developing both cirrhosis (odds ratio [OR], 0.79; 95% confidence interval [CI], 0.72-0.88; P = 8.13 × 10^-6 ) and HCC (OR, 0.77; 95% CI, 0.68-0.89; P = 2.27 × 10^-4 ), whereas carriage of PNPLA3 rs738409:G was associated with an increased risk for developing cirrhosis (OR, 1.70; 95% CI, 1.54-1.88; P = 1.52 × 10^-26 ) and HCC (OR, 1.77; 95% CI, 1.58-1.98; P = 2.31 × 10^-23 ). These associations remained significant after adjusting for age, sex, body mass index, type 2 diabetes, and country. Carriage of HSD17B13 rs72613567:TA attenuated the risk for developing cirrhosis associated with PNPLA3 rs738409:G in both men and women, but the protective effect against the subsequent development of HCC was only observed in men (OR_allelic , 0.75; 95% CI, 0.64-0.87; P = 1.72 × 10^-4 ).

CONCLUSIONS

Carriage of variants in PNPLA3 and HSD17B13 differentially affect the risk for developing advanced alcohol-related liver disease. A genotypic/phenotypic risk score might facilitate earlier diagnosis of HCC in this population.

Hydroxysteroid 17-β dehydrogenase 13 variant increases phospholipids and protects against fibrosis in nonalcoholic fatty liver disease

Carriers of the hydroxysteroid 17-β dehydrogenase 13 (HSD17B13) gene variant (rs72613567:TA) have a reduced risk of NASH and cirrhosis but not steatosis. We determined its effect on liver histology, lipidome, and transcriptome using ultra performance liquid chromatography-mass spectrometry and RNA-seq. In carriers and noncarriers of the gene variant, we also measured pathways of hepatic fatty acids (de novo lipogenesis [DNL] and adipose tissue lipolysis [ATL] using 2H2O and 2H-glycerol) and insulin sensitivity using 3H-glucose and euglycemic-hyperinsulinemic clamp) and plasma cytokines. Carriers and noncarriers had similar age, sex and BMI. Fibrosis was significantly less frequent while phospholipids, but not other lipids, were enriched in the liver in carriers compared with noncarriers. Expression of 274 genes was altered in carriers compared with noncarriers, consisting predominantly of downregulated inflammation-related gene sets. Plasma IL-6 concentrations were lower, but DNL, ATL and hepatic insulin sensitivity were similar between the groups. In conclusion, carriers of the HSD17B13 variant have decreased fibrosis and expression of inflammation-related genes but increased phospholipids in the liver. These changes are not secondary to steatosis, DNL, ATL, or hepatic insulin sensitivity. The increase in phospholipids and decrease in fibrosis are opposite to features of choline-deficient models of liver disease and suggest HSD17B13 as an attractive therapeutic target.

Single-nucleotide polymorphisms (rs342275, rs342293, rs7694379, rs11789898, and rs17824620) showed significant association with lobaplatin-induced thrombocytopenia

This study aimed to investigate single-nucleotide polymorphisms (SNPs) associated with lobaplatin-induced thrombocytopenia in patients with advanced lung cancer in China. Thirty-nine patients who received lobaplatin-based chemotherapy in the 307 Hospitals of Chinese People's Liberation Army from April 2017 to March 2018 were enrolled as study subjects. Peripheral blood DNA was extracted, and 79 candidate SNP positions were selected. A Sanger sequencing platform was employed to measure genotypes for locating the SNP positions associated with lobaplatin-induced thrombocytopenia. Of the 79 candidate genes, SNPs rs342275 and rs7694379 were significantly associated with lobaplatin-induced decrease in platelet (PLT) count (P < 0.05). SNPs rs342275, rs342293, rs11789898, and rs17824620 showed significant association with lobaplatin-induced lowest PLT counts (P < 0.05). SNPs rs342275, rs342293, rs11789898, rs17824620, and rs7694379 can be used as predictors of thrombocytopenia induced by lobaplatin-based chemotherapy in patients with advanced lung cancer in China.

Role of HSD17B13 in the liver physiology and pathophysiology

17β-Hydroxysteroid dehydrogenases (HSD17Bs) comprise a large family of 15 members that are mainly involved in sex hormone metabolism. Some HSD17Bs enzymes also play key roles in cholesterol and fatty acid metabolism. Recent study showed that hydroxysteroid 17β-dehydrogenase 13 (HSD17B13), an enzyme with unknown biological function, is a novel liver-specific lipid droplet (LD)-associated protein in mouse and humans. HSD17B13 expression is markedly upregulated in patients and mice with non-alcoholic fatty liver disease (NAFLD). Hepatic overexpression of HSD17B13 promotes lipid accumulation in the liver. In this review, we summarize recent progress regarding the role of HSD17B13 in the regulation of hepatic lipid homeostasis and discuss genetic, genomic and proteomic evidence supporting the pathogenic role of HSD17B13 in NAFLD. We also emphasize its potential as a biomarker of advanced liver disease, such as non-alcoholic steatohepatitis (NASH) and liver cancer.

17-Beta Hydroxysteroid Dehydrogenase 13 Is a Hepatic Retinol Dehydrogenase Associated With Histological Features of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease. A single-nucleotide polymorphism (SNP), rs6834314, was associated with serum liver enzymes in the general population, presumably reflecting liver fat or injury. We studied rs6834314 and its nearest gene, 17-beta hydroxysteroid dehydrogenase 13 (HSD17B13), to identify associations with histological features of NAFLD and to characterize the functional role of HSD17B13 in NAFLD pathogenesis. The minor allele of rs6834314 was significantly associated with increased steatosis but decreased inflammation, ballooning, Mallory-Denk bodies, and liver enzyme levels in 768 adult Caucasians with biopsy-proven NAFLD and with cirrhosis in the general population. We found two plausible causative variants in the HSD17B13 gene. rs72613567, a splice-site SNP in high linkage with rs6834314 (r² = 0.94) generates splice variants and shows a similar pattern of association with NAFLD histology. Its minor allele generates simultaneous expression of exon 6-skipping and G-nucleotide insertion variants. Another SNP, rs62305723 (encoding a P260S mutation), is significantly associated with decreased ballooning and inflammation. Hepatic expression of HSD17B13 is 5.9-fold higher (P = 0.003) in patients with NAFLD. HSD17B13 is targeted to lipid droplets, requiring the conserved amino acid 22-28 sequence and amino acid 71-106 region. The protein has retinol dehydrogenase (RDH) activity, with enzymatic activity dependent on lipid droplet targeting and cofactor binding site. The exon 6 deletion, G insertion, and naturally occurring P260S mutation all confer loss of enzymatic activity. Conclusion: We demonstrate the association of variants in HSD17B13 with specific features of NAFLD histology and identify the enzyme as a lipid droplet-associated RDH; our data suggest that HSD17B13 plays a role in NAFLD through its enzymatic activity.

Dysregulation of Kupffer Cells/Macrophages and Natural Killer T Cells in Steatohepatitis in LXRα Knockout Male Mice

Liver X receptor (LXR) α expression is mainly localized to metabolic tissues, such as the liver, whereas LXRβ is ubiquitously expressed. LXRα is activated by oxysterols and plays an important role in the regulation of lipid metabolism in metabolic tissues. In macrophages, LXRs stimulate reverse cholesterol transport and regulate immune responses. Although a high-cholesterol diet induces severe steatohepatitis in LXRα-knockout (KO) mice, the underlying mechanisms linking lipid metabolism and immune responses remain largely unknown. In this study, we investigated the role of LXRα in the pathogenesis of steatohepatitis by assessing the effects of a high-fat and high-cholesterol diet (HFCD) on hepatic immune cell proportion and function as well as lipid metabolism in wild-type (WT) and LXRα-KO mice. HFCD feeding induced severe steatohepatitis in LXRα-KO mice compared with WT mice. These mice had higher cholesterol levels in the plasma and the liver and dysregulated expression of LXR target and proinflammatory genes in both whole liver samples and isolated hepatic mononuclear cells. Flow cytometry showed an increase in CD68+CD11b+ Kupffer cells/macrophages and a decrease in invariant natural killer T cells in the liver of HFCD-fed LXRα-KO mice. These mice were more susceptible to lipopolysaccharide-induced liver injury and resistant to inflammatory responses against α-galactosylceramide or concanavalin-A treatment. The findings provide evidence for activation of bone marrow-derived Kupffer cells/macrophages and dysfunction of invariant natural killer T cells in LXRα-KO mouse liver. These findings indicate that LXRα regulates hepatic immune function along with lipid metabolism and protects against the pathogenesis of nonalcoholic steatohepatitis.

Hydroxysteroid (17β) dehydrogenase 13 deficiency triggers hepatic steatosis and inflammation in mice

Hydroxysteroid (17β) dehydrogenases (HSD17Bs) form an enzyme family characterized by their ability to catalyze reactions in steroid and lipid metabolism. In the present study, we characterized the phenotype of HSD17B13-knockout (HSD17B13KO) mice deficient in Hsd17b13. In these studies, hepatic steatosis was detected in HSD17B13KO male mice, indicated by histologic analysis and by the increased triglyceride concentration in the liver, whereas reproductive performance and serum steroid concentrations were normal in HSD17B13KO mice. In line with these changes, the expression of key proteins in fatty acid synthesis, such as FAS, acetyl-CoA carboxylase 1, and SCD1, was increased in the HSD17B13KO liver. Furthermore, the knockout liver showed an increase in 2 acylcarnitines, suggesting impaired mitochondrial β-oxidation in the presence of unaltered malonyl CoA and AMPK expression. The glucose tolerance did not differ between wild-type and HSD17B13KO mice in the presence of lower levels of glucose 6-phosphatase in HSD17B13KO liver compared with wild-type liver. Furthermore, microgranulomas and increased portal inflammation together with up-regulation of immune response genes were observed in HSD17B13KO mice. Our data indicate that disruption of Hsd17b13 impairs hepatic-lipid metabolism in mice, resulting in liver steatosis and inflammation, but the enzyme does not play a major role in the regulation of reproductive functions.-Adam, M., Heikelä, H., Sobolewski, C., Portius, D., Mäki-Jouppila, J., Mehmood, A., Adhikari, P., Esposito, I., Elo, L. L., Zhang, F.-P., Ruohonen, S. T., Strauss, L., Foti, M., Poutanen, M. Hydroxysteroid (17β) dehydrogenase 13 deficiency triggers hepatic steatosis and inflammation in mice.