Thyroid hormone receptor alpha modulates fibrogenesis in hepatic stellate cells.

OBJECTIVE: Progressive hepatic fibrosis can be considered the final stage of chronic liver disease. Hepatic stellate cells (HSC) play a central role in liver fibrogenesis. Thyroid hormones (TH, e.g. thyroxine; T4 and triiodothyronine; T3) significantly affect development, growth, cell differentiation and metabolism through activation of TH receptor α and/or ß (TRα/ß). Here, we evaluated the influence of TH in hepatic fibrogenesis. DESIGN: Human liver tissue was obtained from explanted livers following transplantation. TRα-deficient (TRα-KO) and wild-type (WT) mice were fed a control or a profibrogenic methionine-choline deficient (MCD) diet. Liver tissue was assessed by qRT-PCR for fibrogenic gene expression. In vitro, HSC were treated with TGFß in the presence or absence of T3. HSC with stable TRα knockdown and TRα deficient mouse embryonic fibroblasts (MEF) were used to determine receptor-specific function. Activation of HSC and MEF was assessed using the wound healing assay, Western blotting, and qRT-PCR. RESULTS: TRα and TRß expression is downregulated in the liver during hepatic fibrogenesis in humans and mice. TRα represents the dominant isoform in HSC. In vitro, T3 blunted TGFß-induced expression of fibrogenic genes in HSC and abrogated wound healing by modulating TGFß signalling, which depended on TRα presence. In vivo, TRα-KO enhanced MCD diet-induced liver fibrogenesis. CONCLUSION: These observations indicate that TH action in non-parenchymal cells is highly relevant. The interaction of TRα with TH regulates the phenotype of HSC via the TGFß signalling pathway. Thus, the TH-TR axis may be a valuable target for future therapy of liver fibrosis.

Impact of Obesity and Metabolic Syndrome on IBD Outcomes.

PURPOSE OF REVIEW: The recent surge in inflammatory bowel disease (IBD) cases has paralleled a significant rise in obesity and metabolic comorbidities rates. In this article, we explore the potential influence of obesity and associated metabolic comorbidities on disease progression, complications, treatment response, surgical outcomes, health economics, and the potential impact of obesity treatment on the course of IBD. FINDINGS: Contrary to visceral adiposity, obesity does not consistently result in an increased risk of IBD-related complications. Patients with IBD have a higher risk of acute arterial events, likely linked to systemic inflammation. Substantial evidence suggests that obesity has a negative impact on the response to IBD treatment, with this effect being most thoroughly studied in biologics and immunomodulators. The rates of overall complications and post-operative infections are higher in patients who are obese. There are limited but promising data regarding the impact of weight loss techniques, including exercise, medications, and bariatric interventions, on the outcomes in IBD. Both obesity and diabetes have adverse effects on the overall quality of life and place an increased financial burden on the IBD population. A growing body of evidence indicates a connection between obesity and associated metabolic comorbidities and negative outcomes in IBD, yet further efforts are required to fully understand this relationship.

The Presence of Periodontitis Exacerbates Non-Alcoholic Fatty Liver Disease via Sphingolipid Metabolism-Associated Insulin Resistance and Hepatic Inflammation in Mice with Metabolic Syndrome.

Clinical studies have shown that periodontitis is associated with non-alcoholic fatty liver disease (NAFLD). However, it remains unclear if periodontitis contributes to the progression of NAFLD. In this study, we generated a mouse model with high-fat diet (HFD)-induced metabolic syndrome (MetS) and NAFLD and oral P. gingivalis inoculation-induced periodontitis. Results showed that the presence of periodontitis increased insulin resistance and hepatic inflammation and exacerbated the progression of NAFLD. To determine the role of sphingolipid metabolism in the association between NAFLD and periodontitis, we also treated mice with imipramine, an inhibitor of acid sphingomyelinase (ASMase), and demonstrated that imipramine treatment significantly alleviated insulin resistance and hepatic inflammation, and improved NAFLD. Studies performed in vitro showed that lipopolysaccharide (LPS) and palmitic acid (PA), a major saturated fatty acid associated with MetS and NAFLD, synergistically increased the production of ceramide, a bioactive sphingolipid involved in NAFLD progression in macrophages but imipramine effectively reversed the ceramide production stimulated by LPS and PA. Taken together, this study showed for the first time that the presence of periodontitis contributed to the progression of NAFLD, likely due to alterations in sphingolipid metabolism that led to exacerbated insulin resistance and hepatic inflammation. This study also showed that targeting ASMase with imipramine improves NAFLD by reducing insulin resistance and hepatic inflammation.

Phosphorylation and Stabilization of PIN1 by JNK Promote Intrahepatic Cholangiocarcinoma Growth.

BACKGROUND AND AIMS: Intrahepatic cholangiocarcinoma (ICC) is a highly aggressive type of liver cancer in urgent need of treatment options. Aberrant activation of the c-Jun N-terminal kinase (JNK) pathway is a key feature in ICC and an attractive candidate target for its treatment. However, the mechanisms by which constitutive JNK activation promotes ICC growth, and therefore the key downstream effectors of this pathway, remain unknown for their applicability as therapeutic targets. Our aim was to obtain a better mechanistic understanding of the role of JNK signaling in ICC that could open up therapeutic opportunities. APPROACH AND RESULTS: Using loss-of-function and gain-of-function studies in vitro and in vivo, we show that activation of the JNK pathway promotes ICC cell proliferation by affecting the protein stability of peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1), a key driver of tumorigenesis. PIN1 is highly expressed in ICC primary tumors, and its expression positively correlates with active JNK. Mechanistically, the JNK kinases directly bind to and phosphorylate PIN1 at Ser115, and this phosphorylation prevents PIN1 mono-ubiquitination at Lys117 and its proteasomal degradation. Moreover, pharmacological inhibition of PIN1 through all-trans retinoic acid, a Food and Drug Administration-approved drug, impairs the growth of both cultured and xenografted ICC cells. CONCLUSIONS: Our findings implicate the JNK-PIN1 regulatory axis as a functionally important determinant for ICC growth, and provide a rationale for therapeutic targeting of JNK activation through PIN1 inhibition.

GPR40 deficiency is associated with hepatic FAT/CD36 upregulation, steatosis, inflammation, and cell injury in C57BL/6 mice.

G-protein-coupled receptor 40 (GPR40) is highly expressed in pancreatic islets, and its activation increases glucose-stimulated insulin secretion from pancreas. Therefore, GPR40 is considered as a target for type 2 diabetes mellitus (T2DM). Since nonalcoholic fatty liver disease (NAFLD) is associated with T2DM and GPR40 is also expressed by hepatocytes and macrophages, it is important to understand the role of GPR40 in NAFLD. However, the role of GPR40 in NAFLD in animal models has not been well defined. In this study, we fed wild-type or GPR40 knockout C57BL/6 mice a high-fat diet (HFD) for 20 wk and then assessed the effect of GPR40 deficiency on HFD-induced NAFLD. Assays on metabolic parameters showed that an HFD increased body weight, glucose, insulin, insulin resistance, cholesterol, and alanine aminotransferase (ALT), and GPR40 deficiency did not mitigate the HFD-induced metabolic abnormalities. In contrast, we found that GPR40 deficiency was associated with increased body weight, insulin, insulin resistance, cholesterol, and ALT in control mice fed a low-fat diet (LFD). Surprisingly, histology and Oil Red O staining showed that GPR40 deficiency in LFD-fed mice was associated with steatosis. Immunohistochemical analysis showed that GPR40 deficiency also increased F4/80, a macrophage biomarker, in LFD-fed mice. Furthermore, results showed that GPR40 deficiency led to a robust upregulation of hepatic fatty acid translocase (FAT)/CD36 expression. Finally, our in vitro studies showed that GPR40 knockdown by siRNA or a GPR40 antagonist increased palmitic acid-induced FAT/CD36 mRNA in hepatocytes. Taken together, this study indicates that GPR40 plays an important role in homeostasis of hepatic metabolism and inflammation and inhibits nonalcoholic steatohepatitis by possible modulation of FAT/CD36 expression.

Hepatokines and adipokines in NASH-related hepatocellular carcinoma.

The incidence of hepatocellular carcinoma (HCC) is increasing in industrialised societies; this is likely secondary to the increasing burden of non-alcoholic fatty liver disease (NAFLD), its progressive form non-alcoholic steatohepatitis (NASH), and the metabolic syndrome. Cumulative studies suggest that NAFLD-related HCC may also develop in non-cirrhotic livers. However, prognosis and survival do not differ between NAFLD- or virus-associated HCC. Thus, research has increasingly focused on NAFLD-related risk factors to better understand the biology of hepatocarcinogenesis and to develop new diagnostic, preventive, and therapeutic strategies. One important aspect thereof is the role of hepatokines and adipokines in NAFLD/NASH-related HCC. In this review, we compile current data supporting the use of hepatokines and adipokines as potential markers of disease progression in NAFLD or as early markers of NAFLD-related HCC. While much work must be done to elucidate the mechanisms and interactions underlying alterations to hepatokines and adipokines, current data support the possible utility of these factors - in particular, angiopoietin-like proteins, fibroblast growth factors, and apelin - for detection or even as therapeutic targets in NAFLD-related HCC.

Targeting myosin 1c inhibits murine hepatic fibrogenesis.

Myosin 1c (Myo1c) is an unconventional myosin that modulates signaling pathways involved in tissue injury and repair. In this study, we observed that Myo1c expression is significantly upregulated in human chronic liver disease such as nonalcoholic steatohepatitis (NASH) and in animal models of liver fibrosis. High throughput data from the GEO-database identified similar Myo1c upregulation in mice and human liver fibrosis. Notably, transforming growth factor-ß1 (TGF-ß1) stimulation to hepatic stellate cells (HSCs), the liver pericyte and key cell type responsible for the deposition of extracellular matrix, upregulates Myo1c expression, whereas genetic depletion or pharmacological inhibition of Myo1c blunted TGF-ß-induced fibrogenic responses, resulting in repression of α-smooth muscle actin (α-SMA) and collagen type I α 1 chain (Col1α1) mRNA. Myo1c deletion also decreased fibrogenic processes such as cell proliferation, wound healing response, and contractility when compared with vehicle-treated HSCs. Importantly, phosphorylation of mothers against decapentaplegic homolog 2 (SMAD2) and mothers against decapentaplegic homolog 3 (SMAD3) were significantly blunted upon Myo1c inhibition in GRX cells as well as Myo1c knockout (Myo1c-KO) mouse embryonic fibroblasts (MEFs) upon TGF-ß stimulation. Using the genetic Myo1c-KO mice, we confirmed that Myo1c is critical for fibrogenesis, as Myo1c-KO mice were resistant to carbon tetrachloride (CCl4)-induced liver fibrosis. Histological and immunostaining analysis of liver sections showed that deposition of collagen fibers and α-SMA expression were significantly reduced in Myo1c-KO mice upon liver injury. Collectively, these results demonstrate that Myo1c mediates hepatic fibrogenesis by modulating TGF-ß signaling and suggest that inhibiting this process may have clinical application in treating liver fibrosis.NEW & NOTEWORTHY The incidences of liver fibrosis are growing at a rapid pace and have become one of the leading causes of end-stage liver disease. Although TGF-ß1 is known to play a prominent role in transforming cells to produce excessive extracellular matrix that lead to hepatic fibrosis, the therapies targeting TGF-ß1 have achieved very limited clinical impact. This study highlights motor protein myosin-1c-mediated mechanisms that serve as novel regulators of TGF-ß1 signaling and fibrosis.

Anti-TNFα treatment in Crohn's disease: Impact on hepatic steatosis, gut-derived hormones and metabolic status.

BACKGROUND AND AIMS: An association between Crohn's disease (CD) and hepatic steatosis has been reported. However, the underlying mechanisms of steatosis progression in CD are not clear. Among the most effective CD treatments are agents that inhibit Tumor-Necrosis-Factor (TNF) activity, yet it is unclear why anti-TNFα agents would affect steatosis in CD. Recent studies suggest that microbiome can affect both, CD and steatosis pathogenesis. Therefore, we here analysed a potential relationship between anti-TNF treatment and hepatic steatosis in CD, focusing on the gut-liver axis. METHODS: This cross-sectional study evaluated patients with established CD, with and without anti-TNFα treatment, analysing serum markers of liver injury, measurement of transient elastography, controlled attenuation parameter (CAP) and MRI for fat detection. Changes in lipid and metabolic profiles were assessed by serum and stool lipidomics and metabolimics. Additionally, we analysed gut microbiota composition and mediators of bile acid (BA) signalling via stool and serum analysis. RESULTS: Patients on anti-TNFα treatment had less hepatic steatosis as assessed by CAP and MRI. Serum FGF19 levels were significantly higher in patients on anti-TNFα therapy and associate with reduced steatosis and increased bowel motility. Neutral lipids including triglycerides were reduced in the serum of patients on anti-TNF treatment. Bacteria involved in BA metabolism and FGF19 regulation, including Firmicutes, showed group-specific alterations with low levels in patients without anti-TNFα treatment. Low abundance of Firmicutes was associated with higher triglyceride levels. CONCLUSIONS: Anti-TNFα treatment is associated with reduced steatosis, lower triglyceride levels, alterations in FXR-signalling (eg FGF19) and microbiota composition in CD.

A Review of the Epidemiology, Pathophysiology, and Efficacy of Anti-diabetic Drugs Used in the Treatment of Nonalcoholic Fatty Liver Disease.

In recent years, epidemiological studies have consistently demonstrated that the coexistence of nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM) is strongly associated with increased mortality and morbidity related to hepatic- and extrahepatic causes. Indeed, compared with the general population, patients with T2DM are more likely to be diagnosed with more severe forms of NAFLD (i.e., nonalcoholic steatohepatitis (NASH) with liver fibrosis). There is an ongoing debate whether NALFD is a consequence of diabetes or whether NAFLD is simply a component and manifestation of the metabolic syndrome, since liver fat (steatosis) and even more advanced stages of liver fibrosis can occur in the absence of diabetes. Nevertheless, insulin resistance is a key component of the mechanism of NAFLD development; furthermore, therapies that lower blood glucose concentrations also appear to be effective in the treatment of NAFLD. Here, we will discuss the pathophysiological and epidemiological associations between NAFLD and T2DM. We will also review currently available anti-diabetic agents with their regard to their efficacy of NAFLD/NASH treatment.

Amitriptyline inhibits nonalcoholic steatohepatitis and atherosclerosis induced by high-fat diet and LPS through modulation of sphingolipid metabolism.

We reported previously that increased acid sphingomyelinase (ASMase)-catalyzed hydrolysis of sphingomyelin, which leads to increases in ceramide and sphingosine 1 phosphate (S1P), played a key role in the synergistic upregulation of proinflammatory cytokines by palmitic acid (PA), a major saturated fatty acid, and lipopolysaccharide (LPS) in macrophages. Since macrophages are vital players in nonalcoholic steatohepatitis (NASH) and atherosclerosis, we assessed the effect of ASMase inhibition on NASH and atherosclerosis cooperatively induced by high-PA-containing high-fat diet (HP-HFD) and LPS in LDL receptor-deficient (LDLR-/-) mice. LDLR-/- mice were fed HP-HFD, injected with low dose of LPS and treated with or without the ASMase inhibitor amitriptyline. The neutral sphingomyelinase inhibitor GW4869 was used as control. Metabolic study showed that both amitriptyline and GW4869 reduced glucose, lipids, and insulin resistance. Histological analysis and Oil Red O staining showed that amitriptyline robustly reduced hepatic steatosis while GW4869 had modest effects. Interestingly, immunohistochemical study showed that amitriptyline, but not GW4869, strongly reduced hepatic inflammation. Furthermore, results showed that both amitriptyline and GW4869 attenuated atherosclerosis. To elucidate the underlying mechanisms whereby amitriptyline inhibited both NASH and atherosclerosis, but GW4869 only inhibited atherosclerosis, we found that amitriptyline, but not GW4869, downregulated proinflammatory cytokines in macrophages. Finally, we found that inhibition of sphingosine 1 phosphate production is a potential mechanism whereby amitriptyline inhibited proinflammatory cytokines. Collectively, this study showed that amitriptyline inhibited NASH and atherosclerosis through modulation of sphingolipid metabolism in LDLR-/- mice, indicating that sphingolipid metabolism in macrophages plays a crucial role in the linkage of NASH and atherosclerosis.

Osteopontin splice variants and polymorphisms in cancer progression and prognosis.

Osteopontin (OPN) is an extracellular matrix protein that is overexpressed in various cancers and promotes oncogenic features including cell proliferation, survival, migration, and angiogenesis, among others. OPN can participate in the regulation of the tumor microenvironment, affecting both cancer and neighboring cells. Here, we review the roles of OPN splice variants (a, b, c) in cancer development, progression, and prognosis, and also discuss the identities of isoforms 4 and 5. We also discussed how single-nucleotide polymorphisms (SNPs) of the OPN gene are an additional factor influencing the level of OPN in individuals, modulating the risks of cancer development and outcome.

The motor protein Myo1c regulates transforming growth factor-ß-signaling and fibrosis in podocytes.

Transforming growth factor-ß (TGF-ß) is known to play a critical role in the pathogenesis of many progressive podocyte diseases. However, the molecular mechanisms regulating TGF-ß signaling in podocytes remain unclear. Using a podocyte-specific myosin (Myo)1c knockout, we demonstrate whether Myo1c is critical for TGF-ß-signaling in podocyte disease pathogenesis. Specifically, podocyte-specific Myo1c knockout mice were resistant to fibrotic injury induced by Adriamycin or nephrotoxic serum. Further, loss of Myo1c also protected from injury in the TGF-ß-dependent unilateral ureteral obstruction mouse model of renal interstitial fibrosis. Mechanistic analyses showed that loss of Myo1c significantly blunted TGF-ß signaling through downregulation of canonical and non-canonical TGF-ß pathways. Interestingly, nuclear rather than the cytoplasmic Myo1c was found to play a central role in controlling TGF-ß signaling through transcriptional regulation. Differential expression analysis of nuclear Myo1c-associated gene promoters showed that nuclear Myo1c targeted the TGF-ß responsive gene growth differentiation factor (GDF)-15 and directly bound to the GDF-15 promoter. Importantly, GDF15 was found to be involved in podocyte pathogenesis, where GDF15 was upregulated in glomeruli of patients with focal segmental glomerulosclerosis. Thus, Myo1c-mediated regulation of TGF-ß-responsive genes is central to the pathogenesis of podocyte injury. Hence, inhibiting this process may have clinical application in treating podocytopathies.

Current treatment options for nonalcoholic fatty liver disease.

PURPOSE OF REVIEW: Nonalcoholic fatty liver disease (NAFLD) is the leading cause of liver disease in the United States and is strongly associated to the metabolic syndrome. In this review, we will discuss the evidence behind the current recommendations on lifestyle modifications and available treatment options for NAFLD. RECENT FINDINGS: The unrelenting rise in obesity and diabetes epidemic has led to a large healthcare burden from NAFLD and it is projected to continue to grow over the next two decades. Lifestyle modification that leads to weight loss is effective at treating NAFLD, but these modifications require a multidisciplinary approach for success in the real world. Multiple pharmacologic treatment options have been studied with promising results, but none have been approved for treatment in the United States. Clinical trials are on-going to study further pharmacologic treatment alternatives. SUMMARY: NAFLD is the most common chronic liver disease in United States, and an independent risk factor for mortality. Implementation of lifestyle modifications through a multidisciplinary approach and careful selection of patients for pharmacologic interventions will be essential for successful management of NAFLD.

Non-nutritive sweeteners and their association with the metabolic syndrome and non-alcoholic fatty liver disease: a review of the literature.

PURPOSE: Non-alcoholic fatty liver disease (NAFLD) is increasing in incidence worldwide, paralleling epidemics in obesity and metabolic syndrome. Widely considered the hepatic manifestation of the metabolic syndrome, NAFLD is associated with significant morbidity, mortality, and increased healthcare costs. There is an abundance of data linking sugar-sweetened beverages, and fructose, in particular, to the metabolic syndrome and NAFLD. As a result, non-nutritive sweeteners (NNSs) are frequently substituted for sugar in drinks and a variety of foods. However, despite the widespread consumption of NNSs, there is growing concern about their impact on metabolic health. METHODS: This review examines the experimental and clinical evidence on non-nutritive sweetener (NNS) consumption and features of the metabolic syndrome, including NAFLD. RESULTS: Experimental animal studies show that NNS consumption can induce glucose intolerance, increased food consumption, and weight gain, with proposed mechanisms including altered gut microbiome, inhibition of protective intestinal enzymes, and increased appetite. The evidence from clinical studies is more controversial. Observational studies overwhelmingly show an association between NNS consumption and features of the metabolic syndrome, and this includes NAFLD when analyses are not adjusted for obesity. The evidence from randomized-controlled trials in humans is sparse and conflicting, and primarily evaluates weight-related outcomes. CONCLUSION: Further research is urgently needed to evaluate NNS consumption and its relationship with NAFLD and the gut microbiome in humans.

Nonalcoholic Fatty Liver Disease Among Individuals with HIV Mono-infection: A Growing Concern?

PURPOSE OF REVIEW: Liver disease is a leading cause of non-AIDS-related death in the HIV population since the introduction of highly active antiretroviral treatment (HAART). Recent studies suggest that patients with HIV are at high risk for nonalcoholic fatty liver disease (NAFLD) and progressive liver fibrosis. Evidence for the prevalence, risk factors, and diagnostic methodologies of NAFLD in patients with HIV mono-infection is summarized here. RECENT FINDINGS: Although limited, published studies suggest that the prevalence of NAFLD is higher (30-50%) and progresses at an increased rate in patients with HIV compared to the general population. Identifying those at risk for significant liver fibrosis is critical, preferably with non-invasive screening tests. While there is a paucity of evidence in this population, transient elastography (TE) appears to provide a sensitive, non-invasive screening modality. Identifying NAFLD early will allow for dietary and lifestyle interventions, as well as future drug therapies to decrease the risk of progressive liver fibrosis and cirrhosis in the high-risk HIV population. Clinicians should be aware of this risk and consider using TE for NAFLD diagnosis and surveillance.

Low Free Triiodothyronine Is Associated with Advanced Fibrosis in Patients at High Risk for Nonalcoholic Steatohepatitis.

BACKGROUND: Thyroid hormone is critical for tissue-organ development, growth, differentiation, and metabolism. In murine models of advanced nonalcoholic steatohepatitis (NASH), the administration of T3 reduced liver triglyceride, repressed liver inflammation, and attenuated injury. In recent studies of patients with NASH, hypothyroidism was noted to be associated with more advanced NASH. These findings suggest that thyroid hormone function might be a modulator of nonalcoholic fatty liver disease (NAFLD) outcomes. AIMS: Herein, we evaluated the correlation between plasma TSH/free T3 (fT3)/free T4 (fT4) levels and (non-invasive) surrogate markers of NAFLD fibrosis. METHODS: We performed a retrospective analysis of 144 patients who were seen in our NASH outpatient clinic between 2015 and 2017. Each patient underwent a standard anthropometric assessment, laboratory and clinical evaluations, and liver stiffness measurements by transient elastography (Fibroscan). Univariate analysis and multivariate linear and logistic regression analysis were used to identify factors independently associated with NASH and advanced fibrosis. RESULTS: Low fT3 values but not TSH and fT4 were associated with higher liver stiffness and higher NAFLD fibrosis score, respectively. fT3 and TSH values correlated significantly with indices of liver disease including INR, albumin, ALT, AST, bilirubin, and platelets. In multivariate analyses, a low fT3 was independently associated with high NFS scores (OR 0.169, CI 0.05-0.54, p = 0.003) and was also associated with high liver stiffness readings (OR 0.326, CI 0.135-0.785, p = 0.001). CONCLUSION: A low-normal thyroid hormone function is predictive of NASH and advanced fibrosis and may have a pathogenic role in modulating NAFLD outcomes.

Role of the Circadian Clock in the Metabolic Syndrome and Nonalcoholic Fatty Liver Disease.

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in industrialized nations and is strongly associated with the metabolic syndrome. The prevalence of NAFLD continues to rise along with the epidemic of the metabolic syndrome. Metabolic homeostasis is linked to the circadian clock (rhythm), with multiple signaling pathways in organs regulated by circadian clock genes, and recent studies of circadian clock gene functions suggest that disruption of the circadian rhythm is associated with significant morbidity and mortality, including the metabolic syndrome. In the industrialized world, various human behaviors and activities such as work and eating patterns, jet lag, and sleep deprivation interfere with the circadian rhythm, leading to perturbations in metabolism and development of the metabolic syndrome. In this review, we discuss how disruption of the circadian rhythm is associated with various metabolic conditions that comprise the metabolic syndrome and NAFLD.

Osteopontin regulates the cross-talk between phosphatidylcholine and cholesterol metabolism in mouse liver.

Osteopontin (OPN) is involved in different liver pathologies in which metabolic dysregulation is a hallmark. Here, we investigated whether OPN could alter liver, and more specifically hepatocyte, lipid metabolism and the mechanism involved. In mice, lack of OPN enhanced cholesterol 7α-hydroxylase (CYP7A1) levels and promoted loss of phosphatidylcholine (PC) content in liver; in vivo treatment with recombinant (r)OPN caused opposite effects. rOPN directly decreased CYP7A1 levels through activation of focal adhesion kinase-AKT signaling in hepatocytes. PC content was also decreased in OPN-deficient (OPN-KO) hepatocytes in which de novo FA and PC synthesis was lower, whereas cholesterol (CHOL) synthesis was higher, than in WT hepatocytes. In vivo inhibition of cholesterogenesis normalized liver PC content in OPN-KO mice, demonstrating that OPN regulates the cross-talk between liver CHOL and PC metabolism. Matched liver and serum samples showed a positive correlation between serum OPN levels and liver PC and CHOL concentration in nonobese patients with nonalcoholic fatty liver. In conclusion, OPN regulates CYP7A1 levels and the metabolic fate of liver acetyl-CoA as a result of CHOL and PC metabolism interplay. The results suggest that CYP7A1 is a main axis and that serum OPN could disrupt liver PC and CHOL metabolism, contributing to nonalcoholic fatty liver disease progression in nonobese patients.

Osteopontin is a proximal effector of leptin-mediated non-alcoholic steatohepatitis (NASH) fibrosis.

INTRODUCTION: Liver fibrosis develops when hepatic stellate cells (HSC) are activated into collagen-producing myofibroblasts. In non-alcoholic steatohepatitis (NASH), the adipokine leptin is upregulated, and promotes liver fibrosis by directly activating HSC via the hedgehog pathway. We reported that hedgehog-regulated osteopontin (OPN) plays a key role in promoting liver fibrosis. Herein, we evaluated if OPN mediates leptin-profibrogenic effects in NASH. METHODS: Leptin-deficient (ob/ob) and wild-type (WT) mice were fed control or methionine-choline deficient (MCD) diet. Liver tissues were assessed by Sirius-red, OPN and αSMA IHC, and qRT-PCR for fibrogenic genes. In vitro, HSC with stable OPN (or control) knockdown were treated with recombinant (r)leptin and OPN-neutralizing or sham-aptamers. HSC response to OPN loss was assessed by wound healing assay. OPN-aptamers were also added to precision-cut liver slices (PCLS), and administered to MCD-fed WT (leptin-intact) mice to determine if OPN neutralization abrogated fibrogenesis. RESULTS: MCD-fed WT mice developed NASH-fibrosis, upregulated OPN, and accumulated αSMA+ cells. Conversely, MCD-fed ob/ob mice developed less fibrosis and accumulated fewer αSMA+ and OPN+ cells. In vitro, leptin-treated HSC upregulated OPN, αSMA, collagen 1α1 and TGFß mRNA by nearly 3-fold, but this effect was blunted by OPN loss. Inhibition of PI3K and transduction of dominant negative-Akt abrogated leptin-mediated OPN induction, while constitutive active-Akt upregulated OPN. Finally, OPN neutralization reduced leptin-mediated fibrogenesis in both PCLS and MCD-fed mice. CONCLUSION: OPN overexpression in NASH enhances leptin-mediated fibrogenesis via PI3K/Akt. OPN neutralization significantly reduces NASH fibrosis, reinforcing the potential utility of targeting OPN in the treatment of patients with advanced NASH.