Role of integrins in fibrosing liver diseases

Alcohol and inflammatory responses: summary of the 2013 Alcohol and Immunology Research Interest Group (AIRIG) meeting

Loyola University Chicago, Health Sciences Campus in Maywood, Illinois hosted the 18th annual Alcohol and Immunology Research Interest Group (AIRIG) meeting on November 22, 2013. This year's meeting emphasized alcohol's effect on inflammatory responses in diverse disease states and injury conditions. The meeting consisted of three plenary sessions demonstrating the adverse effects of alcohol, specifically, liver inflammation, adverse systemic effects, and alcohol's role in infection and immunology. Researchers also presented insight on modulation of microRNAs and stress proteins following alcohol consumption. Additionally, researchers revealed sex- and concentration-dependent differences in alcohol-mediated pathologies.

Therapeutic targeting of liver inflammation and fibrosis by nanomedicine

Nanomedicine constitutes the emerging field of medical applications for nanotechnology such as nanomaterial-based drug delivery systems. This technology may hold exceptional potential for novel therapeutic approaches to liver diseases. The specific and unspecific targeting of macrophages, hepatic stellate cells (HSC), hepatocytes, and liver sinusoidal endothelial cells (LSEC) using nanomedicine has been developed and tested in preclinical settings. These four major cell types in the liver are crucially involved in the complex sequence of events that occurs during the initiation and maintenance of liver inflammation and fibrosis. Targeting different cell types can be based on their capacity to ingest surrounding material, endocytosis, and specificity for a single cell type can be achieved by targeting characteristic structures such as receptors, sugar moieties or peptide sequences. Macrophages and especially the liver-resident Kupffer cells are in the focus of nanomedicine due to their highly efficient and unspecific uptake of most nanomaterials as well as due to their critical pathogenic functions during inflammation and fibrogenesis. The mannose receptor enables targeting macrophages in liver disease, but macrophages can also become activated by certain nanomaterials, such as peptide-modified gold nanorods (AuNRs) that render them proinflammatory. HSC, the main collagen-producing cells during fibrosis, are currently targeted using nanoconstructs that recognize the mannose 6-phosphate and insulin-like growth factor II, peroxisome proliferator activated receptor 1, platelet-derived growth factor (PDGF) receptor β, or integrins. Targeting of the major liver parenchymal cell, the hepatocyte, has only recently been achieved with high specificity by mimicking apolipoproteins, naturally occurring nanoparticles of the body. LSEC were found to be targeted most efficiently using carboxy-modified micelles and their integrin receptors. This review will summarize important functions of these cell types in healthy and diseased livers and discuss current strategies of cell-specific targeting for liver diseases by nanomedicine.

Adipocyte exosomes induce transforming growth factor beta pathway dysregulation in hepatocytes: a novel paradigm for obesity-related liver disease

BACKGROUND

The pathogenesis of nonalcoholic fatty liver disease (NAFLD) has been attributed to increased systemic inflammation and insulin resistance mediated by visceral adipose tissue (VAT), although the exact mechanisms are undefined. Exosomes are membrane-derived vesicles containing messenger RNA, microRNA, and proteins, which have been implicated in cancer, neurodegenerative, and autoimmune diseases, which we postulated may be involved in obesity-related diseases. We isolated exosomes from VAT, characterized their content, and identified their potential targets. Targets included the transforming growth factor beta (TGF-β) pathway, which has been linked to NAFLD. We hypothesized that adipocyte exosomes would integrate into HepG2 and hepatic stellate cell lines and cause dysregulation of the TGF-β pathway.

METHODS

Exosomes from VAT from obese and lean patients were isolated and fluorescently labeled, then applied to cultured hepatic cell lines. After incubation, culture slides were imaged to detect exosome uptake. In separate experiments, exosomes were applied to cultured cells and incubated 48-h. Gene expression of TGF-β pathway mediators was analyzed by polymerase chain reaction, and compared with cells, which were not exposed to exosomes.

RESULTS

Fluorescent-labeled exosomes integrated into both cell types and deposited in a perinuclear distribution. Exosome exposure caused increased tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) and integrin ανβ-5 expression and decreased matrix metalloproteinase-7 and plasminogen activator inhibitor-1 expression in to HepG2 cells and increased expression of TIMP-1, TIMP-4, Smad-3, integrins ανβ-5 and ανβ-8, and matrix metalloproteinase-9 in hepatic stellate cells.

CONCLUSIONS

Exosomes from VAT integrate into liver cells and induce dysregulation of TGF-β pathway members in vitro and offers an intriguing possibility for the pathogenesis of NAFLD.

Hepatic stellate cells and liver fibrosis

Hepatic stellate cells are resident perisinusoidal cells distributed throughout the liver, with a remarkable range of functions in normal and injured liver. Derived embryologically from septum transversum mesenchyme, their precursors include submesothelial cells that invade the liver parenchyma from the hepatic capsule. In normal adult liver, their most characteristic feature is the presence of cytoplasmic perinuclear droplets that are laden with retinyl (vitamin A) esters. Normal stellate cells display several patterns of intermediate filaments expression (e.g., desmin, vimentin, and/or glial fibrillary acidic protein) suggesting that there are subpopulations within this parental cell type. In the normal liver, stellate cells participate in retinoid storage, vasoregulation through endothelial cell interactions, extracellular matrix homeostasis, drug detoxification, immunotolerance, and possibly the preservation of hepatocyte mass through secretion of mitogens including hepatocyte growth factor. During liver injury, stellate cells activate into alpha smooth muscle actin-expressing contractile myofibroblasts, which contribute to vascular distortion and increased vascular resistance, thereby promoting portal hypertension. Other features of stellate cell activation include mitogen-mediated proliferation, increased fibrogenesis driven by connective tissue growth factor, and transforming growth factor beta 1, amplified inflammation and immunoregulation, and altered matrix degradation. Evolving areas of interest in stellate cell biology seek to understand mechanisms of their clearance during fibrosis resolution by either apoptosis, senescence, or reversion, and their contribution to hepatic stem cell amplification, regeneration, and hepatocellular cancer.

Nanotechnology applications for the therapy of liver fibrosis

Chronic liver diseases represent a major global health problem both for their high prevalence worldwide and, in the more advanced stages, for the limited available curative treatment options. In fact, when lesions of different etiologies chronically affect the liver, triggering the fibrogenesis mechanisms, damage has already occurred and the progression of fibrosis will have a major clinical impact entailing severe complications, expensive treatments and death in end-stage liver disease. Despite significant advances in the understanding of the mechanisms of liver fibrinogenesis, the drugs used in liver fibrosis treatment still have a limited therapeutic effect. Many drugs showing potent antifibrotic activities in vitro often exhibit only minor effects in vivo because insufficient concentrations accumulate around the target cell and adverse effects result as other non-target cells are affected. Hepatic stellate cells play a critical role in liver fibrogenesis , thus they are the target cells of antifibrotic therapy. The application of nanoparticles has emerged as a rapidly evolving area for the safe delivery of various therapeutic agents (including drugs and nucleic acid) in the treatment of various pathologies, including liver disease. In this review, we give an overview of the various nanotechnology approaches used in the treatment of liver fibrosis.

Genetic variants in the PNPLA3 gene are associated with nonalcoholic steatohepatitis

In this study, we report the association of the rs738407, rs738409, and rs2896019 variants of the patatin-like phospholipase domain-containing protein 3 (PNPLA3) (adiponutrin) gene with nonalcoholic steatohepatitis (NASH) (χ(2)=14.528, p=0.001; χ(2)=18.882, p=0.000; χ(2)=7.449, p=0.024, respectively) in 80 patients with NASH and 303 healthy controls. We genotyped the subjects using three polymerase chain reaction-restriction fragment length polymorphism methods developed in our laboratory. Our findings confirm the findings of the recent case-control and genome-wide association studies carried out in different populations around the world. Thus, the three variants in PNPLA3 gene may be a genetic risk factor for NASH.

Hepatic fibrosis and the microenvironment: fertile soil for hepatocellular carcinoma development

Hepatocellular carcinoma is an emerging worldwide health threat that has few curative treatment options and poor overall survival. Progressive hepatic fibrosis is a common pathway for all forms of chronic liver disease and is closely linked epidemiologically to hepatocellular carcinoma risk. However, the molecular events that predispose a fibrotic liver to cancer development remain elusive. Nonetheless, a permissive hepatic microenvironment provides fertile soil for transition of damaged hepatocytes into hepatocellular carcinoma. Key predisposing features include alterations in the extracellular matrix, bidirectional signaling pathways between parenchymal and nonparenchymal cells, and immune dysfunction. Emerging research into the contributions of autophagy, tumor-associated fibroblasts, and hepatocellular carcinoma progenitor cells to this dangerous milieu also provides new mechanistic underpinnings to explain the contribution of fibrosis to cancer. As effective antifibrotic therapies are developed, these approaches could attenuate the rising surge of hepatocellular carcinoma associated with chronic liver disease.

Assembly of human organs from stem cells to study liver disease

Recently, significant developments in the field of liver tissue engineering have raised new possibilities for the study of complex physiological and pathophysiological processes in vitro, as well as the potential to assemble entire organs for transplantation. Human-induced pluripotent stem cells have been differentiated into relatively functional populations of hepatic cells, and novel techniques to generate whole organ acellular three-dimensional scaffolds have been developed. In this review, we highlight the most recent advances in organ assembly regarding the development of liver tissue in vitro. We emphasize applications that involve multiple types of cells with a biomimetic spatial organization for which three-dimensional configurations could be used for drug development or to explain mechanisms of disease. We also discuss applications of liver organotypic surrogates and the challenges of translating the highly promising new field of tissue engineering into a proven platform for predicting drug metabolism and toxicity.

Diet-induced mouse model of fatty liver disease and nonalcoholic steatohepatitis reflecting clinical disease progression and methods of assessment

Shortcomings of previously reported preclinical models of nonalcoholic steatohepatitis (NASH) include inadequate methods used to induce disease and assess liver pathology. We have developed a dietary model of NASH displaying features observed clinically and methods for objectively assessing disease progression. Mice fed a diet containing 40% fat (of which ∼18% was trans fat), 22% fructose, and 2% cholesterol developed three stages of nonalcoholic fatty liver disease (steatosis, steatohepatitis with fibrosis, and cirrhosis) as assessed by histological and biochemical methods. Using digital pathology to reconstruct the left lateral and right medial lobes of the liver, we made comparisons between and within lobes to determine the uniformity of collagen deposition, which in turn informed experimental sampling methods for histological, biochemical, and gene expression analyses. Gene expression analyses conducted with animals stratified by disease severity led to the identification of several genes for which expression highly correlated with the histological assessment of fibrosis. Importantly, we have established a biopsy method allowing assessment of disease progression. Mice subjected to liver biopsy recovered well from the procedure compared with sham-operated controls with no apparent effect on liver function. Tissue obtained by biopsy was sufficient for gene and protein expression analyses, providing the opportunity to establish an objective method of assessing liver pathology before subjecting animals to treatment. The improved assessment techniques and the observation that mice fed the high-fat diet exhibit many clinically relevant characteristics of NASH establish a preclinical model for identifying pharmacological interventions with greater likelihood of translating to the clinic.

A new strategy for treatment of liver fibrosis: letting MicroRNAs do the job

MicroRNAs (miRNAs) are short, endogenous, noncoding RNA molecules that regulate gene expression at a post-translational level. MiRNAs have been recognized in the regulation of physiological conditions. Moreover, awareness of the association between dysregulated miRNAs and human diseases is increasing, which consequently brings miRNAs to the frontline in the development of novel therapeutic strategies. We review the latest advances in our knowledge of the involvement of miRNAs in fibrosis with particular emphasis on hepatic fibrosis and the possibilities in the near future for miRNA-based therapy for targeted treatment of liver fibrosis. With recent advances in our understanding of the important role of senescence in the resolution of activated hepatic stellate cells (HSCs), we suggested the therapeutic potential of inducing activated HSCs into senescence by an miRNA-based strategy.

Evolving therapies for liver fibrosis

Fibrosis is an intrinsic response to chronic injury, maintaining organ integrity when extensive necrosis or apoptosis occurs. With protracted damage, fibrosis can progress toward excessive scarring and organ failure, as in liver cirrhosis. To date, antifibrotic treatment of fibrosis represents an unconquered area for drug development, with enormous potential but also high risks. Preclinical research has yielded numerous targets for antifibrotic agents, some of which have entered early-phase clinical studies, but progress has been hampered due to the relative lack of sensitive and specific biomarkers to measure fibrosis progression or reversal. Here we focus on antifibrotic approaches for liver that address specific cell types and functional units that orchestrate fibrotic wound healing responses and have a sound preclinical database or antifibrotic activity in early clinical trials. We also touch upon relevant clinical study endpoints, optimal study design, and developments in fibrosis imaging and biomarkers.

A vitamin D receptor/SMAD genomic circuit gates hepatic fibrotic response

Liver fibrosis is a reversible wound-healing response involving TGFβ1/SMAD activation of hepatic stellate cells (HSCs). It results from excessive deposition of extracellular matrix components and can lead to impairment of liver function. Here, we show that vitamin D receptor (VDR) ligands inhibit HSC activation by TGFβ1 and abrogate liver fibrosis, whereas Vdr knockout mice spontaneously develop hepatic fibrosis. Mechanistically, we show that TGFβ1 signaling causes a redistribution of genome-wide VDR-binding sites (VDR cistrome) in HSCs and facilitates VDR binding at SMAD3 profibrotic target genes via TGFβ1-dependent chromatin remodeling. In the presence of VDR ligands, VDR binding to the coregulated genes reduces SMAD3 occupancy at these sites, inhibiting fibrosis. These results reveal an intersecting VDR/SMAD genomic circuit that regulates hepatic fibrogenesis and define a role for VDR as an endocrine checkpoint to modulate the wound-healing response in liver. Furthermore, the findings suggest VDR ligands as a potential therapy for liver fibrosis.

Genome-wide scan revealed that polymorphisms in the PNPLA3, SAMM50, and PARVB genes are associated with development and progression of nonalcoholic fatty liver disease in Japan

We examined the genetic background of nonalcoholic fatty liver disease (NAFLD) in the Japanese population, by performing a genome-wide association study (GWAS). For GWAS, 392 Japanese NAFLD subjects and 934 control individuals were analyzed. For replication studies, 172 NAFLD and 1,012 control subjects were monitored. After quality control, 261,540 single-nucleotide polymorphisms (SNPs) in autosomal chromosomes were analyzed using a trend test. Association analysis was also performed using multiple logistic regression analysis using genotypes, age, gender and body mass index (BMI) as independent variables. Multiple linear regression analyses were performed to evaluate allelic effect of significant SNPs on biochemical traits and histological parameters adjusted by age, gender, and BMI. Rs738409 in the PNPLA3 gene was most strongly associated with NAFLD after adjustment (P = 6.8 × 10(-14), OR = 2.05). Rs2896019, and rs381062 in the PNPLA3 gene, rs738491, rs3761472, and rs2143571 in the SAMM50 gene, rs6006473, rs5764455, and rs6006611 in the PARVB gene had also significant P values (<2.0 × 10(-10)) and high odds ratios (1.84-2.02). These SNPs were found to be in the same linkage disequilibrium block and were associated with decreased serum triglycerides and increased aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in NAFLD patients. These SNPs were associated with steatosis grade and NAFLD activity score (NAS). Rs738409, rs2896019, rs738491, rs6006473, rs5764455, and rs6006611 were associated with fibrosis. Polymorphisms in the SAMM50 and PARVB genes in addition to those in the PNPLA3 gene were observed to be associated with the development and progression of NAFLD.

Lymphocyte subsets in alcoholic liver disease

AIM

To compare lymphocyte subsets between healthy controls and alcoholics with liver disease.

METHODS

The patient cohort for this study included individuals who were suspected to have alcoholic liver disease (ALD) and who had undergone liver biopsy (for disease grading and staging, doubts about diagnosis, or concurrent liver disease; n = 56). Normal controls included patients who were admitted for elective cholecystectomy due to non-complicated gallstones (n = 27). Formalin-fixed, paraffin-embedded liver biopsy specimens were sectioned and stained with hematoxylin and eosin and Perls' Prussian blue. The non-alcoholic steatohepatitis score was used to assess markers of ALD. Lymphocyte population subsets were determined by flow cytometry. T lymphocytes were identified (CD3(+)), and then further subdivided into CD4(+) or CD8(+) populations. B lymphocytes (CD19(+)) and natural killer (NK) cell numbers were also measured. In addition to assessing lymphocyte subpopulation differences between ALD patients and controls, we also compared subsets of alcoholic patients without cirrhosis or abstinent cirrhotic patients to normal controls.

RESULTS

The patient cohort primarily consisted of older men. Active alcoholism was present in 66.1%. Reported average daily alcohol intake was 164.9 g and the average lifetime cumulative intake was 2211.6 kg. Cirrhosis was present in 39.3% of the patients and 66.1% had significant fibrosis (perisinusoidal and portal/periportal fibrosis, bridging fibrosis, or cirrhosis) in their liver samples. The average Mayo end-stage liver disease score was 7.6. No hereditary hemochromatosis genotypes were found. ALD patients (n = 56) presented with significant lymphopenia (1.5 × 10(9)/L ± 0.5 × 10(9)/L vs 2.1 × 10(9)/L ± 0.5 × 10(9)/L, P < 0.0001), due to a decrease in all lymphocyte subpopulations, except for NK lymphocytes: CD3(+) (1013.0 ± 406.2/mm(3) vs 1523.0 ± 364.6/mm(3), P < 0.0001), CD4(+) (713.5 ± 284.7/mm(3) vs 992.4 ± 274.7/mm(3), P < 0.0001), CD8(+) (262.3 ± 140.4/mm(3) vs 478.9 ± 164.6/mm(3), P < 0.0001), and CD19(+) (120.6 ± 76.1/mm(3) vs 264.6 ± 88.0/mm(3), P < 0.0001). CD8(+) lymphocytes suffered the greatest reduction, as evidenced by an increase in the CD4(+)/CD8(+) ratio (3.1 ± 1.3 vs 2.3 ± 0.9, P = 0.013). This ratio was associated with the stage of fibrosis on liver biopsy (r s = 0.342, P = 0.01) and with Child-Pugh score (r s = 0.482, P = 0.02). The number of CD8(+) lymphocytes also had a positive association with serum ferritin levels (r s = 0.345, P = 0.009). Considering only patients with active alcoholism but not cirrhosis (n = 27), we found similar reductions in total lymphocyte counts (1.8 × 10(9)/L ± 0.3 × 10(9)/L vs 2.1 × 10(9)/L ± 0.5 × 10(9)/L, P = 0.018), and in populations of CD3(+) (1164.7 ± 376.6/mm(3) vs 1523.0 ± 364.6/mm(3), P = 0.001), CD4(+) (759.8 ± 265.0/mm(3) vs 992.4 ± 274.7/mm(3), P = 0.003), CD8(+) (330.9 ± 156.3/mm(3) vs 478.9 ± 164.6/mm(3), P = 0.002), and CD19(+) (108.8 ± 64.2/mm(3) vs 264.6 ± 88.0/mm(3), P < 0.0001). In these patients, the CD4(+)/CD8(+) ratio and the number of NK lymphocytes was not significantly different, compared to controls. Comparing patients with liver cirrhosis but without active alcohol consumption (n = 11), we also found significant lymphopenia (1.3 × 10(9)/L ± 0.6 × 10(9)/L vs 2.1 × 10(9)/L ± 0.5 × 10(9)/L, P < 0.0001) and decreases in populations of CD3(+) (945.5 ± 547.4/mm(3) vs 1523.0 ± 364.6/mm(3), P = 0.003), CD4(+) (745.2 ± 389.0/mm(3) vs 992.4 ± 274.7/mm(3), P = 0.032), CD8(+) (233.9 ± 120.0/mm(3) vs 478.9 ± 164.6/mm(3), P < 0.0001), and CD19(+) (150.8 ± 76.1/mm(3) vs 264.6 ± 88.0/mm(3), P = 0.001). The NK lymphocyte count was not significantly different, but, in this group, there was a significant increase in the CD4(+)/CD8(+) ratio (3.5 ± 1.3 vs 2.3 ± 0.9, P = 0.01).

CONCLUSION

All patient subsets presented with decreased lymphocyte counts, but only patients with advanced fibrosis presented with a significant increase in the CD4(+)/CD8(+) ratio.

MicroRNA expression profiling in HCV-infected human hepatoma cells identifies potential anti-viral targets induced by interferon-α

Objective

Increasing evidence suggests that miRNAs have a profound impact on host defense to Hepatitis C virus (HCV) infection and clinical outcome of standard HCV therapy. In this study, we investigated modulation of miRNA expression in Huh7.5 hepatoma cells by HCV infection and in vitro interferon-αtreatment.

Methods

MiRNA expression profiling was determined using Human miRNA TaqMan® Arrays followed by rigorous pairwise statistical analysis. MiRNA inhibitors assessed the functional effects of miRNAs on HCV replication. Computational analysis predicted anti-correlated mRNA targets and their involvement in host cellular pathways. Quantitative RTPCR confirmed the expression of predicted miRNA-mRNA correlated pairs in HCV-infected Huh7.5 cells with and without interferon-α.

Results

Seven miRNAs (miR-30b, miR-30c, miR-130a, miR-192, miR-301, miR-324-5p, and miR-565) were down-regulated in HCV-infected Huh7.5 cells (p<0.05) and subsequently up-regulated following interferon-α treatment (p<0.01). The miR-30(a-d) cluster and miR-130a/301 and their putative mRNA targets were predicted to be associated with cellular pathways that involve Hepatitis C virus entry, propagation and host response to viral infection.

Conclusions

HCV differentially modulates miRNAs to facilitate entry and early establishment of infection in vitro. Interferon-α appears to neutralize the effect of HCV replication on miRNA regulation thus providing a potential mechanism of action in eradicating HCV from hepatocytes.

Impact of common variation in bone-related genes on type 2 diabetes and related traits

Exploring genetic pleiotropy can provide clues to a mechanism underlying the observed epidemiological association between type 2 diabetes and heightened fracture risk. We examined genetic variants associated with bone mineral density (BMD) for association with type 2 diabetes and glycemic traits in large well-phenotyped and -genotyped consortia. We undertook follow-up analysis in ∼19,000 individuals and assessed gene expression. We queried single nucleotide polymorphisms (SNPs) associated with BMD at levels of genome-wide significance, variants in linkage disequilibrium (r(2) > 0.5), and BMD candidate genes. SNP rs6867040, at the ITGA1 locus, was associated with a 0.0166 mmol/L (0.004) increase in fasting glucose per C allele in the combined analysis. Genetic variants in the ITGA1 locus were associated with its expression in the liver but not in adipose tissue. ITGA1 variants appeared among the top loci associated with type 2 diabetes, fasting insulin, β-cell function by homeostasis model assessment, and 2-h post-oral glucose tolerance test glucose and insulin levels. ITGA1 has demonstrated genetic pleiotropy in prior studies, and its suggested role in liver fibrosis, insulin secretion, and bone healing lends credence to its contribution to both osteoporosis and type 2 diabetes. These findings further underscore the link between skeletal and glucose metabolism and highlight a locus to direct future investigations.