Reactive nitrogen species switch on early extracellular matrix remodeling via induction of MMP1 and TNFalpha

Redox Biology and Liver Fibrosis

Hepatic fibrosis is a complex process that develops in chronic liver diseases. Even though the initiation and progression of fibrosis rely on the underlying etiology, mutual mechanisms can be recognized and targeted for therapeutic purposes. Irrespective of the primary cause of liver disease, persistent damage to parenchymal cells triggers the overproduction of reactive species, with the consequent disruption of redox balance. Reactive species are important mediators for the homeostasis of both hepatocytes and non-parenchymal liver cells. Indeed, other than acting as cytotoxic agents, reactive species are able to modulate specific signaling pathways that may be relevant to hepatic fibrogenesis. After a brief introduction to redox biology and the mechanisms of fibrogenesis, this review aims to summarize the current evidence of the involvement of redox-dependent pathways in liver fibrosis and focuses on possible therapeutic targets.

An Activatable Probe with Aggregation-Induced Emission for Detecting and Imaging Herbal Medicine Induced Liver Injury with Optoacoustic Imaging and NIR-II Fluorescence Imaging

Whilte herbal medicines are widely used for health promotion and therapy for chronic conditions, inappropriate use of them may cause adverse effects like liver injury, and accurately evaluating their hepatotoxicity is of great significance for public health. Herein, an activatable probe QY-N for diagnosing herbal-medicine-induced liver injury by detecting hepatic NO with NIR-II fluorescence and multispectral optoacoustic tomography (MSOT) imaging is demonstrated. The probe includes a bismethoxyphenyl-amine-containing dihydroxanthene serving as electron donor, a quinolinium as electron acceptor, and a butylamine as recognition group and fluorescence quencher. The hepatic level of NO reacts with butylamine, thereby generating the activated probe QY-NO which exhibits a red-shifted absorption band (700-850 nm) for optoacoustic imaging and generates strong emission (910-1110 nm) for NIR-II fluorescence imaging. QY-NO is aggregation-induced-emission (AIE) active, which ensures strong emission in aggregated state. QY-N is utilized in the triptolide-induced liver injury mouse model, and experimental results demonstrate the QY-N can be activated by hepatic NO and thus be used in detecting herbal-medicine-induced liver injury. The temporal and spatial information provided by three-dimensional MSOT images well delineates the site and size of liver injury. Moreover, QY-N has also been employed to monitor rehabilitation of liver injury during treatment process.

Molecular Mechanisms That Link Oxidative Stress, Inflammation, and Fibrosis in the Liver

Activated hepatic stellate cells (HSCs) and myofibroblasts are the main producers of extracellular matrix (ECM) proteins that form the fibrotic tissue that leads to hepatic fibrosis. Reactive oxygen species (ROS) can directly activate HSCs or induce inflammation or programmed cell death, especially pyroptosis, in hepatocytes, which in turn activates HSCs and fibroblasts to produce ECM proteins. Therefore, antioxidants and the nuclear factor E2-related factor-2 signaling pathway play critical roles in modulating the profibrogenic response. The master proinflammatory factors nuclear factor-κB (NF-κB) and the nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome may coordinate to produce and activate profibrogenic molecules such as interleukins 1β and 18, which effectively activate HSCs, to produce large amounts of fibrotic proteins. Furthermore, the NLRP3 inflammasome activates pro-caspase 1, which is upregulated by NF-κB, to produce caspase 1, which induces pyroptosis via gasdermin and the activation of HSCs. ROS play central roles in the activation of the NF-κB and NLRP3 signaling pathways via IκB (an inhibitor of NF-κB) and thioredoxin-interacting protein, respectively, thereby linking the molecular mechanisms of oxidative stress, inflammation and fibrosis. Elucidating these molecular pathways may pave the way for the development of therapeutic tools to interfere with specific targets.

Danger signals in liver injury and restoration of homeostasis

Damage-associated molecular patterns are signalling molecules involved in inflammatory responses and restoration of homeostasis. Chronic release of these molecules can also promote inflammation in the context of liver disease. Herein, we provide a comprehensive summary of the role of damage-associated molecular patterns as danger signals in liver injury. We consider the role of reactive oxygen species and reactive nitrogen species as inducers of damage-associated molecular patterns, as well as how specific damage-associated molecular patterns participate in the pathogenesis of chronic liver diseases such as alcohol-related liver disease, non-alcoholic steatohepatitis, liver fibrosis and liver cancer. In addition, we discuss the role of damage-associated molecular patterns in ischaemia reperfusion injury and liver transplantation and highlight current studies in which blockade of specific damage-associated molecular patterns has proven beneficial in humans and mice.

BAY 41-2272 Attenuates CTGF Expression via sGC/cGMP-Independent Pathway in TGFβ1-Activated Hepatic Stellate Cells

Activation of hepatic stellate cells (HSCs) is a critical pathogenic feature of liver fibrosis and cirrhosis. BAY 41-2272 is a canonical non-nitric oxide (NO)-based soluble guanylyl cyclase (sGC) stimulator that triggers cyclic guanosine monophosphate (cGMP) signaling for attenuation of fibrotic disorders; however, the impact of BAY 41-2272 on HSC activation remains ill-defined. Transforming growth factor (TGF)β and its downstream connective tissue growth factor (CTGF or cellular communication network factor 2, CCN2) are critical fibrogenic cytokines for accelerating HSC activation. Here, we identified that BAY 41-2272 significantly inhibited the TGFβ1-induced mRNA and protein expression of CTGF in mouse primary HSCs. Indeed, BAY 41-2272 increased the sGC activity and cGMP levels that were potentiated by two NO donors and inhibited by a specific sGC inhibitor, ODQ. Surprisingly, the inhibitory effects of BAY 41-2272 on CTGF expression were independent of the sGC/cGMP pathway in TGFβ1-activated primary HSCs. BAY 41-2272 selectively restricted the TGFβ1-induced phosphorylation of Akt but not canonical Smad2/3 in primary HSCs. Together, we illustrate a unique framework of BAY 41-2272 for inhibiting TGFβ1-induced CTGF upregulation and HSC activation via a noncanonical Akt-dependent but sGC/cGMP-independent pathway.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: focus on the cancer hallmark of tumor angiogenesis

One of the important 'hallmarks' of cancer is angiogenesis, which is the process of formation of new blood vessels that are necessary for tumor expansion, invasion and metastasis. Under normal physiological conditions, angiogenesis is well balanced and controlled by endogenous proangiogenic factors and antiangiogenic factors. However, factors produced by cancer cells, cancer stem cells and other cell types in the tumor stroma can disrupt the balance so that the tumor microenvironment favors tumor angiogenesis. These factors include vascular endothelial growth factor, endothelial tissue factor and other membrane bound receptors that mediate multiple intracellular signaling pathways that contribute to tumor angiogenesis. Though environmental exposures to certain chemicals have been found to initiate and promote tumor development, the role of these exposures (particularly to low doses of multiple substances), is largely unknown in relation to tumor angiogenesis. This review summarizes the evidence of the role of environmental chemical bioactivity and exposure in tumor angiogenesis and carcinogenesis. We identify a number of ubiquitous (prototypical) chemicals with disruptive potential that may warrant further investigation given their selectivity for high-throughput screening assay targets associated with proangiogenic pathways. We also consider the cross-hallmark relationships of a number of important angiogenic pathway targets with other cancer hallmarks and we make recommendations for future research. Understanding of the role of low-dose exposure of chemicals with disruptive potential could help us refine our approach to cancer risk assessment, and may ultimately aid in preventing cancer by reducing or eliminating exposures to synergistic mixtures of chemicals with carcinogenic potential.

Transplantation and inflammation: implications for the modification of chemokine function

Oxidative stress is a major and recurring cause of damage during inflammation, especially following organ transplantation. Initial ischaemia–reperfusion injury causes the production of many reactive oxygen and nitrogen species, and subsequent recruitment and activation of inflammatory cells can lead to further oxidative stress. This stress is well known to cause damage at the cellular level, for example by induction of senescence leading to the production of a characteristic senescence-associated secretory phenotype. Chemokines are an important component of the senescence-associated secretory phenotype, recruiting further leucocytes and reinforcing the stress and senescence responses. As well as inducing the production of proteins, including chemokines, oxidative stress can alter proteins themselves, both directly and by induction of enzymes capable of modification. These alterations can lead to important modifications to their biological activity and also alter detection by some antibodies, potentially limiting the biological relevance of some immunochemical and proteomic biomarkers. Peroxynitrite, a reactive nitrogen species generated during inflammation and ischaemia, can cause such modifications by nitrating chemokines. Matrix metalloproteinases, released by many stressed cells, can cleave chemokines, altering function, while peptidylarginine deiminases can inactivate certain chemokines by citrullination. This review discusses the relationship between inflammation and post-translational modification, focusing on the functional modulation of transplant-relevant pro-inflammatory chemokines.

Extracellular matrix and liver disease

SIGNIFICANCE

The extracellular matrix (ECM) is a dynamic microenvironment that undergoes continuous remodeling, particularly during injury and wound healing. Chronic liver injury of many different etiologies such as viral hepatitis, alcohol abuse, drug-induced liver injury, obesity and insulin resistance, metabolic disorders, and autoimmune disease is characterized by excessive deposition of ECM proteins in response to persistent liver damage.

CRITICAL ISSUES

This review describes the main collagenous and noncollagenous components from the ECM that play a significant role in pathological matrix deposition during liver disease. We define how increased myofibroblasts (MF) from different origins are at the forefront of liver fibrosis and how liver cell-specific regulation of the complex scarring process occurs.

RECENT ADVANCES

Particular attention is paid to the role of cytokines, growth factors, reactive oxygen species, and newly identified matricellular proteins in the regulation of fibrillar type I collagen, a field to which our laboratory has significantly contributed over the years. We compile data from recent literature on the potential mechanisms driving fibrosis resolution such as MF' apoptosis, senescence, and reversal to quiescence.

FUTURE DIRECTIONS

We conclude with a brief description of how epigenetics, an evolving field, can regulate the behavior of MF and of how new "omics" tools may advance our understanding of the mechanisms by which the fibrogenic response to liver injury occurs.

Osteopontin delays resolution of liver fibrosis

To date, considerable progress has been made both in the mechanisms driving liver fibrosis and in the prevention of disease progression. Resolution of liver fibrosis is an emerging field in hepatology; yet, the mediators involved remain elusive. Earlier work from our laboratory demonstrated that the matricellular cytokine osteopontin (OPN) is pro-fibrogenic by promoting hepatic stellate cell (HSC) activation and extracellular matrix (ECM) deposition in vitro and in vivo and specifically by governing fibrillar collagen-I expression, the key pro-fibrogenic protein. Here we hypothesized that OPN could also delay the resolution of liver fibrosis by sustaining collagen-I synthesis or by preventing its degradation. To demonstrate this, wild-type (WT) and OPN-knockout (Opn(-/-)) mice were administered thioacetamide (TAA) in the drinking water for 4 months. Half of the mice were killed at 4 months to assess the extent of fibrosis at the peak of injury, and the rest of the mice were killed 2 months after TAA withdrawal to determine the rate of fibrosis resolution. Following TAA cessation, livers from Opn(-/-) mice showed no centrilobular and parenchymal necrosis along with faster ECM remodeling than WT mice. The latter was quantified by less fibrillar collagen-I immunostaining. Western blot analysis demonstrated a significant decrease in fibrillar collagen-I and in tissue inhibitor of metalloproteinase-1 (TIMP-1) in Opn(-/-) mice undergoing fibrosis resolution compared with WT mice. In conclusion, these results suggest that OPN delays liver fibrosis resolution due to sustained fibrillar collagen-I deposition; hence, inhibiting OPN could be an effective therapeutic strategy for resolving liver fibrosis.

Local NO synthase inhibition produces histological and functional recovery in Achilles tendon of rats after tenotomy: tendon repair and local NOS inhibition

Repair of injured tendon is a very slow process and involves the release of many molecules, including nitric oxide. We investigate the influence of local nitrergic inhibition in histological and functional recovery of injured Achilles tendon. A standard murine model of tendon injury by rupture was used. The animals were divided into three experimental groups: control, injury + vehicle (normal saline) and injury + Nω-nitro-L-arginine methyl ester (L-NAME). The products were injected into the paratendinous region every 2 days and body weight gain and Achilles functional index (AFI) were evaluated on days 0, 7, 14 and 21 after tendon injury. On day 21 post-injury, the animals were killed to evaluate nitric oxide production and tissue organization. We observed that tendon surgical division led to increased tissue nitrite levels, which were reduced in L-NAME-treated rats. The AFI revealed functional recovery of L-NAME-treated animals on day 21 post-injury, which was not observed in the saline-treated group. Microscopic analysis of hematoxylin-eosin staining and collagen autofluorescence showed that L-NAME-treated rats had more aligned areas of collagen fibers and that the diameter of newly organized collagen in this group was also greater than that in the vehicle-treated one. We demonstrate that local treatment with L-NAME significantly improves the functional parameters and accelerates histomorphological recovery.

Review of experimental models for inducing hepatic cirrhosis by bile duct ligation and carbon tetrachloride injection

PURPOSE

To present a review about a comparative study of bile duct ligation versus carbon tetrachloride Injection for inducing experimental liver cirrhosis.

METHODS

This research was made through Medline/PubMed and SciELO web sites looking for papers on the content "induction of liver cirrhosis in rats". We have found 107 articles but only 30 were selected from 2004 to 2011.

RESULTS

The most common methods used for inducing liver cirrhosis in the rat were administration of carbon tetrachloride (CCl4) and bile duct ligation (BDL). CCl4 has induced cirrhosis from 36 hours to 18 weeks after injection and BDL from seven days to four weeks after surgery.

CONCLUSION

For a safer inducing cirrhosis method BDL is better than CCl4 because of the absence of toxicity for researches and shorter time for achieving it.

Fibromodulin, an oxidative stress-sensitive proteoglycan, regulates the fibrogenic response to liver injury in mice

BACKGROUND & AIMS

Collagen I deposition contributes to liver fibrosis, yet little is known about other factors that mediate this process. Fibromodulin is a liver proteoglycan that regulates extracellular matrix organization and is induced by fibrogenic stimuli. We propose that fibromodulin contributes to the pathogenesis of fibrosis by regulating the fibrogenic phenotype of hepatic stellate cells (HSCs).

METHODS

We analyzed liver samples from patients with hepatitis C-associated cirrhosis and healthy individuals (controls). We used a coculture model to study interactions among rat HSCs, hepatocytes, and sinusoidal endothelial cells. We induced fibrosis in livers of wild-type and Fmod(-/-) mice by bile duct ligation, injection of CCl(4), or administration of thioacetamide.

RESULTS

Liver samples from patients with cirrhosis had higher levels of fibromodulin messenger RNA and protein than controls. Bile duct ligation, CCl(4), and thioacetamide each increased levels of fibromodulin protein in wild-type mice. HSCs, hepatocytes, and sinusoidal endothelial cells produced and secreted fibromodulin. Infection of HSCs with an adenovirus that expressed fibromodulin increased expression of collagen I and α-smooth muscle actin, indicating increased activation of HSCs and fibrogenic potential. Recombinant fibromodulin promoted proliferation, migration, and invasion of HSCs, contributing to their fibrogenic activity. Fibromodulin was sensitive to reactive oxygen species. HepG2 cells that express cytochrome P450 2E1 produced fibromodulin, and HSCs increased fibromodulin production in response to pro-oxidants. In mice, administration of an antioxidant prevented the increase in fibromodulin in response to CCl(4). Coculture of hepatocytes or sinusoidal endothelial cells with HSCs increased the levels of reactive oxygen species in the culture medium, along with collagen I and fibromodulin proteins; this increase was prevented by catalase. Fibromodulin bound to collagen I, but the binding did not prevent collagen I degradation by matrix metalloproteinase 13. Bile duct ligation caused liver fibrosis in wild-type but not Fmod(-/-) mice.

CONCLUSIONS

Fibromodulin levels are increased in livers of patients with cirrhosis. Hepatic fibromodulin activates HSCs and promotes collagen I deposition, which leads to liver fibrosis in mice.

A systems biology approach for understanding the collagen regulatory network in alcoholic liver disease

Among the pathogenesis and risk factors of alcoholic liver disease (ALD) are the source of dietary fat, obesity, insulin resistance, adipokines and acetaldehyde. Translocation of Gram-negative bacteria from the gut, the subsequent effects mediated by endotoxin, and the increased production of matricellular proteins, cytokines, chemokines and growth factors, actively participate in the progression of liver injury. In addition, generation of reactive oxygen and nitrogen species and the activation of non-parenchymal cells also contribute to the pathophysiology of ALD. A key event leading to liver damage is the transition of quiescent hepatic stellate cells into activated myofibroblasts, with the consequent deposition of fibrillar collagen I resulting in significant scarring. Thus, it is becoming clearer that matricellular proteins are critical players in the pathophysiology of liver disease; however, additional mechanistic insight is needed to understand the signalling pathways involved in the up-regulation of collagen I protein. At present, systems biology approaches are helping to answer the many unresolved questions in this field and are allowing to more comprehensively identify protein networks regulating pathological collagen I deposition in hopes of determining how to prevent the onset of liver fibrosis and/or to slow disease progression. Thus, this review article provides a snapshot on current efforts for identifying pathological protein regulatory networks in the liver using systems biology tools. These approaches hold great promise for future research in liver disease.

Extracellular matrix bioengineering and systems biology approaches in liver disease

The extracellular matrix (ECM) in the liver as well as in many organs comprises a peripheral network linking numerous macromolecules typically classified into collagens, microfibrillar proteins, proteoglycans, chemokines, growth factors and glycoproteins. In addition to its role as an essential structural and physiological component, it plays a vital role in driving key cellular events such as cell adhesion, migration, proliferation, differentiation and survival. Any structural inherited or acquired defect and/or metabolic or pathologic alteration in the hepatic ECM may cause cellular and organ responses leading to the development or progression of liver disease. Therefore, the ECM molecules are key players in tissue engraftment and in the pathophysiology of liver disease. In this review we provide a snapshot on current efforts for understanding its role in physiological and non-physiological states, by describing how tissue engineering platforms can enhance in vitro and in vivo models of liver disease, by providing examples where bioengineered ECM can serve as systems biology approaches to study the ECM, and then by evaluating pathological protein regulatory networks in the liver using systems biology tools. These approaches hold great promise for future research.

Cannabidiol causes activated hepatic stellate cell death through a mechanism of endoplasmic reticulum stress-induced apoptosis

The major cellular event in the development and progression of liver fibrosis is the activation of hepatic stellate cells (HSCs). Activated HSCs proliferate and produce excess collagen, leading to accumulation of scar matrix and fibrotic liver. As such, the induction of activated HSC death has been proposed as a means to achieve resolution of liver fibrosis. Here we demonstrate that cannabidiol (CBD), a major non-psychoactive component of the plant Cannabis sativa, induces apoptosis in activated HSCs through a cannabinoid receptor-independent mechanism. CBD elicits an endoplasmic reticulum (ER) stress response, characterized by changes in ER morphology and the initiation of RNA-dependent protein kinase-like ER kinase-, activating transcription factor-6-, and inositol-requiring ER-to-nucleus signal kinase-1 (IRE1)-mediated signaling cascades. Furthermore, CBD induces downstream activation of the pro-apoptotic IRE1/ASK1/c-Jun N-terminal kinase pathway, leading to HSC death. Importantly, we show that this mechanism of CBD-induced ER stress-mediated apoptosis is specific to activated HSCs, as it occurs in activated human and rat HSC lines, and in primary in vivo-activated mouse HSCs, but not in quiescent HSCs or primary hepatocytes from rat. Finally, we provide evidence that the elevated basal level of ER stress in activated HSCs has a role in their susceptibility to the pro-apoptotic effect of CBD. We propose that CBD, by selectively inducing death of activated HSCs, represents a potential therapeutic agent for the treatment of liver fibrosis.

AT1R-CB₁R heteromerization reveals a new mechanism for the pathogenic properties of angiotensin II

The mechanism of G protein-coupled receptor (GPCR) signal integration is controversial. While GPCR assembly into hetero-oligomers facilitates signal integration of different receptor types, cross-talk between Gαi- and Gαq-coupled receptors is often thought to be oligomerization independent. In this study, we examined the mechanism of signal integration between the Gαi-coupled type I cannabinoid receptor (CB(1)R) and the Gαq-coupled AT1R. We find that these two receptors functionally interact, resulting in the potentiation of AT1R signalling and coupling of AT1R to multiple G proteins. Importantly, using several methods, that is, co-immunoprecipitation and resonance energy transfer assays, as well as receptor- and heteromer-selective antibodies, we show that AT1R and CB(1)R form receptor heteromers. We examined the physiological relevance of this interaction in hepatic stellate cells from ethanol-administered rats in which CB(1)R is upregulated. We found a significant upregulation of AT1R-CB(1)R heteromers and enhancement of angiotensin II-mediated signalling, as compared with cells from control animals. Moreover, blocking CB(1)R activity prevented angiotensin II-mediated mitogenic signalling and profibrogenic gene expression. These results provide a molecular basis for the pivotal role of heteromer-dependent signal integration in pathology.

Transforming growth factor-α attenuates hepatic fibrosis: possible involvement of matrix metalloproteinase-1

BACKGROUND

The effect of transforming growth factor (TGF)-α on fibrosis varies between cell types and the role of TGF-α in hepatic fibrosis has not been fully elucidated.

METHODS

We examined the effect of TGF-α on hepatic fibrosis using TGF-α-expressing transgenic mice fed a methionine- and choline-deficient (MCD) diet and human hepatic stellate cells (HSCs) line LX-2, rat and human primary HSCs.

RESULTS

Although the expression levels of the tissue inhibitor of metalloproteinases-1 and α1(I) collagen mRNA were unchanged, feeding the TGF-α transgenic mice the MCD diet resulted in greater expression of the murine functional analogue of matrix metalloproteinase-1 (MMP-1), MMP-13 mRNA and protein and attenuated hepatic fibrosis compared with wild-type mice. TGF-α overexpression did not affect the extent of the steatosis, oxidative stress and hepatic inflammation in the MCD diet-fed mice. The effect of TGF-α on the fibrogenic and anti-fibrogenic gene expressions varied between cell types in vitro. TGF-α increased MMP-1 mRNA expressions that were completely blocked by gefitinib in LX-2 cells. The extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal kinase and p38 pathways were involved in MMP-1 mRNA expression in LX-2 cells. Although TGF-α increased the phosphorylation of p38, the p38 inhibitor activated the RAS-ERK pathway and increased TGF-α-induced MMP-1 mRNA expression, which suggested that there may be a crosstalk between the RAS-ERK and the p38 pathways in LX-2 cells.

CONCLUSIONS

The TGF-α may attenuate hepatic fibrosis in part because of upregulation of the expression of MMP-1. The balance between fibrogenic and anti-fibrogenic gene expression and between the activity of the RAS-ERK and the p38 pathways may be crucial for the fibrotic process.

HIV and HCV cooperatively promote hepatic fibrogenesis via induction of reactive oxygen species and NFkappaB

HIV/HCV coinfection leads to accelerated hepatic fibrosis progression, with higher rates of cirrhosis, liver failure, and liver death than does HCV mono-infection. However, the profibrogenic role of HIV on hepatocytes and hepatic stellate cells (HSC) has not been fully clarified. We hypothesized that HIV, HCV induce liver fibrosis through altered regulation of the production of extracellular matrix and matrix metalloproteinases. We examined the fibrogenesis- and fibrolysis-related gene activity in LX2 HSC and Huh7.5.1 cells in the presence of inactivated CXCR4 and CCR5 HIV, as well as HCV JFH1 virus. The role of reactive oxygen species (ROS) upon fibrosis gene expression was assessed using the ROS inhibitor. Fibrosis-related transcripts including procollagen α1(I) (CoL1A), TIMP1, and MMP3 mRNA were measured by qPCR. TIMP1 and MMP3 protein expression were assessed by ELISA. We found that inactivated CXCR4 HIV and CCR5 HIV increased CoL1A, and TIMP1 expression in both HSC and Huh7.5.1 cells; the addition of JFH1 HCV further increased CoL1A and TIMP1 expression. CXCR4 HIV and CCR5 HIV induced ROS production in HSC and Huh7.5.1 cells which was further enhanced by JFH1 HCV. The ROS inhibitor DPI abrogated HIV-and HCV-induced CoL1A and TIMP1 expression. HIV and HCV-induced CoL1A and TIMP1 expression were also blocked by NFκB siRNA. Our data provide further evidence that HIV and HCV independently regulate hepatic fibrosis progression through the generation of ROS; this regulation occurs in an NFκB-dependent fashion. Strategies to limit the viral induction of oxidative stress are warranted to inhibit fibrogenesis.

Hepatitis C virus regulates transforming growth factor beta1 production through the generation of reactive oxygen species in a nuclear factor kappaB-dependent manner

BACKGROUND & AIMS

The generation of oxidative stress and transforming growth factor beta1 (TGF-beta1) production play important roles in liver fibrogenesis. We have previously shown that hepatitis C virus (HCV) increases hepatocyte TGF-beta1 expression. However, the mechanisms by which this induction occurs have not been well studied. We explored the possibility that HCV infection regulates TGF-beta1 expression through the generation of reactive oxygen species (ROS), which act through > or =1 of the p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and nuclear factor kappaB (NFkappaB) signaling pathways to induce TGF-beta1 expression.

METHODS

We used small molecule inhibitors and short interfering RNAs to knock down these pathways to study the mechanism by which HCV regulates TGF-beta1 production in the infectious JFH1 model.

RESULTS

We demonstrated that HCV induces ROS and TGF-beta1 expression. We further found that JFH1 induces the phosphorylation of p38MAPK, JNK, ERK, and NFkappaB. We also found that HCV-mediated TGF-beta1 enhancement occurs through a ROS-induced and p38 MAPK, JNK, ERK1/2, NFkappaB-dependent pathway.

CONCLUSIONS

These findings provide further evidence to support the hypothesis that HCV enhances hepatic fibrosis progression through the generation of ROS and induction of TGF-beta1. Strategies to limit the viral induction of oxidative stress appear to be warranted to inhibit fibrogenesis.