The XBP1 Arm of the Unfolded Protein Response Induces Fibrogenic Activity in Hepatic Stellate Cells Through Autophagy.
ABSTRACT: Autophagy and the unfolded protein response (UPR) both promote activation of hepatic stellate cells (HSC), however the link between the two stimuli remains unclear. Here we have explored the role of X-box binding protein 1 (XBP1), one of three UPR effector pathways and sought to establish the interdependence between autophagy and the UPR during HSC activation. XBP1 induction accompanied both culture-based HSC activation and ER stress induced by tunicamycin. Ectopic overexpression of XBP1 induced collagen 1-alpha expression in HSCs, which was inhibited by knockdown of ATG7, a critical autophagy mediator. Genome-wide transcriptomic profiling indicated an upregulation of collagen synthesis pathways, but not of the transforming growth factor (TGF)-b pathway, a canonical fibrogenic driver, suggesting that XBP1 activates a specific subset of fibrogenesis pathways independent of TGF-?1. XBP1 target gene signatures were significantly induced in rodent liver fibrosis models (n?=?3-5) and in human samples of non-alcoholic fatty liver disease (NAFLD) (n?=?72-135). Thus, XBP1-mediated UPR contributes to fibrogenic HSC activation and is functionally linked to cellular autophagy.
Project description:BACKGROUND AND AIM: We previously established that endoplasmic reticulum stress leads to unfolded protein response (UPR) that promotes liver fibrosis by activating hepatic stellate cell (HSC). We aimed to determine the role of X-box binding protein 1 (XBP1), one of three UPR effector pathways, in the fibrogenic HSC activation. METHODS: XBP1 expression was measured by qPCR in tunicamycin-treated human HSC lines (TWNT4 and LX2) and culture-activated human primary HSCs. XBP1 was overexpressed in primary human HSCs and the HSC lines, and fibrogenic genes (COL1A1, ACTA2, PDGFRB, MMP2, TIMP1) and encoded proteins were assessed by qPCR and Western blotting, respectively. Autophagy was inhibited by knockdown of ATG7. Genome-wide transcriptome profiling was performed to determine modulated molecular pathway by XBP1. In vivo XBP1 activation was assessed in transcriptome datasets of fibrotic mouse models and immunohistochemistry of human liver tissues. RESULTS: XBP1 overexpression accompanied both tunicamycin- and culture-based HSC activation. Ectopic overexpression of XBP1 induced fibrogenic gene expression in the HSC lines, which was inhibited by knockdown of ATG7. UPR pathway together with PDGFRB pathway, a hallmark of HSC activation, were induced in transcriptome profiles of XBP1-transduced HSC lines. Some known fibrogenic pathways such as transforming growth factor (TGF)-beta pathway were not induced, suggesting partial contribution of XBP1 to the entire fibrogenic HSC activation machinery. XBP1 target gene signature defined in our XBP1-overexpressing HSC lines was significantly induced in liver tissue transcriptome profiles of carbon tetrachloride-treated or bile duct-ligated mouse models, and XBP1 and alpha-smooth muscle actin (encoded by ACTA2, another hallmark of HSC activation) were co-localized in human fibrotic liver tissues, collectively supporting involvement of XBP1 in HSC activation and fibrogesis in vivo. CONCLUSIONS: XBP1-mediated UPR is at least partially responsible for fibrogenic HSC activation via autophagy. Overall design: Human hepatic stellate cell lines (LX2 and TWNT4) were lentivirally transduced by either unspliced or spliced XBP1 gene and cultured for 96h.
Project description:Fibrogenesis encompasses the deposition of matrix proteins, such as collagen I, by hepatic stellate cells (HSCs) that culminates in cirrhosis. Fibrogenic signals drive transcription of procollagen I, which enters the endoplasmic reticulum (ER), is trafficked through the secretory pathway, and released to generate extracellular matrix. Alternatively, disruption of procollagen I ER export could activate the unfolded protein response (UPR) and drive HSC apoptosis. Using a small interfering RNA screen, we identified Transport and Golgi organization 1 (TANGO1) as a potential participant in collagen I secretion. We investigated the role of TANGO1 in procollagen I secretion in HSCs and liver fibrogenesis. Depletion of TANGO1 in HSCs blocked collagen I secretion without affecting other matrix proteins. Disruption of secretion led to procollagen I retention within the ER, induction of the UPR, and HSC apoptosis. In wild-type (WT) HSCs, both TANGO1 and the UPR were induced by transforming growth factor ? (TGF?). As the UPR up-regulates proteins involved in secretion, we studied whether TANGO1 was a target of the UPR. We found that UPR signaling is responsible for up-regulating TANGO1 in response to TGF?, and this mechanism is mediated by the transcription factor X-box binding protein 1 (XBP1). In vivo, murine and human cirrhotic tissue displayed increased TANGO1 messenger RNA levels. Finally, TANGO1+/- mice displayed less hepatic fibrosis compared to WT mice in two separate murine models: CCl4 and bile duct ligation. CONCLUSION:Loss of TANGO1 leads to procollagen I retention in the ER, which promotes UPR-mediated HSC apoptosis. TANGO1 regulation during HSC activation occurs through a UPR-dependent mechanism that requires the transcription factor, XBP1. Finally, TANGO1 is critical for fibrogenesis through mediating HSC homeostasis. The work reveals a unique role for TANGO1 and the UPR in facilitating collagen I secretion and fibrogenesis. (Hepatology 2017;65:983-998).
Project description:Metabolic stress during liver injury enhances autophagy and provokes stellate cell activation, with secretion of scar matrix. Conditions that augment protein synthesis increase demands on the endoplasmic reticulum (ER) folding capacity and trigger the unfolded protein response (UPR) to cope with resulting ER stress. Generation of reactive oxygen species (ROS) is a common feature of hepatic fibrogenesis, and crosstalk between oxidant stress and ER stress has been proposed. The aim of our study was to determine the impact of oxidant and ER stress on stellate cell activation.Oxidant stress was induced in hepatic stellate cells using H2O2 in culture or by ethanol feeding in vivo, and the UPR was analyzed. Because the branch of the UPR mainly affected was IRE?, we blocked this pathway in stellate cells and analyzed the fibrogenic response, together with autophagy and downstream MAPK signaling. The Nrf2 antioxidant response was also evaluated in stellate cells under oxidant stress conditions.H2O2 treatment in culture or ethanol feeding in vivo increased the UPR based on splicing of XBP1 mRNA, which triggered autophagy. The Nrf2-mediated antioxidant response, as measured by qRT-PCR of its target genes was also induced under ER stress conditions. Conversely, blockade of the IRE1? pathway in stellate cells significantly decreased both their activation and autophagic activity in a p38 MAPK-dependent manner, leading to a reduced fibrogenic response.These data implicate mechanisms underlying protein folding quality control in regulating the fibrogenic response in hepatic stellate cells.
Project description:Because of the contribution of ethanol and polyunsaturated fatty acids (PUFAs) to alcoholic liver disease, we investigated whether chronic ethanol administration and arachidonic acid (AA) could synergistically mediate Kupffer cell (KC) activation and modulate the stellate cell (HSC) fibrogenic response.(1) the effects of ethanol and AA on KC and HSC were as follows: Cell proliferation, lipid peroxidation, H(2)O(2), O(2).(-), nicotinamide adenine dinucleotide phosphate reduced form (NADPH) oxidase activity, and tumor necrosis factor alpha (TNF-alpha) were higher in KC(ethanol) than in KC(control), and were enhanced by AA; HSC(ethanol) proliferated faster, increased collagen, and showed higher GSH than HSC(control), with modest effects by AA. (2) AA effects on the control co-culture: We previously reported the ability of KC to induce a pro-fibrogenic response in HSC via reactive oxygen species (ROS)-dependent mechanisms; we now show that AA further increases cell proliferation and collagen in the control co-culture. The latter was prevented by vitamin E (an antioxidant) and by diphenyleneiodonium (a NADPH oxidase inhibitor). (3) Ethanol effects on the co-cultures: Co-culture with KC(control) or KC(ethanol) induced HSC(control) and HSC(ethanol) proliferation; however, the pro-fibrogenic response in HSC(ethanol) was suppressed because of up-regulation of TNF-alpha and GSH, which was prevented by a TNF-alpha neutralizing antibody (Ab) and by L-buthionine-sulfoximine, a GSH-depleting agent. (4) Ethanol plus AA effects on the co-cultures: AA lowered TNF-alpha in the HSC(control) co-cultures, allowing for enhanced collagen deposition; furthermore, AA restored the pro-fibrogenic response in the HSC(ethanol) co-cultures by counteracting the up-regulation of TNF-alpha and GSH with a significant increase in GSSG and in pro-fibrogenic transforming growth factor beta (TGF-beta).These results unveil synergism between ethanol and AA to the mechanism whereby KC mediate ECM remodeling and suggest that even if chronic ethanol consumption sensitizes HSC to up-regulate anti-fibrogenic signals, their effects are blunted by a second "hit" such as AA.
Project description:Transforming growth factor ? (TGF?) potently activates hepatic stellate cells (HSCs), which promotes production and secretion of extracellular matrix (ECM) proteins and hepatic fibrogenesis. Increased ECM synthesis and secretion in response to TGF? is associated with endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). TGF? and UPR signaling pathways are tightly intertwined during HSC activation, but the regulatory mechanism that connects these two pathways is poorly understood. Here, we found that TGF? treatment of immortalized HSCs (i.e. LX-2 cells) induces phosphorylation of the UPR sensor inositol-requiring enzyme 1? (IRE1?) in a SMAD2/3-procollagen I-dependent manner. We further show that IRE1? mediates HSC activation downstream of TGF? and that its role depends on activation of a signaling cascade involving apoptosis signaling kinase 1 (ASK1) and c-Jun N-terminal kinase (JNK). ASK1-JNK signaling promoted phosphorylation of the UPR-associated transcription factor CCAAT/enhancer binding protein ? (C/EBP?), which is crucial for TGF?- or IRE1?-mediated LX-2 activation. Pharmacological inhibition of C/EBP? expression with the antiviral drug adefovir dipivoxil attenuated TGF?-mediated activation of LX-2 or primary rat HSCs in vitro and hepatic fibrogenesis in vivo Finally, we identified a critical relationship between C/EBP? and the transcriptional regulator p300 during HSC activation. p300 knockdown disrupted TGF?- or UPR-induced HSC activation, and pharmacological inhibition of the C/EBP?-p300 complex decreased TGF?-induced HSC activation. These results indicate that TGF?-induced IRE1? signaling is critical for HSC activation through a C/EBP?-p300-dependent mechanism and suggest C/EBP? as a druggable target for managing fibrosis.
Project description:Progressive liver fibrosis is characterized by the deposition of collagen by activated hepatic stellate cells (HSCs). Activation of HSCs is a multiple receptor-driven process in which profibrotic signals are enhanced and antifibrotic pathways are suppressed. Here we report the discovery of a signalling platform comprising G protein subunit, G?i and GIV, its guanine exchange factor (GEF), which serves as a central hub within the fibrogenic signalling network initiated by diverse classes of receptors. GIV is expressed in the liver after fibrogenic injury and is required for HSC activation. Once expressed, GIV enhances the profibrotic (PI3K-Akt-FoxO1 and TGF?-SMAD) and inhibits the antifibrotic (cAMP-PKA-pCREB) pathways to skew the signalling network in favour of fibrosis, all via activation of G?i. We also provide evidence that GIV may serve as a biomarker for progression of fibrosis after liver injury and a therapeutic target for arresting and/or reversing HSC activation during liver fibrosis.
Project description:Hepatic fibrogenesis involves the activation of hepatic stellate cells (HSCs), which synthesize excess extracellular matrix and contribute to the development of liver fibrosis. In a prior study we tested the effect of combined treatment with taurine, epigallocatechin gallate and genistein on the development of alcohol-induced liver fibrosis in vitro. In this study, the biological activity of the combination of these molecules was assessed by measuring its effect on cell proliferation, fibrosis-related gene expression, and proteomic expression profiling in the activated HSC cell line, HSC-T6. HSC-T6 cells were incubated with different concentrations of the drug combination taurine, epigallocatechin gallate and genistein. Cell proliferation was evaluated by MTT assay. Transforming growth factor ?1 (TGF-?1), collagen type I (Col-I), matrix metalloproteinase-2 (MMP-2), and tissue inhibitor of metalloproteinases 1 and 2 (TIMP-1 and TIMP-2) mRNA were analyzed by semi-quantitative reverse-transcription PCR. Proteomic profiling of HSC-T6 cells was also performed by SELDI-TOF-MS. Combined drug treatment significantly inhibited cell proliferation and TGF-?1, Col-I, TIMP-1 and TIMP-2 mRNA expression in activated HSC-T6 cells, while the expression of MMP-2 mRNA increased. A total of 176 protein m/z peaks were identified. The intensities of 10 protein peaks were downregulated and two protein peaks were upregulated in HSC-T6 cells after combined drug treatment. In conclusion, combined drug treatment with taurine, epigallocatechin gallate and genistein can inhibit HSC proliferation, and impact fibrosis-related gene and protein expression. The antifibrotic effects of this drug combination may be due to its effects on the expression of fibrogenic genes.
Project description:Cathepsins have been best characterized in tumorigenesis and cell death and implicated in liver fibrosis; however, whether cathepsins directly regulate hepatic stellate cell (HSC) activation and proliferation, hence modulating their fibrogenic potential, is largely unknown. Here, we show that expression of cathepsin B (CtsB) and cathepsin D (CtsD) is negligible in quiescent HSCs but parallels the increase of alpha-smooth muscle actin and transforming growth factor-beta during in vitro mouse HSC activation. Both cathepsins are necessary for HSC transdifferentiation into myofibroblasts, because their silencing or inhibition decreased HSC proliferation and the expression of phenotypic markers of HSC activation, with similar results observed with the human HSC cell line LX2. CtsB inhibition blunted AKT phosphorylation in activated HSCs in response to platelet-derived growth factor. Moreover, during in vivo liver fibrogenesis caused by CCl(4) administration, CtsB expression increased in HSCs but not in hepatocytes, and its inactivation mitigated CCl(4)-induced inflammation, HSC activation, and collagen deposition.These findings support a critical role for cathepsins in HSC activation, suggesting that the antagonism of cathepsins in HSCs may be of relevance for the treatment of liver fibrosis.
Project description:Glaucoma, a prevalent blinding disease is commonly associated with increased intraocular pressure due to impaired aqueous humor (AH) drainage through the trabecular meshwork (TM). Although increased TM tissue contraction and stiffness in association with accumulation of extracellular matrix (ECM) are believed to be partly responsible for increased resistance to AH outflow, the extracellular cues and intracellular mechanisms regulating TM cell contraction and ECM production are not well defined. This study tested the hypothesis that sustained activation of Rho GTPase signaling induced by lysophosphatidic acid (LPA), TGF-?, and connective tissue growth factor (CTGF) influences TM cell plasticity and fibrogenic activity which may eventually impact resistance to AH outflow. Various experiments performed using human TM cells revealed that constitutively active RhoA (RhoAV14), TGF-?2, LPA, and CTGF significantly increase the levels and expression of Fibroblast Specific Protein-1 (FSP-1), ?-smooth muscle actin (?SMA), collagen-1A1 and secretory total collagen, as determined by q-RT-PCR, immunofluorescence, immunoblot, flow cytometry and the Sircol assay. Significantly, these changes appear to be mediated by Serum Response Factor (SRF), myocardin-related transcription factor (MRTF-A), Slug, and Twist-1, which are transcriptional regulators known to control cell plasticity, myofibroblast generation/activation and fibrogenic activity. Additionally, the Rho kinase inhibitor-Y27632 and anti-fibrotic agent-pirfenidone were both found to suppress the TGF-?2-induced expression of ?SMA, FSP-1, and collagen-1A1. Taken together, these observations demonstrate the significance of RhoA/Rho kinase signaling in regulation of TM cell plasticity, fibrogenic activity, and myofibroblast activation, events with potential implications for the pathobiology of elevated intraocular pressure in glaucoma patients.
Project description:Type I collagen accumulates during liver fibrosis primarily because ?-complex protein-2 (?CP(2)), encoded by the poly(rC) binding protein 2 (PCBP2) gene, binds to the 3' end of the collagen mRNA and increases its half-life. This study aimed to reverse the pro-fibrogenic effect of alcohol on hepatic stellate cells (HSCs) by silencing the PCBP2 gene with siRNA.The silencing effects of a series of predesigned PCBP2 siRNAs were evaluated in the rat hepatic stellate cell line, HSC-T6. The pro-fibrogenic effects of alcohol on the expression levels of PCBP2 and type-I collagen were examined by several methods. The effect of PCBP2 siRNA on the stability of type I collagen ?1(I) mRNA was investigated by an in vitro mRNA decay assay.We identified one potent PCBP2 siRNA that reversed the alcohol-induced expression of PCBP2 in HSCs. The decay rate of the collagen ?1(I) mRNA increased significantly in HSCs treated with the PCBP2 siRNA.This study provides the first evidence that alcohol up-regulates the expression of PCBP2, which subsequently increases the half-life of collagen ?1(I) mRNA. Silencing of PCBP2 using siRNA may provide a promising strategy to reverse the alcohol-induced pro-fibrogenic effects in HSCs.