Varinder S. Athwal

Understanding the role of SOX9 in acquired diseases: lessons from development.

The transcription factor SOX9 is crucial for multiple aspects of development. Mutations in SOX9 cause campomelic dysplasia, a haploinsufficiency disorder concordant with the expression profile of SOX9 during embryogenesis. The mechanistic understanding of development has revealed roles for SOX9 in regulating cartilage extracellular matrix (ECM) production and cell proliferation, among others. More recently, it transpires that SOX9 becomes expressed and induces destructive ECM components in organ fibrosis and related disorders. Although commonly absent from the parent cell type, SOX9 is expressed in a wide range of cancers, where it regulates cell proliferation. These data have potential diagnostic, prognostic and therapeutic relevance, suggesting that disease mechanisms might result from re-expressing this developmental transcription factor in ectopic locations.

Osteopontin is a novel downstream target of SOX9 with diagnostic implications for progression of liver fibrosis in humans

Osteopontin (OPN) is an important component of the extracellular matrix (ECM), which promotes liver fibrosis and has been described as a biomarker for its severity. Previously, we have demonstrated that Sex‐determining region Y‐box 9 (SOX9) is ectopically expressed during activation of hepatic stellate cells (HSC) when it is responsible for the production of type 1 collagen, which causes scar formation in liver fibrosis. Here, we demonstrate that SOX9 regulates OPN. During normal development and in the mature liver, SOX9 and OPN are coexpressed in the biliary duct. In rodent and human models of fibrosis, both proteins were increased and colocalized to fibrotic regions in vivo and in culture‐activated HSCs. SOX9 bound a conserved upstream region of the OPN gene, and abrogation of Sox9 in HSCs significantly decreased OPN production. Hedgehog (Hh) signaling has previously been shown to regulate OPN expression directly by glioblastoma (GLI) 1. Our data indicate that in models of liver fibrosis, Hh signaling more likely acts through SOX9 to modulate OPN. In contrast to Gli2 and Gli3, Gli1 is sparse in HSCs and is not increased upon activation. Furthermore, reduction of GLI2, but not GLI3, decreased the expression of both SOX9 and OPN, whereas overexpressing SOX9 or constitutively active GLI2 could rescue the antagonistic effects of cyclopamine on OPN expression. Conclusion: These data reinforce SOX9, downstream of Hh signaling, as a core factor mediating the expression of ECM components involved in liver fibrosis. Understanding the role and regulation of SOX9 during liver fibrosis will provide insight into its potential modulation as an antifibrotic therapy or as a means of identifying potential ECM targets, similar to OPN, as biomarkers of fibrosis. (HEPATOLOGY 2012;56:1108–1116)

PAK proteins and YAP-1 signalling downstream of integrin beta-1 in myofibroblasts promote liver fibrosis

Fibrosis due to extracellular matrix (ECM) secretion from myofibroblasts complicates many chronic liver diseases causing scarring and organ failure. Integrin-dependent interaction with scar ECM promotes pro-fibrotic features. However, the pathological intracellular mechanism in liver myofibroblasts is not completely understood, and further insight could enable therapeutic efforts to reverse fibrosis. Here, we show that integrin beta-1, capable of binding integrin alpha-11, regulates the pro-fibrotic phenotype of myofibroblasts. Integrin beta-1 expression is upregulated in pro-fibrotic myofibroblasts in vivo and is required in vitro for production of fibrotic ECM components, myofibroblast proliferation, migration and contraction. Serine/threonine-protein kinase proteins, also known as P21-activated kinase (PAK), and the mechanosensitive factor, Yes-associated protein 1 (YAP-1) are core mediators of pro-fibrotic integrin beta-1 signalling, with YAP-1 capable of perpetuating integrin beta-1 expression. Pharmacological inhibition of either pathway in vivo attenuates liver fibrosis. PAK protein inhibition, in particular, markedly inactivates the pro-fibrotic myofibroblast phenotype, limits scarring from different hepatic insults and represents a new tractable therapeutic target for treating liver fibrosis.

The XBP1 Arm of the Unfolded Protein Response Induces Fibrogenic Activity in Hepatic Stellate Cells Through Autophagy

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-β1. 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.

Epimorphin Alters the Inhibitory Effects of SOX9 on Mmp13 in Activated Hepatic Stellate Cells

Background and Aims Liver fibrosis is a major cause of morbidity and mortality. It is characterised by excessive extracellular matrix (ECM) deposition from activated hepatic stellate cells (HSCs). Although potentially reversible, treatment remains limited. Understanding how ECM influences the pathogenesis of the disease may provide insight into novel therapeutic targets for the disease. The extracellular protein Epimorphin (EPIM) has been implicated in tissue repair mechanisms in several tissues, partially, through its ability to manipulate proteases. In this study, we have identified that EPIM modulates the ECM environment produced by activated hepatic stellate cells (HSCs), in part, through down-regulation of pro-fibrotic Sex-determining region Y-box 9 (SOX9). Methods Influence of EPIM on ECM was investigated in cultured primary rat HSCs. Activated HSCs were treated with recombinant EPIM or SOX9 siRNA. Core fibrotic factors were evaluated by immunoblotting, qPCR and chromatin immunoprecipitation (ChIP). Results During HSC activation EPIM became significantly decreased in contrast to pro-fibrotic markers SOX9, Collagen type 1 (COL1), and α- Smooth muscle actin (α-SMA). Treatment of activated HSCs with recombinant EPIM caused a reduction in α-SMA, SOX9, COL1 and Osteopontin (OPN), while increasing expression of the collagenase matrix metalloproteinase 13 (MMP13). Sox9 abrogation in activated HSCs increased EPIM and MMP13 expression. Conclusion These data provide evidence for EPIM and SOX9 functioning by mutual negative feedback to regulate attributes of the quiescent or activated state of HSCs. Further understanding of EPIMs role may lead to opportunities to modulate SOX9 as a therapeutic avenue for liver fibrosis.

SOX9 predicts progression toward cirrhosis in patients while its loss protects against liver fibrosis

Fibrosis and organ failure is a common endpoint for many chronic liver diseases. Much is known about the upstream inflammatory mechanisms provoking fibrosis and downstream potential for tissue remodeling. However, less is known about the transcriptional regulation in vivo governing fibrotic matrix deposition by liver myofibroblasts. This gap in understanding has hampered molecular predictions of disease severity and clinical progression and restricted targets for antifibrotic drug development. In this study, we show the prevalence of SOX9 in biopsies from patients with chronic liver disease correlated with fibrosis severity and accurately predicted disease progression toward cirrhosis. Inactivation of Sox9 in mice protected against both parenchymal and biliary fibrosis, and improved liver function and ameliorated chronic inflammation. SOX9 was downstream of mechanosignaling factor, YAP1. These data demonstrate a role for SOX9 in liver fibrosis and open the way for the transcription factor and its dependent pathways as new diagnostic, prognostic, and therapeutic targets in patients with liver fibrosis.

Secondary sclerosing cholangitis following extracorporeal membrane oxygenation for acute respiratory distress in polytrauma

Secondary sclerosing cholangitis is a recently identified phenomenon affecting the biliary tree. A subtype has been described in critically ill patients (SSC‐CIP). However, underlying mechanisms are unknown, and few cases have been reported following extracorporeal membrane oxygenation (ECMO). We present a 19‐year‐old male with SSC‐CIP after ECMO following major trauma.

OC-028 Identification of SOX9 as a novel mechanism to explain aspects of liver fibrosis

Introduction Fibrosis of the liver is characterised by progressive accumulation of extracellular matrix (ECM) proteins and is a major cause of morbidity and mortality in the UK. Several cell-types are responsible for this, but a major role is played by activation of the hepatic stellate cell (HSC). We have identified ectopic expression of the Sry-box transcription factor, SOX9, in activated HSCs as a novel mechanism to explain aspects of liver fibrosis. Methods Livers were collected from carbon tetrachloride induced fibrotic and control rats and processed for fixed tissue. Rat hepatic stellate cells (HSCs) were isolated using established perfusion techniques and cultured on tissue culture plastic to activate over 4, 7 and 10 days. The immortalised human LX2 cell line was also used. Results In fixed fibrotic rat livers α-smooth muscle actin (α-sma) was detected in activated HSCs with collagen type 1 (Col1) rich fibrotic tracts found disrupting normal tissue architecture. Nuclear Sox9 staining was detected in the same regions as α-sma and Col1. In quiescent HSCs isolated from rat liver, negative for α-sma and col1, Sox9 was absent. However during activation of HSCs, both Sox9 and Col1 were robustly expressed. In these activated Col1-expressing HSCs, Sox9 localised to the nucleus surrounded by α-sma positive cytoplasm. SOX9 knockdown in activated HSCs using RNA interference caused a commensurate reduction in Col1 protein expression (∼60%). The pro-fibrotic cytokine transforming growth factor β (TGF-β) induced expression of SOX9 by ∼3-fold in rat HSCs and ∼2.5-fold in the human stellate cell line LX2s. Conclusion We have identified SOX9 as a novel mediator of ECM in liver fibrosis. Our data demonstrate that SOX9 expression occurs during activation of HSCs, a major cell type responsible for liver fibrosis, when, under the influence of TGF-β signalling it causes Col1 production, the predominant collagen deposited in organ fibrosis. Lessening SOX9 levels similarly reduced Col1 production. These data suggest targeted reduction of SOX9 offers potential therapeutic application to ameliorate fibrosis and related conditions of the liver.