Yan Bi

Vascular endothelial growth factor promotes fibrosis resolution and repair in mice.

BACKGROUND & AIMS Vascular endothelial growth factor (VEGF)-induced angiogenesis is implicated in fibrogenesis and portal hypertension. However, the function of VEGF in fibrosis resolution has not been explored. METHODS We developed a cholecystojejunostomy procedure to reconstruct biliary flow after bile duct ligation in C57BL/6 mice to generate a model of fibrosis resolution. These mice were then given injections of VEGF-neutralizing (mcr84) or control antibodies, and other mice received an adenovirus that expressed mouse VEGF or a control vector. The procedure was also performed on macrophage fas-induced apoptosis mice, in which macrophages can be selectively depleted. Liver and blood samples were collected and analyzed in immunohistochemical, morphometric, vascular permeability, real-time polymerase chain reaction, and flow cytometry assays. RESULTS VEGF-neutralizing antibodies prevented development of fibrosis but also disrupted hepatic tissue repair and fibrosis resolution. During fibrosis resolution, VEGF inhibition impaired liver sinusoidal permeability, which was associated with reduced monocyte migration, adhesion, and infiltration of fibrotic liver. Scar-associated macrophages contributed to this process by producing the chemokine (C-X-C motif) ligand 9 (CXCL9) and matrix metalloproteinase 13. Resolution of fibrosis was impaired in macrophage fas-induced apoptosis mice but increased after overexpression of CXCL9. CONCLUSIONS In a mouse model of liver fibrosis resolution, VEGF promoted fibrogenesis, but was also required for hepatic tissue repair and fibrosis resolution. We observed that VEGF regulates vascular permeability, monocyte infiltration, and scar-associated macrophages function.

Chronic Passive Venous Congestion drives Hepatic Fibrogenesis via Sinusoidal Thrombosis and Mechanical Forces

Chronic passive hepatic congestion (congestive hepatopathy) leads to hepatic fibrosis; however, the mechanisms involved in this process are not well understood. We developed a murine experimental model of congestive hepatopathy through partial ligation of the inferior vena cava (pIVCL). C57BL/6 and transgenic mice overexpressing tissue factor pathway inhibitor (SM22α‐TFPI) were subjected to pIVCL or sham. Liver and blood samples were collected and analyzed in immunohistochemical, morphometric, real‐time polymerase chain reaction, and western blot assays. Hepatic fibrosis and portal pressure were significantly increased after pIVCL concurrent with hepatic stellate cell (HSC) activation. Liver stiffness, as assessed by magnetic resonance elastography, correlated with portal pressure and preceded fibrosis in our model. Hepatic sinusoidal thrombosis as evidenced by fibrin deposition was demonstrated both in mice after pIVCL as well as in humans with congestive hepatopathy. Warfarin treatment and TFPI overexpression both had a protective effect on fibrosis development and HSC activation after pIVCL. In vitro studies show that congestion stimulates HSC fibronectin (FN) fibril assembly through direct effects of thrombi as well as by virtue of mechanical strain. Pretreatment with either Mab13 or Cytochalasin‐D, to inhibit β‐integrin or actin polymerization, respectively, significantly reduced fibrin and stretch‐induced FN fibril assembly. Conclusion: Chronic hepatic congestion leads to sinusoidal thrombosis and strain, which in turn promote hepatic fibrosis. These studies mechanistically link congestive hepatopathy to hepatic fibrosis. (Hepatology 2015;61:648‐659)

Endocytosis of collagen by hepatic stellate cells regulates extracellular matrix dynamics

Hepatic stellate cells (HSCs) generate matrix, which in turn may also regulate HSCs function during liver fibrosis. We hypothesized that HSCs may endocytose matrix proteins to sense and respond to changes in microenvironment. Primary human HSCs, LX2, or mouse embryonic fibroblasts (MEFs) [wild-type; c-abl(-/-); or Yes, Src, and Fyn knockout mice (YSF(-/-))] were incubated with fluorescent-labeled collagen or gelatin. Fluorescence-activated cell sorting analysis and confocal microscopy were used for measuring cellular internalization of matrix proteins. Targeted PCR array and quantitative real-time PCR were used to evaluate gene expression changes. HSCs and LX2 cells endocytose collagens in a concentration- and time-dependent manner. Endocytosed collagen colocalized with Dextran 10K, a marker of macropinocytosis, and 5-ethylisopropyl amiloride, an inhibitor of macropinocytosis, reduced collagen internalization by 46%. Cytochalasin D and ML7 blocked collagen internalization by 47% and 45%, respectively, indicating that actin and myosin are critical for collagen endocytosis. Wortmannin and AKT inhibitor blocked collagen internalization by 70% and 89%, respectively, indicating that matrix macropinocytosis requires phosphoinositide-3-kinase (PI3K)/AKT signaling. Overexpression of dominant-negative dynamin-2 K44A blocked matrix internalization by 77%, indicating a role for dynamin-2 in matrix macropinocytosis. Whereas c-abl(-/-) MEF showed impaired matrix endocytosis, YSF(-/-) MEF surprisingly showed increased matrix endocytosis. It was also associated with complex gene regulations that related with matrix dynamics, including increased matrix metalloproteinase 9 (MMP-9) mRNA levels and zymographic activity. HSCs endocytose matrix proteins through macropinocytosis that requires a signaling network composed of PI3K/AKT, dynamin-2, and c-abl. Interaction with extracellular matrix regulates matrix dynamics through modulating multiple gene expressions including MMP-9.

Steroid-Responsive Chronic Pancreatitides: Autoimmune Pancreatitis and Idiopathic Duct-Centric Chronic Pancreatitis

Two different forms of steroid-responsive pancreatitides are recognized, with both being referred to as “autoimmune pancreatitis.” They differ significantly in their clinical, histological, and epidemiological features. It has recently been suggested that the term “AIP” be reserved for the disease associated with elevated serum and tissue IgG4, while the term idiopathic duct centric chronic pancreatitis (IDCP) be used for pancreas-specific form. Clinically the most frequent presentation is painless obstructive jaundice with a mass/enlargement of the pancreas at imaging, and the differential diagnosis with cancer is frequently difficult. AIP is part of a multiorgan disorder called IgG4-related disease and any organ may be involved. Therefore, more than 50 % of the patients suffering from AIP present an inflammatory involvement of other organs (particularly bile ducts, kidneys, and salivary glands). Serum IgG4 elevation is not pathognomonic of AIP and serum IgG4 should be used in combination with other features to make a diagnosis of AIP. Both AIP and IDCP respond to steroids. In relapses of AIP the use of immunosuppressive drugs or of biologic agents may be considered.

Detecting fibrosis without a liver biopsy: getting to the fat of the issue

It is critical to assess the degree of liver fibrosis for clinical management. However, liver biopsy has many drawbacks and is invasive. Promising non-invasive methods including serum markers and new imaging studies to predict liver fibrosis have been developed in past decades. This editorial provides a succinct overview and update of the new non-invasive technologies, especially the three-dimensional magnetic resonance imaging (3-D MRI) that has been studied by Dr. Kawamura’s group in Japan. It also highlights the merit and weakness of this 3D-MRI technology in predicting liver fibrosis and indicates future studies to understand where 3D-MRI fits into the current armamentarium of non-invasive serum-based and imaging technologies.