Fibronectin transcription in liver cells: promoter occupation and function in sinusoidal endothelial cells and hepatocytes

Adiponectin Inhibits NLRP3 Inflammasome Activation in Nonalcoholic Steatohepatitis via AMPK-JNK/ErK1/2-NFκB/ROS Signaling Pathways

Adiponectin, an adipose-derived adipokine, possesses a hepatoprotective role in various liver disorders. It has been reported that hypoadiponectinemia can affect with the progression of non-alcoholic fatty liver diseases (NAFLD). Inflammasome activation has been recognized to play a major role during the progression of NAFLD. This research aimed to explore the effect of adiponectin on palmitate (PA)-mediated NLRP3 inflammasome activation and its potential molecular mechanisms. Male adiponectin-knockout (adiponectin-KO) mice and C57BL/6 (wild-type) mice were fed a high-fat-diet (HFD) for 12 weeks as an in vivo model of non-alcoholic steatohepatitis (NASH). Serum biochemical markers, liver histology and inflammasome-related gene and protein expression were determined. In addition, the hepatocytes isolated from wide type mice were exposed to PA in the absence or presence of adiponectin and/or AMPK inhibitor. The activation of NLRP3 inflammasome was assessed by mRNA and protein expression. Furthermore, ROS production and related signaling pathways were also evaluated. In the in vivo experiments, excessive hepatic steatosis with increased NLRP3 inflammasome and its complex expression were found in adiponectin-KO mice compared to wild-type mice. Moreover, the expression levels of NLRP3 inflammasome pathway molecules (NFκB and ROS) were upregulated, while the phosphorylation levels of AMPK, JNK, and Erk1/2 were downregulated in adiponectin-KO mice compared with wild-type mice. In the in vitro study, PA increased lipid droplet deposition, NF-kB signaling and ROS production. Additionally, PA significantly promoted NLRP3 inflammasome activation and complex gene and protein expression in hepatocytes. Adiponectin could abolish PA-mediated inflammasome activation and decrease ROS production, which was reversed by AMPK inhibitor (compound C). Furthermore, the results showed that the inhibitory effect of adiponectin on PA-mediated inflammasome activation was regulated by AMPK-JNK/ErK1/2-NFκB/ROS signaling pathway. Adiponectin inhibited PA-mediated NLRP3 inflammasome activation in hepatocytes. Adiponectin analogs or AMPK agonists could serve as a potential novel agent for preventing or delaying the progression of NASH and NAFLD.

Fibronectin is a stress responsive gene regulated by HSF1 in response to geldanamycin

Fibronectin is an extracellular matrix glycoprotein with key roles in cell adhesion and migration. Hsp90 binds directly to fibronectin and Hsp90 depletion regulates fibronectin matrix stability. Where inhibition of Hsp90 with a C-terminal inhibitor, novobiocin, reduced the fibronectin matrix, treatment with an N-terminal inhibitor, geldanamycin, increased fibronectin levels. Geldanamycin treatment induced a stress response and a strong dose and time dependent increase in fibronectin mRNA via activation of the fibronectin promoter. Three putative heat shock elements (HSEs) were identified in the fibronectin promoter. Loss of two of these HSEs reduced both basal and geldanamycin-induced promoter activity, as did inhibition of the stress-responsive transcription factor HSF1. Binding of HSF1 to one of the putative HSE was confirmed by ChIP under basal conditions, and occupancy shown to increase with geldanamycin treatment. These data support the hypothesis that fibronectin is stress-responsive and a functional HSF1 target gene. COLA42 and LAMB3 mRNA levels were also increased with geldanamycin indicating that regulation of extracellular matrix (ECM) genes by HSF1 may be a wider phenomenon. Taken together, these data have implications for our understanding of ECM dynamics in stress-related diseases in which HSF1 is activated, and where the clinical application of N-terminal Hsp90 inhibitors is intended.

A novel mechanism of abnormal hematological indices in liver cirrhosis: bone marrow endothelial cell dysfunction caused by humoral inhibitor affects the hematopoietic function of bone marrow

Abnormal hematological indices (HIs), a complication of liver cirrhosis (LC), present difficulties in the treatment of LC and pose a serious threat to the survival of patients. LC is a dynamic wound-healing process that occurs in response to repeated liver injury and is a chronic disorder associated with changes in various organs and tissues. It has been reported that humoral inhibitor in the formation of LC could affect the hematogenic functions of bone marrow (BM) by acting on erythroid differentiation. This indicates that the BM microenvironment is affected by humoral inhibitor in LC. Bone marrow endothelial cells (BMECs) are very important components of the BM microenvironment that function as the cytoskeleton to support the adhesion of hematopoietic stem cells (HSCs). In addition, they can secrete cytokines, which have important functions in regulating positioning, homing, proliferation, differentiation and other functions of HSCs on the BM microenvironment. These functions of BMECs may be affected due to direct contact with blood and long-term exposure to an environment with humoral inhibitor in the presence of LC. Multiple studies have shown that during the formation of LC, hepatic sinusoid endothelial cells were damaged and secreted cytokines and matrix proteins. Moreover, these cytokines and matrix proteins were involved in the formation and development of LC. Similar in function to mature-stage BM, liver at the embryonic stage also functions as a type of hematogenic organ. With similar anatomical position and functions to that of hepatic sinusoid endothelial cells, BMECs may undergo similar changes and impair hematogenic function of BM. More importantly, we found even more convincing evidence in that the humoral inhibitor in LC could lead to the ultrastructural damage of BMECs that were positively related to the degree of severity of LC. Therefore, we hypothesise the existence of a novel mechanism for abnormal HIs in LC: the continuous humoral inhibitor may lead to abnormal cytokine secretion of BMECs and attenuate their supporting functions, and such alterations of BMECs may lead to BM microenvironment disorder and dysfunction of HSCs, finally causing abnormal HIs.

Host cell cytokines induced by Chlamydia pneumoniae decrease the expression of interstitial collagens and fibronectin in fibroblasts

Chlamydia pneumoniae infection has been associated with chronic obstructive airway disease (COPD), asthma, and atherosclerosis. Inflammation and airway remodeling in asthma and COPD result in subepithelial fibrosis that is characterized by the deposition of interstitial collagens and fibronectin. The progression of atherosclerosis is also accompanied by an increased production of interstitial collagens in the intima. As shown by reverse transcription-PCR and immunoblotting, infection of human fibroblasts and smooth muscle cells by C. pneumoniae TW-183 downregulated the expression of type I and III collagen and fibronectin, whereas the level of type IV collagen remained unchanged. Conditioned medium from infected fibroblasts as well as epithelial WISH cells also reduced the expression of interstitial collagens and fibronectin in uninfected cells. In experiments using blocking antibodies, beta interferon was found to contribute to the inhibitory effects of conditioned medium collected from infected fibroblasts. In contrast, downregulation of matrix protein expression by conditioned medium from epithelial cells was caused by interleukin-1alpha, which was not secreted from fibroblasts following chlamydial infection. C. pneumoniae-mediated inhibition of collagen and fibronectin expression was diminished following transfection of fibroblasts with specific small interfering RNA targeting the transcription factor CCAAT/enhancer-binding protein beta. The downregulation of interstitial collagens and fibronectin by the Chlamydia-induced host cell cytokine response may modulate tissue remodeling processes in airway diseases. In atherosclerosis the inhibition of collagen synthesis by C. pneumoniae infection may promote plaque vulnerability, thereby increasing the risk of plaque rupture.

Successive observation of laminin and hyaluronic acid on the formation of non-alcoholic fatty liver fibrosis in rabbits

AIM: To observe the changes of laminin (LN) and hyaluronic acid (HA) on the formation of non-alcoholic fatty liver fibrosis in rabbits.

METHODS: Firstly, the rabbit models of fatty liver and liver fibrosis were set up by hypercholesteremia. Liver tissues were collected and the histopathological changes were observed using transmission endoscopy and staining methods. Immunohistochemistry was used to detect LN expression and radioimmunoassy was used the measure serum HA concentration. Successive observation was used to outline the dynamic changes of basement membrane of hepatic sinusoid during the formation of non-alcoholic fatty liver fibrosis in rabbits.

RESULTS: Sinusoidal capillarization was characterized by defenestration of sinusoidal endothelial cells (SEC) and formation of basement membrane. Along with the formation of liver fibrosis, the positive expression (area percentage) of LN on sinusoidal wall and the concentration (mg/L) of serum HA increased gradually, and both of them reached the peak at 8 wk; there were significant differences in contrast with those in the normal group (LN: 25.2 ± 1.0 vs 5.1 ± 0.7, P < 0.01; serum HA: 1422.18 ± 20.9 vs 1189.3 ± 13.1, P < 0.01). After stopping high-sterone feeding, the positive expression of LN and concentration of HA decreased gradually.

CONCLUSION: The changes of serum HA concentration are in accordance with the defenestration of hepatic sinusoid and LN changes. LN and HA may be used as cardinal markers for hepatic sinusoidal capillarization and liver fibrosis.