Prevention of cultured rat stellate cell transformation and endothelin-B receptor upregulation by retinoic acid

U-shaped association of serum vitamin A concentrations with all-cause mortality in patients with NAFLD: results from the NHANES database prospective cohort study

Background

Previous studies have demonstrated a significant association between serum vitamin A concentration and non-alcoholic fatty liver disease (NAFLD) development. However, the long-term prognostic implications of serum vitamin A in patients with NAFLD remain underexplored. This study aims to investigate whether there exists a correlation between serum vitamin A concentrations and overall mortality among subjects diagnosed with NAFLD.

Methods

To investigate the association between serum vitamin A concentrations and NAFLD outcomes, we conducted prospective cohort studies using data from the 1999-2006 and 2017-2018 National Health and Nutrition Examination Survey (NHANES). We utilized a multivariate Cox regression model to explore the relationship between serum vitamin A levels and all-cause mortality. Survival curves related to serum vitamin A were constructed using the Kaplan-Meier method. Additionally, the restricted cubic splines (RCS) method was applied to examine potential nonlinear relationships between serum vitamin A concentrations and all-cause mortality of NAFLD.

Results

Over a median follow-up period of 10.3 years, a total of 1,399 all-cause deaths were recorded. The weighted average concentration of serum vitamin A was 61.48 ± 0.37 μg/dL. After adjusting for potential confounders, a significant U-shaped relationship was identified between serum vitamin A concentrations and the risk of all-cause mortality in NAFLD patients. This relationship was particularly pronounced in men and elderly individuals aged 60 to 85.

Conclusion

Our study reveals a significant non-linear relationship between serum vitamin A concentrations and the risk of all-cause mortality in patients with NAFLD. These findings underscore the importance of monitoring and maintaining optimal serum vitamin A levels to potentially improve survival outcomes in NAFLD patients.

Pro- and Anti-fibrogenic Functions of Gram-Negative Bacterial Lipopolysaccharide in the Liver

Extensive research performed over several decades has identified cells participating in the initiation and progression of fibrosis, and the numerous underlying inter- and intra-cellular signaling pathways. However, liver fibrosis continues to be a major clinical challenge as the precise targets of treatment are still elusive. Activation of physiologically quiescent perisinusoidal hepatic stellate cells (HSCs) to a myofibroblastic proliferating, contractile and fibrogenic phenotype is a critical event in the pathogenesis of chronic liver disease. Thus, elucidation of the mechanisms of the reversal to quiescence or inhibition of activated HSCs, and/or their elimination via apoptosis has been the focus of intense investigation. Lipopolysaccharide (LPS), a gut-resident Gram-negative bacterial endotoxin, is a powerful pro-inflammatory molecule implicated in hepatic injury, inflammation and fibrosis. In both acute and chronic liver injury, portal venous levels of LPS are elevated due to increased intestinal permeability. LPS, via CD14 and Toll-like receptor 4 (TLR4) and its adapter molecules, stimulates macrophages, neutrophils and several other cell types to produce inflammatory mediators as well as factors that can activate HSCs and stimulate their fibrogenic activity. LPS also stimulates synthesis of pro- and anti-inflammatory cytokines/chemokines, growth mediators and molecules of immune regulation by HSCs. However, LPS was found to arrest proliferation of activated HSCs and to convert them into non-fibrogenic phenotype. Interestingly, LPS can elicit responses in HSCs independent of CD14 and TLR4. Identifying and/or developing non-inflammatory but anti-fibrogenic mimetics of LPS could be relevant for treating liver fibrosis.

Senescence in hepatic stellate cells as a mechanism of liver fibrosis reversal: a putative synergy between retinoic acid and PPAR-gamma signalings

Hepatic stellate cells (HSCs), also known as perisinusoidal cells, are pericytes found in the perisinusoidal space of the liver. HSCs are the major cell type involved in liver fibrosis, which is the formation of scar tissue in response to liver damage. When the liver is damaged, stellate cells can shift into an activated state, characterized by proliferation, contractility and chemotaxis. The activated HSCs secrete collagen scar tissue, which can lead to cirrhosis. Recent studies have shown that in vivo activation of HSCs by fibrogenic agents can eventually lead to senescence of these cells, which would contribute to reversal of fibrosis although it may also favor the insurgence of liver cancer. HSCs in their non-active form store huge amounts of retinoic acid derivatives in lipid droplets, which are progressively depleted upon cell activation in injured liver. Retinoic acid is a metabolite of vitamin A (retinol) that mediates the functions of vitamin A, generally required for growth and development. The precise function of retinoic acid and its alterations in HSCs has yet to be elucidated, and nonetheless in various cell types retinoic acid and its receptors (RAR and RXR) are known to act synergistically with peroxisome proliferator-activated receptor gamma (PPAR-gamma) signaling through the activity of transcriptional heterodimers. Here, we review the recent advancements in the understanding of how retinoic acid signaling modulates the fibrogenic potential of HSCs and proposes a synergistic combined action with PPAR-gamma in the reversal of liver fibrosis.

Retinoic acid inhibits pancreatic cancer cell migration and EMT through the downregulation of IL-6 in cancer associated fibroblast cells

Retinoic acid (RA) is a small molecular derivative of vitamin A that is stored in quiescent stellate cells in pancreas stroma. Cancer associated fibroblasts (CAFs) are activated fibroblast cells in pancreatic ductal adenocarcinoma tumor microenvironment. We treated CAFs with RA and found that these cells became static due to the low expression of α-SMA, FAP, and IL-6 and decreased production of extracellular matrix (ECM). Furthermore, we verified that the low secretion of IL-6 from CAFs was related to RA-induced inhibition of migration and epithelial-mesenchymal transition (EMT) of tumor cells. However, RA could not inhibit the migration and EMT of tumor cells directly. Therefore, our study showed that one of the therapeutic effects of RA on tumor cells is through its modulation of CAFs in tumor microenvironment. The tumor microenvironment plays an important role in promoting tumor migration and might be a promising target of biological treatment.

A novel bidirectional interaction between endothelin-3 and retinoic acid in rat enteric nervous system precursors

BACKGROUND

Signaling through the endothelin receptor B (EDNRB) is critical for the development of the enteric nervous system (ENS) and mutations in endothelin system genes cause Hirschsprung's aganglionosis in humans. Penetrance of the disease is modulated by other genetic factors. Mutations affecting retinoic acid (RA) signaling also produce aganglionosis in mice. Thus, we hypothesized that RA and endothelin signaling pathways may interact in controlling development of the ENS.

METHODS

Rat immunoselected ENS precursor cells were cultured with the EDNRB ligand endothelin-3, an EDNRB-selective antagonist (BQ-788), and/or RA for 3 or 14 days. mRNA levels of genes related to ENS development, RA- and EDNRB-signaling were measured at 3 days. Proliferating cells and cells expressing neuronal, glial, and myofibroblast markers were quantified.

RESULTS

Culture of isolated ENS precursors for 3 days with RA decreases expression of the endothelin-3 gene and that of its activation enzyme. These changes are associated with glial proliferation, a higher percentage of glia, and a lower percentage of neurons compared to cultures without RA. These changes are independent of EDNRB signaling. Conversely, EDNRB activation in these cultures decreases expression of RA receptors β and γ mRNA and affects the expression of the RA synthetic and degradative enzymes. These gene expression changes are associated with reduced glial proliferation and a lower percentage of glia in the culture. Over 14 days in the absence of EDNRB signaling, RA induces the formation of a heterocellular plexus replete with ganglia, glia and myofibroblasts.

CONCLUSIONS

A complex endothelin-RA interaction exists that coordinately regulates the development of rat ENS precursors in vitro. These results suggest that environmental RA may modulate the expression of aganglionosis in individuals with endothelin mutations.

Endothelin and hepatic wound healing

Liver wound healing is a coordinated response to injury caused by infections (hepatitis) or toxins (alcohol) or other processes where activation of hepatic stellate cells are a central component. During stellate cell activation, a major phenotypic transformation occurs which leads to increased production of increased extracellular matrix proteins and smooth muscle α-actin the results is organ dysfunction due to gross architectural disruption and impaired blood flow. Endothelin-1 (ET-1) is produced in increased amounts and the cellular source of ET-1 shifts from endothelial cells to stellate cells during liver injury thus setting a feedback loop which accentuates further activation, stellate cell proliferation, and production of extracellular matrix proteins. Therapy directed at intervening the ET-1 signaling pathway has significant therapeutic potential in patients with liver disease.

All-trans retinoic acid diminishes collagen production in a hepatic stellate cell line via suppression of active protein-1 and c-Jun N-terminal kinase signal

Following acute and chronic liver injury, hepatic stellate cells (HSCs) become activated to undergo a phenotypic transformation into myofibroblast-like cells and lose their retinol content, but the mechanisms of retinoid loss and its potential roles in HSCs activation and liver fibrosis are not understood. The influence of retinoids on HSCs and hepatic fibrosis remains controversial. The purpose of this study was to evaluate the effects of all-trans retinoid acid (ATRA) on cell proliferation, mRNA expression of collagen genes [procollagen α1 (I), procollagen α1 (III)], profibrogenic genes (TGF-β(1), CTGF, MMP-2, TIMP-1, TIMP-2, PAI-1), fibrolytic genes (MMP-3, MMP-13) and the upstream element (JNK and AP-1) in the rat hepatic stellate cell line (CFSC-2G). Cell proliferation was evaluated by measuring BrdU incorporation. The mRNA expression levels of collagen genes [procollagen α1 (I), procollagen α1 (III)], profibrogenic genes (TGF-β(1), CTGF, MMP-2, TIMP-1, TIMP-2, PAI-1), and fibrolytic genes (MMP-3, MMP-13) were quantitatively detected by using real-time PCR. The mRNA expression of JNK and AP-1 was quantified by RT-PCR. The results showed that ATRA inhibited HSCs proliferation and diminished the mRNA expression of collagen genes [procollagen α1 (I), procollagen α1 (III)] and profibrogenic genes (TGF-β(1), CTGF, MMP-2, TIMP-1, TIMP-2, PAI-1), and significantly stimulated the mRNA expression of MMP-3 and MMP-13 in HSCs by suppressing the mRNA expression of JNK and AP-1. These findings suggested that ATRA could inhibit proliferation and collagen production of HSCs via the suppression of active protein-1 and c-Jun N-terminal kinase signal, then decrease the mRNAs expression of profibrogenic genes (TGF-β(1), CTGF, MMP-2, TIMP-1, TIMP-2, PAI-1), and significantly induce the mRNA expression of MMP-3 and MMP-13.

Inhibition of endothelin-1-mediated contraction of hepatic stellate cells by FXR ligand

Activation of hepatic stellate cells (HSCs) plays an important role in the development of cirrhosis through the increased production of collagen and the enhanced contractile response to vasoactive mediators such as endothelin-1 (ET-1). The farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily that is highly expressed in liver, kidneys, adrenals, and intestine. FXR is also expressed in HSCs and activation of FXR in HSCs is associated with significant decreases in collagen production. However, little is known about the roles of FXR in the regulation of contraction of HSCs. We report in this study that treatment of quiescent HSCs with GW4064, a synthetic FXR agonist, significantly inhibited the HSC transdifferentiation, which was associated with an inhibition of the upregulation of ET-1 expression. These GW4064-treated cells also showed reduced contractile response to ET-1 in comparison to HSCs without GW4064 treatment. We have further shown that GW4064 treatment inhibited the ET-1-mediated contraction in fully activated HSCs. To elucidate the potential mechanism we showed that GW4064 inhibited ET-1-mediated activation of Rho/ROCK pathway in activated HSCs. Our studies unveiled a new mechanism that might contribute to the anti-cirrhotic effects of FXR ligands.

p38-MAPK- and caspase-3-mediated superoxide-induced apoptosis of rat hepatic stellate cells: reversal by retinoic acid

Reactive oxygen species (ROS) activate retinoid-containing quiescent hepatic stellate cells (qHSCs) to retinoid-deficient fibrogenic myofibroblast-like cells (aHSCs). However, ROS also cause apoptosis of aHSCs, and apoptotic aHSCs are observed in inflammatory fibrotic liver. Here, we investigated mechanisms of the effects of oxidative stress on the survival of qHSCs and aHSCs. HSCs from normal rat liver were used after overnight culture (qHSCs), or in 3-5 passages (aHSCs). For in vivo induction of oxidative stress, tert-butylhydroperoxide was injected into control and CCl4-induced cirrhotic rats. Spontaneous caspase-3 activation and apoptosis, observed in cultured qHSCs, decreased with time and were unaffected by superoxide. In contrast, superoxide caused caspase-3 and p38-MAPK activation, reduction in Bcl-xL expression, and apoptosis in aHSCs. Inhibition of caspase-3 and p38-MAPK did not affect the viability of qHSCs in the absence or presence of superoxide, but inhibited superoxide-induced death of aHSCs. Glutathione (GSH) level and activities of superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) were lower in aHSCs than qHSCs. Superoxide increased GSH content, and activities of SOD, catalase and GPx in qHSCs but not in aHSCs. Incubation of 13-cis-retinoic acid (RA)-treated aHSCs with superoxide increased their GSH content significantly, and prevented superoxide-induced p38-MAPK and caspase-3 activation while dramatically reducing the extent of apoptosis. Finally, oxidative stress induced in vivo caused apoptosis of aHSCs in cirrhotic but not of qHSCs in control rats. These results suggest that the absence of retinoids render aHSCs susceptible to superoxide-induced apoptosis via caspase-3 and p38-MAPK activation.

All-trans-retinoic acid ameliorates carbon tetrachloride-induced liver fibrosis in mice through modulating cytokine production

BACKGROUND/AIMS

Liver fibrosis with any aetiology, induced by the transdifferentiation and proliferation of hepatic stellate cells (HSCs) to produce collagen, is characterized by progressive worsening in liver function, leading to a high incidence of death. We have recently reported that all-trans-retinoic acid (ATRA) suppresses the transdifferentiation and proliferation of lung fibroblasts and prevents radiation- or bleomycin-induced lung fibrosis.

METHODS

We examined the impact of ATRA on carbon tetrachloride (CCl(4))-induced liver fibrosis. We performed histological examinations and quantitative measurements of transforming growth factor (TGF)-beta1 and interleukin (IL)-6 in CCl(4)-treated mouse liver tissues with or without the administration of ATRA, and investigated the effect of ATRA on the production of the cytokines in quiescent and activated HSCs.

RESULTS

CCl(4)-induced liver fibrosis was attenuated in histology by intraperitoneal administration of ATRA, and the overall survival rate at 12 weeks was 26.5% without ATRA (n=25), whereas it was 75.0% (n=24) in the treatment group (P=0.0187). In vitro studies disclosed that the administration of ATRA reduced (i) the production of TGF-beta1, IL-6 and collagen from HSCs, (ii) TGF-beta-dependent transdifferentiation of the cells and IL-6-dependent cell proliferation and (iii) the activities of nuclear factor-kappaB p65 and p38mitogen-activated protein kinase, which stimulate the production of TGF-beta1 and IL-6, which could be the mechanism underlying the preventive effect of ATRA on liver fibrosis.

CONCLUSIONS

Our findings indicate that ATRA ameliorates liver fibrosis. As the oral administration of the drug results in good compliance, ATRA could be a novel approach in the treatment of liver fibrosis.

Retinol and alpha-tocopherol in morbid obesity and nonalcoholic fatty liver disease

BACKGROUND

We aimed to study serum retinol and alpha-tocopherol in a cohort of obese patients and their possible association with several obesity-related conditions, given that the former may be implicated in a diminished capacity of anti-inflammatory and antioxidant potential in obese patients.

METHODS

Eighty patients with morbid obesity participated in the study. Many clinical and biochemical variables were measured including serum retinol, alpha-tocopherol, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) concentrations. Fatty liver was detected by ultrasonography.

RESULTS

Both serum retinol and alpha-tocopherol inversely correlated with body mass index (r = -0.334, P = 0.002 and r = -0.299, P = 0.007, respectively). Serum retinol inversely correlated with AST (r = -0.236, P = 0.036) and ALT (r = -0.241, P = 0.032). Multivariate regression analyses confirmed these results after correcting for the effects of other variables. Eighty-five percent of patients had fatty liver. When restricting the analysis to them, multivariate regression identified male sex (beta = 0.451, P = 0.003), age (beta = -0.275, P = 0.039), and serum retinol concentrations (beta = -0.414, P = 0.005) as predictive variables on serum AST (R (2) = 0.230, F = 3.408, P = 0.009) and male sex (beta = 0.448, P = 0.003), age (beta = -0.236, P = 0.046), insulin resistance determined by homeostasis model assessment (beta = 0.243, P = 0.050), and serum retinol concentrations (beta = -0.305, P = 0.022) as predictive variables on serum ALT (R (2) = 0.296, F = 5.817, P = 0.001).

CONCLUSION

Serum retinol and alpha-tocopherol concentrations are inversely associated with body mass index in morbid obesity, and serum retinol is also inversely associated with serum concentrations of transaminases in those patients with nonalcoholic fatty liver disease.

Endothelin-1 mediated regulation of extracellular matrix collagens in cells of human lamina cribrosa

Endothelin-1 (ET-1), a potent vaso-active peptide, mediates extracellular matrix regulation resulting in an increase in collagen deposition in various cell types and tissues and has been proposed to play a key role in glaucoma pathology. The role of ET-1 in the regulation of extracellular matrix collagens at the level of optic nerve head is not known. In this study we have examined the role of ET-1 in extracellular matrix collagen regulation in primary cultures of human lamina cribrosa cells. Our hypothesis is that ET-1 increases remodeling of the ECM of cells of the lamina cribrosa. Such actions could contribute to the development of optic neuropathy. QPCR analysis revealed that ET-1 mediated an increase in mRNA levels of collagen type I alpha1 and collagen type VI alpha1 chains at all doses of ET-1 with a significant increase at 1nM and 10nM concentration in LC cells. A dose-dependent increase in collagen type I and type VI protein deposition and secretion was also observed by Western blot in response to ET-1 and was significant at 10nM and 100nM concentrations of ET-1. ET-1 increased the [3H] proline uptake in LC cells suggesting that ET-1 contributed to an increase in total collagen synthesis in LC cells. ET-1-mediated increase in collagen type I, type VI and total collagen synthesis was significantly blocked by the ET(A) receptor antagonist, BQ610, as well as with the ET(B) receptor antagonist, BQ788, suggesting the involvement of both receptor subtypes in ET-1 mediated collagen synthesis in LC cells. These results suggest that ET-1 regulates extracellular matrix collagen synthesis in LC cells and may contribute to ECM remodeling at the level of LC of POAG subjects who have elevated plasma and aqueous humor levels of endothelin-1.

Blockade of endothelinergic receptors prevents development of proliferative vitreoretinopathy in mice

Proliferative vitreoretinopathy (PVR) is characterized by severe glial remodeling. Glial activation and proliferation that occur in brain diseases are modulated by endothelin-1 (ET-1) and its receptor B (ETR-B). Because retinal astrocytes contain ET-1 and express ETR-B, we studied the changes of these molecules in an experimental mouse model of PVR and in human PVR. Both ET-1 and ETR-B immunoreactivities increased in mouse retina after induction of PVR with dispase. Epi- and subretinal outgrowths also displayed these immunoreactivities in both human and experimental PVR. Additionally, myofibroblasts and other membranous cell types showed both ET-1 and ETR-B immunoreactivities. In early stages of experimentally induced PVR, prepro-ET-1 and ETR-B mRNA levels increased in the retina. These mRNA levels also increased after retinal detachment (RD) produced by subretinal injection. Treatment of mice with tezosentan, an antagonist of endothelinergic receptors, reduced the histopathological hallmarks of dispase-induced PVR: retinal folding, epiretinal outgrowth, and gliosis. Our findings in human and in dispase-induced PVR support the involvement of endothelinergic pathways in retinal glial activation and the phenotypic transformations that underlie the growth of membranes in this pathology. Elucidating these pathways further will help to develop pharmacological treatments to prevent PVR. In addition, the presence of ET-1 and ETR-B in human fibrous membranes suggests that similar treatments could be helpful after PVR has been established.

Prediagnostic level of serum retinol in relation to reduced risk of hepatocellular carcinoma

BACKGROUND

Retinol and its derivatives (retinoids), which have antioxidant activity and promote cell differentiation, may protect against the development of hepatocellular carcinoma (HCC) by controlling hepatocellular differentiation and reducing inflammatory responses.

METHODS

We examined prospectively the relationship between prediagnostic serum concentrations of retinol, alpha-carotene; beta-carotene; beta-cryptoxanthin; lutein; lycopene; zeaxanthin; alpha-, gamma-, and delta-tocopherols; and selenium and the risk of developing HCC among 213 patients with HCC and 1087 matched control subjects from a cohort of 18,244 men in Shanghai, China, who were monitored from 1986 through 2001. Odds ratios (ORs) and 95% confidence intervals (CIs) for men by quartile of serum concentrations of micronutrients were estimated by using logistic regression with adjustment for cigarette smoking status, alcohol intake, self-reported history of physician-diagnosed hepatitis or liver cirrhosis at recruitment, and seropositivity for hepatitis B surface antigen (HBsAg). All statistical tests were two-sided.

RESULTS

Men with high prediagnostic serum retinol levels had a lower risk of HCC than men in the lowest quartile (Q2 versus Q1, OR = 0.37, 95% CI = 0.22 to 0.61; Q3 versus Q1, OR = 0.30, 95% CI = 0.17 to 0.50; and Q4 versus Q1, OR = 0.13, 95% CI = 0.06 to 0.26; Ptrend < .001). A statistically significant interaction was observed between retinol and HBsAg seropositivity on HCC risk; HBsAg-positive men in the lowest tertile of retinol had a greater than 70-fold higher risk (OR = 72.7, 95% CI = 31.6 to 167.4) of HCC than HBsAg-negative men in the highest tertile of retinol (Pinteraction = .018). No independent effect of serum levels of alpha-carotene; beta-carotene; beta-cryptoxanthin; lutein; lycopene; zeaxanthin; alpha-, gamma-, and delta-tocopherols; or selenium on HCC risk were observed.

CONCLUSION

High prediagnostic serum level of retinol is associated with a decreased risk of HCC in this population.

Normal rat hepatic stellate cells respond to endotoxin in LBP-independent manner to produce inhibitor(s) of DNA synthesis in hepatocytes

Endotoxin is implicated in the pathology of acute liver failure. The mechanisms of its actions on quiescent hepatic stellate cells (qHSCs) and their implications in hepatocyte injury are incompletely understood. We investigated effects of endotoxin (bacterial lipopolysaccharide; LPS) on qHSCs and subsequently on hepatocytes. After overnight culture following their isolation, qHSCs were incubated with or without endotoxin for 24 h. The cells and the culture supernatant were analyzed for cytokines and nitric oxide (NO) synthesis. The effects of qHSC-conditioned media on hepatocytes were then determined. LPS increased inducible NO synthase expression, stimulated NO synthesis, and inhibited DNA synthesis in qHSCs. qHSC-conditioned medium inhibited DNA synthesis in hepatocytes without affecting NO synthesis, while LPS (1-1,000 ng/ml)-conditioned qHSC medium stimulated NO synthesis and caused further inhibition of DNA synthesis and apoptosis. These effects of LPS were more pronounced when qHSCs were incubated with serum, but not with LPS-binding protein (LBP) although CD14 (a receptor for LPS-LBP complex) was found in qHSCs. LPS stimulated the synthesis of TNF-alpha, interleukin (IL)-6, and IL-1beta but not of TGF-beta in qHSCs. Individually or together, L-N(G)-monomethylarginine and antibodies to IL-1beta, IL-6, and TNF-alpha only partly reversed qHSC + LPS-conditioned medium-induced inhibition of DNA synthesis in hepatocytes. These results suggest that the effects of LPS on qHSCs are novel, occurring without the aid of LBP/CD14. They also indicate that other factors, in addition to NO, TGF-beta, TNF-alpha, IL-1beta, and IL-6 are involved in the mechanisms of the growth inhibitory effects of qHSCs on hepatocytes.

Hyaluronic acid inhibits adhesion of hepatic stellate cells in spite of its stimulation of DNA synthesis

Unbalanced accumulation of fibers in extracellular matrix (ECM) results from attachment and activation of hepatic stellate cells (HSCs) during chronic liver diseases, in which the content of hyaluronic acid (HA), a glycosaminoglycan, in ECM changes. No information is available on the effect of HA on adhesion and activation of HSCs although that of collagen (Col) on HSCs was extensively studied. This study investigated the effects of HA with or without Col on adhesion of HSCs or the rate of DNA synthesis. Attachment of primary cultured HSCs was microscopically monitored in the plate simultaneously coated with HA or other ECM components. HA inhibited adhesion of quiescent HSCs at least up to 7 days after seeding, whereas HSCs were adherent to plastic or type I collagen (Col-I), type III collagen (Col-III), type IV collagen (Col-IV) or fibronectin. Both microscopy and alpha-smooth muscle actin immunocytochemistry revealed that the number of HSCs, which had been re-seeded after 15 days of culture, attached to HA-coated area was remarkably lower compared to that of HSCs on Col-I or plastic. Incorporation of HA into Col-I prevented adhesion of activated HSCs to matrix film. The number of HSCs adherent to HA at early times after seeding was minimal and significantly lower than that of the cells adherent to plastic. In contrast, either Col-I or Col-IV increased the number of adherent cells. Attachment of HSCs to plastic was inhibited by soluble HA in culture medium. CD44, the cell surface receptor to which HA binds, was immunochemically detected in HSCs. Adhesion of HSCs to plastic, HA or Col-I was not changed by anti-CD44 antibody. Either HA or Col increased the basal or platelet-derived growth factor-inducible rate of thymidine incorporation into DNA in HSCs. In conclusion, HA inhibits adhesion of quiescent or activated HSCs in spite of its stimulation of DNA synthesis, whereas Col increases HSC attachment and DNA synthesis, and inhibition of HSC adhesion by HA does not involve CD44.

Involvement of C/EBP-alpha gene in in vitro activation of rat hepatic stellate cells

Hepatic stellate cells (HSCs) play key roles in hepatic fibrosis. One of the most striking alterations in activated HSCs is loss of cytoplasmic lipid droplets. However, the association of lipid storage with the activation of HSCs remains unclear. CCAAT/enhancer-binding proteins family (C/EBPs), especially C/EBP-alpha, controls differentiation of adipocytes. We suggested that C/EBP-alpha gene may be involved in HSCs activation. The present results showed that the expression levels of C/EBP-alpha and C/EBP-beta genes declined in activated HSCs. Over-expression of C/EBP-alpha gene in activated HSCs: (1) inhibited HSCs proliferation, extracellular matrix-producing, alpha-smooth muscle actin gene expression, and induced rebound of cytoplasmic lipid droplets; (2) reduced retinoic acid receptor-beta, C/EBP-delta and -beta gene expressions, but increased the active form C/EBP-beta PSer(105), and induced retinoid X receptor-alpha gene expression; and (3) did not affect the protein level of p16INK4a, p21Cip1/WAF1 or p27Kip1. In conclusions, C/EBP-alpha gene is involved in in vitro activation of rat HSCs.

Differential modulation of rat hepatic stellate phenotype by natural and synthetic retinoids

Activation of hepatic stellate cells (HSC) is a central event in the pathogenesis of liver fibrosis during chronic liver injury. We examined the expression of retinoic acid (RAR) and retinoid X receptors (RXR) during HSC activation and evaluated the influence of natural and synthetic retinoic acids (RA) on the phenotype of culture-activated HSC. The expression of the major RAR/RXR subtypes and isoforms was analyzed by Northern hybridization. Presence of functional receptor proteins was established by gel shift analysis. Retinoic acids, RAR, and RXR selective agonists and an RAR antagonist were used to evaluate the effects of retinoid signalling on matrix synthesis by Northern blotting and immunoprecipitation, and on cell proliferation by BrdU incorporation. The 9-cisRA and synthetic RXR agonists reduced HSC proliferation and synthesis of collagen I and fibronectin. All-trans RA and RAR agonists both reduced the synthesis of collagen I, collagen III, and fibronectin, but showed a different effect on cell proliferation. Synthetic RAR agonists did not affect HSC proliferation, indicating that ATRA inhibits cell growth independent of its interaction with RARs. In contrast, RAR specific antagonists enhance HSC proliferation and demonstrate that RARs control proliferation in a negative way. In conclusion, natural RAs and synthetic RAR or RXR specific ligands exert differential effects on activated HSC. Our observations may explain prior divergent results obtained following retinoid administration to cultured stellate cells or to animals subjected to fibrogenic stimuli.