Activated stellate (Ito) cells possess voltage-activated calcium current

Role of B Cell-Activating Factor in Fibrosis Progression in a Murine Model of Non-Alcoholic Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease all over the world. Therapeutic strategies targeting its multidirectional pathways are required. Particularly, fibrosis is closely associated with its prognosis. We previously found that B cell-activating factor (BAFF) is associated with severity of NAFLD. Here, we determined the direct in vivo role of BAFF in the development of liver fibrosis. Histological and biochemical analyses were performed using wild-type and BAFF-deficient mice. We established a murine model of non-alcoholic steatohepatitis (NASH) using carbon tetrachloride injection accompanied by high-fat/high-cholesterol diet feeding. Additionally, in vitro analysis using mouse macrophage-like cell line RAW264.7 and primary hepatic stellate cells was performed. Hepatic steatosis and inflammation, and most importantly, the progression of liver fibrosis, were ameliorated in BAFF-deficient mice compared to those wild-type mice in our model. Additionally, BAFF deficiency reduced the number of CD11c⁺ M1-type macrophages in the liver. Moreover, BAFF stimulated RAW264.7 cells to secrete nitric oxide and tumor necrosis factor α, which drove the activation of hepatic stellate cells. This indicates that BAFF plays a crucial role in NASH development and may be a promising therapeutic target for NASH.

Switching-on of serotonergic calcium signaling in activated hepatic stellate cells

AIM

To investigate serotonergic Ca²+ signaling and the expression of 5-hydroxytryptamine (5-HT) receptors, as well as Ca²+ transporting proteins, in hepatic stellate cells (HSCs).

METHODS

The intracellular Ca²+ concentration [Ca²+](i) of isolated rat HSCs was measured with a fluorescence microscopic imaging system. Quantitative PCR was performed to determine the transcriptional levels of 5-HT receptors and endoplasmic reticulum (ER) proteins involved in Ca²+ storage and release in cultured rat HSCs.

RESULTS

Distinct from quiescent cells, activated HSCs exhibited [Ca²+](i) transients following treatment with 5-HT, which was abolished by U-73122, a phospholipase C inhibitor. Upregulation of 5-HT(2A) and 5-HT(2B) receptors, but not 5-HT₃, was prominent during trans-differentiation of HSCs. Pretreatment with ritanserin, a 5-HT₂ antagonist, inhibited [Ca²+](i) changes upon application of 5-HT. Expression of type 1 inositol-5'-triphosphate receptor and type 2 sarcoplasmic/endoplasmic reticulum Ca²+ ATPase were also increased during activation of HSCs and serve as the major isotypes for ER Ca²+ storage and release in activated HSCs. Ca²+ binding chaperone proteins of the ER, including calreticulin, calnexin and calsequestrin, were up-regulated following activation of HSCs.

CONCLUSION

The appearance of 5-HT-induced [Ca²+](i) response accompanied by upregulation of metabotropic 5-HT₂ receptors and Ca²+ transporting/chaperone ER proteins may participate in the activating process of HSCs.

Plasma membrane calcium ATPase isoform 3 expression in single cells isolated from rat liver

The plasma membrane Ca(2+)-ATPase (PMCA) located in the hepatocyte is a controversial molecule in itself since it displays different features to those regarded as canonical for P-type Ca(2+)-ATPases, and from which transcript expression as well as catalytic activity continues to be under active investigation. Our aim in this study was to explore at a first glance, pmca isoform distribution using isolated parenchymal and non-parenchymal cells from rat liver tissue. Expression of pmca transcripts was analyzed in fresh or cell-enriched culture preparations, confirming pmca1 and pmca4 as the housekeeping isoforms in all cell types studied (hepatocytes, Kupffer cells, and stellate cells). However, for the first time we show expression of pmca3 transcripts edited at two different sites in both hepatocytes and non-parenchymal cells. Interestingly, employing non-parenchymal cells we demonstrate the specific expression of pmca3e transcripts previously considered nearly exclusive of excitable tissues. Real-time PCR quantification shows a significant decrease of pmca3 transcripts in cultured Kupffer and hepatic stellate cells in comparison with fresh cells. The presence of pmca2 along with pmca3 in all liver cell types studied suggests that high affinity isoforms are relevant to the adequate management of calcium in liver tissue, particularly when hepatic cells become activated by diverse stimuli.

The GABAB receptor inhibits activation of hepatic stellate cells

BACKGROUND/AIMS

Angiotensin II (Ang II) plays an important role in the activation of hepatic stellate cells (HSCs). In this study it was found that expression of the GABA(B) receptor was elevated in HSCs treated with Ang II. We attempted to elucidate the mechanism of the GABA(B) receptor in HSCs activation.

METHODS

First, the target gene (GABA(B) receptor) was screened by gene chip in HSCs treated with Ang II. Second, the biological function of the GABA(B) receptor was analyzed by MTT, cell-cycle assay, real-time PCR, and western blot. The methods of MTT and cell-cycle assay were used to evaluate the effect of the GABA(B) receptor on proliferation and DNA synthesis of HSCs. Expression of ECM, TGF-beta1, and alpha-SMA was analyzed by real-time PCR and western blot.

RESULTS

The GABA(B) receptor's specific agonist CGP35348 inhibited the activation of HSCs, which could be partially reversed by the GABA(B) receptor's antagonist.

CONCLUSIONS

Our in-vitro results demonstrated that the GABA(B) receptor could inhibit HSCs activation.

Prostacyclin in liver disease: a potential therapeutic option

Complex molecular and cellular mechanisms are involved in the initiation and progression of hepatic fibrosis. Recent studies have shown that hepatic stellate cells, endothelin, cytokines and prostacyclin play crucial roles in this pathology. Prostacyclin exerts vasorelaxant, antioxidant and antifibrotic properties that prevent the development of fibrosis and cirrhosis in liver diseases. In this editorial, the authors discuss some of the molecular and cellular mechanisms involved in the initiation and progression of liver fibrosis and the role played by prostacyclin in counteracting it. At the moment, however, only limited information is available from clinical studies demonstrating the effectiveness of prostacyclin in liver diseases and this makes it difficult to draw any conclusions; further efforts are necessary to verify whether prostacyclin, alone or in combination with other drugs, may be a valid therapeutic option in liver diseases.

[Ca2+]i-independent contractile force generation by rat hepatic stellate cells in response to endothelin-1

The contractile force generated by hepatic stellate cells in response to endothelin-1 contributes to sinusoidal blood flow regulation and hepatic fibrosis. This study's aim was to directly test the widely held view that changes in cytosolic Ca2+ concentration ([Ca2+]i) mediate stellate cell force generation. Contractile force generation by primary cultures of rat hepatic stellate cells grown in three-dimensional collagen gels was directly and quantitatively measured using a force transducer. Stellate cell [Ca2+]i, myosin activation, and migration were quantified using standard techniques. [Ca2+]i was modulated using ionomycin, BAPTA, KCl, and removal of extracellular Ca2+. Removal of extracellular Ca2+ did not alter endothelin-1-stimulated force development or [Ca2+]i. Ionomycin, a Ca2+ ionophore, triggered an increase in [Ca2+]i that was three times greater than that stimulated by endothelin-1, but only induced 16% of the force and 38% of the myosin regulatory light chain (MLC) phosphorylation induced by endothelin-1. Physiological increases in [Ca2+]i induced by hyperkalemia had no effect on contractile force. Loading BAPTA, a Ca2+ chelator, in stellate cells completely blocked endothelin-1-induced increases in [Ca2+]i but had no effect on endothelin-1-stimulated force generation or MLC phosphorylation. In contrast, Y-27632, a selective rho-associated kinase inhibitor, inhibited endothelin-1-stimulated force generation by at least 70% and MLC phosphorylation by at least 80%. Taken together, these observations indicate that changes in [Ca2+]i are neither necessary nor sufficient for contractile force generation by rat stellate cells. Our results challenge the current model of contractile regulation in hepatic stellate cells and have important implications for our understanding of hepatic pathophysiology.

Iloprost: an adjunctive approach to chronic viral hepatitis treatment

Chronic viral liver disease may evolve to cirrhosis. The medical treatment to slow down this passage is based on anti-viral and anti-fibrotic properties of interferon. Recently, we evidenced significant increase of portal vein flow velocity and volume after a prostacyclin analog (iloprost) infusion in subjects without and with chronic viral hepatitis. On the basis of these results and considering both the pathophysiology of viral liver disease and the mechanism of action of iloprost in portal microcirculation, we hypothesize that it may be of some efficacy in chronic liver disease ameliorating the portal hemodynamics and producing an anti-oxidant liver effect.

Leptin facilitates proliferation of hepatic stellate cells through up-regulation of platelet-derived growth factor receptor

In the present study, we investigated the effect of leptin on proliferation of hepatic stellate cells (HSCs) in vitro. Proliferation of 3-day cultured rat HSCs was assessed by incorporation of 5-bromo-2'-deoxyuridine (BrdU) into the nuclei. The percentages of BrdU-positive cells were increased in the presence of PDGF-BB (5 ng/ml) for 8h as expected. Co-incubation with leptin (10-100 nM) potentiates this PDGF-dependent increase in BrdU positive cells in a dose-dependent manner. Messenger RNA for PDGF receptor alpha and beta subunits was increased almost 2- to 3-fold by incubation with leptin for 6h. Further, pre-incubation with leptin for 6h enhanced PDGF-induced increases in phospho-p44/42 MAP kinase and phospho-Akt levels in a dose-dependent manner. In the same condition, however, leptin per se did not increase phospho-STAT 3 and phospho-p44/42 MAP kinase levels. Instead, leptin increased phospho-Akt levels in HSCs within 30 min, suggesting that the phosphatidylinositol 3 kinase (PI3K)/Akt pathway is involved in the mechanism by which leptin accelerates the proliferation of HSCs. In conclusion, the present study clearly indicated that leptin potentiates PDGF-dependent proliferative responses of HSCs in vitro.

Improved Hepatic Perfusion After Iloprost Infusion in Patients with HCV Chronic Infection: A Pilot Study with Possible Therapeutic Implications

We performed a pilot study to evaluate whether portal flow volume (PFV) changed in subjects with chronic hepatitis C virus (HCV) infection with respect to control patients after infusion of iloprost, a prostacyclin analog. Six subjects with chronic HCV infection and arteriopathy of the lower limbs (CHCVIA) and 4 control patients affected only by HCV infection (CHCV) were studied with color Doppler sonography. CHCVIA patients were examined before and after 3 days of iloprost infusion, and CHCV patients were examined before and after 3 days with no treatment. In each patient, PFV was obtained after calculating portal flow velocity (PV), portal diameter, and portal vein cross-sectional area. The mean difference between basal and final values of the PFV of CHCVIA patients was significant (p = 0.03), as was the difference in the PFV (final values expressed as percent of basal values) in CHCVIA patients compared with those obtained in the CHCV patients (p = 0.01). We have observed significant improvement in hepatic perfusion in CHCVIA patients compared with CHCV patients after iloprost infusion. In light of these results, we suggest some possible therapeutic implications in patients with HCV infection. Further studies are necessary to confirm this hypothesis.

Leptin is required for fibrogenic responses induced by thioacetamide in the murine liver

In this study, we investigated hepatic fibrogenesis caused by long-term thioacetamide (TAA) administration in ob/ob mice, a naturally occurring leptin deficient animal. In the lean littermates, prominent hepatic fibrosis, as well as positive staining for alpha smooth muscle actin (alpha-SMA), was induced by treatment with TAA (200 microg/g, IP, 3 times per week) for 4 to 8 weeks as expected. In sharp contrast, almost no hepatic fibrosis developed in ob/ob mice given the equivalent doses of TAA, where specific staining for alpha-SMA barely was detected. Induction of alpha1(I) procollagen mRNA caused by TAA also was prevented in ob/ob mice almost completely. Further, transforming growth factor beta (TGF-beta) mRNA was increased in the liver after TAA treatment for 4 weeks in lean littermates, which also was prevented in ob/ob mice. Interestingly, fibrotic septa in the hepatic lobules, as well as increases in alpha1(I) procollagen mRNA, was observed in ob/ob mice, when they were injected with recombinant murine leptin (1 microg/g daily) in combination with TAA treatment. Leptin per se did not cause any fibrotic changes in the liver in ob/ob mice. These findings clearly indicated that leptin deficiency is responsible for the resistance to TAA-induced profibrogenic responses in ob/ob mice. In conclusion, leptin appears to promote profibrogenic responses in the liver, in part, by up-regulation of TGF-beta.

Leptin receptor-mediated signaling regulates hepatic fibrogenesis and remodeling of extracellular matrix in the rat

BACKGROUND & AIMS

In this study, we investigated the role of leptin and its receptors (Ob-R) in profibrogenic responses in the liver using Zucker (fa/fa) rats, a natural occurring Ob-R-deficient animal.

METHODS

Male Zucker (fa/fa) rats and their lean (+/?) littermates were given intraperitoneal injections of thioacetamide (TAA) (200 mg/kg body wt, 3 times/wk) for 4-8 weeks, and progression of hepatic fibrosis was evaluated. In vitro transactivation of hepatic stellate cells (HSCs) isolated from Zucker rats was evaluated by Western blotting and immunocytochemistry for alpha-smooth muscle actin and type I collagen. Further, a long-form Ob-R (Ob-Rb) in sinusoidal endothelial cells (SECs) and Kupffer cells was identified by reverse-transcription polymerase chain reaction. Moreover, transforming growth factor (TGF)-beta1 messenger RNA in LSE cells, a human SEC-derived cell line, was measured by Northern blotting.

RESULTS

Although the normal liver does not produce leptin, activated HSCs produced leptin in vivo during fibrogenesis caused by TAA. In Zucker rats, TAA-induced hepatic fibrosis was prevented almost completely, whereas induction of TGF-beta1 and activation of HSCs were abolished. It is less likely, however, that leptin plays an essential role in the activation of HSCs as a strong autocrine regulator, because HSCs isolated from Zucker rats undergo normal transactivation process in vitro. In contrast, SECs and Kupffer cells contain Ob-Rb, through which leptin up-regulates the expression of matrix remodeling genes including TGF-beta1.

CONCLUSIONS

Collectively, these findings indicated that leptin and its functional receptors (Ob-Rb) play a pivotal role in profibrogenic responses in the liver.

Pioglitazone prevents early-phase hepatic fibrogenesis caused by carbon tetrachloride

Here we investigated the effect of pioglitazone, a peroxisome proliferator-activated receptor (PPAR)-gamma ligand, on early-phase hepatic fibrogenesis in vivo caused by acute carbon tetrachloride (CCl(4)) administration in the rat. Pioglitazone (1 mg/kg BW) prevented pericentral fibrosis and induction of alpha-smooth muscle actin (SMA) 72 h after CCl(4) administration (1 ml/kg BW). CCl(4) induction of alpha1(I)procollagen mRNA in the liver was blunted by pioglitazone to the levels almost 2/3 of CCl(4) alone. Pioglitazone also prevented CCl(4)-induced hepatic inflammation and necrosis, as well as increases in serum tumor necrosis factor-alpha levels. Further, pioglitazone inhibited the induction of alphaSMA and type I collagen in primary cultured hepatic stellate cells in a dose-dependent manner. In conclusion, pioglitazone inhibits both hepatic inflammation and activation of hepatic stellate cells, thereby ameliorating early-phase fibrogenesis in the liver following acute CCl(4).

Inhibitory effect of Y-27632, a ROCK inhibitor, on progression of rat liver fibrosis in association with inactivation of hepatic stellate cells

BACKGROUND/AIMS

Activation of hepatic stellate cells (HSCs) is a final common pathway of liver fibrosis. Recently, it has been demonstrated that the small GTPase Rho is involved in HSCs activation, and that Y-27632, an inhibitor of Rho-kinase which is an effector that acts downstream of Rho, inhibits Rho-associated effects. The objective of the current study was to investigate the inhibitory effects of Y-27632 on the activation of HSCs and the progression of liver fibrosis.

METHODS

Y-27632 (1, 10, 100 microM) was added to HSCs isolated from normal rat liver.

RESULTS

HSCs maintained the 'star-like' configuration of the quiescent stage in the presence of Y-27632, as well as inhibition of the expression of Na+/Ca2+ exchanger mRNA which was reported to be an indicator of HSCs activation. In addition, when Y-27632 (30 mg/kg body weight) was administered to rats with carbon tetrachloride-induced liver fibrosis, collagen deposition was inhibited, the hepatic hydroxyproline content was decreased, and the serum hyaluronic acid level was reduced. Moreover, Y-27632 reduced the number of smooth muscle alpha-actin-positive cells and transforming growth factor-beta1-positive cells, and inhibited the expression of Na/Ca2+ exchanger mRNA.

CONCLUSIONS

These findings indicate that Y-27632 may be useful for the clinical management of liver fibrosis.