Inhibitory effects of microRNA 19b in hepatic stellate cell-mediated fibrogenesis.

UNLABELLED: Hepatic stellate cell (HSC) activation is a pivotal event in initiation and progression of hepatic fibrosis and a major contributor to collagen deposition driven by transforming growth factor beta (TGF-ß). MicroRNAs (miRs), small noncoding RNAs modulating messenger RNA (mRNA) and protein expression, have emerged as key regulatory molecules in chronic liver disease. We investigated differentially expressed miRs in quiescent and activated HSCs to identify novel regulators of profibrotic TGF-ß signaling. miR microarray analysis was performed on quiescent and activated rat HSCs. Members of the miR-17-92 cluster (19a, 19b, 92a) were significantly down-regulated in activated HSCs. Because miR 19b showed the highest fold-change of the cluster members, activated HSCs were transfected with miR 19b mimic or negative control and TGF-ß signaling and HSC activation assessed. miR 19b expression was determined in fibrotic rat and human liver specimens. miR 19b mimic negatively regulated TGF-ß signaling components demonstrated by decreased TGF-ß receptor II (TGF-ßRII) and SMAD3 expression. Computational prediction of miR 19b binding to the 3' untranslated region of TGF-ßRII was validated by luciferase reporter assay. Inhibition of TGF-ß signaling by miR 19b was confirmed by decreased expression of type I collagen and by blocking TGF-ß-induced expression of α1(I) and α2(I) procollagen mRNAs. miR 19b blunted the activated HSC phenotype by morphological assessment and decreased smooth muscle α-actin expression. Additionally, miR 19b expression was markedly diminished in fibrotic rat liver compared with normal liver; similarly, miR 19b expression was markedly down-regulated in fibrotic compared with normal human livers. CONCLUSION: miR 19b is a novel regulator of TGF-ß signaling in HSCs, suggesting a potential therapeutic approach for hepatic fibrosis.

Altered aquaporin expression and role in apoptosis during hepatic stellate cell activation.

BACKGROUND: Hepatic stellate cells (HSCs) are effector cells of hepatic fibrosis contributing to excessive collagen deposition and scar matrix formation. Sustained HSC activation leads to hepatic cirrhosis, a leading cause of liver-related death. Reversal of hepatic fibrosis has been attributed to the induction of HSC apoptosis. Aquaporins (AQPs) are critical proteinacious channels that mediate cellular water loss during the initiation and progression of apoptosis. AIMS: This study examined AQP expression in quiescent and activated HSCs and determined the responsiveness to AQP-dependent apoptosis. METHODS: Aquaporin gene and protein expressions in quiescent and activated HSCs were determined by reverse transcription polymerase chain reaction and Western blot analyses. AQP function was determined by cell swelling and apoptotic assays in the absence and presence of HgCl(2) , a non-specific AQP inhibitor. RESULTS: In this study, we report that activated HSCs showed no detectable expression of AQP 1, 5, 8, 9 and 12 mRNAs but expression was observed in quiescent HSCs. Similarly, AQP 0, 1, 8 and 9 protein was not detected in activated HSCs but was measured in quiescent HSCs. Dual fluorescent immunohistochemistry confirmed that AQP expression is decreased in activated HSCs in a model of liver injury. Functional studies demonstrated that quiescent HSCs were highly susceptible to osmotic challenge and apoptotic stimulus, whereas activated HSCs were less responsive. Finally, apoptosis was abrogated by the inhibition of AQP-dependent water movement. CONCLUSIONS: These findings demonstrate that increased resistance to apoptosis in activated HSCs is due, at least in part, to the changes in AQP expression and function that occur following HSC activation.

S-adenosyl-L-methionine inhibits collagen secretion in hepatic stellate cells via increased ubiquitination.

BACKGROUND: Liver fibrosis is the excessive accumulation of extracellular matrix (ECM) components that disrupt normal liver microcirculation and lead to organ injury. Hepatic stellate cells (HSCs), following transdifferentiation, are the central mediators of hepatic fibrosis through increased secretion of ECM components, including type I collagen. AIMS: The mechanism(s) by which the antioxidant S-adenosyl-L-methionine (SAMe) acts to modulate type I collagen secretion in activated HSCs was examined. METHODS: Hepatic stellate cells were culture-activated for 13-15 days and treated with SAMe. Type I collagen, proteasomal activity and resident endoplasmic reticulum (ER) protein [78-kDa glucose-regulated protein (Grp78) and protein disulphide isomerase (PDI)] expression were measured. Nuclear factor-κB (NF-κB) activity, and its role in SAMe-mediated collagen inhibition, was determined. Type I collagen polyubiquitination was examined. RESULTS: S-adenosyl-L-methionine significantly inhibited type I collagen secretion without significant changes in type I collagen mRNA expression. SAMe also increased NF-κB activity, and blocking NF-κB activity using a dominant-negative IκBα abolished the SAMe-mediated type I collagen secretion. Examination of the post-transcriptional fate of procollagen demonstrated that SAMe treatment led to intracellular type I collagen polyubiquitination accompanied by diminution of proteasomal activity. Expression of Grp78 and PDI (resident ER proteins) were significantly decreased by SAMe treatment. CONCLUSIONS: S-adenosyl-L-methionine inhibits collagen processing leading to increased ubiquitination and decreased secretion. These findings represent a novel mechanism for modulating type I collagen expression in activated HSCs.

microRNAs: fad or future of liver disease.

microRNAs (miRs) are small non-coding RNAs that regulate both mRNA and protein expression of target genes, which results in alterations in mRNA stability or translation inhibition. miRs influence at least one third of all human transcripts and are known regulators of various important cellular growth and differentiation factors. miRs have recently emerged as key regulatory molecules in chronic liver disease. This review details recent contributions to the field of miRs that influence liver development and the broad spectrum of disease, from non-alcoholic fatty liver disease to fibrosis/cirrhosis, with particular emphasis on hepatic stellate cells and potential use of miRs as therapeutic tools.

Nonmuscle myosin II regulates migration but not contraction in rat hepatic stellate cells.

AIM: To identify and characterize the function of nonmuscle myosin II (NMM II) isoforms in primary rat hepatic stellate cells (HSCs). METHODS: Primary HSCs were isolated from male Sprague-Dawley rats by pronase/collagenase digestion. Total RNA and protein were harvested from quiescent and culture-activated HSCs. NMM II isoform (II-A, II-B and II-C) gene and protein expression were measured by RealTime polymerase chain reaction and Western blot analyses respectively. NMM II protein localization was visualized in vitro using immunocytochemical analysis. For in vivo assessment, liver tissue was harvested from bile duct-ligated (BDL) rats and NMM IIisoform expression determined by immunohistochemistry. Using a selective myosin II inhibitor and siRNA-mediated knockdown of each isoform, NMM II functionality in primary rat HSCs was determined by contraction and migration assays. RESULTS: NMM II-A and II-B mRNA expression was increased in culture-activated HSCs (Day 14) with significant increases seen in all pair-wise comparisons (II-A: 12.67 ± 0.99 (quiescent) vs 17.36 ± 0.78 (Day 14), P < 0.05; II-B: 4.94 ± 0.62 (quiescent) vs 13.90 ±0.85 (Day 14), P < 0.001). Protein expression exhibited similar expression patterns (II-A: 1.87 ± 2.50 (quiescent) vs 58.64 ± 8.76 (Day 14), P < 0.05; II-B: 1.17 ± 1.93 (quiescent) vs 103.71 ± 21.73 (Day 14), P < 0.05). No significant differences were observed in NMM II-C mRNA and protein expression between quiescent and activated HSCs. In culture-activated HSCs, NMM II-A and II-B merged with F-actin at the cellular periphery and throughout cytoplasm respectively. In vitro studies showed increased expression of NMM II-B in HSCs activated by BDL compared to sham-operated animals. There were no apparent increases of NMM II-A and II-C protein expression in HSCs during hepatic BDL injury. To determine the contribution of NMM II-A and II-B to migration and contraction, NMM II-A and II-B expression were downregulated with siRNA. NMM II-A and/or II-B siRNA inhibited HSC migration by approximately 25% compared to scramble siRNA-treated cells. Conversely, siRNA-mediated NMM II-A and II-B inhibition had no significant effect on HSC contraction; however, contraction was inhibited with the myosin II inhibitor, blebbistatin (38.7% ± 1.9%). CONCLUSION: Increased expression of NMM II-A and II-B regulates HSC migration, while other myosin IIclasses likely modulate contraction, contributing to development and severity of liver fibrosis.

Opioid-like compound exerts anti-fibrotic activity via decreased hepatic stellate cell activation and inflammation.

Hepatic fibrosis is characterized by excess type I collagen deposition and exacerbated inflammatory response. Naltrexone, an opioid receptor antagonist used for treating alcohol abuse, attenuates hepatocellular injury in fibrotic animal models, which can be accompanied by deleterious side effects. Additionally, opioid neurotransmission is upregulated in patients with inflammatory liver disease. Several derivatives of Naltrexone, Nalmefene (Nal) and JKB-119, exert immunomodulatory activity; however, unlike Nal, JKB-119 does not show significant opioid receptor antagonism. To delineate the potential hepatoprotective effects of these compounds, we investigated if JKB-119 and Nal could modulate activation of hepatic stellate cells (HSCs), primary effector cells that secrete type I collagen and inflammatory mediators during liver injury. Our results demonstrated that Nal or JKB-119 treatment decreased smooth muscle α-actin, a marker of HSC activation, mRNA and protein expression. Despite decreased collagen mRNA expression, both compounds increased intracellular collagen protein expression; however, inhibition of collagen secretion was observed. To address a possible mechanism for suppressed collagen secretion or retention of intracellular collagen, endoplasmic (ER) protein expression and matrix metalloproteinase (MMP) activity were examined. While no change in ER protein expression (Grp78, PDI, Hsp47) was observed, MMP13 mRNA expression was dramatically increased. In an acute LPS inflammatory injury animal model, JKB-119 treatment decreased liver injury (ALT), plasma TNFα and PMN liver infiltration. Overall, these results suggest that JKB-119 can directly inhibit HSC activation attributed to anti-inflammatory activity and may, therefore, attenuate inflammation associated with HSC activation and liver disease.

Neonatal androgenization exacerbates alcohol-induced liver injury in adult rats, an effect abrogated by estrogen.

Alcoholic liver disease (ALD) affects millions of people worldwide and is a major cause of morbidity and mortality. However, fewer than 10% of heavy drinkers progress to later stages of injury, suggesting other factors in ALD development, including environmental exposures and genetics. Females display greater susceptibility to the early damaging effects of ethanol. Estrogen (E2) and ethanol metabolizing enzymes (cytochrome P450, CYP450) are implicated in sex differences of ALD. Sex steroid hormones are developmentally regulated by the hypothalamic-pituitary-gonadal (HPG) axis, which controls sex-specific cycling of gonadal steroid production and expression of hepatic enzymes. The aim of this study was to determine if early postnatal inhibition of adult cyclic E2 alters ethanol metabolizing enzyme expression contributing to the development of ALD in adulthood. An androgenized rat model was used to inhibit cyclic E2 production. Control females (Ctrl), androgenized females (Andro) and Andro females with E2 implants were administered either an ethanol or isocalorically-matched control Lieber-DeCarli diet for four weeks and liver injury and CYP450 expression assessed. Androgenization exacerbated the deleterious effects of ethanol demonstrated by increased steatosis, lipid peroxidation, profibrotic gene expression and decreased antioxidant defenses compared to Ctrl. Additionally, CYP2E1 expression was down-regulated in Andro animals on both diets. No change was observed in CYP1A2 protein expression. Further, continuous exogenous administration of E2 to Andro in adulthood attenuated these effects, suggesting that E2 has protective effects in the androgenized animal. Therefore, early postnatal inhibition of cyclic E2 modulates development and progression of ALD in adulthood.

Daily genetic profiling indicates JAK/STAT signaling promotes early hepatic stellate cell transdifferentiation.

AIM: To identify signaling pathways and genes that initiate and commit hepatic stellate cells (HSCs) to transdifferentiation. METHODS: Primary HSCs were isolated from male Sprague-Dawley rats and cultured on plastic for 0-10 d. Gene expression was assessed daily (quiescent to day 10 culture-activation) by real time polymerase chain reaction and data clustered using AMADA software. The significance of JAK/STAT signaling to HSC transdifferentiation was determined by treating cells with a JAK2 inhibitor. RESULTS: Genetic cluster analyses, based on expression of these 21 genes, showed similar expression profiles on days 1-3, days 5 and 6, and days 7-10, while freshly isolated cells (day Q) and day 4 cells were genotypically distinct from any of the other days. Additionally, gene expression clustering revealed strong upregulation of interleukin-6, JAK2 and STAT3 mRNA in the early stages of activation. Inhibition of the JAK/STAT signaling pathway impeded the morphological transdifferentiation of HSCs which correlated with decreased mRNA expression of several profibrotic genes including collagens, α-SMA, PDGFR and TGFßR. CONCLUSION: These data demonstrate unique clustered genetic profiles during the daily progression of HSC transdifferentiation and that JAK/STAT signaling may be critical in the early stages of transdifferentiation.