Lack of EGFR catalytic activity in hepatocytes improves liver regeneration following DDC-induced cholestatic injury by promoting a pro-restorative inflammatory response.

Despite the well-known hepatoprotective role of the epidermal growth factor receptor (EGFR) pathway upon acute damage, its specific actions during chronic liver disease, particularly cholestatic injury, remain ambiguous and unresolved. Here, we analyzed the consequences of inactivating EGFR signaling in the liver on the regenerative response following cholestatic injury. For that, transgenic mice overexpressing a dominant negative mutant human EGFR lacking tyrosine kinase activity (ΔEGFR) in albumin-positive cells were submitted to liver damage induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC), an experimental model resembling human primary sclerosing cholangitis. Our results show an early activation of EGFR after 1-2 days of a DDC-supplemented diet, followed by a signaling switch-off. Furthermore, ΔEGFR mice showed less liver damage and a more efficient regeneration following DDC injury. Analysis of the mechanisms driving this effect revealed an enhanced activation of mitogenic/survival signals, AKT and ERK1/2-MAPKs, and changes in cell turnover consistent with a quicker resolution of damage in response to DDC. These changes were concomitant with profound differences in the profile of intrahepatic immune cells, consisting of a shift in the M1/M2 balance towards M2 polarity, and the Cd4/Cd8 ratio in favor of Cd4 lymphocytes, overall supporting an immune cell switch into a pro-restorative phenotype. Interestingly, ΔEGFR livers also displayed an amplified ductular reaction, with increased expression of EPCAM and an increased number of CK19-positive ductular structures in portal areas, demonstrating an overexpansion of ductular progenitor cells. In summary, our work supports the notion that hepatocyte-specific EGFR activity acts as a key player in the crosstalk between parenchymal and non-parenchymal hepatic cells, promoting the pro-inflammatory response activated during cholestatic injury and therefore contributing to the pathogenesis of cholestatic liver disease. © 2022 The Pathological Society of Great Britain and Ireland.

c-Met Signaling Is Essential for Mouse Adult Liver Progenitor Cells Expansion After Transforming Growth Factor-ß-Induced Epithelial-Mesenchymal Transition and Regulates Cell Phenotypic Switch.

Adult hepatic progenitor cells (HPCs)/oval cells are bipotential progenitors that participate in liver repair responses upon chronic injury. Recent findings highlight HPCs plasticity and importance of the HPCs niche signals to determine their fate during the regenerative process, favoring either fibrogenesis or damage resolution. Transforming growth factor-ß (TGF-ß) and hepatocyte growth factor (HGF) are among the key signals involved in liver regeneration and as component of HPCs niche regulates HPCs biology. Here, we characterize the TGF-ß-triggered epithelial-mesenchymal transition (EMT) response in oval cells, its effects on cell fate in vivo, and the regulatory effect of the HGF/c-Met signaling. Our data show that chronic treatment with TGF-ß triggers a partial EMT in oval cells based on coexpression of epithelial and mesenchymal markers. The phenotypic and functional profiling indicates that TGF-ß-induced EMT is not associated with stemness but rather represents a step forward along hepatic lineage. This phenotypic transition confers advantageous traits to HPCs including survival, migratory/invasive and metabolic benefit, overall enhancing the regenerative potential of oval cells upon transplantation into a carbon tetrachloride-damaged liver. We further uncover a key contribution of the HGF/c-Met pathway to modulate the TGF-ß-mediated EMT response. It allows oval cells expansion after EMT by controlling oxidative stress and apoptosis, likely via Twist regulation, and it counterbalances EMT by maintaining epithelial properties. Our work provides evidence that a coordinated and balanced action of TGF-ß and HGF are critical for achievement of the optimal regenerative potential of HPCs, opening new therapeutic perspectives. Stem Cells 2019;37:1108-1118.

Bone morphogenetic protein 9 as a key regulator of liver progenitor cells in DDC-induced cholestatic liver injury.

BACKGROUND & AIMS: Bone morphogenetic protein 9 (BMP9) interferes with liver regeneration upon acute injury, while promoting fibrosis upon carbon tetrachloride-induced chronic injury. We have now addressed the role of BMP9 in 3,5 diethoxicarbonyl-1,4 dihydrocollidine (DDC)-induced cholestatic liver injury, a model of liver regeneration mediated by hepatic progenitor cell (known as oval cell), exemplified as ductular reaction and oval cell expansion. METHODS: WT and BMP9KO mice were submitted to DDC diet. Livers were examined for liver injury, fibrosis, inflammation and oval cell expansion by serum biochemistry, histology, RT-qPCR and western blot. BMP9 signalling and effects in oval cells were studied in vitro using western blot and transcriptional assays, plus functional assays of DNA synthesis, cell viability and apoptosis. Crosslinking assays and short hairpin RNA approaches were used to identify the receptors mediating BMP9 effects. RESULTS: Deletion of BMP9 reduces liver damage and fibrosis, but enhances inflammation upon DDC feeding. Molecularly, absence of BMP9 results in overactivation of PI3K/AKT, ERK-MAPKs and c-Met signalling pathways, which together with an enhanced ductular reaction and oval cell expansion evidence an improved regenerative response and decreased damage in response to DDC feeding. Importantly, BMP9 directly targets oval cells, it activates SMAD1,5,8, decreases cell growth and promotes apoptosis, effects that are mediated by Activin Receptor-Like Kinase 2 (ALK2) type I receptor. CONCLUSIONS: We identify BMP9 as a negative regulator of oval cell expansion in cholestatic injury, its deletion enhancing liver regeneration. Likewise, our work further supports BMP9 as an attractive therapeutic target for chronic liver diseases.

p38 MAPK down-regulates fibulin 3 expression through methylation of gene regulatory sequences: role in migration and invasion.

p38 MAPKs regulate migration and invasion. However, the mechanisms involved are only partially known. We had previously identified fibulin 3, which plays a role in migration, invasion, and tumorigenesis, as a gene regulated by p38α. We have characterized in detail how p38 MAPK regulates fibulin 3 expression and its role. We describe here for the first time that p38α, p38γ, and p38δ down-regulate fibulin 3 expression. p38α has a stronger effect, and it does so through hypermethylation of CpG sites in the regulatory sequences of the gene. This would be mediated by the DNA methylase, DNMT3A, which is down-regulated in cells lacking p38α, but once re-introduced represses Fibulin 3 expression. p38α through HuR stabilizes dnmt3a mRNA leading to an increase in DNMT3A protein levels. Moreover, by knocking-down fibulin 3, we have found that Fibulin 3 inhibits migration and invasion in MEFs by mechanisms involving p38α/ß inhibition. Hence, p38α pro-migratory/invasive effect might be, at least in part, mediated by fibulin 3 down-regulation in MEFs. In contrast, in HCT116 cells, Fibulin 3 promotes migration and invasion through a mechanism dependent on p38α and/or p38ß activation. Furthermore, Fibulin 3 promotes in vitro and in vivo tumor growth of HCT116 cells through a mechanism dependent on p38α, which surprisingly acts as a potent inducer of tumor growth. At the same time, p38α limits fibulin 3 expression, which might represent a negative feed-back loop.

BMP9-Induced Survival Effect in Liver Tumor Cells Requires p38MAPK Activation.

The study of bone morphogenetic proteins (BMPs) role in tumorigenic processes, and specifically in the liver, has gathered importance in the last few years. Previous studies have shown that BMP9 is overexpressed in about 40% of hepatocellular carcinoma (HCC) patients. In vitro data have also shown evidence that BMP9 has a pro-tumorigenic action, not only by inducing epithelial to mesenchymal transition (EMT) and migration, but also by promoting proliferation and survival in liver cancer cells. However, the precise mechanisms driving these effects have not yet been established. In the present work, we deepened our studies into the intracellular mechanisms implicated in the BMP9 proliferative and pro-survival effect on liver tumor cells. In HepG2 cells, BMP9 induces both Smad and non-Smad signaling cascades, specifically PI3K/AKT and p38MAPK. However, only the p38MAPK pathway contributes to the BMP9 growth-promoting effect on these cells. Using genetic and pharmacological approaches, we demonstrate that p38MAPK activation, although dispensable for the BMP9 proliferative activity, is required for the BMP9 protective effect on serum withdrawal-induced apoptosis. These findings contribute to a better understanding of the signaling pathways involved in the BMP9 pro-tumorigenic role in liver tumor cells.

Uncovering a Novel Functional Interaction Between Adult Hepatic Progenitor Cells, Inflammation and EGFR Signaling During Bile Acids-Induced Injury.

Chronic cholestatic damage is associated to both accumulation of cytotoxic levels of bile acids and expansion of adult hepatic progenitor cells (HPC) as part of the ductular reaction contributing to the regenerative response. Here, we report a bile acid-specific cytotoxic response in mouse HPC, which is partially impaired by EGF signaling. Additionally, we show that EGF synergizes with bile acids to trigger inflammatory signaling and NLRP3 inflammasome activation in HPC. Aiming at understanding the impact of this HPC specific response on the liver microenvironment we run a proteomic analysis of HPC secretome. Data show an enrichment in immune and TGF-ß regulators, ECM components and remodeling proteins in HPC secretome. Consistently, HPC-derived conditioned medium promotes hepatic stellate cell (HSC) activation and macrophage M1-like polarization. Strikingly, EGF and bile acids co-treatment leads to profound changes in the secretome composition, illustrated by an abolishment of HSC activating effect and by promoting macrophage M2-like polarization. Collectively, we provide new specific mechanisms behind HPC regulatory action during cholestatic liver injury, with an active role in cellular interactome and inflammatory response regulation. Moreover, findings prove a key contribution for EGFR signaling jointly with bile acids in HPC-mediated actions.

BMP9 Promotes an Epithelial Phenotype and a Hepatocyte-like Gene Expression Profile in Adult Hepatic Progenitor Cells.

Bone morphogenetic protein 9 (BMP9), a member of the TGF-ß superfamily, has emerged as a new player in chronic liver diseases (CLDs). Its levels increase in the fibrotic liver where it promotes fibrogenesis. It also regulates hepatic progenitor cells (oval cells in rodents), a cell population that contributes to repopulate the liver and recover functionality upon severe damage, but it can also be pro-fibrogenic, depending upon the hepatic microenvironment. Here we analyze the effect of chronic exposure to BMP9 in oval cells. We show that cells chronically treated with BMP9 (B9T-OC) display a more epithelial and hepatocyte-like phenotype while acquiring proliferative and survival advantages. Since our previous studies had revealed a functional crosstalk between BMP9 and the HGF/c-Met signaling pathways in oval cells, we analyzed a possible role for HGF/c-Met in BMP9-induced long-term effects. Data evidence that active c-Met signaling is necessary to obtain maximum effects in terms of BMP9-triggered hepatocytic differentiation potential, further supporting functionally relevant cooperation between these pathways. In conclusion, our work reveals a novel action of BMP9 in liver cells and helps elucidate the mechanisms that serve to increase oval cell regenerative potential, which could be therapeutically modulated in CLD.

Transient focal cerebral ischemia significantly alters not only EAATs but also VGLUTs expression in rats: relevance of changes in reactive astroglia.

The involvement of plasma membrane glutamate transporters (EAATs - excitatory aminoacid transporters) in the pathophysiology of ischemia has been widely studied, but little is known about the role of vesicular glutamate transporters (VGLUTs) in the ischemic process. We analyzed the expression of VGLUT1-3 in the cortex and caudate-putamen of rats subjected to transient middle cerebral artery occlusion. Western blot and immunohistochemistry revealed an increase of VGLUT1 signal in cortex and caudate-putamen until 3 days of reperfusion followed by a reduction 7 days after the ischemic insult. By contrast, VGLUT2 and 3 were drastically reduced. Confocal microscopy revealed an increase in VGLUT2 and 3 immunolabelling in the reactive astrocytes of the ischemic corpus callosum and cortex. Changes in VGLUTs and EAATs expression were differently correlated to neurological deficits. Interestingly, changes in VGLUT1 and EAAT2 expression showed a significant positive correlation in caudate-putamen. Taken together, these results suggest a contribution of VGLUTs to glutamate release in these structures, which could promote neuroblast migration and neurogenesis during ischemic recovery, and a possible interplay with EAATs in the regulation of glutamate levels, at least in the first stages of ischemic recovery.

Neuroprotection by Phytoestrogens in the Model of Deprivation and Resupply of Oxygen and Glucose In Vitro: The Contribution of Autophagy and Related Signaling Mechanisms.

Phytoestrogens can have a neuroprotective effect towards ischemia-reperfusion-induced neuronal damage. However, their mechanism of action has not been well described. In this work, we investigate the type of neuronal cell death induced by oxygen and glucose deprivation (OGD) and resupply (OGDR) and pinpoint some of the signaling mechanisms whereby the neuroprotective effects of phytoestrogens occur in these conditions. First, we found that autophagy initiation affords neuronal protection upon neuronal damage induced by OGD and OGDR. The mammalian target of rapamycin/ribosomal S6 kinase (mTOR/S6K) pathway is blocked in these conditions, and we provide evidence that this is mediated by modulation of both the 5' AMP-activated protein kinase (AMPK) and phosphatidylinositol-3-kinase/protein kinase B (PI3K/AKT) pathways. These are dampened up or down, respectively, under OGDR-induced neuronal damage. In contrast, the MAPK-Erk kinase/extracellular signal-regulated kinase (MEK/ERK) pathway is increased under these conditions. Regarding the pathways affected by phytoestrogens, we show that their protective properties require autophagy initiation, but at later stages, they decrease mitogen-activated protein kinase (MAPK) and AMPK activation and increase mTOR/S6K activation. Collectively, our results put forward a novel mode of action where phytoestrogens play a dual role in the regulation of autophagy by acting as autophagy initiation enhancers when autophagy is a neuroprotective and pro-survival mechanism, and as autophagy initiation inhibitors when autophagy is a pro-death mechanism. Finally, our results support the therapeutic potential of phytoestrogens in brain ischemia by modulating autophagy.

A Signaling Crosstalk between BMP9 and HGF/c-Met Regulates Mouse Adult Liver Progenitor Cell Survival.

During chronic liver disease, hepatic progenitor cells (HPC, oval cells in rodents) become activated, proliferate, and differentiate into cholangiocytes and/or hepatocytes contributing to the final outcome of the regenerative process in a context-dependent fashion. Here, we analyze the crosstalk between the hepatocyte growth factor (HGF)/c-Met signaling axis, key for liver regeneration, and bone morphogenetic protein (BMP)9, a BMP family ligand that has emerged as a critical regulator of liver pathology. Our results show that HGF/c-Met signaling blocks BMP9-mediated apoptotic cell death, while it potentiates small mothers against decapentaplegic (SMAD)1 signaling triggered by BMP9 in oval cells. Interestingly, HGF-induced overactivation of SMAD1, -5, -8 requires the upregulation of TGF-ß type receptor activin receptor-like kinase (ALK)1, and both ALK1 and SMAD1 are required for the counteracting effect of HGF on BMP9 apoptotic activity. On the other hand, we also prove that BMP9 triggers the activation of p38MAPK in oval cells, which drives BMP9-apoptotic cell death. Therefore, our data support a model in which BMP9 and HGF/c-Met signaling axes establish a signaling crosstalk via ALK1 that modulates the balance between the two pathways with opposing activities, SMAD1 (pro-survival) and p38 mitogen-activated protein kinases (p38MAPK; pro-apoptotic), which determines oval cell fate. These data help delineate the complex signaling network established during chronic liver injury and its impact on the oval cell regenerative response.

Signaling mechanisms of interferon gamma induced apoptosis in chromaffin cells: involvement of nNOS, iNOS, and NFkappaB.

Previous work of our group stated that exogenously added and endogenous nitric oxide (NO) generated by cytokines induce apoptosis in chromaffin cells. In this work, we investigate the specific regulation of the NO synthase (NOS) isoforms, inducible NOS (iNOS) and neuronal NOS (nNOS), and their particular participation in cell death induced by interferon gamma (IFNgamma). Lipopolysaccharide (LPS) and IFNgamma increase iNOS expression, with no effect on nNOS expression. On the other hand, dexamethasone increases basal nNOS expression but decreases LPS + IFNgamma-induced iNOS expression. IFNgamma-induced cell death was abolished by W-1400, a specific iNOS inhibitor, but only partially by nNOS inhibitors [N-omega-propyl- L-arginine (N-PLA), 3-Bromo-7-nitroindazol (7-NI), L-methyl thiocitrulline and N-methyl L-arginine], indicating the main iNOS participation in chromaffin cell death. IFNgamma and LPS induce nuclear factor kappaB (NFkappaB) translocation to the nucleus, a process implicated in activation of iNOS expression, as inhibition of NFkappaB translocation, by SN50, decreased iNOS expression. In addition, IFNgamma and LPS induce (847)SernNOS phosphorylation, inhibiting nNOS activity. Both processes, nNOS phosphorylation and iNOS expression induced by LPS + IFNgamma, are regulated by Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway, as IFNgamma increases (727)STAT-3 phosphorylation and specific inhibitors of JAK/STAT pathway, such as AG490, inhibited both processes. Taken together, these results support the hypothesis of an inactivating phosphorylation of nNOS by IFNgamma, via JAK/STAT, in bovine chromaffin cells. Low NO concentrations achieved by this event, would activate NFkappaB translocation, increasing iNOS expression and generating, this last, high apoptotic NO concentrations.

Tetrahydroisoquinoline-Derived Urea and 2,5-Diketopiperazine Derivatives as Selective Antagonists of the Transient Receptor Potential Melastatin 8 (TRPM8) Channel Receptor and Antiprostate Cancer Agents.

Tetrahydroisoquinoline derivatives containing embedded urea functions were identified as selective TRPM8 channel receptor antagonists. Structure-activity relationships were investigated, with the following conclusions: (a) The urea function and the tetrahydroisoquinoline system are necessary for activity. (b) Bis(1-aryl-6,7dimethoxy-1,2,3,4-tetrahydroisoquinolyl)ureas are more active than compounds containing one tetrahydroisoquinoline ring and than an open phenetylamine ureide. (c) Trans compounds are more active than their cis isomers. (d) Aryl substituents are better than alkyls at the isoquinoline C-1 position. (e) Electron-withdrawing substituents lead to higher activities. The most potent compound is the 4-F derivative, with IC50 in the 10(-8) M range and selectivities around 1000:1 for most other TRP receptors. Selected compounds were found to be active in reducing the growth of LNCaP prostate cancer cells. TRPM8 inhibition reduces proliferation in the tumor cells tested but not in nontumor prostate cells, suggesting that the activity against prostate cancer is linked to TRPM8 inhibition.

BMP9 is a proliferative and survival factor for human hepatocellular carcinoma cells.

TGF-ß family members play a relevant role in tumorigenic processes, including hepatocellular carcinoma (HCC), but a specific implication of the Bone Morphogenetic Protein (BMP) subfamily is still unknown. Although originally isolated from fetal liver, little is known about BMP9, a BMP family member, and its role in liver physiology and pathology. Our results show that BMP9 promotes growth in HCC cells, but not in immortalized human hepatocytes. In the liver cancer cell line HepG2, BMP9 triggers Smad1,5,8 phosphorylation and inhibitor of DNA binding 1 (Id1) expression up- regulation. Importantly, by using chemical inhibitors, ligand trap and gene silencing approaches we demonstrate that HepG2 cells autocrinely produce BMP9 that supports their proliferation and anchorage independent growth. Additionally, our data reveal that in HepG2 cells BMP9 triggers cell cycle progression, and strikingly, completely abolishes the increase in the percentage of apoptotic cells induced by long-term incubation in low serum. Collectively, our data unveil a dual role for BMP9, both promoting a proliferative response and exerting a remarkable anti-apoptotic function in HepG2 cells, which result in a robust BMP9 effect on liver cancer cell growth. Finally, we show that BMP9 expression is increased in 40% of human HCC tissues compared with normal human liver as revealed by immunohistochemistry analysis, suggesting that BMP9 signaling may be relevant during hepatocarcinogenesis in vivo. Our findings provide new clues for a better understanding of BMPs contribution, and in particular BMP9, in HCC pathogenesis that may result in the development of effective and targeted therapeutic interventions.

Mouse hepatic oval cells require Met-dependent PI3K to impair TGF-ß-induced oxidative stress and apoptosis.

We have previously shown that oval cells harboring a genetically inactivated Met tyrosine kinase (Met(-/-) oval cells) are more sensitive to TGF-ß-induced apoptosis than cells expressing a functional Met (Met(flx/flx)), demonstrating that the HGF/Met axis plays a pivotal role in oval cell survival. Here, we have examined the mechanism behind this effect and have found that TGF-ß induced a mitochondria-dependent apoptotic cell death in Met(flx/flx) and Met(-/-) oval cells, associated with a marked increase in levels of the BH3-only proteins Bim and Bmf. Bmf plays a key role during TGF-ß-mediated apoptosis since knocking down of BMF significantly diminished the apoptotic response in Met(-/-) oval cells. TGF-ß also induced oxidative stress accompanied by NADPH oxidase 4 (Nox4) mRNA up-regulation and decreased protein levels of antioxidant enzymes. Antioxidants inhibit both TGF-ß-induced caspase 3 activity and Bmf up-regulation, revealing an oxidative stress-dependent Bmf regulation by TGF-ß. Notably, oxidative stress-related events were strongly amplified in Met(-/-) oval cells, emphasizing the critical role of Met in promoting survival. Pharmacological inhibition of PI3K did impair HGF-driven protection from TGF-ß-induced apoptosis and increased sensitivity of Met(flx/flx) oval cells to TGF-ß by enhancing oxidative stress, reaching apoptotic indices similar to those obtained in Met(-/-) oval cells. Interestingly, both PI3K inhibition and/or knockdown itself resulted in caspase-3 activation and loss of viability in Met(flx/flx) oval cells, whereas no effect was observed in Met(-/-) oval cells. Altogether, results presented here provide solid evidences that both paracrine and autocrine HGF/Met signaling requires PI3K to promote mouse hepatic oval cell survival against TGF-ß-induced oxidative stress and apoptosis.

Mechanisms of nitric oxide-induced apoptosis in bovine chromaffin cells: Role of mitochondria and apoptotic proteins.

The aim of this work was to establish the possible involvement of mitochondria in the apoptotic event triggered by nitric oxide (NO) in chromaffin cells. Using bovine chromaffin cells in primary culture and several NO donors (SNP, SNAP, and GSNO) at apoptotic concentrations (50 microM-1 mM), we have shown that NO induces a time-dependent decrease in the mitochondrial transmembrane potential (DeltaPsi(m)), which correlates with the appearance of hypodiploid cells. Disruption in DeltaPsi(m) is followed by cytochrome c release to the cytosol, which in turn precedes caspase 3 activation. In this mechanism participates the Bcl-2 protein family, because NO donors downregulate the expression of anti-apoptotic members of the family such as Bcl-2 and Bcl-XL, and increase the expression of pro-apoptotic members, Bax and Bcl-Xs, inductors of cytochrome c release to cytosol. Different cell signaling pathways seem to regulate Bax induction and Bcl-2 inhibition because decreased Bcl-2 levels are detected later than enhanced Bax expression. The tumour suppressor protein p53 is also upregulated in a very early phase (30 min) of the NO-induced apoptosis and may be responsible for the further induction of Bax expression. Finally, the translocation of NF-kappaB to the nucleus seems to be another early event in NO-induced apoptosis and it may be involved in the regulation of p53 expression. These results support strongly the participation of mitochondrial mechanisms in NO-induced apoptosis in chromaffin cells and suggest that these cells may be good models for the investigation of molecular basis of neurodegeneration and neuroprotection.