Exacerbated atherosclerosis in progeria is prevented by progerin elimination in vascular smooth muscle cells but not endothelial cells

Hutchinson-Gilford progeria syndrome (HGPS) is a rare disease caused by the expression of progerin, a mutant protein that accelerates aging and precipitates death. Given that atherosclerosis complications are the main cause of death in progeria, here, we investigated whether progerin-induced atherosclerosis is prevented in HGPSrev-Cdh5-CreERT2 and HGPSrev-SM22α-Cre mice with progerin suppression in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs), respectively. HGPSrev-Cdh5-CreERT2 mice were undistinguishable from HGPSrev mice with ubiquitous progerin expression, in contrast with the ameliorated progeroid phenotype of HGPSrev-SM22α-Cre mice. To study atherosclerosis, we generated atheroprone mouse models by overexpressing a PCSK9 gain-of-function mutant. While HGPSrev-Cdh5-CreERT2 and HGPSrev mice developed a similar level of excessive atherosclerosis, plaque development in HGPSrev-SM22α-Cre mice was reduced to wild-type levels. Our studies demonstrate that progerin suppression in VSMCs, but not in ECs, prevents exacerbated atherosclerosis in progeroid mice.

Coronary and carotid artery dysfunction and KV7 overexpression in a mouse model of Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is an extremely rare genetic disease caused by expression of progerin, a lamin A variant that is also expressed at low levels in non-HGPS individuals. Although HGPS patients die predominantly from myocardial infarction and stroke, the mechanisms that provoke pathological alterations in the coronary and cerebral arteries in HGPS remain ill defined. Here, we assessed vascular function in the coronary arteries (CorAs) and carotid arteries (CarAs) of progerin-expressing LmnaG609G/G609G mice (G609G), both in resting conditions and after hypoxic stimulus. Wire myography, pharmacological screening, and gene expression studies demonstrated vascular atony and stenosis, as well as other functional alterations in progeroid CorAs and CarAs and aorta. These defects were associated with loss of vascular smooth muscle cells and overexpression of the KV7 family of voltage-dependent potassium channels. Compared with wild-type controls, G609G mice showed reduced median survival upon chronic isoproterenol exposure, a baseline state of chronic cardiac hypoxia characterized by overexpression of hypoxia-inducible factor 1α and 3α genes, and increased cardiac vascularization. Our results shed light on the mechanisms underlying progerin-induced coronary and carotid artery disease and identify KV7 channels as a candidate target for the treatment of HGPS.

Retinal Pigment Epithelium-Secreted VEGF-A Induces Alpha-2-Macroglobulin Expression in Endothelial Cells

Alpha-2-macroglobulin (A2M) is a protease inhibitor that regulates extracellular matrix (ECM) stability and turnover. Here, we show that A2M is expressed by endothelial cells (ECs) from human eye choroid. We demonstrate that retinal pigment epithelium (RPE)-conditioned medium induces A2M expression specifically in ECs. Experiments using chemical inhibitors, blocking antibodies, and recombinant proteins revealed a key role of VEGF-A in RPE-mediated A2M induction in ECs. Furthermore, incubation of ECs with RPE-conditioned medium reduces matrix metalloproteinase-2 gelatinase activity of culture supernatants, which is partially restored after A2M knockdown in ECs. We propose that dysfunctional RPE or choroidal blood vessels, as observed in retinal diseases such as age-related macular degeneration, may disrupt the crosstalk mechanism we describe here leading to alterations in the homeostasis of choroidal ECM, Bruch's membrane and visual function.

Cardiovascular Progerin Suppression and Lamin A Restoration Rescue Hutchinson-Gilford Progeria Syndrome

BACKGROUND

Hutchinson-Gilford progeria syndrome (HGPS) is a rare disorder characterized by premature aging and death mainly because of myocardial infarction, stroke, or heart failure. The disease is provoked by progerin, a variant of lamin A expressed in most differentiated cells. Patients look healthy at birth, and symptoms typically emerge in the first or second year of life. Assessing the reversibility of progerin-induced damage and the relative contribution of specific cell types is critical to determining the potential benefits of late treatment and to developing new therapies.

METHODS

We used CRISPR-Cas9 technology to generate Lmna^{HGPSrev/HGPSrev} (HGPSrev) mice engineered to ubiquitously express progerin while lacking lamin A and allowing progerin suppression and lamin A restoration in a time- and cell type-specific manner on Cre recombinase activation. We characterized the phenotype of HGPSrev mice and crossed them with Cre transgenic lines to assess the effects of suppressing progerin and restoring lamin A ubiquitously at different disease stages as well as specifically in vascular smooth muscle cells and cardiomyocytes.

RESULTS

Like patients with HGPS, HGPSrev mice appear healthy at birth and progressively develop HGPS symptoms, including failure to thrive, lipodystrophy, vascular smooth muscle cell loss, vascular fibrosis, electrocardiographic anomalies, and precocious death (median lifespan of 15 months versus 26 months in wild-type controls, P<0.0001). Ubiquitous progerin suppression and lamin A restoration significantly extended lifespan when induced in 6-month-old mildly symptomatic mice and even in severely ill animals aged 13 months, although the benefit was much more pronounced on early intervention (84.5% lifespan extension in mildly symptomatic mice, P<0.0001, and 6.7% in severely ill mice, P<0.01). It is remarkable that major vascular alterations were prevented and lifespan normalized in HGPSrev mice when progerin suppression and lamin A restoration were restricted to vascular smooth muscle cells and cardiomyocytes.

CONCLUSIONS

HGPSrev mice constitute a new experimental model for advancing knowledge of HGPS. Our findings suggest that it is never too late to treat HGPS, although benefit is much more pronounced when progerin is targeted in mice with mild symptoms. Despite the broad expression pattern of progerin and its deleterious effects in many organs, restricting its suppression to vascular smooth muscle cells and cardiomyocytes is sufficient to prevent vascular disease and normalize lifespan.

Apical CLC-2 in retinal pigment epithelium is crucial for survival of the outer retina

Knockout of the chloride channel protein 2 (CLC‐2; CLCN2) results in fast progressing blindness in mice. Retinal Pigment Epithelium (RPE) and photoreceptors undergo, in parallel, rapid, and profound morphological changes and degeneration. Immunohistochemistry and electron microscopy of the outer retina and electroretinography of the CLC‐2 KO mouse demonstrated normal morphology at postnatal day 2, followed by drastic changes in RPE and photoreceptor morphology and loss of vision during the first postnatal month. To investigate whether the RPE or the photoreceptors are the primary cause of the degeneration, we injected lentiviruses carrying HA‐tagged CLC‐2 with an RPE‐specific promotor in the subretinal space of CLC‐2‐KO mice at the time of eye opening. As expected, CLC‐2‐HA was expressed exclusively in RPE; strikingly, this procedure rescued the degeneration of both RPE and photoreceptors. Light response in transduced eyes was also recovered. Only a fraction of RPE was transduced with the lentivirus; however, the entire RPE monolayer appears healthy, even the RPE cells not expressing the CLC‐2‐HA. Surprisingly, in contrast with previous physiological observations that postulate that CLC‐2 has a basolateral localization in RPE, our immunofluorescence experiments demonstrated CLC‐2 has an apical distribution, facing the subretinal space and the photoreceptor outer segments. Our findings suggest that CLC‐2 does not play the postulated role in fluid transport at the basolateral membrane. Rather, they suggest that CLC‐2 performs a critical homeostatic role in the subretinal compartment involving a chloride regulatory mechanism that is critical for the survival of both RPE and photoreceptors.

Single-cell profiling reveals an endothelium-mediated immunomodulatory pathway in the eye choroid

The activity and survival of retinal photoreceptors depend on support functions performed by the retinal pigment epithelium (RPE) and on oxygen and nutrients delivered by blood vessels in the underlying choroid. By combining single-cell and bulk RNA sequencing, we categorized mouse RPE/choroid cell types and characterized the tissue-specific transcriptomic features of choroidal endothelial cells. We found that choroidal endothelium adjacent to the RPE expresses high levels of Indian Hedgehog and identified its downstream target as stromal GLI1+ mesenchymal stem cell-like cells. In vivo genetic impairment of Hedgehog signaling induced significant loss of choroidal mast cells, as well as an altered inflammatory response and exacerbated visual function defects after retinal damage. Our studies reveal the cellular and molecular landscape of adult RPE/choroid and uncover a Hedgehog-regulated choroidal immunomodulatory signaling circuit. These results open new avenues for the study and treatment of retinal vascular diseases and choroid-related inflammatory blinding disorders.

Clathrin and clathrin adaptor AP-1 control apical trafficking of megalin in the biosynthetic and recycling routes

Megalin (gp330, LRP-2) is a protein structurally related to the low-density lipoprotein receptor family that displays a large luminal domain with multiligand binding properties. Megalin localizes to the apical surface of multiple epithelia, where it participates in endocytosis of a variety of ligands performing roles important for development or homeostasis. We recently described the apical recycling pathway of megalin in Madin–Darby canine kidney (MDCK) cells and found that it is a long-lived, fast recycling receptor with a recycling turnover of 15 min and a half-life of 4.8 h. Previous work implicated clathrin and clathrin adaptors in the polarized trafficking of fast recycling basolateral receptors. Hence, here we study the role of clathrin and clathrin adaptors in megalin’s apical localization and trafficking. Targeted silencing of clathrin or the γ1 subunit of clathrin adaptor AP-1 by RNA interference in MDCK cells disrupted apical localization of megalin, causing its redistribution to the basolateral membrane. In contrast, silencing of the γ2 subunit of AP-1 had no effect on megalin polarity. Trafficking assays we developed using FM4-HA-miniMegalin-GFP, a reversible conditional endoplasmic reticulum–retained chimera, revealed that clathrin and AP-1 silencing disrupted apical sorting of megalin in both biosynthetic and recycling routes. Our experiments demonstrate that clathrin and AP-1 control the sorting of an apical transmembrane protein.

Concerted regulation of retinal pigment epithelium basement membrane and barrier function by angiocrine factors

The outer blood-retina barrier is established through the coordinated terminal maturation of the retinal pigment epithelium (RPE), fenestrated choroid endothelial cells (ECs) and Bruch's membrane, a highly organized basement membrane that lies between both cell types. Here we study the contribution of choroid ECs to this process by comparing their gene expression profile before (P5) and after (P30) the critical postnatal period when mice acquire mature visual function. Transcriptome analyses show that expression of extracellular matrix-related genes changes dramatically over this period. Co-culture experiments support the existence of a novel regulatory pathway: ECs secrete factors that remodel RPE basement membrane, and integrin receptors sense these changes triggering Rho GTPase signals that modulate RPE tight junctions and enhance RPE barrier function. We anticipate our results will spawn a search for additional roles of choroid ECs in RPE physiology and disease.

Directional Fluid Transport across Organ-Blood Barriers: Physiology and Cell Biology

Directional fluid flow is an essential process for embryo development as well as for organ and organism homeostasis. Here, we review the diverse structure of various organ-blood barriers, the driving forces, transporters, and polarity mechanisms that regulate fluid transport across them, focusing on kidney-, eye-, and brain-blood barriers. We end by discussing how cross talk between barrier epithelial and endothelial cells, perivascular cells, and basement membrane signaling contribute to generate and maintain organ-blood barriers.

Caveolin-1 deficiency induces a MEK-ERK1/2-Snail-1-dependent epithelial-mesenchymal transition and fibrosis during peritoneal dialysis

Peritoneal dialysis (PD) is a form of renal replacement therapy whose repeated use can alter dialytic function through induction of epithelial–mesenchymal transition (EMT) and fibrosis, eventually leading to PD discontinuation. The peritoneum from Cav1^−/− mice showed increased EMT, thickness, and fibrosis. Exposure of Cav1^−/− mice to PD fluids further increased peritoneal membrane thickness, altered permeability, and increased the number of FSP-1/cytokeratin-positive cells invading the sub-mesothelial stroma. High-throughput quantitative proteomics revealed increased abundance of collagens, FN, and laminin, as well as proteins related to TGF-β activity in matrices derived from Cav1^−/− cells. Lack of Cav1 was associated with hyperactivation of a MEK-ERK1/2-Snail-1 pathway that regulated the Smad2-3/Smad1-5-8 balance. Pharmacological blockade of MEK rescued E-cadherin and ZO-1 inter-cellular junction localization, reduced fibrosis, and restored peritoneal function in Cav1^−/− mice. Moreover, treatment of human PD-patient-derived MCs with drugs increasing Cav1 levels, as well as ectopic Cav1 expression, induced re-acquisition of epithelial features. This study demonstrates a pivotal role of Cav1 in the balance of epithelial versus mesenchymal state and suggests targets for the prevention of fibrosis during PD.

Basolateral sorting of chloride channel 2 is mediated by interactions between a dileucine motif and the clathrin adaptor AP-1

ClC-2 is a ubiquitous chloride channel that regulates cell volume, ion transport, and acid-base balance. Mice knocked out for ClC-2 are blind and sterile. Basolateral localization of ClC-2 in epithelia is mediated by the interaction of a dileucine motif with a highly conserved pocket in the γ1-σ1A hemicomplex of AP-1.

In spite of the many key cellular functions of chloride channels, the mechanisms that mediate their subcellular localization are largely unknown. ClC-2 is a ubiquitous chloride channel usually localized to the basolateral domain of epithelia that regulates cell volume, ion transport, and acid–base balance; mice knocked out for ClC-2 are blind and sterile. Previous work suggested that CLC-2 is sorted basolaterally by TIFS⁸¹²LL, a dileucine motif in CLC-2's C-terminal domain. However, our in silico modeling of ClC-2 suggested that this motif was buried within the channel's dimerization interface and identified two cytoplasmically exposed dileucine motifs, ESMI⁶²³LL and QVVA⁶³⁵LL, as candidate sorting signals. Alanine mutagenesis and trafficking assays support a scenario in which ESMI⁶²³LL acts as the authentic basolateral signal of ClC-2. Silencing experiments and yeast three-hybrid assays demonstrated that both ubiquitous (AP-1A) and epithelium-specific (AP-1B) forms of the tetrameric clathrin adaptor AP-1 are capable of carrying out basolateral sorting of ClC-2 through interactions of ESMI⁶²³LL with a highly conserved pocket in their γ1-σ1A hemicomplex.

Plasma membrane protein polarity and trafficking in RPE cells: past, present and future

The retinal pigment epithelium (RPE) comprises a monolayer of polarized pigmented epithelial cells that is strategically interposed between the neural retina and the fenestrated choroid capillaries. The RPE performs a variety of vectorial transport functions (water, ions, metabolites, nutrients and waste products) that regulate the composition of the subretinal space and support the functions of photoreceptors (PRs) and other cells in the neural retina. To this end, RPE cells display a polarized distribution of channels, transporters and receptors in their plasma membrane (PM) that is remarkably different from that found in conventional extra-ocular epithelia, e.g. intestine, kidney, and gall bladder. This characteristic PM protein polarity of RPE cells depends on the interplay of sorting signals in the RPE PM proteins and sorting mechanisms and biosynthetic/recycling trafficking routes in the RPE cell. Although considerable progress has been made in our understanding of the RPE trafficking machinery, most available data have been obtained from immortalized RPE cell lines that only partially maintain the RPE phenotype and by extrapolation of data obtained in the prototype Madin-Darby Canine Kidney (MDCK) cell line. The increasing availability of RPE cell cultures that more closely resemble the RPE in vivo together with the advent of advanced live imaging microscopy techniques provides a platform and an opportunity to rapidly expand our understanding of how polarized protein trafficking contributes to RPE PM polarity.

Galectin-4-mediated transcytosis of transferrin receptor

Some native epithelia, for example, retinal pigment epithelium (RPE) and kidney proximal tubule (KPT), constitutively lack the basolateral sorting adaptor AP-1B; this results in many basolateral plasma membrane proteins being repositioned to the apical domain, where they perform essential functions for their host organs. We recently reported the underlying apical polarity reversal mechanism: in the absence of AP-1B-mediated basolateral sorting, basolateral proteins are shuttled to the apical plasma membrane through a transcytotic pathway mediated by the plus-end kinesin KIF16B. Here, we demonstrate that this apical transcytotic pathway requires apical sorting of basolateral proteins, which is mediated by apical signals and galectin-4. Using RPE and KPT cell lines, and AP-1B-knockdown MDCK cells, we show that mutation of the N-glycan linked to N727 in the basolateral marker transferrin receptor (TfR) or knockdown of galectin-4 inhibits TfR transcytosis to apical recycling endosomes and the apical plasma membrane, and promotes TfR lysosomal targeting and subsequent degradation. Our results report a new role of galectins in basolateral to apical epithelial transcytosis.

Liver X receptor α-mediated regulation of lipogenesis by core and NS5A proteins contributes to HCV-induced liver steatosis and HCV replication

Molecular mechanisms contributing to hepatitis C virus (HCV)-associated steatosis are not well established, although HCV gene expression has been shown to alter host cell cholesterol/lipid metabolism. As liver X receptors (LXRs) play a role as key modulators of metabolism signaling in the development of steatosis, we aimed to investigate in an HCV in vitro model the effect of HCV NS5A protein, core protein, and viral replication on the intracellular lipid accumulation and the LXRα-regulated expression of lipogenic genes. The effects of LXRα siRNA or agonist GW3965 treatment on lipogenesis and HCV replication capacity in our HCV replicon system were also examined. NS5A- and core-expressing cells and replicon-containing cells exhibited an increase of lipid accumulation by inducing the gene expression and the transcriptional activity of LXRα, and leading to an increased expression of its lipogenic target genes sterol regulatory element binding protein-1c, peroxisome proliferator-activated receptor-γ, and fatty acid synthase. Transcriptional induction by NS5A protein, core protein, and viral replication occurred via LXR response element activation in the lipogenic gene promoter. No physical association between HCV proteins and LXRα was observed, whereas NS5A and core proteins indirectly upregulated LXRα through the phosphatidylinositol 3-kinase pathway. Finally, it was found that LXRα knockdown or agonist-mediated LXRα induction directly regulated HCV-induced lipogenesis and HCV replication efficiency in replicon-containing cells. Combined, our data suggest that LXRα-mediated regulation of lipogenesis by core and NS5A proteins may contribute to HCV-induced liver steatosis and to the efficient replication of HCV.

Interplay among cellular polarization, lipoprotein metabolism and hepatitis C virus entry

Hepatitis C virus (HCV) infects more than three million new individuals worldwide each year. In a high percentage of patients, acute infections become chronic, eventually progressing to fibrosis, cirrhosis, and hepatocellular carcinoma. Given the lack of effective prophylactic or therapeutic vaccines, and the limited sustained virological response rates to current therapies, new approaches are needed to prevent, control, and clear HCV infection. Entry into the host cell, being the first step of the viral cycle, is a potential target for the design of new antiviral compounds. Despite the recent discovery of the tight junction-associated proteins claudin-1 and occludin as HCV co-receptors, which is an important step towards the understanding of HCV entry, the precise mechanisms are still largely unknown. In addition, increasing evidence indicates that tools that are broadly employed to study HCV infection do not accurately reflect the real process in terms of viral particle composition and host cell phenotype. Thus, systems that more closely mimic natural infection are urgently required to elucidate the mechanisms of HCV entry, which will in turn help to design antiviral strategies against this part of the infection process.

p38 maintains E-cadherin expression by modulating TAK1-NF-kappa B during epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT) of peritoneal mesothelial cells is a pathological process that occurs during peritoneal dialysis. EMT leads to peritoneal fibrosis, ultrafiltration failure and eventually to the discontinuation of therapy. Signaling pathways involved in mesothelial EMT are thus of great interest, but are mostly unknown. We used primary mesothelial cells from human omentum to analyze the role of the p38 MAPK signaling pathway in the induction of EMT. The use of specific inhibitors, a dominant-negative p38 mutant and lentiviral silencing of p38α demonstrated that p38 promotes E-cadherin expression both in untreated cells and in cells co-stimulated with the EMT-inducing stimuli transforming growth factor (TGF)-β1 and interleukin (IL)-1β. p38 inhibition also led to disorganization and downregulation of cytokeratin filaments and zonula occludens (ZO)-1, whereas expression of vimentin was increased. Analysis of transcription factors that repress E-cadherin expression showed that p38 blockade inhibited expression of Snail1 while increasing expression of Twist. Nuclear translocation and transcriptional activity of p65 NF-κB, an important inducer of EMT, was increased by p38 inhibition. Moreover, p38 inhibition increased the phosphorylation of TGF-β-activated kinase 1 (TAK1), NF-κB and IκBα. The effect of p38 inhibition on E-cadherin expression was rescued by modulating the TAK1-NF-κB pathway. Our results demonstrate that p38 maintains E-cadherin expression by suppressing TAK1-NF-κB signaling, thus impeding the induction of EMT in human primary mesothelial cells. This represents a novel role of p38 as a brake or 'gatekeeper' of EMT induction by maintaining E-cadherin levels.

Expression of pituitary tumor-transforming gene 1 (PTTG1)/securin in hepatitis B virus (HBV)-associated liver diseases: evidence for an HBV X protein-mediated inhibition of PTTG1 ubiquitination and degradation

Chronic infection with hepatitis B virus (HBV) is strongly associated with hepatocellular carcinoma (HCC), and the viral HBx protein plays a crucial role in the pathogenesis of liver tumors. Because the protooncogene pituitary tumor-transforming gene 1 (PTTG1) is overexpressed in HCC, we investigated the regulation of this protein by HBx. We analyzed PTTG1 expression levels in liver biopsies from patients chronically infected with HBV, presenting different disease stages, and from HBx transgenic mice. PTTG1 was undetectable in biopsies from chronic hepatitis B patients or from normal mouse livers. In contrast, hyperplastic livers from transgenic mice and biopsies from patients with cirrhosis, presented PTTG1 expression which was found mainly in HBx-expressing hepatocytes. PTTG1 staining was further increased in HCC specimens. Experiments in vitro revealed that HBx induced a marked accumulation of PTTG1 protein without affecting its messenger RNA levels. HBx expression promoted the inhibition of PTTG1 ubiquitination, which in turn impaired its degradation by the proteasome. Glutathione S-transferase pull-down and co-immunoprecipitation experiments demonstrated that the interaction between PTTG1 and the Skp1-Cul1-F-box ubiquitin ligase complex (SCF) was partially disrupted, possibly through a mechanism involving protein-protein interactions of HBx with PTTG1 and/or SCF. Furthermore, confocal analysis revealed that HBx colocalized with PTTG1 and Cul1. We propose that HBx promotes an abnormal accumulation of PTTG1, which may provide new insights into the molecular mechanisms of HBV-related pathogenesis of progressive liver disease leading to HCC development.

Increased circulating pro-inflammatory cytokines and Th17 lymphocytes in Hashimoto's thyroiditis

CONTEXT

Th17 lymphocytes play an important role in different chronic inflammatory and autoimmune conditions.

AIM

The aim of the study was to explore the status of Th17 cells in patients with autoimmune thyroid diseases (AITD).

DESIGN

We assessed the serum levels and in vitro synthesis of IL-17 and IL-22 and of different cytokines (IL-6, IL-15, and IL-23) involved in the differentiation of Th17 cells in the peripheral blood and thyroid glands of 26 patients with AITD, eight with Graves' disease, and 18 with Hashimoto's thyroiditis (HT) as well as 10 healthy controls.

RESULTS

We found enhanced levels of T cells synthesizing IL-17 and IL-22 in the peripheral blood from AITD patients, mainly in those with HT. In addition, a stronger expression of IL-17 and IL-22 and an enhanced number of IL-23R(+) cells was detected in thyroid glands from HT patients compared with Graves' disease or controls. Furthermore, increased concentrations of IL-6 and IL-15 were detected in sera from HT patients, whereas serum levels of IL-23 tended to be higher in these patients. Finally, an enhanced in vitro differentiation of T lymphocytes into Th17 cells induced by IL-23/IL-6 was observed in AITD patients. Accordingly, a strong induction of RORC2 gene was detected in lymphocytes from HT patients when stimulated with IL-23.

CONCLUSION

Our results indicate that there is an increased differentiation of Th17 lymphocytes and an enhanced synthesis of Th17 cytokines in AITD, mainly in HT. These phenomena may have an important role in the pathogenesis of thyroid autoimmunity.

Hepatitis C virus NS5A and core proteins induce oxidative stress-mediated calcium signalling alterations in hepatocytes

BACKGROUND/AIMS

The hepatitis C virus (HCV) structural core and non-structural NS5A proteins induce in liver cells a series of intracellular events, including elevation of reactive oxygen and nitrogen species (ROS/RNS). Since oxidative stress is associated to altered intracellular Ca(2+) homeostasis, we aimed to investigate the effect of these proteins on Ca(2+) mobilization in human hepatocyte-derived transfected cells, and the protective effect of quercetin treatment.

METHODS

Ca(2+) mobilization and actin reorganization were determined by spectrofluorimetry. Production of ROS/RNS was determined by flow cytometry.

RESULTS

Cells transfected with NS5A and core proteins showed enhanced ROS/RNS production and resting cytosolic Ca(2+) concentration, and reduced Ca(2+) concentration into the stores. Phenylephrine-evoked Ca(2+) release, Ca(2+) entry and extrusion by the plasma membrane Ca(2+)-ATPase were significantly reduced in transfected cells. Similar effects were observed in cytokine-activated cells. Phenylephrine-evoked actin reorganization was reduced in the presence of core and NS5A proteins. These effects were significantly prevented by quercetin. Altered Ca(2+) mobilization and increased calpain activation were observed in replicon-containing cells.

CONCLUSIONS

NS5A and core proteins induce oxidative stress-mediated Ca(2+) homeostasis alterations in human hepatocyte-derived cells, which might underlie the effects of both proteins in the pathogenesis of liver disorders associated to HCV infection.

Epithelial-to-mesenchymal transition of peritoneal mesothelial cells is regulated by an ERK/NF-kappaB/Snail1 pathway

Epithelial-to-mesenchymal transition (EMT) occurs in fibrotic diseases affecting the kidney, liver and lung, and in the peritoneum of patients undergoing peritoneal dialysis. EMT in the peritoneum is linked to peritoneal membrane dysfunction, and its establishment limits the effectiveness of peritoneal dialysis. The molecular regulation of EMT in the peritoneum is thus of interest from basic and clinical perspectives. Treatment of primary human mesothelial cells (MCs) with effluent from patients undergoing peritoneal dialysis induced a genuine EMT, characterized by downregulated E-cadherin and cytokeratin expression, cell scattering, and spindle-like morphology. This EMT was replicated by co-stimulation with transforming growth factor (TGF)-beta1 and interleukin (IL)-1beta. Retroviral overexpression of a mutant inhibitor of kappaB (IkappaB) demonstrated that NF-kappaB activation is required for E-cadherin and cytokeratin downregulation during EMT. Pre-treatment with the MAP kinase kinase (MEK)-1/2 inhibitor U0126 showed that cytokine-triggered NF-kappaB nuclear translocation and transcriptional activity are mediated by activation of extracellular regulated kinase (ERK). Cytokine-mediated induction of mRNA expression of the transcription factor Snail1, a repressor of E-cadherin expression and a potent inducer of EMT, was prevented by blockade of ERK or NF-kappaB. Finally, blockade of ERK/NF-kappaB signaling in ex vivo MCs that were cultured from peritoneal dialysis effluents reverted cells to an epithelioid morphology, upregulated E-cadherin and cytokeratin expression, and downregulated Snail1 expression. Modulation of the ERK/NF-kappaB/Snail1 pathway may provide a means of counteracting the progressive structural and functional deterioration of the peritoneal membrane during peritoneal dialysis.

Hepatitis C virus envelope components alter localization of hepatocyte tight junction-associated proteins and promote occludin retention in the endoplasmic reticulum

Hepatocyte tight junctions (TJ) play key roles in characteristic liver functions, including bile formation and secretion. Infection by hepatitis C virus (HCV) may cause alterations of the liver architecture and disruption of the bile duct, which ultimately can lead to cholestasis. Herein, we employed the HCV replicon system to analyze the effect of HCV on TJ organization. TJ-associated proteins occludin, claudin-1, and Zonula Occludens protein-1 (ZO-1) disappeared from their normal localization at the border of adjacent cells in Huh7 clones harboring genomic but not subgenomic replicons expressing only the nonstructural proteins. Furthermore, cells containing genomic replicons showed a cytoplasmic accumulation of occludin in the endoplasmic reticulum (ER). TJ-associated function, measured as FITC-dextran paracellular permeability, of genomic replicon-containing cells, was also altered. Interestingly, clearance of the HCV replicon by interferon-alpha (IFN-alpha) treatment and by short hairpin RNA (shRNA) significantly restored the localization of TJ-associated proteins. Transient expression of all HCV structural proteins, but not core protein alone, altered the localization of TJ-associated proteins in Huh7 cells and in clones with subgenomic replicons. Confocal analysis showed that accumulation of occludin in the ER partially co-localized with HCV envelope glycoprotein E2. E2/occludin association was further confirmed by co-immunoprecipitation and pull-down assays. Additionally, using a cell culture model of HCV infection, we observed the cytoplasmic dot-like accumulation of occludin in infected Huh7 cells.

CONCLUSION

We propose that HCV structural proteins, most likely those of the viral envelope, promote alterations of TJ-associated proteins, which may provide new insights for HCV-related pathogenesis.

AM3, a natural glycoconjugate, induces the functional maturation of human dendritic cells

BACKGROUND AND PURPOSE

Dendritic cells (DCs) are dedicated antigen-presenting cells able to initiate specific immune responses and their maturation is critical for the induction of antigen-specific T-lymphocyte responses. Here, we have investigated the effects of Inmunoferon-active principle (AM3), the active agent of a commercial immunomodulatory drug, on human monocyte-derived DCs (MDDCs).

EXPERIMENTAL APPROACH

MDDCs derived from healthy and hepatitis C virus (HCV)-infected patients were stimulated with AM3. We analysed the expression of cell surface proteins by flow cytometry, that of cytokine production by ELISA, and the expression of chemokines and chemokine receptors by RNase protection assays. T-lymphocyte proliferation was assessed in mixed lymphocyte reactions, protein expression by western blot and luciferase-based reporter methods, and Toll-like receptor (TLR)-blocking antibodies were employed to analyse TLR activity.

KEY RESULTS

In MDDCs, AM3 induced or enhanced expression of CD54, CD83, CD86, HLA-DR, chemokines and chemokine receptors, interleukin (IL)-12p70 and IL-10. Furthermore, AM3 stimulated MDDCs to increase proliferation of allogenic T cells. AM3 triggered nuclear translocation of NF-kappaB and phosphorylation of p38 mitogen-activated protein kinase. AM3 promoted NF-kappaB activation in a TLR-4-dependent manner, and blocking TLR-4 activity attenuated the enhanced expression of CD80, CD83 and CD86 induced by AM3. AM3 enhanced the expression of maturation-associated markers in MDDCs from HCV-infected patients and increased the proliferation of T lymphocytes induced by these MDDCs.

CONCLUSIONS AND IMPLICATIONS

These results underline the effects of AM3 in promoting maturation of MDDCs and suggest that AM3 might be useful in regulating immune responses in pathophysiological situations requiring DC maturation.

A Polypodium leucotomos extract inhibits solar-simulated radiation-induced TNF-alpha and iNOS expression, transcriptional activation and apoptosis

In this report, we have examined the molecular basis of the photoprotective effect of a hydrophilic extract of the fern Polypodium leucotomos (PL) in vitro, using a solar simulator as the source of UV radiation (SSR). We found that pretreatment of human keratinocytes with PL inhibited SSR-mediated increase of tumor necrosis factor (TNF)-alpha and also abrogated nitric oxide (NO) production. Consistent with this, PL blocked the induction of inducible nitric oxide synthase (iNOS) elicited by SSR. In addition, PL inhibited the SSR-mediated transcriptional activation of NF-kappaB and AP1. Finally, we demonstrated that pretreatment with PL exerted a cytoprotective effect against SSR-induced damage, resulting in increased cell survival. Together, these data postulate a multifactor mechanism of protection not exclusively reliant on the antioxidant capability of PL, and strengthen the basic knowledge on the photoprotective effect of this botanical agent.

Hepatitis C virus core protein regulates p300/CBP co-activation function. Possible role in the regulation of NF-AT1 transcriptional activity

Hepatitis C virus (HCV) core is a viral structural protein; it also participates in some cellular processes, including transcriptional regulation. However, the mechanisms of core-mediated transcriptional regulation remain poorly understood. Oncogenic virus proteins often target p300/CBP, a known co-activator of a wide variety of transcription factors, to regulate the expression of cellular and viral genes. Here we demonstrate, for the first time, that HCV core protein interacts with p300/CBP and enhances both its acetyl-transferase and transcriptional activities. In addition, we demonstrate that nuclear core protein activates the NH2-terminal transcription activation domain (TAD) of NF-AT1 in a p300/CBP-dependent manner. We propose a model in which core protein regulates the co-activation function of p300/CBP and activates NF-AT1, and probably other p300/CBP-regulated transcription factors, by a novel mechanism involving the regulation of the acetylation state of histones and/or components of the transcriptional machinery.

Increased intrahepatic cyclooxygenase 2, matrix metalloproteinase 2, and matrix metalloproteinase 9 expression is associated with progressive liver disease in chronic hepatitis C virus infection: role of viral core and NS5A proteins

BACKGROUND

Cyclooxygenase 2 (COX-2) and matrix metalloproteinases (MMPs) have been implicated in tissue injury and fibrogenesis in animal models but little is known regarding their role in hepatitis C virus (HCV) related liver disease in humans.

AIMS

To characterise the intrahepatic expression pattern of COX-2 and MMPs in chronic HCV infection and determine whether HCV core and NS5A proteins could promote their expression in cultured hepatocyte derived cell lines.

PATIENTS

Thirty two anti-HCV+ and 10 anti-HCV- patients were studied.

METHODS

Western blot, reverse transcription-polymerase chain reaction (RT-PCR), enzyme immunoassay, and immunohistochemistry were used to assess the expression pattern of COX-2 and MMPs in liver biopsy samples from all patients. COX-2 gene expression and MMP-9 protein levels were also determined by immunoblot, RT-PCR, and luciferase assays in core and NS5A transfected hepatocyte derived cells.

RESULTS

The intrahepatic expression level of COX-2, MMP-2, and MMP-9 was significantly higher in HCV+ than in HCV- patients, increasing with the fibrotic stage of liver disease. We further demonstrated that COX-2 mRNA, protein, and activity were induced in resting and activated core and NS5A transfectants. Both viral proteins induced transcriptional activity of the COX-2 gene promoter whereas core, but not NS5A, exerted an inducer effect on MMP-9 protein levels in cultured hepatocyte derived cells.

CONCLUSIONS

Intrahepatic COX-2, MMP-2, and MMP-9 overexpression is associated with progressive hepatic fibrosis in chronic HCV infection, suggesting their pathogenic role in fibrogenesis. HCV core and NS5A proteins were able to upregulate COX-2 and MMP-9 gene expression in hepatocyte derived cells, providing a potential mechanism for hepatic fibrosis during chronic HCV infection.

The hepatitis B virus X protein binds to and activates the NH(2)-terminal trans-activation domain of nuclear factor of activated T cells-1

We have previously reported that the hepatitis B virus X protein (HBx) activates nuclear factor of activated T cells (NF-AT), a key regulator of the immune system, by a calcium/calcineurin-dependent pathway, involving dephosphorylation and nuclear translocation of this transcription factor. In addition, we showed that HBx synergizes with potent calcium-mobilizing stimuli to activate NF-AT-dependent transcription, suggesting that additional mechanisms might also be operative in the activation of NF-AT by HBx. Here we demonstrate that HBx activates the NH(2)-terminal transcription activation domain (TAD) of NF-AT1 by a mechanism involving protein-protein interaction. Targeting of HBx to the nucleus did not affect its ability to induce the transcriptional activity of NF-AT1. In contrast, mutations of HBx affecting its functional interaction with general transcription factors abrogated the HBx-induced activity of NF-AT1. Together these results indicate that HBx may exert its function by acting as a nuclear coactivator of NF-AT1.