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GH pathway has been shown to play a major role in liver regeneration through the control of epidermal growth factor receptor (EGFR) activation. This pathway is down-regulated in nonalcoholic fatty liver disease. Because regeneration is known to be impaired in fatty livers, we wondered whether a deregulation of the GH/EGFR pathway could explain this deficiency. Hepatic EGFR expression and triglyceride levels were quantified in liver biopsies of 32 obese patients with different degrees of steatosis. We showed a significant inverse correlation between liver EGFR expression and the level of hepatic steatosis. GH/EGFR down-regulation was also demonstrated in 2 steatosis mouse models, a genetic (ob/ob) and a methionine and choline-deficient diet mouse model, in correlation with liver regeneration defect. ob/ob mice exhibited a more severe liver regeneration defect after partial hepatectomy (PH) than methionine and choline-deficient diet-fed mice, a difference that could be explained by a decrease in signal transducer and activator of transcription 3 phosphorylation 32 hours after PH. Having checked that GH deficiency accounted for the GH signaling pathway down-regulation in the liver of ob/ob mice, we showed that GH administration in these mice led to a partial rescue in hepatocyte proliferation after PH associated with a concomitant restoration of liver EGFR expression and signal transducer and activator of trnascription 3 activation. In conclusion, we propose that the GH/EGFR pathway down-regulation is a general mechanism responsible for liver regeneration deficiency associated with steatosis, which could be partially rescued by GH administration.

Since many years, Wnt canonical pathway was known to be involved in proliferation and cell fate. More recently, Hippo pathway has been recognized as a major actor in the control of organ size homeostasis. Both pathways are induced in the activation of stem cells, modulated during carcinogenesis and both use a second messenger, a cascade of phosphorylations and the same ubiquitin ligase degradation complex. Enough for their roads to cross! This review highlights the recent advances in the understanding of the complex crosstalks between Wnt/β-catenin and Hippo/YAP pathways, focusing on two tissues, liver and intestine. In the future, we hope that the identification of the molecular mechanisms underlining these entangled relationships will open towards novel therapeutic strategies for digestive carcinogenesis., (© 2013 médecine/sciences – Inserm.)

Intrahepatic malignant tumours include hepatocellular carcinomas (HCC), cholangiocarcinomas (CC) and combined hepatocholangiocarcinomas (cHCC-CC), a group of rare and poorly characterized tumours that exhibit both biliary and hepatocytic differentiation. The aim of the study was to characterize the molecular pathways specifically associated with cHCC-CC pathogenesis. We performed a genome-wide transcriptional analysis of 20 histologically defined cHCC-CC and compared them with a series of typical HCC and of CC. Data were analysed by gene set enrichment and integrative genomics and results were further validated in situ by tissue microarray using an independent series of 152 tumours. We report that cHCC-CC exhibit stem/progenitor features, a down-regulation of the hepatocyte differentiation program and a commitment to the biliary lineage. TGFβ and Wnt/β-catenin were identified as the two major signalling pathways activated in cHCC-CC. A β-catenin signature distinct from that observed in well-differentiated HCC with mutant β-catenin was found in cHCC-CC. This signature was associated with microenvironment remodelling and TGFβ activation. Furthermore, integrative genomics revealed that cHCC-CC share characteristics of poorly differentiated HCC with stem cell traits and poor prognosis. The common traits displayed by CC, cHCC-CC and some HCC suggest that these tumours could originate from stem/progenitor cell(s) and raised the hypothesis of a potential continuum between intrahepatic CC, cHCC-CC and poorly differentiated HCC.

Unraveling the molecular clues of liver proliferation has become conceivable thanks to the model of two-third hepatectomy. The synchronicity and the well-scheduled aspect of this process allow scientists to slowly decipher this mystery. During this phenomenon, quiescent hepatocytes of the remnant lobes are able to reenter into the cell cycle initiating the G1-S progression synchronously before completing the cell cycle. The major role played by this step of the cell cycle has been emphasized by loss-of-function studies showing a delay or a lack of coordination in the hepatocytes G1-S progression. Two growth factor receptors, c-Met and EGFR, tightly drive this transition. Due to the level of complexity surrounding EGFR signaling, involving numerous ligands, highly controlled regulations and multiple downstream pathways, we chose to focus on the EGFR pathway for this paper. We will first describe the EGFR pathway in its integrity and then address its essential role in the G1/S phase transition for hepatocyte proliferation. Recently, other levels of control have been discovered to monitor this pathway, which will lead us to discuss regulations of the EGFR pathway and highlight the potential effect of misregulations in pathologies.

It has been suggested that increasing age is correlated with an acceleration of the progression of liver fibrosis induced by various agents, such as hepatitis C virus or chronic alcohol consumption. However, the cellular and molecular changes underlying this predisposition are not entirely understood. In the context of an aging population, it becomes challenging to decipher the mechanisms responsible for this higher susceptibility of older individuals to this acquired liver disorder. To address this issue, we induced liver fibrosis by carbon tetrachloride (CCl(4)) chronic administration to 8-week- and 15-month-old mice. We confirmed that susceptibility to fibrosis development increased with age and showed that aging did not affect fibrosis resolution capacity. We then focused on the impairment of hepatocyte proliferation, oxidative stress, and inflammation as potential mechanisms accelerating the development of fibrosis in the elderly. We detected no inhibition of hepatocyte proliferation after CCl(4) injury in 15-month-old mice, whereas it was inhibited after a partial hepatectomy. Finally, we observed that, in a context in which liver oxidative stress was not differentially increased in both experimental groups, there was a higher recruitment of inflammatory cells, including mostly macrophages and lymphocytes, oriented toward a T helper 2 (T(H)2) response in older mice. Our data show that in conditions of equivalent levels of oxidative stress and maintained hepatocyte proliferative capacity, an increased inflammatory reaction mainly composed of CD4(+) lymphocytes and macrophages expressing T(H)2 cytokines is the main factor involved in the higher susceptibility to fibrosis with increasing age.

GH is a pleiotropic hormone that plays a major role in proliferation, differentiation, and metabolism via its specific receptor. It has been previously suggested that GH signaling pathways are required for normal liver regeneration but the molecular mechanisms involved have yet to be determined. The aim of this study was to identify the mechanisms by which GH controls liver regeneration. We performed two thirds partial hepatectomies in GH receptor (GHR)-deficient mice and wild-type littermates and showed a blunted progression in the G(1)/S transition phase of the mutant hepatocytes. This impaired liver regeneration was not corrected by reestablishing IGF-1 expression. Although the initial response to partial hepatectomy at the priming phase appeared to be similar between mutant and wild-type mice, cell cycle progression was significantly blunted in mutant mice. The main defect in GHR-deficient mice was the deficiency of the epidermal growth factor receptor activation during the process of liver regeneration. Finally, among the pathways activated downstream of GHR during G(1) phase progression, namely Erk1/2, Akt, and signal transducer and activator of transcription 3, we only found a reduced Erk1/2 phosphorylation in mutant mice. In conclusion, our results demonstrate that GH signaling plays a major role in liver regeneration and strongly suggest that it acts through the activation of both epidermal growth factor receptor and Erk1/2 pathways.

Aim: To develop and validate a transient micro-elastography device to measure liver stiffness (LS) in mice., Methods: A novel transient micro-elastography (TME) device, dedicated to LS measurements in mice with a range of measurement from 1-170 kPa, was developed using an optimized vibration frequency of 300 Hz and a 2 mm piston. The novel probe was validated in a classical fibrosis model (CCl(4)) and in a transgenic murine model of systemic amyloidosis., Results: TME could be successfully performed in control mice below the xiphoid cartilage, with a mean LS of 4.4 ± 1.3 kPa, a mean success rate of 88%, and an excellent intra-observer agreement (0.98). Treatment with CCl(4) over seven weeks drastically increased LS as compared to controls (18.2 ± 3.7 kPa vs 3.6 ± 1.2 kPa). Moreover, fibrosis stage was highly correlated with LS (Spearman coefficient = 0.88, P < 0.01). In the amyloidosis model, much higher LS values were obtained, reaching maximum values of > 150 kPa. LS significantly correlated with the amyloidosis index (0.93, P < 0.0001) and the plasma concentration of mutant hapoA-II (0.62, P < 0.005)., Conclusion: Here, we have established the first non-invasive approach to measure LS in mice, and have successfully validated it in two murine models of high LS.

The role of hepatocyte apoptosis in the physiopathology of obstructive cholestasis is still controversial. Although some data have strongly suggested that hepatocellular cholestatic injury is due to Fas-mediated hepatocyte apoptosis, some others concluded that necrosis, rather than apoptosis, represents the main type of hepatocyte death in chronic cholestasis. Moreover, it has also been suggested that the reduced liver injury observed in the absence of Fas receptor after bile duct ligation was not due to lower hepatocyte apoptosis but to the indirect role of this receptor in non-hepatocytic cells such as cholangiocytes and inflammatory cells. The aim of this work was therefore to determine whether a protection against cell death limited to hepatocytes could be sufficient to reduce liver injury and delay cholestatic fibrosis. With this purpose, we performed bile duct ligation in transgenic mice overexpressing Bcl-2 in hepatocytes and in wild-type littermates. We found that, compared with necrosis, apoptosis was negligible in this model. Our results also showed that hepatocyte Bcl-2 expression protected hepatocytes against liver injury only in the early steps of the disease. This protection was correlated with reduced mitochondrial dysfunction and lipid peroxidation. However, in contrast to Fas receptor-deficient lpr mice, fibrosis progression was not hampered and liver inflammatory response was not reduced by Bcl-2 overexpression. These results therefore comfort the hypothesis that Fas-mediated apoptotic hepatocyte pathway is not a significant contributing factor to the clinical features observed in cholestasis. Moreover, in the absence of a blunted inflammatory response in transgenic mice, Bcl-2 protection against hepatocyte mitochondrial dysfunction and lipid peroxidation was not sufficient to block fibrosis progression.

The liver has an extraordinary faculty to regenerate. Hepatocytes are highly differentiated cells that, despite a resting G0 state in the normal quiescent liver, can re-enter the cell cycle to reconstitute the organ after an injury. However, the first cell therapy approaches trying to harness this specific characteristic of the hepatocytes came up against the competition with resident hepatocytes in the ability to proliferate. This review will describe the different rodent models that have been developed in the last 15 years to demonstrate the concept of liver repopulation with transplanted cells harbouring a selective advantage over resident hepatocytes. Examples will then be given to show how these models demonstrated the therapeutic efficiency of cell transplantation in specific disorders. The transplantation of human hepatocytes into some of these mouse models led to the creation of humanized livers. These humanized mice provide a powerful tool to study the physiopathology of human hepatotropic pathogens and to develop drugs against them. Finally, emphasis will be placed on the role of these rodent models in the demonstration of the hepatocytic potential of stem cells.

Accumulating evidence indicates that oxidative stress is involved in the physiopathology of liver fibrogenesis. However, amid the global context of hepatic oxidative stress, the specific role of hepatocyte mitochondrial dysfunction in the fibrogenic process is still unknown. The aim of this study was to determine whether a targeted protection of hepatocytes against mitochondrial dysfunction could modulate fibrosis progression. We induced liver fibrogenesis by chronic carbon tetrachloride treatment (3 or 6 weeks of biweekly injections) in transgenic mice expressing Bcl-2 in their hepatocytes or in normal control mice. Analyses of mitochondrial DNA, respiratory chain complexes, and lipid peroxidation showed that Bcl-2 transgenic animals were protected against mitochondrial dysfunction and oxidative stress resulting from carbon tetrachloride injury. Picrosirius red staining, alpha-smooth muscle actin immunohistochemistry, and real-time PCR for transforming growth factor-beta and collagen alpha-I revealed that Bcl-2 transgenic mice presented reduced fibrosis at early stages of fibrogenesis. However, at later stages increased nonmitochondrial/nonhepatocytic oxidative stress eventually overcame the capacity of Bcl-2 overexpression to prevent the fibrotic process. In conclusion, we demonstrate for the first time that specific protection against hepatocyte mitochondrial dysfunction plays a preventive role in early stages of fibrogenesis, delaying its onset. However, with the persistence of the aggression, this protection is no longer sufficient to impede fibrosis progression.

Inflammation has been shown to induce the progression of fibrosis in response to liver injury. Among inflammatory cells, macrophages and lymphocytes play major roles in both the constitution and resolution of liver fibrosis. The chemokine receptor CCR2 is involved in the recruitment of monocytes to injury sites, and it is known to be induced during the progression of fibrosis in humans. However, its specific role during this process has not yet been unveiled. We first demonstrated that, compared with wild-type mice, CCR2 knockout animals presented a delay in liver injury after acute CCl(4) injection, accompanied by a reduction in infiltrating macrophage populations. We then induced fibrosis using repeated injections of CCl(4) and observed a significantly lower level of fibrotic scars at the peak of fibrosis in mutant animals compared with control mice. This diminished fibrosis was associated with a reduction in F4/80(+)CD11b(+) and CD11c(+) populations at the sites of injury. Subsequent analysis of the kinetics of the resolution of fibrosis showed that fibrosis rapidly regressed in wild-type, but not in CCR2(-/-) mice. The persistence of hepatic injury in mutant animals was correlated with sustained tissue inhibitor of metalloproteinase-1 mRNA expression levels and a reduction in matrix metalloproteinase-2 and matrix metalloproteinase-13 expression levels. In conclusion, these findings underline the role of the CCR2 signaling pathway in both the constitution and resolution of liver fibrotic scars.

Background: The effect of regression of cirrhosis in chronic hepatitis C is unknown., Objective: To evaluate the relation between regression of cirrhosis and clinical outcome in patients with chronic hepatitis C after antiviral therapy., Design: A cohort of patients with cirrhosis treated between 1988 and 2001., Setting: Hepatology unit of a tertiary care center in France., Patients: 96 patients with chronic hepatitis C and biopsy-proven cirrhosis (METAVIR score F4) who were treated with an interferon-based regimen and had at least 1 posttreatment liver biopsy. Patients were followed until November 2006., Measurements: Occurrence of a combined end point of liver-related events (ascites, hepatic encephalopathy, variceal bleeding, spontaneous bacterial peritonitis, hepatocellular carcinoma, or liver transplantation) and death in patients with regression of cirrhosis (defined as a decrease from 4 to

Orthotopic liver transplantation is limited by the shortage of liver donors, leading to elderly patients being enrolled as donors with increasing frequency. Alternative strategies such as cell therapy are therefore needed. Because transplanted hepatocytes do not proliferate into a recipient liver, repopulation strategies have been developed. We have previously published a proof of concept that hepatocytes harboring a survival selective advantage can efficiently repopulate a mouse liver. We develop here an alternative approach by conferring a selective proliferative advantage on transplanted hepatocytes over resident ones. FoxM1B is a transcription factor that, when over-expressed into hepatocytes, accelerates the cell cycle and maintains the hepatocyte in vivo proliferative capacity of aged livers. We now demonstrate that transplanted hepatocytes over-expressing FoxM1B repopulate the liver of mice subjected to continuous injury far more efficiently than control hepatocytes. We show that old hepatocytes that over-express FoxM1B retain their cell division capacity and repopulate liver as well as young ones, in contrast with old non-modified hepatocytes, which lose their proliferative capacity. In conclusion, our results point to the potential use of FoxM1B expression in hepatocyte-based therapy protocols in diseases where host hepatocytes are chronically injured, especially if donor hepatocytes come from old livers.

Various immediate early genes (IEGs) upregulated during the early process of liver regeneration are transcriptional targets of the serum response factor (SRF). We show here that the expression of SRF is rapidly induced in rodent liver after partial hepatectomy. Because the inactivation of the SRF gene in mice is embryonic lethal, the in vivo role of SRF in liver regeneration after partial hepatectomy was analyzed in mutant mice conditionally deleted for SRF in the liver. We demonstrate that SRF is not an essential factor for liver ontogenesis. However, adult mutant mice show impaired liver regeneration after partial hepatectomy, associated with a blunted upregulation of various SRF target IEGs. In conclusion, our work suggests that SRF is an early response transcription factor that may contribute to the initial phases of liver regeneration through its activation of IEGs.

The Serum Response Factor (SRF) is widely expressed transcription factor acting at the confluence of multiple signaling pathways and has been implicated in the control of differentiation, growth, and cell death. In the present study, we found that SRF is expressed in the developing and adult pancreas. To explore the possible role of SRF in this organ, we have generated mutant mice with conditional disruption of the Srf gene. Such mutants presented normal development of both the exocrine and endocrine pancreas indicating that SRF is dispensable for pancreas ontogenesis. However, after weaning, these mice developed profound morphological alterations of the exocrine pancreas, which were reminiscent of severe pancreatitis. In these mice, massive acinar injury, Nuclear Factor Kappa B activation and proinflammatory cytokines release led to complete destruction of the exocrine pancreas and its replacement by adipose tissue. Despite these changes, the organization and function of the endocrine islets of Langerhans remained well-preserved. This new animal model of spontaneous pancreatitis could prove a valuable tool to gain further insight into the physiopathology of this disease.

Hepatocytes have the unique capacity to self-renew and repair the liver ad integrum when stimulated to proliferate by liver injury. However, transplantation of isolated hepatocytes is usually not sufficiently efficient for therapeutic purposes. We conferred a survival advantage on transplanted hepatocytes and showed that they were able to repopulate almost the entire mouse liver after repeated injury. In contrast, we found that bone marrow stem cell transdifferentiation was inadequate for therapeutic liver regeneration. Current data on liver stem cells will be discussed.

In the liver, the importance of apoptosis is not only evident during development and homeostasis of the biliary tree but plays also a prominent role in liver pathogenesis. Ligand binding to cell surface death receptors such as Fas activates the extrinsic pathway. This pathway predominates in autoimmune liver diseases, viral hepatitis, liver allograft rejection. Hepatocyte apoptosis is also significantly increased in patients with alcoholic hepatitis and nonalcoholic steatohepatitis and correlates with disease severity and hepatic fibrosis. We have used this specific susceptibility of the liver to apoptosis to develop two different approaches: 1) a cell therapy strategy based on a survival advantage to an apoptotic stimulus conferred to transplanted hepatocytes and 2) a new model of hepatocyte conditional ablation based on a controlled activation of the cell death program.

Allogenic hepatocyte transplantation or autologous transplantation of genetically modified hepatocytes has been used successfully to correct congenital or acquired liver diseases and can be considered as an alternative to orthotopic liver transplantation. However, hepatocytes are neither easily maintained in culture nor efficiently genetically modified and are very sensitive to dissociation before their reimplantation into the recipient. These difficulties have greatly limited the use of an ex vivo approach in clinical trials. In the present study, we have shown that primary human and rat hepatocytes can be efficiently transduced with a FLAP lentiviral vector without the need for plating and culture. Efficient transduction of nonadherent primary hepatocytes was achieved with a short period of contact with vector particles, without modifying hepatocyte viability, and using reduced amounts of vector. We also showed that the presence of the DNA FLAP in the vector construct was essential to reach high levels of transduction. Moreover, transplanted into uPA/SCID mouse liver, lentivirally transduced primary human hepatocytes extensively repopulated their liver and maintained a differentiated and functional phenotype as assessed by the stable detection of human albumin and antitrypsin in the serum of the animals for months. In conclusion, the use of FLAP lentiviral vectors allows, in a short period of time, a high transduction efficiency of human functional and reimplantable hepatocytes. This work therefore opens new perspectives for the development of human clinical trials based on liver-directed ex vivo gene therapy.

Studying the effects of the loss of a specific cell type is a powerful approach in biology. Here we present a method based on the controlled activation of the apoptotic machinery. We expressed a modified caspase-3-containing chemical inducer of dimerization (CID)-binding sites in the livers of transgenic mice. In the absence of CID, no liver injury was detectable, underlining the absence of leakage in our system. In contrast, injection of the CID produced activation of the chimeric caspase-3, which led to a dose-dependent pure hepatocyte ablation with subsequent regeneration. This method is effective in both growing and nongrowing cells, and is therefore applicable to a wide range of cells and tissues. Moreover, because apoptosis has been described in numerous pathological circumstances, this system is useful for generating mouse models of human disorders as well as for studying the recovery or regeneration of tissues after cell loss.

Among all vectors designed for gene therapy purposes, adenovirus appears to be the most efficient in vivo vehicle to transduce the broadest spectrum of cellular targets. However, the deleterious immunogenicity of this viral vector impedes its use in chronic diseases. Non-viral vectors, such as naked DNA, are attractive alternatives for safety and technical issues, such as scale-up production. Naked DNA injection, greatly improved when combined with electroporation, showed great potential in adult animals, especially when directed to the muscle. We have recently proven the therapeutic effect of a neonatal single intramuscular injection of a cardiotrophin-1 (CT-1)-encoding adenovirus in a hereditary disease mouse model of human motor neuron disease, the progressive motor neuronopathy (pmn) mutant. We now demonstrate that a single injection/electroporation of a CT-1-encoding plasmid in neonate pmn mice is almost as efficient as adenovirus-mediated gene transfer with respect to survival, muscular function and neuroprotection of the animals. Treated mice gain global weight, their mean lifespan is extended by 25%, all their electromyographic parameters are improved and myelinated axons of their phrenic nerves are protected. Moreover, we show that re-injection/electroporation leads to improvements in this neuroprotection. We therefore demonstrate for the first time the therapeutic efficacy of neonatal intramuscular DNA injection/electroporation in a murine model of a human hereditary disorder.

The present study evaluates the effectiveness of ischemic preconditioning and Bcl-2 overexpression against the liver and lung damage that follow hepatic ischemia-reperfusion and investigates the underlying protective mechanisms. Preconditioning and Bcl-2, respectively, reduced the increased tumor necrosis factor (TNF) and macrophage inflammatory protein-2 (MIP)-2 levels observed after hepatic reperfusion. Bcl-2 overexpression or anti-MIP-2 pretreatment seems to be more effective than preconditioning or anti-TNF pretreatment against inflammatory response, microcirculatory disorders, and subsequent hepatic ischemia-reperfusion injury. Furthermore, each one of these strategies individually was unable to completely inhibit hepatic injury. The combination of preconditioning and Bcl-2 overexpression as well as the combined anti-TNF and anti-MIP-2 pretreatment totally prevented hepatic injury, whereas the benefits of preconditioning and Bcl-2 were abolished by TNF and MIP-2. In contrast to preconditioning, Bcl-2 did not modify lung damage induced by hepatic reperfusion. This could be explained by the differential effect of both treatments on TNF release. Anti-TNF therapy or preconditioning, by reducing TNF release, reduced pulmonary inflammatory response, whereas the benefits of preconditioning on lung damage were abolished by TNF. Thus, the induction of both Bcl-2 overexpression in liver and preconditioning, as well as pharmacological strategies that simulated their benefits, such as anti-TNF and anti-MIP-2 therapies, could be new strategies aimed to reduce lung damage and inhibit the hepatic injury associated with hepatic ischemia-reperfusion.

Cell-based therapy may some day be a therapeutic alternative to liver transplantation. Recent observations indicating that hematopoietic stem cells can differentiate into hepatocytes have opened new therapeutic prospects. However, the clinical relevance of this phenomenon is unknown. We have previously developed a strategy based on the protective effect of Bcl-2 against Fas-mediated apoptosis to selectively amplify a small number of hepatocytes in vivo. We now show that this approach can be used to amplify a minor population of bone marrow-derived hepatocytes. Normal mice were transplanted with unfractionated bone marrow cells from transgenic animals expressing Bcl-2 under the control of a liver-specific promoter. Recipients were then submitted to weekly injections of the anti-Fas antibody, Jo2. Upon sacrifice, the liver of the recipients showed bone marrow-derived clusters of mature hepatocytes expressing Bcl-2, which showed that the hepatocyte progeny of a genetically modified bone marrow can be selectively expanded in vivo. In contrast, no Bcl-2 expression could be detected without the selective pressure of Jo2, suggesting that differentiation of bone marrow cells into mature hepatocytes is very inefficient under physiologic conditions. We conclude that a selection strategy will be required to achieve a therapeutic level of liver repopulation with bone marrow-derived hepatocytes.

Liver repopulation could constitute a potential therapeutic alternative to liver transplantation in the future. Therefore, the development of liver repopulation strategies is of major interest. We have previously reported that Bcl-2-expressing hepatocytes are resistant to Fas-mediated apoptosis and that these hepatocytes, when transplanted into the spleen, are able to repopulate the liver of normal mice submitted to Fas-mediated apoptosis. We now show that Bcl-x(L)-overexpressing hepatocytes are able to repopulate up to 10% of a normal mouse liver treated with successive injections of anti-Fas antibody. We show that a twofold overexpression of Bcl-x(L) is sufficient to confer a selective advantage to hepatocytes submitted to anti-Fas antibody. Moreover, repopulation percentages obtained here were comparable to those obtained when Bcl-2 hepatocytes were transplanted, suggesting that both proteins are equivalent in conferring a selective advantage to hepatocytes submitted to anti-Fas antibody.

Stable gene transfer into hepatocytes has been proposed to compensate for genetic deficiencies that affect liver function, or to deliver diffusible factors into the circulation. This strategy can be achieved using retroviral vectors; however, cell division must occur. We describe a simple and reproductive method that enables the induction of hepatocyte replication in a controlled fashion, thus allowing an efficient in vivo retroviral liver transduction that is applicable to mouse models of human genetic disorders. The approach is based on liver susceptibility to apoptosis via the Fas/CD95 pathway. We show that, 4 days following a single Fas agonist antibody (JO2) injection, hepatocyte replication occurs, the intensity of which is correlated with the level of the induced hepatic cytolysis. This treatment enables in vivo liver transduction, and its efficiency also correlates with the level of hepatic cytolysis. When recombinant retroviral vectors were infused intravenously during the period of hepatocyte replication, 15.4% +/- 1.7% of the hepatocytes were transduced, reaching up to 32.5%.

Liver repopulation constitutes an attractive approach for the treatment of liver disorders or of diseases requiring abundant secretion of an active protein. We have described previously a model of selective repopulation of a normal liver by Fas/CD95-resistant hepatocytes, in which we achieved up to 16% hepatocyte repopulation. In the present study, we investigated the therapeutic efficacy of this strategy. With this aim, apolipoprotein E (ApoE) knockout mice were transplanted with Fas/CD95-resistant hepatocytes which constitutively express ApoE. Transplanted mice were submitted to weekly injections of non-lethal doses of the Fas agonist antibody Jo2. After 8 weeks of treatment, we obtained up to 30% of the normal level of plasma ApoE. ApoE secretion was accompanied by a drastic and significant decrease in total plasma cholesterol, which even fell to normal levels. Moreover, this secretion was sufficient to markedly reduce the progression of atherosclerosis. These results demonstrate the efficacy of this repopulation approach for correcting a deficiency in a protein secreted by the liver.

Fas ligand (CD95L) and tumor necrosis factor-alpha (TNF-alpha) are pivotal inducers of hepatocyte apoptosis. Uncontrolled activation of these two systems is involved in several forms of liver injury. Although the broad antiapoptotic action of Bcl-2 and Bcl-xL has been clearly established in various apoptotic pathways, their ability to inhibit the Fas/CD95- and TNF-alpha-mediated apoptotic signal has remained controversial. We have demonstrated that the expression of BCL-2 in hepatocytes protects them against Fas-induced fulminant hepatitis in transgenic mice. The present study shows that transgenic mice overexpressing BCL-XL in hepatocytes are also protected from Fas-induced apoptosis in a dose-dependent manner. Bcl-xL and Bcl-2 were protective without any change in the level of endogenous Bcl-xL or Bax and inhibited hepatic caspase-3-like activity. In vivo injection of TNF-alpha caused massive apoptosis and death only when transcription was inhibited. Under these conditions, PK-BCL-XL mice were partially protected from liver injury and death but PK-BCL-2 mice were not. A similar differential protective effect of Bcl-xL and Bcl-2 transgenes was observed when Fas/CD95 was activated and transcription blocked. These results suggest that apoptosis triggered by activation of both Fas/CD95 and TNF-alpha receptors is to some extent counteracted by the transcription-dependent protective effects, which are essential for the antiapoptotic activity of Bcl-2 but not of Bcl-xL. Therefore, Bcl-xL and Bcl-2 appear to have different antiapoptotic effects in the liver whose characterization could facilitate their use to prevent the uncontrolled apoptosis of hepatocytes.

Hepatocyte transplantation might represent a potential therapeutic alternative to liver transplantation in the future; however, transplanted cells have a limited capacity to repopulate the liver, as they do not proliferate under normal conditions. Recently, studies in urokinase (uPA) transgenic mice and in fumarylacetoacetate hydrolase (FAH)-deficient mice have shown that the liver can be repopulated by genetically engineered hepatocytes harboring a selective advantage over resident hepatocytes. We have reported that transgenic mice expressing human Bcl-2 in their hepatocytes are protected from Fas/CD95-mediated liver apoptosis. We now show that Bcl-2 transplanted hepatocytes selectively repopulate the liver of mice treated with nonlethal doses of the anti-Fas antibody Jo2. FK 506 immunosuppressed mice were transplanted by splenic injection with Bcl-2 hepatocytes. The livers of female recipients were repopulated by male Bcl-2 transgenic hepatocytes, as much as 16%, after 8 to 12 administrations of Jo2. This only occurred after anti-Fas treatment, confirming that resistance to Fas-induced apoptosis constituted the selective advantage of these transplanted hepatocytes. Thus, we have demonstrated a method for increasing genetic reconstitution of the liver through selective repopulation with modified transgenic hepatocytes, which will allow optimization of cell and gene therapy in the liver.

We transferred a reporter gene to Schwann cells to test whether they might serve as an endoneurial delivery system for therapeutic proteins. A replication-defective adenoviral vector carrying the gene for beta-galactosidase (lacZ) was injected into the distal segment of intact or crushed sciatic nerves of adult rats, and the expression of lacZ was histochemically assessed. Less than 1% of the Schwann cells became reactive in intact nerves, but up to 18% of the proliferating Schwann cells of injured nerves expressed lacZ. Gene expression decayed with time but might persist for up to 2 months. It was enhanced by immunosuppression: daily cyclosporin A injections reduced both proliferation of Schwann cells and lymphocytic infiltration of the nerve, whereas tolerance induced by a single intrathymic injection of the vector 4 days after birth abolished the inflammatory response but not the proliferation of Schwann cells. The vector itself did not impede axonal regeneration. The results indicate that adenoviral gene transfer to Schwann cells in injured nerves is possible and suggest that induced production of neurotrophic factor may represent a therapeutic supplement to surgical nerve repair.

CArG boxes, whose consensus sequence is CC(A/T)6GG, are involved in two very different types of transcriptional responses: response of immediate early genes to serum, mediated by so-called Serum Response Elements (SRE), and transcriptional activation of muscle-specific genes during muscle differentiation. Although previous studies have shown that the Serum Response Factor (SRF) binds to muscular CArG boxes, the role of such a binding in muscle-specific activation of CArG box-dependent genes was not directly demonstrated. Here, by transient co-transfection experiments, we demonstrate that intact SRF is required for muscle-specific transcriptional activation through CArG boxes.

Gene therapy for heart diseases requires availability of an efficient vector for gene transfer into myocardium. Recombinant adenovirus expressing the Escherichia coli beta-galactosidase (beta-Gal) gene was shown to infect rat cardiocytes efficiently in vivo. However, a time course of gene expression showed that transgene expression was maximal during the first week following injection, then declined and disappeared by day 21. An immunosuppressive treatment prolonged beta-Gal expression for at least 21 days. On the contrary, a preimmunization of the animals by two intraperitoneal injections of the vector led to a decreased transgene expression 48 hr after intramyocardial injection and to a barely detectable expression at the sixth day. Appearance of adenovirus neutralizing antibodies in preimmunized animals could have contributed to such a refractoriness to further adenoviral infection. Finally, a neonatal intrathymic injection of the vector was able to induce long-term LacZ expression for more than 2 months after heart injection, although neutralizing as well as anti-beta-Gal antibodies were detected in sera of the animals. These results indicate that an immune response against first-generation replication-defective adenoviral vectors is a major cause of transient transgene expression, a cellular response being most probably responsible for ablation of transgene expression in immunocompetent animals.

Due to their quiescent nature and spatial complexity, many target tissues for gene therapy will require novel strategies. An alternative to ex vivo gene transfer, providing many technical advantages and possibly allowing sufficient transfer of the therapeutic gene, is direct in vivo delivery of the vehicle. For a favorable outcome, this procedure is dependent on a high-titer vector, fully competent before post-mitotic cells. In view of the restrictions with the use of retroviruses, we investigated the potentials of adenovirus. Adenoviruses have as primary targets of infection the differentiated epithelial cell. The large DNA genome of the virus hints to a large cloning capacity. Furthermore, the wild type adenovirus has been largely used in man as a vaccine against adenovirus-induced respiratory disease. Taken together, the biological characteristics of adenovirus and the precedent of administration to humans are suggestive of adenovirus-based gene therapy for diseases involving a variety of quiescent tissues. The use of a replication-defective adenovirus carrying a gene encoding a nuclearly-targeted beta-galactosidase Ad.RSV beta gal demonstrated that replication-defective adenovirus offers an efficient means to transfer a gene for extended periods of time in the liver, muscle, lung and brain (1-6).

Duchene muscular dystrophy (DMD) is a fatal progressive X-linked muscle disorder, caused by mutations in the dystrophin gene. We have investigated adenovirus-mediated transfer of a dystrophin minigene in a mutant mouse lacking dystrophin, the mdx mouse. We report here that six months after a single intramuscular injection of a recombinant adenovirus containing a human dystrophin minigene, a large number of dystrophin-positive fibres are still detected in the injected muscles. Moreover, although the minigene encodes a truncated protein, its expression is able to protect the fibres efficiently against the degeneration process that affects the dystrophin-deficient mdx myofibres.

Duchenne progressive muscular dystrophy is a lethal and common X-linked genetic disease caused by the absence of dystrophin, a 427K protein encoded by a 14 kilobase transcript. Two approaches have been proposed to correct the dystrophin deficiency in muscle. The first, myoblast transfer therapy, uses cells from normal donors, whereas the second involves direct intramuscular injection of recombinant plasmids expressing dystrophin. Adenovirus is an efficient vector for in vivo expression of various foreign genes. It has recently been demonstrated that a recombinant adenovirus expressing the lac-Z reporter gene can infect stably many mouse tissues, particularly muscle and heart. We have tested the ability of a recombinant adenovirus, containing a 6.3 kilobase pair Becker-like dystrophin complementary DNA driven by the Rous sarcoma virus promoter to direct the expression of a 'minidystrophin' in infected 293 cells and C2 myoblasts, and in the mdx mouse, after intramuscular injection. We report here that in vivo, we have obtained a sarcolemmal immunostaining in up to 50% of fibres of the injected muscle.