Recruitment of host progenitor cells in rat liver transplants

A rat liver cell atlas reveals intrahepatic myeloid heterogeneity

The large size and vascular accessibility of the laboratory rat (Rattus norvegicus) make it an ideal hepatic animal model for diseases that require surgical manipulation. Often, the disease susceptibility and outcomes of inflammatory pathologies vary significantly between strains. This study uses single-cell transcriptomics to better understand the complex cellular network of the rat liver, as well as to unravel the cellular and molecular sources of inter-strain hepatic variation. We generated single-cell and single-nucleus transcriptomic maps of the livers of healthy Dark Agouti and Lewis rat strains and developed a factor analysis-based bioinformatics analysis pipeline to study data covariates, such as strain and batch. Using this approach, we discovered transcriptomic variation within the hepatocyte and myeloid populations that underlie distinct cell states between rat strains. This finding will help provide a reference for future investigations on strain-dependent outcomes of surgical experiment models.

Stromal cell-derived factor-1/CXC chemokine receptor 4 axis in injury repair and renal transplantation

Stem cell therapy has shown promise in treating a variety of pathologies, such as myocardial infarction, ischaemic stroke and organ transplantation. The stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor-4 (CXCR4) axis plays a key role in stem cell mobilization. This review describes the important role of SDF-1 in tissue injury and how it works in tissue revascularization and regeneration via CXCR4. Furthermore, factors influencing the SDF-1/CXCR4 axis and its clinical potential in ischaemia reperfusion injury, such as renal transplantation, are discussed. Exploring signalling pathways of the SDF-1/CXCR4 axis will contribute to the development of stem cell therapy so that more clinical problems can be solved. Controlling directional homing of stem cells through the SDF-1/CXCR4 axis is key to improving the efficacy of stem cell therapy for tissue injury. CXCR4 antagonists may also be effective in increasing circulating levels of adult stem cells, thereby exerting beneficial effects on damaged or inflamed tissues in diseases that are currently not treated by standard approaches.

Fibrosis in small syngeneic rat liver grafts because of damaged bone marrow stem cells from chronic alcohol consumption

A patient with liver failure due to chronic and acute alcohol abuse under consideration for an urgent liver transplant shortly after stopping alcohol may have residual abnormalities that threaten transplant success, particularly for a small graft. To address this, we studied a model in which reduced-size (50%) Lewis rat livers are transplanted into green fluorescence protein transgenic Lewis recipients after they are fed alcohol or a control diet for 5 weeks. Here we show that normal small Lewis grafts transplanted to alcohol-fed Lewis hosts developed fibrosis, whereas no fibrosis was observed in control-fed recipients. Host-derived CD133 + 8-hydroxy-2'-deoxyguanosine (8-OHdG) cells were significantly increased in livers recovered from both alcohol-fed and control recipients, but only alcohol-fed recipients demonstrated co-staining (a marker of oxidative DNA damage). α smooth muscle actin (α-SMA) staining, a marker for myofibroblasts, also co-localized with CD133 + cells only in the livers of alcohol-fed recipients. Immunostaining and polymerase chain reaction analysis confirmed that chronic alcohol consumption decreased the proportion of bone marrow stem cells (BMSCs) expressing CD133, c-Kit, and chemokine (C-X-C motif) receptor 4 markers and caused oxidative mitochondria DNA (mtDNA) damage. Culture of CD133 + cells from normal rats with medium containing 3% ethanol for 48 hours resulted in elevated mitochondrial 8-OHdG and mtDNA deletion, and ethanol exposure diminished CD133 expression but dramatically increased α-SMA expression. In conclusion, oxidative mtDNA damage and deletions occur in BMSCs of chronic alcohol-fed recipients, and these damaged cells mobilize to the small liver grafts and become myofibroblasts where they play a key role in the subsequent development of fibrosis. Liver Transplantation 23 1564-1576 2017 AASLD.

miR-706 inhibits the oxidative stress-induced activation of PKCα/TAOK1 in liver fibrogenesis

Oxidative stress induces the activation of liver fibrogenic cells (myofibroblasts), thus promoting the expression of fibrosis-related genes, leading to hepatic fibrogenesis. MicroRNAs (miRNAs) are a new class of small RNAs ~18–25 nucleotides in length involved in post-transcriptional regulation of gene expression. Wound-healing and remodeling processes in liver fibrosis have been associated with changes in hepatic miRNA expression. However, the role of miR-706 in liver fibrogenesis is currently unknown. In the present study, we show that miR-706 is abundantly expressed in hepatocytes. Moreover, oxidative stress leads to a significant downregulation of miR-706, and the further reintroduction of miR-706 inhibits oxidative stress-induced expression of fibrosis-related markers such as α-SMA. Subsequent studies revealed that miR-706 directly inhibits PKCα and TAOK1 expression via binding to the 3′-untranslated region, preventing epithelial mesenchymal transition. In vivo studies showed that intravenous injection of miR-706 agomir successfully increases hepatic miR-706 and decreases α-SMA, PKCα, and TAOK1 protein levels in livers of carbon tetrachloride (CCl₄)-treated mice. In summary, this study reveals a protective role for miR-706 by blocking the oxidative stress-induced activation of PKCα/TAOK1. Our results further identify a major implication for miR-706 in preventing hepatic fibrogenesis and suggest that miR-706 may be a suitable molecular target for anti-fibrosis therapy.

Cyclosporine A disposition, hepatic and renal tolerance in Wistar rat

Cyclosporine A, a potent calcineurin inhibitor, has been widely used in organ transplantation and in the treatment of autoimmune diseases. It has, however, been shown to induce serious renal and hepatic side effects. The drug is also used in preclinical studies, but with little published information on the optimal dose and route of administration in rodents. Objectives of this study were to identify efficient and safe doses of cyclosporine A in rodent and to assess its effects on hepatic and renal functions. For this purpose, we tested the effects of different doses and administration routes of cyclosporine A (5, 2.5 and 1 mg/kg) administered during 28 days intraperitoneally, or by gastric feeding on Wistar rats. Our data indicate that rats injected intraperitoneally with 5 mg/kg/2d (every two days) exhibited trough cyclosporine A levels within known therapeutic range in human, but were subject to blood cyclosporine A accumulation, whereas the 5 mg/kg/d gavage resulted in only a small cyclosporine A accumulation over time. In both cases this accumulation was not deleterious to renal and hepatic functions, as shown by transaminase, urea, creatinine and bilirubin measurements.

Re-evaluation of hepatocyte replacement by recipient-derived cells after allogenic liver transplantation: Discrepancy between clinical observations and a rat model

AIM

Reports suggest that hepatocyte replacement by recipient-derived cells is an active phenomenon after allogenic liver transplantation in rats. However, this phenomenon is rarely observed in humans, and further evaluation is necessary to bridge the gap between clinical practice and animal experiment.

METHODS

Fifty percent volume of the liver from green fluorescent protein (GFP) transgenic Lewis rats were transplanted into wild-type Dark Agouti (DA) rats, in which GFP negative hepatocytes were considered as host (DA rat)-derived cells. The transplanted liver was observed on whole imaging system and fluorescent microscope 7-10 days after transplantation. As a different method from previous reports, hepatocytes isolated from transplanted livers were cultured, and the expression of GFP was examined.

RESULTS

The sliced liver (2 mm) after allogenic transplantation demonstrated decreased intensity of GFP signals compared with the positive control. The hematoxylin-eosin staining of the section revealed abundant infiltration of inflammatory cells, suggesting an immunological rejection reaction. Large polygonal cells with significantly decreased or negative GFP signals were also demonstrated, which was consistent with the results of previous studies. However, cell culturing demonstrated that none of the examined albumin positive large polygonal cells were host-derived cells. The same results were obtained irrespective of reconstruction of hepatic artery.

CONCLUSION

Our result implies that rejection reaction does not promote parenchymal replacement by recipient-derived cells, in contrast to previous reports. If so, the phenomena occurring in rats are consistent with clinical observation of liver transplantation in humans.

Chimeric Allografts Induced by Short-Term Treatment With Stem Cell-Mobilizing Agents Result in Long-Term Kidney Transplant Survival Without Immunosuppression: A Study in Rats

Transplant tolerance allowing the elimination of lifelong immunosuppression has been the goal of research for 60 years. The induction of mixed chimerism has shown promise and has been extended successfully to large animals and to the clinic; however, it remains cumbersome and requires heavy early immunosuppression. In this study, we reported that four injections of AMD3100, a CXCR4 antagonist, plus eight injections of low-dose FK506 (0.05 mg/kg per day) in the first week after kidney transplantation extended survival, but death from renal failure occurred at 30-90 days. Repeating the same course of AMD3100 and FK506 at 1, 2 and 3 mo after transplant resulted in 92% allograft acceptance (n = 12) at 7 mo, normal kidney function and histology with no further treatment. Transplant acceptance was associated with the influx of host stem cells, resulting in a hybrid kidney and a modulated host immune response. Confirmation of these results could initiate a paradigm shift in posttransplant therapy.

Chimeric Allografts Induced by Short-Term Treatment With Stem Cell Mobilizing Agents Result in Long-Term Kidney Transplant Survival Without Immunosuppression: II, Study in Miniature Swine

Transplantation is now lifesaving therapy for patients with end-stage organ failure but requires lifelong immunosuppression with resultant morbidity. Current immunosuppressive strategies inhibit T cell activation and prevent donor-recipient engagement. Therefore, it is not surprising that few host cells are demonstrated in donor grafts. However, our recent small animal studies found large numbers of recipient stem cells present after transplantation and pharmacological mobilization, resulting in a chimeric, repopulated organ. We now confirm these findings in a well-characterized large animal preclinical model. Here, we show that AMD3100 and FK506 mobilization of endogenous stem cells immediately post kidney transplantation combined with repeat therapy at 1, 2, and 3 months led to drug-free long-term survival in maximally immunologically mismatched swine. Three long-term recipients have stable chimeric transplants, preserved antidonor skin graft responses, and normal serum creatinine levels despite withdrawal of all medication for 3 years.

Pretransplant replacement of donor liver grafts with recipient Kupffer cells attenuates liver graft rejection in rats

BACKGROUND AND AIM

Rejection of liver grafts is a difficult issue that has not been resolved. Preoperative replacement of liver cells in the graft with cells from the intended recipient may attenuate rejection. We investigated whether preoperative transplant of recipient bone marrow cells (BMCs) to the donor replaced liver allograft cells and attenuated rejection.

METHODS

We used a rat model of allogeneic liver transplant (LT) from Dark Agouti (DA) to Lewis (LEW) rats. In BMC group, DA rats received BMC transplants from LacZ-transgenic LEW rats at 1 week before LT. In the control group, DA rats received no preoperative treatment. We evaluated graft damage at 7 days after LT and the survival of the recipient rats.

RESULTS

Rats in the BMC group experienced prolonged survival that was abrogated by the administration of gadolinium chloride to donors at 24 h before LT. Serum concentrations of total bilirubin and hyaluronic acid on day 7 were significantly lower in the BMC group, and histopathological analyses revealed that rejection of the liver graft was attenuated. X-gal staining and immunohistostaining of the liver graft revealed that BMCs engrafted in the sinusoidal space differentiated into Kupffer cells.

CONCLUSIONS

Preoperative transplant of recipient BMCs to LT donors replaced donor Kupffer cells and attenuated post-LT rejection, indicating that this strategy may increase the success of LT.

Postconditioning attenuates renal ischemia-reperfusion injury by mobilization of stem cells

BACKGROUND

We recently showed that reactive oxygen species (ROS) and mitochondrial DNA damage and deletions were attenuated by postconditioning (POC). It is not known, however, whether a population of progenitor cells is recruited by POC and is responsible for repair of renal tubular epithelial cells after ischemic injury.

METHODS

The model of renal POC was induced by 45 min clamping of the left renal artery and right nephrectomy followed by 7 min of short-time full reperfusion and 3 cycles of 30 s ischemia and 30 s reperfusion. The lymphocyte compartment of peripheral blood was evaluated by fluorescence-activated cell sorting (FACS) to determine expression of the bone marrow-derived progenitor cell markers CXC-chemokine receptor 4 (CXCR4), c-Kit, and CD34, at 12 h, 1 day and 3 days post-ischemia. Serum and kidney tissue were collected for analysis at 3 and 7 days post-ischemia.

RESULTS

Renal functional and structural recovery was markedly improved by POC, which increased the number of CXCR4(+) and CD34(+) stem cells in peripheral blood and kidney tissue. Inhibition of ROS burst by POC was likely associated with increased hypoxia-inducible factor-1 expression, which may further promote stromal cell-derived factor 1 (SDF-1) expression.

CONCLUSIONS

The mechanisms of stem cell recruitment to the injured foci mobilized by POC appear to be mediated by moderate oxidative stress, which may lead to increased SDF-1 expression.

Effect of liver regeneration on malignant hepatic tumors

Liver regeneration after major surgery may activate occult micrometastases and facilitate tumor growth, leading to liver tumor recurrence. Molecular changes during liver regeneration can provide a microenvironment that stimulates intrahepatic tumor propagation through alterations in cellular signaling pathways, where activation and proliferation of mature hepatocytes, hepatic progenitor cells, non-parenchymal liver cells might favor both liver regeneration and tumor growth. This review highlights recent advances of tumor growth and development in the regenerating liver, possible mechanisms and clinical implications.

Molecular mechanisms of stem cell therapy in alcoholic liver disease

Alcoholic liver disease affects a great number of people worldwide. With limited therapeutic options, stem cell therapy offers significant potential for these patients. To date, a limited number of clinical trials have produced transient clinical responses to cell therapy in patients with alcoholic liver disease. Stem cell therapy to reorganize the postnatal liver is an important theme and mission for patients with chronic liver disorders including alcoholic liver injury. We therefore should redevelop the evidence of cell-based liver regeneration therapy, focusing on targets (disease, patient's status and hepatic function), materials (cells, cytokines and genes), and methodology (stem cell types and their derived microparticles, transplantation route, implantation technology and tissue engineering). In this review, we summarize the recent findings regarding the experimental and clinical use of mesenchymal and liver stem cells, focusing mainly on the treatment of alcoholic liver disorders and their relevance in the field of regenerative medicine, and advances on the role of microvesicles and exosomes in this process. We discuss new advances in stem cell therapy from liver regeneration to liver re-organization, which is involved in the recent progress of on-going clinical trials, basic research in stem cell therapy and liver regeneration, and updated exosomes/microvesicles recovery/repairing technology.

Extrahepatic stem cells mobilized from the bone marrow by the supplementation of branched-chain amino acids ameliorate liver regeneration in an animal model

BACKGROUND AND AIMS

In recent years, bone marrow (BM)-derived stem cell repopulation of injured organs has been increasingly observed; however, the extent to which it occurs and its clinical relevance remain unclear. Here, we investigated on the potential of extrahepatic stem cells to become hepatocytes using the treatment of the oral supplementation of branched-chain amino acids (BCAA).

METHODS

In the first, Sprague-Dawley (SD) rats were administered BCAA to promote liver regeneration; in the second, syngenic liver transplantations using wild-type SD rats that do not express green fluorescent protein (GFP) as syngenic donors and GFP-transgenic SD rats as recipients to confirm that an extrahepatic source of cells (GFP(+)) could repopulate the transplanted (GFP(-)) liver were performed.

RESULTS

Treatment of the oral supplementation of BCAA for 2-3 weeks before transplantation to promote liver regeneration resulted in greater than 7 days graft volume, with extensive spotty conversion of a small wild-type graft to the recipient GFP(+) genotype. The treatment by oral supplementation of BCAA resulted in higher levels of CD34+SDF+c-kit+ stem cells in the blood and liver after liver transplantation. Liver repopulation could be achieved with hepatocytes that bone marrow-derived from stem cells proliferated.

CONCLUSIONS

We have identified extrahepatic stem cell migration from the BM to the injured liver as a mechanism underlying liver regeneration that supports hepatocyte proliferation in diseased liver. Our results suggested that BCAA is able to mobilize a population of BM-derived cells that contribute to hepatic regeneration.

Interleukin-6 is required for cell cycle arrest and activation of DNA repair enzymes after partial hepatectomy in mice

Background

Interleukin-6 (IL-6) has been shown to be vital for liver regeneration, however the specific mechanisms and factors involved remain incompletely defined. The present study aimed to investigate whether IL-6 exerts its protective effects via arresting the cell cycle allowing base excision and repair of oxidized DNA after hepatectomy.

Results

Following seventy percent partial hepatectomy (PH) in wild type (WT) mice IL-6 serum levels increased reaching peak levels at 3 hours. This was associated with markers of cell cycle arrest as p21 expression was increased and cyclin D1 and proliferating cell nuclear antigen (PCNA) expression decreased. In the absence of IL-6, markers of cell cycle arrest were absent and the number of bromodeoxyuridine (BrdU) positive cells was significantly higher at 28, 32 and 36 hours after PH. The mRNAs for DNA repair enzymes, including Neil-1, 8-oxodGTPase, OGG1, Apex1, and UDG (DNA glycosylase) were increased 2 to 4 fold in WT mice at 6 and/or 12 hours after PH compared to IL-6 knockout (KO) mice. The protein levels of Neil1 and OGG1 were also significantly increased in WT mice compared to KO mice. Pathological changes were far greater and survival was less in IL-6 KO mice than in WT mice. Administration of IL-6 in KO mice restored p21 and DNA repair enzyme expression to wild-type levels and survival was improved.

Conclusions

IL-6 caused cell cycle arrest and delayed proliferation during the first day after PH. This delay was associated with the activation of DNA repair enzymes resulting in accurate replication and restoration of hepatic mass.

Host stem cells repopulate liver allografts: reverse chimerism

Liver transplant has become life-saving therapy for thousands of patients with end stage liver disease in the United States, but chronic rejection and the toxicities of immunosuppression remain significant obstacles to the further expansion of this modality and "transplant tolerance" remains a central goal in the field. So we and others are looking for alternative post-transplant strategies. We set out to 'engineer' repopulation after transplantation in a strain combination [dark agouti (DA) to Lewis green fluorescent protein+ (LEW GFP+)] which rejects liver grafts strongly, a model that more closely resembles the situation in humans. Our central finding is purposeful manipulation of the immune response with low dose immunosuppression and liberation of stem cells for a very short period after transplantation results in long-term transplant acceptance by two mechanisms: transforming the liver (donor) to self (host) phenotype, and auto-suppression of the specific allograft response.

Successful transplantation of reduced-sized rat alcoholic fatty livers made possible by mobilization of host stem cells

Livers from Lewis rats fed with 7% alcohol for 5 weeks were used for transplantation. Reduced sized (50%) livers or whole livers were transplanted into normal DA recipients, which, in this strain combination, survive indefinitely when the donor has not been fed alcohol. However, none of the rats survived a whole fatty liver transplant while six of seven recipients of reduced sized alcoholic liver grafts survived long term. SDF-1 and HGF were significantly increased in reduced size liver grafts compared to whole liver grafts. Lineage-negative Thy-1+CXCR4+CD133+ stem cells were significantly increased in the peripheral blood and in allografts after reduced size fatty liver transplantation. In contrast, there were meager increases in cells reactive with anti Thy-1, CXCR4 and CD133 in peripheral blood and allografts in whole alcoholic liver recipients. The provision of plerixafor, a stem cell mobilizer, salvaged 5 of 10 whole fatty liver grafts. Conversely, blocking SDF-1 activity with neutralizing antibodies diminished stem cell recruitment and four of five reduced sized fatty liver recipients died. Thus chemokine insufficiency was associated with transplant failure of whole grafts, which was overcome by the increased regenerative requirements promoted by the small grafts and mediated by SDF-1 resulting in stem cell influx.

Integrating repopulation and regeneration of the auxiliarily transplanted small liver graft: the solution for organ shortage and immunosuppression

Cirrhosis is a common yet generally irreversible medical condition which would cause damaged liver function and regeneration after resection. When the disease progressed to end stage, liver transplantation, cadaveric or live donor, would be the only way to eliminate the disease. But both have their confinements, such as organ shortage, detriments to the donors, and immunosuppression. Now that the techniques of auxiliary transplantation are in practice, and the phenomenon of graft repopulated by cells of host origin has been observed, and that elevated blood inflow would stimulate the regenerative response, the combination of the three might give rise to a non-immunogeneic customized liver. We hypotheses that it can be achieved through a auxiliary transplantation of a extremely small but normal graft combined with progressive portal control on the portal inflow of the native liver to induce atrophy of the cirrhotic liver and the regeneration of the graft, as well as postoperative administration of bone marrow mobilizing agents and reduced administration of immunosuppressants to initiate repopulation. This will not only solve the issue of organ shortage as one organ can be shared by more, and in case of live donor, less detriments would occur due to reduced size needed; but diminish, even eliminate the adverse effect caused by immunosuppression as well.

Mobilization of host stem cells enables long-term liver transplant acceptance in a strongly rejecting rat strain combination

Careful examination of liver, kidney and heart transplants in human recipients has revealed small numbers of host bone marrow derived stem cells in the graft. If the limited recipient repopulation of a donor graft that is currently observed could be facilitated, it is possible that conversion to a predominantly host phenotype would permit long-term graft function without immunosuppression. We proposed to "engineer" repopulation after transplant in a strain combination (dark agouti [DA] to Lewis green fluorescent protein+[LEW GFP+]) which rejects liver grafts strongly, a model that more closely resembles the situation in humans. Treatment on days 0, 1, 2, 3 and 7 after transplantation with low-dose (0.1 mg/kg) tacrolimus (T) designed to blunt rejection combined with plerixafor (P) to mobilize host stem cells resulted in greater than 180 days graft survival with extensive albeit spotty conversion of a small (50%) DA graft to the recipient LEW GFP+ genotype. Subsequent skin grafting revealed donor-specific graft prolongation. The T plus P treatment resulted in higher levels of Lin-Thy1+CD34+CD133+ stem cells and Foxp3+ regulatory T cells in the blood and liver at day 7. Thus, pharmacological mobilization of host stem cells sustains liver allografts by two mechanisms: repopulation of injured donor cells and regulation of the immune response.

Stem cells in acute liver failure

Patients with acute liver failure are a particularly challenging group, with unique difficulties faced in treatment decisions. Life-saving therapy is available, but organ shortage, delays in transplantation, and complications in management result in a high mortality in this group of patients even after transplant. Any pharmacologic intervention that improved outcomes in this population of critically ill patients would be of great benefit. Based on available evidence, different scenarios of participation of HSCs in liver recovery are conceivable. Encouraging HSCs to differentiate into hepatocytes or supply paracrine and cellular level support to accelerate ongoing local repair mechanisms and assist a failing liver with inadequate mass and functional capacity might be directed to occur effectively in humans. Evidence within small animal models of liver injury and observations within the human population suggest that this might also be encouraged. The use of pharmacologic agents to mobilize hematopoietic stem cells is well established and effectively used in a different population of patients. As such, extending the use of these drugs, such as plerixafor, to the human population has a sound basis. However, there is a need for clarification of the mechanisms by which these cells exert their effect as well as which specific population of cells is involved in the regenerative process. To be clinically relevant in scenarios of acute liver failure, stem cell mobilizing strategies would have to impact survival when administered well after injury. Applications in other settings may also prove useful. Limits to liver resection exist where the size of the future liver remnant governs the extent of resection possible. Preexisting functional impairment may be restrictive, and strategies involving stem cells may assist the future liver remnant in both normal and functionally impaired livers. Benefit has already been reported from treatment with G-CSF in other injured tissues, including the injured myocardium and acutely injured kidney. However, as yet no clinical trial exists to assess the effects of stem cell mobilization in humans with acute liver failure. The familiarity in the use of and success demonstrated in the clinical and experimental use of plerixafor and G-CSF make exploration of hematopoietic stem cells as therapy in patients with acute liver failure appealing.

Interleukin-6 is an important mediator for mitochondrial DNA repair after alcoholic liver injury in mice

We investigated the hypothesis that a prominent effect of chronic ethanol consumption is mitochondrial DNA (mtDNA) injury and compared this injury in IL-6 knockout (KO) and wild-type (WT) mice. Ethanol feeding for 4 weeks resulted in steatosis and oxidative mtDNA damage (8-OHdG) in both IL-6KO and WT mice. However, the WT mice were able to repair the injury by increased production of mtDNA repair enzymes (OGG-1, Neil 1) and check point (p21, p53) proteins and avoid the mtDNA mutations. By contrast the IL-6 KO mice were unable to repair mtDNA resulting in deletions and diminished transcription of the mtDNA encoded protein cytochrome c oxidase subunit-I (COI). The mitochondrial injury was reflected by decreased membrane potential, reduced levels of ATP, and apoptosis-inducing factor (AIF)-induced apoptosis.

CONCLUSION

IL-6 plays a critical role in allowing the liver to recover from significant mtDNA oxidation caused by alcohol. The data suggests that IL-6 activates mtDNA repair enzymes and induces cell cycle arrest allowing time for mtDNA repair.

Stem cell mobilization is life saving in an animal model of acute liver failure

OBJECTIVE

No therapy except liver transplantation currently exists for patients with acute liver failure (ALF). The aim of this study was to determine whether pharmacologic mobilization of endogenous hematopoietic stem cells (HSCs) can aid in liver repair and improve survival in an animal model of ALF.

METHODS

Rodents were treated with a single near-lethal intraperitoneal injection of carbon tetrachloride (CCl4). After 12 hours, animals were randomized to receive plerixafor and granulocyte colony-stimulating factor (G-CSF), agents known to mobilize marrow-derived stem cells, or saline vehicle injection. Mice were observed for survival, and serial assessment of liver injury by serum transaminase measurements, and histologic analysis was performed.

RESULTS

In our ALF model, 7-day survival after injection of CCl4 was 25%. Administration of plerixafor and G-CSF following CCl4 resulted in 87% survival (n = 8, P < 0.05). On serial histopathologic analysis, animals treated with plerixafor and G-CSF demonstrated less hepatic injury compared with control animals. Evaluation of peripheral blood demonstrated an increase in circulating HSCs in response to plerixafor and G-CSF, and immunostaining suggested the infiltration of HSCs into the hepatic parenchyma after stem cell mobilization.

CONCLUSIONS

Our results suggest a possible new treatment strategy for patients with ALF, a group for whom either liver transplantation or death is frequently the outcome. Pharmacologic agents that mobilize HSCs may lead to an infiltration of the injured liver with cells that may participate in or expedite liver regeneration. This therapy has the potential to avert liver transplantation in some patients with ALF and may be of benefit in a wide variety of medical and surgical patients with liver injury.

Identification of the rat NKG2D ligands, RAE1L and RRLT, and their role in allograft rejection

NKG2D is a receptor expressed by NK cells and subsets of T lymphocytes. On NK cells, NKG2D functions as a stimulatory receptor that induces effector functions. We cloned and expressed two rat NKG2D ligands, both members of the RAE1 family, RAE1L and RRLT, and demonstrate that these ligands can induce IFN-gamma secretion and cytotoxicity by rat NK cells. To examine changes in expression of NKG2D and the NKG2D ligands RAE1L and RRLT after transplantation, we used a Dark Agouti (DA)-->Lewis rat model of liver transplantation. NKG2D expression was significantly increased in allogeneic liver grafts by day 7 post-transplant. Ligands of NKG2D, absent in normal liver, were readily detected in both syngeneic and allogeneic liver grafts by day 1 post-transplant. By day 7 post-transplant, hepatocyte RAE1L and RRLT expression was significantly and specifically increased in liver allografts. In contrast to acute rejection that develops in the DA-->Lewis model, transplantation of Lewis livers into DA recipients (Lewis-->DA) results in spontaneous tolerance. Interestingly, expression of RAE1L and RRLT is low in Lewis-->DA liver allografts, but significantly increased in DA-->Lewis liver allografts undergoing rejection. In conclusion, our results suggest that expression of NKG2D ligands may be important in allograft rejection.