TGFß1 priming enhances CXCR3-mediated mesenchymal stromal cell engraftment to the liver and enhances anti-inflammatory efficacy.

The immunomodulatory characteristics of mesenchymal stromal cells (MSC) confers them with potential therapeutic value in the treatment of inflammatory/immune-mediated conditions. Previous studies have reported only modest beneficial effects in murine models of liver injury. In our study we explored the role of MSC priming to enhance their effectiveness. Herein we demonstrate that stimulation of human MSC with cytokine TGß1 enhances their homing and engraftment to human and murine hepatic sinusoidal endothelium in vivo and in vitro, which was mediated by increased expression of CXCR3. Alongside improved hepatic homing there was also greater reduction in liver inflammation and necrosis, with no adverse effects, in the CCL4 murine model of liver injury treated with primed MSC. Priming of MSCs with TGFß1 is a novel strategy to improve the anti-inflammatory efficacy of MSCs.

Contact-dependent depletion of hydrogen peroxide by catalase is a novel mechanism of myeloid-derived suppressor cell induction operating in human hepatic stellate cells.

Myeloid-derived suppressor cells (MDSC) represent a unique cell population with distinct immunosuppressive properties that have been demonstrated to shape the outcome of malignant diseases. Recently, human hepatic stellate cells (HSC) have been reported to induce monocytic-MDSC from mature CD14(+) monocytes in a contact-dependent manner. We now report a novel and unexpected mechanism by which CD14(+)HLADR(low/-) suppressive cells are induced by catalase-mediated depletion of hydrogen peroxide (H2O2). Incubation of CD14(+) monocytes with catalase led to a significant induction of functional MDSC compared with media alone, and H2O2 levels inversely correlated with MDSC frequency (r = -0.6555, p < 0.05). Catalase was detected in primary HSC and a stromal cell line, and addition of the competitive catalase inhibitor hydroxylamine resulted in a dose-dependent impairment of MDSC induction and concomitant increase of H2O2 levels. The NADPH-oxidase subunit gp91 was significantly increased in catalase-induced MDSC as determined by quantitative PCR outlining the importance of oxidative burst for the induction of MDSC. These findings represent a so far unrecognized link between immunosuppression by MDSC and metabolism. Moreover, this mechanism potentially explains how stromal cells can induce a favorable immunological microenvironment in the context of tissue oxidative stress such as occurs during cancer therapy.

CD248/endosialin critically regulates hepatic stellate cell proliferation during chronic liver injury via a PDGF-regulated mechanism.

INTRODUCTION: CD248 (endosialin) is a stromal cell marker expressed on fibroblasts and pericytes. During liver injury, myofibroblasts are the main source of fibrotic matrix. OBJECTIVE: To determine the role of CD248 in the development of liver fibrosis in the rodent and human setting. DESIGN: CD248 expression was studied by immunostaining and quantitative PCR in both normal and diseased human and murine liver tissue and isolated hepatic stellate cells (HSCs). Hepatic fibrosis was induced in CD248(-/-) and wild-type controls with carbon tetrachloride (CCl4) treatment. RESULTS: Expression of CD248 was seen in normal liver of humans and mice but was significantly increased in liver injury using both immunostaining and gene expression assays. CD248 was co-expressed with a range of fibroblast/HSC markers including desmin, vimentin and α-smooth muscle actin (α-SMA) in murine and human liver sections. CD248 expression was restricted to isolated primary murine and human HSC. Collagen deposition and α-SMA expression, but not inflammation and neoangiogenesis, was reduced in CD248(-/-) mice compared with wild-type mice after CCl4 treatment. Isolated HSC from wild-type and CD248(-/-) mice expressed platelet-derived growth factor receptor α (PDGFR-α) and PDGFR-ß at similar levels. As expected, PDGF-BB stimulation induced proliferation of wild-type HSC, whereas CD248(-/-) HSC did not demonstrate a proliferative response to PDGF-BB. Abrogated PDGF signalling in CD248(-/-) HSC was confirmed by significantly reduced c-fos expression in CD248(-/-) HSC compared with wild-type HSC. CONCLUSIONS: Our data show that deletion of CD248 reduces susceptibility to liver fibrosis via an effect on PDGF signalling, making it an attractive clinical target for the treatment of liver injury.

Dysregulated hepatic expression of glucose transporters in chronic disease: contribution of semicarbazide-sensitive amine oxidase to hepatic glucose uptake.

Insulin resistance is common in patients with chronic liver disease (CLD). Serum levels of soluble vascular adhesion protein-1 (VAP-1) are also increased in these patients. The amine oxidase activity of VAP-1 stimulates glucose uptake via translocation of transporters to the cell membrane in adipocytes and smooth muscle cells. We aimed to document human hepatocellular expression of glucose transporters (GLUTs) and to determine if VAP-1 activity influences receptor expression and hepatic glucose uptake. Quantitative PCR and immunocytochemistry were used to study human liver tissue and cultured cells. We also used tissue slices from humans and VAP-1-deficient mice to assay glucose uptake and measure hepatocellular responses to stimulation. We report upregulation of GLUT1, -3, -5, -6, -7, -8, -9, -10, -11, -12, and -13 in CLD. VAP-1 expression and enzyme activity increased in disease, and provision of substrate to hepatic VAP-1 drives hepatic glucose uptake. This effect was sensitive to inhibition of VAP-1 and could be recapitulated by H2O2. VAP-1 activity also altered expression and subcellular localization of GLUT2, -4, -9, -10, and -13. Therefore, we show, for the first time, alterations in hepatocellular expression of glucose and fructose transporters in CLD and provide evidence that the semicarbazide-sensitive amine oxidase activity of VAP-1 modifies hepatic glucose homeostasis and may contribute to patterns of GLUT expression in chronic disease.

Non-enzymatic dissociation of human mesenchymal stromal cells improves chemokine-dependent migration and maintains immunosuppressive function.

BACKGROUND AIMS: Human bone marrow-derived mesenchymal stromal cells (MSC) can suppress inflammation; therefore their therapeutic potential is being explored in clinical trials. Poor engraftment of infused MSC limits their therapeutic utility; this may be caused by MSC processing before infusion, in particular the method of their detachment from culture. METHODS: Enzymatic methods of detaching MSC (Accutase and TrypLE) were compared with non-enzymatic methods (Cell Dissociation Buffer [CDB], ethylenediamine tetra-acetic acid and scraping) for their effect on MSC viability, chemokine receptor expression, multi-potency, immunomodulation and chemokine-dependent migration. RESULTS: TrypLE detachment preserved MSC viability and tri-lineage potential compared with non-enzymatic methods; however, this resulted in near complete loss of surface chemokine receptor expression. Of the non-enzymatic methods, CDB detachment preserved the highest viability while retaining significant tri-lineage differentiation potential. Once re-plated, CDB-detached MSC regained their original morphology and reached confluence, unlike with the use of other non-enzymatic methods. Viability was significantly reduced with the use of ethylenediamine tetra-acetic acid and further reduced with the use of cell scraping. Addition of 1% serum during CDB detachment led to higher MSC numbers entering autophagy and increased MSC recovery after re-plating. TrypLE and CDB-detached MSC suppressed CD3(+)CD4(+)CD25(-) T-cell proliferation, although TrypLE-detached MSC exhibited superior suppression at 1:20 ratio. CDB detachment retained surface chemokine receptor expression and consequently increased migration to CCL22, CXCL12 and CCL4, in contrast with TrypLE-detached MSC. CONCLUSIONS: This study demonstrates that non-enzymatic detachment of MSC with the use of CDB minimizes the negative impact on cell viability, multipotency and immunomodulation while retaining chemokine-dependent migration, which may be of importance in MSC delivery and engraftment in sites of injury.

Human mesenchymal stem cells are recruited to injured liver in a ß1-integrin and CD44 dependent manner.

UNLABELLED: Human bone marrow mesenchymal stem cells (hMSCs) have shown benefit in clinical trials of patients with liver disease. Efficient delivery of cells to target organs is critical to improving their effectiveness. This requires an understanding of the mechanisms governing cellular engraftment into the liver. Binding of hMSCs to normal/injured liver tissue, purified extracellular matrices, and human hepatic sinusoidal endothelial cells (HSECs) were quantified in static and flow conditions. To define the mechanisms underpinning hMSC interactions, neutralizing adhesion molecule antibodies were used. Fluorescently labelled hMSCs were infused intraportally into CCl(4) -injured mice with and without neutralizing antibodies. hMSCs expressed high levels of CD29/ß1-integrin and CD44. Using liver tissue binding assays, hMSC adhesion was greatest in diseased human liver versus normal liver (32.2 cells/field versus 20.5 cells/field [P = 0.048]). Neutralizing antibodies against CD29 and CD44 reduced hMSC binding to diseased liver by 34% and 35%, respectively (P = 0.05). hMSCs rolled at 528 µm/second on HSECs in flow assays. This rolling was abolished by CD29 blockade on hMSCs and vascular cell adhesion molecule-1 (VCAM-1) blockade on HSECs. Firm adhesion to HSECs was reduced by CD29 (55% [P = 0.002]) and CD44 (51% [P = 0.04]) blockade. Neutralizing antibodies to CD29 and CD44 reduced hepatic engraftment of hMSCs in murine liver from 4.45 cells/field to 2.88 cells/field (P = 0.025) and 2.35 cells/field (P = 0.03), respectively. hMSCs expressed modest levels of chemokine receptors including CCR4, CCR5, and CXCR3, but these made little contribution to hMSC adhesion in this setting. CONCLUSION: hMSCs bind preferentially to injured liver. Rolling of hMSCs is regulated by CD29/VCAM-1, whereas CD29/CD44 interactions with VCAM-1, fibronectin, and hyaluronan on HSECs determine firm adhesion both in vitro and in vivo as demonstrated using a murine model of liver injury.

Bone marrow mesenchymal stem cells and liver regeneration: believe the hypoxia!

There are limited data on the efficacy of mesenchymal stem cells (MSCs) in models of extensive hepatic resection. In the previous issue of Stem Cell Research & Therapy, Yu and colleagues demonstrate that transient hypoxic preconditioning of MSCs improves their efficacy in a rat model of massive hepatectomy. This effect appears to be mediated, in part, by increased vascular endothelial growth factor (VEGF) production by the preconditioned MSCs as well as the injured liver. Neutralizing VEGF antibodies ameliorated the benefit of hypoxia-preconditioned MSCs, establishing VEGF as a key mediator of their benefit. This novel approach merits further exploration both mechanistically and to establish the functional advantages of MSCs in other injury settings.

Functional consequences of human lymphocyte cryopreservation: implications for subsequent interactions of cells with endothelium.

In order to understand human inflammatory diseases and to develop and assess new therapeutic strategies targeting leukocyte recruitment to tissue, it is necessary to study human lymphocyte interactions with endothelium. It is often not practical to carry out assays on fresh human samples and therefore cells may be cryopreserved and batched for later study. Furthermore, many forms of adoptive cell therapy use cryopreserved cells that are required to migrate to tissue after infusion in vivo. The consequences of cryopreservation on the adhesion and migration of leukocytes is not known leading us to study the effects of cryopreservation on lymphocyte phenotype, migration, and adhesion. Cryopreservation and subsequent thawing did not alter the proportion of retrieved T cell subsets. Overall levels of expression of ß1 or ß2 integrins were unaffected but marked changes were observed in other relevant receptors. Expression of CD69, a transmembrane protein that plays a critical role in lymphocyte egress from tissues and the chemokine receptor CXCR4, increased on thawed populations and levels of CD62L and CXCR3 were reduced on thawed cells but restored if cells were allowed to recover after thawing. These changes were associated with modulation of the ability of lymphocytes to migrate across cytokine-stimulated monolayers of endothelium toward recombinant CXCL11 and CXCL12. Thus cryopreservation and thawing of lymphocytes induces changes in their adhesive phenotype and modulates their ability to migrate across endothelial monolayers. These findings have implications for in vitro experimentation and for cell therapy in which cryopreserved cells are expected to migrate when reinfused into patients.

Lack of effect of a single injection of human C-reactive protein on murine lupus or nephrotoxic nephritis.

OBJECTIVE: It has been reported that a single dose of human C-reactive protein (CRP) can prevent and reverse the renal damage in murine models of spontaneous lupus, as well as the rapid-onset immune complex disease induced in the accelerated nephrotoxic nephritis (ANTN) model. This study was undertaken to attempt to replicate these observations using a highly purified and fully characterized human CRP preparation. METHODS: (NZB x NZW)F(1) (NZB/NZW) mice were treated with a single 200-microg subcutaneous injection of CRP or control reagents either before disease onset at 4 months of age or when high-grade proteinuria was present at 7 months of age. Mice were monitored at least monthly for proteinuria and autoantibody levels. ANTN was induced by preimmunizing C57BL/6 mice with sheep IgG, followed 5 days later by injection of sheep anti-mouse glomerular basement membrane antibody and CRP or control reagents. Renal disease was assessed by regular urinalysis and histologic evaluation. RESULTS: CRP treatment of NZB/NZW mice, either early or late in the disease, had no effect on proteinuria, autoantibody titers, or survival. CRP administration did not reduce renal injury or alter disease in the ANTN model. Human serum amyloid P component, a pentraxin protein that is very closely related to CRP, similarly had no effect. CONCLUSION: Our completely negative observations do not confirm that human CRP has reproducible antiinflammatory or immunomodulatory effects in these murine models, nor do they support the suggestion that CRP might be useful for therapy of lupus or immune complex-mediated nephritis.