High expression of heme oxygenase-1 in target organs may attenuate acute graft-versus-host disease through regulation of immune balance of TH17/Treg

Re-establishing immune tolerance in multiple sclerosis: focusing on novel mechanisms of mesenchymal stem cell regulation of Th17/Treg balance

The T-helper 17 (Th17) cell and regulatory T cell (Treg) axis plays a crucial role in the development of multiple sclerosis (MS), which is regarded as an immune imbalance between pro-inflammatory cytokines and the maintenance of immune tolerance. Mesenchymal stem cell (MSC)-mediated therapies have received increasing attention in MS research. In MS and its animal model experimental autoimmune encephalomyelitis, MSC injection was shown to alter the differentiation of CD4+T cells. This alteration occurred by inducing anergy and reduction in the number of Th17 cells, stimulating the polarization of antigen-specific Treg to reverse the imbalance of the Th17/Treg axis, reducing the inflammatory cascade response and demyelination, and restoring an overall state of immune tolerance. In this review, we summarize the mechanisms by which MSCs regulate the balance between Th17 cells and Tregs, including extracellular vesicles, mitochondrial transfer, metabolic reprogramming, and autophagy. We aimed to identify new targets for MS treatment using cellular therapy by analyzing MSC-mediated Th17-to-Treg polarization.

Dissecting the regulatory network of transcription factors in T cell phenotype/functioning during GVHD and GVT

Transcription factors play a major role in regulation and orchestration of immune responses. The immunological context of the response can alter the regulatory networks required for proper functioning. While these networks have been well-studied in canonical immune contexts like infection, the transcription factor landscape during alloactivation remains unclear. This review addresses how transcription factors contribute to the functioning of mature alloactivated T cells. This review will also examine how these factors form a regulatory network to control alloresponses, with a focus specifically on those factors expressed by and controlling activity of T cells of the various subsets involved in graft-versus-host disease (GVHD) and graft-versus-tumor (GVT) responses.

Arsenic Trioxide Combining Leflunomide Activates Nrf2-ARE-HO-1 Signaling Pathway and Protects Heart Xenografts

OBJECTIVE

To investigate the molecular mechanisms underlying the effects of arsenic trioxide (As₂O₃) in combination with leflunomide on the hamster-to-rat heart xenotransplant.

METHODS

Transplantation of LVG hamster hearts to Lewis rats was performed by anastomosis of vessels in the neck using end-to-end anastomosis with a non-suture cuff technique. Four groups of recipient rats (n=6 in each) were treated with normal saline (control), As₂O₃ [5 mg/(kg·day) intraperitoneally], leflunomide [5 mg/(kg·d) orally], or leflunomide [5 mg/(kg·d)+As₂O₃ [5 mg/(kg·d)] in combination. Donor hearts and/or rat spleens were harvested and analyzed 4 days after transplantation. Quantitative reverse-transcription polymerase chain reaction and Western blot analysis were performed to detect the expression of the nuclear factor erythroid-derived factor 2-related factor (Nrf2) and its target gene heme oxygenase-1 (HO-1), Treg cell marker fork-head Box P3 (FOXP3), apoptosis-associated proteins Bcl-2, Bax, and cleaved caspase-3. Immunohistochemical staining was used to detect the levels of inflammatory natural killer cell and macrophage infiltration, intercellular cell adhesion molecule-1 (ICAM-1) and complement C3.

RESULTS

Expression of Nrf2-ARE-HO-1 signaling pathway was upregulated in heart xenografts in rats treated with As₂O₃ plus leflunomide compared with control rats or rats treated with either drug alone (P<0.01), and this was accompanied by an increased Treg cells in the recipient rat spleen (P<0.01). In contrast, the expressions of Bax, cleaved caspase-3, ICAM-1, and complement C3, and infiltration of inflammatory cells in the xenografts were inhibited by As₂O₃ plus leflunomide treatment (P<0.01).

CONCLUSION

Combination treatment with As₂O₃ and leflunomide protected hamster heart-xenografts in recipient rats.

Regulation of inflammation by the antioxidant haem oxygenase 1

Haem oxygenase 1 (HO-1), an inducible enzyme responsible for the breakdown of haem, is primarily considered an antioxidant, and has long been overlooked by immunologists. However, research over the past two decades in particular has demonstrated that HO-1 also exhibits numerous anti-inflammatory properties. These emerging immunomodulatory functions have made HO-1 an appealing target for treatment of diseases characterized by high levels of chronic inflammation. In this Review, we present an introduction to HO-1 for immunologists, including an overview of its roles in iron metabolism and antioxidant defence, and the factors which regulate its expression. We discuss the impact of HO-1 induction in specific immune cell populations and provide new insights into the immunomodulation that accompanies haem catabolism, including its relationship to immunometabolism. Furthermore, we highlight the therapeutic potential of HO-1 induction to treat chronic inflammatory and autoimmune diseases, and the issues faced when trying to translate such therapies to the clinic. Finally, we examine a number of alternative, safer strategies that are under investigation to harness the therapeutic potential of HO-1, including the use of phytochemicals, novel HO-1 inducers and carbon monoxide-based therapies.

Heme oxygenase-1: Equally important in allogeneic hematopoietic stem cell transplantation and organ transplantation?

The intracellular enzyme heme oxygenase-1 (HO-1) is responsible for the degradation of cell-free (cf) heme. Cfheme, released upon cell damage and cell death from hemoglobin, mitochondria and myoglobin, functions as a powerful damage-associated molecular pattern (DAMP). Indeed, cfheme plays a role in a myriad of diseases characterized by (systemic) inflammation, and its rapid degradation by HO-1 is pivotal to maintain homeostasis. In the past decade, HO-1 has been extensively studied for its potential protective role in different transplantation settings, including allogeneic hematopoietic stem cell transplantation (HSCT), solid organ transplantation and pancreatic islet transplantation. These studies have shown that HO-1 can be induced by a wide range of molecules, and that induction of HO-1 has the potential to significantly reduce the incidence and severity of transplantation-related complications such as graft-versus-host disease (GvHD) and ischemia/reperfusion injury (IRI). As such, further investigation into the use of HO-1-inducing agents in human transplantation settings to facilitate the potential use of these agents in the clinic is warranted. In this review, we summarize the literature of the past 10 years on the role of HO-1 in allogeneic HSCT, solid organ transplantation (focusing on kidney and liver) and pancreatic islet transplantation. Furthermore, we provide a hypothesis about the way that HO-1 is able to provide protection against acute GvHD after allogeneic HSCT. A total of 48 research articles and 17 review articles were included in this review.

The role of heme oxygenase-1 in hematopoietic system and its microenvironment

Hematopoietic system transports all necessary nutrients to the whole organism and provides the immunological protection. Blood cells have high turnover, therefore, this system must be dynamically controlled and must have broad regeneration potential. In this review, we summarize how this complex system is regulated by the heme oxygenase-1 (HO-1)-an enzyme, which degrades heme to biliverdin, ferrous ion and carbon monoxide. First, we discuss how HO-1 influences hematopoietic stem cells (HSC) self-renewal, aging and differentiation. We also describe a critical role of HO-1 in endothelial cells and mesenchymal stromal cells that constitute the specialized bone marrow niche of HSC. We further discuss the molecular and cellular mechanisms by which HO-1 modulates innate and adaptive immune responses. Finally, we highlight how modulation of HO-1 activity regulates the mobilization of bone marrow hematopoietic cells to peripheral blood. We critically discuss the issue of metalloporphyrins, commonly used pharmacological modulators of HO-1 activity, and raise the issue of their important HO-1-independent activities.

κ‑opioid receptor agonist U50488H attenuates postoperative cognitive dysfunction of cardiopulmonary bypass rats through the PI3K/AKT/Nrf2/HO‑1 pathway

Postoperative cognitive dysfunction (POCD) is a common complication following cardiopulmonary bypass (CPB). U50488H, a κ‑opioid receptor (KOR) agonist, can specifically activate KORs on hippocampal nerve cells, resulting in neuroprotective effects. The present study established a CPB rat model, observed the protective effect of U50488H on CPB‑induced POCD and brain damage and explored the regulatory mechanism of the PI3K/AKT/nuclear factor erythroid 2‑related factor 2 (Nrf2)/heme oxygenase (HO)‑1 pathway. Sprague‑Dawley rats were divided into the following groups: Sham operation (Sham group), CPB (CPB group), KOR agonist (U50488H) + CPB (U50488H group), CPB + U50488H + HO‑1 antagonist (ZnPP‑IX; ZnPP group) and CPB + U50488H + PI3K antagonist (LY294002; LY294002 group), with 10 rats in each group. Neurological scores and the Morris water maze test were used to evaluate cognitive function; hematoxylin and eosin and terminal deoxynucleotidyl transferase dUTP nick end labeling assays were performed to observe hippocampal neuron damage in rats. Immunofluorescence was used to detect reactive oxygen species, glial fibrillary acidic protein and Nrf2 expression in the hippocampus. Enzyme‑linked immunosorbent assays were used to detect inflammatory and oxidative stress factors. Western blotting was used to examine the expression of PI3K/AKT/Nrf2/HO‑1‑related proteins. It was demonstrated that U50488H significantly reduced the neural function score of rats with POCD induced by CPB, relieved cognitive dysfunction, reduced hippocampal neuron damage, inhibited the rate of apoptosis, repaired oxidative stress injury and protected against brain damage caused by CPB. In addition, U50488H could promote Nrf2 entry into the nucleus and upregulate HO‑1 and thioredoxin 1 (Trx1) expression. In CPB rats treated with PI3K inhibitors, less Nrf2 was detected in the nucleus and HO‑1 and Trx‑1 expression levels were reduced in the nucleus. Therefore, U50488H, a KOR agonist, can activate Nrf2/HO‑1 via the PI3K/AKT pathway to improve cognitive function and reduce brain damage in CPB rats.

Donor-Derived Myeloid Heme Oxygenase-1 Controls the Development of Graft-Versus-Host Disease

Graft-versus-host disease (GVHD) remains a major clinical drawback of allogeneic hematopoietic stem cell transplantation (HSCT). Here, we investigated how the stress responsive heme catabolizing enzyme heme oxygenase-1 (HO-1, encoded by HMOX1) regulates GVHD in response to allogeneic hematopoietic stem cell transplantation in mice and humans. We found that deletion of the Hmox1 allele, specifically in the myeloid compartment of mouse donor bone marrow, promotes the development of aggressive GVHD after allogeneic transplantation. The mechanism driving GVHD in mice transplanted with allogeneic bone marrow lacking HO-1 expression in the myeloid compartment involves enhanced T cell alloreactivity. The clinical relevance of these observations was validated in two independent cohorts of HSCT patients. Individuals transplanted with hematopoietic stem cells from donors carrying a long homozygous (GT)n repeat polymorphism (L/L) in the HMOX1 promoter, which is associated with lower HO-1 expression, were at higher risk of developing severe acute GVHD as compared to donors carrying a short (GT)n repeat (S/L or S/S) polymorphism associated with higher HO-1 expression. In this study, we showed the unique importance of donor-derived myeloid HO-1 in the prevention of lethal experimental GVHD and we corroborated this observation by demonstrating the association between human HMOX1 (GT)n microsatellite polymorphisms and the incidence of severe acute GVHD in two independent HSCT patient cohorts. Donor-derived myeloid HO-1 constitutes a potential therapeutic target for HSCT patients and large-scale prospective studies in HSCT patients are necessary to validate the HO-1 L/L genotype as an independent risk factor for developing severe acute GVHD.

Key Metabolic Pathways in MSC-Mediated Immunomodulation: Implications for the Prophylaxis and Treatment of Graft Versus Host Disease

Mesenchymal stromal cells (MSCs) are spindle-shaped, plastic-adherent cells in vitro with potent immunosuppressive activity both in vitro and in vivo. MSCs have been employed as a cellular immunotherapy in diverse preclinical models and clinical trials, but most commonly as agents for the prophylaxis or therapy of graft versus host disease after hematopoietic cell transplantation. In addition to the oft studied secreted cytokines, several metabolic pathways intrinsic to MSCs, notably indoleamine 2,3-dioxygenase, prostaglandin E2, hypoxia-inducible factor 1 α, heme oxygenase-1, as well as energy-generating metabolism, have been shown to play roles in the immunomodulatory activity of MSCs. In this review, we discuss these key metabolic pathways in MSCs which have been reported to contribute to MSC therapeutic effects in the setting of hematopoietic cell transplantation and graft versus host disease. Understanding the contribution of MSC metabolism to immunomodulatory activity may substantially inform the development of future clinical applications of MSCs.

Mechanisms behind the Immunoregulatory Dialogue between Mesenchymal Stem Cells and Th17 Cells

Mesenchymal stem cells (MSCs) exhibit potent immunoregulatory abilities by interacting with cells of the adaptive and innate immune system. In vitro, MSCs inhibit the differentiation of T cells into T helper 17 (Th17) cells and repress their proliferation. In vivo, the administration of MSCs to treat various experimental inflammatory and autoimmune diseases, such as rheumatoid arthritis, type 1 diabetes, multiple sclerosis, systemic lupus erythematosus, and bowel disease showed promising therapeutic results. These therapeutic properties mediated by MSCs are associated with an attenuated immune response characterized by a reduced frequency of Th17 cells and the generation of regulatory T cells. In this manuscript, we review how MSC and Th17 cells interact, communicate, and exchange information through different ways such as cell-to-cell contact, secretion of soluble factors, and organelle transfer. Moreover, we discuss the consequences of this dynamic dialogue between MSC and Th17 well described by their phenotypic and functional plasticity.

Donor Heme Oxygenase-1 Promoter Gene Polymorphism Predicts Survival after Unrelated Bone Marrow Transplantation for High-Risk Patients

Heme oxygenase-1 (HO-1), an intracellular enzyme that catalyzes the degradation of heme into biliverdin, free iron, and carbon monoxide, exerts anti-inflammatory and cytoprotective effects against endothelial cell injury. The HO-1 promoter gene has one important single-nucleotide polymorphism (SNP) rs2071746 (-413A>T) that is functional, and the A allele has been reported to be associated with higher HO-1 expression levels than the T allele. We investigated the influence of the HO-1 rs2071746 SNP on the transplant outcomes in 593 patients with hematological malignancies undergoing unrelated, human leukocyte antigen (HLA)-matched, T-cell-replete bone marrow transplantation (BMT) through the Japan Donor Marrow Program. In patients with high-risk diseases, the donor A/A or A/T genotype was associated with better 5 year overall survival (35% vs. 25%; p = 0.03) and 5 year disease-free survival (35% vs. 22%; p = 0.0072), compared to the donor T/T genotype. These effects were not observed in patients with low-risk diseases. The current findings therefore indicate that HO-1 rs2071746 genotyping could be useful for selecting donors and tailoring transplant strategies for patients with high-risk hematologic malignancies.

Glucocorticoid resistance of allogeneic T cells alters the gene expression profile in the inflamed small intestine of mice suffering from acute graft-versus-host disease

Glucocorticoids (GCs) play an important role in controlling acute graft-versus-host disease (aGvHD), a frequent complication of allogeneic hematopoietic stem cell transplantation. The anti-inflammatory activity of GCs is mainly ascribed to the modulation of T cells and macrophages, for which reason a genetically induced GC resistance of either of these cell types causes aggravated aGvHD. Since only a few genes are currently known that are differentially regulated under these conditions, we analyzed the expression of 54 candidate genes in the inflamed small intestine of mice suffering from aGvHD when either allogeneic T cells or host myeloid cells were GC resistant using a microfluidic dynamic array platform for high-throughput quantitative PCR. The majority of genes categorized as cytokines (e.g. Il2, Il6), chemokines (e.g. Ccl2, Cxcl1), cell surface receptors (e.g. Fasl, Ctla4) and intracellular molecules (e.g. Dusp1, Arg1) were upregulated in mice transplanted with GC resistant allogeneic T cells. Moreover, the expression of several genes linked to energy metabolism (e.g. Glut1) was altered. Surprisingly, mice harboring GC resistant myeloid cells showed almost no changes in gene expression despite their fatal disease course after aGvHD induction. To identify additional genes in the inflamed small intestine that were affected by a GC resistance of allogeneic T cells, we performed an RNAseq analysis, which uncovered more than 500 differentially expressed transcripts (e.g. Cxcr6, Glut3, Otc, Aoc1, Il1r1, Sphk1) that were enriched for biological processes associated with inflammation and tissue disassembly. The changes in gene expression could be confirmed during full-blown disease but hardly any of them in the preclinical phase using high-throughput quantitative PCR. Further analysis of some of these genes revealed a highly selective expression pattern in T cells, intestinal epithelial cells and macrophages, which correlated with their regulation during disease progression. Collectively, we identified an altered gene expression profile caused by GC resistance of transplanted allogeneic T cells, which could help to define new targets for aGvHD therapy.

[Research progress in mesenchymal stem cells modified by Heme oxygenase 1]

OBJECTIVE

To review the literature reports on research progress of Heme oxygenase 1 (HO-1) modified mesenchymal stem cells (MSCs).

METHODS

The significance, effects, and related mechanism of HO-1 modification of MSCs were summarized by consulting the related literatures and reports of HO-1 modification of MSCs.

RESULTS

HO-1 modification of MSCs has important research value. It can effectively enhance the anti-oxidative stress and anti-apoptotic properties of MSCs in complex internal environment after transplantation into vivo. It can also effectively enhance the immune regulation function of MSCs. It can improve the anti-injury, repair, and immune regulation effect of MSCs in various disease models and research fields.

CONCLUSION

The basic research of HO-1 modified MSCs has made remarkable progress, which is expected to be applied in clinical trials and provide theoretical basis and reference value for stem cell therapy.

Salvianolic acid B ameliorates liver injury in a murine aGvHD model by decreasing inflammatory responses via upregulation of HO-1

Acute graft-versus-host disease (aGvHD) remains lethal, even after allogeneic hematopoietic stem cell transplantation. Inflammatory responses play an important role in aGvHD. Salvianolic acid B (Sal B) has been widely reported to have a major effect on the anti-inflammatory response, but these effects in an aGvHD model have never been reported. B6 donor splenocytes were transplanted into unirradiated BDF1 recipients and liver and serum were collected on day 14 after transplantation with or without Sal B administration. We measured the expression of pro-inflammatory cytokines and chemokines and other manifestations in aGvHD mice after Sal B treatment. Sal B ameliorated liver injury in aGvHD and promoted survival in mice. Sal B treatment resulted in decreased expression of pro-inflammatory cytokines and chemokines whose expressions in liver are normally elevated by aGvHD. Furthermore, Sal B treatment also enhanced PGC-1α expression in liver tissue and HO-1 expression in nonparenchymal cells. In addition, HO-1 inhibitor abrogated the improvement of survival rate of mice with aGvHD. These results indicated that the protective effect of Sal B relies on suppressing the inflammatory response phase in the aGvHD model, presumably by inducing HO-1. Taken together our data showed that Sal B ameliorates liver injury in aGvHD by decreasing inflammatory responses via upregulation of HO-1. It may provide a novel way to deal with this disease.

Human placenta-derived mesenchymal stem cells ameliorate GVHD by modulating Th17/Tr1 balance via expression of PD-L2

AIMS

To examine whether human placenta mesenchymal stem/stromal cells (hpMSCs) mitigate graft-versus-host-disease (GVHD) via regulation of Th17 and Tr1.

MATERIALS AND METHODS

hpMSCs or phosphate buffered saline (PBS, as a control) were injected into humanized xeno-GVHD NOD/SCID mouse model. Effects on body weights and survival times were determined. In addition, various assays, including flow cytometry (FCM) and HE stain, were performed on tissues (liver, spleen, lung and intestine) from these hpMSCs versus PBS treated GVHD mice. Th17 cell number in vitro was analyzed by FCM.

KEY FINDINGS

hpMSCs reduced weight loss, along with IL-6 and IL-17 production to prolong the survival of GVHD mice. Th17 cell number was down-regulated obviously in hpMSCs treated GVHD mice. Conversely, Tr1 cell number and TGF-β production were enhanced by hpMSCs. Moreover, knockdown of programmed death ligand 2 (PD-L2) increased Th17 cell number from PMA activated T cells co-cultured with hpMSCs.

SIGNIFICANCE

hpMSCs can modulate the balance between Th17 and Tr1 cells to alleviate GVHD. In addition, PD-L2 as expressed on hpMSCs inhibits the generation of Th17 subset from activated T cells. These data suggest that hpMSCs attenuate GVHD through inhibition of severe inflammatory responses resulting from T cell differentiation.

Expanded Regulatory T Cells Induce Alternatively Activated Monocytes With a Reduced Capacity to Expand T Helper-17 Cells

Regulatory T cells (Tregs) are essential in maintaining peripheral immunological tolerance by modulating several subsets of the immune system including monocytes. Under inflammatory conditions, monocytes migrate into the tissues, where they differentiate into dendritic cells or tissue-resident macrophages. As a result of their context-dependent plasticity, monocytes have been implicated in the development/progression of graft-vs-host disease (GvHD), autoimmune diseases and allograft rejection. In the last decade, Tregs have been exploited for their use in cell therapy with the aim to induce tolerance after solid organ transplantation and for the treatment of autoimmune diseases and GvHD. To date, safety and feasibility of Treg infusion has been demonstrated; however, many questions of how these cells induce tolerance have been raised and need to be answered. As monocytes constitute the major cellular component in inflamed tissues, we have developed an in vitro model to test how Tregs modulate their phenotype and function. We demonstrated that expanded Tregs can drive monocytes toward an alternatively activated state more efficiently than freshly isolated Tregs. The effect of expanded Tregs on monocytes led to a reduced production of pro-inflammatory cytokines (IL-6 and tumor necrosis factor-α) and NF-κB activation. Furthermore, monocytes co-cultured with expanded Tregs downregulated the expression of co-stimulatory and MHC-class II molecules with a concomitant upregulation of M2 macrophage specific markers, CD206, heme oxygenase-1, and increased interleukin-10 production. Importantly, monocytes co-cultured with expanded Tregs showed a reduced capacity to expand IL-17-producing T cells compared with monocyte cultured with freshly isolated Tregs and conventional T cells. The capacity to decrease the expansion of pro-inflammatory Th-17 was not cytokine mediated but the consequence of their lower expression of the co-stimulatory molecule CD86. Our data suggest that expanded Tregs have the capacity to induce phenotypical and functional changes in monocytes that might be crucial for tolerance induction in transplantation and the prevention/treatment of GvHD and autoimmune diseases.

HO-1 regulates the function of Treg: Association with the immune intolerance in vitiligo

In vitiligo, cutaneous depigmentation is accompanied by increased T cell cytolytic activity targeting melanocytes, indicating that autoimmune tolerance is disrupted. The inhibited amount and function of Tregs have been indicated to be involved in the autoimmune intolerance in vitiligo, however, with the conclusion still controversial and the involved mechanism unknown. In this study, we explored the molecular and cellular alterations accounting for the impaired Treg response in vitiligo. Our results showed that the amount of Tregs was drastically reduced in peripheral blood of active vitiligo patients. Furthermore, the immunoregulatory function of Tregs was attenuated, with lower expression of CTLA4, IL‐10 and TGF‐β. Moreover, the expression of HO‐1, a functional modulator of Tregs, was decreased in vitiligo Tregs, and the concentrations of HO‐1 metabolites, including bilirubin, CoHb and iron, were correspondingly decreased in serum of vitiligo patients. In addition, we treated the Tregs from vitiligo patients with Hemin, an agonist of HO‐1, and found that enhanced HO‐1 expression restored the function of Tregs by up‐regulating IL‐10 expression. Our study demonstrates the essential role of HO‐1 in the impaired Treg response in vitiligo and indicates the potential of HO‐1 as a therapeutic target in vitiligo management.

The Emerging Link Between the Complement Cascade and Purinergic Signaling in Stress Hematopoiesis

Innate immunity plays an important role in orchestrating the immune response, and the complement cascade (ComC) is a major component of this ancient defense system, which is activated by the classical-, alternative-, or mannan-binding lectin (MBL) pathways. However, the MBL-dependent ComC-activation pathway has been somewhat underappreciated for many years; recent evidence indicates that it plays a crucial role in regulating the trafficking of hematopoietic stem/progenitor cells (HSPCs) by promoting their egress from bone marrow (BM) into peripheral blood (PB). This process is initiated by the release of danger-associated molecular patterns (DAMPs) from BM cells, including the most abundant member of this family, adenosine triphosphate (ATP). This nucleotide is well known as a ubiquitous intracellular molecular energy source, but when secreted becomes an important extracellular nucleotide signaling molecule and mediator of purinergic signaling. What is important for the topic of this review, ATP released from BM cells is recognized as a DAMP by MBL, and the MBL-dependent pathway of ComC activation induces a state of "sterile inflammation" in the BM microenvironment. This activation of the ComC by MBL leads to the release of several potent mediators, including the anaphylatoxins C5a and _desArgC5a, which are crucial for egress of HSPCs into the circulation. In parallel, as a ligand for purinergic receptors, ATP affects mobilization of HSPCs by activating other pro-mobilizing pathways. This emerging link between the release of ATP, which on the one hand is an activator of the MBL pathway of the ComC and on the other hand is a purinergic signaling molecule, will be discussed in this review. This mechanism plays an important role in triggering defense mechanisms in response to tissue/organ injury but may also have a negative impact by triggering autoimmune disorders, aging of HSPCs, induction of myelodysplasia, and graft-versus-host disease after transplantation of histoincompatible hematopoietic cells.

Immunomodulatory effects of bone marrow mesenchymal stem cells overexpressing heme oxygenase-1: Protective effects on acute rejection following reduced-size liver transplantation in a rat model

Here we explore the T-lymphocyte suppressive and immunomodulatory effects of bone marrow mesenchymal stem cells (BMMSCs) overexpressing heme oxygenase-1 (HO-1) on acute rejection following reduced-size liver transplantation (RLT) in a rat model. The proliferation activity, cell cycle progression, secretion of proinflammatory cytokines, expression of CD25 and CD71 in lymphocytes, and activity of NK cells were found to be significantly lowered, and the proportion of regulatory T cells (Tregs) was found to be increased relative to BMMSCs when Adv-HO-1/BMMSCs were co-cultured with Con A ex vivo; secretion of anti-inflammatory cytokines was significantly higher. When treated with saline, BMMSCs or Adv-HO-1/BMMSCs, post-transplantation rats receiving Adv-HO-1/BMMSCs showed better median survival time, lower rejection activity index, higher anti-inflammatory cytokine levels, lower proinflammatory cytokine levels, more peripheral Tregs, and lower natural killer cell viability. These results suggest that HO-1 enhanced and prolonged the effects of BMMSCs on acute rejection following RLT, with immunomodulatory effects in which adaptive and innate immunity, as well as paracrine signaling, may play important roles.

Luteolin protects mice from severe acute pancreatitis by exerting HO-1-mediated anti-inflammatory and antioxidant effects

Reseda odorata L. has long been used in traditional Asian medicine for the treatment of diseases associated with oxidative injury and acute inflammation, such as endotoxemia, acute lung injury, acute myocardial infarction and hepatitis. Luteolin, the main component of Reseda odorata L., which is also widely found in many natural herbs and vege-tables, has been shown to induce heme oxygenase-1 (HO-1) expression to exert anti-inflammatory and antioxidant effects. In this study, we aimed to examine the effects of luteolin on mice with severe acute pancreatitis (SAP), and to explore the underlying mechanisms. Cerulein and lipopolysaccharide were used to induce SAP in male Institute of Cancer Research (ICR) mice in the SAP group. The SAP group was divided into 4 subgroups, as follows: the vehicle, luteolin, zinc protoporphyrin (ZnPP) only, and luteolin (Lut) + ZnPP (luteolin plus zinc protoporphyrin treatment) groups. The wet/dry weight ratios, hematoxylin and eosin staining and pathological scores of pancreatic tissues were assessed and compared to those of the control mice. Amylase, lipase, nuclear factor-κB (NF-κB) and myeloperoxidase activities, and malondialdehyde, tumor necrosis factor α (TNFα), interleukin (IL)-6, IL-10 and HO-1 levels, as well as the expression of HO-1 were determined in serum and/or pancreatic tissue samples. SAP was successfully induced in male mice compared to normal control mice. The wet/dry weight ratios, pathological scores, and amylase and lipase activity, as well as the levels of TNFα and IL-6 were significantly reduced in the pancreatic tissues of the mice in the Lut group compared with those of the mice in the vehicle group. The Lut group exhibited a significant increase in HO-1 expression in the pancreas and enhanced serum HO-1 and IL-10 levels compared with the vehicle group. The suppression of HO-1 activity in the ZnPP group significantly abolished the protective effects of luteolin. NF-κB expression in the pancreatic tissues from the mice in the Lut + ZnPP group was significantly increased following the suppression of HO-1 activity. On the whole, our findings demonstrate that luteolin protects mice from SAP by inducing HO-1-mediated anti-inflammatory and antioxidant activities, in association with the suppression of the activation of the NF-κB pathway.