Fas transduces dual apoptotic and trophic signals in hematopoietic progenitors

Dioscin Regulating Bone Marrow Apoptosis in Aplastic Anemia

Background

Aplastic anemia (AA), a disease of bone marrow failure, is caused by CD8⁺T mediated apoptosis of hematopoietic cells. However, traditional immunosuppressive therapy (IST) has severe liver and kidney toxicity and even cannot achieve the expected therapeutic effect in some patients.

Purpose

Our study is aimed to investigate the effect and mechanism of dioscin (DNS) for treating AA.

Methods

Briefly, we established and evaluated the AA mouse model, DNS and positive control drugs were used for intervention treatment. After 14 days of intervention, femoral bone marrow pathology, bone marrow mononuclear cells (BMMCs) apoptosis rate, bone marrow CD34+ cell surface Fas (CD95) expression and Fas signaling pathway key proteins were detected.

Results

After the establishment of the AA mouse model, the number of peripheral blood cells including granulocytes, erythrocytes, hemoglobin, platelets and reticulocytes in the AA group model was significantly decreased compared with the group control (P < 0.01). The degree of bone marrow hyperplasia in the sternum and femur is extremely low. After different drug interventions, compared with the group model, the number of peripheral blood cells in the AA mice rebounded significantly in group DNS (P < 0.01). Not only that the apoptosis rate of BM-MCs decreased (P < 0.01), meanwhile, the CD95 molecule expressed on the CD34+ bone marrow cells had a significant decline (P < 0.01), and the expression level of the key proteins of Fas signaling pathway was also significantly decreased (P < 0.01).

Conclusion

DNS recovered the peripheral pancytopenia and bone marrow failure in AA mice. DNS reduced the key protein of Fas signaling pathway level to inhibit apoptosis of bone marrow cells to treat AA.

Biomedical Applications of Translational Optical Imaging: From Molecules to Humans

Light is a powerful investigational tool in biomedicine, at all levels of structural organization. Its multitude of features (intensity, wavelength, polarization, interference, coherence, timing, non-linear absorption, and even interactions with itself) able to create contrast, and thus images that detail the makeup and functioning of the living state can and should be combined for maximum effect, especially if one seeks simultaneously high spatiotemporal resolution and discrimination ability within a living organism. The resulting high relevance should be directed towards a better understanding, detection of abnormalities, and ultimately cogent, precise, and effective intervention. The new optical methods and their combinations needed to address modern surgery in the operating room of the future, and major diseases such as cancer and neurodegeneration are reviewed here, with emphasis on our own work and highlighting selected applications focusing on quantitation, early detection, treatment assessment, and clinical relevance, and more generally matching the quality of the optical detection approach to the complexity of the disease. This should provide guidance for future advanced theranostics, emphasizing a tighter coupling-spatially and temporally-between detection, diagnosis, and treatment, in the hope that technologic sophistication such as that of a Mars rover can be translationally deployed in the clinic, for saving and improving lives.

Brief ex vivo Fas-ligand incubation attenuates GvHD without compromising stem cell graft performance

Graft versus host disease (GvHD) remains a limiting factor for successful hematopoietic stem cell transplantation (HSCT). T cells and antigen-presenting cells (APCs) are major components of the hematopoietic G-CSF mobilized peripheral blood cell (MPBC) graft. Here we show that a short incubation (2 h) of MPBCs with hexameric Fas ligand (FasL) selectively induces apoptosis of specific donor T cell subsets and APCs but not of CD34⁺ cells. FasL treatment preferentially induces apoptosis in mature T cell subsets which express high levels of Fas (CD95), such as T stem cell memory, T central memory, and T effector memory cells, as well as T_H1 and T_H17 cells. Anti-CD3/CD28 stimulated T cells derived from FasL-treated-MPBCs express lower levels of CD25 and secrete lower levels of IFN-γ as compared to control cells not treated with FasL. FasL treatment also induces apoptosis of transitional, naïve, memory and plasmablastoid B cells leading to a reduction in their numbers in the graft and following engraftment in transplanted mice. Most importantly, ex vivo treatment of MPBCs with FasL prior to transplant in conditioned NOD-scid IL2Rγ^null (NSG) mice prevented GvHD while preserving graft versus leukemia (GvL) effects, and leading to robust stem cell engraftment.

Localized Immunomodulation with PD-L1 Results in Sustained Survival and Function of Allogeneic Islets without Chronic Immunosuppression

Allogeneic islet transplantation is limited by adverse effects of chronic immunosuppression used to control rejection. The programmed cell death 1 pathway as an important immune checkpoint has the potential to obviate the need for chronic immunosuppression. We generated an oligomeric form of programmed cell death 1 ligand chimeric with core streptavidin (SA-PDL1) that inhibited the T effector cell response to alloantigens and converted T conventional cells into CD4⁺Foxp3⁺ T regulatory cells. The SA-PDL1 protein was effectively displayed on the surface of biotinylated mouse islets without a negative impact islet viability and insulin secretion. Transplantation of SA-PDL1-engineered islet grafts with a short course of rapamycin regimen resulted in sustained graft survival and function in >90% of allogeneic recipients over a 100-d observation period. Long-term survival was associated with increased levels of intragraft transcripts for innate and adaptive immune regulatory factors, including IDO-1, arginase-1, Foxp3, TGF-β, IL-10, and decreased levels of proinflammatory T-bet, IL-1β, TNF-α, and IFN-γ as assessed on day 3 posttransplantation. T cells of long-term graft recipients generated a proliferative response to donor Ags at a similar magnitude to T cells of naive animals, suggestive of the localized nature of tolerance. Immunohistochemical analyses showed intense peri-islet infiltration of T regulatory cells in long-term grafts and systemic depletion of this cell population resulted in prompt rejection. The transient display of SA-PDL1 protein on the surface of islets serves as a practical means of localized immunomodulation that accomplishes sustained graft survival in the absence of chronic immunosuppression with potential clinical implications.

T11TS repress gliomagenic apoptosis of bone marrow hematopoietic stem cells

Combating gliomagenic global immunosuppression is one of the emerging key for improving prognosis in malignant glioma. Apoptosis plays a pivotal role within the adult hematopoietic system particularly in regulating the cells of immune system. Gliomagenic regulation of apoptotic mediators within bone marrow milieu has not been elucidated. We previously demonstrated that administration of membrane glycopeptides T11 target structure (T11TS) not only rejuvenate bone marrow hematopoietic stem cells (BMHSCs) from glioma mediated hibernation by inhibiting gliomagenic overexpression of Ang-1/Tie-2 but also stimulate glioma mediated diminution of expression CD34, c-kit, and Sca-1 markers. In the present study, we investigated the impact of glioma on apoptotic signaling cascades of BMHSCs and consequences following T11TS therapy. Bone marrow smear and Annexin V staining confirm gliomagenic acceleration of apoptotic fate of BMHSCs whereas T11TS treatment in glioma-bearing rats disrupted apoptosis of BMHSCs. Flowcytometry, immunoblotting, and immunofluorescence imagining results revealed multi potent T11TS not only significantly downregulates gliomagenic overexpression of Fas, Fas L, Bid, and caspase-8, the pro-apoptotic extrinsic mediators but also strongly inhibits cytosolic release of cytochrome-c, Apf-1, and Bax to deactivate gliomagenic caspase-9, 3 the key intrinsic apoptotic mediators followed by up modulation of anti-apoptotic Bcl-2 in glioma associated HSCs. T11TS is also able to diminish the perforin-granzyme B mediated apoptotic verdict of BMHSCs during gliomagenesis. The anti-apoptotic action of T11TS on glioma associated BMHSCs provide a crucial insight into how T11TS exerts its immunomodulatory action against glioma mediated immune devastation.

Bone Marrow Homing Enriches Stem Cells Responsible for Neogenesis of Insulin-Producing Cells, While Radiation Decreases Homing Efficiency

Small-sized adult bone marrow cells isolated by counterflow centrifugal elutriation and depleted of lineage markers (Fr25lin(-)) have the capacity to differentiate into insulin-producing cells and stabilize glycemic control. This study assessed competitive migration of syngeneic stem cells to the bone marrow and islets in a murine model of chemical diabetes. VLA-4 is expressed in ∼ 25% of these cells, whereas CXCR4 is not detected, however, it is transcriptionally upregulated (6-fold). The possibility to enrich stem cells by a bone marrow homing (BM-H) functional assay was assessed in sequential transplants. Fr25lin(-) cells labeled with PKH26 were grafted into primary myeloablated recipients, and mitotically quiescent Fr25lin(-)PKH(bright) cells were sorted from the bone marrow after 2 days. The contribution of bone marrow-homed stem cells was remarkably higher in secondary recipients compared to freshly elutriated cells. The therapeutic efficacy was further increased by omission of irradiation in the secondary recipients, showing a 25-fold enrichment of islet-reconstituting cells by the bone marrow homing assay. Donor cells identified by the green fluorescent protein (GFP) and a genomic marker in sex-mismatched transplants upregulated PDX-1 and produced proinsulin, affirming the capacity of BM-H cells to convert in the injured islets. There was no evidence of transcriptional priming of freshly elutriated subsets to express PDX-1, insulin, and other markers of endocrine progenitors, indicating that the bone marrow harbors stem cells with versatile differentiation capacity. Affinity to the bone marrow can be used to enrich stem cells for pancreatic regeneration, and reciprocally, conditioning reduces the competitive incorporation in the injured islets.

Engineering of bone marrow cells with fas-ligand protein-enhances donor-specific tolerance to solid organs

Effective immunomodulation to induce tolerance to tissue/organ allografts is attained by infusion of donor lymphocytes endowed with killing capacity through ectopic expression of a short-lived Fas-ligand (FasL) protein. The same approach has proven effective in improving hematopoietic stem and progenitor cell engraftment. This study evaluates the possibility of substitution of immune cells for bone marrow cells (BMC) to induce FasL-mediated tolerance to solid organ grafts. Expression of FasL protein on BMC increased the survival of simultaneously grafted vascularized heterotopic cardiac grafts to 90%, as compared to 30% in recipients of naïve BMC. Similar results were obtained for skin allografts implanted into radiation chimeras at 1 week after bone marrow transplantation. Further reduction of preparative conditioning to busulfan resulted in acceptance of donor skin implanted at 2 weeks after transplantation of naïve and FasL-coated BMC, whereas third-party grafts were acutely rejected. The levels of donor chimerism were in the range of 0.7% to 12% at the time of skin grafting, with higher levels in recipients of FasL-coated BMC. It is concluded that FasL-mediated abrogation of alloimmune responses can be effectively attained with BMC. There is no threshold of donor chimerism, but tolerance to solid organs evolves during the process of donor-host mutual acceptance.

Interferon and tumor necrosis factor as humoral mechanisms coupling hematopoietic activity to inflammation and injury

Enhanced hematopoiesis accompanies systemic responses to injury and infection. Tumor necrosis factor (TNF) produced by injured cells and interferons (IFNs) secreted by inflammatory cells is a co-product of the process of clearance of debris and removal of still viable but dysfunctional cells. Concomitantly, these cytokines induce hematopoietic stem and progenitor cell (HSPC) activity as an intrinsic component of the systemic response. The proposed scenario includes induction of HSPC activity by type I (IFNα/β) and II (IFNγ) receptors within the quiescent bone marrow niches rendering progenitors responsive to additional signals. TNFα converges as a non-selective stimulant of HSPC activity and both cytokines synergize with other growth factors in promoting differentiation. These physiological signaling pathways of stress hematopoiesis occur quite frequent and do not cause HSPC extinction. The proposed role of IFNs and TNFs in stress hematopoiesis commends revision of their alleged involvement in bone marrow failure syndromes.

Physiological functions of TNF family receptor/ligand interactions in hematopoiesis and transplantation

Secretion of ligands of the tumor necrosis factor (TNF) superfamily is a conserved response of parenchymal tissues to injury and inflammation that commonly perpetuates elimination of dysfunctional cellular components by apoptosis. The same signals of tissue injury that induce apoptosis in somatic cells activate stem cells and initiate the process of tissue regeneration as a coupling mechanism of injury and recovery. Hematopoietic stem and progenitor cells upregulate the TNF family receptors under stress conditions and are transduced with trophic signals. The progeny gradually acquires sensitivity to receptor-mediated apoptosis along the differentiation process, which becomes the major mechanism of negative regulation of mature proliferating hematopoietic lineages and immune homeostasis. Receptor/ligand interactions of the TNF family are physiological mechanisms transducing the need for repair, which may be harnessed in pathological conditions and transplantation. Because these interactions are physiological mechanisms of injury, neutralization of these pathways has to be carefully considered in disorders that do not involve intrinsic aberrations of excessive susceptibility to apoptosis.

Antigen-Specific Priming is Dispensable in Depletion of Apoptosis-Sensitive T Cells for GvHD Prophylaxis

Prophylactic approaches to graft versus host disease (GvHD) have employed both phenotypic reduction of T cells and selective elimination of host-primed donor T cells in vitro and in vivo. An additional approach to GvHD prophylaxis by functional depletion of apoptosis-sensitive donor T cells without host-specific sensitization ex vivo showed remarkable reduction in GHD incidence and severity. We address the role and significance of antigen-specific sensitization of donor T cells and discuss the mechanisms of functional T cell purging by apoptosis for GvHD prevention. Host-specific sensitization is dispensable because migration is antigen-independent and donor T cell sensitization is mediated by multiple and redundant mechanisms of presentation of major and minor histocompatibility complex and tissue antigens by donor and host antigen-presenting cells. Our data suggest that potential murine and human GvH effectors reside within subsets of preactivated T cells susceptible to negative regulation by apoptosis prior to encounter of and sensitization to specific antigens.

Resistance of hematopoietic progenitors to Fas-mediated apoptosis is actively sustained by NFκB with a characteristic transcriptional signature

Umbilical cord blood (UCB) is a good source of hematopoietic progenitors with increasing implementation in the clinical transplant setting. This study evaluates the molecular mechanisms of progenitor resistance to apoptosis triggered by Fas cross-linking. CD34(+) and lineage-negative progenitors survive short-term ex vivo incubation and are not induced into apoptosis by Fas cross-linking. Furthermore, brief exposure of UCB cells to Fas-ligand for 24-48 h does not impair quantitative severe combine immune deficiency (SCID) reconstitution activity and appears to foster myelomonocyte reconstitution. The transcriptome of Fas receptor-positive CD34(+) cells that survived an apoptotic challenge showed significant transcriptional upregulation of caspase-8, mucosa-associated lymphoid tissue lymphoma translocation gene-1 (MALT1), HtrA2, and GSK3β in addition to higher levels of c-FLICE inhibitory protein (FLIP), Bcl-2, and cytosolic inhibitor of apoptosis protein (cIAP) in all Fas-positive cells. Most prominent is the transcriptional upregulation of several key components the NFκB1 pathway including the membrane receptors TGF-β, interleukin-1 (IL-1), and TCR, the associated factor TNF receptor-associated factor-6 (TRAF6), and the converting enzymes TGF-β-activated kinase-1 (TAK1), double-stranded RNA-activated protein kinase (PKR), and α-catalytic subunit of IκB kinase (IKKα), that promote activation and nuclear translocation of this transcription factor. These data indicate that hematopoietic progenitors are not insensitive to apoptosis but are actively shielded from the extrinsic and intrinsic apoptotic pathways. This may occur through inherent transcriptional upregulation of the entire NFκB pathway in the presence of competent apoptotic signaling.

Two distinct mechanisms mediate the involvement of bone marrow cells in islet remodeling: neogenesis of insulin-producing cells and support of islet recovery

We have recently reported that small-sized bone marrow cells (BMCs) isolated by counterflow centrifugal elutriation and depleted of lineage markers (Fr25lin(-)) have the capacity to differentiate and contribute to regeneration of injured islets. In this study, we assess some of the characteristics of these cells compared to elutriated hematopoietic progenitors (R/O) and whole BMCs in a murine model of streptozotocin-induced chemical diabetes. The GFP(bright)CD45(+) progeny of whole BMCs and R/O progenitors progressively infiltrate the pancreas with evolution of donor chimerism; are found at islet perimeter, vascular, and ductal walls; and have a modest impact on islet recovery from injury. In contrast, Fr25lin(-) cells incorporate in the islets, convert to GFP(dim)CD45(-)PDX-1(+) phenotypes, produce proinsulin, and secrete insulin with significant contribution to stabilization of glucose homeostasis. The elutriated Fr25lin(-) cells express low levels of CD45 and are negative for SCA-1 and c-kit, as removal of cells expressing these markers did not impair conversion to produce insulin. BMCs mediate two synergistic mechanisms that contribute to islet recovery from injury: support of islet remodeling by hematopoietic cells and neogenesis of insulin-producing cells from stem cells.

Essential roles of PKA, iNOS, CD95/CD95L, and terminal caspases in suppression of eosinopoiesis by PGE2 and other cAMP-elevating agents

Up- and downregulation of eosinopoiesis control pulmonary eosinophilia in human asthma. In mice, eosinopoiesis is suppressed in vitro by prostaglandin E2 (PGE2) and in vivo by diethylcarbamazine, through a proapoptotic mechanism sequentially requiring inducible NO synthase (iNOS) and the ligand for death receptor CD95 (CD95L). We examined the roles of iNOS, cAMP-mediated signaling, caspases, and CD95L/CD95 in suppression of eosinopoiesis by PGE2 and other agents signaling through cAMP. Bone-marrow collected from BALB/c mice, or from iNOS-, CD95-, or CD95L-deficient mutants (and wild-type controls), was cultured with interleukin-5 (IL-5), alone or associated with PGE2, cAMP-inducing/mimetic agents, caspase inhibitor zVAD-fmk, iNOS inhibitor aminoguanidine, or combinations thereof, and eosinopoiesis was evaluated at various times. PGE2, added up to 24 hours of culture, dose-dependently suppressed eosinopoiesis, by inducing apoptosis. This effect was (a) paralleled by induction of iNOS in eosinophils; (b) duplicated by sodium nitroprusside, isoproterenol, and cAMP-inducing/mimetic agents; (c) prevented by protein kinase A inhibition. NO was produced through iNOS by dibutyryl-cAMP-stimulated bone-marrow. Overall, PGE2 and isoproterenol shared a requirement for four effector elements (iNOS, CD95L, CD95, and terminal caspases), which together define a pathway targeted by several soluble up- and downmodulators of eosinopoiesis, including drugs, mediators of inflammation, and cytokines.

TNF-α has tropic rather than apoptotic activity in human hematopoietic progenitors: involvement of TNF receptor-1 and caspase-8

Tumor necrosis factor-α (TNF-α) has been suggested to exert detrimental effects on hematopoietic progenitor function that might limit the success of transplants. In this study, we assessed the influences of TNF-α and its two cognate receptors on the function of fresh umbilical cord blood (UCB) and cryopreserved mobilized peripheral blood (mPB). CD34(+) progenitors from both sources are less susceptible to spontaneous apoptosis than lineage-committed cells and are not induced into apoptosis by TNF-α. Consequently, the activity of UCB-derived severe combined immune deficiency (SCID) reconstituting cells and long-term culture-initiating cells is unaffected by this cytokine. On the contrary, transient exposure of cells from both sources to TNF-α stimulates the activity of myeloid progenitors, which persists in vivo in UCB cell transplants. Progenitor stimulation is selectively mediated by TNF-R1 and involves activation of caspase-8, without redundant activity of TNF-R2. Despite significant differences between fresh UCB cells and cryopreserved mPB cells in susceptibility to apoptosis and time to activation, TNF-α is primarily involved in tropic signaling in hematopoietic progenitors from both sources. Cytokine-mediated tropism cautions against TNF-α neutralization under conditions of stress hematopoiesis and may be particularly beneficial in overcoming the limitations of UCB cell transplants.

VEGF induces neuroglial differentiation in bone marrow-derived stem cells and promotes microglia conversion following mobilization with GM-CSF

PURPOSE

Evaluation of potential tropic effects of vascular endothelial growth factor (VEGF) on the incorporation and differentiation of bone-marrow-derived stem cells (BMSCs) in a murine model of anterior ischemic optic neuropathy (AION).

METHODS

In the first approach, small-sized subset of BMCs were isolated from GFP donors mice by counterflow centrifugal elutriation and depleted of hematopoietic lineages (Fr25lin(-)). These cells were injected into a peripheral vein (1 × 10(6) in 0.2 ml) or inoculated intravitreally (2 × 10(5)) to syngeneic mice, with or without intravitreal injection of 5 μg/2μL VEGF, simultaneously with AION induction. In a second approach, hematopoietic cells were substituted by myelablative transplant of syngeseic GFP + bone marrow cells. After 3 months, progenitors were mobilized with granulocyte-macrophage colony-stimulating factor (GM-CSF) followed by VEGF inoculation into the vitreous body and AION induction . Engraftment and phenotype were examined by immunohistochemistry and FISH at 4 and 24 weeks post-transplantation, and VEGF receptors were determined by real time PCR.

RESULTS

VEGF had no quantitative effect on incorporation of elutriated cells in the injured retina, yet it induced early expression of neuroal markers in cells incorporated in the RGC layer and promoted durable gliosis, most prominent perivascular astrocytes. These effects were mediated by VEGF-R1/Flt-1, which is constitutively expresses in the elutriated fraction of stem cells. Mobilization with GM-CSF limited the differentiation of bone marrow progenitors to microglia, which was also fostered by VEGF.

CONCLUSIONS

VEGF signaling mediated by Flt-1 induces early neural and sustained astrocytic differentiation of stem cells elutriated from adult bone-marrow, with significant contribution to stabilization retinal architecture following ischemic injury.

Low FasL levels promote proliferation of human bone marrow-derived mesenchymal stem cells, higher levels inhibit their differentiation into adipocytes

Mesenchymal stem cells (MSCs) are multipotent progenitor cells that can differentiate into several cell types. Bone marrow (BM)-MSCs mainly differentiate into osteoblasts or adipocytes. MSC interactions with their microenvironment directly affect their self-renewal/differentiation program. Here, we show for the first time that Fas ligand (FasL), a well-explored proapoptotic cytokine, can promote proliferation of BM-derived MSCs in vitro and inhibits their differentiation into adipocytes. BM-MSCs treated with a low FasL dose (0.5 ng/ml) proliferated more rapidly than untreated cells without undergoing spontaneous differentiation or apoptosis, whereas higher doses (25 ng/ml) induced significant though not massive BM-MSC death, with surviving cells maintaining a stem cell phenotype. At the molecular level, 0.5 ng/ml FasL induced ERK1/2 phosphorylation and survivin upregulation, whereas 25 ng/ml FasL induced caspase activation. Importantly, 25 ng/ml FasL reversibly prevented BM-MSC differentiation into adipocytes by modulating peroxisome proliferator-activated receptor gamma (PPARγ) and FABP4/aP2 expression induced by adipogenic medium. All such effects were inhibited by anti-Fas neutralizing antibody. The in vitro data regarding adipogenesis were confirmed using Fas(lpr) mutant mice, where higher PPARγ and FABP4/aP2 mRNA and protein levels were documented in whole tibia. These data show for the first time that the FasL/Fas system can have a role in BM-MSC biology via regulation of both proliferation and adipogenesis, and may have clinical relevance because circulating Fas/FasL levels decline with age and several age-related conditions, including osteoporosis, are characterized by adipocyte accumulation in BM.

Failure of chimerism formation and tolerance induction from Fas ligand mutant bone marrow donors after nonmyeloablative conditioning

Formation of donor-recipient mixed chimerism after nonmyeloablative conditioning allows co-existence of donor and recipient hematopoietic stem cells, with solid organ allograft tolerance and less likeliness of graft versus host development. Using a post-transplant bronchiolitis obliterans murine model, we aimed to test the hypothesis that allograft preservation after mixed chimerism formation is dependent on the presence of a functional Fas ligand (FasL) on donor hematopoietic cells. To form mixed chimerism, two aliquots of 30 × 10(6) whole bone marrow cells (BMC) from either wild-type C57BL/6 in one group, or transgenic gld mice with mutant FasL (d = 0 and 2+) in the other were used, with both groups receiving intravenous busulfan (10mg/kg) on d-1 and intraperitoneal cyclophosphamide (200mg/kg) on d+1. Tracheal allografts obtained from C57BL/6 mice were implanted into recipient BALB/c mice subcutaneously on d = 0. Tracheal allografts were harvested at d+28 post-transplant and were evaluated by histopathology. Mixed chimerism formation was detected in wild type C57BL/6 whole BMC recipients, which was accompanied by tracheal allograft acceptance with near normal structure at d+28 post implantation. However, in recipients of FasL mutant whole BMC, neither mixed chimerism formation nor tracheal allograft acceptance was obtained. We thus conclude that bone marrow cells lacking functional FasL molecules could not be engrafted in allogeneic recipients to form stable mixed chimerism after nonmyeloablative conditioning, thus not allowing tracheal allograft acceptance.

TNF-α/Fas-RIP-1-induced cell death signaling separates murine hematopoietic stem cells/progenitors into 2 distinct populations

We studied the effects of TNF-α and Fas-induced death signaling in hematopoietic stem and progenitor cells (HSPCs) by examining their contributions to the development of bone marrow failure syndromes in Tak1-knockout mice (Tak1(-/-)). We found that complete inactivation of TNF-α signaling by deleting both of its receptors, 1 and 2 (Tnfr1(-/-)r2(-/-)), can prevent the death of 30% to 40% of Tak1(-/-) HSPCs and partially repress the bone marrow failure phenotype of Tak1(-/-) mice. Fas deletion can prevent the death of 5% to 10% of Tak1(-/-) HSPCs but fails to further improve the survival of Tak1(-/-)Tnfr1(-/-)r2(-/-) HSPCs, suggesting that Fas might induce death within a subset of TNF-α-sensitive HSPCs. This TNF-α/Fas-induced cell death is a type of receptor-interacting protein-1 (RIP-1)-dependent programmed necrosis called necroptosis, which can be prevented by necrostatin-1, a specific RIP-1 inhibitor. In addition, we found that the remaining Tak1(-/-) HSPCs died of apoptosis mediated by the caspase-8-dependent extrinsic apoptotic pathway. This apoptosis can be converted into necroptosis by the inhibition of caspase-8 and prevented by inhibiting both caspase-8 and RIP-1 activities. We concluded that HSPCs are heterogeneous populations in response to death signaling stimulation. Tak1 mediates a critical survival signal, which protects against both TNF-α/Fas-RIP-1-dependent necroptosis and TNF-α/Fas-independent apoptosis in HSPCs.

Primitive stem cells derived from bone marrow express glial and neuronal markers and support revascularization in injured retina exposed to ischemic and mechanical damage

Ischemic or mechanical injury to the optic nerve is an irreversible cause of vision loss, associated with limited regeneration and poor response to neuroprotective agents. The aim of this study was to assess the capacity of adult bone marrow cells to participate in retinal regeneration following the induction of anterior ischemic optic neuropathy (AION) and optic nerve crush (ONC) in a rodent model. The small-sized subset of cells isolated by elutriation and lineage depletion (Fr25lin(-)) was found to be negative for the neuroglial markers nestin and glial fibrillary acidic protein (GFAP). Syngeneic donor cells, identified by genomic marker in sex-mismatched transplants and green fluorescent protein, incorporated into the injured retina (AION and ONC) at a frequency of 0.35%-0.45% after intravenous infusion and 1.8%-2% after intravitreous implantation. Perivascular cells with astrocytic morphology expressing GFAP and vimentin were of the predominant lineage that engrafted after AION injury; 10%-18% of the donor cells incorporated in the retinal ganglion cell layer and expressed NeuN, Thy-1, neurofilament, and beta-tubulin III. The Fr25lin(-) cells displayed an excellent capacity to migrate to sites of tissue disruption and developed coordinated site-specific morphological and phenotypic neural and glial markers. In addition to cellular reconstitution of the injured retinal layers, these cells contributed to endothelial revascularization and apparently supported remodeling by secretion of insulin-like growth factor-1. These results suggest that elutriated autologous adult bone marrow-derived stem cells may serve as an accessible source for cellular reconstitution of the retina following injury.

Tumor necrosis factor receptors support murine hematopoietic progenitor function in the early stages of engraftment

Tumor necrosis factor (TNF) family receptors/ligands are important participants in hematopoietic homeostasis, in particular as essential negative expansion regulators of differentiated clones. As a prominent injury cytokine, TNF-alpha has been traditionally considered to suppress donor hematopoietic stem and progenitor cell function after transplantation. We monitored the involvement of TNF receptors (TNF-R) 1 and 2 in murine hematopoietic cell engraftment and their inter-relationship with Fas. Transplantation of lineage-negative (lin(-)) bone marrow cells (BMC) from TNF receptor-deficient mice into wild-type recipients showed defective early engraftment and loss of durable hematopoietic contribution upon recovery of host hematopoiesis. Consistently, cells deficient in TNF receptors had reduced competitive capacity as compared to wild-type progenitors. The TNF receptors were acutely upregulated in bone marrow (BM)-homed donor cells (wild-type) early after transplantation, being expressed in 60%-75% of the donor cells after 6 days. Both TNF receptors were detected in fast cycling, early differentiating progenitors, and were ubiquitously expressed in the most primitive progenitors with long-term reconstituting potential (lin(-)c-kit(+) stem cell antigen (SCA)-1(+)). BM-homed donor cells were insensitive to apoptosis induced by TNF-alpha and Fas-ligand and their combination, despite reciprocal inductive cross talk between the TNF and Fas receptors. The engraftment supporting effect of TNF-alpha is attributed to stimulation of progenitors through TNF-R1, which involves activation of the caspase cascade. This stimulatory effect was not observed for TNF-R2, and this receptor did not assume redundant stimulatory function in TNFR1-deficient cells. It is concluded that TNF-alpha plays a tropic role early after transplantation, which is essential to successful progenitor engraftment.

Regulatory functions of TRAIL in hematopoietic progenitors: human umbilical cord blood and murine bone marrow transplantation

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) signaling pathway has selective toxicity to malignant cells. The TRAIL receptors DR4 and DR5 are expressed at low levels in human umbilical cord blood cells (3-15%) and are upregulated by incubation with the cognate ligand, triggering apoptosis in 70-80% of receptor-positive cells (P<0.001). Apoptosis is not induced in hematopoietic progenitors, as determined from sustained severe combined immunodeficiency reconstituting potential and clonogenic activity. Furthermore, elimination of dead cells after incubation with TRAIL for 72 h results in a threefold enrichment in myeloid progenitors. Exposure to TRAIL in semisolid cultures showed synergistic activity of DR4 and granulocyte/macrophage colony-stimulating factor in recruiting lineage-negative (lin(-)) and CD34(+) progenitors and in promoting the formation of large colonies. In murine bone marrow, approximately 30% of lin(-) cells express TRAIL-R2 (the only murine receptor), and the receptor is upregulated after transplantation in cycling and differentiating donor cells that home to the host marrow. However, this receptor is almost ubiquitously expressed in the most primitive (lin(-)SCA-1(+)c-kit(+)) progenitors, and stimulates the clonogenic activity of lin(-) cells (P<0.001), suggesting a tropic function after transplantation. It is concluded that TRAIL does not trigger apoptosis in hematopoietic progenitors, and upregulation of its cognate receptors under stress conditions mediates tropic signaling that supports recovery from hypoplasia.

Tweak induces proliferation in renal tubular epithelium: a role in uninephrectomy induced renal hyperplasia

The tumour necrosis factor (TNF) family member TWEAK activates the Fn14 receptor and has pro-apoptotic, proliferative and pro-inflammatory actions that depend on the cell type and the microenvironment. We explored the proliferative actions of TWEAK on cultured tubular cells and in vivo on renal tubules. Additionally, we studied the role of TWEAK in compensatory proliferation following unilateral nephrectomy and in an inflammatory model of acute kidney injury (AKI) induced by a folic acid overdose. TWEAK increased the proliferation, cell number and cyclin D1 expression of cultured tubular cells, in vitro. Exposure to serum increased TWEAK and Fn14 expression and the proliferative response to TWEAK. TWEAK activated the mitogen-activated protein kinases ERK and p38, the phosphatidyl-inositol 3-kinase (PI3K)/Akt pathway and NF-κB. TWEAK-induced proliferation was prevented by inhibitors of these protein kinases and by the NF-κB inhibitor parthenolide. TWEAK-induced tubular cell proliferation as assessed by PCNA and cyclin D1 expression in the kidneys of adult healthy mice in vivo. By contrast, TWEAK knock-out mice displayed lower tubular cell proliferation in the remnant kidney following unilateral nephrectomy, a non-inflammatory model. This is consistent with TWEAK-induced proliferation on cultured tubular cells in the absence of inflammatory cytokines. Consistent with our previously published data, in the presence of inflammatory cytokines TWEAK promoted apoptosis, not proliferation, of cultured tubular cells. In this regard, TWEAK knock-out mice with AKI displayed less tubular apoptosis and proliferation, as well as improved renal function. In conclusion, TWEAK actions in tubular cells are context dependent. In a non-inflammatory milieu TWEAK induces proliferation of tubular epithelium. This may be relevant for compensatory renal hyperplasia following nephrectomy.

Upregulation of Fas and downregulation of CD94/NKG2A inhibitory receptors on circulating natural killer cells in patients with new-onset psoriasis

BACKGROUND

Psoriasis has been considered as a T-helper 1 cell-mediated autoimmune disease driven by collaboration with multiple components of innate and acquired immune cells. Natural killer (NK) cells have been shown to bridge innate and acquired immunity, and thus could potentially contribute to the pathophysiology of psoriasis.

OBJECTIVES

To investigate the phenotypic changes of circulating NK cells in patients with new-onset psoriasis.

METHODS

Fifteen patients with plaque psoriasis (eight women and seven men) who visited our clinic after their first episode of psoriasis and did not have a history of previous systemic therapy or phototherapy participated in this study. Peripheral blood mononuclear cells were isolated and stained with a panel of antibodies against cell surface receptors expressed on T and/or NK cells and analysed by flow cytometry.

RESULTS

As compared with normal healthy volunteers, patients with new-onset psoriasis showed no significant changes in numbers of peripheral NK, NK-T or T cells. NK activating receptors 2B4, CD48, NKG2D, CD16 and CD56 were found to be unchanged in new-onset psoriasis. However, the expression of Fas (activation-induced death receptor) was upregulated, whereas the expression of the NK inhibitory receptors CD94 and NKG2A was dramatically reduced on NK cells of new-onset psoriasis. These changes occurred at the level of mean fluorescent intensity, but minimally affected percentages of cells expressing Fas, CD94 and NKG2A.

CONCLUSIONS

Our findings demonstrate that changes in the expression of Fas and CD94/NKG2A receptors on NK cells may occur during new-onset psoriasis, and are likely to contribute to the pathogenesis of psoriasis.

The haemopoietic stem cell: between apoptosis and self renewal

Self renewal and apoptosis of haemopoietic stem cells (HSC) represent major factors that determine the size of the haemopoietic cell mass. Changes in self renewal above or below the steady state value of 0.5 will result in either bone marrow expansion or aplasia, respectively. Despite the growing body of research that describes the potential role of HSC, there is still very little information on the mechanisms that govern HSC self renewal and apoptosis. Considerable insight into the role of HSC in many diseases has been gained in recent years. In light of their crucial importance, this article reviews recent developments in the understanding of the molecular, biological, and physiological characteristics of haemopoietic stem cells.

TAK1 is required for the survival of hematopoietic cells and hepatocytes in mice

Transforming growth factor beta-activated kinase 1 (TAK1), a member of the MAPKKK family, is a key mediator of proinflammatory and stress signals. Activation of TAK1 by proinflammatory cytokines and T and B cell receptors induces the nuclear localization of nuclear factor kappaB (NF-kappaB) and the activation of c-Jun N-terminal kinase (JNK)/AP1 and P38, which play important roles in mediating inflammation, immune responses, T and B cell activation, and epithelial cell survival. Here, we report that TAK1 is critical for the survival of both hematopoietic cells and hepatocytes. Deletion of TAK1 results in bone marrow (BM) and liver failure in mice due to the massive apoptotic death of hematopoietic cells and hepatocytes. Hematopoietic stem cells and progenitors were among those hematopoietic cells affected by TAK1 deletion-induced cell death. This apoptotic cell death is autonomous, as demonstrated by reciprocal BM transplantation. Deletion of TAK1 resulted in the inactivation of both JNK and NF-kappaB signaling, as well as the down-regulation of expression of prosurvival genes.