Interferon-gamma and tumor necrosis factor-alpha synergistically enhance the immunosuppressive capacity of human umbilical-cordderived mesenchymal stem cells by increasing PD-L1 expression

BACKGROUND The immunosuppressive capacity of mesenchymal stem cells(MSCs)is dependent on the“license”of several proinflammatory factors to express immunosuppressive factors such as programmed cell death 1 ligand 1(PD-L1),which determines the clinical therapeutic efficacy of MSCs for inflammatory or immune diseases.In MSCs,interferon-gamma(IFN-γ)is a key inducer of PD-L1 expression,which is synergistically enhanced by tumor necrosis factor-alpha(TNF-α);however,the underlying mechanism is unclear.AIM To reveal the mechanism of pretreated MSCs express high PD-L1 and explore the application of pretreated MSCs in ulcerative colitis.METHODS We assessed PD-L1 expression in human umbilical-cord-derived MSCs(hUC-MSCs)induced by IFN-γand TNF-α,alone or in combination.Additionally,we performed signal pathway inhibitor experiments as well as RNA interference experiments to elucidate the molecular mechanism by which IFN-γalone or in combination with TNF-αinduces PD-L1 expression.Moreover,we used luciferase reporter gene experiments to verify the binding sites of the transcription factors of each signal transduction pathway to the targeted gene promoters.Finally,we evaluated the immunosuppressive capacity of hUC-MSCs treated with IFN-γand TNF-αin both an in vitro mixed lymphocyte culture assay,and in vivo in mice with dextran sulfate sodium-induced acute colitis.RESULTS Our results suggest that IFN-γinduction alone upregulates PD-L1 expression in hUC-MSCs while TNF-αalone does not,and that the co-induction of IFN-γand TNF-αpromotes higher expression of PD-L1.IFN-γinduces hUCMSCs to express PD-L1,in which IFN-γactivates the JAK/STAT1 signaling pathway,up-regulates the expression of the interferon regulatory factor 1(IRF1)transcription factor,promotes the binding of IRF1 and the PD-L1 gene promoter,and finally promotes PD-L1 mRNA.Although TNF-αalone did not induce PD-L1 expression in hUCMSCs,the addition of TNF-αsignificantly enhanced IFN-γ-induced JAK/STAT1/IRF1 activation.TNF-αupregulated IFN-γreceptor expression through activation of the nuclear factor kappa-B signaling pathway,which significantly enhanced IFN-γsignaling.Finally,co-induced hUC-MSCs have a stronger inhibitory effect on lymphocyte proliferation,and significantly ameliorate weight loss,mucosal damage,inflammatory cell infiltration,and up-regulation of inflammatory factors in colitis mice.CONCLUSION Overall,our results suggest that IFN-γand TNF-αenhance both the immunosuppressive ability of hUC-MSCs and their efficacy in ulcerative colitis by synergistically inducing high expression of PD-L1.

The Flower of Youth Blooms on the Plateau

Li Yilei is the winner of the May 1st Labour Medal of Tibet Autonomous Region,the 5th Model Worker of Tibet Autonomous Region,and employee of Shigatse Branch of Tibet Marketing Company.On the eve of May 4,2014,Li Yilei read a message from General Secretary Xi Jinping to the youth on the Internet that"let the flower of youth bloom wherever the motherland needs it most and write a wonderful life in the great practice of realising the Chinese Dream".She has been longing for Tibet,and it suddenly occurred to her that she could go to the frontier,where the motherland needed her the most!

The expression mechanism of programmed cell death 1 ligand 1 and its role in immunomodulatory ability of mesenchymal stem cells

Programmed cell death 1 ligand 1(PD-L1)is an important immunosuppressive molecule,which inhibits the function of T cells and other immune cells by binding to the receptor programmed cell death-1.The PD-L1 expression disorder plays an important role in the occurrence,development,and treatment of sepsis or other inflammatory diseases,and has become an important target for the treatment of these diseases.Mesenchymal stem cells(MSCs)are a kind of pluripotent stem cells with multiple differentiation potential.In recent years,MSCs have been found to have a strong immunosuppressive ability and are used to treat various inflammatory insults caused by hyperimmune diseases.Moreover,PD-L1 is deeply involved in the immunosuppressive events of MSCs and plays an important role in the treatment of various diseases.In this review,we will summarize the main regulatory mechanism of PD-L1 expression,and discuss various biological functions of PD-L1 in the immune regulation of MSCs.

Elevated Levels of Naturally-Occurring Autoantibodies Against the Extracellular Domain of p75NTR Aggravate the Pathology of Alzheimer's Disease

The extracellular domain(p75ECD)of p75 neurotrophin receptor(p75NTR)antagonizes Aβ neurotoxicity and promotes Aβclearance in Alzheimer’s disease(AD).The impaired shedding of p75ECD is a key pathological process in AD,but its regulatory mechanism is largely unknown.This study was designed to investigate the presence and alterations of naturally-occurring autoantibodies against p75ECD(p75ECD-NAbs)in AD patients and their effects on AD pathology.We found that the cerebrospinal fluid(CSF)level of p75ECD-NAbs was increased in AD,and negatively associated with the CSF levels of p75ECD.Transgenic AD mice actively immunized with p75ECD showed a lower level of p75ECD and more severe AD pathology in the brain,as well as worse cognitive functions than the control groups,which were immunized with Re-p75ECD(the reverse sequence of p75ECD)and phosphate-buffered saline,respectively.These findings demonstrate the impact of p75ECD-NAbs on p75NTR/p75ECD imbalance,providing a novel insight into the role of autoimmunity and p75NTR in AD.

Transplantation of adult spinal cord grafts into spinal cord transected rats improves their locomotor function

Grafted embryonic central neural tissue pieces can recover function of hemisected spinal cord in neonatal rats and promote axonal growth in adults. However, spinal cord segments from adults have not been used as donor segments for allogeneic transplantation. Here, we utilized adult spinal cord tissue grafts(aSCGs) as donor constructs for repairing complete spinal cord injury(SCI). Moreover, to provide a favourable microenvironment for SCI treatment, a growth factor cocktail containing three growth factors(brain-derived neurotrophic factor, neurotrophin-3 and vascular endothelial growth factor), was applied to the aSCG transplants. We found that the locomotor function was significantly improved 12 weeks after transplantation of aSCGs into the spinal cord lesion site in adult rats. Transplantation of aSCGs combined with these growth factors enhanced neuron and oligodendrocyte survival and functional restoration. These encouraging results indicate that treatment of complete SCI by transplanting aSCGs, especially in the presence of growth factors, has a positive effect on motor functional recovery, and therefore could be considered as a possible therapeutic strategy for SCI.

Allotransplantation of adult spinal cord tissues after complete transected spinal cord injury: long-term survival and functional recovery in canines

Spinal cord injury(SCI), especially complete transected SCI, leads to loss of cells and extracellular matrix and functional impairments. In a previous study, we transplanted adult spinal cord tissues(aSCTs) to replace lost tissues and facilitate recovery in a rat SCI model. However, rodents display considerable differences from human patients in the scale, anatomy and functions of spinal cord systems, and responses after injury. Thus, use of a large animal SCI model is required to examine the repair efficiency of potential therapeutic approaches. In this study, we transplanted allogenic aSCTs from adult dogs to the lesion area of canines after complete transection of the thoracic spinal cord, and investigated the long-term cell survival and functional recovery. To enhance repair efficiency, a growth factor cocktail was added during aSCT transplantation, providing a favorable microenvironment. The results showed that transplantation of a SCTs, in particular with the addition of growth factors, significantly improves locomotor function restoration and increases the number of neurofilament-, microtubule-associated protein2-, 5-hydroxytryptamine-, choline acetyltransferase-and tyrosine hydroxylase-positive neurons in the lesion area at 6 months post-surgery. In addition, we demonstrated that donor neurons in a SCTs can survive for a long period after transplantation. This study showed for the first time that transplanting aSCTs combined with growth factor supplementation facilitates reconstruction of injured spinal cords, and consequently promotes long lasting motor function recovery in a large animal complete transected SCI model, and therefore could be considered as a possible therapeutic strategy in humans.

Chronic hypoperfusion due to intracranial large artery stenosis is not associated with cerebralβ-amyloid deposition and brain atrophy

Background:Insufficient cerebral perfusion is suggested to play a role in the development of Alzheimer disease(AD).However,there is a lack of direct evidence indicating whether hypoperfusion causes or aggravates AD pathology.We investigated the effect of chronic cerebral hypoperfusion on AD-related pathology in humans.Methods:We enrolled a group of cognitively normal patients(median age:64 years)with unilateral chronic cerebral hypoperfusion.Regions of interest with the most pronounced hypoperfusion changes were chosen in the hypoperfused region and were then mirrored in the contralateral hemisphere to create a control region with normal perfusion.11C-Pittsburgh compound-positron emission tomography standard uptake ratios and brain atrophy indices were calculated from the computed tomography images of each patient.Results:The median age of the 10 participants,consisting of 4 males and 6 females,was 64 years(47-76 years).We found that there were no differences in standard uptake ratios of the cortex(volume of interest[VOI]:P=0.721,region of interest[ROI]:P=0.241)and grey/white ratio(VOI:P=0.333,ROI:P=0.445)and brain atrophy indices(Bicaudate,Bifrontal,Evans,Cella,Cella media,and Ventricular index,P>0.05)between the hypoperfused regions and contralateral normally perfused regions in patients with unilateral chronic cerebral hypoperfusion.Conclusion:Our findings suggest that chronic hypoperfusion due to large vessel stenosis may not directly induce cerebralβ-amyloid deposition and neurodegeneration in humans.

Naturally-Occurring Antibodies Against Bim are Decreased in Alzheimer’s Disease and Attenuate AD-type Pathology in a Mouse Model

Increased neuronal apoptosis is an important pathological feature of Alzheimer’s disease(AD).The Bcl-2-interacting mediator of cell death(Bim)mediates amyloid-beta(Aβ)-induced neuronal apoptosis.Naturally-occurring antibodies against Bim(NAbs-Bim)exist in human blood,with their levels and functions unknown in AD.In this study,we found that circulating NAbs-Bim were decreased in AD patients.Plasma levels of NAbs-Bim were negatively associated with brain amyloid burden and positively associated with cognitive functions.Furthermore,NAbs-Bim purified from intravenous immunoglobulin rescued the behavioral deficits and ameliorated Aβdeposition,tau hyperphosphorylation,microgliosis,and neuronal apoptosis in APP/PS1 mice.In vitro investigations demonstrated that NAbs-Bim were neuroprotective against AD through neutralizing Bim-directed neuronal apoptosis and the amyloidogenic processing of amyloid precursor protein.These findings indicate that the decrease of NAbs-Bim might contribute to the pathogenesis of AD and immunotherapies targeting Bim hold promise for the treatment of AD.