Activated protein C inhibits pancreatic islet inflammation, stimulates T regulatory cells, and prevents diabetes in non-obese diabetic (NOD) mice

Engineering Pancreatic Islets to Transiently Codisplay on Their Surface Thrombomodulin and CD47 Immunomodulatory Proteins as a Means of Mitigating Instant Blood-Mediated Inflammatory Reaction following Intraportal Transplantation

Most pancreatic islets are destroyed immediately after intraportal transplantation by an instant blood-mediated inflammatory reaction (IBMIR) generated through activation of coagulation, complement, and proinflammatory pathways. Thus, effective mitigation of IBMIR may be contingent on the combined use of agents targeting these pathways for modulation. CD47 and thrombomodulin (TM) are two molecules with distinct functions in regulating coagulation and proinflammatory responses. We previously reported that the islet surface can be modified with biotin for transient display of novel forms of these two molecules chimeric with streptavidin (SA), that is, thrombomodulin chimeric with SA (SA-TM) and CD47 chimeric with SA (SA-CD47), as single agents with improved engraftment following intraportal transplantation. This study aimed to test whether islets can be coengineered with SA-TM and SA-CD47 molecules as a combinatorial approach to improve engraftment by inhibiting IBMIR. Mouse islets were effectively coengineered with both molecules without a detectable negative impact on their viability and metabolic function. Coengineered islets were refractory to destruction by IBMIR ex vivo and showed enhanced engraftment and sustained function in a marginal mass syngeneic intraportal transplantation model. Improved engraftment correlated with a reduction in intragraft innate immune infiltrates, particularly neutrophils and M1 macrophages. Moreover, transcripts for various intragraft procoagulatory and proinflammatory agents, including tissue factor, HMGB1 (high-mobility group box-1), IL-1β, IL-6, TNF-α, IFN-γ, and MIP-1α, were significantly reduced in coengineered islets. These data demonstrate that the transient codisplay of SA-TM and SA-CD47 proteins on the islet surface is a facile and effective platform to modulate procoagulatory and inflammatory responses with implications for both autologous and allogeneic islet transplantation.

Endothelial Protein C Receptor and Its Impact on Rheumatic Disease

Endothelial Protein C Receptor (EPCR) is a key regulator of the activated protein C anti-coagulation pathway due to its role in the binding and activation of this protein. EPCR also binds to other ligands such as Factor VII and X, γδ T-cells, plasmodium falciparum erythrocyte membrane protein 1, and Secretory group V Phospholipases A2, facilitating ligand-specific functions. The functions of EPCR can also be regulated by soluble (s)EPCR that competes for the binding sites of membrane-bound (m)EPCR. sEPCR is created when mEPCR is shed from the cell surface. The propensity of shedding alters depending on the genetic haplotype of the EPCR gene that an individual may possess. EPCR plays an active role in normal homeostasis, anti-coagulation pathways, inflammation, and cell stemness. Due to these properties, EPCR is considered a potential effector/mediator of inflammatory diseases. Rheumatic diseases such as rheumatoid arthritis and systemic lupus erythematosus are autoimmune/inflammatory conditions that are associated with elevated EPCR levels and disease activity, potentially driven by EPCR. This review highlights the functions of EPCR and its contribution to rheumatic diseases.

Engineering pancreatic islets with a novel form of thrombomodulin protein to overcome early graft loss triggered by instant blood-mediated inflammatory reaction

The instant blood-mediated inflammatory reaction (IBMIR) is initiated by innate immune responses that cause substantial islet loss after intraportal transplantation. Thrombomodulin (TM) is a multifaceted innate immune modulator. In this study, we report the generation of a chimeric form of thrombomodulin with streptavidin (SA-TM) for transient display on the surface of islets modified with biotin to mitigate IBMIR. SA-TM protein expressed in insect cells showed the expected structural and functional features. SA-TM converted protein C into activated protein C, blocked phagocytosis of xenogeneic cells by mouse macrophages and inhibited neutrophil activation. SA-TM was effectively displayed on the surface of biotinylated islets without a negative effect on their viability or function. Islets engineered with SA-TM showed improved engraftment and established euglycemia in 83% of diabetic recipients when compared with 29% of recipients transplanted with SA-engineered islets as control in a syngeneic minimal mass intraportal transplantation model. Enhanced engraftment and function of SA-TM-engineered islets were associated with the inhibition of intragraft proinflammatory innate cellular and soluble mediators of IBMIR, such as macrophages, neutrophils, high-mobility group box 1, tissue factor, macrophage chemoattractant protein-1, interleukin-1β, interleukin-6, tumor necrosis factor-α, interferon-γ. Transient display of SA-TM protein on the islet surface to modulate innate immune responses causing islet graft destruction has clinical potential for autologous and allogeneic islet transplantation.

The protein C pathways

PURPOSE OF REVIEW

To provide an overview of the state-of-the-art in protein C (PC) pathway research.

RECENT FINDINGS

The PC pathway is crucial for maintaining hemostasis to prevent venous thromboembolism. This is evident from genetic mutations that result in impaired PC pathway activity and contribute to increased venous thromboembolism risk in affected individuals. In addition to its anticoagulant role, activated PC (APC) also mediates a complex, pleiotropic role in the maintenance of vascular cell health, which it achieves via anti-inflammatory and antiapoptotic cell signaling on endothelial cells. Emerging data have demonstrated that cell signaling by APC, mediated by multiple receptor interactions on different cell types, also confers cytoprotective and anti-inflammatory benefits. Defects in both arms of the PC pathway are associated with increased susceptibility to thrombo-inflammatory disease in various preclinical thrombotic, proinflammatory and neurological disease models. Moreover, recent studies have identified attenuation of anticoagulant PC pathway activity as an exciting therapeutic opportunity to promote hemostasis in patients with inherited or acquired bleeding disorders.

SUMMARY

In this review, we provide an overview of some recent developments in our understanding of the PC pathways.

Activated Protein C Protects against Murine Contact Dermatitis by Suppressing Protease-Activated Receptor 2

Atopic dermatitis (AD) is a chronic inflammatory skin disease associated with excessive inflammation and defective skin barrier function. Activated protein C (APC) is a natural anticoagulant with anti-inflammatory and barrier protective functions. However, the effect of APC on AD and its engagement with protease activated receptor (PAR)1 and PAR2 are unknown. Methods: Contact hypersensitivity (CHS), a model for human AD, was induced in PAR1 knockout (KO), PAR2KO and matched wild type (WT) mice using 2,4-dinitrofluorobenzene (DNFB). Recombinant human APC was administered into these mice as preventative or therapeutic treatment. The effect of APC and PAR1KO or PARKO on CHS was assessed via measurement of ear thickness, skin histologic changes, inflammatory cytokine levels, Th cell phenotypes and keratinocyte function. Results: Compared to WT, PAR2KO but not PAR1KO mice displayed less severe CHS when assessed by ear thickness; PAR1KO CHS skin had less mast cells, lower levels of IFN-γ, IL-4, IL-17 and IL-22, and higher levels of IL-1β, IL-6 and TGF-β1, whereas PAR2KO CHS skin only contained lower levels of IL-22 and IgE. Both PAR1KO and PAR2KO spleen cells had less Th1/Th17/Th22/Treg cells. In normal skin, PAR1 was present at the stratum granulosum and spinosum, whereas PAR2 at the upper layers of the epidermis. In CHS, however, the expression of PAR1 and PAR2 were increased and spread to the whole epidermis. In vitro, compared to WT cells, PAR1KO keratinocytes grew much slower, had a lower survival rate and higher para permeability, while PAR2KO cells grew faster, were resistant to apoptosis and para permeability. APC inhibited CHS as a therapeutic but not as a preventative treatment only in WT and PAR1KO mice. APC therapy reduced skin inflammation, suppressed epidermal PAR2 expression, promoted keratinocyte growth, survival, and barrier function in both WT and PAR1KO cells, but not in PAR2KO cells. Conclusions: APC therapy can mitigate CHS. Although APC acts through both PAR1 and PAR2 to regulate Th and mast cells, suppression of clinical disease in mice is achieved mainly via inhibition of PAR2 alone. Thus, APC may confer broad therapeutic benefits as a disease-modifying treatment for AD.

Activated Protein C Ameliorates Diabetic Cardiomyopathy via Modulating OTUB1/YB-1/MEF2B Axis

Aims: The pathogenesis of diabetic cardiomyopathy (DCM) is complex and the detailed mechanism remains unclear. Coagulation protease activated Protein C (aPC) has been reported to have a protective effect in diabetic microvascular disease. Here, we investigated whether aPC could play a protective role in the occurrence and development of major diabetic complication DCM, and its underlying molecular mechanism.

Methods and Results: In a mouse model of streptozotocin (STZ) induced DCM, endogenous aPC levels were reduced. Restoring aPC levels by exogenous administration of zymogen protein C (PC) improved cardiac function of diabetic mice measured by echocardiography and invasive hemodynamics. The cytoprotective effect of aPC in DCM is mediated by transcription factor Y-box binding protein-1 (YB-1). Mechanistically, MEF2B lies downstream of YB-1 and YB-1/MEF2B interaction restrains deleterious MEF2B promoter activity in DCM. The regulation of YB-1 on MEF2B transcription was analyzed by dual-luciferase and chromatin immunoprecipitation assays. In diabetic mice, aPC ameliorated YB-1 degradation via reducing its K48 ubiquitination through deubiquitinating enzyme otubain-1 (OTUB1) and improving the interaction between YB-1 and OTUB1. Using specific agonists and blocking antibodies, PAR1 and EPCR were identified as crucial receptors for aPC's dependent cytoprotective signaling.

Conclusion: These data identify that the cytoprotective aPC signaling via PAR1/EPCR maintains YB-1 levels by preventing the ubiquitination and subsequent proteasomal degradation of YB-1 via OTUB1. By suppressing MEF2B transcription, YB-1 can protect against DCM. Collectively, the current study uncovered the important role of OTUB1/YB-1/MEF2B axis in DCM and targeting this pathway might offer a new therapeutic strategy for DCM.

Translational Perspective: DCM is emerging at epidemic rate recently and the underlying mechanism remains unclear. This study explored the protective cell signaling mechanisms of aPC in mouse models of DCM. As a former FDA approved anti-sepsis drug, aPC along with its derivatives can be applied from bench to bed and can be explored as a new strategy for personalized treatment for DCM. Mechanistically, OTUB1/YB-1/MEF2B axis plays a critical role in the occurrence and development of DCM and offers a potential avenue for therapeutic targeting of DCM.

Thrombin generation and activity in multiple sclerosis

The coagulation cascade and immune system are intricately linked, highly regulated and respond cooperatively in response to injury and infection. Increasingly, evidence of hyper-coagulation has been associated with autoimmune disorders, including multiple sclerosis (MS). The pathophysiology of MS includes immune cell activation and recruitment to the central nervous system (CNS) where they degrade myelin sheaths, leaving neuronal axons exposed to damaging inflammatory mediators. Breakdown of the blood-brain barrier (BBB) facilitates the entry of peripheral immune cells. Evidence of thrombin activity has been identified within the CNS of MS patients and studies using animal models of experimental autoimmune encephalomyelitis (EAE), suggest increased thrombin generation and activity may play a role in the pathogenesis of MS as well as inhibit remyelination processes. Thrombin is a serine protease capable of cleaving multiple substrates, including protease activated receptors (PARs), fibrinogen, and protein C. Cleavage of all three of these substrates represent pathways through which thrombin activity may exert immuno-regulatory effects and regulate permeability of the BBB during MS and EAE. In this review, we summarize evidence that thrombin activity directly, through PARs, and indirectly, through fibrin formation and activation of protein C influences neuro-immune responses associated with MS and EAE pathology.

Coagulation/Complement Activation and Cerebral Hypoperfusion in Relapsing-Remitting Multiple Sclerosis

Introduction

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system with an underlying immune-mediated and inflammatory pathogenesis. Innate immunity, in addition to the adaptive immune system, plays a relevant role in MS pathogenesis. It represents the immediate non-specific defense against infections through the intrinsic effector mechanism “immunothrombosis” linking inflammation and coagulation. Moreover, decreased cerebral blood volume (CBV), cerebral blood flow (CBF), and prolonged mean transit time (MTT) have been widely demonstrated by MRI in MS patients. We hypothesized that coagulation/complement and platelet activation during MS relapse, likely during viral infections, could be related to CBF decrease. Our specific aims are to evaluate whether there are differences in serum/plasma levels of coagulation/complement factors between relapsing-remitting (RR) MS patients (RRMS) in relapse and those in remission and healthy controls as well as to assess whether brain hemodynamic changes detected by MRI occur in relapse compared with remission. This will allow us to correlate coagulation status with perfusion and demographic/clinical features in MS patients.

Materials and Methods

This is a multi-center, prospective, controlled study. RRMS patients (1° group: 30 patients in relapse; 2° group: 30 patients in remission) and age/sex-matched controls (3° group: 30 subjects) will be enrolled in the study. Patients and controls will be tested for either coagulation/complement (C3, C4, C4a, C9, PT, aPTT, fibrinogen, factor II, VIII, and X, D-dimer, antithrombin, protein C, protein S, von-Willebrand factor), soluble markers of endothelial damage (thrombomodulin, Endothelial Protein C Receptor), antiphospholipid antibodies, lupus anticoagulant, complete blood count, viral serological assays, or microRNA microarray. Patients will undergo dynamic susceptibility contrast-enhanced MRI using a 3.0-T scanner to evaluate CBF, CBV, MTT, lesion number, and volume.

Statistical Analysis

ANOVA and unpaired t-tests will be used. The level of significance was set at p ≤ 0.05.

Discussion

Identifying a link between activation of coagulation/complement system and cerebral hypoperfusion could improve the identification of novel molecular and/or imaging biomarkers and targets, leading to the development of new effective therapeutic strategies in MS.

Clinical Trial Registration

Clinicaltrials.gov, identifier NCT04380220.

Cell biology of activated protein C

PURPOSE OF REVIEW

The serine protease activated protein C (aPC) was initially characterized as an endogenous anticoagulant, but in addition conveys anti-inflammatory, barrier-protective, and pro cell-survival functions. Its endogenous anticoagulant function hampered the successful and continuous implantation of aPC as a therapeutic agent in septic patients. However, it became increasingly apparent that aPC controls cellular function largely independent of its anticoagulant effects through cell-specific and context-specific receptor complexes and intracellular signaling pathways. The purpose of this review is to outline the mechanisms of aPC-dependent cell signaling and its intracellular molecular targets.

RECENT FINDINGS

With the advent of new therapeutic agents either modulating directly and specifically the activity of coagulation proteases or interfering with protease-activated receptor signaling a better understanding not only of the receptor mechanisms but also of the intracellular signaling mechanisms controlled by aPC in a disease-specific and context-specific fashion, is required to tailor new therapeutic approaches based on aPC's anti-inflammatory, barrier-protective, and pro cell-survival functions.

SUMMARY

This review summarizes recent insights into the intracellular signaling pathways controlled by aPC in a cell-specific and context-specific fashion. We focus on aPC-mediated barrier protection, inhibition of inflammation, and cytoprotecting within this review.

Activated protein C targets immune cells and rheumatoid synovial fibroblasts to prevent inflammatory arthritis in mice

Objectives

To investigate whether activated protein C (APC), a physiological anticoagulant can inhibit the inflammatory/invasive properties of immune cells and rheumatoid arthritis synovial fibroblasts (RASFs) in vitro and prevent inflammatory arthritis in murine antigen-induced arthritis (AIA) and CIA models.

Methods

RASFs isolated from synovial tissues of patients with RA, human peripheral blood mononuclear cells (PBMCs) and mouse thymus cells were treated with APC or TNF-α/IL-17 and the following assays were performed: RASF proliferation and invasion by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and cell invasion assays, respectively; cytokines and signalling molecules using ELISA or western blot; Th1 and Th17 phenotypes in human PBMCs or mouse thymus cells by flow cytometry. The in vivo effect of APC was evaluated in AIA and CIA models.

Results

In vitro, APC inhibited IL-1β, IL-17 and TNF-α production, IL-17-stimulated cell proliferation and invasion and p21 and nuclear factor κB activation in RASFs. In mouse thymus cells and human PBMCs, APC suppressed Th1 and Th17 phenotypes. In vivo, APC inhibited pannus formation, cartilage destruction and arthritis incidence/severity in both CIA and AIA models. In CIA, serum levels of IL-1β, IL-6, IL-17, TNF-α and soluble endothelial protein C receptor were significantly reduced by APC treatment. Blocking endothelial protein C receptor, the specific receptor for APC, abolished the early or preventative effect of APC in AIA.

Conclusion

APC prevents the onset and development of arthritis in CIA and AIA models via suppressing inflammation, Th1/Th17 phenotypes and RASF invasion, which is likely mediated via endothelial protein C receptor.

Activated protein C ameliorates chronic graft-versus-host disease by PAR1-dependent biased cell signaling on T cells

Soluble thrombomodulin plasma concentrations are elevated in steroid-resistant graft-versus-host disease (GVHD), implying endothelial hypofunctioning for thrombomodulin-dependent generation of activated protein C's (APC) anticoagulant, anti-inflammatory, and antiapoptotic functions. Recombinant thrombomodulin or APC administration decreases acute GVHD, manifested by intense inflammation and tissue destruction. Here, we administered recombinant murine wild-type (WT) APC to mice with established chronic GVHD (cGVHD), a less-inflammatory autoimmune-like disease. WT APC normalized bronchiolitis obliterans-induced pulmonary dysfunction. Signaling-selective APC variants (3A-APC [APC with lysine 191-193 replaced with 3 alanines] or 5A-APC [APC with lysine 191-193 replaced with 3 alanines and arginine 229/230 replaced with 2 alanines]) with normal cytoprotective properties, but greatly reduced anticoagulant activity, provided similar results. Mechanistically, WT APC and signaling-selective variants reduced T follicular helper cells, germinal center formation, immunoglobulin, and collagen deposition. WT APC can potentially cleave protease-activated receptor 1 (PAR1) at Arg41 or Arg46, the latter causing anti-inflammatory signaling. cGVHD was reduced in recipients of T cells from WT PAR1 or mutated Gln41-PAR1 donors but not from mutated Gln46-PAR1 donors. These data implicate donor T-cell APC-induced noncanonical cleavage at Arg46-PAR1, which is known to confer cytoprotective and anti-inflammatory activities. Together, these data indicate that APC anticoagulant activity is dispensable, whereas anti-inflammatory signaling and cytoprotective cell signaling by APC are essential. Because a phase 2 ischemic stroke clinical trial did not raise any safety issues for 3A-APC treatment, our studies provide a foundational platform for testing in clinical cGVHD therapy.

The Cardioprotective Signaling Activity of Activated Protein C in Heart Failure and Ischemic Heart Diseases

Activated protein C (APC) is a vitamin-K dependent plasma serine protease, which functions as a natural anticoagulant to downregulate thrombin generation in the clotting cascade. APC also modulates cellular homeostasis by exhibiting potent cytoprotective and anti-inflammatory signaling activities. The beneficial cytoprotective effects of APC have been extensively studied and confirmed in a number of preclinical disease and injury models including sepsis, type-1 diabetes and various ischemia/reperfusion diseases. It is now well-known that APC modulates downstream cell signaling networks and transcriptome profiles when it binds to the endothelial protein C receptor (EPCR) to activate protease-activated receptor 1 (PAR1) on various cell types. However, despite much progress, details of the downstream signaling mechanism of APC and its crosstalk with other signaling networks are far from being fully understood. In this review, we focus on the cardioprotective properties of APC in ischemic heart disease and heart failure with a special emphasis on recent discoveries related to the modulatory effect of APC on AMP-activated protein kinase (AMPK), PI3K/AKT, and mTORC1 signaling pathways. The cytoprotective properties of APC might provide a novel strategy for future therapies in cardiac diseases.

Activated Protein C in Cutaneous Wound Healing: From Bench to Bedside

Independent of its well-known anticoagulation effects, activated protein C (APC) exhibits pleiotropic cytoprotective properties. These include anti-inflammatory actions, anti-apoptosis, and endothelial and epithelial barrier stabilisation. Such beneficial effects have made APC an attractive target of research in a plethora of physiological and pathophysiological processes. Of note, the past decade or so has seen the emergence of its roles in cutaneous wound healing-a complex process involving inflammation, proliferation and remodelling. This review will highlight APC's functions and mechanisms, and detail its pre-clinical and clinical studies on cutaneous wound healing.

A Perspective of Coagulation Dysfunction in Multiple Sclerosis and in Experimental Allergic Encephalomyelitis

A key role of both coagulation and vascular thrombosis has been reported since the first descriptions of multiple sclerosis (MS). Subsequently, the observation of a close concordance between perivascular fibrin(ogen) deposition and the occurrence of clinical signs in experimental allergic encephalomyelitis (EAE), an animal model of MS, led to numerous investigations focused on the role of thrombin and fibrin(ogen). Indeed, the activation of microglia, resident innate immune cells, occurs early after fibrinogen leakage in the pre-demyelinating lesion stage of EAE and MS. Thrombin has both neuroprotective and pro-apoptotic effects according to its concentration. After exposure to high concentrations of thrombin, astrocytes become reactive and lose their neuroprotective and supportive functions, microglia proliferate, and produce reactive oxygen species, IL-1β, and TNFα. Heparin inhibits the thrombin generation and suppresses EAE. Platelets play an important role too. Indeed, in the acute phase of the disease, they begin the inflammatory response in the central nervous system by producing of IL-1alpha and triggering and amplifying the immune response. Their depletion, on the contrary, ameliorates the course of EAE. Finally, it has been proven that the use of several anticoagulant agents can successfully improve EAE. Altogether, these studies highlight the role of the coagulation pathway in the pathophysiology of MS and suggest possible therapeutic targets that may complement existing treatments.

Endothelial microparticles released by activated protein C protect beta cells through EPCR/PAR1 and annexin A1/FPR2 pathways in islets

Islet transplantation is associated with early ischaemia/reperfusion, localized coagulation and redox-sensitive endothelial dysfunction. In animal models, islet cytoprotection by activated protein C (aPC) restores islet vascularization and protects graft function, suggesting that aPC triggers various lineages. aPC also prompts the release of endothelial MP that bear EPCR, its specific receptor. Microparticles (MP) are plasma membrane procoagulant vesicles, surrogate markers of stress and cellular effectors. We measured the cytoprotective effects of aPC on endothelial and insulin-secreting Rin-m5f β-cells and its role in autocrine and paracrine MP-mediated cell crosstalk under conditions of oxidative stress. MP from aPC-treated primary endothelial (EC) or β-cells were applied to H2 O2 -treated Rin-m5f. aPC activity was measured by enzymatic assay and ROS species by dihydroethidium. The capture of PKH26-stained MP and the expression of EPCR were probed by fluorescence microscopy and apoptosis by flow cytometry. aPC treatment enhanced both annexin A1 (ANXA1) and PAR-1 expression in EC and to a lesser extent in β-cells. MP from aPC-treated EC (eMaPC ) exhibited high EPCR and annexin A1 content, protected β-cells, restored insulin secretion and were captured by 80% of β cells in a phosphatidylserine and ANXA1-dependent mechanism. eMP activated EPCR/PAR-1 and ANXA1/FPR2-dependent pathways and up-regulated the expression of EPCR, and of FPR2/ALX, the ANXA1 receptor. Cytoprotection was confirmed in H2 O2 -treated rat islets with increased viability (62% versus 48% H2 O2 ), reduced apoptosis and preserved insulin secretion in response to glucose elevation (16 versus 5 ng/ml insulin per 10 islets). MP may prove a promising therapeutic tool in the protection of transplanted islets.

Activated protein C protects from GvHD via PAR2/PAR3 signalling in regulatory T-cells

Graft-vs.-host disease (GvHD) is a major complication of allogenic hematopoietic stem-cell(HSC) transplantation. GvHD is associated with loss of endothelial thrombomodulin, but the relevance of this for the adaptive immune response to transplanted HSCs remains unknown. Here we show that the protease-activated protein C (aPC), which is generated by thrombomodulin, ameliorates GvHD aPC restricts allogenic T-cell activation via the protease activated receptor (PAR)2/PAR3 heterodimer on regulatory T-cells (Tregs, CD4+FOXP3+). Preincubation of pan T-cells with aPC prior to transplantation increases the frequency of Tregs and protects from GvHD. Preincubation of human T-cells (HLA-DR4-CD4+) with aPC prior to transplantation into humanized (NSG-AB°DR4) mice ameliorates graft-vs.-host disease. The protective effect of aPC on GvHD does not compromise the graft vs. leukaemia effect in two independent tumor cell models. Ex vivo preincubation of T-cells with aPC, aPC-based therapies, or targeting PAR2/PAR3 on T-cells may provide a safe and effective approach to mitigate GvHD.Graft-vs.-host disease is a complication of allogenic hematopoietic stem cell transplantation, and is associated with endothelial dysfunction. Here the authors show that activated protein C signals via PAR2/PAR3 to expand Treg cells, mitigating the disease in mice.

Novel technologies to engineer graft for tolerance induction

PURPOSE OF REVIEW

Conquering allograft rejection remains an elusive goal in spite of recent breakthroughs in the field of immunosuppression. Much of the problem lies in the toxicity and side-effects of long-term use of systemic immunosuppressant drugs, which are sometimes ineffective in controlling rejection, but also hinder establishment of transplant tolerance. In this review, we discuss novel technologies that use grafts engineered with immunomodulatory molecules as a means of inducing tolerance.

RECENT FINDINGS

Several recent studies have demonstrated the feasibility of engineering cells, tissues, or solid organ grafts with immunoregulatory biologics to achieve long termgraft survival without the use of chronic immunosuppression. This approach was shown to primarily change the ratio of T effector versus CD4+CD25+FoxP3+ T regulatory cells within the graft microenvironment in favor of attaining localized tolerance induction and maintenance.

SUMMARY

Localized immunomodulation using biologic-engineered allografts represent a new paradigm for achieving long-term graft survival in the absence of chronic use of immunosuppression. The manipulation of the graft, rather than the recipient, not only ensures short- and long-term safety by minimizing the adverse effects of immunosuppression, but also allows retention of immune competency critical for the ability of the recipient to fight infections and cancer.

Anti-inflammatory effects of activated protein C on human dendritic cells

Activated protein C (APC) has an anticoagulant action and plays an important role in blood coagulation homeostasis. In addition to its anticoagulant action, APC is known to have cytoprotective effects, such as anti-apoptotic action and endothelial barrier protection, on vascular endothelial cells and monocytes. However, the effects of APC on DCs have not been clarified. To investigate the effects of APC on human DCs, monocytes were isolated from peripheral blood and DC differentiation induced with LPS. APC significantly inhibited the production of inflammatory cytokines TNF-α and IL-6 during differentiation of immature DCs to mature DCs, but did not inhibit the production of IL-12 and anti-inflammatory cytokine IL-10. Interestingly, treatment with 5 μg/mL, but not 25 μg/mL, of APC significantly enhanced production of IL-10. In addition, protein C, which is the zymogen of APC, did not affect production of these cytokines. On the other hand, flow cytometric analysis of DC's surface molecules indicated that APC does not significantly affect expression of CD83, a marker of mDC differentiation, and the co-stimulatory molecules CD40, CD80 and CD86. These results suggest that APC has anti-inflammatory effects on human DCs and may be effective against some inflammatory diseases in which the pathogenesis involves TNF-α and/or IL-6 production.

TAK1 inhibition prevents the development of autoimmune diabetes in NOD mice

Transforming growth factor-β activated kinase-1 (TAK1, Map3k7), a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, is essential in innate and adaptive immune responses. We postulated that blockade of TAK1 would affect autoimmune diabetes in non-obese diabetic (NOD) mice. Administration of 5Z-7-oxozeaenol (OZ), a TAK1 inhibitor, decreased the incidence and delayed the onset of autoimmune diabetes in both spontaneous and accelerated (cyclophosphamide-induced) experimental NOD mice. OZ also reduced insulitis, preserved islet function, increased the expression of α1- antitrypsin (AAT), and severely inhibited NF-κB and JNK/AP-1 signaling pathways in immune organs and pancreatic tissues. Importantly, TAK1 inhibition by OZ elicited a Th1 to Th2 cytokine shift, and increased TGF-β1 production in cultured T lymphocytes supernatants. Systemic TAK1 inhibition induced immature DCs with lower expressions of MHC-II and CD86, attenuated DC-mediated T cell proliferation in allogeneic MLR, and production of cytokine IL-12p70 in DCs suspensions. The results indicate that TAK1 inhibition with OZ was associated with a lower frequency of autoimmune diabetes in NOD mice. The net effect of TAK1 inhibition in NOD mice therefore appears to be protective rather than disease-enhancing. Strategies targeting TAK1 specifically in NOD mice might prove useful for the treatment of autoimmune diabetes in general.

Cell painting with an engineered EPCR to augment the protein C system

The protein C (PC) system conveys beneficial anticoagulant and cytoprotective effects in numerous in vivo disease models. The endothelial protein C receptor (EPCR) plays a central role in these pathways as cofactor for PC activation and by enhancing activated protein C (APC)-mediated protease-activated receptor (PAR) activation. During inflammatory disease, expression of EPCR on cell membranes is often diminished thereby limiting PC activation and APC's effects on cells. Here a caveolae-targeting glycosylphosphatidylinositol (GPI)-anchored EPCR (EPCR-GPI) was engineered to restore EPCR's bioavailability via "cell painting." The painting efficiency of EPCR-GPI on EPCR-depleted endothelial cells was time- and dose-dependent. The EPCR-GPI bioavailability after painting was long lasting since EPCR surface levels reached 400 % of wild-type cells after 2 hours and remained > 200 % for 24 hours. EPCR-GPI painting conveyed APC binding to EPCR-depleted endothelial cells where EPCR was lost due to shedding or shRNA. EPCR painting normalised PC activation on EPCR-depleted cells indicating that EPCR-GPI is functional active on painted cells. Caveolin-1 lipid rafts were enriched in EPCR after painting due to the GPI-anchor targeting caveolae. Accordingly, EPCR painting supported PAR1 and PAR3 cleavage by APC and augmented PAR1-dependent Akt phosphorylation by APC. Thus, EPCR-GPI painting achieved physiological relevant surface levels on endothelial cells, restored APC binding to EPCR-depleted cells, supported PC activation, and enhanced APC-mediated PAR cleavage and cytoprotective signalling. Therefore, EPCR-GPI provides a novel tool to restore the bioavailability and functionality of EPCR on EPCR- depleted and -deficient cells.

Activated protein C modulates the proinflammatory activity of dendritic cells

Background

Previous studies have demonstrated the beneficial activity of activated protein C in allergic diseases including bronchial asthma and rhinitis. However, the exact mechanism of action of activated protein C in allergies is unclear. In this study, we hypothesized that pharmacological doses of activated protein C can modulate allergic inflammation by inhibiting dendritic cells.

Materials and methods

Dendritic cells were prepared using murine bone marrow progenitor cells and human peripheral monocytes. Bronchial asthma was induced in mice that received intratracheal instillation of ovalbumin-pulsed dendritic cells.

Results

Activated protein C significantly increased the differentiation of tolerogenic plasmacytoid dendritic cells and the secretion of type I interferons, but it significantly reduced lipopolysaccharide-mediated maturation and the secretion of inflammatory cytokines in myeloid dendritic cells. Activated protein C also inhibited maturation and the secretion of inflammatory cytokines in monocyte-derived dendritic cells. Activated protein C-treated dendritic cells were less effective when differentiating naïve CD4 T-cells from Th1 or Th2 cells, and the cellular effect of activated protein C was mediated by its receptors. Mice that received adoptive transfer of activated protein C-treated ovalbumin-pulsed dendritic cells had significantly less airway hyperresponsiveness, significantly decreased lung concentrations of Th1 and Th2 cytokines, and less plasma concentration of immunoglobulin E when compared to control mice.

Conclusion

These results suggest that dendritic cells mediate the immunosuppressive effect of activated protein C during allergic inflammation.

Multiple mechanisms involved in diabetes protection by lipopolysaccharide in non-obese diabetic mice

Toll-like receptor 4 (TLR4) activation has been proposed to be important for islet cell inflammation and eventually β cell loss in the course of type 1 diabetes (T1D) development. However, according to the "hygiene hypothesis", bacterial endotoxin lipopolysaccharide (LPS), an agonist on TLR4, inhibits T1D progression. Here we investigated possible mechanisms for the protective effect of LPS on T1D development in non-obese diabetic (NOD) mice. We found that LPS administration to NOD mice during the prediabetic state neither prevented nor reversed insulitis, but delayed the onset and decreased the incidence of diabetes, and that a multiple-injection protocol is more effective than a single LPS intervention. Further, LPS administration suppressed spleen T lymphocyte proliferation, increased the generation of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs), reduced the synthesis of strong Th1 proinflammatory cytokines, and downregulated TLR4 and its downstream MyD88-dependent signaling pathway. Most importantly, multiple injections of LPS induced a potential tolerogenic dendritic cell (DC) subset with low TLR4 expression without influencing the DC phenotype. Explanting DCs from repeated LPS-treated NOD mice into NOD/SCID diabetic mice conferred sustained protective effects against the progression of diabetes in the recipients. Overall, these results suggest that multiple mechanisms are involved in the protective effects of LPS against the development of diabetes in NOD diabetic mice. These include Treg induction, down-regulation of TLR4 and its downstream MyD88-dependent signaling pathway, and the emergence of a potential tolerogenic DC subset.

Activated protein C: biased for translation

The homeostatic blood protease, activated protein C (APC), can function as (1) an antithrombotic on the basis of inactivation of clotting factors Va and VIIIa; (2) a cytoprotective on the basis of endothelial barrier stabilization and anti-inflammatory and antiapoptotic actions; and (3) a regenerative on the basis of stimulation of neurogenesis, angiogenesis, and wound healing. Pharmacologic therapies using recombinant human and murine APCs indicate that APC provides effective acute or chronic therapies for a strikingly diverse range of preclinical injury models. APC reduces the damage caused by the following: ischemia/reperfusion in brain, heart, and kidney; pulmonary, kidney, and gastrointestinal inflammation; sepsis; Ebola virus; diabetes; and total lethal body radiation. For these beneficial effects, APC alters cell signaling networks and gene expression profiles by activating protease-activated receptors 1 and 3. APC's activation of these G protein-coupled receptors differs completely from thrombin's activation mechanism due to biased signaling via either G proteins or β-arrestin-2. To reduce APC-associated bleeding risk, APC variants were engineered to lack >90% anticoagulant activity but retain normal cell signaling. Such a neuroprotective variant, 3K3A-APC (Lys191-193Ala), has advanced to clinical trials for ischemic stroke. A rich data set of preclinical knowledge provides a solid foundation for potential translation of APC variants to future novel therapies.

[Importance of diabetic nephropathy in childhood. Clinical findings and basic research in recent decades]

Over the past decades diabetes mellitus is becoming a global pandemic affecting more than 371 million people worldwide. Parallel with the increasing prevalence of type 1 diabetes, there is a growing number of type 2 diabetes cases among children and adolescents that poses new challenges to pediatricians. Diabetic nephropathy is one of the major causes of end stage renal disease, developing in approximately 30% of diabetic patients. However, overt nephropathy is rare in childhood; screening and ongoing assessment for the earliest manifestation of renal injury is extremely important in this young population, as well. Although in the past decades intensive research activity focused on understanding of the pathomechanism of diabetic nephropathy and invention of new therapeutic approaches, prevention and definitive care are still urgently needed. The clinical section of the article summarizes the present state of epidemiology, diagnosis and current therapies of childhood diabetic nephropathy. Then, the authors discuss the state of basic research and show a few promising targets for drug development.

Activated protein C: A regulator of human skin epidermal keratinocyte function

Activated protein C (APC) is a physiological anticoagulant, derived from its precursor protein C (PC). Independent of its anticoagulation, APC possesses strong anti-inflammatory, anti-apoptotic and barrier protective properties which appear to be protective in a number of disorders including chronic wound healing. The epidermis is the outermost skin layer and provides the first line of defence against the external environment. Keratinocytes are the most predominant cells in the epidermis and play a critical role in maintaining epidermal barrier function. PC/APC and its receptor, endothelial protein C receptor (EPCR), once thought to be restricted to the endothelium, are abundantly expressed by skin epidermal keratinocytes. These cells respond to APC by upregulating proliferation, migration and matrix metalloproteinase-2 activity and inhibiting apoptosis/inflammation leading to a wound healing phenotype. APC also increases barrier function of keratinocyte monolayers by promoting the expression of tight junction proteins and re-distributing them to cell-cell contacts. These cytoprotective properties of APC are mediated through EPCR, protease-activated receptors, epidermal growth factor receptor or Tie2. Future preventive and therapeutic uses of APC in skin disorders associated with disruption of barrier function and inflammation look promising. This review will focus on APC’s function in skin epidermis/keratinocytes and its therapeutical potential in skin inflammatory conditions.

Inflammation-associated activation of coagulation and immune regulation by the protein C pathway

The inflammation-induced activation of the protein C pathway provides negative feedback inhibition of coagulation and exerts coagulation-independent anti-inflammatory and cytoprotective effects. The balance between these activities of aPC modulates the outcome of diverse inflammatory diseases such as encephalitis, diabetes, and sepsis; and is affected by naturally occurring aPC-resistance of coagulation factor V Leiden.

Activated protein C based therapeutic strategies in chronic diseases

Activated protein C (aPC) is a natural anticoagulant and a potent anti-inflammatory and cytoprotective agent. At the expense of increased bleeding risk aPC has been used - with some success - in sepsis. The design of cytoprotective-selective aPC variants circumvents this limitation of increased bleeding, reviving the interest in aPC as a therapeutic agent. Emerging studies suggest that aPC`s beneficial effects are not restricted to acute illness, but likewise relevant in chronic diseases, such as diabetic nephropathy, neurodegeneration or wound healing. Epigenetic regulation of gene expression, reduction of oxidative stress, and regulation of ROS-dependent transcription factors are potential mechanisms of sustained cytoprotective effects of aPC in chronic diseases. Given the available data it seems questionable whether a unifying mechanism of aPC dependent cytoprotection in acute and chronic diseases exists. In addition, the signalling pathways employed by aPC are tissue and cell specific. The mechanistic insights gained from studies exploring aPC`s effects in various diseases may hence lay ground for tissue and disease specific therapeutic approaches. This review outlines recent investigations into the mechanisms and consequences of long-term modulation of aPC-signalling in models of chronic diseases.

Activated protein C and its potential applications in prevention of islet β-cell damage and diabetes

Activated protein C (APC) is derived from its precursor, protein C (PC). Originally thought to be synthesized exclusively by the liver, recent reports have shown that PC is also produced by many other cells including pancreatic islet β cells. APC functions as a physiological anticoagulant with anti-inflammatory, anti-apoptotic, and barrier-stabilizing properties. APC exerts its protective effects via an intriguing mechanism requiring combinations of endothelial PC receptor, protease-activated receptors, epidermal growth factor receptor, Tie2 or CD11b, depending on cell types. Diabetes is a chronic condition resulted from the body's inability to produce and/or properly use insulin. The prevalence of diabetes has risen dramatically and has become one of the major causes of premature mortality and morbidity worldwide. Diabetes prevention is an ideal approach to reduce this burden. Type 1 and type 2 diabetes are the major forms of diabetes mellitus, and both are characterized by an autoimmune response, intraislet inflammation, β-cell apoptosis, and progressive β-cell loss. Protecting β-cell from damage is critical in both prevention and treatment of diabetes. Recent in vitro and animal studies show that APC's strong anti-inflammatory and anti-apoptotic properties are beneficial in preventing β-cell destruction and diabetes in the NOD mouse model of type 1 diabetes. Future preventive and therapeutic uses of APC in diabetes look very promising.

Transgene expression in various organs post BM-HSC transplantation

Gene therapy mediated by bone marrow-derived hematopoietic stem cells (BM-HSC) has been widely used in treating genetic deficiencies in both pre-clinical and clinical settings. Using mitotically inactive cell-targeting lentivirus with separate promoters for our gene of interest (the murine MHC class II (MHCII) chaperone, invariant chain (Ii)) and a GFP reporter, we monitored the expression and function of introduced Ii in various types of professional antigen presenting cells (B cells, macrophages and DC) from different organs (spleen, pancreatic lymph nodes (PLN), BM and blood). Ii and GFP were detected. Ii levels correlated with GFP levels only in macrophages and monocytes from spleen, monocytes from PLN and macrophage precursors from blood. By cell type, Ii levels in PLN cells were more similar to those in spleen cells than to those in blood or BM cells. Functionally, Ii expressed in PLN or spleen had more effect on MHCII abundance than Ii expressed in BM or blood. The results have implications for analysis of the outcomes of gene therapy when both therapeutic and reporter genes are introduced. The findings also have implications for understanding the development of immune molecule function.

Total coumarins from Urtica dentata Hand prevent murine autoimmune diabetes via suppression of the TLR4-signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Urtica dentata Hand (UDH), the root of Laportea bulbifera (Sieb. et. Zucc.) Wedd, has been traditionally used in traditional Chinese medicine as an anti-inflammatory and immuno-regulatory agent for rheumatoid arthritis and some other autoimmune diseases treatment. And the coumarins are the major components of UDH.

AIM OF THE STUDY

To investigate the effect of total coumarins (TC) isolated from UDH on the development of autoimmune diabetes.

MATERIALS AND METHODS

Eight-week-old non-obese diabetic (NOD) mice were randomly divided into four groups: control group, low-dose (37.5 mg/kg), middle-dose (75 mg/kg), and high-dose (150 mg/kg) TC-treatment groups. NOD mice were then given with a suspension of TC or saline by intragastric (i.g.) administration every other day. After 4 weeks of treatment, 8 mice at 12-weeks of age per group were randomly selected to be sacrificed to perform intraperitoneal glucose tolerance test, examine histopathological insulitis, spleen T lymphocyte proliferation, the percentage of CD4+CD25+Foxp3+ T regulatory cell (Treg), dendritic cell (DC) surface molecules, toll-like receptor (TLR)4 expression and signal pathways involved. The remaining 10 mice per group were kept until 26 weeks of age to assess the incidence of diabetes. We also studied the direct effect of TC on DC and CD4+CD25+ Tregs in vitro.

RESULTS

Treatment with TC for 4 weeks significantly inhibited insulitis, increased pancreatic islet number, delayed the onset and decreased the development of diabetes by 26 weeks of age in NOD mice, compared with the untreated control mice. TC suppressed spleen T lymphocyte proliferation, induced Th2-biased cytokine response, the generation of CD4+CD25+Foxp3+ Tregs and Foxp3 mRNA expression. And TC-treated DCs were characterized as low expression of MHC class II and CD86 molecules. TLR4 gene and protein expressions in the spleen, thymus and pancreas were down-regulated in TC-treated groups. The key molecules in the downstream signaling cascades of TLR4, including myeloid differentiation factor (MyD)88, nuclear factor (NF)-κB, IL-1β, Toll-IL-1 receptor domain-containing adaptor inducing interferon-β(TRIF), TRIF-related adaptor molecule (TRAM), interferon regulatory factor (IRF)-3 and IFN-β, all decreased significantly in TC groups, suggesting that TC inhibits both MyD88-dependent and -independent pathways of TLR4. At the cellular level, however, TLR4 protein expression in DCs, but not in Tregs, was downregulated by TC. And TC strengthened the role of DC, not Treg, in negative immune regulation in vitro. In contrast, anti-TLR4 antibody could block the effect of TC on DCs immune function.

CONCLUSION

These results suggest that TC extracted from UDH prevent the development of autoimmune diabetes in NOD mice via suppression of the TLR4-signaling pathways. TC maintain the DCs in an immature tolerogenic state, at least in part, mediated by down-regulating TLR4-signaling pathways in DCs, then enhance Treg differentiation, shift toward Th2 and suppress T lymphocyte proliferation.

Anti-fibrosis therapy and diabetic nephropathy

Diabetes mellitus is rapidly becoming a global health issue that may overtake cancer during the next two decades as it covertly affects multiple organ systems that goes undiagnosed long after the onset. A number of complications are associated with poorly controlled hyperglycemia. Diabetic nephropathy is one of the most common complications of diabetes mellitus. Other than angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blocker (ARB) there is not much in the armamentarium with which to treat patients with overt diabetic nephropathy. Research points towards a multifactorial etiology and complex interplay of several pathogenic pathways that can contribute to the declining kidney function in diabetes. Patients with diabetic nephropathy (and with any chronic kidney disease) eventually develop kidney fibrosis. Despite the financial and labor investment spent on determining the basic mechanism of fibrosis, not much progress has been made in terms of therapeutic targets available to us today. This may be in part due to paucity in the experimental animal models available. However, there now seems to be a concerted effort from several pharmaceutical companies to develop a drug that would halt/delay the process of fibrosis, if not reverse it. This review discusses the current state of research in the field while staying within the context of diabetic nephropathy.