Endothelial protein C receptor and protease-activated receptor-1 mediate induction of a wound-healing phenotype in human keratinocytes by activated protein C

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.

The APC-EPCR-PAR1 axis in sickle cell disease

Sickle Cell Disease (SCD) is a group of inherited hemoglobinopathies. Sickle cell anemia (SCA) is caused by a homozygous mutation in the β-globin generating sickle hemoglobin (HbS). Deoxygenation leads to pathologic polymerization of HbS and sickling of erythrocytes. The two predominant pathologies of SCD are hemolytic anemia and vaso-occlusive episodes (VOE), along with sequelae of complications including acute chest syndrome, hepatopathy, nephropathy, pulmonary hypertension, venous thromboembolism, and stroke. SCD is associated with endothelial activation due to the release of danger-associated molecular patterns (DAMPs) such as heme, recurrent ischemia-reperfusion injury, and chronic thrombin generation and inflammation. Endothelial cell activation is mediated, in part, by thrombin-dependent activation of protease-activated receptor 1 (PAR1), a G protein coupled receptor that plays a role in platelet activation, endothelial permeability, inflammation, and cytotoxicity. PAR1 can also be activated by activated protein C (APC), which promotes endothelial barrier protection and cytoprotective signaling. Notably, the APC system is dysregulated in SCD. This mini-review will discuss activation of PAR1 by APC and thrombin, the APC-EPCR-PAR1 axis, and their potential roles in SCD.

Protease-activated receptors in health and disease

Proteases are signaling molecules that specifically control cellular functions by cleaving protease-activated receptors (PARs). The four known PARs are members of the large family of G protein-coupled receptors. These transmembrane receptors control most physiological and pathological processes and are the target of a large proportion of therapeutic drugs. Signaling proteases include enzymes from the circulation; from immune, inflammatory epithelial, and cancer cells; as well as from commensal and pathogenic bacteria. Advances in our understanding of the structure and function of PARs provide insights into how diverse proteases activate these receptors to regulate physiological and pathological processes in most tissues and organ systems. The realization that proteases and PARs are key mediators of disease, coupled with advances in understanding the atomic level structure of PARs and their mechanisms of signaling in subcellular microdomains, has spurred the development of antagonists, some of which have advanced to the clinic. Herein we review the discovery, structure, and function of this receptor system, highlight the contribution of PARs to homeostatic control, and discuss the potential of PAR antagonists for the treatment of major diseases.

Identification of a broad lipid repertoire associated to the endothelial cell protein C receptor (EPCR)

Evidence is mounting that the nature of the lipid bound to the endothelial cell protein C receptor (EPCR) has an impact on its biological roles, as observed in anticoagulation and more recently, in autoimmune disease. Phosphatidylethanolamine and phosphatidylcholine species dominate the EPCR lipid cargo, yet, the extent of diversity in the EPCR-associated lipid repertoire is still unknown and remains to be uncovered. We undertook mass spectrometry analyses to decipher the EPCR lipidome, and identified species not yet described as EPCR ligands, such as phosphatidylinositols and phosphatidylserines. Remarkably, we found further, more structurally divergent lipids classes, represented by ceramides and sphingomyelins, both in less abundant quantities. In support of our mass spectrometry results and previous studies, high-resolution crystal structures of EPCR in three different space groups point to a prevalent diacyl phospholipid moiety in EPCR’s pocket but a mobile and ambiguous lipid polar head group. In sum, these studies indicate that EPCR can associate with varied lipid classes, which might impact its properties in anticoagulation and the onset of autoimmune disease.

Therapeutic values of chick early amniotic fluid (ceAF) that facilitates wound healing via potentiating a SASP-mediated transient senescence

Inflammatory, proliferative and remodeling phases constitute a cutaneous wound healing program. Therapeutic applications and medication are available; however, they commonly are comprised of fortified preservatives that might prolong the healing process. Chick early amniotic fluids (ceAF) contain native therapeutic factors with balanced chemokines, cytokines and growth-related factors; their origins in principle dictate no existence of harmful agents that would otherwise hamper embryo development. Instead, they possess a spectrum of molecules driving expeditious mitotic divisions and possibly exerting other functions. Employing both in vitro and in vivo models, we examined ceAF's therapeutic potentials in wound healing and found intriguing involvement of transient senescence, known to be intimately intermingled with Senescence Associated Secretory Phenotypes (SASP) that function in addition to or in conjunction with ceAF to facilitate wound healing. In our cutaneous wound healing models, a low dose of ceAF exhibited the best efficacies; however, higher doses attenuated the wound healing presumably by inducing p16 expression over a threshold. Our studies thus link an INK4/ARF locus-mediated signaling cascade to cutaneous wound healing, suggesting therapeutic potentials of ceAF exerting functions likely by driving transient senescence, expediting cellular proliferation, migration, and describing a homeostatic and balanced dosage strategy in medical intervention.

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.

Sex-dependent effects of genetic upregulation of activated protein C on delayed effects of acute radiation exposure in the mouse heart, small intestine, and skin

Accidental exposure to ionizing radiation may lead to delayed effects of acute radiation exposure (DEARE) in many organ systems. Activated protein C (APC) is a known mitigator of the acute radiation syndrome. To examine the role of APC in DEARE, we used a transgenic mouse model with 2- to 3-fold increased plasma levels of APC (high in APC, APCHi). Male and female APCHi mice and wild-type littermates were exposed to 9.5 Gy γ-rays with their hind-legs (bone marrow) shielded from radiation to allow long-term survival. At 3 and 6 months after irradiation, cardiac function was measured with ultrasonography. At 3 months, radiation increased cardiac dimensions in APCHi males, while decreases were seen in wild-type females. At this early time point, APCHi mice of both sexes were more susceptible to radiation-induced changes in systolic function compared to wild-types. At 6 months, a decrease in systolic function was mainly seen in male mice of both genotypes. At 6 months, specimens of heart, small intestine and dorsal skin were collected for tissue analysis. Female APCHi mice showed the most severe radiation-induced deposition of cardiac collagens but were protected against a radiation-induced loss of microvascular density. Both male and female APCHi mice were protected against a radiation induced upregulation of toll-like receptor 4 in the heart, but this did not translate into a clear protection against immune cell infiltration. In the small intestine, the APCHi genotype had no effect on an increase in the number of myeloperoxidase positive cells (seen mostly in females) or an increase in the expression of T-cell marker CD2 (males). Lastly, both male and female APCHi mice were protected against radiation-induced epidermal thickening and increase in 3-nitrotyrosine positive keratinocytes. In conclusion, prolonged high levels of APC in a transgenic mouse model had little effects on indicators of DEARE in the heart, small intestine and skin, with some differential effects in male compared to female mice.

Novel positive allosteric modulator of protease-activated receptor 1 promotes skin wound healing in hairless mice

BACKGROUND AND PURPOSE

Protease-activated receptor 1 (PAR1) is a GPCR expressed in several skin cell types, including keratinocyte and dermal fibroblast. PAR1 activation plays a crucial role in the process of skin wound healing such as thrombosis, inflammation, proliferation and tissue repair. In the present study, we identified a novel positive allosteric modulator of PAR1, GB83, and investigated its effect on skin wound healing.

EXPERIMENTAL APPROACH

The enhancement of PAR1 activity by GB83 was measured using Fluo-4 calcium assay. In silico docking analysis of GB83 in PAR1 was performed using dock ligands method (CDOCKER) with CHARMm force field. Effects of GB83 on cell viability and gene expression were observed using MTS assay and quantitative real-time PCRs, respectively. SKH-1 hairless mice were used to investigate the wound healing effect of GB83.

KEY RESULTS

We demonstrated that GB83 did not activate PAR1 by itself but strongly enhanced PAR1 activation by thrombin and PAR1-activating peptide (AP). In silico docking analysis revealed that GB83 can bind to the PAR1 binding site of vorapaxar. GB83 significantly promoted PAR1-mediated cell viability and migration. In addition, the enhancement of PAR1 activity by GB83 strongly increased gene expression of TGF-β, fibronectin and type I collagen in vitro and promoted skin wound healing in vivo.

CONCLUSION AND IMPLICATIONS

Our results revealed that GB83 is the first positive allosteric modulator of PAR1 and it can be a useful pharmacological tool for studying PAR1 and a potential therapeutic agent for skin wound healing.

Innate Lymphocyte Mechanisms in Skin Diseases

Innate lymphocyte populations are emerging as key effectors in tissue homeostasis, microbial defense, and inflammatory skin disease. The cells are evolutionarily ancient and carry conserved principles of function, which can be achieved through shared or unique specific mechanisms. Recent technological and treatment advances have provided insight into heterogeneity within and between individuals and species. Similar pathways can extend through to adaptive lymphocytes, which softens the margins with innate lymphocyte populations and allows investigation of nonredundant pathways of immunity and inflammation that might be amenable to therapeutic intervention. Here, we review advances in understanding of innate lymphocyte biology with a focus on skin disease and the roles of commensal and pathogen responses and tissue homeostasis.

Contribution of platelets, the coagulation and fibrinolytic systems to cutaneous wound healing

Wound healing is a complex process that consists of multiple phases, each of which are indispensable for adequate repair. Timely initiation and resolution of each of these phases namely, hemostasis, inflammation, proliferation and tissue remodeling, is critical for promoting healing and avoiding excess scar formation. While platelets have long been known to influence the healing process, other components of blood particularly coagulation factors and the fibrinolytic system also contribute to efficient wound repair. This review aims to summarize our current understanding of the role of platelets, the coagulation and fibrinolytic systems in cutaneous wound healing, with a focus on how these components communicate with immune and non-immune cells in the wound microenvironment. We also outline current and potential therapeutic strategies to improve the management of chronic, non-healing wounds.

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.

Endothelial Protein C Receptor (EPCR), Protease Activated Receptor-1 (PAR-1) and Their Interplay in Cancer Growth and Metastatic Dissemination

Endothelial protein C receptor (EPCR) and protease activated receptor 1 (PAR-1) by themselves play important role in cancer growth and dissemination. Moreover, interactions between the two receptors are essential for tumor progression. EPCR is a cell surface transmembrane glycoprotein localized predominantly on endothelial cells (ECs). It is a vital component of the activated protein C (APC)—mediated anticoagulant and cytoprotective signaling cascade. PAR-1, which belongs to a family of G protein–coupled cell surface receptors, is also widely distributed on endothelial and blood cells, where it plays a critical role in hemostasis. Both EPCR and PAR-1, generally considered coagulation-related receptors, are implicated in carcinogenesis and dissemination of diverse tumor types, and their expression correlates with clinical outcome of cancer patients. Existing data explain some mechanisms by which EPCR/PAR-1 affects cancer growth and metastasis; however, the exact molecular basis of cancer invasion associated with the signaling is still obscure. Here, we discuss the role of EPCR and PAR-1 reciprocal interactions in cancer progression as well as potential therapeutic options targeted specifically to interact with EPCR/PAR-1-induced signaling in cancer patients.

Thrombin promotes PAI-1 expression and migration in keratinocytes via ERK dependent Smad linker region phosphorylation

Keratinocyte proliferation and migration is essential during re-epithelialisation for the restoration of the epithelial barrier during skin wound healing. Numerous growth factors are involved in the stimulation of keratinocyte proliferation and migration. The signalling pathways that drive these processes during wound healing are not well defined. This study investigated thrombin-mediated signalling in keratinocytes. The thrombin receptor, protease-activated receptor 1 (PAR-1) is a seven transmembrane G-protein coupled receptor that is known to transactivate the epidermal growth factor receptor (EGFR). Immortalized human keratinocytes (HaCaT cells) were treated with thrombin and selective inhibitors to EGFR and MAP kinases. Whole cell lysates were separated on SDS-PAGE and analysed by Western blot using antibodies against transcription factor Smad2. Quantitative real-time polymerase chain reaction was used to measure the mRNA expression of PAI-1 while scratch wound assays were used to measure keratinocyte migration. Western blot data showed that thrombin mediates PAR-1 transactivation of EGFR and the downstream phosphorylation of the transcription factor Smad2 linker (Smad2L) region. ERK1/2 inhibition by UO126 caused a decrease in Smad2L phosphorylation while the p38 inhibitor SB202190 and JNK inhibitor SP600125 did not. Smad2L Ser250 was specifically phosphorylated by this thrombin mediated pathway while Ser245 and Ser255 were not. Thrombin increased PAI-1 mRNA expression and keratinocyte migration and this was reduced when either EGFR or ERK1/2 were blocked. Taken together these results show that thrombin mediated mRNA expression of PAI-1 in keratinocytes and migration occurs via EGFR transactivation and involves signalling intermediates ERK1/2 and Smad2 and may be a key pathway in skin wound healing.

Endothelial protein C receptor is overexpressed in colorectal cancer as a result of amplification and hypomethylation of chromosome 20q

Endothelial Protein C Receptor (EPCR) is a Major Histocompatibility Complex homologue, with established roles downregulating coagulation and in endothelial protection. Expressed predominantly on endothelium, EPCR affects inflammatory, apoptotic and cell proliferation pathways by binding to activated protein C (APC). However, EPCR can also be expressed on cancer cells, although the underlying reasons are unclear. Moreover, although EPCR has been linked with chemosensitivity in lung cancer, its clinical significance in many tumours is unknown. Here, we explored its significance in colorectal cancer (CRC). Bioinformatic methods revealed EPCR overexpression in many epithelial cancers, which was confirmed on CRC epithelial tumour cells by immunohistochemistry. EPCR upregulation resulted from gene amplification and DNA hypomethylation, and occurred in concert with a cohort of neighbouring genes on chromosome 20q, a region previously implicated in chemoresistance. As in endothelial cells, EPCR reproducibly mediated ERK pathway activation in a model CRC cell line following APC treatment. However, EPCR knockdown studies failed to highlight compelling EPCR‐intrinsic impact on CRC cell phenotype, with limited effects on chemosensitivity and no effect on invasion observed, while EPCR appeared to decrease CRC cell migration. Consistent with these observations, differential EPCR expression did not influence response to chemotherapy in a human CRC cohort. Our results provide a compelling explanation for how EPCR is upregulated in diverse epithelial malignancies. They indicate that the clinical significance of EPCR varies across different tumour types. Furthermore, they raise the possibility that the prognostic significance of EPCR in certain tumours relates significantly to co‐upregulation of neighbouring genes on chromosome 20q. Therefore, efforts to exploit EPCR as a prognostic marker should be focussed on specific tumours, and in such scenarios EPCR‐co‐dysregulated genes may represent potential axes for therapeutic intervention.

The Endothelial Protein C Receptor Is a Potential Stem Cell Marker for Epidermal Keratinocytes

Endothelial protein C receptor (EPCR) is a specific receptor for anticoagulant protein C and expressed by human epidermis and cultured keratinocytes. Here we investigated whether: (a) the level of EPCR in keratinocytes is associated with their growth potential; and (b) EPCR is a potential marker for human epidermal stem cells. Human keratinocytes isolated from foreskins or adult skin tissues were transfected with EPCR siRNA or EPCR overexpressing plasmids. Cell proliferation, long term proliferation potential, colony forming efficiency (CFE), and in vitro epidermal regeneration ability of EPCR^high and EPCR^l °^w cells were assessed. The expression and colocalization of EPCR with stem cell markers p63, integrin β1, and activation of MAP kinases were detected by flow cytometry, immunofluorescence staining, or Western blot. Results showed that EPCR was highly expressed by the basal layer of skin epidermis. EPCR^high cells were associated with the highest levels of p63 and integrin β1. Most EPCR^high cells were smaller in size, formed larger colonies and had a greater long term growth potential, CFE, holoclone formation, and in vitro epidermal regeneration ability when compared to EPCR^l °^w cells. Blocking EPCR resulted in keratinocyte apoptosis, particularly in nondifferentiated conditions. Cell proliferation and p63 expression were reduced by blocking EPCR and enhanced by overexpressing this receptor. These data indicate that EPCR can regulate p63, is associated with highly proliferative keratinocytes, and is a potential human epidermal stem cell marker. Stem Cells 2017;35:1786-1798.

Activated protein C binds directly to Tie2: possible beneficial effects on endothelial barrier function

Activated protein C (APC) is a natural anticoagulant with strong anti-inflammatory, anti-apoptotic, and barrier stabilizing properties. These cytoprotective properties of APC are thought to be exerted through its pathway involving the binding of APC to endothelial protein C receptor and cleavage of protease-activated receptors. In this study, we found that APC enhanced endothelial barrier integrity via a novel pathway, by binding directly to and activating Tie2, a transmembrane endothelial tyrosine kinase receptor. Binding assays demonstrated that APC competed with the only known ligands of Tie2, the angiopoietins (Angs). APC bound directly to Tie2 (Kd ~3 nM), with markedly stronger binding affinity than Ang2. After binding, APC rapidly activated Tie2 to enhance endothelial barrier function as shown by Evan's blue dye transfer across confluent cell monolayers and in vivo studies. Blocking Tie2 restricted endothelial barrier integrity. This study highlights a novel mechanism by which APC binds directly to Tie2 to enhance endothelial barrier integrity, which helps to explain APC's protective effects in vascular leakage-related pathologies.

All hands on DE(T)C: Epithelial-resident γδ T cells respond to tissue injury

Immunology has traditionally focused on the lymphocytes circulating among primary lymphoid organs while the large reservoir of tissue-resident T cells have received relatively less attention. In epithelia, these populations are comprised of significant, and sometimes exclusive, subsets of γδ T cells that are highly specialized in promoting tissue homeostasis. As the epithelial layers of the skin and gut are permanently exposed to the environment, they are continually subject to injury and therefore require highly efficient repair processes to maintain barrier functions. Here, we review the role of γδ T cells in promoting wound healing, a critical and complex process occurring in the skin and other barrier sites.

Use of dermal injection of activated protein C for treatment of large chronic wounds secondary to pyoderma gangrenosum

BACKGROUND

Pyoderma gangrenosum (PG) is a systemic disease that presents with cutaneous necrotizing ulceration, producing deep necrotic ulcers, usually with a raised, undermined, violaceous border. Treatment typically involves high dose immunosuppressive drugs, but more recently anti-tumour necrosis factor and monoclonal antibodies have been used. Activated protein C (APC) stimulates wound healing in patients with treatment-refractory skin ulcers, possibly by stimulating angiogenesis and re-epithelialization, and preventing inflammation.

AIM

To investigate whether APC may be beneficial as a treatment for ulcers related to cutaneous PG.

METHODS

Two patients were recruited with a clinical history and physical and histopathological evidence of acute PG. A total of 400 μg (1.0 mL) of APC was injected subcutaneously into the dermal edge of necrotic PG ulcers weekly for a total treatment period of 6 weeks. Photographs were taken, and clinical progress, ulcer size and pain score were monitored during this period and after the cessation of treatment, at weeks 8 and 12.

RESULTS

Over the 12 weeks of the trial, APC led to a reduction in wound size from 3.8 cm(2) to 0.8 cm(2) in patient 1 (78.9% decrease) and from 41 cm(2) to 16 cm(2) in patient 2 (70.0% decrease, respectively), and a reduction in pain scores from 10 to 0 (100% decrease) in both patients.

CONCLUSION

Although this study has limited because of its small sample size and lack of a true placebo group, it does indicate that APC has potential as a therapeutic option for patients with chronic skin ulcers from PG.

Proteinase-activated Receptor 1 Contributed to Up-regulation of Enkephalin in Keratinocytes of Patients with Obstructive Jaundice

Background:

Skin synthesis of endogenous opioids such as enkephalin is considered to be increased in cholestatic rodents, which may induce antinociception in cholestatic liver disease. No studies have reported yet the expression of skin enkephalin in patients with cholestasis.

Methods:

Electrical pain threshold, postoperative morphine consumption, and skin enkephalin expression were measured in patients with jaundice (n = 18) and control patients (n = 16). Male Sprague–Dawley rats (n = 52) and human keratinocyte cell line HaCaT were used in vivo and in vitro studies, respectively. Nociceptive thresholds and plasma and skin levels of methionine-enkephalin were compared in protease-activated receptors-1–antagonized and control bile duct–ligated rats. In in vitro study, the effect on thrombin-induced enkephalin expression was examined and the role of extracellular regulated protein kinases 1/2 and p38 was investigated.

Results:

The authors found that: (1) the electrical pain threshold (mean ± SD) was 1.1 ± 0.1 mA in control patients, whereas it was significantly increased in patients with jaundice (1.7 ± 0.3 mA); 48-h postoperative morphine consumption was approximately 50% higher in the control group than that in the group with jaundice; (2) Skin keratinocytes enkephalin expression was increased in the patients with jaundice; (3) Protease-activated receptors-1 antagonist 1 μg·kg−1·day−1 treatment to the bile duct–ligated rats significantly reduced plasma levels of methionine-enkephalin, nociceptive thresholds, and keratinocytes enkephalin expression; and (4) protease-activated receptors-1 activation induced enkephalin expression through phosphorylation of extracellular regulated protein kinases 1/2 and p38 in keratinocytes.

Conclusion:

Protease-activated receptors-1 activation in peripheral keratinocytes may play an important role in the local synthesis of enkephalin during cholestasis.

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.

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.

Peptide-agonist of protease-activated receptor (PAR 1), similar to activated protein C, promotesproliferation in keratinocytes and wound healing of epithelial layer

Activated protein C (APC) is serine protease hemostasis, independent of its anticoagulant activity, exhibits anti-inflammatory and anti-apoptotic properties that determine the possibility of the protective effects of APC in different diseases, including sepsis and chronic wound healing. APC, binding of endothelial protein C receptor (EPCR) and specifically cleaving PAR1 receptor and releasing peptide agonist PAR1 stabilizes not only endothelial cells, but also many others, including epidermal keratinocytes of the skin. We develop the hypothesis that the cytoprotective effect of APC on the cells, involved in wound healing, seem to imitate peptide - analogous of PAR1 "tethered ligand" that activate PAR1. In our work, we synthesized a peptide (AP9) – analogue of PAR1 tethered ligand, released by APC, and firstly showed that peptide AP9 (0.1-10 мM), like to APC (0.01-100 nM), stimulates the proliferative activity of human primary keratinocytes. Using a model of the formation of epithelial wounds in vitro we found that peptide AP9, as well as protease APC, accelerates wound healing. Using specific antibodies to the receptor PAR1 and EPCR was studied the receptor mechanism of AP9 action in wound healing compared with the action of APС. The necessity of both receptors – PAR1 and EPСR, for proliferative activity of agonists was revealed. Identified in our work imitation by peptide AP9 – PAR1 ligand, APC acts on keratinocytes suggests the possibility of using a peptide AP9 to stimulate tissue repair.

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.

Treatment of chronic diabetic lower leg ulcers with activated protein C: a randomised placebo-controlled, double-blind pilot clinical trial

Lower leg ulcers are a serious and long-term complication in patients with diabetes and pose a major health concern because of the increasing number of patients diagnosed with diabetes each year. This study sought to evaluate the clinical benefit of topical activated protein C (APC) on chronic lower leg ulcers in patients with diabetes. Twelve patients were randomly assigned to receive either APC (N = 6) or physiological saline (placebo; N = 6) in a randomised, placebo-controlled, double-blind pilot clinical trial. Treatment was administered topically, twice weekly for 6 weeks with final follow-up at 20 weeks. Wound area was significantly reduced to 34·8 ± 16·4% of week 0 levels at 20 weeks in APC-treated wounds (p = 0·01). At 20 weeks, three APC-treated wounds had completely healed, compared to one saline-treated wound. Full-thickness wound edge skin biopsies showed reduced inflammatory cell infiltration and increased vascular proliferation following APC treatment. Patient stress scores were also significantly reduced following APC treatment (p < 0·05), demonstrating improved patient quality of life as assessed by the Cardiff Wound Impact Questionnaire. This pilot trial suggests that APC is a safe topical agent for healing chronic lower leg ulcers in patients with diabetes and provides supporting evidence for a larger clinical trial.

Activated protein C differentially regulates both viability and differentiation of osteoblasts mediated by bisphosphonates

Activated protein C (APC) is a cytoprotective anticoagulant that can promote cutaneous healing. We examined the effect of APC on viability and differentiation of the osteoblastic line, MG63, in the presence and absence of bisphosphonates (BPs). Osteoblasts were cultured and treated for 24 or 48 h with Alendronate (Aln), Zoledronate (Zol) or Pamidronate (Pam) at concentrations ranging from 10⁻⁴ to 10⁻⁶ ℳ. Cell differentiation was measured using type 1 collagen production, Alizarin red staining and alkaline phosphatase activity, whereas cell viability was assessed using MTT and crystal violet assays. All three BPs induced MG63 cell death in a dose- and time-dependent manner. Pam- and Zol-related cell death was prevented by APC treatment; however, cell death induced by Aln was accelerated by APC. APC induced MG63 cell differentiation that was enhanced by Aln, but inhibited by Pam or Zol. Endothelial protein C receptor (EPCR) was expressed by MG63 cells and mediated the protective effect of APC on Zol-induced viability. In summary, we have demonstrated that (1) APC favorably regulates MG63 viability and differentiation toward bone growth, (2) APC differentially regulates the effects of specific BPs and (3) at least part of the effects of APC is mediated through EPCR. These findings highlight the potential importance of the PC pathway in bone physiology and provide strong evidence that APC may influence bone cells and has potential to be a therapeutic drug for bone regeneration, depending on concurrent BP treatment.

Low circulating protein C levels are associated with lower leg ulcers in patients with diabetes

Activated protein C (APC) promotes angiogenesis and reepithelialisation and accelerates healing of diabetic ulcers. The aim of this study was to determine the relationship between the incidence of lower leg ulcers and plasma levels of APC's precursor, protein C (PC), in diabetic patients. Patients with diabetes who had a lower leg ulcer(s) for >6 months (n = 36) were compared with age-, type of diabetes-, and sex-matched subjects with diabetes but without an ulcer (n = 36, controls). Total PC was assessed using a routine PC colorimetric assay. There was a significantly (P < 0.001) lower level of plasma PC in patients with ulcers (103.3 ± 22.7, mean ± SD) compared with control (127.1 ± 34.0) subjects, when corrected for age and matched for gender and type of diabetes. Ulcer type (neuropathic, ischaemic, or mixed) was not a significant covariate for plasma PC levels (P = 0.35). There was no correlation between PC levels and gender, type of diabetes, HbA1c, or C-reactive protein in either group. In summary, decreased circulating PC levels are associated with, and may predispose to, lower leg ulceration in patients with diabetes.

The endothelial cell protein C receptor: cell surface conductor of cytoprotective coagulation factor signaling

Increasing evidence links blood coagulation proteins with the regulation of acute and chronic inflammatory disease. Of particular interest are vitamin K-dependent proteases, which are generated as a hemostatic response to vascular injury, but can also initiate signal transduction via interactions with vascular receptors. The endothelial cell protein C receptor (EPCR) is a multi-ligand vitamin K-dependent protein receptor for zymogen and activated forms of plasma protein C and factor VII. Although the physiological role of the EPCR-FVII(a) interaction is not well-understood, protein C binding to EPCR facilitates rapid generation of APC in response to excessive thrombin generation, and is a central requirement for the multiple signal-transduction cascades initiated by APC on both vascular endothelial and innate immune cells. Exciting recent studies have highlighted the emerging role of EPCR in modulating the cytoprotective properties of APC in a number of diverse inflammatory disorders. In this review, we describe the structure-function relationships, signal transduction pathways, and cellular interactions that enable EPCR to modulate the anticoagulant and anti-inflammatory properties of its vitamin K-dependent protein ligands, and examine the relevance of EPCR to both thrombotic and inflammation-associated disease.

Is EPCR a multi-ligand receptor? Pros and cons

In the last decade, the endothelial cell protein C/activated protein C receptor (EPCR) has received considerable attention. The role initially attributed to EPCR, i.e. the enhancement of protein C (PC) activation by the thrombin-thrombomodulin complex on the surface of the large vessels, although important, did not go beyond the haemostasis scenario. However, the discovery of the cytoprotective, anti-inflammatory and anti-apoptotic features of the activated PC (APC) and the required involvement of EPCR for APC to exert such actions did place the receptor in a privileged position in the crosstalk between coagulation and inflammation. The last five years have shown that PC/APC are not the only molecules able to interact with EPCR. Factor VII/VIIa (FVII/VIIa) and factor Xa (FXa), two other serine proteases that play a central role in haemostasis and are also involved in signalling processes influencing wound healing, tissue remodelling, inflammation or metastasis, have been reported to bind to EPCR. These observations have paved the way for an exploration of unsuspected new roles for the receptor. This review aims to offer a new image of EPCR in the light of its extended panel of ligands. A brief update of what is known about the APC-evoked EPCR-dependent cell signalling mechanisms is provided, but special care has been taken to assemble all the information available about the interaction of EPCR with FVII/VIIa and FXa.

Protease activated receptor-2 mediates activated protein C-induced cutaneous wound healing via inhibition of p38

Activated protein C (APC) is a natural anticoagulant that exerts anti-inflammatory and cytoprotective properties mediated through the protease activated receptor (PAR)-1. APC can also proteolytically cleave PAR-2, although subsequent function is unknown. On the basis of recent evidence that APC promotes wound healing, the aim of this study was to determine whether APC acts through PARs to heal murine excisional wounds or to regulate human cultured keratinocyte function and to determine the signaling mechanisms. Topical administration of APC accelerated wound healing in wild-type mice and, unexpectedly, in PAR-1 knockout mice. PAR-2 knockout mice healed significantly slower than wild-type mice, and healing was not altered by adding APC, indicating that APC acts through PAR-2 to heal wounds. In cultured human primary keratinocytes, APC enhanced PAR-2, stimulated proliferation, activated phosphatidylinositol 3-kinase/Src/Akt, and inhibited phosphorylated (P)-p38. Inhibiting PAR-1 or PAR-2, by small-interfering RNA or blocking antibody, reversed APC-induced keratinocyte proliferation and Akt activation. Blocking PAR-2, but not PAR-1, reversed the inhibition of P-p38 by APC. Furthermore, inhibition of P-p38 accelerated wound healing in wild-type mice. In summary, although APC acts through both PAR-1 and PAR-2 to activate Akt and to increase keratinocyte proliferation, APC-induced murine wound healing depends on PAR-2 activity and inhibition of P-p38.

Reversible protease-activated receptor 1 downregulation mediated by Ankaferd blood stopper inducible with lipopolysaccharides inside the human umbilical vein endothelial cells

Ankaferd Blood Stopper (ABS) is a novel topical hemostatic agent with pleiotropic actions indicated in clinical hemorrhages. Protease-activated receptor 1 (PAR-1) is located in the crossroads of hemostasis, inflammation, infection, apoptosis and tumorigenesis. ABS-induced formation of the protein network with vital erythroid aggregation covers the entire physiological hemostatic process. The aim of this study is to assess the effects of ABS on PAR-1 in the Human Umbilical Vein Endothelial Cells (HUVEC) model, in relation to the "ipopolysaccharides (LPS)-challenge" to endothelium. For this purpose, ABS 10 μL and 100 μL, had been applied to HUVEC within the time periods of 5 minutes (min), 25 min, 50 min, 6 hours (h) and 24 h. The cells have lifted from the plastic surface and adhered to each other during theABSapplication to the HUVECs. After 24 hours the cells returned to normal baseline level. We observed dose-dependent reversible PAR-1 down-regulation mediated by ABS inside the human umbilical vein endothelial cells. ABS-induced sustained PAR-1 down-regulation in the presence of LPS. Those findings indicated that ABS hemostatic agent may act as a topical biological response modifier by acting on PAR-1 at the vascular endothelial and cellular level.

Activated protein C enhances human keratinocyte barrier integrity via sequential activation of epidermal growth factor receptor and Tie2

Keratinocytes play a critical role in maintaining epidermal barrier function. Activated protein C (APC), a natural anticoagulant with anti-inflammatory and endothelial barrier protective properties, significantly increased the barrier impedance of keratinocyte monolayers, measured by electric cell substrate impedance sensing and FITC-dextran flux. In response to APC, Tie2, a tyrosine kinase receptor, was rapidly activated within 30 min, and relocated to cell-cell contacts. APC also increased junction proteins zona occludens, claudin-1 and VE-cadherin. Inhibition of Tie2 by its peptide inhibitor or small interfering RNA abolished the barrier protective effect of APC. Interestingly, APC did not activate Tie2 through its major ligand, angiopoietin-1, but instead acted by binding to endothelial protein C receptor, cleaving protease-activated receptor-1 and transactivating EGF receptor. Furthermore, when activation of Akt, but not ERK, was inhibited, the barrier protective effect of APC on keratinocytes was abolished. Thus, APC activates Tie2, via a mechanism requiring, in sequential order, the receptors, endothelial protein C receptor, protease-activated receptor-1, and EGF receptor, which selectively enhances the PI3K/Akt signaling to enhance junctional complexes and reduce keratinocyte permeability.

The endothelial protein C receptor supports tissue factor ternary coagulation initiation complex signaling through protease-activated receptors

Protease-activated receptor (PAR) signaling is closely linked to the cellular activation of the pro- and anticoagulant pathways. The endothelial protein C receptor (EPCR) is crucial for signaling by activated protein C through PAR1, but EPCR may have additional roles by interacting with the 4-carboxyglutamic acid domains of procoagulant coagulation factors VII (FVII) and X (FX). Here we show that soluble EPCR regulates the interaction of FX with human or mouse tissue factor (TF)-FVIIa complexes. Mutagenesis of the FVIIa 4-carboxyglutamic acid domain and dose titrations with FX showed that EPCR interacted primarily with FX to attenuate FX activation in lipid-free assay systems. In human cell models of TF signaling, antibody inhibition of EPCR selectively blocked PAR activation by the ternary TF-FVIIa-FXa complex but not by the non-coagulant TF-FVIIa binary complex. Heterologous expression of EPCR promoted PAR1 and PAR2 cleavage by FXa in the ternary complex but did not alter PAR2 cleavage by TF-FVIIa. In murine smooth muscle cells that constitutively express EPCR and TF, thrombin and FVIIa/FX but not FVIIa alone induced PAR1-dependent signaling. Although thrombin signaling was unchanged, cells with genetically reduced levels of EPCR no longer showed a signaling response to the ternary complex. These results demonstrate that EPCR interacts with the ternary TF coagulation initiation complex to enable PAR signaling and suggest that EPCR may play a role in regulating the biology of TF-expressing extravascular and vessel wall cells that are exposed to limited concentrations of FVIIa and FX provided by ectopic synthesis or vascular leakage.

Adenosine regulates thrombomodulin and endothelial protein C receptor expression in folliculostellate cells of the pituitary gland

Adenosine stimulates the release of interleukin 6 (IL-6) and vascular endothelial growth factor from folliculostellate cells of the anterior pituitary gland indicating that such cells are also involved in the communication between the immune and endocrine systems during stress and inflammation. In order to understand the precise actions of adenosine on folliculostellate cells, DNA microarray analysis was used to determine global changes in gene expression. Hierarchical clusters revealed, of the genes that had altered expression, the majority were suppressed and many, such as B cell translocation gene 2 and cyclin-dependent kinase inhibitor 2b were related to cell cycle arrest or inhibition of proliferation. Several of the up-regulated genes were associated with cytokine signalling or membrane receptor activity. The most notable of these being IL-6, sulfiredoxin 1, endothelial protein C receptor (EPCR) and thrombomodulin (THBD) which can all play a role in controlling inflammation. The EPCR and THBD pathway is well known in anti-coagulation but also has anti-inflammatory and anti-apoptotic properties. Up-regulation of EPCR and THBD in folliculostellate cells was confirmed by qRT-PCR and western blotting analysis and their expression were also demonstrated in many of the hormone-secreting cells of the anterior pituitary gland. Our findings suggest that adenosine can stimulate expression of stress and inflammation related genes from folliculostellate cells of the anterior pituitary gland. These genes include EPCR and THBD, neither of which has been previously identified in the pituitary gland.

Activated protein C prevents glutamate- and thrombin-induced activation of nuclear factor-kappaB in cultured hippocampal neurons

Brain injury is associated with neuroinflammation, neurodegeneration, and also blood coagulation with thrombin formation and generation of activated protein C (APC). We have previously shown that APC, a serine protease of hemostasis, at very low concentrations has protective effects in rat hippocampal and cortical neurons at glutamate-induced excitotoxicity through protease-activated receptor-1 (PAR-1) or endothelial receptor of protein C (EPCR)/PAR-1. The transcription factor nuclear factor kappaB (NF-kappaB) takes part in regulating neuronal survival in several pathological conditions. To elucidate the impact of NF-kappaB in APC-mediated cell survival, we investigated nuclear translocation of NF-kappaB p65 at glutamate- or thrombin-induced toxicity in hippocampal neurons. We used immunoassay and immunostaining with confocal microscopy with anti-NF-kappaBp65 antibody. We show that APC at concentrations as low as 1-2 nM inhibits translocation of NF-kappaB p65 into the nucleus of cultured rat hippocampal neurons, induced by 100 muM glutamate or 50 nM thrombin (but not 10 nM). The blocking effect of APC on NF-kappaB p65 translocation was observed at 1 and 4 h after treatment of neurons with glutamate, when the NF-kappaBp 65 level in the nucleus was significantly above the basal level. Then we investigated whether the binding of APC to EPCR/PAR-1 is required to control NF-kappaB activation. Antibodies blocking PAR-1 (ATAP2) or EPCR (P-20) abolished the APC-induced decrease of nuclear level of NF-kappaB p65 at glutamate-induced toxicity, whereas control antibodies to PAR-1 (S-19) and EPCR (IgG) exerted no effect. Thus, we suggest that the activation of NF-kappaB in rat hippocampal neurons mediates the glutamate- and thrombin-activated cell death program, which is reduced by exposure of cells to APC. APC induces the reduction of the nuclear level of NF-kappaB p65 in hippocampal neurons at glutamate-induced excitotoxicity via binding to EPCR and subsequent PAR-1 activation and signaling.

Liver myofibroblasts activate protein C and respond to activated protein C

AIM: To study the protein C activation system in human liver myofibroblasts, and the effects of activated protein C (APC) on these cells.

METHODS: Human liver myofibroblasts were obtained by outgrowth. Expression of protease activated receptor 1 (PAR-1), endothelial protein C receptor (EPCR) and thrombomodulin (TM) was analyzed by flow cytometry. Extracellular signal-regulated kinase (ERK)1/2 activation was assessed by Western blotting using anti-phospho-ERK antibodies. Collagen synthesis was studied with real-time reverse transcription-polymerase chain reaction (RT-PCR). Activation of protein C was studied by incubating liver myofibroblasts with zymogen protein C in the presence of thrombin and detecting the generation of APC with a colorimetric assay using a peptide substrate.

RESULTS: Primary cultures of human liver myofibroblasts expressed EPCR on their surface, together with PAR-1 and TM. This receptor system was functional since exposure of myofibroblasts to APC induced ERK1/2 phosphorylation in a dose- and time-dependent manner. Furthermore, APC significantly upregulated the expression of collagen mRNA, as shown by real-time RT-PCR. Collagen upregulation was controlled through the ERK pathway as it was inhibited when using the mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor PD98059. Finally, using a cell-based colorimetric assay, we showed that intact myofibroblasts converted protein C into APC in the presence of thrombin.

CONCLUSION: These data suggest that APC is a new modulator of liver myofibroblast activity and contributes to the pathophysiology of chronic liver diseases.

Activated protein C utilizes the angiopoietin/Tie2 axis to promote endothelial barrier function

Activated protein C (APC) is an anticoagulant, approved as a treatment for severe sepsis, that can prevent apoptosis, inflammation, and vascular leakage. The aim of this study was to investigate whether APC protects endothelial barrier function through the angiopoietin (Ang)/Tie2 axis. APC significantly up-regulated gene and protein expression of Tie2 and Ang1 in a dose (0.01-10 microg/ml)- and time (0.5-24 h)-dependent manner in human umbilical vein endothelial cells (HUVECs). Interestingly, it markedly inhibited Ang2 with an IC(50) of approximately 0.1 microg/ml. HUVEC permeability, measured using Evans blue dye transfer, was significantly reduced in the presence of APC, and, in concordance, the tight junction associated protein zona occludens (ZO)-1 was up-regulated and localized peripherally around cells, compared with controls. Smooth muscle cell migration toward APC-stimulated HUVECs was elevated compared with unstimulated cells. Blocking antibodies and small interfering (si) RNA treatment, compared with isotype (IgG) or scrambled siRNA controls, showed that APC requires 3 receptors, the endothelial protein C receptor, protease-activated receptor 1, and Tie2 to perform all these barrier stabilization functions. In summary, this study demonstrates that APC has novel effects on the Ang/Tie2 axis, which enhance endothelial barrier function and are likely to contribute to its therapeutic effect in sepsis and other diseases associated with vascular leakage.-Minhas, N., Xue, M., Fukudome, K., Jackson, C. J. Activated protein C utilizes the angiopoietin/Tie2 axis to promote endothelial barrier function.

Activated protein C stimulates osteoblast proliferation via endothelial protein C receptor

INTRODUCTION

Bone is continually remodeled by the action of osteoblasts, osteocytes, and osteoclasts. Resting osteoblasts are able to proliferate and differentiate into mature osteoblasts when physiologically required, as after tissue injury. Activated protein C (APC) is a serine protease that functions in anticoagulation, anti-inflammation, anti-apoptosis, cell proliferation, and wound repair. In this study, we examined the effect of APC on osteoblast proliferation and differentiation.

MATERIALS AND METHODS

We examined the presence of protein C in human fracture hematoma by immunohistochemical staining. We then evaluated the effect of APC, diisopropyl fluorophosphate-inactivated APC (DIP-APC) or protein C zymogen on normal human osteoblast (NHOst) proliferation using tetrazolium salt assay in the presence or absence of aprotinin, hirudin, protein C, antibody against protein C, endothelial protein C receptor (EPCR) or protease-activated receptor (PAR)-1. Finally, activation of p44/42 MAP kinase was evaluated by Western blot analysis.

RESULTS

Both APC and DIP-APC increased osteoblast proliferation in a dose-dependent manner, while protein C did not. The APC-induced increased proliferation of osteoblast was not affected by aprotinin, hirudin, and anti-protein C antibody which inhibits the protease activity of APC. Treatment with protein C or anti-EPCR antibody which inhibits APC binding to EPCR inhibited APC-mediated osteoblast proliferation, while treatment with anti-PAR-1 antibody did not. APC promoted the phosphorylation of p44/42 MAP kinase within osteoblasts; this effect was inhibited by the anti-EPCR antibody.

CONCLUSIONS

APC stimulates osteoblast proliferation by activating p44/42 MAP kinase through a mechanism that requires EPCR but not PAR-1 or the proteolytic activity of APC. APC generated at fracture sites may contribute to fracture healing by promoting osteoblast proliferation.

Endothelial protein C receptor is expressed in rat cortical and hippocampal neurons and is necessary for protective effect of activated protein C at glutamate excitotoxicity

Activated protein C (APC) is an anticoagulant and anti-inflammatory factor that acts via endothelial protein C receptor (EPCR). Interestingly, APC also exhibits neuroprotective activities. In the present study, we demonstrate for the first time expression of EPCR, the receptor for APC, in rat cortical and hippocampal neurons. Moreover, exposing the neurons to glutamate excitotoxicity we studied the functional consequence of the expression of EPCR. By cytotoxicity assay we showed that EPCR was necessary for the APC-mediated protective effect in both neuronal cell types in culture. The effect of APC was abrogated in the presence of blocking EPCR antibodies. Analysis of neuronal death by cell labelling with dyes which allow distinguishing living and dead cells confirmed that the anti-apoptotic effect of APC was dependent on both EPCR and protease-activated receptor-1. Thus, we suggest that binding of APC to EPCR on neurons and subsequent activation of protease-activated receptor-1 by the complex of APC-EPCR promotes survival mechanisms after exposure of neurons to damaging factors.

Thrombin and activated protein C inhibit the expression of secretory group IIA phospholipase A(2) in the TNF-alpha-activated endothelial cells by EPCR and PAR-1 dependent mechanisms

INTRODUCTION

Thrombin and tumor necrosis factor (TNF)-alpha up-regulate the expression of proinflammatory molecules in human umbilical vein endothelial cells (HUVECs). However, activated protein C (APC) down-regulates the expression of the same molecules. The expression level of secretory group IIA phospholipase A(2) (sPLA(2)-IIA) is known to be elevated in inflammatory disorders including in sepsis. Here, we investigated the effects of APC and thrombin on the expression of sPLA(2)-IIA and extracellular signal-regulated kinase (ERK) in HUVECs.

MATERIALS AND METHODS

The expression level of sPLA(2)-IIA was quantitatively measured by an enzyme-linked-immunosorbent-assay following stimulation of HUVECs with either thrombin or TNF-alpha in the absence and presence of the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor LY294002 and the cholesterol-depleting drug methyl-beta-cyclodextrin (MbetaCD).

RESULTS AND CONCLUSIONS

Thrombin had no effect on the expression of sPLA(2)-IIA in HUVECs, however, TNF-alpha potently induced its expression. The prior treatment of cells with APC inhibited expression of sPLA(2)-IIA through the EPCR-dependent cleavage of PAR-1. Further studies revealed that if HUVECs were pretreated with the zymogen protein C to occupy EPCR, thrombin also inhibited the TNF-alpha-mediated expression of sPLA(2)-IIA through the cleavage of PAR-1. The EPCR-dependent cleavage of PAR-1 by both APC and thrombin increased the phosphorylation of ERK 1/2. Pretreatment of cells with either LY294002 or MbetaCD abolished the inhibitory activity of both APC and thrombin against sPLA(2)-IIA expression, suggesting that the protein C occupancy of EPCR confers a PI3-kinase dependent protective activity for thrombin such that its cleavage of the lipid-raft localized PAR-1 inhibits the TNF-alpha-mediated expression of sPLA(2)-IIA in HUVECs.

Activated protein C ligation of ApoER2 (LRP8) causes Dab1-dependent signaling in U937 cells

Binding of activated protein C (APC) to cells triggers multiple beneficial cytoprotective activities that suppress apoptosis, inflammation, and endothelial barrier breakdown. One paradigm for APC's signaling emphasizes its binding to endothelial cell protein C receptor (EPCR) and subsequent protease activated receptor (PAR)-1 activation. Here we used human monocytic-like U937 cells to evaluate apolipoprotein E receptor 2 (ApoER2)-dependent signaling by APC and found that APC initiated rapid phosphorylation of Tyr-220 in the adaptor protein disabled-1 (Dab1) and of Ser-473 in Akt. APC also induced phosphorylation of Ser-9 in glycogen synthase kinase 3beta (GSK3beta), which was blocked by the PI3K inhibitor LY294002. Receptor-associated protein (RAP), a general antagonist for binding of ligands to LDL receptor family members, inhibited APC-induced phosphorylation of Dab1 and GSK3beta, whereas anti-EPCR or anti-PAR1 blocking antibodies did not. Knocking down ApoER2 by using siRNA-ablated APC induced Dab1 phosphorylation, suggesting that RAP-sensitive APC-induced signaling requires ApoER2. In surface plasmon resonance equilibrium binding studies, APC bound with high affinity to soluble (s) ApoER2 (apparent K(d), approximately 30 nM) but not to soluble very low density lipoprotein receptor. RAP blocked APC binding to sApoER2 but not to sEPCR. RAP blocked binding of U937 cells to immobilized APC. RAP also blocked APC's ability to inhibit endotoxin-induced tissue factor pro-coagulant activity of U937 cells. Thus, we propose that ligation of ApoER2 by APC signals via Dab1 phosphorylation and subsequent activation of PI3K and Akt and inactivation of GSK3beta, thereby contributing to APC's beneficial effects on cells.

New therapeutic applications for the anticoagulant, activated protein C

BACKGROUND

Activated protein C (APC) is derived from its precursor, protein C (PC). Originally thought to be synthesised exclusively by the liver, recent reports have shown that PC is also produced by endothelial cells, smooth muscle cells, keratinocytes and some leukocytes.

OBJECTIVE

To provide an update on the emerging therapeutic effects of APC.

RESULTS/CONCLUSION

APC functions as an anticoagulant with cytoprotective, anti-inflammatory and antiapoptotic properties. In vitro and preclinical data have revealed that APC exerts its protective effects via an intriguing mechanism requiring endothelial protein C receptor and protease activated receptor-1. Approved as a therapeutic agent for severe sepsis, APC is emerging as a potential treatment for a number of autoimmune and inflammatory diseases including spinal cord injury, asthma, chronic wounds and possibly rheumatoid arthritis. The future therapeutic uses of APC look very promising.

Activated protein C mediates a healing phenotype in cultured tenocytes

Tendon injuries cause considerable morbidity in the general adult population. The tenocytes within the tendon have the full capacity to heal the tendon intrinsically. Activated protein C (APC) plays an important role in coagulation and inflammation and more recently has been shown to promote cutaneous wound healing. In this study we examined whether APC can induce a wound healing phenotype in tenocytes. Sheep tenocytes were treated with APC, endothelial protein C receptor (EPCR) blocking antibody (RCR252) and/or EPCR small interfering (si)RNA. Cell proliferation and migration were measured by crystal violet assay and a scratch wounding assay, respectively. The expression of EPCR, matrix metalloproteinase (MMP)-2, type I collagen and MAP kinase activity were detected by real time PCR, zymography, immunofluorescence, immunohistochemistry and Western blotting. APC stimulated proliferation, MMP-2 activity and type I collagen deposition in a dose-dependent manner and promoted migration of cultured tenocytes. APC dose-dependently stimulated phosphorylated (P)-ERK2 and inhibited P-p38. Interestingly, tenocytes expressed EPCR protein, which was up-regulated by APC. When tenocytes were pre-treated with RCR252 or EPCR siRNA the effect of APC on proliferation, MMP-2 and type 1 collagen synthesis and MAP kinases was blocked. APC promotes the growth, MMP-2 activity, type I collagen deposition and migration of tenocytes. Furthermore, EPCR is expressed by tenocytes and mediates the actions of APC, at least partly by signalling through selective MAP kinases. These data implicate APC as a potential healing agent for injured tendons.

Activated protein C--an anticoagulant that does more than stop clots

Activated protein C (APC) is a glycoprotein derived from its precursor, protein C and formed by the cleavage of an activation peptide by thrombin bound to thrombomodulin. Originally thought to be synthesized exclusively by the liver, recent reports have shown that protein C is synthesized by endothelial cells, keratinocytes and some hematopoietic cells. APC functions as a physiological anticoagulant with cytoprotective, anti-inflammatory and anti-apoptotic properties. In vitro and preclinical data have revealed that APC exerts its protective effects via an intriguing mechanism requiring endothelial protein C receptor and the thrombin receptor, protease-activated receptor-1. Remarkably, even though APC cleaves this receptor in an identical fashion to thrombin, it exerts opposing effects. Recently approved as a therapeutic agent for severe sepsis, APC is now emerging as a potential treatment for a number of autoimmune and inflammatory diseases including lung disorders, spinal cord injury and chronic wounds. The future pharmacologic use of APC holds remarkable promise.

Differential regulation of matrix metalloproteinase 2 and matrix metalloproteinase 9 by activated protein C: relevance to inflammation in rheumatoid arthritis

OBJECTIVE

To investigate the in vitro effect of activated protein C (APC), a natural anticoagulant and novel antiinflammatory agent, on the regulation of the gelatinases matrix metalloproteinase 2 (MMP-2) and MMP-9.

METHODS

Synovial fibroblasts and peripheral blood monocytes isolated from patients with rheumatoid arthritis (RA) or osteoarthritis (OA) and Mono Mac6 cells were used in this study. After treatment, cells and culture supernatants were collected for zymography, enzyme-linked immunosorbent assay, reverse transcription-polymerase chain reaction, and Western blot analysis.

RESULTS

Fibroblasts and monocytes from RA patients produced substantially more MMP-9 than did those from OA patients; however, there was no difference in MMP-2 production. The addition of recombinant APC markedly reduced MMP-9 at the gene and protein levels. In contrast, APC up-regulated and activated MMP-2. Using a blocking antibody to the endothelial protein C receptor (EPCR), we showed that the inhibition of MMP-9 by APC was EPCR-dependent. Furthermore, APC directly suppressed the production of tumor necrosis factor (TNF) and the activation of NF-kappaB and MAP kinase p38, and inhibitors of NF-kappaB or p38 reduced the production of MMP-9, suggesting that APC inhibits MMP-9 by blocking TNF, NF-kappaB, and p38. Thus, APC acts on MMP-9 by binding to EPCRs on the cell surface and, subsequently, inhibiting the intracellular activation of the proinflammatory signaling molecules NF-kappaB and p38.

CONCLUSION

APC appears to be the first physiologic agent to inhibit the production of proinflammatory MMP-9, yet increase antiinflammatory MMP-2 activity. Our results provide the initial evidence that APC may be beneficial in the prevention of inflammation and joint destruction in RA.

On interaction of activated protein C with human aortic smooth muscle cells attenuating the secretory group IIA phospholipase A2 expression

INTRODUCTION

Pharmacological restriction of secretory group IIA phospholipase A(2) (sPLA(2)-IIA) expression is thought to be beneficial in the treatment of inflammatory diseases such as sepsis and septic shock. In this study we investigated the effects of activated protein C (APC) on sPLA(2)-IIA expression, phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, and on DNA-binding activities of nuclear factor-kappaB (NF-kappaB) and CCAAT box enhancer binding protein-beta (C/EBP-beta) in human aortic smooth muscle cells (HASMC).

MATERIALS AND METHODS

To achieve elevated sPLA(2)-IIA production as occurring during inflammation, HASMC were stimulated with interferon-gamma (IFN-gamma) alone and in combination with other inductors, thus modeling the strong sPLA(2)-IIA elevation by inflammation.

RESULTS AND CONCLUSIONS

APC inhibited the stimulated expression of sPLA(2)-IIA in HASMC dose-dependently (1-300 nM). At the same time, APC increased the phosphorylation of ERK 1/2 and decreased NF-kappaB and C/EBP-beta DNA-binding activities in these cells, as compared with respective stimulated controls. Reverse transcriptase-polymerase chain reaction and cell-based ELISA reveal an endothelial protein C receptor (EPCR) expression in HASMC. Application of antibodies against EPCR and protease-activated receptor-1 (PAR-1) reduced the APC-induced ERK 1/2 activation and the treatment of cells with a PAR-1 antagonist diminished the sPLA(2)-IIA inhibition. The obtained results show that APC effectively suppresses the up-regulated sPLA(2)-IIA expression, which might contribute to the reported beneficial effects of APC in the treatment of severe inflammatory disorders.