Activated protein C modulates the proinflammatory activity of dendritic cells

Endothelial cell protein C receptor regulates neutrophil extracellular trap-mediated rheumatoid arthritis disease progression

Endothelial cell protein C receptor (EPCR) is a 46 kDa transmembrane protein receptor, expressed in most immune cells (T cells, monocytes, dendritic cells, polymorphonuclear neutrophils [PMN]). EPCR reportedly plays a vital role in rheumatoid arthritis (RA). Our results confirmed that EPCR expression exists in the PMN of RA patients, and animal experiments demonstrated that down-regulation of EPCR expression affects disease progression in collagen-induced arthritis (CIA) mice. PMN is the immune cell type that first enters the site of inflammation in the early stages of inflammation. In the early stage of RA, PMN cells migrate into the joint cavity and function in the process of RA synovial inflammation, aggravating the bone destruction found in RA and mediating the progression of RA disease progression. We verified the differences in EPCR expression in PMN cells between RA and osteoarthritis (OA) patients by Western blot and then confirmed this difference in animals. We found that CIA mice treated with PMN-neutralizing antibody intervention had reduced disease performance. On this basis, EPCR was knocked down at the same time. The therapeutic effect of PMN-neutralizing antibody treatment was subsequently diminished. To explore the relationship between EPCR and PMN in RA, we used immunofluorescence to detect the expression of PMN-neutrophil extracellular traps (NETs) in RA patients and used EPCR neutralizing antibodies as an intervention. The results showed that the formation of PMN-NETs in RA patients increased. Finally, through in vitro intervention experiments involving EPCR and PMN transcriptome analysis of the peripheral blood of RA patients, we concluded that EPCR may regulate the formation of PMN-NETs in RA patients through the activated protein C (APC)-EPCR signaling pathway, thereby affecting the progression of disease in RA patients.

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.

Imbalanced Coagulation in the Airway of Type-2 High Asthma with Comorbid Obesity

Asthma is a common, chronic airway inflammatory disease marked by airway hyperresponsiveness, inflammation, and remodeling. Asthma incidence has increased rapidly in the past few decades and recent multicenter analyses have revealed several unique asthma endotypes. Of these, type-2 high asthma with comorbid obesity presents a unique clinical challenge marked by increased resistance to standard therapies and exacerbated disease development. The extrinsic coagulation pathway plays a significant role in both type-2 high asthma and obesity. The type-2 high asthma airway is marked by increased procoagulant potential, which is readily activated following damage to airway tissue. In this review, we summarize the current understanding of the role the extrinsic coagulation pathway plays in the airway of type-2 high asthma with comorbid obesity. We propose that asthma control is worsened in obesity as a result of a systemic and local airway shift towards a procoagulant and anti-fibrinolytic environment. Lastly, we hypothesize bariatric surgery as a treatment for improved asthma management in type-2 high asthma with comorbid obesity, facilitated by normalization of systemic procoagulant and pro-inflammatory mediators. A better understanding of attenuated coagulation parameters in the airway following bariatric surgery will advance our knowledge of biomolecular pathways driving asthma pathobiology in patients with obesity.

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.