Changes to fibrinolysis in patients with systemic lupus erythematosus are associated with endothelial cell damage and inflammation, but not antiphospholipid antibodies

The Roles of Fibrinolytic Factors in Bone Destruction Caused by Inflammation

Chronic inflammatory diseases, such as rheumatoid arthritis, spondyloarthritis, systemic lupus erythematosus, Crohn's disease, periodontitis, and carcinoma metastasis frequently result in bone destruction. Pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and IL-17 are known to influence bone loss by promoting the differentiation and activation of osteoclasts. Fibrinolytic factors, such as plasminogen (Plg), plasmin, urokinase-type plasminogen activator (uPA), its receptor (uPAR), tissue-type plasminogen activator (tPA), α2-antiplasmin (α2AP), and plasminogen activator inhibitor-1 (PAI-1) are expressed in osteoclasts and osteoblasts and are considered essential in maintaining bone homeostasis by regulating the functions of both osteoclasts and osteoblasts. Additionally, fibrinolytic factors are associated with the regulation of inflammation and the immune system. This review explores the roles of fibrinolytic factors in bone destruction caused by inflammation.

α2AP is associated with the development of lupus nephritis through the regulation of plasmin inhibition and inflammatory responses

Introduction

Lupus nephritis (LN) is a common complication of systemic lupus erythematosus (SLE), which is a chronic autoimmune disease. However, the detailed mechanisms underlying this disorder have remained unclear. Alpha2‐antiplasmin (α2AP) is known to perform various functions, such as plasmin inhibition and cytokine production, and to be associated with immune and inflammatory responses.

Methods

We investigated the roles of α2AP in the pathogenesis of LN using a pristane‐induced lupus mouse model.

Results

The levels of plasmin‐α2AP complex and α2AP were elevated in the lupus model mice. In addition, α2AP deficiency attenuated the pristane‐induced glomerular cell proliferation, mesangial matrix expansion, collagen production, fibrin deposition, immunoglobulin G deposition, and proinflammatory cytokine production in the model mice. We also showed that interferon‐γ (IFN‐γ), which is an essential inducer of LN, induced α2AP production through the c‐Jun N‐terminal kinase (JNK) pathway in fibroblasts. In addition, plasmin attenuated the IFN‐γ‐induced proinflammatory cytokine production through the AMPK pathway in macrophages, and α2AP eliminated these effects. Furthermore, we showed that α2AP induced proinflammatory cytokine production through the ERK1/2 and JNK pathways in macrophages.

Conclusion

α2AP regulates the inflammatory responses through plasmin inhibition and proinflammatory cytokine production and is associated with the development of LN. Our findings may be used to develop a novel therapeutic approach for SLE.

Lytic Susceptibility, Structure, and Mechanical Properties of Fibrin in Systemic Lupus Erythematosus

Among complications of systemic lupus erythematosus (SLE), thrombotic events are relatively common and contribute significantly to the morbidity and mortality rates. An increased risk of thrombosis in various diseases has been shown to be associated with the lytic stability and mechanical stiffness of the fibrin clot determined by its structure. Here we studied alterations of the fibrin clot properties in relation to disease severity in SLE patients. Plasma clots from 28 SLE patients were characterized by the kinetics of formation and fibrinolytic dissolution (using dynamic turbidimetry), the network and fiber ultrastructure (scanning electron microscopy), viscoelasticity (shear rheometry), and the rate and degree of crosslinking (Western blotting) correlated with the disease activity, blood composition, and compared to clotting of pooled normal human plasma. Clots made from plasma of SLE patients were lysed faster with exogenous t-PA than control clots from normal plasma without a significant difference between those from active (SLEDAI>4) and inactive (SLEDAI<4) SLE patients. Clots from the blood of patients with active SLE were characterized by significantly slower onset, but faster rate of fibrin polymerization and a higher optical density due to thicker fibers compared to those from inactive SLE and control pooled normal plasma. The rheological parameters of the clots (storage and loss moduli) were significantly increased in the active SLE patients along with enhanced fibrin crosslinking and hyperfibrinogenemia. The structural and rheological alterations displayed a strong positive correlation with high fibrinogen levels and other laboratory markers of immune inflammation. In conclusion, changes in the blood composition associated with active systemic inflammation in SLE cause significant alterations in the lytic resistance of fibrin clots associated with changes in polymerization kinetics, viscoelastic properties, and structure. The formation of more rigid prothrombotic fibrin clots in the plasma of SLE patients is likely due to the inflammatory hyperfibrinogenemia and greater extent of crosslinking. However, the higher susceptibility of the SLE clots to fibrinolysis may be a protective and/or compensatory mechanism that reduces the risk of thrombotic complications and improves patient outcomes.