Mice with a severe deficiency in protein C display prothrombotic and proinflammatory phenotypes and compromised maternal reproductive capabilities

Dysregulated haemostasis in thrombo-inflammatory disease

Inflammatory disease is often associated with an increased incidence of venous thromboembolism in affected patients, although in most instances, the mechanistic basis for this increased thrombogenicity remains poorly understood. Acute infection, as exemplified by sepsis, malaria and most recently, COVID-19, drives 'immunothrombosis', where the immune defence response to capture and neutralise invading pathogens causes concurrent activation of deleterious prothrombotic cellular and biological responses. Moreover, dysregulated innate and adaptive immune responses in patients with chronic inflammatory conditions, such as inflammatory bowel disease, allergies, and neurodegenerative disorders, are now recognised to occur in parallel with activation of coagulation. In this review, we describe the detailed cellular and biochemical mechanisms that cause inflammation-driven haemostatic dysregulation, including aberrant contact pathway activation, increased tissue factor activity and release, innate immune cell activation and programmed cell death, and T cell-mediated changes in thrombus resolution. In addition, we consider how lifestyle changes increasingly associated with modern life, such as circadian rhythm disruption, chronic stress and old age, are increasingly implicated in unbalancing haemostasis. Finally, we describe the emergence of potential therapies with broad-ranging immunothrombotic functions, and how drug development in this area is challenged by our nascent understanding of the key molecular and cellular parameters that control the shared nodes of proinflammatory and procoagulant pathways. Despite the increasing recognition and understanding of the prothrombotic nature of inflammatory disease, significant challenges remain in effectively managing affected patients, and new therapeutic approaches to curtail the key pathogenic steps in immune response-driven thrombosis are urgently required.

Thrombin spatial distribution determines protein C activation during hemostasis and thrombosis

Rebalancing the hemostatic system by targeting endogenous anticoagulant pathways, like the protein C (PC) system, is being tested as a means of improving hemostasis in patients with hemophilia. Recent intravital studies of hemostasis demonstrated that, in some vascular contexts, thrombin activity is sequestered in the extravascular compartment. These findings raise important questions about the context-dependent contribution of activated PC (APC) to the hemostatic response, because PC activation occurs on the surface of endothelial cells. We used a combination of pharmacologic, genetic, imaging, and computational approaches to examine the relationships among thrombin spatial distribution, PC activation, and APC anticoagulant function. We found that inhibition of APC activity, in mice either harboring the factor V Leiden mutation or infused with an APC-blocking antibody, significantly enhanced fibrin formation and platelet activation in a microvascular injury model, consistent with the role of APC as an anticoagulant. In contrast, inhibition of APC activity had no effect on hemostasis after penetrating injury of the mouse jugular vein. Computational studies showed that differences in blood velocity, injury size, and vessel geometry determine the localization of thrombin generation and, consequently, the extent of PC activation. Computational predictions were tested in vivo and showed that when thrombin generation occurred intravascularly, without penetration of the vessel wall, inhibition of APC significantly increased fibrin formation in the jugular vein. Together, these studies show the importance of thrombin spatial distribution in determining PC activation during hemostasis and thrombosis.

A bioinformatic search for correspondence between differentially expressed genes of domestic versus wild animals and orthologous human genes altering reproductive potential

One of the greatest achievements of genetics in the 20th century is D.K. Belyaev’s discovery of destabilizing selection during the domestication of animals and that this selection affects only gene expression regulation (not gene structure) and inf luences systems of neuroendocrine control of ontogenesis in a stressful environment. Among the experimental data generalized by Belyaev’s discovery, there are also f indings about accelerated extinc tion of testes’ hormonal function and disrupted seasonality of reproduction of domesticated foxes in comparison with their wild congeners. To date, Belyaev’s discovery has already been repeatedly conf irmed, for example, by independent observations during deer domestication, during the use of rats as laboratory animals, after the reintroduction of endangered species such as Przewalski’s horse, and during the creation of a Siberian reserve population of the Siberian grouse when it had reached an endangered status in natural habitats. A genome-wide comparison among humans, several domestic animals, and some of their wild congeners has given rise to the concept of self-domestication syndrome, which includes autism spectrum disorders. In our previous study, we created a bioinformatic model of human self-domestication syndrome using differentially expressed genes (DEGs; of domestic animals versus their wild congeners) orthologous to the human genes (mainly, nervous-system genes) whose changes in expression affect reproductive potential, i. e., growth of the number of humans in the absence of restrictions caused by limiting factors. Here, we applied this model to 68 human genes whose changes in expression alter the reproductive health of women and men and to 3080 DEGs of domestic versus wild animals. As a result, in domestic animals, we identif ied 16 and 4 DEGs, the expression changes of which are codirected with changes in the expression of the human orthologous genes decreasing and increasing human reproductive potential, respectively. The wild animals had 9 and 11 such DEGs, respectively. This difference between domestic and wild animals was signif icant according to Pearson’s χ2 test (p < 0.05) and Fisher’s exact test (p < 0.05). We discuss the results from the standpoint of restoration of endangered animal species whose natural habitats are subject to an anthropogenic impact.

Immunotherapy in sepsis - brake or accelerate?

Sepsis, a life threating syndrome characterized by organ failure after infection, is the most common cause of death in hospitalized patients. The treatment of sepsis is generally supportive in nature, involving the administration of intravenous fluids, vasoactive substances and oxygen plus antibiotics to eliminate the pathogen. No drugs have been approved specifically for the treatment of sepsis, and clinical trials of potential therapies have failed to reduce mortality - suggesting that new approaches are needed. Abnormalities in the immune response elicited by the pathogen, ranging from excessive inflammation to immunosuppression, contribute to disease pathogenesis. Although hundreds of immunomodulatory agents are potentially available, it remains unclear which patient benefits from which immune therapy at a given time point. Results indicate the importance of personalized therapy, specifically the need to identify the type of intervention required by each individual patient at a given point in the disease process. To address this issue will require using biomarkers to stratify patients based on their individual immune status. This article reviews recent and ongoing clinical investigations using immunostimulatory or immunosuppressive therapies against sepsis including non-pharmacological and novel preclinical approaches.

Coagulopathies and inflammatory diseases: '…glimpse of a Snark'

Coagulopathies and inflammatory diseases, ostensibly, have distinct underlying molecular bases. Notwithstanding, both are host defense mechanisms to physical injury. In invertebrates, clotting can function directly in anti-pathogen defense. Molecules of the vertebrate clotting cascade have also been directly linked to the regulation of inflammation. We posit that thrombophilia may provide resistance against pathogens in vertebrates. The selective pressure of improved anti-pathogen defense may have retained mutations associated with a thrombophilic state in the human population and directly contributed to enhanced inflammation. Indeed, in some inflammatory diseases, at least a subset of patients can be identified as hypercoagulable. Therefore, anticoagulants such as warfarin or apixaban may have a therapeutic role in some inflammatory diseases.

Candidate SNP markers of reproductive potential are predicted by a significant change in the affinity of TATA-binding protein for human gene promoters

BACKGROUND

The progress of medicine, science, technology, education, and culture improves, year by year, quality of life and life expectancy of the populace. The modern human has a chance to further improve the quality and duration of his/her life and the lives of his/her loved ones by bringing their lifestyle in line with their sequenced individual genomes. With this in mind, one of genome-based developments at the junction of personalized medicine and bioinformatics will be considered in this work, where we used two Web services: (i) SNP_TATA_Comparator to search for alleles with a single nucleotide polymorphism (SNP) that alters the affinity of TATA-binding protein (TBP) for the TATA boxes of human gene promoters and (ii) PubMed to look for retrospective clinical reviews on changes in physiological indicators of reproductive potential in carriers of these alleles.

RESULTS

A total of 126 SNP markers of female reproductive potential, capable of altering the affinity of TBP for gene promoters, were found using the two above-mentioned Web services. For example, 10 candidate SNP markers of thrombosis (e.g., rs563763767) can cause overproduction of coagulation inducers. In pregnant women, Hughes syndrome provokes thrombosis with a fatal outcome although this syndrome can be diagnosed and eliminated even at the earliest stages of its development. Thus, in women carrying any of the above SNPs, preventive treatment of this syndrome before a planned pregnancy can reduce the risk of death. Similarly, seven SNP markers predicted here (e.g., rs774688955) can elevate the risk of myocardial infarction. In line with Bowles' lifespan theory, women carrying any of these SNPs may modify their lifestyle to improve their longevity if they can take under advisement that risks of myocardial infarction increase with age of the mother, total number of pregnancies, in multiple pregnancies, pregnancies under the age of 20, hypertension, preeclampsia, menstrual cycle irregularity, and in women smokers.

CONCLUSIONS

According to Bowles' lifespan theory-which links reproductive potential, quality of life, and life expectancy-the above information was compiled for those who would like to reduce risks of diseases corresponding to alleles in own sequenced genomes. Candidate SNP markers can focus the clinical analysis of unannotated SNPs, after which they may become useful for people who would like to bring their lifestyle in line with their sequenced individual genomes.

5B9, a monoclonal antiplatelet factor 4/heparin IgG with a human Fc fragment that mimics heparin-induced thrombocytopenia antibodies

Essentials No humanized monoclonal antibody was available to study heparin-induced thrombocytopenia (HIT). We developed the first anti-platelet factor 4 (PF4)/heparin antibody with a human Fc fragment. This antibody (5B9) fully mimics the effects of human HIT antibodies. 5B9 binds two regions within PF4 that may be critical for the pathogenicity of HIT antibodies.

SUMMARY

Background The diagnosis of heparin-induced thrombocytopenia (HIT) is based on clinical and biological criteria, but a standard is lacking for laboratory assays. Moreover, no humanized HIT antibody is available for pathophysiological studies. Objective To characterise 5B9, a chimeric monoclonal antibody, which fully mimics the effects of human HIT antibodies. Methods/Results 5B9, a chimeric anti-platelet factor 4/heparin complexes IgG1 antibody, was obtained after immunizing specific transgenic mice. 5B9 induced heparin FcγRIIA-dependent platelet aggregation and tissue factor mRNA synthesis in monocytes. It also induced significant thrombocytopenia and thrombin generation in mice expressing human PF4 and FcγRIIA receptors. The binding of 5B9 to PF4/H complexes was inhibited by 15 of 25 HIT plasma samples and only three of 25 samples containing non-pathogenic anti-PF4/H antibodies. KKO, a murine IgG2b HIT antibody, also inhibited the binding of 5B9 to PF4/H, suggesting that epitopes recognized by both antibodies are close. A docking analysis based on VH and VL sequences of 5B9 showed that binding of 5B9 Fab to PF4 involved 12 and 12 residues in B and D monomers, respectively, including seven previously identified as critical to the formation of a PF4/KKO complex. Two regions (Asp-7 to Thr-15 and Ala-32 to Thr-38) therefore appeared important for the binding of 5B9 and KKO on PF4 modified by heparin. Conclusions 5B9 is the first anti-PF4/H monoclonal antibody with a human Fc fragment, which induces similar cellular activation as HIT antibodies. Moreover, 5B9 binds epitopes within PF4 that are likely to be critical for the pathogenicity of HIT antibodies.

Can adjunctive therapies augment the efficacy of endovascular thrombolysis? A potential role for activated protein C

In the management of acute ischemic stroke, vessel recanalization correlates with functional status, mortality, cost, and other outcome measures. Thrombolysis with intravenous tissue plasminogen activator has many limitations that restrict its applicability, but recent advances in the development of mechanical thrombectomy devices as well as improved systems of stroke care have resulted in greater likelihood of vessel revascularization. Nonetheless, there remains substantial discrepancy between rates of recanalization and rates of favorable outcome. The poor neurological recovery among some stroke patients despite successful recanalization confirms the need for adjuvant pharmacological therapy for neuroprotection and/or neurorestoration. Prior clinical trials of such drugs may have failed due to the inability of the agent to access the ischemic tissue beyond the occluded artery. A protocol that couples revascularization with concurrent delivery of a neuroprotectant drug offers the potential to enhance the benefit of thrombolysis. Analogs of activated protein C (APC) exert pleiotropic anti-inflammatory, anti-apoptotic, antithrombotic, cytoprotective, and neuroregenerative effects in ischemic stroke and thus appear to be promising candidates for this novel approach. A multicenter, prospective, double-blinded, dose-escalation Phase 2 randomized clinical trial has enrolled 110 patients to assess the safety, pharmacokinetics, and efficacy of human recombinant 3K3A-APC following endovascular thrombolysis. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Targeting activated protein C to treat hemophilia

PURPOSE OF REVIEW

Hemophilia is a debilitating disease, marked by frequent, painful bleeding events, joint deterioration and early death. All current treatments consist of i.v. infusions of replacement factor or other procoagulant factors, and are incompletely effective, due in part to the short half-lives of the proteins. An alternative approach is to rebalance hemostasis by inhibiting natural anticoagulant mechanisms. In this article, we explain why activated protein C (APC) is an appropriate and safe target for the treatment of hemophilia.

RECENT FINDINGS

A serpin (serine protease inhibitor) was engineered to specifically inhibit APC and was found to rescue hemostasis in a hemophilia mouse model, even after a severe tail clip injury. However, APC is also anti-inflammatory and has cytoprotective activities, raising safety concerns over the use of an APC inhibitor to treat hemophilia. We summarize the molecular basis of the anticoagulant and signaling activities of APC to assess the potential impact of targeting APC.

SUMMARY

We conclude that the signaling and anticoagulant functions of APC are in spatially and kinetically distinct compartments, and that it is possible to specifically inhibit the anticoagulant activity of APC. Targeting APC with a serpin is remarkably effective and may be safe for long-term prophylactic use in the treatment of hemophilia.

Thrombin activation of protein C requires prior processing by a liver proprotein convertase

Protein C, a secretory vitamin K-dependent anticoagulant serine protease, inactivates factors Va/VIIIa. It is exclusively synthesized in liver hepatocytes as an inactive zymogen (proprotein C). In humans, thrombin cleavage of the propeptide at PR²²¹↓ results in activated protein C (APC; residues 222-461). However, the propeptide is also cleaved by a furin-like proprotein convertase(s) (PCs) at KKRSHLKR¹⁹⁹↓ (underlined basic residues critical for the recognition by PCs), but the order of cleavage is unknown. Herein, we present evidence that at the surface of COS-1 cells, mouse proprotein C is first cleaved by the convertases furin, PC5/6A, and PACE4. In mice, this cleavage occurs at the equivalent site, KKRKILKR¹⁹⁸↓, and requires the presence of Arg¹⁹⁸ at P1 and a combination of two other basic residues at either P2 (Lys¹⁹⁷), P6 (Arg¹⁹³), or P8 (Lys¹⁹¹) positions. Notably, the thrombin-resistant R221A mutant is still cleaved by these PCs, revealing that convertase cleavage can precede thrombin activation. This conclusion was supported by the fact that the APC-specific activity in the medium of COS-1 cells is exclusively dependent on prior cleavage by the convertases, because both R198A and R221A lack protein C activity. Primary cultures of hepatocytes derived from wild-type or hepatocyte-specific furin, PC5/6, or complete PACE4 knock-out mice suggested that the cleavage of overexpressed proprotein C is predominantly performed by furin intracellularly and by all three proprotein convertases at the cell surface. Indeed, plasma analyses of single-proprotein convertase-knock-out mice showed that loss of the convertase furin or PC5/6 in hepatocytes results in a ∼30% decrease in APC levels, with no significant contribution from PACE4. We conclude that prior convertase cleavage of protein C in hepatocytes is critical for its thrombin activation.

Activated protein C promotes neuroprotection: mechanisms and translation to the clinic

Activated protein C (APC) is a plasma serine protease that is capable of antithrombotic, anti-inflammatory, anti-apoptotic, and cell-signaling activities. Animal injury studies show that recombinant APC and some of its mutants are remarkably therapeutic for a wide range of injuries. In particular, for neurologic injuries, APC reduces damage caused by ischemia/reperfusion in the brain, by acute brain trauma, and by chronic neurodegenerative conditions. For these neuroprotective effects, APC requires endothelial cell protein C receptor. APC activates cell signaling networks with alterations in gene expression profiles by activating protease activated receptors 1 and 3. To minimize APC-induced bleeding risk, APC variants were engineered to lack > 90% anticoagulant activity but retain normal cell signaling. The neuroprotective APC mutant, 3K3A-APC which has Lys191-193 mutated to Ala191-193, is very neuroprotective and it is currently in clinical trials for ischemic stroke.

S2'-subsite variations between human and mouse enzymes (plasmin, factor XIa, kallikrein) elucidate inhibition differences by tissue factor pathway inhibitor -2 domain1-wild-type, Leu17Arg-mutant and aprotinin

Essentials Current antifibrinolytics - aminocaproic acid and tranexamic acid-can cause seizures or renal injury. KD1L17R -KT , aprotinin and tranexamic acid were tested in a modified mouse tail-amputation model. S2'-subsite variations between human and mouse factor XIa result in vastly different inhibition profiles. KD1L17R -KT reduces blood loss and D-dimer levels in mouse with unobserved seizures or renal injury.

SUMMARY

Background Using tissue factor pathway inhibitor (TFPI)-2 Kunitz domain1 (KD1), we obtained a bifunctional antifibrinolytic molecule (KD1L17R -KT ) with C-terminal lysine (kringle domain binding) and P2'-residue arginine (improved specificity towards plasmin). KD1L17R -KT strongly inhibited human plasmin (hPm), with no inhibition of human kallikrein (hKLK) or factor XIa (hXIa). Furthermore, KD1L17R -KT reduced blood loss comparable to aprotinin in a mouse liver-laceration model of organ hemorrhage. However, effectiveness of these antifibrinolytic agents in a model of hemorrhage mimicking extremity trauma and their inhibition efficiencies for mouse enzymes (mPm, mKLK or mXIa) remain to be determined. Objective To determine potential differences in inhibition constants of various antifibrinolytic agents against mouse and human enzymes and test their effectiveness in a modified mouse tail-amputation hemorrhage model. Methods/Results Unexpectedly, mXIa was inhibited with ~ 17-fold increased affinity by aprotinin (Ki ~ 20 nm) and with measurable affinity for KD1L17R -KT (Ki ~ 3 μm); in contrast, KD1WT -VT inhibited hXIa or mXIa with similar affinity. Compared with hPm, mPm had ~ 3-fold reduced affinity, whereas species specificity for hKLK and mKLK was comparable for each inhibitor. S2'-subsite variations largely accounted for the observed differences. KD1L17R -KT and aprotinin were more effective than KD1WT -VT or tranexamic acid in inhibiting tPA-induced mouse plasma clot lysis. Further, KD1L17R -KT was more effective than KD1WT -VT and was comparable to aprotinin and tranexamic acid in reducing blood loss and D-dimer levels in the mouse tail-amputation model. Conclusions Inhibitor potencies differ between antifibrinolytic agents against human and mouse enzymes. KD1L17R -KT is effective in reducing blood loss in a tail-amputation model that mimics extremity injury.

Novel Functions of the Anticoagulant Activated Protein C in Maintaining Skin Barrier Integrity to Impact on Skin Disease

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. When the barrier is disrupted any of a number of diseases, such as chronic wounds, psoriasis, pemphigus, atopic dermatitis or toxic epidermal necrolysis, can take hold. Activated protein C (APC) or its precursor, protein C, is abundantly expressed by skin epidermal keratinocytes and stimulates their proliferation and migration, and inhibits apoptosis and inflammation, leading to a healing phenotype. Importantly, APC also increases the barrier function of keratinocytes by promoting expression and cell-cell contact redistribution of tight junction proteins. These cytoprotective properties of APC on epidermal keratinocytes place it as an exciting new therapy for skin disorders associated with the disruption of barrier function and inflammation.

Deficiency of superoxide dismutase impairs protein C activation and enhances susceptibility to experimental thrombosis

OBJECTIVE

Clinical evidence suggests an association between oxidative stress and vascular disease, and in vitro studies have demonstrated that reactive oxygen species can have prothrombotic effects on vascular and blood cells. It remains unclear, however, whether elevated levels of reactive oxygen species accelerate susceptibility to experimental thrombosis in vivo.

APPROACH AND RESULTS

Using a murine model with genetic deficiency in superoxide dismutase-1 (SOD1), we measured susceptibility to carotid artery thrombosis in response to photochemical injury. We found that SOD1-deficient (Sod1(-/-)) mice formed stable arterial occlusions significantly faster than wild-type (Sod1(+/+)) mice (P<0.05). Sod1(-/-) mice also developed significantly larger venous thrombi than Sod1(+/+) mice after inferior vena cava ligation (P<0.05). Activation of protein C by thrombin in lung was diminished in Sod1(-/-) mice (P<0.05 versus Sod1(+/+) mice), and generation of activated protein C in response to infusion of thrombin in vivo was decreased in Sod1(-/-) mice (P<0.05 versus Sod1(+/+) mice). SOD1 deficiency had no effect on the expression of thrombomodulin, endothelial protein C receptor, or tissue factor in lung or levels of protein C in plasma. Exposure of human thrombomodulin to superoxide in vitro caused oxidation of multiple methionine residues, including critical methionine 388, and a 40% decrease in thrombomodulin-dependent activation of protein C (P<0.05). SOD and catalase protected against superoxide-induced methionine oxidation and restored protein C activation in vitro (P<0.05).

CONCLUSIONS

SOD prevents thrombomodulin methionine oxidation, promotes protein C activation, and protects against arterial and venous thrombosis in mice.

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.

Thrombophilic Mutations and Polymorphisms, Alone or in Combination, and Recurrent Spontaneous Abortion

Generally, recurrent spontaneous abortions (RSAs) have no identifiable cause; yet, vascular alterations during pregnancy may be associated with pregnancy loss. Therefore, we evaluated the association between thrombophilic mutations and RSAs. This case–control study was conducted in 112 patients who had RSAs and 98 health control women. Genomic DNA was extracted from whole blood, and polymorphism genotyping was conducted using polymerase chain reaction. The following 6 genetic variants were analyzed: factor V Leiden, prothrombin mutation, methylenetetrahydrofolate reductase C677T and A1298C, plasminogen activator inhibitor type 1 (4G>5G), and factor XIII G103T (V34L). No correlations were found in any of the investigated polymorphisms. Moreover, 35.0% of cases and 25.5% of controls had at least 2 mutations in combination, and 4.8% of cases and 5.1% of controls had 3, but these combinations were not associated with additional risk. In conclusion, we found no association between the polymorphisms studied and the occurrence of RSAs.

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.

Loss of the cytoskeletal protein Pdlim7 predisposes mice to heart defects and hemostatic dysfunction

The actin-associated protein Pdlim7 is essential for heart and fin development in zebrafish; however, the expression and function of this PDZ-LIM family member in the mammal has remained unclear. Here, we show that Pdlim7 predominantly localizes to actin-rich structures in mice including the heart, vascular smooth muscle, and platelets. To test the requirement for Pdlim7 in mammalian development and function, we analyzed a mouse strain with global genetic inactivation of Pdlim7. We demonstrate that Pdlim7 loss-of-function leads to significant postnatal mortality. Inactivation of Pdlim7 does not disrupt cardiac development, but causes mild cardiac dysfunction in adult mice. Adult Pdlim7^-/- mice displayed increased mitral and tricuspid valve annulus to body weight ratios. These structural aberrations in Pdlim7^-/- mice were supported by three-dimensional reconstructions of adult cardiac valves, which revealed increased surface area to volume ratios for the mitral and tricuspid valve leaflets. Unexpectedly, we found that loss of Pdlim7 triggers systemic venous and arterial thrombosis, leading to significant mortality shortly after birth in Pdlim7^+/- (11/60) and Pdlim7^-/- (19/35) mice. In line with a prothrombotic phenotype, adult Pdlim7^-/- mice exhibit dramatically decreased tail bleed times compared to controls. These findings reveal a novel and unexpected function for Pdlim7 in maintaining proper hemostasis in neonatal and adult mice.

Role of the coagulation system in development

The generation of knock out mice urged researchers, not always voluntarily, to newly define developmental functions of the gene knocked out. Among others, this has led to the establishment of the field of developmental haemostasis. The work in this field identified a role of coagulation proteases and their regulators independent of haemostasis in the embryo proper. Rather, coagulation proteases regulate cellular function through receptor dependent signalling in the embryo proper, both within and outside the vasculature. Likewise, coagulation proteases modulate placental development independent of haemostasis through mechanisms involving the activation of maternal myeloid derived cells. The following review summarizes the current knowledge in the field of developmental haemostasis and pinpoints open questions within this evolving field.

Antibody SPC-54 provides acute in vivo blockage of the murine protein C system

Multiple protective effects of pharmacological activated protein C (APC) are reported in several organ pathologies. To help evaluate the endogenous murine PC system, we characterized a rat monoclonal anti-mouse PC antibody, SPC-54, which inhibited the amidolytic and anticoagulant activities of murine APC by>95%. SPC-54 blocked active site titration of purified APC using the active site titrant, biotinylated FPR-chloromethylketone, showing that SPC-54 blocks access to APC's active site to inhibit all enzymatic activity. A single injection of SPC-54 (10mg/kg) neutralized circulating PC in mice for at least 7days, and immunoblotting and immuno-precipitation with protein G-agarose confirmed that SPC-54 in vivo was bound to PC in plasma. Pre-infusion of SPC-54 in tissue factor-induced murine acute thromboembolism experiments caused a major decrease in mean survival time compared to controls (7min vs. 42.5min, P=0.0016). SPC-54 decreased lung perfusion in this model by 54% when monitored by vascular perfusion methodologies using infrared fluorescence of Evans blue dye. In LD50 endotoxemia murine models, SPC-54 infused at 7hr after endotoxin administration increased mortality from 42% to 100% (P<0.001). In summary, monoclonal antibody SPC-54 ablates in vitro and in vivo APC protective functions and enzymatic activity. The ability of SPC-54 to block the endogenous PC/APC system provides a powerful tool to understand better the role of the endogenous PC system in murine injury models and in cell bioassays and also to neutralize the enzymatic activities of murine APC in any assay system.

Unexpected role of anticoagulant protein C in controlling epithelial barrier integrity and intestinal inflammation

The protein C (PC) pathway is a well-characterized coagulation system. Endothelial PC receptors and thrombomodulin mediate the conversion of PC to its activated form, a potent anticoagulant and anti-inflammatory molecule. Here we show that the PC pathway is expressed on intestinal epithelial cells. The epithelial expression of PC and endothelial PC receptor is down-regulated In patients with inflammatory bowel disease. PC(-/-)/PC(Tg) mice, expressing only 3% of WT PC, developed spontaneous intestinal inflammation and were prone to severe experimental colitis. These mice also demonstrated spontaneous elevated production of inflammatory cytokines and increased intestinal permeability. Structural analysis of epithelial tight junction molecules revealed that lack of PC leads to decreased JAM-A and claudin-3 expression and an altered pattern of ZO-1 expression. In vitro, treatment of epithelial cells with activated PC led to protection of tight junction disruption induced by TNF-α, and in vivo, topical treatment with activated PC led to mucosal healing and amelioration of colitis. Taken together, these findings demonstrate that the PC pathway is a unique system involved in controlling intestinal homeostasis and inflammation by regulating epithelial barrier function.

An accompanying genetic severe deficiency of tissue factor protects mice with a protein C deficiency from lethal endotoxemia

Mice with a severe genetic deficiency of protein C (PC), PC(-/-)PC(tg4), display enhanced susceptibility to lethal effects of gram-negative endotoxemia induced by lipopolysaccharide (LPS), whereas mice severely deficient in tissue factor (TF), TF(-/-)hTF(tg), are protected from LPS-mediated lethality. In this study, we show that a simultaneous severe deficiency of TF protected low-PC mice from LPS-induced death, resulting in a survival profile similar to that experienced by wild-type (WT) mice. Plasma and whole blood coagulation assays, the latter measured by thromboelastography, demonstrated development of coagulopathies in LPS-treated mice, which were more severe in the case of the doubly deficient TF(-/-)hTF(tg)/PC(-/-)PC(tg4) mice, mainly reflecting earlier signs of disseminated intravascular coagulation in this latter cohort. Markers of inflammation were also elevated in response to LPS in both groups of mice at times just preceding death. We conclude that whereas coagulopathies are more exacerbated in LPS-treated TF(-/-)hTF(tg)/PC(-/-)PC(tg4) mice, the lowering of TF levels in mice with an accompanying severe PC deficiency confers protection against death compared with mice with a single severe PC deficiency. This suggests that proteases generated as a result of factor VIIa/TF-mediated thrombin generation play a mechanistic role in the enhanced lethality seen under very low PC conditions in an endotoxemia model in mice.

Endogenous protein C is essential for the functional integrity of human endothelial cells

Circulating protein C (PC) plays a vital role as an anti-coagulant and anti-inflammatory mediator. We show here that human endothelial cells produce PC that acts through novel mediators to enhance their own functional integrity. When endogenous PC or its receptor, endothelial protein C receptor (EPCR), was suppressed by small interfering (si) RNA, human umbilical cord endothelial cell (HUVEC) proliferation was decreased and apoptosis elevated. Interestingly, PC or EPCR siRNA significantly increased HUVEC permeability, which is likely via reduction of the angiopoietin (Ang)1/Ang2 ratio and inhibition of the peripheral localization of the tight junction protein, zona occludins-1. In addition, PC or EPCR siRNA inhibited type IV collagen and matrix metalloproteinase-2, providing the first evidence that PC contributes to vascular basement membrane formation. These newly described actions of endogenous PC act to stabilize endothelial cells and enhance barrier function, to potentially promote the functional integrity of blood vessels.

The protein C pathway in tissue inflammation and injury: pathogenic role and therapeutic implications

Inflammation and coagulation are closely linked interdependent processes. Under physiologic conditions, the tissue microcirculation functions in anticoagulant and anti-inflammatory fashions. However, when inflammation occurs, coagulation is also set in motion and actively participates in enhancing inflammation. Recently, novel and unexpected roles of hemostasis in the humoral and cellular components of innate immunity have been described. In particular, the protein C system, besides its well-recognized role in anticoagulation, plays a crucial role in inflammation. Indeed, the protein C system is now emerging as a novel participant in the pathogenesis of acute and chronic inflammatory diseases, such as sepsis, asthma, inflammatory bowel disease, atherosclerosis, and lung and heart inflammation, and may emerge as unexpected therapeutic targets for intervention.

The protein C pathway in tissue inflammation and injury: pathogenic role and therapeutic implications

Inflammation and coagulation are closely linked interdependent processes. Under physiologic conditions, the tissue microcirculation functions in anticoagulant and anti-inflammatory fashions. However, when inflammation occurs, coagulation is also set in motion and actively participates in enhancing inflammation. Recently, novel and unexpected roles of hemostasis in the humoral and cellular components of innate immunity have been described. In particular, the protein C system, besides its well-recognized role in anticoagulation, plays a crucial role in inflammation. Indeed, the protein C system is now emerging as a novel participant in the pathogenesis of acute and chronic inflammatory diseases, such as sepsis, asthma, inflammatory bowel disease, atherosclerosis, and lung and heart inflammation, and may emerge as unexpected therapeutic targets for intervention.

Vitamin K, an example of triage theory: is micronutrient inadequacy linked to diseases of aging?

The triage theory posits that some functions of micronutrients (the approximately 40 essential vitamins, minerals, fatty acids, and amino acids) are restricted during shortage and that functions required for short-term survival take precedence over those that are less essential. Insidious changes accumulate as a consequence of restriction, which increases the risk of diseases of aging. For 16 known vitamin K-dependent (VKD) proteins, we evaluated the relative lethality of 11 known mouse knockout mutants to categorize essentiality. Results indicate that 5 VKD proteins that are required for coagulation had critical functions (knockouts were embryonic lethal), whereas the knockouts of 5 less critical VKD proteins [osteocalcin, matrix Gla protein (Mgp), growth arrest specific protein 6, transforming growth factor beta-inducible protein (Tgfbi or betaig-h3), and periostin] survived at least through weaning. The VKD gamma-carboxylation of the 5 essential VKD proteins in the liver and the 5 nonessential proteins in nonhepatic tissues sets up a dichotomy that takes advantage of the preferential distribution of dietary vitamin K1 to the liver to preserve coagulation function when vitamin K1 is limiting. Genetic loss of less critical VKD proteins, dietary vitamin K inadequacy, human polymorphisms or mutations, and vitamin K deficiency induced by chronic anticoagulant (warfarin/coumadin) therapy are all linked to age-associated conditions: bone fragility after estrogen loss (osteocalcin) and arterial calcification linked to cardiovascular disease (Mgp). There is increased spontaneous cancer in Tgfbi mouse knockouts, and knockdown of Tgfbi causes mitotic spindle abnormalities. A triage perspective reinforces recommendations of some experts that much of the population and warfarin/coumadin patients may not receive sufficient vitamin K for optimal function of VKD proteins that are important to maintain long-term health.

In vivo veritas: Thrombosis mechanisms in animal models

Experimental models have enhanced our understanding of atherothrombosis pathophysiology and have played a major role in the search for adequate therapeutic interventions. Various animal models have been developed to simulate thrombosis and to study in vivo parameters related to hemodynamics and rheology that lead to thrombogenesis. Although no model completely mimics the human condition, much can be learned from existing models about specific biologic processes in disease causation and therapeutic intervention. In general, large animals such as pigs and monkeys have been better suited to study atherosclerosis and arterial and venous thrombosis than smaller species such as rats, rabbits, and dogs. On the other hand, mouse models of arterial and venous thrombosis have attracted increasing interest over the past two decades, owing to direct availability of a growing number of genetically modified mice, improved technical feasibility, standardization of new models of local thrombosis, and low maintenance costs. To simulate rupture of an atherosclerotic plaque, models of arterial thrombosis often involve vascular injury, which can be achieved by several means. There is no animal model that is sufficiently tall, that can mimic the ability of humans to walk upright, and that possesses the calf muscle pump that plays an important role in human venous hemodynamics. A number of spontaneous or genetically engineered animals with overexpression or deletion of various elements in the coagulation, platelet, and fibrinolysis pathways are now available. These animal models can replicate important aspects of thrombosis in humans, and provide a valuable resource in the development of novel concepts of disease mechanisms in human patients.

Generation and phenotypic analysis of protein S-deficient mice

Protein S (PS) is an important natural anticoagulant with potentially multiple biologic functions. To investigate further the role of PS in vivo, we generated Pros(+/-) heterozygous mice. In the null (-) allele, the Pros exons 3 to 7 have been excised through conditional gene targeting. Pros(+/-) mice did not present any signs of spontaneous thrombosis and had reduced PS plasma levels and activated protein C cofactor activity in plasma coagulation and thrombin generation assays. Tissue factor pathway inhibitor cofactor activity of PS could not be demonstrated. Heterozygous Pros(+/-) mice exhibited a notable thrombotic phenotype in vivo when challenged in a tissue factor-induced thromboembolism model. No viable Pros(-/-) mice were obtained through mating of Pros(+/-) parents. Most E17.5 Pros(-/-) embryos were found dead with severe intracranial hemorrhages and most likely presented consumptive coagulopathy, as demonstrated by intravascular and interstitial fibrin deposition and an increased number of megakaryocytes in the liver, suggesting peripheral thrombocytopenia. A few E17.5 Pros(-/-) embryos had less severe phenotype, indicating that life-threatening manifestations might occur between E17.5 and the full term. Thus, similar to human phenotypes, mild heterozygous PS deficiency in mice was associated with a thrombotic phenotype, whereas total homozygous deficiency in PS was incompatible with life.

Effect of microgravity on gene expression in mouse brain

Changes in gravitational force such as that experienced by astronauts during space flight induce a redistribution of fluids from the caudad to the cephalad portion of the body together with an elimination of normal head-to-foot hydrostatic pressure gradients. To assess brain gene profile changes associated with microgravity and fluid shift, a large-scale analysis of mRNA expression levels was performed in the brains of 2-week control and hindlimb-unloaded (HU) mice using cDNA microarrays. Although to different extents, all functional categories displayed significantly regulated genes indicating that considerable transcriptomic alterations are induced by HU. Interestingly, the TIC class (transport of small molecules and ions into the cells) had the highest percentage of up-regulated genes, while the most down-regulated genes were those of the JAE class (cell junction, adhesion, extracellular matrix). TIC genes comprised 16% of those whose expression was altered, including sodium channel, nonvoltage-gated 1 beta (Scnn1b), glutamate receptor (Grin1), voltage-dependent anion channel 1 (Vdac1), calcium channel beta 3 subunit (Cacnb3) and others. The analysis performed by GeneMAPP revealed several altered protein classes and functional pathways such as blood coagulation and immune response, learning and memory, ion channels and cell junction. In particular, data indicate that HU causes an alteration in hemostasis which resolves in a shift toward a more hyper-coagulative state with an increased risk of venous thrombosis. Furthermore, HU treatment seems to impact on key steps of synaptic plasticity and learning processes.

Identifying and genotyping transgene integration loci

The random germline integration of genetically engineered transgenes has been a powerful technique to study the role of particular genes in variety of biological processes. Although the identification of the transgene insertion site is often not essential for functional analysis of the transgene, identifying the site can have practical benefit. Enabling one to distinguish between animals that are homozygous or hemizygous for the transgene locus could facilitate breeding strategies to produce animals with a large number of genetic markers. Furthermore, founder lines generated with the same transgene construct may exhibit different phenotypes and levels of transgene expression depending on the site of integration. The goal of this report was to develop a rapid protocol for the identification and verification of transgene insertion sites. To identify host genomic sequences at the coagulation Factor X transgene integration site, DNA from a tail snip of the transgenic mouse was digested with NcoI and circularized using T4 DNA ligase. Using appropriately positioned PCR primers annealing to a transgene fragment distal to a terminal transgene restriction site (NcoI), one could amplify a fragment containing the transgene terminal region and extending into the flanking genomic sequence at the insertion site. DNA sequence determination of the amplicon permitted identification of the insertion site using a BLASTN search. FISH analysis of a metaphase spread of primary fibroblasts derived from the transgenic mouse was consistent with the identification of insertion site near the end of mouse chromosome 14. Identification of transgene insertion sites will facilitate genotyping strategies useful for the construction of mice with multiple engineered genetic markers and to distinguish among different founder lines generated by the same transgene. Furthermore, identification of the insertion site is necessary to analyze unexpected phenotypes that might be caused by insertional inactivation of an endogenous gene.

The protein C pathway in inflammatory bowel disease: the missing link between inflammation and coagulation

Traditionally described as a major anti-coagulant system, the protein C (PC) pathway, consisting of thrombomodulin, the endothelial cell protein C receptor and activated PC (APC), is gaining increasing attention as an important regulator of microvascular inflammation. Although they possess several anti-inflammatory and cytoprotective functions, the expression and function of the components of the PC pathway is downregulated during inflammation. Recent evidence suggests that the PC pathway is defective in patients with inflammatory bowel disease (IBD) and that restoring its function has anti-inflammatory effects on cultured intestinal microvascular endothelial cells and in animal models of colitis. Here, we propose that the PC pathway has an important role in governing intestinal microvascular inflammation and might provide a novel therapeutic target in the management of IBD.

Combined tissue factor pathway inhibitor and thrombomodulin deficiency produces an augmented hypercoagulable state with tissue-specific fibrin deposition

BACKGROUND AND OBJECTIVE

Tissue factor pathway inhibitor (TFPI) and thrombomodulin (TM) are endothelial-associated anticoagulant proteins thought to control hemostasis in specific vascular beds. Here, we have examined the consequences of TFPI deficiency in the presence of a compounding procoagulant state caused by reduced TM function.

METHODS AND RESULTS

TFPI(+/-)/TM(pro/pro) mice are born at less than expected frequency in either TFPI(+/-)/TM(pro/+) or TM(pro/pro) mothers but are born at near the expected frequency in TM(pro/+) mothers. Adult TFPI(+/-)/TM(pro/pro) mice have elevated thrombin-antithrombin complex and increased thrombus volume in an electrical injury model of venous thrombosis. In striking contrast to mice with single deficiency of TFPI or TM, TFPI(+/-)/TM(pro/pro) mice exhibit augmented fibrin deposition not only in the liver, but also in the cerebral microvasculature.

CONCLUSIONS

TFPI(+/-)/TM(pro/pro) mice exhibit partial intrauterine lethality when carried by mothers with an underlying prothrombotic state, providing the first experimental evidence in an animal model that TFPI-dependent control of hemostasis in the vascular bed of the placenta fulfills a critical role for successful pregnancy outcome. In addition to the placenta, partial TFPI deficiency interacts with decreased TM function in an organ selective manner to produce fibrin deposition in other specific vascular beds, the liver and brain.

Activated protein C

Protein C is a vitamin K-dependent plasma protein zymogen whose genetic mild or severe deficiencies are linked with risk for venous thrombosis or neonatal purpura fulminans, respectively. Studies over past decades showed that activated protein C (APC) inactivates factors (F) Va and VIIIa to down-regulate thrombin generation. More recent basic and preclinical research on APC has characterized the direct cytoprotective effects of APC that involve gene expression profile alterations, anti-inflammatory and anti-apoptotic activities and endothelial barrier stabilization. These actions generally require endothelial cell protein C receptor (EPCR) and protease activated receptor-1. Because of these direct cytoprotective actions, APC reduces mortality in murine endotoxemia and severe sepsis models and provides neuroprotective benefits in murine ischemic stroke models. Furthermore, APC reduces mortality in patients with severe sepsis (PROWESS clinical trial). Although much remains to be clarified about mechanisms for APC's direct effects on various cell types, it is clear that APC's molecular features that determine its antithrombotic action are partially distinct from those providing cytoprotective actions because we have engineered recombinant APC variants with selective reduction or retention of either anticoagulant or cytoprotective activities. Such APC variants can provide relatively enhanced levels of either cytoprotective or anticoagulant activities for various therapeutic applications. We speculate that APC variants with reduced anticoagulant action but normal cytoprotective actions hold the promise of reducing bleeding risk because of attenuated anticoagulant activity while reducing mortality based on direct cytoprotective effects on cells.

Fetal gene defects precipitate platelet-mediated pregnancy failure in factor V Leiden mothers

We describe a mouse model of fetal loss in factor V Leiden (FvL) mothers in which fetal loss is triggered when the maternal prothrombotic state coincides with fetal gene defects that reduce activation of the protein C anticoagulant pathway within the placenta. Fetal loss is caused by disruption of placental morphogenesis at the stage of labyrinth layer formation and occurs in the absence of overt placental thrombosis, infarction, or perfusion defects. Platelet depletion or elimination of protease-activated receptor 4 (Par4) from the mother allows normal placentation and prevents fetal loss. These findings establish a cause–effect relationship for the observed epidemiologic association between maternal FvL status and fetal loss and identify fetal gene defects as risk modifiers of pregnancy failure in prothrombotic mothers. Pregnancy failure is mediated by Par4-dependent activation of maternal platelets at the fetomaternal interface and likely involves a pathogenic pathway independent of occlusive thrombosis. Our results further demonstrate that the interaction of two given thrombosis risk factors produces markedly disparate consequences on disease manifestation (i.e., thrombosis or pregnancy loss), depending on the vascular bed in which this interaction occurs.

A coagulation factor VII deficiency protects against acute inflammatory responses in mice

Upregulation of the activated Factor VII (FVIIa)/Tissue Factor complex, downregulation of natural anticoagulation pathways, and inhibition of fibrinolysis, are major contributors to coagulopathies associated with acute inflammation. Provision of FVIIa, and consequent downstream coagulation-related proteases, also stimulates further inflammatory changes, which can result in disseminated intravascular coagulation. Thus, the potential protective effects in vivo of a genetic-based reduction in FVII levels have been investigated in a murine model of acute inflammation, namely lipopolysaccharide (LPS)-induced lethal endotoxaemia. Mice with a total FVII deficiency do not survive the neonatal period. Therefore mice expressing low levels of FVII (FVII(tTA/tTA)), producing sufficient amounts of FVII for survival (approximately 5% of wild-type (WT) FVII), were employed to investigate in vivo pathways involved in the crosstalk between coagulation, inflammation, and survival, consequent to administration of a lethal dose of LPS. The FVII(tTA/tTA) mice presented with reduced mortality, coagulation, and inflammatory responses in comparison with similarly treated WT mice after administration of LPS. The attenuated inflammatory responses in FVII(tTA/tTA) mice were associated with downregulation of Egr-1 signalling. Administration, in vivo, of specific inhibitors of FXa and thrombin demonstrated that the inflammatory responses were unaltered in WT mice, but further reduced in FVII(tTA/tTA) mice. Therefore, a FVII deficiency enhances survival from lethal endotoxaemia both through attenuation of inflammatory responses that result directly from reduced FVIIa levels, and, indirectly, from downregulation of coagulation proteases downstream of the FVII-dependent cascade.

Prothrombotic factors enhance heparin-induced thrombocytopenia and thrombosis in vivo in a mouse model

BACKGROUND

Heparin-induced thrombocytopenia/thrombosis (HIT/T) is a common cause of life- and limb-threatening thrombosis. The development of antibodies that react with complexes of heparin and platelet factor 4 (PF4) is fundamental to the development of the disease. However, anti-PF4/heparin antibodies are far more common than is HIT/T and there is less understanding of the factors that contribute to thrombosis in only a subset of patients.

OBJECTIVES

Both qualitative and quantitative differences in multiple factors (e.g. antibodies, heparin and platelets) may influence the clinical course of patients who develop anti-PF4/heparin antibodies. We examined the hypothesis that host-specific factors, such as comorbid prothrombotic conditions, would exacerbate the pathologic effects of anti-PF4/heparin antibodies.

METHODS AND RESULTS

A mouse model transgenic for human Fcgamma RIIa and PF4 and null for mouse PF4 was used to study the influence of prothrombotic conditions on the effects of anti-PF4/heparin antibodies in vivo. To simulate a prothrombotic milieu, mice were fed a hypercholesterolemic diet (HD). HD-fed mice had elevated plasma cholesterol, increased platelet reactivity and increased endothelial activation relative to mice fed a standard diet (SD). Age- and sex-matched mice from each diet group were treated with an anti-PF4/heparin antibody and heparin. HD-fed mice developed more severe thrombocytopenia than similarly treated SD-fed mice. Mice with moderate to severe thrombocytopenia had elevated plasma levels of thrombin-antithrombin complexes, indicative of increased thrombin generation in vivo. Platelet-fibrin thrombi were observed in multiple organs of HD-fed mice that developed severe thrombocytopenia.

CONCLUSIONS

Host-specific factors, such as prothrombotic changes in platelet reactivity and/or endothelial activation, may influence the development of thrombosis in a subset of patients who develop anti-PF4/heparin antibodies.

The cytoprotective protein C pathway

Protein C is best known for its mild deficiency associated with venous thrombosis risk and severe deficiency associated with neonatal purpura fulminans. Activated protein C (APC) anticoagulant activity involves proteolytic inactivation of factors Va and VIIIa, and APC resistance is often caused by factor V Leiden. Less known is the clinical success of APC in reducing mortality in severe sepsis patients (PROWESS trial) that gave impetus to new directions for basic and preclinical research on APC. This review summarizes insights gleaned from recent in vitro and in vivo studies of the direct cytoprotective effects of APC that include beneficial alterations in gene expression profiles, anti-inflammatory actions, antiapoptotic activities, and stabilization of endothelial barriers. APC's cytoprotection requires its receptor, endothelial cell protein C receptor, and protease-activated receptor-1. Because of its pleiotropic activities, APC has potential roles in the treatment of complex disorders, including sepsis, thrombosis, and ischemic stroke. Although much about molecular mechanisms for APC's effects on cells remains unclear, it is clear that APC's structural features mediating anticoagulant actions and related bleeding risks are distinct from those mediating cytoprotective actions, suggesting the possibility of developing APC variants with an improved profile for the ratio of cytoprotective to anticoagulant actions.

Acute inflammation is exacerbated in mice genetically predisposed to a severe protein C deficiency

The anticoagulant, activated protein C (aPC), possesses antithrombotic, profibrinolytic, anti-inflammatory, and antiapoptotic properties, and the level of this protein is an important marker of acute inflammatory responses. Although infusion of aPC improves survival in a subset of patients with severe sepsis, evidence as to how aPC decreases mortality in these cases is limited. Because a total deficiency of PC shows complete neonatal lethality, no animal model currently exists to address the mechanistic relationships between very low endogenous aPC levels and inflammatory diseases. Here, we show for the first time that novel genetic dosing of PC strongly correlates with survival outcomes following endotoxin (LPS) challenge in mice. The data provide evidence that very low endogenous levels of PC predispose mice to early-onset disseminated intravascular coagulation, thrombocytopenia, hypotension, organ damage, and reduced survival after LPS challenge. Furthermore, evidence of an exacerbated inflammatory response is observed in very low PC mice but is greatly reduced in wild-type cohorts. Reconstitution of low-PC mice with recombinant human aPC improves hypotension and extends survival after LPS challenge. This study directly links host endogenous levels of PC with various coagulation, inflammation, and hemodynamic end points following a severe acute inflammatory challenge.

Placental thrombosis and spontaneous fetal death in mice deficient in ethanolamine kinase 2

Ethanolamine kinase catalyzes the first step in the CDP-ethanolamine pathway for the formation of the major membrane phospholipid phosphatidylethanolamine (PtdEtn). In this work, the predicted Etnk2 cDNA was established as a soluble protein with ethanolamine-specific kinase activity that was most highly expressed in liver. Mice with an inactivated Etnk2 gene were derived, and its absence reduced the rate of PtdEtn synthesis from exogenous ethanolamine in hepatocytes. PtdEtn is a major precursor to phosphatidylcholine in liver; however, Etnk2(-/-) mice did not have reduced amounts of either PtdEtn or phosphatidylcholine or an altered phospholipid molecular species distribution. The knock-out animals were able to adapt to a choline-deficient diet. The Etnk2(-/-) mice exhibited a maternal-specific intrauterine growth retardation phenotype that resulted in a 33% reduction in litter size and frequent perinatal death. Histological analysis of pregnant Etnk2(-/-) females showed that fetal development failed at the late stage of pregnancy in a significant percentage of embryos because of the appearance of extensive placental thrombosis. These results illustrate a non-redundant role for EtnK2 expression in regulating placental hemostasis.

Prophylaxis and treatment of thrombophilia in pregnancy

PURPOSE OF REVIEW

This review addresses the prophylaxis and treatment of thrombophilia in pregnancy, which is associated with increased risk of venous thromboembolism and placental vascular complications.

RECENT FINDINGS

Topics include preventing deep vein thrombosis recurrence in pregnant women with constitutional thrombophilias, using prophylactic heparins throughout pregnancy and postpartum anticoagulants. Cases of thrombosis still occur in the postpartum period and other therapeutics should be tested. Primary prophylaxis is acceptable for high-risk thrombophilias. Early pregnancy losses (before the 10th week) are not associated with constitutional thrombophilias. The natural prognosis of embryonic losses associated with current thrombogenic polymorphisms is good, unlike fetal losses associated with the same thrombophilias: in this case, a prophylactic low-molecular-weight heparin given from the beginning of the 8th week is more efficient than low-dose aspirin. Data are lacking on the prevention of severe preeclampsia, placental abruption, or intrauterine growth restriction in women with constitutional thrombophilias; preliminary results indicate that low-molecular-weight heparin may have some preventive effect. Specific studies are needed.

SUMMARY

Recent studies have shown the limits of available procedures for women with constitutional thrombophilia and have helped define the clinical situations in thrombophilia-related placental insufficiency in which prophylactic low-molecular-weight heparin may be indicated.

A novel ELISA for mouse activated protein C in plasma

The Protein C pathway plays a crucial role in the regulation of thrombosis and inflammation. One of the tools that researchers presently use to elucidate mechanisms of action of activated protein C (APC) is the use of transgenic or gene deletion murine models. To correlate observations in these murine models with the APC levels, there is a need for a sensitive and specific assay for circulating murine APC in plasma. We developed an immunological assay to measure the physiological and pharmacologic levels of circulating murine APC. The sandwich ELISA uses an anti-murine anti-protein C antibody capture antibody and human protein C inhibitor (PCI) as a detection reagent, taking advantage of the facts that the mouse lacks plasma PCI and that human PCI forms a 1/1 stable complex with mouse APC. The amount of complex APC:PCI is detected with an anti-human PCI monoclonal antibody. The assay shows improved sensitivity versus enzyme immunocapture assays commonly used to detect human APC and considerably reduces the processing time.