Platelet matrix metalloprotease-1 mediates thrombogenesis by activating PAR1 at a cryptic ligand site

Exploring the Chemical Features and Biomedical Relevance of Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) are a diverse group of peptides, typically composed of 4 to 40 amino acids, known for their unique ability to transport a wide range of substances-such as small molecules, plasmid DNA, small interfering RNA, proteins, viruses, and nanoparticles-across cellular membranes while preserving the integrity of the cargo. CPPs exhibit passive and non-selective behavior, often requiring functionalization or chemical modification to enhance their specificity and efficacy. The precise mechanisms governing the cellular uptake of CPPs remain ambiguous; however, electrostatic interactions between positively charged amino acids and negatively charged glycosaminoglycans on the membrane, particularly heparan sulfate proteoglycans, are considered the initial crucial step for CPP uptake. Clinical trials have highlighted the potential of CPPs in diagnosing and treating various diseases, including cancer, central nervous system disorders, eye disorders, and diabetes. This review provides a comprehensive overview of CPP classifications, potential applications, transduction mechanisms, and the most relevant algorithms to improve the accuracy and reliability of predictions in CPP development.

One immune cell to bind them all: platelet contribution to neurodegenerative disease

Alzheimer's disease (AD) and related dementias (ADRD) collectively affect a significant portion of the aging population worldwide. The pathological progression of AD involves not only the classical hallmarks of amyloid beta (Aβ) plaque buildup and neurofibrillary tangle development but also the effects of vasculature and chronic inflammatory processes. Recently, platelets have emerged as central players in systemic and neuroinflammation. Studies have shown that patients with altered platelet receptor expression exhibit accelerated cognitive decline independent of traditional risk factors. Additionally, platelets from AD patients exhibit heightened unstimulated activation compared to control groups. Platelet granules contain crucial AD-related proteins like tau and amyloid precursor protein (APP). Dysregulation of platelet exocytosis contributes to disease phenotypes characterized by increased bleeding, stroke, and cognitive decline risk. Recent studies have indicated that these effects are not associated with the quantity of platelets present in circulation. This underscores the hypothesis that disruptions in platelet-mediated inflammation and healing processes may play a crucial role in the development of ADRD. A thorough look at platelets, encompassing their receptors, secreted molecules, and diverse roles in inflammatory interactions with other cells in the circulatory system in AD and ADRD, holds promising prospects for disease management and intervention. This review discusses the pivotal roles of platelets in ADRD.

Multifunctional targeting of docetaxel plus bakuchiol micelles in the treatment of invasion and metastasis of ovarian cancer

The invasion and metastasis of tumors pose significant challenges in the treatment of ovarian cancer (OC), making it difficult to cure. One potential treatment approach that has gained attention is the use of matrix metalloproteinase reactive controlled release micelle preparations. In this study, we developed a novel PEG5000-PVGLIG-hyaluronic acid docetaxel/bakuchiol (PP-HA-DTX/BAK) micelles formulation with desirable characteristics such as particle size, narrow polydispersity index, and a ZETA potential of approximately -5 mV. The surface modification with HA facilitates tumor penetration into the tumor interior, while the incorporation of DSPE-PEG2000-PVGLIG-PEG5000helps conceal DSPE-PEG2000-HA, reducing off-target effects and prolonging drug circulation timein vivo. Bothin vitroandin vivoexperiments demonstrated that these micelles effectively inhibit proliferation, invasion, and metastasis of OC cells while promoting apoptosis. Therefore, our findings suggest that PP-HA-DTX/BAK micelles represent a safe and effective therapeutic strategy for treating OC.

Extracellular proteolysis in cancer: Proteases, substrates, and mechanisms in tumor progression and metastasis

A vast ensemble of extracellular proteins influences the development and progression of cancer, shaped and reshaped by a complex network of extracellular proteases. These proteases, belonging to the distinct classes of metalloproteases, serine proteases, cysteine proteases, and aspartic proteases, play a critical role in cancer. They often become dysregulated in cancer, with increases in pathological protease activity frequently driven by the loss of normal latency controls, diminished regulation by endogenous protease inhibitors, and changes in localization. Dysregulated proteases accelerate tumor progression and metastasis by degrading protein barriers within the extracellular matrix (ECM), stimulating tumor growth, reactivating dormant tumor cells, facilitating tumor cell escape from immune surveillance, and shifting stromal cells toward cancer-promoting behaviors through the precise proteolysis of specific substrates to alter their functions. These crucial substrates include ECM proteins and proteoglycans, soluble proteins secreted by tumor and stromal cells, and extracellular domains of cell surface proteins, including membrane receptors and adhesion proteins. The complexity of the extracellular protease web presents a significant challenge to untangle. Nevertheless, technological strides in proteomics, chemical biology, and the development of new probes and reagents are enabling progress and advancing our understanding of the pivotal importance of extracellular proteolysis in cancer.

Macromolecular crowding in human tenocyte and skin fibroblast cultures: A comparative analysis

Although human tenocytes and dermal fibroblasts have shown promise in tendon engineering, no tissue engineered medicine has been developed due to the prolonged ex vivo time required to develop an implantable device. Considering that macromolecular crowding has the potential to substantially accelerate the development of functional tissue facsimiles, herein we compared human tenocyte and dermal fibroblast behaviour under standard and macromolecular crowding conditions to inform future studies in tendon engineering. Basic cell function analysis made apparent the innocuousness of macromolecular crowding for both cell types. Gene expression analysis of the without macromolecular crowding groups revealed expression of tendon related molecules in human dermal fibroblasts and tenocytes. Protein electrophoresis and immunocytochemistry analyses showed significantly increased and similar deposition of collagen fibres by macromolecular crowding in the two cell types. Proteomics analysis demonstrated great similarities between human tenocyte and dermal fibroblast cultures, as well as the induction of haemostatic, anti-microbial and tissue-protective proteins by macromolecular crowding in both cell populations. Collectively, these data rationalise the use of either human dermal fibroblasts or tenocytes in combination with macromolecular crowding in tendon engineering.

Platelet proteo-transcriptomic profiling validates mediators of thrombosis and proteostasis in patients with myeloproliferative neoplasms

Patients with chronic Myeloproliferative Neoplasms (MPN) including polycythemia vera (PV) and essential thrombocythemia (ET) exhibit unique clinical features, such as a tendency toward thrombosis and hemorrhage, and risk of disease progression to secondary bone marrow fibrosis and/or acute leukemia. Although an increase in blood cell lineage counts (quantitative features) contribute to these morbid sequelae, the significant qualitative abnormalities of myeloid cells that contribute to vascular risk are not well understood. Here, we address this critical knowledge gap via a comprehensive and untargeted profiling of the platelet proteome in a large (n= 140) cohort of patients (from two independent sites) with an established diagnosis of PV and ET (and complement prior work on the MPN platelet transcriptome from a third site). We discover distinct MPN platelet protein expression and confirm key molecular impairments associated with proteostasis and thrombosis mechanisms of potential relevance to MPN pathology. Specifically, we validate expression of high-priority candidate markers from the platelet transcriptome at the platelet proteome (e.g., calreticulin (CALR), Fc gamma receptor (FcγRIIA) and galectin-1 (LGALS1) pointing to their likely significance in the proinflammatory, prothrombotic and profibrotic phenotypes in patients with MPN. Together, our proteo-transcriptomic study identifies the peripherally-derived platelet molecular profile as a potential window into MPN pathophysiology and demonstrates the value of integrative multi-omic approaches in gaining a better understanding of the complex molecular dynamics of disease.

Suppression of Heart Failure With PAR1 Pepducin Technology in a Pressure Overload Model in Mice

BACKGROUND

PAR1 (protease-activated receptor-1) contributes to acute thrombosis, but it is not clear whether the receptor is involved in deleterious inflammatory and profibrotic processes in heart failure. Here, we employ the pepducin technology to determine the effects of targeting PAR1 in a mouse heart failure with reduced ejection fraction model.

METHODS

After undergoing transverse aortic constriction pressure overload or sham surgery, C57BL/6J mice were randomized to daily sc PZ-128 pepducin or vehicle, and cardiac function, inflammation, fibrosis, and molecular analyses conducted at 7 weeks RESULTS: After 7 weeks of transverse aortic constriction, vehicle mice had marked increases in macrophage/monocyte infiltration and fibrosis of the left ventricle as compared with Sham mice. PZ-128 treatment significantly suppressed the inflammatory cell infiltration and cardiac fibrosis. Despite no effect on myocyte cell hypertrophy, PZ-128 afforded a significant reduction in overall left ventricle weight and completely protected against the transverse aortic constriction-induced impairments in left ventricle ejection fraction. PZ-128 significantly suppressed transverse aortic constriction-induced increases in an array of genes involved in myocardial stress, fibrosis, and inflammation.

CONCLUSIONS

The PZ-128 pepducin is highly effective in protecting against cardiac inflammation, fibrosis, and loss of left ventricle function in a mouse model.

Matrix Metalloproteinases Inhibitors in Cancer Treatment: An Updated Review (2013-2023)

Matrix metalloproteinases (MMPs) are identifiable members of proteolytic enzymes that can degrade a wide range of proteins in the extracellular matrix (ECM). MMPs can be categorized into six groups based on their substrate specificity and structural differences: collagenases, gelatinases, stromelysins, matrilysins, metalloelastase, and membrane-type MMPs. MMPs have been linked to a wide variety of biological processes, such as cell transformation and carcinogenesis. Over time, MMPs have been evaluated for their role in cancer progression, migration, and metastasis. Accordingly, various MMPs have become attractive therapeutic targets for anticancer drug development. The first generations of broad-spectrum MMP inhibitors displayed effective inhibitory activities but failed in clinical trials due to poor selectivity. Thanks to the evolution of X-ray crystallography, NMR analysis, and homology modeling studies, it has been possible to characterize the active sites of various MMPs and, consequently, to develop more selective, second-generation MMP inhibitors. In this review, we summarize the computational and synthesis approaches used in the development of MMP inhibitors and their evaluation as potential anticancer agents.

Tissue factor (coagulation factor III): a potential double-edge molecule to be targeted and re-targeted toward cancer

Tissue factor (TF) is a protein that plays a critical role in blood clotting, but recent research has also shown its involvement in cancer development and progression. Herein, we provide an overview of the structure of TF and its involvement in signaling pathways that promote cancer cell proliferation and survival, such as the PI3K/AKT and MAPK pathways. TF overexpression is associated with increased tumor aggressiveness and poor prognosis in various cancers. The review also explores TF's role in promoting cancer cell metastasis, angiogenesis, and venous thromboembolism (VTE). Of note, various TF-targeted therapies, including monoclonal antibodies, small molecule inhibitors, and immunotherapies have been developed, and preclinical and clinical studies demonstrating the efficacy of these therapies in various cancer types are now being evaluated. The potential for re-targeting TF toward cancer cells using TF-conjugated nanoparticles, which have shown promising results in preclinical studies is another intriguing approach in the path of cancer treatment. Although there are still many challenges, TF could possibly be a potential molecule to be used for further cancer therapy as some TF-targeted therapies like Seagen and Genmab's tisotumab vedotin have gained FDA approval for treatment of cervical cancer. Overall, based on the overviewed studies, this review article provides an in-depth overview of the crucial role that TF plays in cancer development and progression, and emphasizes the potential of TF-targeted and re-targeted therapies as potential approaches for the treatment of cancer.

Interactions between Platelets and Tumor Microenvironment Components in Ovarian Cancer and Their Implications for Treatment and Clinical Outcomes

Platelets, the primary operatives of hemostasis that contribute to blood coagulation and wound healing after blood vessel injury, are also involved in pathological conditions, including cancer. Malignancy-associated thrombosis is common in ovarian cancer patients and is associated with poor clinical outcomes. Platelets extravasate into the tumor microenvironment in ovarian cancer and interact with cancer cells and non-cancerous elements. Ovarian cancer cells also activate platelets. The communication between activated platelets, cancer cells, and the tumor microenvironment is via various platelet membrane proteins or mediators released through degranulation or the secretion of microvesicles from platelets. These interactions trigger signaling cascades in tumors that promote ovarian cancer progression, metastasis, and neoangiogenesis. This review discusses how interactions between platelets, cancer cells, cancer stem cells, stromal cells, and the extracellular matrix in the tumor microenvironment influence ovarian cancer progression. It also presents novel potential therapeutic approaches toward this gynecological cancer.

Human osteoarthritis knee joint synovial fluids cleave and activate Proteinase-Activated Receptor (PAR) mediated signaling

Osteoarthritis (OA) is the most prevalent joint disorder with increasing worldwide incidence. Mechanistic insights into OA pathophysiology are evolving and there are currently no disease-modifying OA drugs. An increase in protease activity is linked to progressive degradation of the cartilage in OA. Proteases also trigger inflammation through a family of G protein-coupled receptors (GPCRs) called the Proteinase-Activated Receptors (PARs). PAR signaling can trigger pro-inflammatory responses and targeting PARs is proposed as a therapeutic approach in OA. Several enzymes can cleave the PAR N-terminus, but the endogenous protease activators of PARs in OA remain unclear. Here we characterized PAR activating enzymes in knee joint synovial fluids from OA patients and healthy donors using genetically encoded PAR biosensor expressing cells. Calcium signaling assays were performed to examine receptor activation. The class and type of enzymes cleaving the PARs was further characterized using protease inhibitors and fluorogenic substrates. We find that PAR1, PAR2 and PAR4 activating enzymes are present in knee joint synovial fluids from healthy controls and OA patients. Compared to healthy controls, PAR1 activating enzymes are elevated in OA synovial fluids while PAR4 activating enzyme levels are decreased. Using enzyme class and type selective inhibitors and fluorogenic substrates we find that multiple PAR activating enzymes are present in OA joint fluids and identify serine proteinases (thrombin and trypsin-like) and matrix metalloproteinases as the major classes of PAR activating enzymes in the OA synovial fluids. Synovial fluid driven increase in calcium signaling was significantly reduced in cells treated with PAR1 and PAR2 antagonists, but not in PAR4 antagonist treated cells. OA associated elevation of PAR1 cleavage suggests that targeting this receptor may be beneficial in the treatment of OA.

Plasma protein profiling analysis in patients with atrial fibrillation before and after three different ablation techniques

Background

There are controversies on the pathophysiological alteration in patients with atrial fibrillation (AF) undergoing pulmonary vein isolation using different energy sources.

Objectives

We evaluated the changes in plasma proteins in acute phase post-ablation in patients receiving cryoballoon ablation, radiofrequency balloon ablation, or radiofrequency ablation.

Methods

Blood samples from eight healthy controls and 24 patients with AF were taken on the day of admission, day 1, and day 2 post-ablation and analyzed by the Olink proximity extension assay. Proteins were identified and performed with enrichment analysis. Protein-protein interaction network and module analysis were conducted using Cytoscape software.

Results

Of 181 proteins, 42 proteins in the cryoballoon group, 46 proteins in the radiofrequency balloon group, and 43 proteins in the radiofrequency group significantly changed after ablation. Most of the proteins altered significantly on the first day after ablation. Altered proteins were mainly involved in cytokine-cytokine receptor interaction. Both balloon-based ablations showed a similar shift toward enhancing cell communication and regulation of signaling while inhibiting neutrophil chemotaxis. However, radiofrequency ablation presented a different trend. Seed proteins, including osteopontin, interleukin-6, interleukin-10, C-C motif ligand 8, and matrix metalloproteinase-1, were identified. More significant proteins associated with hemorrhage and coagulation were selected in balloon-based ablations by machine learning.

Conclusion

Plasma protein response after three different ablations in patients with AF mainly occurred on the first day. Radiofrequency balloon ablation shared similar alteration in protein profile as cryoballoon ablation compared with radiofrequency ablation, suggesting that lesion size rather than energy source is the determinant in pathophysiological responses to the ablation.

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.

Granzyme K initiates IL-6 and IL-8 release from epithelial cells by activating protease-activated receptor 2

Granzyme K (GzmK) is a tryptic member of the granzyme family of chymotrypsin-like serine proteases produced by cells of the immune system. Previous studies have indicated that GzmK activates protease-activated receptor 1 (PAR1) enhancing activation of monocytes and wound healing in endothelial cells. Here, we show using peptides and full length proteins that GzmK and, to a lesser extent the related protease GzmA, are capable of activating PAR1 and PAR2. These cleavage events occur at the canonical arginine P1 residue and involve exosite interactions between protease and receptor. Despite cleaving PAR2 at the same point as trypsin, GzmK does not induce a classical Ca2+ flux but instead activates a distinct signalling cascade, involving recruitment of β-arrestin and phosphorylation of ERK. In epithelial A549 cells, PAR2 activation by GzmK results in the release of inflammatory cytokines IL-6 and IL-8. These data suggest that during an immune response GzmK acts as a pro-inflammatory regulator, rather than as a cytotoxin.

Identification of a Distinct Platelet Phenotype in the Elderly: ADP Hypersensitivity Coexists With Platelet PAR (Protease-Activated Receptor)-1 and PAR-4-Mediated Thrombin Resistance

BACKGROUND

Thrombin (via PAR [protease-activated receptor]-1 and PAR-4) and ADP (via P2Y₁₂ receptors) are potent endogenous platelet activators implicated in the development of cardiovascular disease. We aimed to assess whether platelet pathways alter with aging.

METHODS

We characterized platelet activity in community-dwelling volunteers (n=174) in the following age groups: (1) 20 to 30 (young); (2) 40 to 55 (middle-aged); (3) ≥70 years (elderly). Platelet activity was assessed by aggregometry; flow cytometry (surface markers [P-selectin: alpha granule release, CD63: dense granule release, PAC-1 (measure of conformationally active GPIIb/IIIa at the fibrinogen binding site): GPIIb/IIIa conformational activation] measured under basal conditions and after agonist stimulation [ADP, thrombin, PAR-1 agonist or PAR-4 agonist]); receptor cleavage and quantification; fluorometry; calcium flux; ELISA.

RESULTS

The elderly had higher basal platelet activation than the young, evidenced by increased expression of P-selectin, CD63, and PAC-1, which correlated with increasing inflammation (IL [interleukin]-1β/IL-6). The elderly demonstrated higher P2Y₁₂ receptor density, with greater ADP-induced platelet aggregation (P<0.05). However, elderly subjects were resistant to thrombin, achieving less activation in response to thrombin (higher EC₅₀) and to selective stimulation of both PAR-1 and PAR-4, with higher basal PAR-1/PAR-4 cleavage and less inducible PAR-1/PAR-4 cleavage (all P<0.05). Thrombin resistance was attributable to a combination of reduced thrombin orienting receptor GPIbα, reduced secondary ADP contribution to thrombin-mediated activation, and blunted calcium flux. D-Dimer, a marker of in situ thrombin generation, correlated with platelet activation in the circulation, ex vivo thrombin resistance, and circulating inflammatory mediators (TNF [tumor necrosis factor]-α/IL-6).

CONCLUSIONS

Aging is associated with a distinctive platelet phenotype of increased basal activation, ADP hyperreactivity, and thrombin resistance. In situ thrombin generation associated with systemic inflammation may be novel target to prevent cardiovascular disease in the elderly.

Cathepsin S Contributes to Lung Inflammation in Acute Respiratory Distress Syndrome

Rationale: Although the cysteine protease cathepsin S has been implicated in the pathogenesis of several inflammatory lung diseases, its role has not been examined in the context of acute respiratory distress syndrome, a condition that still lacks specific and effective pharmacological treatments. Objectives: To characterize the status of cathepsin S in acute lung inflammation and examine the role of cathepsin S in disease pathogenesis. Methods: Human and mouse model BAL fluid samples were analyzed for the presence and activity of cathepsin S and its endogenous inhibitors. Recombinant cathepsin S was instilled directly into the lungs of mice. The effects of cathepsin S knockout and pharmacological inhibition were examined in two models of acute lung injury. Protease-activated receptor-1 antagonism was used to test a possible mechanism for cathepsin S-mediated inflammation. Measurements and Main Results: Pulmonary cathepsin S concentrations and activity were elevated in acute respiratory distress syndrome, a phenotype possibly exacerbated by the loss of the endogenous antiprotease cystatin SN. Direct cathepsin S instillation into the lungs induced key pathologies of acute respiratory distress syndrome, including neutrophilia and alveolar leakage. Conversely, in murine models of acute lung injury, genetic knockdown and prophylactic or therapeutic inhibition of cathepsin S reduced neutrophil recruitment and protein leakage. Cathepsin S may partly mediate its pathogenic effects via protease-activated receptor-1, because antagonism of this receptor abrogated cathepsin S-induced airway inflammation. Conclusions: Cathepsin S contributes to acute lung injury and may represent a novel therapeutic target for acute respiratory distress syndrome.

Gα12 and Gα13: Versatility in Physiology and Pathology

G protein-coupled receptors (GPCRs), as the largest family of receptors in the human body, are involved in the pathological mechanisms of many diseases. Heterotrimeric G proteins represent the main molecular switch and receive cell surface signals from activated GPCRs. Growing evidence suggests that Gα₁₂ subfamily (Gα_12/13)-mediated signaling plays a crucial role in cellular function and various pathological processes. The current research on the physiological and pathological function of Gα_12/13 is constantly expanding, Changes in the expression levels of Gα_12/13 have been found in a wide range of human diseases. However, the mechanistic research on Gα_12/13 is scattered. This review briefly describes the structural sequences of the Gα_12/13 isoforms and introduces the coupling of GPCRs and non-GPCRs to Gα_12/13. The effects of Gα_12/13 on RhoA and other signaling pathways and their roles in cell proliferation, migration, and immune cell function, are discussed. Finally, we focus on the pathological impacts of Gα_12/13 in cancer, inflammation, metabolic diseases, fibrotic diseases, and circulatory disorders are brought to focus.

Pregnancy-specific expression of protease-activated receptor 1: a therapeutic target for prevention and treatment of preeclampsia?

Neutrophils extensively infiltrate maternal blood vessels in preeclampsia. This could explain why multiple organs are affected in this enigmatic disorder. Lipid peroxides produced by the placenta are probably the first factors that activate neutrophils as they circulate through the intervillous space, but then a second factor specific to pregnancy comes into play, protease-activated receptor 1. The only time neutrophils express protease-activated receptor 1 is during pregnancy. This means that neutrophils can be activated by a mechanism specific to pregnancy, that is, by proteases. Two proteases that are elevated in preeclampsia and activate protease-activated receptor 1 are matrix metalloproteinase-1 and neutrophil elastase. There is an 8-fold increase in vascular protease-activated receptor 1 expression in women with preeclampsia, and protease-activated receptor 1 is also expressed on the placenta, a pregnancy-specific tissue. The question arises if the pregnancy-specific expression of protease-activated receptor 1 is essential to the pathophysiology of preeclampsia. Protease activation of protease-activated receptor 1 in neutrophils of women with normal pregnancies causes activation of RhoA kinase. RhoA kinase phosphorylates nuclear factor-kappa B causing its translocation from the cytosol into the nucleus, increasing the expression of inflammatory genes. This signaling pathway is blocked by inhibition of either protease-activated receptor 1 or RhoA kinase activity. In contrast, neutrophils obtained from preeclamptic women are already activated, with nuclear factor-kappa B localized in the nucleus. Surprisingly, inhibition of either protease-activated receptor 1 or RhoA kinase results in an efflux of nuclear factor-kappa B from the nucleus back into the cytoplasm. Cyclooxygenase-2 seems to be a downstream mediator between protease-activated receptor 1 and RhoA kinase because aspirin inhibits the nuclear translocation of nuclear factor-kappa B and inhibits neutrophil production of superoxide, thromboxane, and tumor necrosis factor alpha. Currently, low-dose aspirin is the standard of care to prevent preeclampsia in high-risk women. Generally, the actions of low-dose aspirin are attributed to selective inhibition of maternal platelet thromboxane production. However, a recent study showed that beneficial effects extend to the placenta, where aspirin corrected the imbalance of increased thromboxane and reduced prostacyclin and oxidative stress. Selective inhibition of placental thromboxane is possible because thromboxane and prostacyclin are compartmentalized. Thromboxane is produced by trophoblast cells and prostacyclin by endothelial cells, so as aspirin crosses the placenta, its levels decline, sparing prostacyclin. Placental oxidative stress is attenuated because cyclooxygenase-2 inhibition decreases the generation of reactive oxygen species to decrease the formation of isoprostanes. The clinical manifestations of preeclampsia can be explained by protease activation of protease-activated receptor 1 in different tissues. In neutrophils, it can account for their activation and inflammatory response. In vascular tissue, protease-activated receptor 1 activation leads to enhanced vascular reactivity to angiotensin II to cause hypertension. In the placenta, it leads to oxidative stress, increased soluble fms-like tyrosine kinase, and thromboxane production. Activation of protease-activated receptor 1 on endothelial cells causes contraction, leading to edema and proteinuria, and activation on platelets leads to coagulation abnormalities. As proteases that activate protease-activated receptor 1 are elevated in the circulation of women with preeclampsia, consideration should be given to the inhibition of protease-activated receptor 1 as a treatment. Recently, The Food and Drug Administration (FDA) approved a protease-activated receptor 1 inhibitor, creating an opportunity to test whether protease-activated receptor 1 inhibition can prevent and/or treat preeclampsia, but a standard dose of aspirin might be just as effective by blocking its downstream actions.

Noncanonical protease-activated receptor 1 regulates lymphatic differentiation in zebrafish

The differentiation of lymphatic progenitors is a crucial step in lymphangiogenesis. However, its underlying mechanism remains unclear. Here, we found that noncanonical protease-activated receptor 1 (par1) regulates the differentiation of lymphatic progenitors in zebrafish embryos. Loss of par1 function impaired lymphatic differentiation by downregulating prox1a expression in parachordal lymphangioblasts and caused compromised thoracic duct formation in zebrafish. Meanwhile, the G protein gnai2a, a par1 downstream effector, was selectively required for lymphatic development in zebrafish, and its mutation mimicked the lymphatic phenotype observed in par1 mutants. Interestingly, mmp13, but not thrombin, was required for lymphatic development in zebrafish. Furthermore, analyses of genetic interactions confirmed that mmp13b serves as a par1 upstream protease to regulate lymphatic development in zebrafish embryos. Mechanistically, par1 promotes flt4 expression and phospho-Erk1/2 activity in the posterior cardinal vein. Taken together, our findings highlight a function of par1 in the regulation of lymphatic differentiation in zebrafish embryos.

Influence of nanoparticles on the haemostatic balance: between thrombosis and haemorrhage

Maintenance of a delicate haemostatic balance or a balance between clotting and bleeding is critical to human health. Irrespective of administration route, nanoparticles can reach the bloodstream and might interrupt the haemostatic balance by interfering with one or more components of the coagulation, anticoagulation, and fibrinolytic systems, which potentially lead to thrombosis or haemorrhage. However, inadequate understanding of their effects on the haemostatic balance, along with the fact that most studies mainly focus on the functionality of nanoparticles while forgetting or leaving behind their risk to the body's haemostatic balance, is a major concern. Hence, our review aims to provide a comprehensive depiction of nanoparticle-haemostatic balance interactions, which has not yet been covered. The synergistic roles of cells and plasma factors participating in haemostatic balance are presented. Possible interactions and interference of each type of nanoparticle with the haemostatic balance are comprehensively discussed, particularly focusing on the underlying mechanisms. Interactions of nanoparticles with innate immunity potentially linked to haemostasis are mentioned. Various physicochemical characteristics that influence the nanoparticle-haemostatic balance are detailed. Challenges and future directions are also proposed. This insight would be valuable for the establishment of nanoparticles that can either avoid unintended interference with the haemostatic balance or purposely downregulate/upregulate its key components in a controlled manner.

Lipopeptide Pepducins as Therapeutic Agents

Pepducins are lipidated peptides that target the intracellular loops of G protein-coupled receptors (GPCRs) in order to modulate transmembrane signaling to internally located effectors. With a wide array of potential activities ranging from partial, biased, or full agonism to antagonism, pepducins represent a versatile class of compounds that can be used to potentially treat diverse human diseases or be employed as novel tools to probe complex mechanisms of receptor activation and signaling in cells and in animals. Here, we describe a number of different pepducins including an advanced compound, PZ-128, that has successfully progressed through phase 2 clinical trials in cardiac patients demonstrating safety and efficacy in suppressing myonecrosis and arterial thrombosis.

Platelet Behavior Contributes to Neuropathologies: A Focus on Alzheimer's and Parkinson's Disease

The functions of platelets are broad. Platelets function in hemostasis and thrombosis, inflammation and immune responses, vascular regulation, and host defense against invading pathogens, among others. These actions are achieved through the release of a wide set of coagulative, vascular, inflammatory, and other factors as well as diverse cell surface receptors involved in the same activities. As active participants in these physiological processes, platelets become involved in signaling pathways and pathological reactions that contribute to diseases that are defined by inflammation (including by pathogen-derived stimuli), vascular dysfunction, and coagulation. These diseases include Alzheimer's and Parkinson's disease, the two most common neurodegenerative diseases. Despite their unique pathological and clinical features, significant shared pathological processes exist between these two conditions, particularly relating to a central inflammatory mechanism involving both neuroinflammation and inflammation in the systemic environment, but also neurovascular dysfunction and coagulopathy, processes which also share initiation factors and receptors. This triad of dysfunction-(neuro)inflammation, neurovascular dysfunction, and hypercoagulation-illustrates the important roles platelets play in neuropathology. Although some mechanisms are understudied in Alzheimer's and Parkinson's disease, a strong case can be made for the relevance of platelets in neurodegeneration-related processes.

Allosteric Modulator Leads Hiding in Plain Site: Developing Peptide and Peptidomimetics as GPCR Allosteric Modulators

Allosteric modulators (AMs) of G-protein coupled receptors (GPCRs) are desirable drug targets because they can produce fewer on-target side effects, improved selectivity, and better biological specificity (e.g., biased signaling or probe dependence) than orthosteric drugs. An underappreciated source for identifying AM leads are peptides and proteins-many of which were evolutionarily selected as AMs-derived from endogenous protein-protein interactions (e.g., transducer/accessory proteins), intramolecular receptor contacts (e.g., pepducins or extracellular domains), endogenous peptides, and exogenous libraries (e.g., nanobodies or conotoxins). Peptides offer distinct advantages over small molecules, including high affinity, good tolerability, and good bioactivity, and specific disadvantages, including relatively poor metabolic stability and bioavailability. Peptidomimetics are molecules that combine the advantages of both peptides and small molecules by mimicking the peptide's chemical features responsible for bioactivity while improving its druggability. This review 1) discusses sources and strategies to identify peptide/peptidomimetic AMs, 2) overviews strategies to convert a peptide lead into more drug-like "peptidomimetic," and 3) critically analyzes the advantages, disadvantages, and future directions of peptidomimetic AMs. While small molecules will and should play a vital role in AM drug discovery, peptidomimetics can complement and even exceed the advantages of small molecules, depending on the target, site, lead, and associated factors.

Effect of Yiqi Huoxue Granules on Platelet Activation Induced by Thrombin

Objective

To study the effects of Yiqi Huoxue (YQHX) granules on platelet activation and aggregation induced by thrombin.

Methods

The effect of YQHX on platelet aggregation rate was detected by platelet aggregation instrument; the effect of YQHX on thrombosis time was observed by the mouse mesentery thrombosis model. DAMI cells were induced to transform into platelet-like granules using PMA, and the effects of SCH (PAR-1 inhibitor) on thrombin-induced changes in platelet intracellular calcium concentration, PAR-1 protein expression, and phosphorylation of MAPK were examined.

Results

Compared with the control group, the platelet aggregation rate, PAR-1 protein expression, phosphorylation of ERK1/2, and p38 protein in the YQHX group decreased (P < 0.05), and there was no significant difference between the YQHX + SCH group and YQHX group (P > 0.05).

Conclusion

YQHX suppresses the platelet activation induced by thrombin by inhibiting PAR-1 expression.

The Road to Low-Dose Aspirin Therapy for the Prevention of Preeclampsia Began with the Placenta

The road to low-dose aspirin therapy for the prevention of preeclampsia began in the 1980s with the discovery that there was increased thromboxane and decreased prostacyclin production in placentas of preeclamptic women. At the time, low-dose aspirin therapy was being used to prevent recurrent myocardial infarction and other thrombotic events based on its ability to selectively inhibit thromboxane synthesis without affecting prostacyclin synthesis. With the discovery that thromboxane was increased in preeclamptic women, it was reasonable to evaluate whether low-dose aspirin would be effective for preeclampsia prevention. The first clinical trials were very promising, but then two large multi-center trials dampened enthusiasm until meta-analysis studies showed aspirin was effective, but with caveats. Low-dose aspirin was most effective when started <16 weeks of gestation and at doses >100 mg/day. It was effective in reducing preterm preeclampsia, but not term preeclampsia, and patient compliance and patient weight were important variables. Despite the effectiveness of low-dose aspirin therapy in correcting the placental imbalance between thromboxane and prostacyclin and reducing oxidative stress, some aspirin-treated women still develop preeclampsia. Alterations in placental sphingolipids and hydroxyeicosatetraenoic acids not affected by aspirin, but with biologic actions that could cause preeclampsia, may explain treatment failures. Consideration should be given to aspirin's effect on neutrophils and pregnancy-specific expression of protease-activated receptor 1, as well as additional mechanisms of action to prevent preeclampsia.

Deficiency of MMP1a (Matrix Metalloprotease 1a) Collagenase Suppresses Development of Atherosclerosis in Mice: Translational Implications for Human Coronary Artery Disease

[Figure: see text].

Platelets and Matrix Metalloproteinases: A Bidirectional Interaction with Multiple Pathophysiologic Implications

Platelets contain and release several matrix metalloproteinases (MMPs), a highly conserved protein family with multiple functions in organism defense and repair. Platelet-released MMPs as well as MMPs generated by other cells within the cardiovascular system modulate platelet function in health and disease. In particular, a normal hemostatic platelet response to vessel wall injury may be transformed into pathological thrombus formation by platelet-released and/or by locally generated MMPs. However, it is becoming increasingly clear that platelets play a role not only in hemostasis but also in immune response, inflammation and allergy, atherosclerosis, and cancer development, and MMPs seem to contribute importantly to this role. A deeper understanding of these mechanisms may open the way to novel therapeutic approaches to the inhibition of their pathogenic effects and lead to significant advances in the treatment of cardiovascular, inflammatory, and neoplastic disorders.

Role of lncRNAs in the Development of Ischemic Stroke and Their Therapeutic Potential

Stroke is a major cause of premature mortality and disability around the world. Therefore, identification of cellular and molecular processes implicated in the pathogenesis and progression of ischemic stroke has become a priority. Long non-coding RNAs (lncRNAs) are emerging as significant players in the pathophysiology of cerebral ischemia. They are involved in different signalling pathways of cellular processes like cell apoptosis, autophagy, angiogenesis, inflammation, and cell death, impacting the progression of cerebral damage. Exploring the functions of these lncRNAs and their mechanism of action may help in the development of promising treatment strategies. In this review, the current knowledge of lncRNAs in ischemic stroke, focusing on the mechanism by which they cause cellular apoptosis, inflammation, and microglial activation, has been summarized. Very few lncRNAs have been functionally annotated. Therefore, the therapies based on lncRNAs still face many hurdles since the potential targets are likely to increase with the identification of new ones. Majority of experiments involving the identification and function of lncRNAs have been carried out in animal models, and the role of lncRNAs in human stroke presents a challenge. However, mitigating these issues through more rational experimental design might lead to the development of lncRNA-based stroke therapies to treat ischemic stroke.

Echis carinatus snake venom metalloprotease-induced toxicities in mice: Therapeutic intervention by a repurposed drug, Tetraethyl thiuram disulfide (Disulfiram)

Echis carinatus (EC) is known as saw-scaled viper and it is endemic to the Indian subcontinent. Envenoming by EC represents a major cause of snakebite mortality and morbidity in the Indian subcontinent. Zinc (Zn++) dependent snake venom metalloproteases (SVMPs) present in Echis carinatus venom (ECV) is well known to cause systemic hemorrhage and coagulopathy in experimental animals. An earlier report has shown that ECV activates neutrophils and releases neutrophil extracellular traps (NETs) that blocks blood vessels leading to severe tissue necrosis. However, the direct involvement of SVMPs in the release of NETs is not clear. Here, we investigated the direct involvement of EC SVMPs in observed pathological symptoms in a preclinical setup using specific Zn++ metal chelator, Tetraethyl thiuram disulfide (TTD)/disulfiram. TTD potently antagonizes the activity of SVMPs-mediated ECM protein degradation in vitro and skin hemorrhage in mice. In addition, TTD protected mice from ECV-induced footpad tissue necrosis by reduced expression of citrullinated H3 (citH3) and myeloperoxidase (MPO) in footpad tissue. TTD also neutralized ECV-induced systemic hemorrhage and conferred protection against lethality in mice. Moreover, TTD inhibited ECV-induced NETosis in human neutrophils and decreased the expression of peptidyl arginine deiminase (PAD) 4, citH3, MPO, and p-ERK. Further, we demonstrated that ECV-induced NETosis and tissue necrosis are mediated via PAR-1-ERK axis. Overall, our results provide an insight into SVMPs-induced toxicities and the promising protective efficacy of TTD can be extrapolated to treat severe tissue necrosis complementing anti-snake venom (ASV).

Platelet Membrane Receptor Proteolysis: Implications for Platelet Function

The activities of adhesion and signaling receptors in platelets are controlled by several mechanisms. An important way of regulation is provided by proteolytic cleavage of several of these receptors, leading to either a gain or a loss of platelet function. The proteases involved are of different origins and types: (i) present as precursor in plasma, (ii) secreted into the plasma by activated platelets or other blood cells, or (iii) intracellularly activated and cleaving cytosolic receptor domains. We provide a comprehensive overview of the proteases acting on the platelet membrane. We describe how these are activated, which are their target proteins, and how their proteolytic activity modulates platelet functions. The review focuses on coagulation-related proteases, plasmin, matrix metalloproteinases, ADAM(TS) isoforms, cathepsins, caspases, and calpains. We also describe how the proteolytic activities are determined by different platelet populations in a thrombus and conversely how proteolysis contributes to the formation of such populations.

Lipid Receptor GPR31 (G-Protein-Coupled Receptor 31) Regulates Platelet Reactivity and Thrombosis Without Affecting Hemostasis

OBJECTIVE

12-LOX (12-lipoxygenase) produces a number of bioactive lipids including 12(S)-HETE that are involved in inflammation and platelet reactivity. The GPR31 (G-protein-coupled receptor 31) is the proposed receptor of 12(S)-HETE; however, it is not known whether the 12(S)-HETE-GPR31 signaling axis serves to enhance or inhibit platelet activity. Approach and Results: Using pepducin technology and biochemical approaches, we provide evidence that 12(S)-HETE-GPR31 signals through Gi to enhance PAR (protease-activated receptor)-4-mediated platelet activation and arterial thrombosis using both human platelets and mouse carotid artery injury models. 12(S)-HETE suppressed AC (adenylyl cyclase) activity through GPR31 and resulted in Rap1 (Ras-related protein 1) and p38 activation and low but detectable calcium flux but did not induce platelet aggregation. A GPR31 third intracellular (i3) loop-derived pepducin, GPR310 (G-protein-coupled receptor 310), significantly inhibited platelet aggregation in response to thrombin, collagen, and PAR4 agonist, AYPGKF, in human and mouse platelets but relative sparing of PAR1 agonist SFLLRN in human platelets. GPR310 treatment gave a highly significant 80% protection (P=0.0018) against ferric chloride-induced carotid artery injury in mice by extending occlusion time, without any effect on tail bleeding. PAR4-mediated dense granule secretion and calcium flux were both attenuated by GPR310. Consistent with these results, GPR310 inhibited 12(S)-HETE-mediated and PAR4-mediated Rap1-GTP and RASA3 translocation to the plasma membrane and attenuated PAR4-Akt and ERK activation. GPR310 caused a right shift in thrombin-mediated human platelet aggregation, comparable to the effects of inhibition of the Gi-coupled P2Y12 receptor. Co-immunoprecipitation studies revealed that GPR31 and PAR4 form a heterodimeric complex in recombinant systems.

CONCLUSIONS

The 12-LOX product 12(S)-HETE stimulates GPR31-Gi-signaling pathways, which enhance thrombin-PAR4 platelet activation and arterial thrombosis in human platelets and mouse models. Suppression of this bioactive lipid pathway, as exemplified by a GPR31 pepducin antagonist, may provide beneficial protective effects against platelet aggregation and arterial thrombosis with minimal effect on hemostasis.

PAR1 (Protease-Activated Receptor 1) Pepducin Therapy Targeting Myocardial Necrosis in Coronary Artery Disease and Acute Coronary Syndrome Patients Undergoing Cardiac Catheterization: A Randomized, Placebo-Controlled, Phase 2 Study

OBJECTIVE

Arterial thrombosis leading to ischemic injury worsens the prognosis of many patients with cardiovascular disease. PZ-128 is a first-in-class pepducin that reversibly inhibits PAR1 (protease-activated receptor 1) on platelets and other vascular cells by targeting the intracellular surface of the receptor. The TRIP-PCI (Thrombin Receptor Inhibitory Pepducin in Percutaneous Coronary Intervention) trial was conducted to assess the safety and efficacy of PZ-128 in patients undergoing cardiac catheterization with intent to perform percutaneous coronary intervention. Approach and Results: In this randomized, double-blind, placebo-controlled, phase 2 trial, 100 patients were randomly assigned (2:1) to receive PZ-128 (0.3 or 0.5 mg/kg), or placebo in a 2-hour infusion initiated just before the start of cardiac catheterization, on top of standard oral antiplatelet therapy. Rates of the primary end point of bleeding were not different between the combined PZ-128 doses (1.6%, 1/62) and placebo group (0%, 0/35). The secondary end points of major adverse coronary events at 30 and 90 days did not significantly differ but were numerically lower in the PZ-128 groups (0% and 2% in the PZ-128 groups, 6% and 6% with placebo, p=0.13, p=0.29, respectively). In the subgroup of patients with elevated baseline cardiac troponin I, the exploratory end point of 30-day major adverse coronary events + myocardial injury showed 83% events in the placebo group versus 31% events in the combined PZ-128 drug groups, an adjusted relative risk of 0.14 (95% CI, 0.02-0.75); P=0.02.

CONCLUSIONS

In this first-in-patient experience, PZ-128 added to standard antiplatelet therapy appeared to be safe, well tolerated, and potentially reduced periprocedural myonecrosis, thus providing the basis for further clinical trials. Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT02561000.

Biased signaling in platelet G-protein coupled receptors

Platelets are small megakaryocyte-derived, anucleate, disk-like structures that play an outsized role in human health and disease. Both a decrease in the number of platelets and a variety of platelet function disorders result in petechiae or bleeding that can be life threatening. Conversely, the inappropriate activation of platelets, within diseased blood vessels, remains the leading cause of death and morbidity by affecting heart attacks and stroke. The fine balance of the platelet state in healthy individuals is controlled by a number of receptor-mediated signaling pathways that allow the platelet to rapidly respond and maintain haemostasis. G-protein coupled receptors (GPCRs) are particularly important regulators of platelet function. Here we focus on the major platelet-expressed GPCRs and discuss the roles of downstream signaling pathways (e.g., different G-protein subtypes or β-arrestin) in regulating the different phases of the platelet activation. Further, we consider the potential for selectively targeting signaling pathways that may contribute to platelet responses in disease through development of biased agonists. Such selective targeting of GPCR-mediated signaling pathways by drugs, often referred to as biased signaling, holds promise in delivering therapeutic interventions that do not present significant side effects, especially in finely balanced physiological systems such as platelet activation in haemostasis.

The domino effect triggered by the tethered ligand of the protease activated receptors

Protease activated receptors (PARs) are G-protein coupled receptors (GPCRs) that have a unique activation mechanism. Unlike other GPCRs that can be activated by free ligands, under physiological conditions, PARs are activated by the tethered ligand, which is a part of their N-terminus that is unmasked by proteolysis. It has been 30 years since the first member of the family, PAR1, was identified. In this review, we will discuss this unique tethered ligand mediate receptor activation of PARs in detail: how they interact with the proteases, the complex structural rearrangement of the receptors upon activation, and the termination of the signaling. We also summarize the structural studies of the PARs and how single nucleotide polymorphisms impact the receptor reactivity. Finally, we review the current strategies for inhibiting PAR function with therapeutic targets for anti-thrombosis. The focus of this review is PAR1 and PAR4 as they are the thrombin signal mediators on human platelets and therapeutics targets. We also include the structural studies of PAR2 as it informs the mechanism of action for PARs in general.

Role of PAR1-Egr1 in the Initiation of Thoracic Aortic Aneurysm in Fbln4-Deficient Mice

Objective:

Remodeling of the extracellular matrix plays a vital role in cardiovascular diseases. Using a mouse model of postnatal ascending aortic aneurysms (termed Fbln4 SMKO ), we have reported that abnormal mechanosensing led to aneurysm formation in Fbln4 SMKO with an upregulation of the mechanosensitive transcription factor, Egr1 (Early growth response 1). However, the role of Egr1 and its upstream regulator(s) in the initiation of aneurysm development and their relationship to an aneurysmal microenvironment are unknown.

Approach and Results:

To investigate the contribution of Egr1 in the aneurysm development, we deleted Egr1 in Fbln4 SMKO mice and generated double knockout mice ( DKO , Fbln4 SMKO ; Egr1 −/− ). Aneurysms were prevented in DKO mice (42.8%) and Fbln4 SMKO ; Egr1 +/− mice (26%). Ingenuity Pathway Analysis identified PAR1 (protease-activated receptor 1) as a potential Egr1 upstream gene. Protein and transcript levels of PAR1 were highly increased in Fbln4 SMKO aortas at postnatal day 1 before aneurysm formed, together with active thrombin and MMP (matrix metalloproteinase)-9, both of which serve as a PAR1 activator. Concordantly, protein levels of PAR1, Egr1, and thrombin were significantly increased in human thoracic aortic aneurysms. In vitro cyclic stretch assays (1.0 Hz, 20% strain, 8 hours) using mouse primary vascular smooth muscle cells induced marked expression of PAR1 and secretion of prothrombin in response to mechanical stretch. Thrombin was sufficient to induce Egr1 expression in a PAR1-dependent manner.

Conclusions:

We propose that thrombin, MMP-9, and mechanical stimuli in the Fbln4 SMKO aorta activate PAR1, leading to the upregulation of Egr1 and initiation of ascending aortic aneurysms.

Proteases Activate Pregnancy Neutrophils by a Protease-Activated Receptor 1 Pathway: Epigenetic Implications for Preeclampsia

We tested a novel hypothesis that elevated levels of proteases in the maternal circulation of preeclamptic women activate neutrophils due to their pregnancy-specific expression of protease-activated receptor 1 (PAR-1). Plasma was collected longitudinally from normal pregnant and preeclamptic women and analyzed for MMP-1 and neutrophil elastase. Neutrophils were isolated for culture and confocal microscopy. Omental fat was collected for immunohistochemistry. Circulating proteases were significantly elevated in preeclampsia. Confocal microscopy revealed that tet methylcytosine dioxygenase 2 (TET2), a DNA de-methylase, and p65 subunit of NF-κB were strongly localized to the nucleus of untreated neutrophils of preeclamptic women, but in untreated neutrophils of normal pregnant women they were restricted to the cytosol. Treatment of normal pregnancy neutrophils with proteases activated PAR-1, leading to activation of RhoA kinase (ROCK), which triggered translocation of TET2 and p65 from the cytosol into the nucleus, mimicking the nuclear localization in neutrophils of preeclamptic women. IL-8, an NF-κB-regulated gene, increased in association with TET2 and p65 nuclear localization. Co-treatment with inhibitors of PAR-1 or ROCK prevented nuclear translocation and IL-8 did not increase. Treatment of preeclamptic pregnancy neutrophils with inhibitors emptied the nucleus of TET2 and p65, mimicking the cytosolic localization of normal pregnancy neutrophils. Expression of PAR-1 and TET2 were markedly increased in omental fat vessels and neutrophils of preeclamptic women. We conclude that elevated levels of circulating proteases in preeclamptic women activate neutrophils due to their pregnancy-specific expression of PAR-1 and speculate that TET2 DNA de-methylation plays a role in the inflammatory response.

A novel role of MMP2 in regulating platelet NOX2 activation

NOX2 has a key role for cellular production of reactive oxidant species (ROS) and although the mechanism of its activation is well known, little is known about its regulation. Metallo-proteinases (MMPs) regulate numerous protein activities both in physiological and pathological conditions but their interplay with NOX2 and ROS formation is still unclear. We performed experimental studies in human platelets and polymorphonuclear leukocytes (PMNs) to investigate the interplay of MMP2 with NOX2 activity. In collagen-stimulated platelets and in PMA-stimulated PMNs from healthy subjects, an immediate burst of ROS was detected at 10 min to then decline at 20 min. Coincidentally, sNOX2-dp, a split-off product of NOX2, increased and peaked at 10 min. ROS production was persistent whereas sNOX2dp is not released in cells treated with MMP2 inhibitor compared to other MMPs inhibitors. Western blot analysis showed the highest MMP2 expression on the cell membrane 10 min after stimulation. Moreover, the co-immunoprecipitation assay confirms the interaction between MMP2 and NOX2 that formed an active immuno-complex. Treating cells with NOX2ds-tat, an inhibitor of NADPH oxidase, significantly reduced ROS formation, sNOX2-dp, MMP2 expression and MMP2-NOX2-complex, which were all restored if cells were added with H₂O₂. The study provides the first evidence that MMP2 has a key role in blunting platelet NOX2 activity and eventually ROS formation.

Design and synthesis of glyco-peptides as anti-cancer agents targeting thrombin-protease activated receptor-1 interaction

Thrombin activates protease-activated receptor-1 (PAR-1) through binding to exosite I and the active site to promote tumor growth. We have developed a new class of anti-cancer glyco-peptides to target exosite I selectively without affecting the active-site-mediated coagulation activity and showed the importance of glycans for the stability and anti-cancer activity of the glyco-peptides.

Synaptic Potentiation at Basal and Apical Dendrites of Hippocampal Pyramidal Neurons Involves Activation of a Distinct Set of Extracellular and Intracellular Molecular Cues

In the central nervous system, several forms of experience-dependent plasticity, learning and memory require the activity-dependent control of synaptic efficacy. Despite substantial progress in describing synaptic plasticity, mechanisms related to heterogeneity of synaptic functions at local circuits remain elusive. Here we studied the functional and molecular aspects of hippocampal circuit plasticity by analyzing excitatory synapses at basal and apical dendrites of mouse hippocampal pyramidal cells (CA1 region) in acute brain slices. In the past decade, activity of metalloproteinases (MMPs) has been implicated as a widespread and critical factor in plasticity mechanisms at various projections in the CNS. However, in the present study we discovered that in striking contrast to apical dendrites, synapses located within basal dendrites undergo MMP-independent synaptic potentiation. We demonstrate that synapse-specific molecular pathway allowing MMPs to rapidly upregulate function of NMDARs in stratum radiatum involved protease activated receptor 1 and intracellular kinases and GTPases activity. In contrast, MMP-independent scaling of synaptic strength in stratum oriens involved dopamine D1/D5 receptors and Src kinases. Results of this study reveal that 2 neighboring synaptic systems differ significantly in extracellular and intracellular cascades that control synaptic gain and provide long-searched transduction pathways relevant for MMP-dependent synaptic plasticity.

Protease Amplification of the Inflammatory Response Induced by Commensal Bacteria: Implications for Racial Disparity in Term and Preterm Birth

Decidual macrophages secrete proteases that activate protease-activated receptor 1 (PAR-1). We hypothesized that activation of the inflammatory response by bacteria is amplified by proteases, initiating labor. In addition, we hypothesized that commensal bacteria trigger an inflammatory response by activating NF-κB and TET methylcytosine dioxygenase 2 (TET2), a DNA de-methylase, via a protease amplified PAR-1, RhoA kinase (ROCK) pathway. To evaluate these hypotheses, we compared responses of mononuclear cells with Lactobacillus crispatus, prevalent in the vaginal microbiome of women of European ancestry, with L. iners and Fusobacterium nucleatum, which are more prevalent in vaginal samples collected from African-American women. Decidual tissue was collected at term not-in-labor (TNL), term labor (TL), spontaneous preterm labor (sPTL), and infected preterm labor (iPTL) and immunostained for PAR-1, TET2, and CD14. Mononuclear cells and THP-1 macrophage cells were treated with bacteria and elastase, a known activator of PAR-1. The inflammatory response was monitored by confocal microscopy of TET2 and the p65 subunit of NF-κB, as well as IL-8 production. Decidual staining for PAR-1, TET2, and CD14 increased TNL < TL < sPTL < iPTL. All treatments stimulated translocation of TET2 and p65 from the cytosol to the nucleus and increased IL-8, but L. iners and F. nucleatum caused more robust responses than L. crispatus. Inhibition of PAR-1 or ROCK prevented TET2 and p65 nuclear translocalization and increases in IL-8. Our findings demonstrate that proteases amplify the inflammatory response to commensal bacteria. The more robust response to bacteria prevalent in African-American women may contribute to racial disparities in preterm birth.

Molecular basis of protease-activated receptor 1 signaling diversity

Protease-activated receptors (PARs) are a family of highly conserved G protein-coupled receptors (GPCRs) that respond to extracellular proteases via a unique proteolysis-dependent activation mechanism. Protease-activated receptor 1 (PAR1) was the first identified member of the receptor family and plays important roles in hemostasis, inflammation and malignancy. The biology underlying PAR1 signaling by its canonical agonist thrombin is well characterized; however, definition of the mechanistic basis of PAR1 signaling by other proteases, including matrix metalloproteases, activated protein C, plasmin, and activated factors VII and X, remains incompletely understood. In this review, we discuss emerging insights into the molecular bases for "biased" PAR1 signaling, including atypical PAR1 proteolysis, PAR1 heterodimer and coreceptor interactions, PAR1 translocation on the membrane surface, and interactions with different G-proteins and β-arrestins upon receptor activation. Moreover, we consider how these new insights into PAR1 signaling have acted to spur development of novel PAR1-targeted therapeutics that act to inhibit, redirect, or fine-tune PAR1 signaling output to treat cardiovascular and inflammatory disease. Finally, we discuss some of the key unanswered questions relating to PAR1 biology, in particular how differences in PAR1 proteolysis, signaling intermediate coupling, and engagement with coreceptors and GPCRs combine to mediate the diversity of identified PAR1 signaling outputs.

4-Hydroxy-7-oxo-5-heptenoic acid lactone is a potent inducer of brain cancer cell invasiveness that may contribute to the failure of anti-angiogenic therapies

Previously, we discovered that free radical-induced oxidative fragmentation of the docosahexaenoate ester of 2-lysophosphatidylcholine produces 4-hydroxy-7-oxo-5-heptenoic acid (HOHA) lactone that, in turn, promotes the migration and invasion of endothelial cells. This suggested that HOHA lactone might similarly promote migration and invasion of glioblastoma multiformae (GBM) brain cancer stem cells (CSCs). A bioinformatics analysis of clinical cancer genomic data revealed that matrix metalloproteinase (MMP)1 and three markers of oxidative stress - superoxide dismutase 2, NADPH oxidase 4, and carbonic anhydrase 9 - are upregulated in human mesenchymal GBM cancer tissue, and that MMP1 is positively correlated to all three of these oxidative stress markers. In addition, elevated levels of MMP1 are indicative of GBM invasion, while low levels of MMP1 indicate survival. We also explored the hypothesis that the transition from the proneural to the more aggressive mesenchymal phenotype, e.g., after treatment with an anti-angiogenic therapy, is promoted by the effects of lipid oxidation products on GBM CSCs. We found that low micromolar concentrations of HOHA lactone increase the cell migration velocity of cultured GBM CSCs, and induce the expression of MMP1 and two protein biomarkers of the proneural to mesenchymal transition (PMT): p65 NF-κβ and vimentin. Exposure of cultured GBM CSCs to HOHA lactone causes an increase in phosphorylation of mitogen-activated protein kinases and Akt kinases that are dependent on both protease-activated receptor 1 (PAR1) and MMP1 activity. We conclude that HOHA lactone promotes the PMT in GBM through the activation of PAR1 and MMP1. This contributes to a fatal flaw in antiangiogenic, chemo, and radiation therapies: they promote oxidative stress and the generation of HOHA lactone in the tumor that fosters a change from the proliferative proneural to the migratory mesenchymal GBM CSC phenotype that seeds new tumor growth. Inhibition of PAR1 and HOHA lactone are potential new therapeutic targets for impeding GBM tumor recurrence.

Rivaroxaban Reduces Arterial Thrombosis by Inhibition of FXa-Driven Platelet Activation via Protease Activated Receptor-1

RATIONALE

A reduced rate of myocardial infarction has been reported in patients with atrial fibrillation treated with FXa (factor Xa) inhibitors including rivaroxaban compared with vitamin K antagonists. At the same time, low-dose rivaroxaban has been shown to reduce mortality and atherothrombotic events in patients with coronary artery disease. Yet, the mechanisms underlying this reduction remain unknown.

OBJECTIVE

In this study, we hypothesized that rivaroxaban's antithrombotic potential is linked to a hitherto unknown rivaroxaban effect that impacts on platelet reactivity and arterial thrombosis.

METHODS AND RESULTS

In this study, we identified FXa as potent, direct agonist of the PAR-1 (protease-activated receptor 1), leading to platelet activation and thrombus formation, which can be inhibited by rivaroxaban. We found that rivaroxaban reduced arterial thrombus stability in a mouse model of arterial thrombosis using intravital microscopy. For in vitro studies, atrial fibrillation patients on permanent rivaroxaban treatment for stroke prevention, respective controls, and patients with new-onset atrial fibrillation before and after first intake of rivaroxaban (time series analysis) were recruited. Platelet aggregation responses, as well as thrombus formation under arterial flow conditions on collagen and atherosclerotic plaque material, were attenuated by rivaroxaban. We show that rivaroxaban's antiplatelet effect is plasma dependent but independent of thrombin and rivaroxaban's anticoagulatory capacity.

CONCLUSIONS

Here, we identified FXa as potent platelet agonist that acts through PAR-1. Therefore, rivaroxaban exerts an antiplatelet effect that together with its well-known potent anticoagulatory capacity might lead to reduced frequency of atherothrombotic events and improved outcome in patients.

Matrix Metalloproteases as Influencers of the Cells' Social Media

Matrix metalloproteinases (MMPs) have been studied in the context of cancer due to their ability to increase cell invasion, and were initially thought to facilitate metastasis solely through the degradation of the extracellular matrix (ECM). MMPs have also been investigated in the context of their ECM remodeling activity in several acute and chronic inflammatory diseases. However, after several MMP inhibitors failed in phase III clinical trials, a global reassessment of their biological functions was undertaken, which has revealed multiple unanticipated functions including the processing of chemokines, cytokines, and cell surface receptors. Despite what their name suggests, the matrix aspect of MMPs could contribute to a lesser part of their physiological functions in inflammatory diseases, as originally anticipated. Here, we present examples of MMP substrates implicated in cell signaling, independent of their ECM functions, and discuss the impact for the use of MMP inhibitors.