Serine and metalloprotease signaling through PAR1 in arterial thrombosis and vascular injury

Blood Plasma Proteins Associated With Heart Rate Variability in Cosmonauts Who Have Completed Long-Duration Space Missions

The study presents the results of evaluating the changes in the concentrations of blood plasma proteins associated with heart rate variability (HRV) in cosmonauts who have completed space missions lasting about 6months. The concentrations of 125 proteins were quantified in biological samples of the cosmonauts' blood plasma. The subgroups of proteins associated with the physiological processes of the HRV autonomic regulation were identified using bioinformatic resources (Immunoglobulin heavy constant mu, Complement C1q subcomponent subunit C, Plasma serine protease inhibitor, Protein-72kDa type IV collagenase, Fibulin-1, Immunoglobulin lambda constant 3). The concentration of these proteins in the blood plasma before the flight, and the dynamics of concentration changes on the 1st and 7th days of the post-flight rehabilitation period differed in the groups of cosmonauts with a predominance of sympathetic or parasympathetic modulating autonomous influences. The dynamics of changes in the concentrations of the identified set of proteins reveal that in cosmonauts with a predominance of sympathetic modulating influences, the mechanisms of autonomic regulation are exposed to significant stress in the recovery period immediately after the completion of the space mission, compared with the cosmonauts with a predominance of parasympathetic modulating influences.

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.

Tumor-associated macrophages (TAMs) depend on MMP1 for their cancer-promoting role

The complex interaction between tumor-associated macrophages (TAMs) and tumor cells through several soluble factors and signaling is essential for colorectal cancer (CRC) progression. However, the molecular mechanism involved remains elusive. In this study, we demonstrated that MMP1 derived from TAMs markedly facilitated colon cancer cell proliferation via accelerating cell cycle transition from G0/G1 to S and G2/M phase. Moreover, exogenous MMP1 activated cdc25a/CDK4-cyclin D1 and p21/cdc2-cyclin B1 complexes through altering c-Myc and ETV4. Mechanistic studies indicated that inhibition of PAR1 or blockage of MAPK/Erk signaling eliminated the proliferation induced by exogenous MMP1 in vitro and in vivo. In addition, ETV4 could bind to the promoter of MMP1 and activate MMP1 transcription, which confirmed the MMP1/ETV4/MMP1 positive feedback. Altogether, our study identified a cytokine paracrine manner between colon cancer cells and TAMs. MMP1/PAR1/Erk1/2/ETV4 positive feedback loop may represent to be a therapeutic target and prognostic marker in CRC.

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.

Platelet-derived calpain cleaves the endothelial protease-activated receptor 1 to induce vascular inflammation in diabetes

Diabetes mellitus is a major risk factor for cardiovascular disease. Platelets from diabetic patients are hyperreactive and release microparticles that carry activated cysteine proteases or calpains. Whether platelet-derived calpains contribute to the development of vascular complications in diabetes is unknown. Here we report that platelet-derived calpain1 (CAPN1) cleaves the protease-activated receptor 1 (PAR-1) on the surface of endothelial cells, which then initiates a signaling cascade that includes the activation of the tumor necrosis factor (TNF)-α converting enzyme (TACE). The latter elicits the shedding of the endothelial protein C receptor and the generation of TNF-α, which in turn, induces intracellular adhesion molecule (ICAM)-1 expression to promote monocyte adhesion. All of the effects of CAPN1 were mimicked by platelet-derived microparticles from diabetic patients or from wild-type mice but not from CAPN1^−/− mice, and were not observed in PAR-1-deficient endothelial cells. Importantly, aortae from diabetic mice expressed less PAR-1 but more ICAM-1 than non-diabetic mice, effects that were prevented by treating diabetic mice with a calpain inhibitor as well as by the platelet specific deletion of CAPN1. Thus, platelet-derived CAPN1 contributes to the initiation of the sterile vascular inflammation associated with diabetes via the cleavage of PAR-1 and the release of TNF-α from the endothelial cell surface.

Protease-activated receptor-1 impedes prostate and intestinal tumor progression in mice

Essentials Protease activated receptor-1 (PAR-1) has been proposed to drive cancer progression. Surprisingly, PAR-1 deletion accelerated tumor progression in two distinct experimental settings. PAR-1 deletion was shown to limit the apoptosis of transformed epithelial cells. Thrombin- and activated protein C-mediated PAR-1 activation have unique effects on tumor cell biology. SUMMARY: Background Multiple studies have implicated protease-activated receptor-1 (PAR-1), a G-protein-coupled receptor activated by proteolytic cleavage of its N-terminus, as one target coupling thrombin-mediated proteolysis to tumor progression. Objective To analyze the role of PAR-1 in the setting of two distinct spontaneously developing tumor models in mice. Methods We interbred PAR-1-deficient mice with Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) mice, which spontaneously develop prostate tumors, and adenomatous polyposis coli Min (APCMin/+ ) mice, which spontaneously develop intestinal adenomas. Results Analyses of TRAMP mice with advanced disease (30 weeks) revealed that PAR-1 deficiency resulted in significantly larger and more aggressive prostate tumors. Prostates collected at an earlier time point (12 weeks of age) revealed that PAR-1 promotes apoptosis in transformed epithelia. In vitro analyses of TRAMP-derived cells revealed that activated protein C-mediated PAR-1 cleavage can induce tumor cell apoptosis, suggesting that tumor cell-intrinsic PAR-1 functions can limit tumor progression. Paralleling results in TRAMP mice, PAR-1-deficient APCMin/+ mice developed three-fold more adenomas than PAR-1-expressing mice, and the adenomas that formed were significantly larger. Moreover, loss of PAR-1 expression was shown to limit apoptosis in transformed intestinal epithelial cells. Conclusions Together, these results demonstrate a previously unrecognized role for PAR-1 in impeding tumor progression in vivo. These results also offer a cautionary note suggesting that long-term PAR-1 inhibition could increase malignancy risk in some contexts.

Targeting PAR1: Now What?

Protease-activated receptors (PARs) are a ubiquitously expressed class of G-protein-coupled receptors (GPCRs) that enable cells to respond to proteases in the extracellular environment in a nuanced and dynamic manner. PAR1 is the archetypal family member and has been the object of large-scale drug development programs since the 1990s. Vorapaxar and drotrecogin-alfa are approved PAR1-targeted therapeutics, but safety concerns have limited the clinical use of vorapaxar and questions regarding the efficacy of drotrecogin-alfa led to its withdrawal from the market. New understanding of mechanisms of PAR1 function, discovery of improved strategies for modifying PAR1 function, and identification of novel indications for PAR1 modulators have provided new opportunities for therapies targeting PAR1. In this review, we critically evaluate prospects for the next generation of PAR1-targeted therapeutics.

The MMP-1/PAR-1 Axis Enhances Proliferation and Neuronal Differentiation of Adult Hippocampal Neural Progenitor Cells

Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that play a role in varied forms of developmental and postnatal neuroplasticity. MMP substrates include protease-activated receptor-1 (PAR-1), a G-protein coupled receptor expressed in hippocampus. We examined proliferation and differentiation of adult neural progenitor cells (aNPCs) from hippocampi of mice that overexpress the potent PAR-1 agonist MMP-1. We found that, as compared to aNPCs from littermate controls, MMP-1 tg aNPCs display enhanced proliferation. Under differentiating conditions, these cells give rise to a higher percentage of MAP-2(+) neurons and a reduced number of oligodendrocyte precursors, and no change in the number of astrocytes. The fact that these results are MMP and PAR-1 dependent is supported by studies with distinct antagonists. Moreover, JSH-23, an inhibitor of NF-κB p65 nuclear translocation, counteracted both the proliferation and differentiation changes seen in MMP-1 tg-derived NPCs. In complementary studies, we found that the percentage of Sox2(+) undifferentiated progenitor cells is increased in hippocampi of MMP-1 tg animals, compared to wt mice. Together, these results add to a growing body of data suggesting that MMPs are effectors of hippocampal neuroplasticity in the adult CNS and that the MMP-1/PAR-1 axis may play a role in neurogenesis following physiological and/or pathological stimuli.

Pepducins and Other Lipidated Peptides as Mechanistic Probes and Therapeutics

Lipopeptides based on the intracellular loops of cell-surface receptors, known as "Pepducins," represent a promising new class of compounds used for the study of membrane proteins and as potential therapeutics in a variety of diseases. Detailed knowledge of the three-dimensional structure of G-protein-coupled receptors (GPCRs) and delineation of the mechanisms of pepducin activation and biased G-protein signaling has facilitated the development of even more potent pepducin allosteric modulators.

Biased agonism of protease-activated receptor 1 by activated protein C caused by noncanonical cleavage at Arg46

Activated protein C (APC) exerts endothelial cytoprotective actions that require protease-activated receptor 1 (PAR1), whereas thrombin acting via PAR1 causes endothelial disruptive, proinflammatory actions. APC's activities, but not thrombin's, require PAR1 located in caveolae. PAR1 is a biased 7-transmembrane receptor because G proteins mediate thrombin's signaling, whereas β-arrestin 2 mediates APC's signaling. Here we elucidate novel mechanisms for APC's initiation of signaling. Biochemical studies of APC's protease specificity showed that APC cleaved PAR1 sequences at both Arg41 and Arg46. That PAR1 cleavage at Arg46 can occur on cells was supported by APC's cleavage of N-terminal-SEAP-tagged R41Q-PAR1 but not R41Q/R46Q-PAR1 mutants transfected into cells and by anti-PAR1 epitope mapping of APC-treated endothelial cells. A synthetic peptide composing PAR1 residues 47-66, TR47, stimulated protective signaling in endothelial cells as reflected in Akt and glycogen synthase kinase 3β phosphorylation, Ras-related C3 botulinum toxin substrate 1 activation, and barrier stabilization effects. In mice, the TR47 peptide reduced VEGF-induced vascular leakage. These in vitro and in vivo data imply that the novel PAR1 N-terminus beginning at residue Asn47, which is generated by APC cleavage at Arg46, mediates APC's cytoprotective signaling and that this unique APC-generated N-terminal peptide tail is a novel biased agonist for PAR1.

Matrix metalloproteases and PAR1 activation

Cardiovascular diseases, including atherothrombosis, are the leading cause of morbidity and mortality in the United States, Europe, and the developed world. Matrix metalloproteases (MMPs) have recently emerged as important mediators of platelet and endothelial function, and atherothrombotic disease. Protease-activated receptor-1 (PAR1) is a G protein-coupled receptor that is classically activated through cleavage of the N-terminal exodomain by the serine protease thrombin. Most recently, 2 MMPs have been discovered to have agonist activity for PAR1. Unexpectedly, MMP-1 and MMP-13 cleave the N-terminal exodomain of PAR1 at noncanonical sites, which result in distinct tethered ligands that activate G-protein signaling pathways. PAR1 exhibits metalloprotease-specific signaling patterns, known as biased agonism, that produce distinct functional outputs by the cell. Here we contrast the mechanisms of canonical (thrombin) and noncanonical (MMP) PAR1 activation, the contribution of MMP-PAR1 signaling to diseases of the vasculature, and the therapeutic potential of inhibiting MMP-PAR1 signaling with MMP inhibitors, including atherothrombotic disease, in-stent restenosis, heart failure, and sepsis.