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The FEBS Journal Apr 2021Proteinase-activated receptors (PARs) are a four-member family of G protein-coupled receptors defined by their irreversible proteolytic mechanism of activation. PARs... (Review)
Review
Proteinase-activated receptors (PARs) are a four-member family of G protein-coupled receptors defined by their irreversible proteolytic mechanism of activation. PARs have emerged as important regulators of various physiological responses and are implicated in numerous pathological conditions. Importantly, PAR1 and PAR4 are critical regulators of platelet function, while PAR2 is well established as a driver of inflammatory responses. PAR-targeted drug development efforts are therefore of great interest. In this review, we provide an overview of recent advances in our understanding of molecular mechanisms underlying PAR activation, effector interaction, and signaling. We also provide an overview of the diverse proteolytic enzymes that are now established as PAR regulators and describe the ability of different enzymes to elicit biased signaling through PARs. Finally, we highlight recent advances in the development of PAR-targeted pharmacological agents and discuss recent structure-activity relationship studies.
Topics: Antineoplastic Agents; Humans; Peptide Hydrolases; Receptor, PAR-1; Receptor, PAR-2; Receptors, G-Protein-Coupled; Receptors, Proteinase-Activated; Receptors, Thrombin; Signal Transduction
PubMed: 33742547
DOI: 10.1111/febs.15829 -
International Journal of Molecular... Aug 2021The catabolic and destructive activity of serine proteases in arthritic joints is well known; however, these enzymes can also signal pain and inflammation in joints. For... (Review)
Review
The catabolic and destructive activity of serine proteases in arthritic joints is well known; however, these enzymes can also signal pain and inflammation in joints. For example, thrombin, trypsin, tryptase, and neutrophil elastase cleave the extracellular N-terminus of a family of G protein-coupled receptors and the remaining tethered ligand sequence then binds to the same receptor to initiate a series of molecular signalling processes. These protease activated receptors (PARs) pervade multiple tissues and cells throughout joints where they have the potential to regulate joint homeostasis. Overall, joint PARs contribute to pain, inflammation, and structural integrity by altering vascular reactivity, nociceptor sensitivity, and tissue remodelling. This review highlights the therapeutic potential of targeting PARs to alleviate the pain and destructive nature of elevated proteases in various arthritic conditions.
Topics: Animals; Arthritis; Humans; Receptor, PAR-1; Receptor, PAR-2; Receptors, Proteinase-Activated; Receptors, Thrombin; Signal Transduction
PubMed: 34502257
DOI: 10.3390/ijms22179352 -
International Journal of Molecular... May 2023Protease-activated receptors (PARs) are a class of integral membrane proteins that are cleaved by a variety of proteases, most notably thrombin, to reveal a tethered... (Review)
Review
Protease-activated receptors (PARs) are a class of integral membrane proteins that are cleaved by a variety of proteases, most notably thrombin, to reveal a tethered ligand and promote activation. PARs are critical mediators of platelet function in hemostasis and thrombosis, and therefore are attractive targets for anti-platelet therapies. Animal models studying platelet PAR physiology have relied heavily on genetically modified mouse strains, which have provided ample insight but have some inherent limitations. The current review aims to summarize the notable PAR expression and functional differences between the mouse and human, in addition to highlighting some recently developed tools to further study human physiology in mouse models.
Topics: Humans; Mice; Animals; Receptors, Proteinase-Activated; Receptors, Thrombin; Species Specificity; Blood Platelets; Thrombin
PubMed: 37176005
DOI: 10.3390/ijms24098298 -
Arteriosclerosis, Thrombosis, and... Nov 2023
Topics: Mice; Animals; Mice, Knockout; Coronary Vessels; Receptors, Thrombin; Receptor, PAR-1; Atherosclerosis; Fibrosis
PubMed: 37767705
DOI: 10.1161/ATVBAHA.123.320046 -
Glia Sep 2021Excessive activation of the thrombin receptor, protease activated receptor 1 (PAR1) is implicated in diverse neuropathologies from neurodegenerative conditions to...
Excessive activation of the thrombin receptor, protease activated receptor 1 (PAR1) is implicated in diverse neuropathologies from neurodegenerative conditions to neurotrauma. PAR1 knockout mice show improved outcomes after experimental spinal cord injury (SCI), however information regarding the underpinning cellular and molecular mechanisms is lacking. Here we demonstrate that genetic blockade of PAR1 in female mice results in improvements in sensorimotor co-ordination after thoracic spinal cord lateral compression injury. We document improved neuron preservation with increases in Synapsin-1 presynaptic proteins and GAP43, a growth cone marker, after a 30 days recovery period. These improvements were coupled to signs of enhanced myelin resiliency and repair, including increases in the number of mature oligodendrocytes, their progenitors and the abundance of myelin basic protein. These significant increases in substrates for neural recovery were accompanied by reduced astrocyte (Serp1) and microglial/monocyte (CD68 and iNOS) pro-inflammatory markers, with coordinate increases in astrocyte (S100A10 and Emp1) and microglial (Arg1) markers reflective of pro-repair activities. Complementary astrocyte-neuron co-culture bioassays suggest astrocytes with PAR1 loss-of-function promote both neuron survival and neurite outgrowth. Additionally, the pro-neurite outgrowth effects of switching off astrocyte PAR1 were blocked by inhibiting TrkB, the high affinity receptor for brain derived neurotrophic factor. Altogether, these studies demonstrate unique modulatory roles for PAR1 in regulating glial-neuron interactions, including the capacity for neurotrophic factor signaling, and underscore its position at neurobiological intersections critical for the response of the CNS to injury and the capacity for regenerative repair and restoration of function.
Topics: Animals; Astrocytes; Female; Mice; Neurons; Receptor, PAR-1; Receptors, Thrombin; Spinal Cord; Spinal Cord Injuries
PubMed: 33887067
DOI: 10.1002/glia.24012 -
British Journal of Clinical Pharmacology Oct 2011Activated platelets stimulate thrombus formation in response to rupture of an atherosclerotic plaque or endothelial cell erosion, promoting atherothrombotic disease.... (Review)
Review
Activated platelets stimulate thrombus formation in response to rupture of an atherosclerotic plaque or endothelial cell erosion, promoting atherothrombotic disease. Multiple pathways contribute to platelet activation. Aspirin, an irreversible inhibitor of thromboxane A2 synthesis, in combination with clopidogrel, an inhibitor of P2Y(12) adenosine diphosphate platelet receptors, represent the current standard-of-care of antiplatelet therapy for patients with acute coronary syndrome and for those undergoing percutaneous coronary intervention. Although these agents have demonstrated significant clinical benefit, the increased risk of bleeding and the recurrence of thrombotic events represent substantial limitations. Thrombin is one of the most important platelet activators. The inhibition of protease-activated receptor 1 showed a good safety profile in preclinical studies. In fact, phase II studies with vorapaxar (SCH530348) and atopaxar (E5555) showed no increase of bleeding events in addition to the current standard-of-care of antiplatelet therapy. Although the results of phase III trials for both drugs are awaited, this family is a promising new addition to the current clinical practice for patients with atherothrombotic disease, not only as an alternative, but also as additional therapy.
Topics: Aspirin; Blood Platelets; Humans; Imines; Lactones; Platelet Aggregation; Platelet Aggregation Inhibitors; Pyridines; Receptors, Thrombin; Thrombosis
PubMed: 21906120
DOI: 10.1111/j.1365-2125.2010.03884.x -
Biomolecules Nov 2021In contrast with the brain and spinal cord, peripheral nerves possess a striking ability to regenerate after damage. This characteristic of the peripheral nervous system... (Review)
Review
In contrast with the brain and spinal cord, peripheral nerves possess a striking ability to regenerate after damage. This characteristic of the peripheral nervous system is mainly due to a specific population of glial cells, the Schwann cells. Schwann cells promptly activate after nerve injury, dedifferentiate assuming a repair phenotype, and assist axon regrowth. In general, tissue injury determines the release of a variety of proteases which, in parallel with the degradation of their specific targets, also activate plasma membrane receptors known as protease-activated receptors (PARs). PAR1, the prototypical member of the PAR family, is also known as thrombin receptor and is present at the Schwann cell plasma membrane. This receptor is emerging as a possible regulator of the pro-regenerative capacity of Schwann cells. Here, we summarize the most recent literature data describing the possible contribution of PAR1 and PAR1-activating proteases in regulating the regeneration of peripheral nerves.
Topics: Animals; Axons; Ligands; Neuroglia; Receptor, PAR-1; Schwann Cells; Thrombin
PubMed: 34827666
DOI: 10.3390/biom11111668 -
Scientific Reports Jun 2018Thrombin is frequently increased in the CNS after injury yet little is known regarding its effects on neural stem cells. Here we show that the subventricular zone (SVZ)...
Thrombin is frequently increased in the CNS after injury yet little is known regarding its effects on neural stem cells. Here we show that the subventricular zone (SVZ) of adult mice lacking the high affinity receptor for thrombin, proteinase activated receptor 1 (PAR1), show increased numbers of Sox2+ and Ki-67+ self-renewing neural stem cells (NSCs) and Olig2+ oligodendrocyte progenitors. SVZ NSCs derived from PAR1-knockout mice, or treated with a PAR1 small molecule inhibitor (SCH79797), exhibited enhanced capacity for self-renewal in vitro, including increases in neurosphere formation and BrdU incorporation. PAR1-knockout SVZ monolayer cultures contained more Nestin, NG2+ and Olig2+ cells indicative of enhancements in expansion and differentiation towards the oligodendrocyte lineage. Cultures of NSCs lacking PAR1 also expressed higher levels of myelin basic protein, proteolipid protein and glial fibrillary acidic protein upon differentiation. Complementing these findings, the corpus callosum and anterior commissure of adult PAR1-knockout mice contained greater numbers of Olig2+ progenitors and CC1+ mature oligodendrocytes. Together these findings highlight PAR1 inhibition as a means to expand adult SVZ NSCs and to promote an increased number of mature myelinating oligodendrocytes in vivo that may be of particular benefit in the context of neural injury where PAR1 agonists such as thrombin are deregulated.
Topics: Animals; Calcium Signaling; Cell Differentiation; Cell Proliferation; Cells, Cultured; Female; Lateral Ventricles; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Neural Stem Cells; Pyrroles; Quinazolines; Receptor, PAR-1; Receptors, Thrombin
PubMed: 29921916
DOI: 10.1038/s41598-018-27613-9 -
Basic Research in Cardiology Jan 2020The deleterious effects of diabetes in the heart are increasingly attributed to inflammatory signaling through the NLRP3 (NOD, LRR and PYD domains-containing protein 3)...
The deleterious effects of diabetes in the heart are increasingly attributed to inflammatory signaling through the NLRP3 (NOD, LRR and PYD domains-containing protein 3) inflammasome. Thrombin antagonists reduce cardiac remodeling and dysfunction in diabetic mice, in part by suppressing fibrin-driven inflammation. The role of cellular thrombin receptor subtypes in this context is not known. We sought to determine the causal involvement of protease-activated receptors (PAR) in inflammatory signaling of the diabetic heart. Mice with diet-induced diabetes showed increased abundance of pro-caspase-1 and pro-interleukin (IL)-1β in the left ventricle (LV), indicating transcriptional NLRP3 inflammasome priming, and augmented cleavage of active caspase-1 and IL-1β, pointing to canonical NLRP3 inflammasome activation. Caspase-11 activation, which mediates non-canonical NLRP3 inflammasome signaling, was not augmented. Formation of the plasma membrane pore-forming protein N-terminal gasdermin D (GDSMD), a prerequisite for IL-1β secretion, was also higher in diabetic vs. control mouse LV. NLRP3, ASC and IL-18 expression did not differ between the groups, nor did expression of PAR1 or PAR2. PAR3 was nearly undetectable. LV abundance of PAR4 by contrast increased with diabetes and correlated positively with active caspase-1. Genetic deletion of PAR4 in mice prevented the diet-induced cleavage of caspase-1, IL-1β and GDSMD. Right atrial appendages from patients with type 2 diabetes also showed higher levels of PAR4, but not of PAR1 or PAR2, than non-diabetic atrial tissue, along with increased abundance of cleaved caspase-1, IL-1β and GSDMD. Human cardiac fibroblasts maintained in high glucose conditions to mimic diabetes also upregulated PAR4 mRNA and protein, and increased PAR4-dependent IL-1β transcription and secretion in response to thrombin, while PAR1 and PAR2 expressions were unaltered. In conclusion, PAR4 drives caspase-1-dependent IL-1β production through the canonical NLRP3 inflammasome pathway in the diabetic heart, providing mechanistic insights into diabetes-associated cardiac thromboinflammation. The emerging PAR4-selective antagonists may provide a feasible approach to prevent cardiac inflammation in patients with diabetes.
Topics: Aged; Animals; Caspase 1; Cells, Cultured; Diabetes Mellitus; Diabetic Cardiomyopathies; Diet, High-Fat; Disease Models, Animal; Female; Fibroblasts; Humans; Inflammasomes; Interleukin-1beta; Intracellular Signaling Peptides and Proteins; Male; Mice, Inbred C57BL; Mice, Knockout; Middle Aged; Myocardium; NLR Family, Pyrin Domain-Containing 3 Protein; Phosphate-Binding Proteins; Receptors, Thrombin; Signal Transduction
PubMed: 31912235
DOI: 10.1007/s00395-019-0771-9 -
Journal of Thrombosis and Haemostasis :... Mar 2017Essentials Whether or not dabigatran enhances the risk of myocardial infarction is under discussion. We measured platelet reactivity and thrombin receptor expression in...
UNLABELLED
Essentials Whether or not dabigatran enhances the risk of myocardial infarction is under discussion. We measured platelet reactivity and thrombin receptor expression in dabigatran patients. Platelet reactivity and thrombin receptor expression is enhanced during dabigatran treatment. This should be considered when choosing the optimal direct oral anticoagulant for individuals.
SUMMARY
Background The direct oral anticoagulant (DOAC) dabigatran is a direct thrombin inhibitor. Its landmark trial, the RE-LY study, observed a trend towards a higher incidence of myocardial infarctions (MIs) in dabigatran-treated patients. Since then, there have been discussions on whether dabigatran increases the risk of MI. Objective In this study, we aimed to assess platelet reactivity and platelet thrombin receptor expression in dabigatran-treated patients. Methods We conducted a cross-sectional study in 13 hospitalized patients with planned initiation of dabigatran medication. Platelet reactivity was measured by light-transmission aggregometry and platelet thrombin receptor expression was measured by flow cytometry analysis. Results Platelet reactivity was higher after initiation of dabigatran medication as compared with baseline (baseline 44 ± 24% vs. dabigatran 70 ± 25%). Accordingly, the density of both platelet thrombin receptors (protease activated receptor [PAR]-1 and PAR-4) on platelets increased during dabigatran treatment (PAR1, baseline 63 ± 11% vs. dabigatran 70 ± 10%; PAR4, baseline 1.1 ± 0.5% vs. dabigatran 1.6 ± 0.9%). Conclusions Dabigatran increases platelet reactivity by enhancing the thrombin receptor density on platelets. This finding should be considered while choosing the optimal DOAC in individualized medicine.
Topics: Administration, Oral; Aged; Anticoagulants; Arachidonic Acid; Atrial Fibrillation; Blood Platelets; Collagen; Cross-Sectional Studies; Dabigatran; Female; Flow Cytometry; Gene Expression Regulation; Humans; Male; Middle Aged; Myocardial Infarction; Pilot Projects; Platelet Aggregation; Receptors, Thrombin; Regression Analysis; Risk Factors; Thrombin
PubMed: 27992120
DOI: 10.1111/jth.13595