Protease-Activated Receptors

Research and Practice in Thrombosis and Haemostasis

2021

Self Cite

Background Protease‐activated receptor (PAR) 1 and PAR4 are key thrombin signal mediators for human platelet activation and aggregation in response to vascular injury. They are primarily activated by thrombin cleavage of the N‐terminus to expose a tethered ligand. In addition to the canonical activation by thrombin, a growing panel of proteases can also elicit PAR1‐ or PAR4‐mediated signal transduction. Recently, complement factor C4a was reported as the first endogenous agonist for both PAR1 and PAR4. Further, it is the first endogenous nontethered ligand that activates PAR1 and PAR4. These studies were conducted with human microvascular cells; the impact of C4a on platelet PARs is unknown. Objectives The goal of this study was to interrogate PAR1 and PAR4 activation by C4a on human platelets. Methods Platelet‐rich plasma (PRP) was isolated from healthy donors. PRP was stimulated with C4a, and the platelet aggregation was measured. Human embryonic kidney (HEK) 293 Flp‐In T‐rex cells were used to further test if C4a stimulation can initiate PAR1‐ or PAR4‐mediated Gα q signaling, which was measured by intracellular calcium mobilization. Results C4a failed to elicit platelet aggregation via PAR1‐ or PAR4‐mediated manner. In addition, no PAR1‐ or PAR4‐mediated calcium mobilization was observed upon C4a stimulation on HEK293 cells. Conclusions Complement factor C4a does not activate PAR1 or PAR4 on human platelets. These data show that PAR1 and PAR4 activation by C4a on microvascular cells likely requires a cofactor, which reinforces the concept of cell type–specific regulation of protease signaling.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Complement factor C4a does not activate protease‐activated receptor 1 (PAR1) or PAR4 on human platelets

Fuente

Research and Practice in Thrombosis and Haemostasis

2021

Self Cite

“…The newly exposed ligand binds intramolecularly to the receptor, inducing a conformational change that initiates signal transduction. (3) In addition to canonical thrombin-mediated signaling, there is a growing panel of identified proteases that also have the ability to activate PARs. (4) PAR1 can be cleaved by activated protein C (APC), matrix metalloproteinase 1 (MMP-1), MMP-2 and MMP-13 at non-canonical sites to generate distinct tethered ligands.…”

Section: Introductionmentioning

confidence: 99%

“…(4) PAR1 can be cleaved by activated protein C (APC), matrix metalloproteinase 1 (MMP-1), MMP-2 and MMP-13 at non-canonical sites to generate distinct tethered ligands. (2,3) These ligands initiate diverse signaling pathways depending on the cell type and cellular cofactors. (4) In addition to thrombin, PAR4 can be activated by trypsin, plasmin, cathepsin G, factor Xa, however, these all cleave at the canonical thrombin site and results the same downstream signaling.…”

Section: Introductionmentioning

confidence: 99%

“…(4) In addition to thrombin, PAR4 can be activated by trypsin, plasmin, cathepsin G, factor Xa, however, these all cleave at the canonical thrombin site and results the same downstream signaling. (3,5,6) Human platelets express PAR1 and PAR4. (3) This dual receptor system works in concert to provide the sensitivity and duration of signaling required for hemostasis.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Complement factor C4a does not activate protease activated receptor 1 (PAR1) or PAR4 on human platelets

2020

Preprint

Self Cite

Word Count text: 1999 Word Count Abstract: 240 Figure Count: 3 Reference Count: 17 Essentials:• C4a is an agonist for both PAR1 and PAR4 on human microvascular cells.• We sought to determine if C4a activates human platelets through PAR1 or PAR4. • C4a does not activate PAR1 and PAR4 on human platelets.• This re-enforces the concept of cell-type specific regulation of PAR signaling. AbstractBackground Protease activated receptor 1 (PAR1) and PAR4 are key thrombin signal mediators for human platelet activation and aggregation in response to vascular injury. They are primarily activated by thrombin cleavage of the N-terminus to expose a tethered ligand. In addition to the canonical activation by thrombin, a growing panel of proteases can also elicit PAR1-or PAR4-mediate signal transduction. Recently, complement factor C4a was reported as the first endogenous agonist for both PAR1 and PAR4. Further, it is the first endogenous non-tethered ligand that activates PAR1 and PAR4. These studies were conducted with human microvascular cells; the impact of C4a on platelet PARs is unknown. ObjectivesThe goal of this study was to interrogate PAR1 and PAR4 activation by C4a on human platelets. Methods Platelet rich plasma (PRP) were isolated from healthy donors. PRP was stimulated with C4a and the platelet aggregation was measured. HEK293 Flp-In T-rex cells were used to further test if C4a stimulation can initiate PAR1-or PAR4-mediated Gαq signaling, which was measured by intracellular calcium mobilization. ResultsC4a failed to elicit platelet aggregation via PAR1-or PAR4-mediated manner. In addition, no PAR1-or PAR4-mediated calcium mobilization was observed upon C4a stimulation on HEK293 cells. Conclusions Complement factor C4a does not activate PAR1 or PAR4 on human platelets. These data show that PAR1 and PAR4 activation by C4a on microvascular cells likely requires a cofactor, which re-enforces the concept of cell-type specific regulation of protease signaling.

Protease‐activated receptors: An illustrated review

Research and Practice in Thrombosis and Haemostasis

Kerlin

2021

Proteases are important regulators of cell behavior, survival, and apoptosis. They communicate to cells directly through a special class of G‐protein–coupled receptors known as protease‐activated receptors (PARs). N‐terminal PAR proteolysis unmasks a neo‐N‐terminus, which serves as a tethered ligand to activate PARs. Using this unique irreversible activation mechanism, PARs relay information across cell membranes. The year 2020 is the 30th year since discovery of the first member of this family, PAR1. In this illustrated review, we highlight achievements in the PAR field over the past 3 decades. Additionally, the known expression profiles of PARs in human tissues and across species are portrayed. We also illustrate the tethered ligand activation mechanism, which is unique to PARs, and PAR regulatory mechanisms. PAR1 was originally named “thrombin receptor” because thrombin was the first protease identified to activate PAR1. However, over the past 30 years, a growing number of proteases have been found to cleave PARs and trigger differential downstream signaling depending on cleavage site, cell type, and species. We exemplify the diversity of PAR1‐mediated signaling outcomes in platelets and endothelial cells as pertinent examples to the hemostasis, thrombosis, and vascular biology fields. Further, the termination and regulation of PAR signaling via endocytosis and currently available pharmacologic approaches are depicted. We conclude with portrayal of clinically translational aspects of PAR biology including pharmacologic manipulation and single‐nucleotide polymorphisms.