Αντικείμενο μελέτης της παρούσας διπλωματικής ερευνητικής εργασίας αποτελεί η ταυτοποίηση και η διερεύνηση της βιολογικής δράσης του πεπτιδίου που αποκόπτεται από τον υποδοχέα PAR1 μετά την ενεργοποίηση του από την θρομβίνη. Το υπεύθυνο γονίδιο για την έκφραση του υποδοχέα PAR1 κωδικοποιεί μια πολυπεπτιδική αλυσίδα μήκους 425 αμινοξέων. Έχει προταθεί ότι τα πρώτα 21-23 αμινοξέα του αμινοτελικού άκρου του μορίου αυτού πιθανόν να αποτελούν σηματοδοτική αλληλουχία υπεύθυνη για την μεταφορά και τοποθέτηση του υποδοχέα στην κυτταρική μεμβράνη. Η σηματοδοτική αυτή αλληλουχία είναι άγνωστο προς το παρόν αν παραμένει στον ώριμο PAR1 υποδοχέα ή απομακρύνεται με πρωτεόλυση πριν την εμφάνιση του PAR1 στην κυτταρική μεμβράνη. Ο υποδοχέας PAR1 ανήκει στην μεγάλη οικογένεια υποδοχέων των επτά διαμεμβρανικών τμημάτων (seven transmembrane domain receptor family) που διασυνδέονται με G πρωτεΐνες (G protein-coupled receptors, GPCRs). Επιπλέον, επειδή η ενεργοποίηση του υποδοχέα απαιτεί την ενζυμική δράση της θρομβίνης, ορίζεται με αυτόν τον τρόπο μία νέα οικογένεια διαμεμβρανικών υποδοχέων που ενεργοποιούνται από πρωτεάσες (Proteinase-Activated Receptors, PARs). Η θρομβίνη αναγνωρίζει για πέψη μια θέση στην αλληλουχία του εξωκυττατικού αμινοτελικού άκρου μεταξύ των αμινοξέων Arg41-Ser42 του υποδοχέα PAR1. Η πέψη αυτού του πεπτιδικού δεσμού οδηγεί στην απελευθέρωση ενός πεπτιδίου (Thrombin Receptor Peptide, TR) και στην δημιουργία ενός νέου αμινοτελικού άκρου για τον υποδοχέα, που λειτουργεί ως αγωνιστής και ενεργοποιεί τον PAR1. Έχει δειχθεί ότι η θρομβίνη και ο υποδοχέας PAR1 εμπλέκονται σε αρκετές παθοφυσιολογικές καταστάσεις. Ωστόσο δεν υπάρχουν επαρκείς πληροφορίες για την δράση του πεπτιδίου που αποκόπτεται. Χρησιμοποιώντας την τεχνολογία HPLC/MS έγινε προσπάθεια για την ταυτοποίηση του πραγματικού μεγέθους του πεπτιδίου που αποκόπτεται από τον PAR1 υποδοχέα. Τα πρώτα αποτελέσματα της εφαρμογής αυτής 55 οδήγησαν στο συμπέρασμα ότι κρίνεται απαραίτητη η περεταίρω βελτίωση των συνθηκών ανίχνευσης του πεπτιδίου, ώστε να επιτρέπεται η ανίχνευση του κατά την φόρτωση 1 ng στην στήλη της υγρής χρωματογραφίας. Πιο συγκεκριμένα η αντιμετώπιση της υψηλής πολικότητας του TR23-41 και η ενίσχυση ευαισθησίας του TR1-41 με την χρήση διαφορετικού διαλύτη ή με την χρήση διαφορετικής στήλης ή και ακόμα ο συνδυασμός διαφορετικού διαλύτη και στήλης, που αποτελεί και την μέχρι τώρα πιο πιθανή εκδοχή αντιμετώπισης των παραπάνω προβλημάτων, πιθανόν να δώσουν λύση στο πρόβλημα ανίχνευσης σε χαμηλές συγκεντρώσεις πεπτιδίου. Επιπλέον με την χρήση τεχνικής ελέγχου DNA σύνθεσης εξετάστηκε η επίδραση του TR1-41 πεπτιδίου σε HUVECs. Σκοπός αυτών των πειραμάτων δεν ήταν μόνο η εύρεση τυχόν βιολογικής δράσης του πεπτιδίου αλλά και η εύρεση ελάχιστης συγκέντρωσης του πεπτιδίου που προκαλεί αναστολή στην σύνθεση του DNA σε καλλιέργειες ενδοθηλιακών κυττάρων στις οποίες έχει προηγηθεί συνθήκες νηστείας. Τα αποτελέσματα αποκάλυψαν ότι το TR1-41 πεπτίδιο προκαλεί αναστολή στην σύνθεση του DNA και μάλιστα σε ελάχιστη συγκέντρωση 30nM, παρουσία ή μη του αυξητικού παράγοντα VEGF. Μελλοντικές έρευνες με βάση τα παραπάνω αποτελέσματα μπορούν να οδηγήσουν στην ταυτοποίηση του πραγματικού μεγέθους του πεπτιδίου που αποκόπτεται μετά την τοποθέτηση και ενεργοποίηση του PAR1 στην κυτταρική μεμβράνη και κατ’ επέκταση στην λεπτομερή διερεύνηση της βιολογικής δράσης του πεπτιδίου αυτού. Γνωρίζοντας την ανάμιξη της θρομβίνης και του υποδοχέα της σε παθοφυσιολογικές καταστάσεις η ταυτοποίηση του πεπτιδίου και η γνώση της βιολογικής του δράσης μελλοντικά θα αποτελέσει ένα χρήσιμο προγνωστικό και διαγνωστικό δείκτη. / In the context of the MSc dissertation described herein, the objective of the research work constitutes in the identification of the real number of amino acids of the peptide that is being released after the activation of PAR1 by thrombin and the examination of its biological action. The responsible gene for the PAR1 expression codifies a polypeptide chain of 425 amino acids. It is under consideration that the first 21-23 amino acids of the exodomain N-terminal sequence of the receptor may be a signaling sequence, responsible for the transfer and placement of the receptor to the cell membrane. It is not known so far if the signaling sequence remains on the receptor after its placement on the cell membrane. PAR1 belongs to the family of the seven transmembrane domain receptor, the G protein-coupled receptors (GPCRs). PAR1 requires the enzymic activity of thrombin for its activation, and so a new family of transmembrane receptors is being defined, the Proteinase-Activated Receptors (PARs). Thrombin recognizes and cleaves the N-terminal exodomain of PAR1 between Arg41-Ser42 amino acids. This cleavage event releases a peptide (Thrombin Receptor Peptide, TR) and so unmasks a new N-terminus of the receptor, which acts as PAR1 agonist and activates the receptor. It has been proved that thrombin and PAR1 are being involved in many pathophysiological situations. So far there isn’t enough information of the biological action of the peptide that is being realized from PAR1. The use of HPLC/MS technology wasn’t able to reveal the real number of this peptide because of the intensity of TR1-41 in 1ng on column and the extreme polarity of TR24-41. instead of these results we strongly believe that the use of different solvents will increase the intensity of TR1-41 in 1ng on column. Also the use of C8 column instead of C4 probably will contribute in the traceability of TR24-41. The biological action of TR1-41 was examined with the use of DNA synthesis control technique in HUVECs cultivation after starvation. These experiments showed that the use of TR1-41 caused reduction of the DNA synthesis in HUVECs. We also examined the lower concentration of TR1-41 57 that was able to reduce the DNA synthesis in HUVECs. TR1-41 was able to reduce DNA synthesis in minimum concentration of 30 nM even in the presence of VEGF. The above results in association with future research can constitute in the identification of the real size of the peptide that is being released after the activation of PAR1, as in the biological action of this peptide. Knowing so far that thrombin and PAR1 are being involved in pathophysiological situations this peptide will constitute in the future as a useful prognostic and diagnostic marker.

O receptor ativado por protease do tipo 1 (PAR1) parece estar associado ao reparo periodontal, enquanto o tipo 2 (PAR2) com a inflamação periodontal. Esses receptores podem ser ativados pelas proteases gingipaina, uma protease secretada pela Porphyromonas gingivalis, um importante periodontopatógeno, e pela proteinase-3 de neutrófilos (P3), que é liberada por neutrófilos quando expostos a um estímulo inflamatório. Uma vez que o diabetes é reconhecido como um fator de risco importante para a doença periodontal, o objetivo deste estudo foi investigar a expressão de PAR1 e de PAR2 e de seus ativadores, gingipaina e P3 no fluido gengival (FG) de pacientes diabéticos com periodontite crônica, antes e após tratamento periodontal não cirúrgico. Amostras de FG e os parâmetros clínicos, como profundidade de sondagem (PS), nível clínico de inserção (NCI), sangramento à sondagem (SS) e índice de placa (IP) foram coletados de pacientes sistemicamente saudáveis e de pacientes com diabetes mellitus do tipo 2 (DMT2) com periodontite crônica , no baseline e após o tratamento periodontal não cirúrgico. As expressões gênicas de PAR1, PAR2, gingipaina e P3 no FG foram quantificadas por qPCR. Os parâmetros clínicos melhoraram significativamente após a terapia periodontal (p <0,01). O diabetes levou ao aumento da expressão de PAR1 no fluido gengival e na presença da periodontite crônica diminuiu significativamente a expressão de PAR1, PAR2 e P3 (p<0,05). Além disso, o tratamento periodontal não cirúrgico em diabéticos resultou no aumento da expressão de PAR1 e de PAR2 (p<0,05). Dentro dos limites do presente estudo, sugerimos que os PARs podem estar associados com a inflamação periodontal em diabéticos. / Protease activated receptor type 1 (PAR1) seems to play a role in periodontal repair, while PAR2 is associated with periodontal inflammation. These receptors can be activated by gingipain, a protease released from Porphyromonas gingivalis, an important periodontal pathogen, and neutrophil proteinase-3 (P3), which is released by neutrophils when exposed to an inflammatory stimulus. Since diabetes is known risk factor to periodontal disease, the aim of this study was to investigate PAR1 and PAR2 mRNA expression at the gingival crevicular fluid (GCF) in diabetic patients with chronic periodontitis, before and after non-surgical periodontal treatment. GCF samples and clinical parameters consisting of measuring probing depth (PD), clinical attachment level (CAL), bleeding on probing (BOP) and plaque index (PI) were collected from systemically healthy patients and patients with type 2 diabetes mellitus with chronic periodontitis, at baseline and after nonsurgical periodontal treatment. PAR1 and PAR2, as well the expression of the activators gingipain and P3 at the GCF were quantified by qPCR. The clinical parameters improved significantly after periodontal therapy (p <0.01). Diabetes led to increased expression of PAR1 in the GCF, and the presence of chronic periodontitis significantly decreased the expression of PAR1, PAR2 and P3 (p <0.05). Moreover, non-surgical periodontal treatment in diabetics resulted in increased expression of PAR1 and PAR2 (p <0.05). Within the limits of this study, we suggest that PARs may be associated with periodontal inflammation in diabetics.

O receptor ativado por protease do tipo 1 (PAR1) parece estar associado ao reparo periodontal, enquanto o tipo 2 (PAR2) com a inflamação periodontal. Esses receptores podem ser ativados pelas proteases gingipaina, uma protease secretada pela Porphyromonas gingivalis, um importante periodontopatógeno, e pela proteinase-3 de neutrófilos (P3), que é liberada por neutrófilos quando expostos a um estímulo inflamatório. Uma vez que o diabetes é reconhecido como um fator de risco importante para a doença periodontal, o objetivo deste estudo foi investigar a expressão de PAR1 e de PAR2 e de seus ativadores, gingipaina e P3 no fluido gengival (FG) de pacientes diabéticos com periodontite crônica, antes e após tratamento periodontal não cirúrgico. Amostras de FG e os parâmetros clínicos, como profundidade de sondagem (PS), nível clínico de inserção (NCI), sangramento à sondagem (SS) e índice de placa (IP) foram coletados de pacientes sistemicamente saudáveis e de pacientes com diabetes mellitus do tipo 2 (DMT2) com periodontite crônica , no baseline e após o tratamento periodontal não cirúrgico. As expressões gênicas de PAR1, PAR2, gingipaina e P3 no FG foram quantificadas por qPCR. Os parâmetros clínicos melhoraram significativamente após a terapia periodontal (p <0,01). O diabetes levou ao aumento da expressão de PAR1 no fluido gengival e na presença da periodontite crônica diminuiu significativamente a expressão de PAR1, PAR2 e P3 (p<0,05). Além disso, o tratamento periodontal não cirúrgico em diabéticos resultou no aumento da expressão de PAR1 e de PAR2 (p<0,05). Dentro dos limites do presente estudo, sugerimos que os PARs podem estar associados com a inflamação periodontal em diabéticos. / Protease activated receptor type 1 (PAR1) seems to play a role in periodontal repair, while PAR2 is associated with periodontal inflammation. These receptors can be activated by gingipain, a protease released from Porphyromonas gingivalis, an important periodontal pathogen, and neutrophil proteinase-3 (P3), which is released by neutrophils when exposed to an inflammatory stimulus. Since diabetes is known risk factor to periodontal disease, the aim of this study was to investigate PAR1 and PAR2 mRNA expression at the gingival crevicular fluid (GCF) in diabetic patients with chronic periodontitis, before and after non-surgical periodontal treatment. GCF samples and clinical parameters consisting of measuring probing depth (PD), clinical attachment level (CAL), bleeding on probing (BOP) and plaque index (PI) were collected from systemically healthy patients and patients with type 2 diabetes mellitus with chronic periodontitis, at baseline and after nonsurgical periodontal treatment. PAR1 and PAR2, as well the expression of the activators gingipain and P3 at the GCF were quantified by qPCR. The clinical parameters improved significantly after periodontal therapy (p <0.01). Diabetes led to increased expression of PAR1 in the GCF, and the presence of chronic periodontitis significantly decreased the expression of PAR1, PAR2 and P3 (p <0.05). Moreover, non-surgical periodontal treatment in diabetics resulted in increased expression of PAR1 and PAR2 (p <0.05). Within the limits of this study, we suggest that PARs may be associated with periodontal inflammation in diabetics.

<p> </p><p>Platelets play a key role in primary haemostasis but are also related to the pathogenesis of arterial thrombosis. Thrombin is the most effective agonist inducing platelet activation. Human platelets express two G-protein coupled thrombin receptors (GPCRs), called protease activated receptor (PAR)1 and PAR4. The aim of this study was to clarify differences in the activities of PAR1 and PAR4, especially focusing on their resistance towards the platelet inhibitor nitric oxide (NO) and their ability to undergo desensitization. For this, PAR1- and PAR4- activating peptides (APs) (SFLLRN and AYPGKF, respectively) were used. Different aspects of platelet activities were studied: aggregation and the rise in intracellular Ca²⁺ concentrations ([Ca²⁺]_i). Aggregation was analyzed with lumiaggregometry, and [Ca²⁺]_i were studied using the fura-2 method. PKC substrate phosphorylation and the expression of PAR1 surface receptors were also analyzed, using Western blot and flow cytometry, respectively. The results from this study showed that NO exerted similar inhibitory effects on the two thrombin receptors. However, PAR1 and PAR4 differed in their ability to undergo desensitization. In cumulative dose-response studies, a low concentration of PAR1-AP induced desensitization of platelets towards higher PAR1-AP concentrations. This was not the case when studying PAR4-AP. The mechanism behind the desensitization of PAR1 to some part involved PKC, at least when studying the mobilization of intracellular Ca²⁺. PAR1 desensitization did not seem to involve receptor internalization and neither did it affect the activity of PAR4. This thus suggests that PAR4 might be a more suitable therapeutic target in the future management of thrombosis.</p><p> </p>

Human platelets are constantly regulated by activating and inhibitory effectors. Thrombin,the most potent platelet agonist, induces signaling through the protease-activated receptors(PARs) 1 and 4 which in turn convey their signal by coupling to G-proteins. Nitric oxide (NO)is a potent platelet inhibitor continuously formed by the endothelium exerting its effect byincreasing cGMP through activation of soluble guanylyl cyclase (sGC). The purpose of thiswork has been to investigate how NO would affect platelets already activated by PARagonists.To examine the different contributions of the PAR1- and PAR4-signals, the selectiveagonist peptides SFLLRN and AYPGKF-NH2 were utilized. Aggregation, Ca2+-mobilization andphosphorylation of threonine 696 in myosin phosphatase target subunit 1 (MYPT1) wereanalyzed. Intriguingly PAR1-, but not PAR4-, agonist provoked aggregation was rapidlyreversed upon NO exposure. PAR-agonist induced Ca2+-mobilization was markedly reducedafter exposure to NO, however this Ca2+-suppression did not cause the disaggregation ofPAR1-agonist evoked platelet aggregation. The reversal of aggregation was suspected to becaused by a cGMP-mediated inhibition of the Rho-kinase/ROCK-signaling pathway. This wassupported by Westen blot analysis where a marked decrease of MYPT1 phosphorylationcompared to basal levels could be observed. In conclusion, NO was found to reverse humanplatelet aggregation evoked by PAR1-activation by inhibition of a Rho-kinase/ROCK-signalingpathway.

Platelets play a key role in primary haemostasis but are also related to the pathogenesis of arterial thrombosis. Thrombin is the most effective agonist inducing platelet activation. Human platelets express two G-protein coupled thrombin receptors (GPCRs), called protease activated receptor (PAR)1 and PAR4. The aim of this study was to clarify differences in the activities of PAR1 and PAR4, especially focusing on their resistance towards the platelet inhibitor nitric oxide (NO) and their ability to undergo desensitization. For this, PAR1- and PAR4- activating peptides (APs) (SFLLRN and AYPGKF, respectively) were used. Different aspects of platelet activities were studied: aggregation and the rise in intracellular Ca2+ concentrations ([Ca2+]i). Aggregation was analyzed with lumiaggregometry, and [Ca2+]i were studied using the fura-2 method. PKC substrate phosphorylation and the expression of PAR1 surface receptors were also analyzed, using Western blot and flow cytometry, respectively. The results from this study showed that NO exerted similar inhibitory effects on the two thrombin receptors. However, PAR1 and PAR4 differed in their ability to undergo desensitization. In cumulative dose-response studies, a low concentration of PAR1-AP induced desensitization of platelets towards higher PAR1-AP concentrations. This was not the case when studying PAR4-AP. The mechanism behind the desensitization of PAR1 to some part involved PKC, at least when studying the mobilization of intracellular Ca2+. PAR1 desensitization did not seem to involve receptor internalization and neither did it affect the activity of PAR4. This thus suggests that PAR4 might be a more suitable therapeutic target in the future management of thrombosis.

Η αγγειογένεση ρυθμίζει πολλές φυσιολογικές και παθολογικές διαδικασίες. Έτσι είναι μεγάλου ενδιαφέροντος να ανακαλυφθούν μηχανισμοί που συμμετέχουν. Στο πρώτο μέρος της μεταπτυχιακής εργασίας πραγματοποιήθηκε η σύνθεση των τριών πεπτιδίων, ανάλογα ΤR1-41). Στην συνέχεια μελετήθηκε ο βιολογικός ρόλος του ΤR1-41. Είναι γνωστό ότι η θρομβίνη, η πρωτεάση σερίνης, έχει κεντρικό ρόλο στην αιμόσταση, και έχει προταθεί για να διαδραματίσει έναν σημαντικό ρόλο στην έναρξη της αγγειογέννεσης μέσω της μεταγωγής σήματος από τους PARs υποδοχέων. Οι PARs αποτελούνται μια νέα οικογένεια πρωτεϊνικών υποδοχέων των επτά διαμεμβρανικών τμημάτων (seven transmembrane domain receptor family) που διασυνδέονται με G πρωτεΐνες. Mοριακές και δομικές μελέτες του υποδοχέα της θρομβίνης, PAR-1, έδειξαν ότι το εξωκυτταρικό αμινοτελικό άκρο του είναι μακρύ και αποτελείται από 75 αμινοξέα. Επιπλέον, στην αλληλουχία του αμινοτελικού άκρου εντοπίστηκε μία θέση θετική για πέψη από τη θρομβίνη στη θέση μεταξύ της Arg41 και Ser42. Πράγματι η σύνδεση της θρομβίνης με τον PAR-1 έχει ως συνέπεια την εκλεκτική υδρόλυση του πεπτιδικού δεσμού LDPR41- S42FLLRN. Το αποτέλεσμα από την υδρόλυση αυτή, είναι η δημιουργία ενός ελεύθερου πεπτιδίου 41 αμινοξέων( Thrombin Receptor Peptide 1-41, TR1-41), και ενός νέου αμινοτελικού άκρου για τον υποδοχέα. Σε αντίθεση με το νέο αμινοτελικό άκρο του υποδοχέα της θρομβίνης (PAR-1), ο ρόλος του πεπτιδίου των 41 αμινοξέων (TR1-41) που αποκόπτεται με τη πρωτεολυτική δράση της θρομβίνης μεταξύ των αμινοξέων Arg41-Ser42 είναι σχεδόν άγνωστος. Στην παρούσα μελέτη, αξιολογήσαμε την επίδραση αυτού του πεπτιδίου (MGPRRLLLVAACFSLCGPLLSARTRARRPESKATNATLDPR) στα καλλιεργημένα ανθρώπινα ενδοθηλιακά κύτταρα. Η έκθεση των ενδοθηλιακών κυττάρων στο πεπτίδιο οδήγησε σε μια δοσοεξαρτώμενη αναστολή του πολλαπλασιασμού των κυττάρων, καθώς επίσης και της δράσης των bFGF και VEGF. Επίσης υπήρχε η ένδειξη ότι το πεπτίδιο TR1-41 αναστέλλει σε συνθήκες ορού 5% FBS, τη δράση bFGF μέσω του μονοπατιού της MAP-κινάσης και μέσω του Erk1/2. Αντίθετα, καμία επίδραση δεν παρατηρήθηκε στα κύτταρα στα οποία χορηγήθηκε το scrambled peptide (πεπτίδιο 41 αμινοξέων με αναγραμματισμένη σειρά αμινοξέων) ή και μικρότερα πεπτίδια αυτού (TRARRPESKATNATLDPR). Επίσης το πεπτίδιο TR1-41 παρουσιάζει ανασταλτική δράση στον πολλαπλασιασμό των HUVECs και άλλων κυτταρικών σειρών. Τέλος, το πεπτίδιο TR1-41 εμπόδισε τον σχηματισμό αγγείων στο in vitro σύστημα της αγγειογέννεσης με υπόστρωμα Matrigel. Tο δεύτερο μέρος του μεταπτυχιακού μελετήθηκε ο βιολογικός ρόλος της ορμόνης μελατονίνης. Η μελατονίνη είναι το σημαντικότερο εκκριτικό προϊόν του κωνοειδούς αδένα και σε γενικές γραμμές εμφανίζει ογκοστατικές, αντιγηραντικές, αντιοξειδωτικές, νευροπροστατευτικές, υπνωτικές, ορεξιογόνες, αναλγητικές, θερμορυθμιστικές,και καρδιαγγειακές ιδιότητες, ενώ παρουσιάζει ανασταλτική δράση στη διαδικασία της αναπαραγωγής και μετατοπίζει τις φάσεις του «βιολογικού ρολογιού». Από τα πειράματά μας στα πρωτογενή ανθρώπινα ενδοθηλιακά κύτταρα (HUVECs) η επίδραση της μελατονίνης φαίνεται διφασική. Στις χαμηλές συγκεντρώσεις μελατονίνης αυξάνεται ο πολλαπλασιασμός των HUVECς. Στις υψηλές συγκεντρώσεις αναστέλλει τον πολλαπλασιασμό των HUVECς. / Angiogenesis regulates many physiological and pathological processes, so it is of great interest to find out which mechanisms that are involved. In the first part of the project we synthesised three peptides, analogs of ΤR1-41 and we studied the biological role of the ΤR1-41. It is known that thrombin, the serine proteinase, best known for its pivotal role in haemostasis, has been proposed to play an important role in the initiation of angiogenesis by a mechanism most likely independent of its coagulant activity and more dependent on signaling via the protease-activated receptors (PARs). PARs consists a novel family of G protein-coupled receptors, which can be activated by proteolytic cleavage of their N-terminal extracellular domain. PAR-1 is the first member of this family to be cloned in which proteolytic cleavage at the R41/S42 bond by thrombin releases a 41 aminoacid peptide and unveils a tethered peptide ligand with the recognition sequence SFLLRN. Despite the wealth of information relating to the role of thrombin and PAR-1 innormal and disease states, a potential biological role of cleaved peptide remains unknown. In the present study, we evaluated the effect of the 41-amino-acid cleaved peptide, (MGPRRLLLVAACFSLCGPLLSARTRARRPESKATNATLDPR) in cultured human endothelial cells. Exposure of endothelial cells to this peptide resulted in a concentration-dependent inhibition of serum-mediated proliferation, as well as of bFGF- and VEGF-induced cell growth. There was the suspicion that the peptide blocked the serum, bFGF-triggered Erk1/2 activation. In contrast, no effect was observed in cells treated with a scramble peptide or with a shorter derivative of parstatin (TRARRPESKATNATLDPR). Finally, ΤR1-41 peptide abrogated tube formation in vitro Matrigel angiogenesis model. These results provide a plausible evidence for a negative role of PAR-1 cleaved peptide in angiogenic cascade and suggest parstatin as target for developing anti-angiogenic agents with potential therapeutic application in cancer and other angiogenesis-related diseases. The second part of the project was the biological role of melatonin. Melatonin is the major secretory product of the pineal gland and is considered an important natural oncostatic agent. From our experiments in human umbilical vein endothelial cells (HUVECs) the effect of melatonin seems to be biphasic. In low concentrations melatonin increased HUVEC proliferation, but in higher concentrations significantly decreased cell proliferation.

Απο τις απαρχές της μελέτης του PAR1, είχε βρεθεί οτι βρίσκεται σε στενή συνάφεια με τον καρκίνο, με ποικιλία πειραμάτων που έγιναν σε καρκινικές σειρές και σε διάφορα πειραματικά μοντέλα ζώων. Οι σκοποί της παρούσας εργασίας μπορούν να συνοψιστούν ως εξης: Η διερεύνηση της έκφρασης του υποδοχέα 1 της θρομβίνης (PAR1) σε καρκινικές σειρές προερχόμενες από ανθρώπινους όγκους και συγκεκριμένα: Στις σειρές από καρκίνο του προστάτη PC3 και LNCaP και στις σειρές από καρκίνο του μαστού MDA-231 και MCF-7. Η διερεύνηση της λειτουργικότητας του παραπάνω υποδοχέα στις προαναφερθείσες σειρές και το αποτέλεσμα της αναστολής του υποδοχέα στην επιβίωση και στον πολλαπλασιασμό των μελετώμενων κυττάρων. Η διερεύνηση της ενεργοποίησης της ΜΑΡ κινάσης μέσω του PAR1. Και τελικά, η διερεύνηση της έκφρασης του PAR-1 σε ασθενείς που χειρουργήθηκαν για καρκίνο του πνεύμονα στην Παν/μιακη Καρδιοθωρακοχειρουργική κλινική της Πάτρας, απο τον Καθηγητή Κο Δ. Δουγένη και την ομάδα του. Ο ανταγωνιστής του PAR-1, SCH 79797, προκάλεσε μείωση του κυτταρικού πολλαπλασιασμού των προαναφερθέντων καρκινικών σειρών, όπως μελετήθηκε με τη μέθοδο ΜΤΤ και την ενσωμάτωση ραδιενεργού θυμιδίνης. Αυτή η μη ειδική ανταπόκριση όλων των μελετώμενων σειρών στον SCH, αποδόθηκε κατόπιν στο γεγονός ότι αυτοί οι ανταγωνιστές δεν ήταν απολύτως εκλεκτικοί για τον PAR-1 όπως πιστευόταν, όταν σχεδιάστηκαν. Ο συγκεκριμένος ανταγωνιστής επιλέχθηκε μεταξύ των λίγων, της μοναδικής κατηγορίας που υπήρχε, όταν ξεκίνησαν τα πειράματα. Η θρομβίνη υπερδιπλασίασε τον πολλαπλασιασμό της σειράς PC3 και δεν είχε κανένα αποτέλεσμα στον πολλαπλασιασμό της σειράς MDA-231. Το τελευταίο συμφωνεί και με προηγούμενη έρευνα όπου καταδείχθηκε ότι η θρομβίνη δεν επηρεάζει τον πολλαπλασιασμό, αλλά μειώνει τη μεταστατικότητα της σειράς MDA-231 (Kamath et al., 2001). Η αύξηση του πολλαπλασιασμού των καρκινικών κυττάρων του προστάτη PC3, από τη θρομβίνη γίνεται μέσω ενεργοποίησης του υποδοχέα της PAR-1, και μέσω ενεργοποίησης της ΜΑΡ κινάσης, όπως φάνηκε από τα πειράματα στα οποία χρησιμοποιήθηκε ο ειδικός αγωνιστής του PAR1, το εξαπεπτίδιο SFLLRN. Από κάποια πρώτα ενδεικτικά πειράματα φαίνεται ότι η ενεργοποίηση της ΜΑΡΚ λαμβάνει χώρα μέσω διενεργοποίησης του EGFR, κάτι που έχει αποδειχθεί για άλλους GPCRs. Η έκφραση του PAR1 όπως μελετήθηκε με RT-PCR, σε δείγματα ασθενών που χειρουργήθηκαν για κακοήθεις όγκους στους πνεύμονες, ανιχνεύθηκε σε όλα τα δείγματα καρκινικού ιστού. Η υψηλότερη έκφραση του PAR1 ανιχνεύθηκε στον ασθενή με μελάνωμα και στον ασθενή του υψηλότερου σταδίου. Φυσικά ο αριθμός των ασθενών που μελετήθηκαν δεν αρκεί για εξαγωγή συμπερασμάτων, αλλά τα παραπάνω αποτελέσματα συμφωνούν με τα γνωστά ως σήμερα ευρήματα για τον PAR1. Παραμένει να διευκρινιστεί η σημασία της αυξημένης έκφρασης του PAR1 σε ασθενείς με κακοήθεις όγκους στους πνεύμονες, αφού πρώτα επιβεβαιωθεί αυτή η αυξημένη έκφραση σε μεγαλύτερο αριθμό ασθενών. / From the onset of studies of PAR1, it has been concluded that this receptor is closely related to cancer. This relationship has been established after various experiments in cancer cell lines and in experimental animal models. The purposes of the present study can be summarized as follows: To explore the expression of PAR1 in cell lines established from human solid tumors and specifically PC3 and LNCaP from prostate cancer and MDA-231 and MCF-7 from breast cancer. To explore the suppression of PAR1 to the above cell lines in cell division. To determine if the activation of PAR1 to the above cell lines leads to MAPK phosphorylation. And ultimatilly, to explore the expression of PAR1 in patients that have been operated for tumor in lungs in Patras University Hospitall by Dr. D. Dougenis and colleagues. It was found that PAR1 is strongly expressed in highly metastatic cell lines PC3 and MDA-231, opposite to the cells LNCaP and MCF-7 that have lower metastatic capacity. The finding for the breast cancer cells MDA-231 and MCF-7 was according to published results (Kamath et al., 2001). PAR1 selective antagonist SCH 79797, reduced cell survival and DNA synthesis to all the above mentioned cell lines, independently of PAR1 expression. These non-specific results contributed to the recent fact that these antagonists were not PAR1 selective finally. Thrombin caused more than 100% induction of DNA synthesis in PC3 cells and had no effect in MDA-231 cells in accordance with published results that thrombin reduces the metastatic capacity of MDA-231 cells (Kamath et al., 2001). This effect of thrombin in PC3 cells, is mediated by activation of PAR1 as it was shown with the use of the selective agonist peptide SFLLRN. The activation of PAR1 by thrombin in PC3 cells leads to MAPK activation as it was shown by Western analysis. Furthrmore, preliminary experiments indicate that MAPK phosphorylation after PAR1 activation may be result of EGFR transactivation. In the sample tissues from patients, PAR1 expression was detected in all cancers with different ODs. The number of the samples is not enough to lead to conclusions, but there are some important observations. The highest level of PAR1 expression as was detected by RT-PCR were found to the sample tissues of the patient diagnosed for melanoma and of the patient with the most advanced stage of lung cancer. More patients shoulde be examined and more experiments to be done in order to proceed to conclusions for the significance of PAR1 in lung cancer.

Platelets act as a fundamental component of the hemostatic process and their activation leads to the formation of a stable clot at the injured endothelium surface. Thrombin, as the important physiological agonist, activates platelets through protease-activated receptors (PARs). Protease-activated receptors are one of the major receptors in platelets and belong to the seven-transmembrane G-protein couple receptor family. Four protease-activated receptors are found, named as PAR1, PAR2, PAR3 and PAR4. Human platelets express PAR1 and PAR4 and murine platelets express PAR4 and PAR3 instead of PAR1. Thrombin activates PARs through a unique mechanism, involving the cleavage of N-terminus of PAR receptors and the newly exposed N-terminus acts as its own tethered ligand to bind and activate the receptor. In this study, we characterized a new PAR1 specific activating peptide (TFRRRLSRATR), generated from the c-terminus of human platelet P2Y1 receptor, and evaluated its biological function. This peptide activated platelets in a concentration-dependent manner, causing shape change, aggregation, secretion and calcium mobilization. Its activation is completely inhibited by using BMS200261, a PAR-1 specific antagonist. Its specificity to PAR1 receptor is further confirmed by using TFRRR-peptide-pretreated washed platelets and murine platelets. The shape change induced by 10 microM peptide was totally abolished by Y-27632, an inhibitor of p160ROCK which is the downstream signal of G12/13 pathways. The TFRRR-peptide, YFLLRNP, and the physiological agonist thrombin selectively activated G12/13 pathways at low concentrations and began to activate both Gq and G12/13 pathways with increased concentrations. Similar to SFLLRN, the TFRRR-peptide caused phosphorylation of Akt and Erk in a P2Y12 receptor-dependent manner, and p-38 MAP kinase activation in a P2Y12-independent manner. The effects of this peptide are elicited by the first six amino acids (TFRRRL) whereas the remaining peptide (LSRATR), TFERRN, or TFEERN had no effects on platelets. Beside thrombin, PARs also can be activated by other proteases. Previous studies in our lab show that plasmin, a major extracellular protease, activates both human and murine platelets through prototypical cleavage of PAR4 (Quinton et al., 2004). In this study, we continue our study and investigate the molecular basis for the differential activation of murine and human platelets by plasmin. Plasmin-induced full aggregation is achieved at lower concentrations (0.1 U/mL) in murine platelets as compared to human platelets (1 U/mL). In COS7 cells expressing the murine PAR4 (mPAR4) receptor, 1 U/mL plasmin caused a higher intracellular calcium mobilization than in cells expressing the human PAR4 (hPAR4) receptor. This difference was reversed when the tethered ligand sequences of mPAR4 and hPAR4 were interchanged through site-directed mutagenesis. This difference between human and murine PAR4 is not because of the cofactor effect of PAR3 in murine platelets by showing that in both transfected cell lines and platelet system, PAR3 inhibits plasmin-induced PAR4 stimulation. All of the data suggest that murine platelets are more sensitive to activation by plasmin than human platelets due to differences in the primary sequence of PAR4. In contrast to thrombin-dependent activation of platelets, wherein PAR3 acts as a co-receptor, mPAR3 inhibits plasmin-induced PAR4 activation. Abnormal platelet activation causes thrombus formation and induces pathological conditions including stroke and atherosclerosis. Antithrombotic therapy is a widely used therapeutic method for stroke. However, currently used agents based on the irreversible inhibition of the platelet cyclooxygenases 1 and 2 or inhibition of P2Y12 receptors can cause unexpected bleeding or resistant side effects. Antithrombotic therapy targeting thrombin signaling is one of the new treatments under investigation and PAR1 antagonists are now in clinical trials. In this study, we investigate the effect of one of thrombin receptors, protease-activated receptor 4 (PAR4) in mice transient middle cerebral artery occlusion/ reperfusion (tMCAO/R) model. Our data show that PAR4 -/- mice have more than 80% reduction in infarct volume and significant improved neurological and motor function after 1 h MCAO followed by 23 h reperfusion. Examination of cellular responses to tMCAO/R indicates that PAR4-/- mice have less cellular death. Platelet/endothelial and leukocyte/endothelial interactions have been shown to play a critical role in the inflammatory responses during cerebral ischemic/reperfusion injury. Comparing wild-type with PAR4-/- mice platelets/endothelial and leukocyte/endothelial interactions, deficiency of PAR4 causes a significant decrease in both platelet/endothelial and leukocyte/endothelial interactions. In addition, PAR4-/- mice attenuate blood-brain barrier (BBB) disruption during tMCAO/R. All the data suggest that deficiency of PAR4 will protect against brain ischemic injury though attenuation of cerebral inflammatory responses including inflammatory cells extravasation and BBB disruption. Protease-activated receptor 4 (PAR4) is the only thrombin receptor existing in both human and murine platelets. The data we get in this study also have a beneficial effect for human study and inhibition of PAR4 may provide a novel potential therapeutic strategy for ischemic injury. / Physiology

La grippe est une maladie respiratoire aigüe, due à une infection par des virus influenza et qui représente un problème important de santé publique. Une meilleure compréhension des interactions entre le virus influenza et son hôte nous permettra de mieux comprendre la physiopathologie de l'infection grippale, et donc, à terme, de mieux se protéger contre la maladie. La morbidité et la mortalité, causées par les infections grippales sévères, sont associées à une dérégulation de la réponse immunitaire, au niveau pulmonaire. Cette inflammation délétère serait à l'origine de dommages collatéraux du poumon, entrainant une diminution de la capacité respiratoire du patient. Bien que les mécanismes impliqués ne soient pas totalement élucidés, de récents travaux mettent en évidence un rôle central des cellules endothéliales dans la dérégulation de la réponse de l'hôte face à l'infection grippale. Lors d'une agression de l'endothélium, le processus physiologique de l'hémostase (activation plaquettaire, coagulation et fibrinolyse) s'active afin de permettre la cicatrisation de la plaie et de maintenir l'intégrité des vaisseaux sanguins. Dans de nombreuses maladies inflammatoires, la seule dérégulation de l'hémostase est directement liée à une réponse inflammatoire délétère. Lors de ma thèse, nous avons émis l'hypothèse que l'hémostase pouvait être à l'origine de la dérégulation inflammatoire durant les infections grippales. Nos données montrent le rôle de deux facteurs fortement impliqués dans l'hémostase : le récepteur activé par la thrombine, PAR-1 (Protease Activated Receptor J) ainsi que le plasminogène, dans l'inflammation délétère des poumons et dans la pathogénicité des virus influenza. Outre le rôle de l'hémostase, nous avons également pu mettre en évidence que le virus influenza incorpore des protéines cellulaires dans l'enveloppe virale, lui permettant d'échapper au système immunitaire, ce qui pourrait aussi contribuer à la dérégulation de la réponse de l'hôte. L'ensemble des résultats obtenus ont permis de mieux comprendre les mécanismes à l'origine d'une réponse immunitaire dérégulée dans les infections grippales et de proposer de nouvelles cibles thérapeutiques pour lutter contre la maladie / Influenza is an acute respiratory disease caused by infection with influenza virus and is a major public health problem. A better understanding of the interaction between influenza virus and host allow us to better understand the pathophysiology of influenza infection, and thus, ultimately, to better protect themselves against the disease. Morbidity and mortality caused by severe influenza infections are associated with dysregulation of the immune response in the lung. This deleterious inflammation is the cause of lung collateral damage, causing a decrease in the patient's breathing capacity. Although the mechanisms involved are not fully understood, recent studies point to a central role of endothelial cells in the deregulation of the host response to influenza infection. During endothelium aggression, the physiological process of hemostasis (platelet activation, coagulation and fibrinolysis) is activated in order to allow wound healing and to maintain the integrity of blood vessels. In many inflammatory diseases, the only dysregulation of hemostasis is directly linked to a deleterious inflammatory response. During my thesis, we hypothesized that hemostasis could be the cause of the inflammatory dysregulation during influenza infections. Our data show the role of two factors strongly involved in hemostasis: the thrombin activated receptor, PAR-1 (protease activated receptor 1) and plasminogen, in the deleterious lung inflammation and in the pathogenicity of influenza virus. Besides the role of hemostasis, we have also been able to show that the influenza virus incorporates cellular proteins in the viral envelope, allowing it to evade the immune system, which could also contribute to the deregulation of the host response. All the results obtained allowed to better understand the mechanisms involved in immune response dysregulation during influenza infection and suggest new therapeutic targets to fight against the disease