Real-world retention rates and effectiveness of secukinumab in psoriasis: Results from a multicenter cohort study (RAILWAY)

Psoriasis is a chronic, immune-mediated inflammatory skin disease with a high negative impact on patient's quality of life. Secukinumab, the first interleukin 17A inhibitor, has been used for the systemic treatment of psoriasis, but its long-term, real-world retention rates in Japan have not been fully investigated. In this multicenter, noninterventional, retrospective chart review study, the retention rate of secukinumab and its effectiveness among patients with psoriasis in Japan was evaluated up to 5 years. Data of patients who received secukinumab after December 26, 2014, were collected from medical charts obtained from seven sites, all certified for biologics use by the Japanese Dermatological Association. Patient characteristics, secukinumab retention, factors affecting secukinumab retention, reason for drug discontinuation, and effectiveness data were collected. The primary end point was secukinumab retention rate at week 52. A total of 123 patients were included in the analysis. Of these, 27 patients discontinued secukinumab by week 52, yielding a 78.0% (95% confidence interval, 69.6-84.4) retention rate at week 52. For patients whose Psoriasis Area and Severity Index (PASI) score was available, mean ± standard deviation PASI at baseline and at week 52 were 9.21 ± 7.37 and 1.4 ± 2.6, respectively. During the entire study period, "insufficient response" was the most common reason for discontinuation, and "history of biologics use" was a factor significantly associated with secukinumab discontinuation (hazard ratio, 1.72; p = 0.018). This study demonstrates the real-world retention rate and effectiveness of secukinumab in patients with psoriasis in Japan for up to 5 years and provides clinical insights into psoriasis treatment strategies.

Psoriasis patient preferences for the use of biologics during the coronavirus era

Understanding patient preferences concerning the use of biologics for psoriasis treatment can support proper treatment selection to satisfy their needs. In Japan, limited studies have reported psoriasis patients' preferences for the use of biologics, and many of those focused on the improvement of skin symptoms. The present study was conducted as a web-based questionnaire survey using the discrete choice experiment approach to investigate the preferences of psoriasis patients for the use of biologics, as well as to describe social and clinical factors that influence these preferences. The following attributes were selected for the discrete choice experiment: efficacy at 1 year, risk of serious infections requiring hospitalization, incidence of injection site reactions, administration route and visits, co-payment, indications, and efficacy on skin symptoms and other manifestations (the last two have not been evaluated in previous studies). Data were collected from October 4 to October 8, 2021. An analysis of data from 357 psoriasis patients indicated that the most preferred attributes for biologics selection were administration route and visits, followed by the risk of serious infections requiring hospitalization. Some differences were observed among specific subgroups. This study demonstrated that patients with psoriasis prefer biologics with a less frequent administration route and visit schedule and a lower risk of serious infections requiring hospitalization, which contrasts with the results obtained in previous studies where the highest importance was placed on drug effectiveness. These results may reflect the personal and social impact of the coronavirus disease outbreak at the time of the survey. The results of this study might help physicians properly select biologics that satisfy psoriasis patients' needs, leading to better treatment adherence.

P–611 Innovative controlled ovarian stimulation (COS) for polycystic ovary syndrome (PCOS) produces high-quality oocytes and no ovarian hyper stimulation syndrome (OHSS)

Study question

How can we find an ovarian stimulation method that does not cause hyper stimulation syndrome but can produce a high pregnancy rate at one cycle?

Summary answer

This newly developed method for PCOS has a higher accumulative clinical outcome for one trial and no OHSS.

What is known already

Almost all conventional treatments for PCOS have managed to avoid OHSS by reducing the number of growing follicles, which are associated with high Estradiol levels and stimulate the production of vessel endothelial growth hormone (VEGF), leading to increased vessel permeability. Low dose FSH administration, In vitro maturation (IVM), Ovarian Drilling and Coasting have been performed to achieve this. However, their actual clinical outcome is still unsatisfactory.

Study design, size, duration

Evaluation of the efficiency of this method was conducted retrospectively at St. Mother Clinic. The embryonic development and the clinical outcome were studied for 34 PCOS patients during the period between November 2018 and December 2019.

Participants/materials, setting, methods

We started injections of FSH (150iu/ml), then we did ultrasound follicle monitoring. GnRH antagonist shots were started when the leading follicle reached 18mm and continued until the largest follicle was 22–24mm and the E2 value was over 4000pg/ml. Letrozole (2.5mg) and leuprorelin acetate (1.88mg) was injected as trigger. Two tablets each of Letrozole, Cabergoline and GnRH antagonist were given for 5 consecutive days after the oocyte retrieval. All embryos were cryopreserved.

Main results and the role of chance

Number of patients and cycles were 34 and 59. Average number of cryopreserved blastocysts was 6.12 (1–16). The frequencies of OHSS (mild, moderate, severe) were 29.4% (10/34), 0% (0/34), 0% (0/34). Average days between oocyte collection and withdrawal hemorrhage was 5.44(5–7). Cryopreservation rate was 100.0% (34/34). Clinical pregnancy rate and miscarriage rate was 42.3% (25/59) and 16.0% (4/25). The cumulative pregnancy rate was 73.7% (25/34). The four remaining unsuccessful cases still have 10,6,3 and 7 frozen embryos. So, there is a high possibility that they become successful, that would bring the cumulative pregnancy rate up to 82.3% (28/34).

Limitations, reasons for caution

This COS for PCOS seems promising, however it is premature to conclude that this method is established. This method requires caution monitoring for hormone level, follicle size and number and coagulant function. It also accompanied with the risk of ovarian hemorrhage on aspiration of a great number of oocytes.

Wider implications of the findings: This COS seems viable for PCOS cases. It could control the cohort of antral follicles with different doses of Letrozole to find the optimal COH method and it could become the first option for COS of PCOS.

Trial registration number

N/A

P–023 Innovative ultra-rapid vitrification method for five or fewer testicular spermatozoa from non-obstructive azoospermic men after microsurgical testicular sperm extraction (Micro-TESE)

Study question

What technique can be used to successfully cryopreserve five or fewer testicular spermatozoa from non-obstructive azoospermic men?

Summary answer

This method for cryopreserving five or fewer spermatozoa from non-obstructive azoospermic men showed a recovery rate above 90% and a survival rate of about 70%.

What is known already

Clinical outcomes of ICSI when using only five or fewer testicular spermatozoa after cryopreservation have been unsuccessful and are considered to be inferior to those using testicular fresh spermatozoa from Micro-TESE. A possible cause of these poor results has been the lack of a successful freezing technique. In these cases, repeated Micro-TESE and simultaneous oocyte pick up has been the only available treatment.

Study design, size, duration

Evaluation of the efficiency of cryopreservation by modified permeable cryoprotectant-free vitrification method (HTF supplemented with 0.1M sucrose and 10% SPS) for five or fewer testicular spermatozoa from 113 non-obstructive azoospermic men using Micro-TESE was conducted retrospectively at St. Mother Clinic between 2011 and 2018.

Participants/materials, setting, methods

This study included 113 non-obstructive azoospermic men. Each motile spermatozoon was carefully aspirated tail first into the pipette, put into a 2-μl microdroplet media of the vitrification medium near the tip of the Cryotop (Kitazato Corporation, Tokyo, Japan) submerged in liquid nitrogen vapor for 2 min and then immediately plunged in liquid nitrogen. The vitrified spermatozoa were warmed by dipping them into a droplet media. Successfully recovered motile sperm were selected and used for ICSI.

Main results and the role of chance

Number of patients, transfer cycles and collected sperms were 113, 192 and 560. Mean age of patients and their wives were 32.0±3.7y and 28.4±5.8y. Clinical pregnancy rate, miscarriage rate, live birth rate and number of live offspring were 24.0% (46/192), 19.6% (9/46), 19.3% (37/192) and 37 (Male: Female = 17: 20). Sperm recovery rate and survival rate were 90.3% (506/560) and 70.4% (356/506). Fertilization rate and mean number of transferred embryos were 51.6% (99/192) and 1.73 (1–2). Mean gestational weeks and mean body weight at birth were 39.23±5.27w and 2852.31±314.28g. No congenital anomalies were observed in any of the babies.

Limitations, reasons for caution

The maximum number of spermatozoa to which this method can be applied successfully is about 10. When the number of aspirated spermatozoa is over 10, some of them change direction and reach the mineral oil, and once this happens, they cannot be expelled out of the pipette.

Wider implications of the findings: This technique is very useful for the cryopreservation of very small numbers of testicular spermatozoa (fewer than 10) in order to avoid or reduce Micro-TESE interventions.

Trial registration number

N/A

Impact of chronic urticaria on quality of life and work in Japan: Results of a real-world study

Little attention has been given to the burden of chronic urticaria (CU) in Japan compared with other skin diseases, such as atopic dermatitis (AD) and psoriasis. The primary objective of the RELEASE study was to evaluate the real‐life quality‐of‐life impairment in CU patients in Japan. Data were collected from 1443 urticaria, 1668 AD and 435 psoriatic patients; 552 urticaria patients who presented urticaria symptoms for over 6 weeks were defined as CU. The mean Dermatology Life Quality Index (DLQI) total score was 4.8, 6.1 and 4.8 in CU, AD and psoriatic patients, respectively. Disease control of urticaria evaluated by the Urticaria Control Test (UCT) and DLQI exhibited a strong correlation with a Spearman's rank correlation coefficient of −0.7158. CU and AD patients had relatively higher scores in all Work Productivity and Activity Impairment – General Health subscales except for absenteeism. At the time of the survey, approximately 64% of CU patients reported UCT scores of <12 and demonstrated higher work productivity loss and activity impairment versus patients with UCT scores of ≥12. Patients with lower UCT scores also displayed a higher percentage of dissatisfaction with their health state and the treatment they received. Approximately 85% of patients with CU had visited dermatology clinics, and less than 20% had visited hospital, indicating existence of a highly burdened population outside specialized centers. These results highlight the unmet medical needs of CU patients, suggesting the need to increase awareness of CU burden among both physicians and patients and to pursue improved real‐life patient care.

Should sexual intercourse be avoided during the embryo transfer cycle? Life-threatening ruptured heterotopic pregnancy after single thawed embryo transfer: case report and review of the literature

BACKGROUND

To report the life-threatening complication of a raptured heterotopic pregnancy occurring from thawed single embryo transfer.

CASE REPORT

A 33-year-old woman underwent in vitro fertilization (IVF) under a step-up regimen. After oocyte collection, blastocysts were frozen, and a single frozen-thawed blastocyst was then transferred according to the natural cycle. On day 17 after embryo transfer, an intrauterine pregnancy was confirmed. On day 28, she complained of sudden abdominal pain and ultrasonography revealed marked fluid retention in the peritoneal cavity. Emergency laparoscopy was performed, revealing hemoperitoneum and a ruptured interstitial heterotopic pregnancy (HP), which was then resected laparoscopically. Because sexual intercourse had occurred shortly before the transfer, a HP comprising a spontaneous pregnancy and a pregnancy achieved by assisted reproductive technology was assumed. The fetus in the uterus survived and was delivered.

CONCLUSION

In this case, however, despite the single embryo transfer during the natural-cycle frozen-thawed embryo transfer process, the risk of life-threatening complication as a HP as a consequence of spontaneous pregnancy after sexual intercourse remained.

Colocalization of neutrophils, extracellular DNA and coagulation factors during NETosis: Development and utility of an immunofluorescence-based microscopy platform

BACKGROUND

Neutrophils, the most populous innate immune cell type, are the first responders to sites of infection and inflammation. Neutrophils can release their DNA to form extracellular traps (NETs), webs of DNA and granular proteases that contribute to pathogen clearance and promote thrombus formation. At present, the study of NETs is in part limited to the qualitative analysis of fluorescence microscopy-based images, thus quantification of the interactions between NETs and coagulation factors remains ill-defined.

AIM

Develop a quantitative method to measure the spatial distribution of DNA and colocalization of coagulation factor binding to neutrophils and NETs utilizing fluorescence-based microscopy.

APPROACH

Human neutrophils were purified from peripheral blood, bound to fibronectin and treated with the PKC-activator phorbol myristate acetate (PMA) to induce neutrophil activation and NETs formation. Samples were incubated with purified coagulation factors or plasma before staining with a DNA-binding dye and coagulation factor-specific antibodies. The spatial distribution of DNA and coagulation factors was imaged via fluorescence microscopy and quantified via a custom-built MATLAB-based image analysis algorithm. The algorithm first established global thresholding parameters on a training set of fluorescence image data and then systematically quantified intensity profiles across treatment conditions. Quantitative comparison of treatment conditions was enabled through the normalization of fluorescent intensities using the number of cells per image to determine the percent and area of DNA and coagulation factor binding per cell.

RESULTS

Upon stimulation with PMA, NETs formation resulted in an increase in the area of DNA per cell. The coagulation factor fibrinogen bound to both the neutrophil cell body as well as NETs, while prothrombin, FX and FVIIa binding was restricted to the neutrophil cell body. The Gla domain of FX was required to mediate FX-neutrophil binding. Activated protein C (APC), but not Gla-less APC, bound to neutrophil cell bodies and NETs in a punctate manner. Neither FXIIa nor FXIa were found to bind either neutrophil cell bodies or NETs. Fibrinogen binding was dependent on extracellular DNA, while FX and APC required phosphatidylserine exposure for binding to activated neutrophils.

CONCLUSIONS

We have developed a quantitative measurement platform to define the spatial localization of fluorescently-labeled coagulation factor binding to neutrophils and extracellular DNA during NETosis.

Biorheology of platelet activation in the bloodstream distal to thrombus formation

Thrombus growth at the site of vascular injury is mediated by the sequential events of platelet recruitment, activation and aggregation concomitant with the initiation of the coagulation cascade, resulting in local thrombin generation and fibrin formation. While the biorheology of a localized thrombus formation has been well studied, it is unclear whether local sites of thrombin generation propagate platelet activation within the bloodstream. In order to study the physical biology of platelet activation downstream of sites of thrombus formation, we developed a platform to measure platelet activation and microaggregate formation in the bloodstream. Our results show that thrombi formed on collagen and tissue factor promote activation and aggregation of platelets in the bloodstream in a convection-dependent manner. Pharmacological inhibition of the coagulation factors (F) X, XI or thrombin dramatically reduced the degree of distal platelet activation and microaggregate formation in the bloodstream without affecting the degree of local platelet deposition and aggregation on a surface of immobilized collagen. Herein we describe the development and an example of the utility of a platform to study platelet activation and microaggregate formation in the bloodstream (convection-limited regime) relative to the local site of thrombus formation.

Abstract 56: Coagulation Factor XI Promotes Distal Platelet Activation and Single Platelet Consumption in the Bloodstream Under Shear Flow

Objective: Coagulation factor XI (FXI) has been shown to contribute to thrombus formation on collagen or tissue factor (TF)-coated surfaces in vitro and in vivo by enhancing thrombin generation. Whether the role of the intrinsic pathway of coagulation is restricted to the local site of thrombus formation is unknown. This study was designed to determine whether FXI could promote both proximal and distal platelet activation and aggregate formation in the bloodstream.

Approach and Results: Pharmacological blockade of FXI activation or thrombin activity in blood did not affect local platelet adhesion, yet reduced local platelet aggregation, thrombin localization and fibrin formation on immobilized collagen and TF under shear flow, ex vivo . Downstream of the thrombus formed on immobilized collagen or collagen and 10 pM TF, platelet CD62P expression and microaggregate formation and progressive platelet consumption were significantly reduced in the presence of FXI-function blocking antibodies or a thrombin inhibitor in a shear rate- and time-dependent manner. In a non-human primate model of thrombus formation, we found that inhibition of FXI reduced single platelet consumption in the bloodstream distal to a site of thrombus formation.

Conclusions: This study demonstrates that the FXI-thrombin axis contributes to distal platelet activation and procoagulant microaggregate formation in the blood flow downstream of the site of thrombus formation. Our data highlights FXI as a novel therapeutic target for inhibiting distal platelet activation without affecting proximal platelet adhesion.

Coagulation Factor XI Promotes Distal Platelet Activation and Single Platelet Consumption in the Bloodstream Under Shear Flow

OBJECTIVE

Coagulation factor XI (FXI) has been shown to contribute to thrombus formation on collagen or tissue factor-coated surfaces in vitro and in vivo by enhancing thrombin generation. Whether the role of the intrinsic pathway of coagulation is restricted to the local site of thrombus formation is unknown. This study was aimed to determine whether FXI could promote both proximal and distal platelet activation and aggregate formation in the bloodstream.

APPROACH AND RESULTS

Pharmacological blockade of FXI activation or thrombin activity in blood did not affect local platelet adhesion, yet reduced local platelet aggregation, thrombin localization, and fibrin formation on immobilized collagen and tissue factor under shear flow, ex vivo. Downstream of the thrombus formed on immobilized collagen or collagen and 10 pmol/L tissue factor, platelet CD62P expression, microaggregate formation, and progressive platelet consumption were significantly reduced in the presence of FXI function-blocking antibodies or a thrombin inhibitor in a shear rate- and time-dependent manner. In a non-human primate model of thrombus formation, we found that inhibition of FXI reduced single platelet consumption in the bloodstream distal to a site of thrombus formation.

CONCLUSIONS

This study demonstrates that the FXI-thrombin axis contributes to distal platelet activation and procoagulant microaggregate formation in the blood flow downstream of the site of thrombus formation. Our data highlight FXI as a novel therapeutic target for inhibiting distal platelet consumption without affecting proximal platelet adhesion.

Critical behavior of subcellular density organization during neutrophil activation and migration

Physical theories of active matter continue to provide a quantitative understanding of dynamic cellular phenomena, including cell locomotion. Although various investigations of the rheology of cells have identified important viscoelastic and traction force parameters for use in these theoretical approaches, a key variable has remained elusive both in theoretical and experimental approaches: the spatiotemporal behavior of the subcellular density. The evolution of the subcellular density has been qualitatively observed for decades as it provides the source of image contrast in label-free imaging modalities (e.g., differential interference contrast, phase contrast) used to investigate cellular specimens. While these modalities directly visualize cell structure, they do not provide quantitative access to the structures being visualized. We present an established quantitative imaging approach, non-interferometric quantitative phase microscopy, to elucidate the subcellular density dynamics in neutrophils undergoing chemokinesis following uniform bacterial peptide stimulation. Through this approach, we identify a power law dependence of the neutrophil mean density on time with a critical point, suggesting a critical density is required for motility on 2D substrates. Next we elucidate a continuum law relating mean cell density, area, and total mass that is conserved during neutrophil polarization and migration. Together, our approach and quantitative findings will enable investigators to define the physics coupling cytoskeletal dynamics with subcellular density dynamics during cell migration.

Abstract 197: p300-Based Acetylation Signaling Regulates Cytoskeletal Reorganization and Procoagulant Phenotype of Platelets

Introduction: Reversible acetylation signaling catalyzed by acetyltransferases and deacetylases regulates multiple cellular events. We recently showed a role for deacetylation signaling in platelet function via the actions of the deacetylase enzyme HDAC6. Here we investigate the role of acetylation mediated by the p300 class of acetyltransferase proteins in platelet function.

Methods: To test the hypothesis that p300 acetylation signaling controls cytoskeletal remodeling and the exposure of phosphatidylserine (PS) in platelets, we used cell biological and hematological methods, including enzymatic assays, microscopy, cell sorting, aggregometry and in vitro assays of thrombus formation.

Results: Platelets express high levels of p300 protein. Upon stimulation with the glycoprotein VI (GPVI) agonist collagen-related peptide (CRP), total platelet acetyltransferase enzyme activity increases. Pre-treatment of platelets with pharmacological inhibitors of p300 blocks agonist-induced acetyltransferase activity and prevents the acetylation of p300 substrate proteins. Inhibition of p300 blocked the deacetylation of HDAC6 and tubulin and disrupted the platelet tubulin cytoskeleton. p300 inhibition also increased basal platelet PS exposure via a caspase-dependent apoptotic pathway. On a functional level, p300 inhibition prevented platelet shape change, aggregation and spreading while increasing the procoagulant activity of platelets in whole blood.

Conclusions: These results suggest that p300-based acetylation signaling regulates separable aspects of platelet function. p300 plays a role in the regulation of the platelet cytoskeleton as well as PS exposure to effect platelet spreading, aggregation, thrombus formation as well as platelet procoagulant activities. Future studies of the platelet acetylome will aim to identify p300 target substrates and specify roles for p300 in in the context of platelet activation, thrombus formation and pathologies of the cardiovascular system.

Acknowledgements: This work is funded by the American Heart Association (13POST13730003 to J.E.A. and 13EIA12630000 to O.J.T.M.) and the National Institutes of Health (R01HL101972 to O.J.T.M.).

Histone deacetylase 6-mediated deacetylation of α-tubulin coordinates cytoskeletal and signaling events during platelet activation

The tubulin cytoskeleton plays a key role in maintaining the characteristic quiescent discoid shape of resting platelets. Upon activation, platelets undergo a dramatic change in shape; however, little is known of how the microtubule system contributes to regulating platelet shape and function. Here we investigated the role of the covalent modification of α-tubulin by acetylation in the regulation of platelet physiology during activation. Superresolution microscopy analysis of the platelet tubulin cytoskeleton showed that the marginal band together with an interconnected web of finer tubulin structures collapsed upon platelet activation with the glycoprotein VI (GPVI)-agonist collagen-related peptide (CRP). Western blot analysis revealed that α-tubulin was acetylated in resting platelets and deacetylated during platelet activation. Tubacin, a specific inhibitor of the tubulin deacetylase HDAC6, prevented tubulin deacetylation upon platelet activation with CRP. Inhibition of HDAC6 upregulated tubulin acetylation and disrupted the organization of the platelet microtubule marginal band without significantly affecting platelet volume changes in response to CRP stimulation. HDAC6 inhibitors also inhibited platelet aggregation in response to CRP and blocked platelet signaling events upstream of platelet Rho GTPase activation. Together, these findings support a role for acetylation signaling in controlling the resting structure of the platelet tubulin marginal band as well as in the coordination of signaling systems that drive platelet cytoskeletal changes and aggregation.

p21-Activated kinase (PAK) regulates cytoskeletal reorganization and directional migration in human neutrophils

Neutrophils serve as a first line of defense in innate immunity owing in part to their ability to rapidly migrate towards chemotactic factors derived from invading pathogens. As a migratory function, neutrophil chemotaxis is regulated by the Rho family of small GTPases. However, the mechanisms by which Rho GTPases orchestrate cytoskeletal dynamics in migrating neutrophils remain ill-defined. In this study, we characterized the role of p21-activated kinase (PAK) downstream of Rho GTPases in cytoskeletal remodeling and chemotactic processes of human neutrophils. We found that PAK activation occurred upon stimulation of neutrophils with f-Met-Leu-Phe (fMLP), and PAK accumulated at the actin-rich leading edge of stimulated neutrophils, suggesting a role for PAK in Rac-dependent actin remodeling. Treatment with the pharmacological PAK inhibitor, PF3758309, abrogated the integrity of RhoA-mediated actomyosin contractility and surface adhesion. Moreover, inhibition of PAK activity impaired neutrophil morphological polarization and directional migration under a gradient of fMLP, and was associated with dysregulated Ca(2+) signaling. These results suggest that PAK serves as an important effector of Rho-family GTPases in neutrophil cytoskeletal reorganization, and plays a key role in driving efficient directional migration of human neutrophils.

Role of coagulation in the recruitment of colon adenocarcinoma cells to thrombus under shear

Colorectal cancer metastases can appear on the peritoneum and in lymph nodes, liver, and lungs, suggesting both hematogenous and lymphatic spreading of the primary tumor. While antithrombotic agents have been shown to reduce both long-term incidence and metastasis, the role of coagulation in facilitating metastasis is ill defined. We investigated the kinetics and molecular mechanisms of metastatic colon adenocarcinoma cell recruitment to thrombi under shear flow, ex vivo. Platelet aggregates were formed by perfusing citrated anticoagulated whole blood over immobilized fibrinogen or fibrillar collagen. Thrombi were formed by perfusing recalcified whole blood over fibrinogen or fibrillar collagen in the presence of coagulation. Cultured colon adenocarcinoma cells (SW620) were perfused either during or following platelet aggregate or thrombus formation. The degree of transient tumor cell interactions (recruitment, rolling, and release) and the number of firmly adhered tumor cells were quantified using fluorescence microscopy. Platelet aggregates and thrombi formed on either fibrinogen- or fibrillar-collagen supported SW620 cell interactions and adhesion under shear. Thrombi or fibrin supported a greater degree of SW620 cell interactions and adhesion compared with platelet aggregates or fibrinogen, respectively, demonstrating that coagulation promoted SW620 cell recruitment under shear. Interestingly, in the absence of anticoagulation, we observed SW620 preferentially binding to thrombus-bound polymorphonuclear leukocytes (PMNs). The addition of purified PMNs to thrombi resulted in a doubling of the number of interacting and bound SW620 cells. Since thrombi often accumulate and activate leukocytes, our findings suggest that leukocytes may play a role in localizing metastases to sites of thrombogenesis.

The PAK system links Rho GTPase signaling to thrombin-mediated platelet activation

Regulation of the platelet actin cytoskeleton by the Rho family of small GTPases is essential for the proper maintenance of hemostasis. However, little is known about how intracellular platelet activation from Rho GTPase family members, including Rac, Cdc42, and Rho, translate into changes in platelet actin structures. To better understand how Rho family GTPases coordinate platelet activation, we identified platelet proteins associated with Rac1, a Rho GTPase family member, and actin regulatory protein essential for platelet hemostatic function. Mass spectrometry analysis revealed that upon platelet activation with thrombin, Rac1 associates with a set of effectors of the p21-activated kinases (PAKs), including GIT1, βPIX, and guanine nucleotide exchange factor GEFH1. Platelet activation by thrombin triggered the PAK-dependent phosphorylation of GIT1, GEFH1, and other PAK effectors, including LIMK1 and Merlin. PAK was also required for the thrombin-mediated activation of the MEK/ERK pathway, Akt, calcium signaling, and phosphatidylserine (PS) exposure. Inhibition of PAK signaling prevented thrombin-induced platelet aggregation and blocked platelet focal adhesion and lamellipodia formation in response to thrombin. Together, these results demonstrate that the PAK signaling system is a key orchestrator of platelet actin dynamics, linking Rho GTPase activation downstream of thrombin stimulation to PAK effector function, MAP kinase activation, calcium signaling, and PS exposure in platelets.

Lysophosphatidylcholine enhances NGF-induced MAPK and Akt signals through the extracellular domain of TrkA in PC12 cells

Lysophosphatidylcholine (LPC) is one of the major lysophospholipids mainly generated by phospholipase A₂ (PLA₂)-mediated hydrolysis of phosphatidylcholine (PC). We previously found that LPC displays neurotrophin-like activity in the rat pheochromocytoma PC12 cells and in cerebellar granule neurons, but the molecular mechanism remains unclear. We report here that LPC specifically enhances nerve growth factor (NGF)-induced signals in PC12 cells. When PC12 cells were treated with NGF, MAPK was phosphorylated, but this phosphorylation was significantly elevated when LPC was added together. In accordance, NGF-induced expression of immediate early genes, c-fos and NGF-IA, was upregulated by LPC. Phosphorylation of the upstream components, MEK and NGF receptor TrkA, was also promoted by LPC, which was in line with increased phosphorylation of Akt. In contrast, LPC did not enhance epidermal growth factor (EGF)-, basic fibroblast growth factor-, or insulin-like growth factor-1-induced signals. Studies using TrkA/EGF receptor chimeras demonstrated that the extracellular domain, but not the transmembrane or intracellular domains, of TrkA is responsible for the effect of LPC. Exogenously-added secretory PLA₂ (sPLA₂) enhanced NGF-induced MAPK phosphorylation at a comparable level to LPC, suggesting that LPC generated in situ by sPLA₂-mediated hydrolysis of membrane PC stimulated NGF-TrkA signal. Taken together, these results indicate a specific role and function of LPC on NGF-TrkA signaling pathway.

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LPC potentiates NGF-induced MAPK and Akt phosphorylation in PC12 cells.

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LPC enhances NGF-induced MEK and TrkA phosphorylation.

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LPC does not affect the signals of EGF, FGF, and IGF-1.

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The effect of LPC requires the extracellular domain of TrkA.

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sPLA2 also potentiates NGF-induced MAPK phosphorylation.