Platelet Depletion Research Articles

Abstract B036: Platelets promote in vitro osteosarcoma cell migration and in vivo metastatic lung seeding

Abstract Osteosarcoma (OS) is the most common primary bone cancer worldwide where it mainly affects adolescents. Metastatic OS has a 20% survival rate and treatment options remain poor, thus understanding mechanisms that contribute to OS metastasis is critical for improved patient outcomes. Platelets, commonly recognized for their role in hemostasis, have been shown to promote metastasis in several cancer models. However, most previous studies investigating platelet contributions to metastasis have focused on carcinomas while their role in osteosarcoma remains poorly understood. Previous studies by our lab have shown that platelet interactions with breast cancer cells resulted in increased migration in vitro and increased lung metastases in vivo. Thus, we hypothesized that OS cell migration will be enhanced in the presence of platelets, and that platelet depletion in vivo will inhibit OS lung seeding. Cell suspensions of SaOs2 and MG63.3 cells in serum free media were fluorescently stained and seeded, in triplicates, in the top chamber of an 8um pore Fluoroblock migration assay wells. In the bottom chamber, media and either Tyrode’s buffer or 1.5x106 isolated human platelets were added. The presence of platelets resulted in a 3.5- and 4.6-fold increase of migrated MG63.3 and SaOs2 cells respectively. For in vivo analysis, cohorts of eight-week-old, male Nod Scid-Gamma (NSG), Nod Scid, and Nude mice were randomly assigned to either the control or platelet depletion group. Mice were depleted of platelets by administration of Anti-Platelet glycoprotein Ib alpha (GPIbα) antibody and, 5x105 GFP transduced MG63.3 cells were injected via tail vein. 24 hrs later, the mice were euthanized, and lungs were collected and microscopically imaged. Platelet depletion in NSG mice resulted in a 48% reduction in MG63.3 lung seeding compared to the isotype control recipient mice. This result was more dramatic in the less immunocompromised Nude and Nod Scid mice with a 61% and 87% reduction of MG63.3 lung seeding in the platelet depleted mice respectively. Finally, RNAseq and was performed on seven OS cell lines co-cultured with isolated mouse platelets, and alterations in gene expression were compared to control cells. Gene Enrichment Set Analysis (GSEA) of the data indicated that platelet co-incubation significantly upregulated pathways related to inflammatory responses, Tumor Necrosis Factor (TNF)-a signaling, and Interleukin (IL)-6 signaling. These results suggest that platelet secreted factors facilitate OS cell migration in vitro while an immune dependent mechanism is involved in the role of platelets in the in vivo lung seeding of OS cells. Citation Format: Olivia K. Travis, Ruishan Wang, Myriam Labelle. Platelets promote in vitro osteosarcoma cell migration and in vivo metastatic lung seeding [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr B036.

Platelets play a dual role in the pathophysiology of transfusion-related acute lung injury

Platelets are increasingly recognized as key regulators of inflammatory and immune responses, through their interaction with endothelium and immune cells. Therefore they might have a role in transfusion-related acute lung injury (TRALI), in which endothelial cells and neutrophils are the key players. In this study, by a classic TRALI animal model, combining a custom-designed system for intravital confocal microscopy of pulmonary microvasculature and a platelet tracking technique, we found that thrombin-activated platelets transfusion aggravated TRALI while resting platelets transfusion alleviated TRALI. Promoting endogenous platelets activation also aggravated TRALI while inhibiting endogenous platelets activation alleviated TRALI. Activated platelets interfered with the stability of endothelial barrier function while resting platelets modulated the activation of neutrophils. Anti-thrombin could alleviate TRALI, which was not reproduced upon anti-GPIIbIIIa or anti-P-selectin In conclusion, platelets might play a dual role (protective and pathogenic) in TRALI, the balance between the two roles is highly dependent on whether platelets are activated by thrombin or not. This might explain the conflicting results of previous researches studying the contribution of platelets in TRALI by platelet depletion technology, in which the induction of TRALI and the condition of animals were different, hence the state of platelets during TRALI was different. Moreover, anti-platelet-activation (such as anti-thrombin) might be a better approach than anti-activated-platelets (such as anti-P-selectin) to search for potential therapies in TRALI. Considering the involvement of thrombin-activated platelets in TRALI, anti-thrombin might be needed when blood component transfusion is performed.

In-silico selection of appropriate signal peptides for romiplostim secretory production in Escherichia coli

BackgroundThrombocytopenia is a prevalent condition caused by a reduction in platelet production, increased platelet depletion, or a combination of both processes. Romiplostim, the most potent drug and the only thrombopoietin (TPO) receptor agonist, consists of four TPO receptor–activating peptides fused as a fusion protein to the human IgG1 heavy chain segment. Romiplostim could be produced by recombinant DNA technology in Escherichia coli. Extracellular and periplasmic secretion using signal peptides (SPs) of the recombinant proteins could have several advantages in purification and protein recovery. SPs are short amino-acid sequences used in protein translocation through various membranes. The structure of the different SPs identified in various bacteria and their compatibility with the protein could affect the transfer success and efficacy. ObjectiveThis study aimed to identify the best SP for extracellular secretion of romiplostim to facilitate its purification and reduce production costs in E. coli. MethodsThe amino acid sequences of the SPs and the position of their cleavage sites in the proteins were evaluated using the Signal 5.0 server. The solubility of the proteins produced in E. coli was predicted by protein-sol. The physicochemical parameters of the SPs were analyzed by ProtParam using the ExPASy server. Results/ConclusionWe found that SfmC is the most suitable candidate, followed by TorT and bla. However, this result should be confirmed by further experimental assessment. Furthermore, for the successful secretion of a recombinant protein, the optimal growth conditions should be controlled in addition to a suitable SP.

Abstract PR008: Overcoming PDAC T cell therapy barriers with CD47-targeted costimulatory fusion proteins

Abstract T cell therapy is a promising immunotherapy treatment option that uses genetically modified immune cells (T cells) to eliminate tumors. This approach uses the patients’ own immune cells to generate a “living drug” and can avoid the toxic side effects of other common therapies, such as radiation or chemotherapies. However, the pancreatic ductal adenocarcinoma (PDAC) tumor microenvironment (TME) can establish several obstacles to protect the tumor from T cells, including delivery of inhibitory and death signals that shut down T cells, usurping metabolic nutrients, and recruiting and/or converting immune cells to inhibitory phenotypes that block the T cell response. CD47 is upregulated in PDAC tumors, and patients with CD47hi tumors exhibit worse survival. CD47 serves as a “don’t eat me” signal by binding to the SIRPα receptor on macrophages to block phagocytosis. CD47 expression also inhibits T cell-mediated tumor rejection by blocking cross-presentation of tumor antigens by SIRPα+ dendritic cells. Reagents that interfere with SIRPα-CD47 signaling, such as monoclonal antibodies, are currently in clinical trials and have been shown to synergize with chemotherapy in PDA models, but native CD47 expression can produce erythrocyte and platelet depletion. Costimulatory signals delivered by surface-bound receptors can initiate gene expression programs that address multiple issues in the PDAC TME by mechanisms such as lowering the threshold of activation, altering metabolic programming, and reducing exhaustion. We develop engineering strategies to deliver costimulatory signals to engineered T cells. Immunomodulatory fusion proteins (IFPs) combine the ectodomain of an inhibitory T cell receptor with an intracellular costimulatory signaling domain and we have shown in proof-of-concept studies that this effectively “replaces a brake with an accelerator” in CD8 T cells. We have found that generating IFPs is not as simple as indiscriminately fusing any two proteins together and we have developed critical design concepts that inform the selection of the fusion site, ectodomain and costimulatory signaling domain pairing, and immunological synapse localization to enhance signaling. To develop a CD47-targeted IFP, we combined the SIRPa ectodomain with the CD28 signaling endodomain and tested this technology with our mesothelin-targeted TCR-T cell platform. In in vitrostudies, SIRPa-CD28 T cells exhibited enhanced proliferation, accumulation, and tumor cytotoxicity. SIRPa IFP-T cells exhibited increased intratumoral accumulation and therapeutic efficacy in the KrasLSL-G12D/+; Trp53LSL-R172H/+;p48Cre/+ (KPC) model, without toxicity or erythrocyte depletion. Here we describe how a thoughtfully engineered fusion protein can “armor” T cells against multiple obstacles and significantly improve therapeutic efficacy against PDAC. Citation Format: Shannon Oda, Leah Schmidt, Ashley Thelen, Cody Jenkins, Edison Chiu, Aitong Ruan, Philip Greenberg. Overcoming PDAC T cell therapy barriers with CD47-targeted costimulatory fusion proteins [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr PR008.

Only Acute but Not Chronic Thrombocytopenia Protects Mice against Left Ventricular Dysfunction after Acute Myocardial Infarction.

Platelets are major players of thrombosis and inflammation after acute myocardial infarction (AMI). The impact of thrombocytopenia on platelet-induced cellular processes post AMI is not well defined. The left anterior descending artery was ligated in C57/Bl6 mice and in two thrombocytopenic mouse models to induce AMI. Platelets from STEMI patients and from C57/Bl6 mice displayed enhanced platelet activation after AMI. This allows platelets to migrate into the infarct but not into the remote zone of the left ventricle. Acute thrombocytopenia by antibody-induced platelet depletion resulted in reduced infarct size and improved cardiac function 24 h and 21 days post AMI. This was due to reduced platelet-mediated inflammation after 24 h and reduced scar formation after 21 days post AMI. The collagen composition and interstitial collagen content in the left ventricle were altered due to platelet interaction with cardiac fibroblasts. Acute inflammation was also significantly reduced in Mpl-/- mice with chronic thrombocytopenia, but cardiac remodeling was unaltered. Consequently, left ventricular function, infarct size and scar formation in Mpl-/- mice were comparable to controls. This study discovers a novel role for platelets in cardiac remodeling and reveals that acute but not chronic thrombocytopenia protects left ventricular function post AMI.

New functions of C3G in platelet biology: Contribution to ischemia-induced angiogenesis, tumor metastasis and TPO clearance.

C3G is a Rap1 guanine nucleotide exchange factor that controls platelet activation, aggregation, and the release of α-granule content. Transgenic expression of C3G in platelets produces a net proangiogenic secretome through the retention of thrombospondin-1. In a physiological context, C3G also promotes megakaryocyte maturation and proplatelet formation, but without affecting mature platelet production. The aim of this work is to investigate whether C3G is involved in pathological megakaryopoiesis, as well as its specific role in platelet mediated angiogenesis and tumor metastasis. Using megakaryocyte-specific C3G knockout and transgenic mouse models, we found that both C3G overexpression and deletion promoted platelet-mediated angiogenesis, induced by tumor cell implantation or hindlimb ischemia, through differential release of proangiogenic and antiangiogenic factors. However, only C3G deletion resulted in a higher recruitment of hemangiocytes from the bone marrow. In addition, C3G null expression enhanced thrombopoietin (TPO)-induced platelet production, associated with reduced TPO plasma levels. Moreover, after 5-fluorouracil-induced platelet depletion and rebound, C3G knockout mice showed a defective return to homeostatic platelet levels, indicating impaired platelet turnover. Mechanistically, C3G promotes c-Mpl ubiquitination by inducing Src-mediated c-Cbl phosphorylation and participates in c-Mpl degradation via the proteasome and lysosome systems, affecting TPO internalization. We also unveiled a positive role of platelet C3G in tumor cell-induced platelet aggregation, which facilitated metastatic cell homing and adhesion. Overall, these findings revealed that C3G plays a crucial role in platelet-mediated angiogenesis and metastasis, as well as in platelet level modulation in response to pathogenic stimuli.

Extracorporeal Perfusion of Vascularized Composite Tissues: The Bridging Role of an Emerging Technology in Reconstructive Microsurgery.

Complex defects with exposed critical structures after trauma or tumor resections are routinely reconstructed with free flaps. In the current practice of reconstructive microsurgery, the success rate at high-volume centers is above 95%. However, despite high success rates, free tissue transfer is not without challenges and limitations. The high degree of technical skill and resources needed to perform these lengthy procedures are not fulfilled at every institution globally. In some cases, the availability of recipient vessels can be limited due to vascular disease or prior treatments. Additionally, perioperative patient decompensation could affect outcomes, especially in complex multitrauma patients. Therefore, an improved approach is still needed to ensure reliable flap transfer even in the presence of unanticipated events and compromised recipient vasculature. Considering the major advancements over the past few decades, further improvement at this point requires a paradigm shifting approach. Machine perfusion, classically used in the preservation of solid organs, offers a wide variety of implications for vascularized composite tissues. An extracorporeal perfusion system (EPS), similar to that used during cardiopulmonary bypass, can be used to isolate the tissue via cannulation of the primary artery and vein and provide temporary support. The research on this topic1 can be furthered to enable clinical use of such technology in three distinct purposes (Fig. 1).Fig. 1.: Conceptual schematic of the potential clinical needs that an extracorporeal perfusion system could address. Machine perfusion support could serve three distinct purposes in reconstructive microsurgery: (1) bridge-to-anastomosis, (2) bridge-to-neovascularization for traditional flaps, and (3) bridge-to-neovascularization for bioengineered flaps. Even the uses for purposes 1 and 2 might be rarer occurrences; once the technology is established for purpose 3, its indications will continually expand to cover purposes 1 and 2. Created with BioRender.com.●Bridge-to-anastomosis: An EPS could be used to maintain support of the tissue until transplantation and successful anastomosis to mitigate ischemia/reperfusion injury. This purpose could support the tissues during delays between harvesting and anastomosis such as transportation of composite allografts, temporizing replants, or stabilization of decompensating patients.2,3 ●Bridge-to-neovascularization for traditional flaps: A portable/wearable EPS could be maintained following inset of the tissue over a wound bed and obviate the need to isolate and connect to recipient vessels. Extracorporeal support would continue until sufficient vessel ingrowth and tissue integration has occurred and can be weaned once the neovascularized network itself can provide full tissue support. The basic feasibility of the bridge-to-neovascularization approach in a vessel depleted wound was demonstrated in a small case series and showed that less than 2 weeks of external perfusion could allow sufficient neovascularization.4 ●Bridge-to-neovascularization for bioengineered flaps: The third application has the broadest implications for clinical impact and the field of bioengineered vascularized composite tissues. Currently, although there are limited studies, a major obstacle in engineered vascular networks is thrombosis.5 An EPS would be crucial to ensure successful transfer of engineered constructs with the benefit of closed-system isolated drug delivery (eg, heparin, vasodilatory agents) and conditioned perfusate (eg, platelet depletion) to prevent intravascular thrombosis. Similarly, this closed circuit could be used for delivery of growth factors to induce angiogenesis and facilitate integration of the transferred tissue. In summary, an EPS would address immediate and future problems in complex soft-tissue reconstruction. Recent advancements in the machine perfusion field and its integration with reconstructive microsurgery could open doors for a novel subspecialty. The challenging scenario of extensive tissue loss could be managed without the need for microsurgery using a compact perfusion system. DISCLOSURE The authors have no financial interest to declare in relation to the content of this article.

Platelet depletion enhances lethal, hemorrhagic and myotoxic activities of Bothrops asper snake venom in a murine model

Platelets play key roles in hemostasis, inflammation, immune response, and tissue repair. Although it is known that viperid snake venoms induce thrombocytopenia and platelet hypoaggregation, the roles of these effects in the overall outcome of envenoming are poorly known. This study aimed to assess the effect of platelet depletion on several toxic activities induced by the venom of the Central American viperid snake Bothrops asper in a mouse model. A profound thrombocytopenia was induced in mice by the administration of aspercetin, a C-type lectin-like protein that induces platelet agglutination and drop in platelet counts, while a control group was treated with saline solution instead. Upon envenoming, animals rendered thrombocytopenic developed a higher extent of local and systemic hemorrhage and local myonecrosis, as compared to control envenomed mice. In addition, the median lethal dose (LD50), determined by the intraperitoneal route, was significantly lower in thrombocytopenic mice, underscoring a higher toxicity of venom in these conditions. No difference in the value of LD50 between the two groups was observed when using the intravenous route of injection, and no difference was observed in the magnitude and time-course of footpad edema. Skeletal muscle regeneration was assessed 14 days after venom injection in muscle. Both experimental groups showed a similarly poor regeneration, suggesting that platelets do not play a key role in the regenerative process in these experimental conditions. Results indicate that depletion of platelets increases hemorrhagic and myotoxic effects, as well as overall toxicity, of B. asper venom, implying that platelets play a protective hemostatic role in this model of envenoming.

The safety and performance of the Spectra Optia apheresis system platelet depletion protocol in patients with elevated platelet counts.

Thrombocytosis is a presenting and progressive clinical feature found in multiple disease states. It is characterized by high platelet (PLT) counts (>450 × 109 /L) and can lead to thrombohemorrhagic events. Thrombocytapheresis or platelet depletion (PLTD) can be performed in acutely symptomatic patients suffering from thrombocytosis and may reduce or prevent acute serious complications associated with thrombocythemia thereby enabling patients to receive potentially curative high-dose chemotherapy. This report details the results from 2 clinical studies, one conducted in the European Union (EU) and one in the People's Republic of China, assessing the PLTD procedure on the Spectra Optia Apheresis System. The primary objective of both studies was to assess the safety and performance of the PLTD procedure in patients with elevated PLT counts. Data were collected from 56 participants completing 64 PLTD procedures. The mean percent change in PLT count and collection efficiency (CE1) was 55.1% and 68.5%, respectively. In the EU study, 6 participants experienced a total of 9 adverse events (AEs) and in the China study, 44 participants reported a total of 212 AEs. In both studies, the majority of AEs reported were Grade 2 or lower and no serious AEs, unanticipated adverse device effects, or AEs leading to death were reported. The data collected within these studies indicate that the PLTD procedure is well tolerated and effective at reducing circulating PLTs in patients suffering from thrombocytosis as evaluated by a percent decrease in PLT count, CE1, and AE incidence.

Platelets are indispensable for alveolar development in neonatal mice.

Previous studies suggest that platelets are involved in fetal and adult lung development, but their role in postnatal lung development especially after premature birth is elusive. There is an urgent need to scrutinize this topic because the incidence of bronchopulmonary dysplasia (BPD), a chronic lung disease after premature birth, remains high. We have previously shown impaired platelet biogenesis in infants and rats with BPD. In this study, we investigated the role of anti-CD41 antibody-induced platelet depletion during normal postnatal lung development and thrombopoietin (TPO)-induced platelet biogenesis in mice with experimental BPD. We demonstrate that platelet deficient mice develop a BPD-like phenotype, characterized by enlarged alveoli and vascular remodeling of the small pulmonary arteries, resulting in pulmonary arterial hypertension (PAH)-induced right ventricular hypertrophy (RVH). Vascular remodeling was potentially caused by endothelial dysfunction demonstrated by elevated von Willebrand factor (vWF) concentration in plasma and reduced vWF staining in lung tissue with platelet depletion. Furthermore, TPO-induced platelet biogenesis in mice with experimental BPD improved alveolar simplification and ameliorated vascular remodeling. These findings demonstrate that platelets are indispensable for normal postnatal lung development and attenuation of BPD, probably by maintaining endothelial function.

Platelet-Inspired Intravenous Nanomedicine for Injury-Targeted Direct Delivery of Thrombin to Augment Hemostasis in Coagulopathies.

Severe hemorrhage associated with trauma, surgery, and congenital or drug-induced coagulopathies can be life-threatening and requires rapid hemostatic management via topical, intracavitary, or intravenous routes. For injuries that are not easily accessible externally, intravenous hemostatic approaches are needed. The clinical gold standard for this is transfusion of blood products, but due to donor dependence, specialized storage requirements, high risk of contamination, and short shelf life, blood product use faces significant challenges. Consequently, recent research efforts are being focused on designing biosynthetic intravenous hemostats, using intravenous nanoparticles and polymer systems. Here we report on the design and evaluation of thrombin-loaded injury-site-targeted lipid nanoparticles (t-TLNPs) that can specifically localize at an injury site via platelet-mimetic anchorage to the von Willebrand factor (vWF) and collagen and directly release thrombin via diffusion and phospholipase-triggered particle destabilization, which can locally augment fibrin generation from fibrinogen for hemostatic action. We evaluated t-TLNPs in vitro in human blood and plasma, where hemostatic defects were created by platelet depletion and anticoagulation. Spectrophotometric studies of fibrin generation, rotational thromboelastometry (ROTEM)-based studies of clot viscoelasticity, and BioFlux-based real-time imaging of fibrin generation under simulated vascular flow conditions confirmed that t-TLNPs can restore fibrin in hemostatic dysfunction settings. Finally, the in vivo feasibility of t-TLNPs was tested by prophylactic administration in a tail-clip model and emergency administration in a liver-laceration model in mice with induced hemostatic defects. Treatment with t-TLNPs was able to significantly reduce bleeding in both models. Our studies demonstrate an intravenous nanomedicine approach for injury-site-targeted direct delivery of thrombin to augment hemostasis.

Platelet depletion does not alter long-term functional outcome after cerebral ischaemia in mice

Platelets are key mediators of thrombus formation and inflammation during the acute phase of ischaemic stroke. Particularly, the platelet glycoprotein (GP) receptors GPIbα and GPVI have been shown to mediate platelet adhesion and activation in the ischaemic brain. GPIbα and GPVI blockade could reduce infarct volumes and improve functional outcome in mouse models of acute ischaemic stroke, without concomitantly increasing intracerebral haemorrhage. However, the functional role of platelets during long-term stroke recovery has not been elucidated so far.Thus, we here examined the impact of platelet depletion on post-stroke recovery after transient middle cerebral artery occlusion (tMCAO) in adult male mice. Platelet depleting antibodies or isotype control were applied from day 3–28 after tMCAO in mice matched for infarct size. Long-term functional recovery was assessed over the course of 28 days by behavioural testing encompassing motor and sensorimotorical functions, as well as anxiety-like or spontaneous behaviour. Whole brain flow cytometry and light sheet fluorescent microscopy were used to identify resident and infiltrated immune cell types, and to determine the effects of platelet depletion on the cerebral vascular architecture, respectively.We found that delayed platelet depletion does not improve long-term functional outcome in the tMCAO stroke model. Immune cell abundance, the extent of thrombosis and the organisation of the cerebral vasculature were also comparable between platelet-depleted and control mice. Our study demonstrates that, despite their critical role in the acute stroke setting, platelets appear to contribute only marginally to tissue reorganisation and functional recovery at later stroke stages.

Platelets Inhibit Methicillin-Resistant Staphylococcus aureus by Inducing Hydroxyl Radical-Mediated Apoptosis-Like Cell Death.

ABSTRACTMethicillin-resistant Staphylococcus aureus (MRSA) is one of the most common drug-resistant bacteria and poses a significant threat to human health. Due to the emergence of multidrug resistance, limited drugs are available for the treatment of MRSA infections. In recent years, platelets have been reported to play important roles in inflammation and immune responses, in addition to their functions in blood hemostasis and clotting. We and other researchers have previously reported that platelets can inhibit Staphylococcus aureus growth. However, it remained unclear whether platelets have the same antibacterial effect on drug-resistant strains. In this study, we hypothesized that platelets may also inhibit the growth of MRSA; the results confirmed that platelets significantly inhibited the growth of MRSA in vitro. In a murine model of MRSA infection, we found that a platelet transfusion alleviated the symptoms of MRSA infection; in contrast, depletion of platelets aggravated infective symptoms. Moreover, we observed an overproduction of hydroxyl radicals in MRSA following platelet treatment, which induced apoptosis-like death of MRSA. Our findings demonstrate that platelets can inhibit MRSA growth by promoting the overproduction of hydroxyl radicals and inducing apoptosis-like death.IMPORTANCE The widespread use of antibiotics has led to the emergence of drug-resistant bacteria, particularly multidrug-resistant bacteria. MRSA is the most common drug-resistant bacterium that causes suppurative infections in humans. As only a limited number of drugs are available to treat the infections caused by drug-resistant pathogens, it is imperative to develop novel and effective biological agents for treating MRSA infections. This is the first study to show that platelets can inhibit MRSA growth in vitro and in vivo. Our results revealed that platelets enhanced the production of hydroxyl radicals in MRSA, which induced a series of apoptosis hallmarks in MRSA, including DNA fragmentation, chromosome condensation, phosphatidylserine exposure, membrane potential depolarization, and increased intracellular caspase activity. These findings may further our understanding of platelet function.

Platelet Activation in High D-Dimer Plasma Plays a Role in Acquired Resistance to Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors in Patients with Mutant Lung Adenocarcinoma.

ObjectivePlatelet activation and adhesion to cancer cells increase the release of multiple factors that contribute to EMT and chemoresistance. Elevated levels of D-dimer have been associated with poor clinical outcomes in lung cancer. Platelets in high D-dimer plasma may be activated and implicated in acquired resistance to EGFR TKI in advanced lung adenocarcinoma with mutant EGFR.Materials and MethodsClinical responsive rate (RR), progression-free survival (PFS), and overall survival (OS) were prospectively measured in treatment-naïve lung adenocarcinoma patients with activation mutation. Plasma or platelets from patients with high or low D-dimer level were obtained to investigate the cytotoxic effects of TKIs on mutant cancer cells, and the mechanistic pathways were also explored.ResultsPatients with high D-dimer had worse RR, PFS, and OS. High D-dimer plasma induced resistance to gefitinib, erlotinib, afatinib, or osimertinib in EGFR mutant lung cancer cells. Depletion of platelets in high D-dimer plasma reversed the resistance to TKI. Platelets of high D-dimer plasma had higher adherence capacity to cancer cells, and induced EGFR and Akt activation as well as EMT through Src activation. Inhibition of platelet adherence or activation of Src or Akt conquered the resistance to TKI. The acquired resistance to TKI by high D-dimer plasma was less attributed to secondary gene mutation.ConclusionIncreased platelet activation in the high D-dimer plasma may contribute to first-line acquired EGFR TKI resistance. Thus, therapeutic strategy against platelet activation in patients with high D-dimer levels may improve the efficacy of first-line treatment with EGFR TKI.

Factor analysis of effective platelet-producing ability of fetal liver-derived cells

Objective: To study the different factors affecting platelet production post transplantation of hematopoietic stem cells (HSCs) isolated from different sources in order to explore novel options for treating platelet depletion following HSCs transplantation. Methods: HSCs and their downstream derivatives including myeloid and lymphoid cells (i.e., collective of mononuclear cells (MNCs)), were isolated from E14.5 fetal liver (FL) and bone marrow (BM) of 8-week-old mice by Ficoll separation technique. These cells were subsequently transplanted into the tibia bone marrow cavity of recipient mice post lethal myeloablative treatment in order to construct the FL-MNCs and BM-MNCs transplantation mouse model. Routine blood indices were examined in these recipient mice. The chimeric rate of donor cells in recipient peripheral blood cells were determined by flow cytometry. Different groups of cells involved in platelet reconstruction were analyzed. CD41+megakaryocytes were sorted from fetal liver or bone marrow using magnetic beads, which were then induced to differentiate into platelets in an in vitro assay. Quantitative RT-PCR was used to detect the expression of platelet-related genes in CD41+megakaryocytes from the two sources. Results: Both the FL-MNCs and the BM-MNCs transplantation groups resumed normal hematopoiesis at the 4th week after transplantation, and the blood cells of the recipient mice were largely replaced by the donor cells. Compared with the mice transplanted with BM-MNCs, the platelet level of mice transplanted with FL-MNCs recovered faster and were maintained at a higher level. At week 4, the PLT level of the FL-MNCs group was (1.45±0.37)×1012/L, and of the BM-MNCs group was (1.22±0.24)×1012/L, P<0.05. The FL-MNCs contain a higher proportion of hematopoietic stem cells (Lin-Sca-1+c-Kit+)(7.60%±1.40%) compared to the BM-MNCs (1.10%±0.46%), P<0.01; the proportion of the megakaryocyte progenitor cells (Lin-Sca-1-c-Kit+CD41+CD150+) and mature megakaryocyte cells (CD41+CD42b+), also differ significantly between the FL-MNCs (3.05%±0.22%, 1.60%±0.06%, respectively) and the BM-MNCs (0.15%±0.02%, 0.87%±0.11%, respectively) groups, both P<0.01. In vitro functional studies showed that FL-MNCs-CD41+megakaryocytes could produce proplatelet-like cells more quickly after induction, with proplatelet-like cells formation on day 3 and significant platelet-like particle formation on day 5, in contrast to bone marrow-derived BM-MNCs-CD41+megakaryocytes that failed to form proplatelet-like cell on day 5. In addition, FL-MNCs-CD41+cells expressed higher levels of platelet-related genes, Mpl (3.25-fold), Fog1 (3-fold), and Gata1 (1.5-fold) (P<0.05). Conclusion: Compared with the BM-MNCs group, the FL-MNCs transplantation group appears to have a more efficient platelet implantation effect in the HSCs transplantation recipient in vivo, as well as a higher platelet differentiation rate in vitro. This might be related to a higher proportion of megakaryocytes and higher expression levels of genes such as Mpl, Fog1, and Gata1 that could be important for platelet formation in FL-MNCs-CD41+cells. Further exploration of the specific functions of these genes and the characteristics of the different proportions of the donor cells will provide valuable clues for the future treatment of platelets reconstitution after HSCs transplantation clinically.

Neutrophil extracellular traps regulate ischemic stroke brain injury.

Ischemic stroke prompts a strong inflammatory response, which is associated with exacerbated outcomes. In this study, we investigated mechanistic regulators of neutrophil extracellular trap (NET) formation in stroke and whether they contribute to stroke outcomes. NET-forming neutrophils were found throughout brain tissue of ischemic stroke patients, and elevated plasma NET biomarkers correlated with worse stroke outcomes. Additionally, we observed increased plasma and platelet surface–expressed high-mobility group box 1 (HMGB1) in stroke patients. Mechanistically, platelets were identified as the critical source of HMGB1 that caused NETs in the acute phase of stroke. Depletion of platelets or platelet-specific knockout of HMGB1 significantly reduced plasma HMGB1 and NET levels after stroke, and greatly improved stroke outcomes. We subsequently investigated the therapeutic potential of neonatal NET-inhibitory factor (nNIF) in stroke. Mice treated with nNIF had smaller brain infarcts, improved long-term neurological and motor function, and enhanced survival after stroke. nNIF specifically blocked NET formation without affecting neutrophil recruitment after stroke. Importantly, nNIF also improved stroke outcomes in diabetic and aged mice and was still effective when given 1 hour after stroke onset. These results support a pathological role for NETs in ischemic stroke and warrant further investigation of nNIF for stroke therapy.

Stability of serial platelet and urine protein measurements in patients receiving nusinersen for spinal muscular atrophy.

Introduction/AimsPatients undergoing nusinersen treatment for spinal muscular atrophy are subject to measurements of platelet count and urine protein before each injection due to concern for platelet depletion and renal dysfunction according to the prescribing information. These tests may be uncomfortable or inconvenient and may cause delays in treatment. However, it is still unclear whether these values have been significantly affected by nusinersen treatment. Our aim in this study was to determine whether these measurements ever reached critical values that necessitated withholding treatment at our center.MethodsRecords from 57 patients treated with nusinersen at our institution between 2017 and 2020 were retrospectively analyzed. Laboratory values for platelet count, random urine protein, and total urine protein:creatinine ratio were collected from all patients before each procedure.ResultsMean patient age was 28.9 years (range, 2‐76 years). Mean platelet count was 307 × 109/L (range, 96‐755 × 109/L; normal lab limits, 150‐450 × 109/L), mean random urine protein was 0.164 g/L (range, <0.05‐0.73 g/L), and mean total urine protein:creatinine ratio was 0.885 g per gram creatinine (range, 0.12‐9.71 g per gram creatinine). No laboratory values precluded continuing treatment for any patient.DiscussionAlthough further study on a larger cohort is warranted for more definitive conclusions, it may not be necessary to measure platelet count and urine protein before each nusinersen treatment, particularly in the maintenance phase.

Abstract 155: Divergent Mature Vascular Smooth Muscle Cell Fates Are Directed By Platelet-derived Transcriptomic Codes In Aortic Aneurysms.

Introduction: Loss of vascular smooth-muscle cells (vSMC) and subsequent defective replenishment of functional vSMC de novo are pathological hallmarks of abdominal aortic aneurysm (AAA). Evidence suggests that clusters of progenitors can be reprogrammed into vSMC lineage following vascular injury. However, the landscape of vSMC precursors and reprograming signatures that determine their fate in AAA is undefined. Hypothesis: We hypothesize that quiescent progenitor pools reside in aorta and undergo spatiotemporal fate decision into mature vSMC in AAA. We speculate that distinct ligand-receptor and transcriptional signals gear their pathogenic trajectories into dysfunctional vSMC in AAA. Methods &amp; Results: Single-cell RNA-sequencing (scRNA-seq) identified vascular progenitor cells (Cd34 + Pdgfra + ) in murine (angiotensin II-induced) and human AAA. Pseudotime analysis tracked two differentiation fates of progenitors into divergent mature vSMC pools characterized by enrichment in contractile cytoskeleton machinery (Acta2 + Myh11 + ) or abnormally supplemented with matrix remodeling genes (Mmp2 + Col8a1 + ). Mmp2 + Col8a1 + clusters were dominant in AAA suggesting pathological reprograming in AAA. Gene regulatory network analysis mapped distinct libraries of upstream transcription factors in each mature vSMC states in AAA. Acta2 + Myh11 + and Mmp2 + Col8a1 + transcriptomes were driven by opposing actions of Pparg and its repressor Runx1 respectively. Interestingly, cellular interaction analysis revealed that platelet-derived Pdgfb fueled the phenotypic switch into Mmp2 + Col8a1 + vSMC via its receptor Pdgfra. Dampening Pdgfra signaling by systemic platelet depletion repressed Runx1 activation thereby increasing Pparg transcriptomic activity in progenitors in the aortic wall. This rescued functional regeneration of vSMC (Acta2 + Myh11 + ) with contractile properties consistent with reduced aortic damage and diminished AAA incidence. Conclusion: Our data demonstrate that platelets are novel actors capable of awakening progenitor pools by coding their fate into pathogenic vSMC lineage in AAA. We provide evidence suggesting that strategies aimed at sustaining vSMC contractile destiny could encourage repair of vascular damage in AAA.

Platelets fine-tune effector responses of naïve CD4+ T cells via platelet factor 4-regulated transforming growth factor β signaling

Background and aimPlatelets are an able regulator of CD4+ T cell immunity. Herein, the mechanisms underlying platelet-regulated effector responses of naïve CD4+ T (Tn) cells were investigated.MethodsPlatelet–Tn cell co-cultures of human cells, genetically modified murine models, and high-throughput bioinformatic analyses were combined to elucidate molecular mechanisms of platelet-dependent regulation.ResultsPlatelets exerted sophisticated regulation on effector responses of type 1, 2, and 17 T helper (Th1/Th2/Th17) and regulatory T (Treg) cells, in time-, concentration-, and organ-dependent manners and with close cooperation of transforming growth factor β (TGFβ) and platelet factor 4 (PF4). PF4 at low concentrations reinforced TGFβ signaling by heteromerizing with type III TGFβ receptor (TGFBRIII), and subsequently enhanced TGFBRII expression and TGFβ signaling. High-concentration PF4 had, however, opposite effects by directly binding to TGFBRII, blocking TGFβ–TGFBRII ligation, and thus inhibiting TGFβ signaling. Furthermore, platelet depletion markedly hampered Treg and Th17 responses in the spleen but not in the lymph nodes, blockade of platelet–Tn cell contact diminished platelet effects, while spleen injection of PF4-immobilized microparticles in PF4-deficient mice mimicked platelet effects, suggesting the importance of direct platelet–Tn contact and platelet-bound PF4 for the optimal regulatory effects by platelets.ConclusionPlatelets exert context-dependent regulations on effector responses of Tn cells via PF4-TGFβ duet, suggesting new possibilities of platelet-targeted interventions of T cell immunity.

Platelet depletion does not alter the course of Brucella abortus infection in vivo

Brucellosis is a bacterial disease of animals and a zoonotic infection. Thrombocytopenia is a common outcome in long-lasting brucellosis in humans. Likewise, ex vivo experiments have shown that platelets may play a role in Brucella abortus infections. Following these reports, we explored the course of brucellosis in thrombocytopenic mice, using the non-toxic low-molecular-weight aspercetin protein that depletes platelets in vivo. Aspercetin does not induce systemic hemorrhage or inflammation, and when injected into mice, it generates a rapid dose-dependent drop in platelet counts without affecting central organs, disrupting hematological parameters, or the proinflammatory cytokine profile. Compared to the B. abortus infected control group, the infected thrombocytopenic mice did not show significant differences in the hematological profiles, pathological score, spleen, liver histopathology, or bacterial loads. Except for IL-6, which was higher in the infected thrombocytopenic mice, the TNF-α, IFN-γ and IL-10 did not significantly differ with the PBS-infected group. The results indicate that platelets do not play a significant role in modulating Brucella infection in vivo at the early stages of infection, which is commensurate with the stealthy strategy followed by Brucella organisms at the onset of the disease.