Analysis of the Healthy Platelet Proteome Identifies a New Form of Domain-Specific O-Fucosylation.

Platelet activation induces the secretion of proteins that promote platelet aggregation and inflammation. However, detailed analysis of the released platelet proteome is hampered by platelets' tendency to preactivate during their isolation and a lack of sensitive protocols for low abundance releasate analysis. Here, we detail the most sensitive analysis to date of the platelet releasate proteome with the detection of >1300 proteins. Unbiased scanning for posttranslational modifications within releasate proteins highlighted O-glycosylation as being a major component. For the first time, we detected O-fucosylation on previously uncharacterized sites including multimerin-1 (MMRN1), a major alpha granule protein that supports platelet adhesion to collagen and is a carrier for platelet factor V. The N-terminal elastin microfibril interface (EMI) domain of MMRN1, a key site for protein-protein interaction, was O-fucosylated at a conserved threonine within a new domain context. Our data suggest that either protein O-fucosyltransferase 1, or a novel protein O-fucosyltransferase, may be responsible for this modification. Mutating this O-fucose site on the EMI domain led to a >50% reduction of MMRN1 secretion, supporting a key role of EMI O-fucosylation in MMRN1 secretion. By comparing releasates from resting and thrombin-treated platelets, 202 proteins were found to be significantly released after high-dose thrombin stimulation. Complementary quantification of the platelet lysates identified >3800 proteins, which confirmed the platelet origin of releasate proteins by anticorrelation analysis. Low-dose thrombin treatment yielded a smaller subset of significantly regulated proteins with fewer secretory pathway enzymes. The extensive platelet proteome resource provided here (larancelab.com/platelet-proteome) allows identification of novel regulatory mechanisms for drug targeting to address platelet dysfunction and thrombosis.

Thrombo-inflammatory response in hospitalised patients with COVID-19: a single institution experience.

BACKGROUND: Severe COVID-19 causes acute inflammation, which is complicated by venous thromboembolism events (VTE). However, it is unclear if VTE risk has evolved over time since the COVID-19 outbreak. AIMS: To determine markers of thrombo-inflammation and rates of symptomatic VTE in patients hospitalised for COVID-19 in a metropolitan hospital in Sydney, Australia. METHODS: A retrospective, single-centre, cohort study was performed by reviewing electronic medical records of consecutive patients admitted to Royal Prince Alfred Hospital between March 2020 and September 2021. This period included three waves of COVID-19 outbreaks in Australia with the ancestral, alpha and delta variants. Standard coagulation assays and inflammatory markers were recorded over 4 weeks. RESULTS: A total of 205 patients were consecutively admitted during the study period. Activated partial thromboplastin time, neutrophil count and C-reactive protein (CRP) were significantly increased in patients hospitalised in the intensive care unit (ICU) compared with non-ICU patients. The use of anti-inflammatory medication increased in 2021 compared with 2020. The mortality rate was 7.3% in our cohort. Ninety-four per cent of patients received anticoagulation with 6.3% of patients developing VTE. CONCLUSION: We observed lower rates of VTE compared to the internationally reported rate for the same period. We conclude that in the setting of controlled hospital admission rate and standard anticoagulation guidelines, COVID-19 resulted in similar thrombo-inflammatory response and VTE rates over the first 1.5 years of the pandemic.

"Sticki-ER": Functions of the Platelet Endoplasmic Reticulum.

Significance: The primary role of platelets is to generate a thrombus by platelet activation. Platelet activation relies on calcium mobilization from the endoplasmic reticulum (ER). ER resident proteins, which are externalized upon platelet activation, are essential for the function of platelet surface receptors and intercellular interactions. Recent Advances: The platelet ER is a conduit for changes in cellular function in response to the extracellular milieu. ER homeostasis is maintained by an appropriate redox balance, regulated calcium stores and normal protein folding. Alterations in ER function and ER stress results in ER proteins externalizing to the cell surface, including members of the protein disulfide isomerase family (PDIs) and chaperones. Critical Issues: The platelet ER is central to platelet function, but our understanding of its regulation is incomplete. Previous studies have focused on the function of PDIs in the extracellular space, and much less on their intracellular role. How platelets maintain ER homeostasis and how they direct ER chaperone proteins to facilitate intercellular signalling is unknown. Future Directions: An understanding of ER functions in the platelet is essential as these may determine critical platelet activities such as secretion and adhesion. Studies are necessary to understand the redox reactions of PDIs in the intracellular versus extracellular space, as these differentially affect platelet function. An unresolved question is how platelet ER proteins control calcium release. Regulation of protein folding in the platelet and downstream pathways of ER stress require further evaluation. Targeting the platelet ER may have therapeutic application in metabolic and neoplastic disease.

Serum protein electrophoresis and rheumatoid factor analysis is an effective screening strategy for cryoglobulinaemia.

Accurate serum cryoglobulin detection is important to allow prompt treatment but laboratory testing requires stringent pre-analytical conditions and has long turnaround times. Serum protein electrophoresis (EPG) for paraproteinaemia and rheumatoid factor (RF) analysis may offer an effective initial screening strategy for the presence of cryoglobulinaemia. We retrospectively assessed the sensitivity of ancillary EPG and RF testing for the presence of serum cryoglobulinaemia in 586 eligible cryoglobulin positive samples received at the Royal Prince Alfred and Liverpool Hospital immunopathology laboratories over an 11-year period. Ninety-one percent of all cryoglobulin positive samples had either a detectable paraprotein or RF activity, with greatest sensitivity for type I and type II cryoglobulins (97% and 98%, respectively). The sensitivity remained high irrespective of whether EPG and RF analysis was performed with the same, or different, pre-analytical collection conditions to the cryoglobulin collection (92% vs 90%, p=0.46). Only two patients with detected cryoglobulins and no associated paraprotein or RF activity had clinical features of cryoglobulinaemia and neither required treatment. This study demonstrates that serum EPG and RF analysis has high sensitivity for the detection of clinically relevant cryoglobulinaemia, even when not collected under ideal pre-analytical conditions, and potentially offers a prompt and effective screening strategy.

Multiple Electrode Aggregometry (Multiplate): Functional Assay for Vaccine-Induced (Immune) Thrombotic Thrombocytopenia (VITT).

Vaccine-induced immune thrombotic thrombocytopenia (VITT) was first described in 2021 and represents an adverse reaction to adenoviral vector COVID-19 vaccines AstraZeneca ChAdOx1 nCoV-19 (AZD1222) and Johnson & Johnson Ad26.COV2.S vaccine. VITT is a severe immune platelet activation syndrome with an incidence of 1-2 per 100,000 vaccinations. The features of VITT include thrombocytopenia and thrombosis within 4-42 days of first dose of vaccine. Affected individuals develop platelet-activating antibodies against platelet factor 4 (PF4). The International Society on Thrombosis and Haemostasis recommends both an antigen-binding assay (enzyme-linked immunosorbent assay, ELISA) and a functional platelet activation assay for the diagnostic workup of VITT. Here, the application of multiple electrode aggregometry (Multiplate) is presented as a functional assay for VITT.

Endoplasmic reticulum protein 5 attenuates platelet endoplasmic reticulum stress and secretion in a mouse model.

Extracellular protein disulfide isomerases (PDIs), including PDI, endoplasmic reticulum protein 57 (ERp57), ERp72, ERp46, and ERp5, are required for in vivo thrombus formation in mice. Platelets secrete PDIs upon activation, which regulate platelet aggregation. However, platelets secrete only ∼10% of their PDI content extracellularly. The intracellular role of PDIs in platelet function is unknown. Here, we aim to characterize the role of ERp5 (gene Pdia6) using platelet conditional knockout mice, platelet factor 4 (Pf4) Cre+/ERp5floxed (fl)/fl. Pf4Cre+/ERp5fl/fl mice developed mild macrothrombocytopenia. Platelets deficient in ERp5 showed marked dysregulation of their ER, indicated by a twofold upregulation of ER proteins, including PDI, ERp57, ERp72, ERp46, 78 kilodalton glucose-regulated protein (GRP78), and calreticulin. ERp5-deficient platelets showed an enhanced ER stress response to ex vivo and in vivo ER stress inducers, with enhanced phosphorylation of eukaryotic translation initiation factor 2A and inositol-requiring enzyme 1 (IRE1). ERp5 deficiency was associated with increased secretion of PDIs, an enhanced response to thromboxane A2 receptor activation, and increased thrombus formation in vivo. Our results support that ERp5 acts as a negative regulator of ER stress responses in platelets and highlight the importance of a disulfide isomerase in platelet ER homeostasis. The results also indicate a previously unanticipated role of platelet ER stress in platelet secretion and thrombosis. This may have important implications for the therapeutic applications of ER stress inhibitors in thrombosis.

SUBA-Itraconazole for Primary Antifungal Prophylaxis After Allogeneic Hematopoietic Cell Transplantation.

Background: Itraconazole (ITZ) is an effective agent when used as primary invasive fungal disease (IFD) prophylaxis, but is limited by drug tolerability and variability in serum concentrations. A new formulation, SUBA-itraconazole (for "super bioavailability"; S-ITZ), addresses the limitations of conventional ITZ formulations. Methods: We conducted a retrospective cohort study at 2 Australian centers to evaluate the safety, tolerability, and effectiveness of S-ITZ as primary antifungal prophylaxis in hematopoietic cell transplant (HCT) recipients without grade II-IV acute graft-vs-host disease, from day 1 until approximately day 100 (cohort A) or day 1 until neutrophil engraftment (cohort B). A total of 204 patients and 1410 trough plasma ITZ concentrations were assessed. Results: The incidence of breakthrough proven/probable IFD at day 180 was 1.0% (95% confidence interval [CI], .2%-3.2%), with 1.6% in cohort A and 0% in cohort B, and overall fungal-free survival of proven/probable IFD was 82.9% (95% CI, 76.8%-87.4%). Preengraftment early permanent S-ITZ discontinuation was 3.4% overall, with no significant difference between cohorts. No patients required cessation due to gastrointestinal intolerance attributed to S-ITZ. The geometric mean trough plasma ITZ concentration was 1130ng/mL (interquartile range, 566-1801ng/mL; coefficient of variation, 56.57%) and the median time to achieve therapeutic levels was 10 days. Conclusions: S-ITZ is a safe and well-tolerated oral formulation and is a novel alternative for primary IFD prophylaxis after HCT.

Sclerosing peritonitis post liver transplantation: a rare condition where surgery is an important treatment option.

BACKGROUND: Sclerosing peritonitis (SP) is a rare but potentially fatal complication following orthotopic liver transplantation (OLT). The definitive surgical management is via a laparotomy peritonectomy and enterolysis procedure, but this carries risks particularly in the immunosuppressed transplant patient population. The natural history of SP is known from a handful of case reports and series, which mostly report de novo cases arising early on following OLT. The aim of this study was to identify all cases of de novo SP following OLT and the outcomes of management. METHODS: Cases of SP post OLT were identified from the Australian National Liver Transplantation Unit (New South Wales) database of all 1393 adult patients. RESULTS: Three cases of SP were diagnosed between 2 and over 9 years post-transplantation. Two patients proceeded to laparotomy and a peritonectomy and enterolysis procedure of the cocooned bowel. The third was managed conservatively due to a relatively indolent course and their medical co-morbidities. CONCLUSION: SP should be considered in the differential diagnosis in patients post OLT presenting with symptoms of bowel obstruction, even years following transplantation. Surgery may be required in order to achieve a satisfactory outcome in some cases.

Induction of protein growth factor systems in the ovaries of transgenic mice overexpressing human type 2 lysophosphatidic acid G protein-coupled receptor (LPA2).

The lipid growth factor lysophosphatidic acid (LPA) is produced by ovarian cancer cells in quantities sufficient to attain concentrations of up to 10 microM. An autocrine circuit was demonstrated when ovarian cancer cells, but not normal ovarian surface epithelial cells, were proven to express LPA(2) (Edg-4) and LPA(3) (Edg-7) G protein-coupled receptors for LPA. Human LPA(2) now has been expressed transgenically in C57BL/6 mouse ovaries under direction of the alpha-inhibin large promoter. Human LPA(2) mRNA and protein were detected in all transgenic (TG) mouse ovaries at levels far higher than in other tissues and at least fivefold higher than in cultured lines of human ovarian cancer cells, with the expected sex cord-stromal distribution. Most LPA(2) TG ovaries produced significantly higher levels than non-TG ovaries of type A, but not type B, vascular endothelial growth factor (VEGF), isomers of VEGF-A, and urokinase-type plasminogen activator (uPA). Many LPA(2) TG ovaries had elevated expression of VEGF receptors 1 and 2, and a depressed level of type 2 PA inhibitor. Thus, the LPA-LPA(2) circuit regulates ovarian cells both directly and through increases in protein growth factor systems.

Tropoelastin incorporation into a dermal regeneration template promotes wound angiogenesis.

Severe burn injury results in substantial skin loss and cannot be treated by autografts. The Integra Dermal Regeneration Template (IDRT) is the leading synthetic skin substitute because it allows for wound bed regeneration and wound healing. However, all substitutes suffer from slow blood vessel ingrowth and would benefit considerably from enhanced vascularization to nurture tissue repair. It is shown here that by incorporating the human elastic protein tropoelastin into a dermal regeneration template (TDRT) we can promote angiogenesis in wound healing. In small and large animal models comprising mice and pigs, the hybrid TDRT biomaterial and IDRT show similar contraction to autografts and decrease wound contraction compared to open wounds. In mice, TDRT accelerates early stage angiogenesis by 2 weeks, as evidenced by increased angiogenesis fluorescent radiant efficiency in live animal imaging and the expression of endothelial cell adhesion marker CD146. In the pig, a full thickness wound repair model confirms increased numbers of blood vessels in the regenerating areas of the dermis closest to the hypodermis and immediately below the epidermis at 2 weeks post-surgery. It is concluded that including tropoelastin in a dermal regeneration template has the potential to promote wound repair through enhanced vascularization.

Immunoeffector and immunoregulatory activities of vasoactive intestinal peptide.

Vasoactive intestinal peptide (VIP) and its two G protein-coupled receptors, VPAC1R and VPAC2R, are prominent in the immune system and potently affect T cells and macrophages. VPAC1Rs are expressed constitutively by blood and tissue T cells, with an order of prevalence of Th2>Th1>>Ts, and transmit signals suppressive for migration, proliferation and cytokine production. Immune activation of T cells downregulates VPAC1Rs and upregulates VPAC2Rs. VPAC2Rs mediate T cell chemotaxis, stimulation of some Th2-type cytokines, and inhibition of some Th1-type cytokines. A tentative hypothesis that the VIP-VPAC2R axis is the major neuroregulator of Th2/Th1 balance has been confirmed by finding an increased ratio in CD4 T cells of transgenic (TG) mice, expressing high levels of VPAC2Rs, and a decreased ratio in CD4 T cells of VPAC2R-null (K/O) mice. VPAC2R TG mice exhibit an allergic phenotype, whereas the K/O mice are hypoallergic and have heightened delayed-type hypersensitivity. The mechanisms of VIP-VPAC2R effects include decreased Th2 apoptosis, increased Th2-type cytokine production, and greater generation of Th2 memory cells. VPAC2R antagonists are being developed to alleviate allergic diseases and strengthen effector Th1 cell-mediated immunoprotection.

Differential signaling of T cell generation of IL-4 by wild-type and short-deletion variant of type 2 G protein-coupled receptor for vasoactive intestinal peptide (VPAC2).

Vasoactive intestinal peptide (VIP) released from some neurons and T cells affects T cell migration, cytokine generation, and other functions by binding to constitutively expressed type 1 G protein-coupled receptor (VPAC1) or activation-induced type 2 G protein-coupled receptor (VPAC2). Recently, a short-deletion (SD) splice variant of mouse VPAC2 that lacks 14 amino acids at the end of the last transmembrane domain has been identified in T cells and shown to resemble wild-type (WT) VPAC2 in affinity of VIP binding but to differ by lack of signaling of T cell adenylyl cyclase, migration, and IL-2 secretion. As Th2 cells are the principal source of immune VIP and have the greatest functional responses to VIP, the differences in signals transduced by WT and SD VPAC2 were studied in VPAC2-low D10G4.1 model Th2 cell transfectants individually expressing the respective types of VPAC2 equally. WT and SD VPAC2 Th2 cell transfectants secreted equal amounts of VIP. WT VPAC2 transfectants generated more IL-4 than did SD VPAC2 transfectants, and this increment was dependent on endogenous VIP. Exogenous VIP further increased IL-4 production by WT VPAC2 transfectants but decreased IL-4 production by SD VPAC2 transfectants. Cotransfection of the two constructs diminished VIP enhancement of IL-4 production seen with WT VPAC2 alone by preventing increases in nuclear levels of the requisite transcription factors c-Maf and Jun B. Thus the ratio of two forms of T cell VPAC2 determines the net effect of VIP on IL-4 generation by activated Th2 cells.

Protein kinase C epsilon dependence of the recovery from down-regulation of S1P1 G protein-coupled receptors of T lymphocytes.

Sphingosine 1-phosphate (S1P) from mononuclear phagocytes and platelets signals T cells predominantly through S1P1 G protein-coupled receptors (Rs) to enhance survival, stimulate and suppress migration, and inhibit other immunologically relevant responses. Cellular S1P1 Rs and their signaling functions are rapidly down-regulated by S1P, through a protein kinase C (PKC)-independent mechanism, but characteristics of cell-surface re-expression of down-regulated S1P1 Rs have not been elucidated. T cell chemotactic responses (CT) to 10 and 100 nm S1P and inhibition of T cell chemotaxis to chemokines (CI) by 1 and 3 microm S1P were suppressed after 1 h of preincubation with 100 nm S1P, but recovered fully after 12-24 h of exposure to S1P. Late recovery of down-regulated CT and CI, but not early down-regulation, was suppressed by PKC and PKCepsilon-selective inhibitors and was absent in T cells from PKCepsilon-null mice. The same PKCepsilon inhibitors blocked S1P-evoked increases in T cell nuclear levels of c-Fos and phosphorylated c-Jun and JunD after 24 h, but not 1 h. A mixture of c-Fos plus c-Jun antisense oligonucleotides prevented late recovery of down-regulated CT and CI, without affecting S1P induction of down-regulation. Similarly, S1P-elicited threonine phosphorylation of S1P1 Rs was suppressed by a selective inhibitor of PKCepsilon after 24 h, but not 1 h. Biochemical requisites for recovery of down-regulated S1P1 Rs thus differ from those for S1P induction of down-regulation.

Roles of vasoactive intestinal peptide (VIP) in the expression of different immune phenotypes by wild-type mice and T cell-targeted type II VIP receptor transgenic mice.

Vasoactive intestinal peptide (VIP) and its two G protein-coupled receptors, VPAC1 and VPAC2, are quantitatively prominent and functionally critical in the immune system. Transgenic (T) mice constitutively expressing VPAC2 selectively in CD4 T cells, at levels higher than those found after maximal induction in CD4 T cells of wild-type (N) mice, have elevated blood concentrations of IgE, IgG1, and eosinophils; enhanced immediate-type hypersensitivity; and reduced delayed-type hypersensitivity. In contrast, VPAC2-null (K) mice manifest decreased immediate-type hypersensitivity and enhanced delayed-type hypersensitivity. The phenotypes are attributable to opposite skewing of the Th2/Th1 cytokine ratio, but no studies were conducted on the roles of T cell-derived VIP and altered expansion of the Th subsets. Dependence of the Th phenotype of T mice, but not of N or K mice, on T cell-derived VIP now is proven by showing that eliminating VIP from TCR-stimulated T cell cultures with VIPase IgG normalizes the elevated number of IL-4-secreting CD4 T cells, decreases the secretion of IL-4 and IL-10, and increases the secretion of IFN-gamma. Flexible responsiveness of CD4 T cells from N and K mice, but not T mice, to exogenous VIP in vitro and in vivo is shown by increased numbers of IL-4-secreting CD4 T cells, greater secretion of IL-4 and IL-10, and lesser secretion of IFN-gamma after TCR stimulation with VIP. The level of VIP recognized by CD4 T cells thus is a major determinant of the relative contributions of Th subsets to the immune effector phenotype.

Transduction of multiple effects of sphingosine 1-phosphate (S1P) on T cell functions by the S1P1 G protein-coupled receptor.

Sphingosine 1-phosphate (S1P) in blood, lymph, and immune tissues stimulates and regulates T cell migration through their S1P(1) (endothelial differentiation gene encoded receptor-1) G protein-coupled receptors. We show now that S1P(1)Rs also mediate suppression of T cell proliferation and cytokine production. Uptake of [(3)H]thymidine by mouse CD4 T cells stimulated with anti-CD3 mAbs plus either anti-CD28 or IL-7 was inhibited up to 50% by 10(-9)-10(-6) M S1P. Suppression by S1P required Ca(2+) signaling and was reduced by intracellular cAMP. S1P decreased CD4 T cell generation of IFN-gamma and IL-4, without affecting IL-2. A Th1 line from D011.10 TCR transgenic mice without detectable S1P(1) was refractory to S1P until introduction of S1P(1) by retroviral transduction. S1P then evoked chemotaxis, inhibited chemotaxis to CCL-5 and CCL-21, and suppressed Ag-stimulated proliferation and IFN-gamma production. Thus, S1P(1) signals multiple immune functions of T cells as well as migration and tissue distribution.