Characterization of all small RNAs in and comparisons across cultured megakaryocytes and platelets of healthy individuals and COVID-19 patients

BACKGROUND

The small noncoding RNAs (sncRNAs) in megakaryocytes (MKs) and platelets are not well characterized. Neither is the impact of SARS-CoV-2 infection on the sncRNAs of platelets.

OBJECTIVES

To investigate the sorting of MK sncRNAs into platelets, and the differences in the platelet sncRNAomes of healthy donors (HDs) and COVID-19 patients.

METHODS

We comprehensively profiled sncRNAs from MKs cultured from cord blood-derived CD34+ cells, platelets from HDs, and platelets from patients with moderate and severe SARS-CoV-2 infection. We also comprehensively profiled Argonaute (AGO)-bound sncRNAs from the cultured MKs.

RESULTS

We characterized the sncRNAs in MKs and platelets and can account for ∼95% of all sequenced reads. We found that MKs primarily comprise microRNA isoforms (isomiRs), tRNA-derived fragments (tRFs), rRNA-derived fragments (rRFs), and Y RNA-derived fragments (yRFs) in comparable abundances. The platelets of HDs showed a skewed distribution by comparison: 56.7% of all sncRNAs are yRFs, 34.4% are isomiRs, and <2.0% are tRFs and rRFs. Most isomiRs in MKs and platelets are either noncanonical, nontemplated, or both. When comparing MKs and platelets from HDs, we found numerous isomiRs, tRFs, rRFs, and yRFs showing opposite enrichments or depletions, including molecules from the same parental miRNA arm, tRNA, rRNA, or Y RNA. The sncRNAome of platelets from patients with COVID-19 is skewed compared to that of HDs with only 19.8% of all sncRNAs now being yRFs, isomiRs increasing to 63.6%, and tRFs and rRFs more than tripling their presence to 6.1%.

CONCLUSION

The sncRNAomes of MKs and platelets are very rich and more complex than it has been believed. The evidence suggests complex mechanisms that sort MK sncRNAs into platelets. SARS-CoV-2 infection acutely alters the contents of platelets by changing the relative proportions of their sncRNAs.

Autophagy and its consequences for platelet biology

Autophagy, the continuous recycling of intracellular building blocks, molecules, and organelles is necessary to preserve cellular function and homeostasis. In this context, it was demonstrated that autophagy plays an important role in megakaryopoiesis, the development and differentiation of hematopoietic progenitor cells into megakaryocytes. Furthermore, in recent years, autophagic proteins were detected in platelets, anucleate cells generated by megakaryocytes, responsible for hemostasis, thrombosis, and a key cell in inflammation and host immune responses. In the last decade studies have indicated the occurrence of autophagy in platelets. Moreover, autophagy in platelets was subsequently demonstrated to be involved in platelet aggregation, adhesion, and thrombus formation. Here, we review the current knowledge about autophagy in platelets, its function, and clinical implications. However, at the advent of platelet autophagy research, additional discoveries derived from evolving work will be required to precisely define the contributions of autophagy in platelets, and to expand the ever increasing physiologic and pathologic roles these remarkable and versatile blood cells play.

Alterations in the megakaryocyte transcriptome impacts platelet function in sepsis and COVID-19 infection

Platelets and their parent cell, the megakaryocyte (MK), are increasingly recognized for their roles during infection and inflammation. The MK residing in the bone marrow or arising from precursors trafficked to other organs for development go on to form platelets through thrombopoiesis. Infection, by direct and indirect mechanisms, can alter the transcriptional profile of MKs. The altered environment, whether mediated by inflammatory cytokines or other signaling mechanisms results in an altered platelet transcriptome. Platelets released into the circulation, in turn, interact with each other, circulating leukocytes and endothelial cells and contribute to the clearance of pathogens or the potentiation of pathophysiology through such mechanisms as immunothrombosis. In this article we hope to identify key contributions that explore the impact of an altered transcriptomic landscape during severe, systemic response to infection broadly defined as sepsis, and viral infections, including SARS-CoV2. We include current publications that outline the role of MKs from bone-marrow and extra-medullary sites as well as the circulating platelet. The underlying diseases result in thrombotic complications that exacerbate organ dysfunction and mortality. Understanding the impact of platelets on the pathophysiology of disease may drive therapeutic advances to improve the morbidity and mortality of these deadly afflictions.

Intravenous aviptadil and remdesivir for treatment of COVID-19-associated hypoxaemic respiratory failure in the USA (TESICO): a randomised, placebo-controlled trial

BACKGROUND

There is a clinical need for therapeutics for COVID-19 patients with acute hypoxemic respiratory failure whose 60-day mortality remains at 30-50%. Aviptadil, a lung-protective neuropeptide, and remdesivir, a nucleotide prodrug of an adenosine analog, were compared with placebo among patients with COVID-19 acute hypoxaemic respiratory failure.

METHODS

TESICO was a randomised trial of aviptadil and remdesivir versus placebo at 28 sites in the USA. Hospitalised adult patients were eligible for the study if they had acute hypoxaemic respiratory failure due to confirmed SARS-CoV-2 infection and were within 4 days of the onset of respiratory failure. Participants could be randomly assigned to both study treatments in a 2 × 2 factorial design or to just one of the agents. Participants were randomly assigned with a web-based application. For each site, randomisation was stratified by disease severity (high-flow nasal oxygen or non-invasive ventilation vs invasive mechanical ventilation or extracorporeal membrane oxygenation [ECMO]), and four strata were defined by remdesivir and aviptadil eligibility, as follows: (1) eligible for randomisation to aviptadil and remdesivir in the 2 × 2 factorial design; participants were equally randomly assigned (1:1:1:1) to intravenous aviptadil plus remdesivir, aviptadil plus remdesivir matched placebo, aviptadil matched placebo plus remdesvir, or aviptadil placebo plus remdesivir placebo; (2) eligible for randomisation to aviptadil only because remdesivir was started before randomisation; (3) eligible for randomisation to aviptadil only because remdesivir was contraindicated; and (4) eligible for randomisation to remdesivir only because aviptadil was contraindicated. For participants in strata 2-4, randomisation was 1:1 to the active agent or matched placebo. Aviptadil was administered as a daily 12-h infusion for 3 days, targeting 600 pmol/kg on infusion day 1, 1200 pmol/kg on day 2, and 1800 pmol/kg on day 3. Remdesivir was administered as a 200 mg loading dose, followed by 100 mg daily maintenance doses for up to a 10-day total course. For participants assigned to placebo for either agent, matched saline placebo was administered in identical volumes. For both treatment comparisons, the primary outcome, assessed at day 90, was a six-category ordinal outcome: (1) at home (defined as the type of residence before hospitalisation) and off oxygen (recovered) for at least 77 days, (2) at home and off oxygen for 49-76 days, (3) at home and off oxygen for 1-48 days, (4) not hospitalised but either on supplemental oxygen or not at home, (5) hospitalised or in hospice care, or (6) dead. Mortality up to day 90 was a key secondary outcome. The independent data and safety monitoring board recommended stopping the aviptadil trial on May 25, 2022, for futility. On June 9, 2022, the sponsor stopped the trial of remdesivir due to slow enrolment. The trial is registered with ClinicalTrials.gov, NCT04843761.

FINDINGS

Between April 21, 2021, and May 24, 2022, we enrolled 473 participants in the study. For the aviptadil comparison, 471 participants were randomly assigned to aviptadil or matched placebo. The modified intention-to-treat population comprised 461 participants who received at least a partial infusion of aviptadil (231 participants) or aviptadil matched placebo (230 participants). For the remdesivir comparison, 87 participants were randomly assigned to remdesivir or matched placebo and all received some infusion of remdesivir (44 participants) or remdesivir matched placebo (43 participants). 85 participants were included in the modified intention-to-treat analyses for both agents (ie, those enrolled in the 2 x 2 factorial). For the aviptadil versus placebo comparison, the median age was 57 years (IQR 46-66), 178 (39%) of 461 participants were female, and 246 (53%) were Black, Hispanic, Asian or other (vs 215 [47%] White participants). 431 (94%) of 461 participants were in an intensive care unit at baseline, with 271 (59%) receiving high-flow nasal oxygen or non-invasive ventiliation, 185 (40%) receiving invasive mechanical ventilation, and five (1%) receiving ECMO. The odds ratio (OR) for being in a better category of the primary efficacy endpoint for aviptadil versus placebo at day 90, from a model stratified by baseline disease severity, was 1·11 (95% CI 0·80-1·55; p=0·54). Up to day 90, 86 participants in the aviptadil group and 83 in the placebo group died. The cumulative percentage who died up to day 90 was 38% in the aviptadil group and 36% in the placebo group (hazard ratio 1·04, 95% CI 0·77-1·41; p=0·78). The primary safety outcome of death, serious adverse events, organ failure, serious infection, or grade 3 or 4 adverse events up to day 5 occurred in 146 (63%) of 231 patients in the aviptadil group compared with 129 (56%) of 230 participants in the placebo group (OR 1·40, 95% CI 0·94-2·08; p=0·10).

INTERPRETATION

Among patients with COVID-19-associated acute hypoxaemic respiratory failure, aviptadil did not significantly improve clinical outcomes up to day 90 when compared with placebo. The smaller than planned sample size for the remdesivir trial did not permit definitive conclusions regarding safety or efficacy.

FUNDING

National Institutes of Health.

MAPK-interacting kinase 1 regulates platelet production, activation, and thrombosis

The MAPK-interacting kinase (Mnk) family includes Mnk1 and Mnk2, which are phosphorylated and activated in response to extracellular stimuli. Mnk1 contributes to cellular responses by regulating messenger RNA (mRNA) translation, and mRNA translation influences platelet production and function. However, the role of Mnk1 in megakaryocytes and platelets has not previously been studied. The present study investigated Mnk1 in megakaryocytes and platelets using both pharmacological and genetic approaches. We demonstrate that Mnk1, but not Mnk2, is expressed and active in human and murine megakaryocytes and platelets. Stimulating human and murine megakaryocytes and platelets induced Mnk1 activation and phosphorylation of eIF4E, a downstream target of activated Mnk1 that triggers mRNA translation. Mnk1 inhibition or deletion significantly diminished protein synthesis in megakaryocytes as measured by polysome profiling and [35S]-methionine incorporation assays. Depletion of Mnk1 also reduced megakaryocyte ploidy and proplatelet forming megakaryocytes in vitro and resulted in thrombocytopenia. However, Mnk1 deletion did not affect the half-life of circulating platelets. Platelets from Mnk1 knockout mice exhibited reduced platelet aggregation, α granule secretion, and integrin αIIbβ3 activation. Ribosomal footprint sequencing indicated that Mnk1 regulates the translation of Pla2g4a mRNA (which encodes cPLA2) in megakaryocytes. Consistent with this, Mnk1 ablation reduced cPLA2 activity and thromboxane generation in platelets and megakaryocytes. In vivo, Mnk1 ablation protected against platelet-dependent thromboembolism. These results provide previously unrecognized evidence that Mnk1 regulates mRNA translation and cellular activation in platelets and megakaryocytes, endomitosis and thrombopoiesis, and thrombosis.

IFITM3 regulates fibrinogen endocytosis and platelet reactivity in nonviral sepsis

Platelets and megakaryocytes are critical players in immune responses. Recent reports suggest infection and inflammation alter the megakaryocyte and platelet transcriptome to induce altered platelet reactivity. We determined whether nonviral sepsis induces differential platelet gene expression and reactivity. Nonviral sepsis upregulated IFN-induced transmembrane protein 3 (IFITM3), an IFN-responsive gene that restricts viral replication. As IFITM3 has been linked to clathrin-mediated endocytosis, we determined whether IFITM3 promoted endocytosis of α-granule proteins. IFN stimulation enhanced fibrinogen endocytosis in megakaryocytes and platelets from Ifitm+/+ mice, but not Ifitm-/- mice. IFITM3 overexpression or deletion in megakaryocytes demonstrated IFITM3 was necessary and sufficient to regulate fibrinogen endocytosis. Mechanistically, IFITM3 interacted with clathrin and αIIb and altered their plasma membrane localization into lipid rafts. In vivo IFN administration increased fibrinogen endocytosis, platelet reactivity, and thrombosis in an IFITM-dependent manner. In contrast, Ifitm-/- mice were completely rescued from IFN-induced platelet hyperreactivity and thrombosis. During murine sepsis, platelets from Ifitm+/+ mice demonstrated increased fibrinogen content and platelet reactivity, which was dependent on IFN-α and IFITMs. Platelets from patients with nonviral sepsis had increases in platelet IFITM3 expression, fibrinogen content, and hyperreactivity. These data identify IFITM3 as a regulator of platelet endocytosis, hyperreactivity, and thrombosis during inflammatory stress.

Eligibility for Posthospitalization Venous Thromboembolism Prophylaxis in Hospitalized Patients With COVID-19: A Retrospective Cohort Study

Background

A recent randomized trial, the MICHELLE trial, demonstrated improved posthospital outcomes with a 35‐day course of prophylactic rivaroxaban for patients hospitalized with COVID‐19 at high risk of venous thromboembolism. We explored how often these findings may apply to an unselected clinical population of patients hospitalized with COVID‐19.

Methods and Results

Using a 35‐hospital retrospective cohort of patients hospitalized between March 7, 2020, and January 23, 2021, with COVID‐19 (MI‐COVID19 database), we quantified the percentage of hospitalized patients with COVID‐19 who would be eligible for rivaroxaban at discharge per MICHELLE trial criteria and report clinical event rates. The main clinical outcome was derived from the MICHELLE trial and included a composite of symptomatic venous thromboembolism, pulmonary embolus‐related death, nonhemorrhagic stroke, and cardiovascular death at 35 days. Multiple sensitivity analyses tested different eligibility and exclusion criteria definitions to determine the effect on eligibility for postdischarge anticoagulation prophylaxis. Of 2016 patients hospitalized with COVID‐19 who survived to discharge and did not have another indication for anticoagulation, 25.9% (n=523) would be eligible for postdischarge thromboprophylaxis per the MICHELLE trial criteria (range, 2.9%–39.4% on sensitivity analysis). Of the 416 who had discharge anticoagulant data collected, only 13.2% (55/416) were actually prescribed a new anticoagulant at discharge. Of patients eligible for rivaroxaban per the MICHELLE trial, the composite clinical outcome occurred in 1.2% (6/519); similar outcome rates were 5.7% and 0.63% in the MICHELLE trial's control (no anticoagulation) and intervention (rivaroxaban) groups, respectively. Symptomatic venous thromboembolism events and all‐cause mortality were 6.2% (32/519) and 5.66% in the MI‐COVID19 and MICHELLE trial control cohorts, respectively.

Conclusions

Across 35 hospitals in Michigan, ≈1 in 4 patients hospitalized with COVID‐19 would qualify for posthospital thromboprophylaxis. With only 13% of patients actually receiving postdischarge prophylaxis, there is a potential opportunity for improvement in care.

Human platelets display dysregulated sepsis-associated autophagy, induced by altered LC3 protein-protein interaction of the Vici-protein EPG5

Platelets mediate central aspects of host responses during sepsis, an acute profoundly systemic inflammatory response due to infection. Macroautophagy/autophagy, which mediates critical aspects of cellular responses during inflammatory conditions, is known to be a functional cellular process in anucleate platelets, and is essential for normal platelet functions. Nevertheless, how sepsis may alter autophagy in platelets has never been established. Using platelets isolated from septic patients and matched healthy controls, we show that during clinical sepsis, the number of autophagosomes is increased in platelets, most likely due to an accumulation of autophagosomes, some containing mitochondria and indicative of mitophagy. Therefore, autophagy induction or early-stage autophagosome formation (as compared to decreased later-stage autophagosome maturation or autophagosome-late endosome/lysosome fusion) is normal or increased. This was consistent with decreased fusion of autophagosomes with lysosomes in platelets. EPG5 (ectopic P-granules autophagy protein 5 homolog), a protein essential for normal autophagy, expression did increase, while protein-protein interactions between EPG5 and MAP1LC3/LC3 (which orchestrate the fusion of autophagosomes and lysosomes) were significantly reduced in platelets during sepsis. Furthermore, data from a megakaryocyte model demonstrate the importance of TLR4 (toll like receptor 4), LPS-dependent signaling for regulating this mechanism. Similar phenotypes were also observed in platelets isolated from a patient with Vici syndrome: an inherited condition caused by a naturally occurring, loss-of-function mutation in EPG5. Together, we provide evidence that autophagic functions are aberrant in platelets during sepsis, due in part to reduced EPG5-LC3 interactions, regulated by TLR4 engagement, and the resultant accumulation of autophagosomes.Abbreviations: ACTB: beta actin; CLP: cecal ligation and puncture; Co-IP: co-immunoprecipitation; DAP: death associated protein; DMSO: dimethyl sulfoxide; EPG5: ectopic P-granules autophagy protein 5 homolog; ECL: enhanced chemiluminescence; HBSS: Hanks' balanced salt solution; HRP: horseradish peroxidase; ICU: intensive care unit; LPS: lipopolysaccharide; LAMP1: lysosomal associated membrane protein 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; MKs: megakaryocytes; PFA: paraformaldehyde; PBS: phosphate-buffered saline; PLA: proximity ligation assay; pRT-PCR: quantitative real-time polymerase chain reaction; RT: room temperature; SQSTM1/p62: sequestosome 1; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TLR4: toll like receptor 4; TEM: transmission electron microscopy; WGA: wheat germ agglutinin.

COVID-19 generates hyaluronan fragments that directly induce endothelial barrier dysfunction

Vascular injury has emerged as a complication contributing to morbidity in coronavirus disease 2019 (COVID-19). The glycosaminoglycan hyaluronan (HA) is a major component of the glycocalyx, a protective layer of glycoconjugates that lines the vascular lumen and regulates key endothelial cell functions. During critical illness, as in the case of sepsis, enzymes degrade the glycocalyx, releasing fragments with pathologic activities into circulation and thereby exacerbating disease. Here, we analyzed levels of circulating glycosaminoglycans in 46 patients with COVID-19 ranging from moderate to severe clinical severity and measured activities of corresponding degradative enzymes. This report provides evidence that the glycocalyx becomes significantly damaged in patients with COVID-19 and corresponds with severity of disease. Circulating HA fragments and hyaluronidase, 2 signatures of glycocalyx injury, strongly associate with sequential organ failure assessment scores and with increased inflammatory cytokine levels in patients with COVID-19. Pulmonary microvascular endothelial cells exposed to COVID-19 milieu show dysregulated HA biosynthesis and degradation, leading to production of pathological HA fragments that are released into circulation. Finally, we show that HA fragments present at high levels in COVID-19 patient plasma can directly induce endothelial barrier dysfunction in a ROCK- and CD44-dependent manner, indicating a role for HA in the vascular pathology of COVID-19.

Platelet MHC class I mediates CD8+ T-cell suppression during sepsis

Circulating platelets interact with leukocytes to modulate host immune and thrombotic responses. In sepsis, platelet-leukocyte interactions are increased and have been associated with adverse clinical events, including increased platelet-T-cell interactions. Sepsis is associated with reduced CD8+ T-cell numbers and functional responses, but whether platelets regulate CD8+ T-cell responses during sepsis remains unknown. In our current study, we systemically evaluated platelet antigen internalization and presentation through major histocompatibility complex class I (MHC-I) and their effects on antigen-specific CD8+ T cells in sepsis in vivo and ex vivo. We discovered that both human and murine platelets internalize and proteolyze exogenous antigens, generating peptides that are loaded onto MHC-I. The expression of platelet MHC-I, but not platelet MHC-II, is significantly increased in human and murine platelets during sepsis and in human megakaryocytes stimulated with agonists generated systemically during sepsis (eg, interferon-γ and lipopolysaccharide). Upregulation of platelet MHC-I during sepsis increases antigen cross-presentation and interactions with CD8+ T cells in an antigen-specific manner. Using a platelet lineage-specific MHC-I-deficient mouse strain (B2Mf/f-Pf4Cre), we demonstrate that platelet MHC-I regulates antigen-specific CD8+ T-cell proliferation in vitro, as well as the number and functional responses of CD8+ T cells in vivo, during sepsis. Loss of platelet MHC-I reduces sepsis-associated mortality in mice in an antigen-specific setting. These data identify a new mechanism by which platelets, through MHC-I, process and cross-present antigens, engage antigen-specific CD8+ T cells, and regulate CD8+ T-cell numbers, functional responses, and outcomes during sepsis.

Comparison of the coagulopathies associated with COVID-19 and sepsis

BACKGROUND

Coronavirus disease 2019 (COVID-19) is associated with activation of coagulation that mainly presents as thrombosis. Sepsis is also associated with activation of coagulation that mainly presents as disseminated intravascular coagulation. Many studies have reported increased levels of plasma d-dimer in patients with COVID-19 that is associated with severity, thrombosis, and mortality.

OBJECTIVES

The aim of this study was to compare levels of circulating extracellular vesicle tissue factor (EVTF) activity and active plasminogen activator inhibitor 1 (PAI-1) in plasma from patients with COVID-19 or sepsis.

METHODS

We measured levels of d-dimer, EVTF activity, and active PAI-1 in plasma samples from patients with COVID-19 (intensive care unit [ICU], N = 15; and non-ICU, N = 20) and patients with sepsis (N = 35).

RESULTS

Patients with COVID-19 had significantly higher levels of d-dimer, EVTF activity, and active PAI-1 compared with healthy controls. Patients with sepsis had significantly higher levels of d-dimer and EVTF activity compared with healthy controls. Levels of d-dimer were significantly lower in patients with COVID-19 compared with patients with sepsis. Levels of EVTF activity were significantly higher in ICU patients with COVID-19 compared with patients with sepsis. Levels of active PAI-1 were significantly higher in patients with COVID-19 compared with patients with sepsis.

CONCLUSIONS

High levels of both EVTF activity and active PAI-1 may promote thrombosis in patients with COVID-19 due to simultaneous activation of coagulation and inhibition of fibrinolysis. The high levels of active PAI-1 in patients with COVID-19 may limit plasmin degradation of crosslinked fibrin and the release of d-dimer. This may explain the lower levels of D-dimer in patients with COVID-19 compared with patients with sepsis.

Heparanase expression and activity are increased in platelets during clinical sepsis

BACKGROUND

Heparanase (HPSE) is the only known mammalian enzyme that can degrade heparan sulfate. Heparan sulfate proteoglycans are essential components of the glycocalyx, and maintain physiological barriers between the blood and endothelial cells. HPSE increases during sepsis, which contributes to injurious glyocalyx degradation, loss of endothelial barrier function, and mortality.

OBJECTIVES

As platelets are one of the most abundant cellular sources of HPSE, we sought to determine whether HPSE expression and activity increases in human platelets during clinical sepsis. We also examined associations between platelet HPSE expression and clinical outcomes.

PATIENTS/METHODS

Expression and activity of HPSE was determined in platelets isolated from septic patients (n = 59) and, for comparison, sex-matched healthy donors (n = 46) using complementary transcriptomic, proteomic, and functional enzymatic assays. Septic patients were followed for the primary outcome of mortality, and clinical data were captured prospectively for septic patients.

RESULTS

The mRNA expression of HPSE was significantly increased in platelets isolated from septic patients. Ribosomal footprint profiling, followed by [S35] methionine labeling assays, demonstrated that HPSE mRNA translation and HPSE protein synthesis were significantly upregulated in platelets during sepsis. While both the pro- and active forms of HPSE protein increased in platelets during sepsis, only the active form of HPSE protein significantly correlated with sepsis-associated mortality. Consistent with transcriptomic and proteomic upregulation, HPSE enzymatic activity was also increased in platelets during sepsis.

CONCLUSIONS

During clinical sepsis HPSE, translation, and enzymatic activity are increased in platelets. Increased expression of the active form of HPSE protein is associated with sepsis-associated mortality.

Passive Immunity Trial for Our Nation (PassITON): study protocol for a randomized placebo-control clinical trial evaluating COVID-19 convalescent plasma in hospitalized adults

BACKGROUND

Convalescent plasma is being used widely as a treatment for coronavirus disease 2019 (COVID-19). However, the clinical efficacy of COVID-19 convalescent plasma is unclear.

METHODS

The Passive Immunity Trial for Our Nation (PassITON) is a multicenter, placebo-controlled, blinded, randomized clinical trial being conducted in the USA to provide high-quality evidence on the efficacy of COVID-19 convalescent plasma as a treatment for adults hospitalized with symptomatic disease. Adults hospitalized with COVID-19 with respiratory symptoms for less than 14 days are eligible. Enrolled patients are randomized in a 1:1 ratio to 1 unit (200-399 mL) of COVID-19 convalescent plasma that has demonstrated neutralizing function using a SARS-CoV-2 chimeric virus neutralization assay. Study treatments are administered in a blinded fashion and patients are followed for 28 days. The primary outcome is clinical status 14 days after study treatment as measured on a 7-category ordinal scale assessing mortality, respiratory support, and return to normal activities of daily living. Key secondary outcomes include mortality and oxygen-free days. The trial is projected to enroll 1000 patients and is designed to detect an odds ratio ≤ 0.73 for the primary outcome.

DISCUSSION

This trial will provide the most robust data available to date on the efficacy of COVID-19 convalescent plasma for the treatment of adults hospitalized with acute moderate to severe COVID-19. These data will be useful to guide the treatment of COVID-19 patients in the current pandemic and for informing decisions about whether developing a standardized infrastructure for collecting and disseminating convalescent plasma to prepare for future viral pandemics is indicated.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04362176 . Registered on 24 April 2020.

SARS-CoV-2 innate effector associations and viral load in early nasopharyngeal infection

COVID‐19 causes severe disease with poor outcomes. We tested the hypothesis that early SARS‐CoV‐2 viral infection disrupts innate immune responses. These changes may be important for understanding subsequent clinical outcomes. We obtained residual nasopharyngeal swab samples from individuals who requested COVID‐19 testing for symptoms at drive‐through COVID‐19 clinical testing sites operated by the University of Utah. We applied multiplex immunoassays, real‐time polymerase chain reaction assays and quantitative proteomics to 20 virus‐positive and 20 virus‐negative samples. ACE‐2 transcripts increased with infection (OR =17.4, 95% CI [CI] =4.78–63.8) and increasing viral N1 protein transcript load (OR =1.16, CI =1.10–1.23). Transcripts for two interferons (IFN) were elevated, IFN‐λ1 (OR =71, CI =7.07–713) and IFN‐λ2 (OR =40.2, CI =3.86–419), and closely associated with viral N1 transcripts (OR =1.35, CI =1.23–1.49 and OR =1.33 CI =1.20–1.47, respectively). Only transcripts for IP‐10 were increased among systemic inflammatory cytokines that we examined (OR =131, CI =1.01–2620). We found widespread discrepancies between transcription and translation. IFN proteins were unchanged or decreased in infected samples (IFN‐γ OR =0.90 CI =0.33–0.79, IFN‐λ2,3 OR =0.60 CI =0.48–0.74) suggesting viral‐induced shut‐off of host antiviral protein responses. However, proteins for IP‐10 (OR =3.74 CI =2.07–6.77) and several interferon‐stimulated genes (ISG) increased with viral load (BST‐1 OR =25.1, CI =3.33–188; IFIT1 OR =19.5, CI =4.25–89.2; IFIT3 OR =245, CI =15–4020; MX‐1 OR =3.33, CI =1.44–7.70). Older age was associated with substantial modifications of some effects. Ambulatory symptomatic patients had an innate immune response with SARS‐CoV‐2 infection characterized by elevated IFN, proinflammatory cytokine and ISG transcripts, but there is evidence of a viral‐induced host shut‐off of antiviral responses. Our findings may characterize the disrupted immune landscape common in patients with early disease.

Passive Immunity Trial for Our Nation (PassITON): study protocol for a randomized placebo-control clinical trial evaluating COVID-19 convalescent plasma in hospitalized adults

Background: Convalescent plasma is being used widely as a treatment for coronavirus disease 2019 (COVID-19). However, the clinical efficacy of COVID-19 convalescent plasma is unclear. Methods: The Pass ive I mmunity T rial for O ur N ation (PassITON), is a multicenter, placebo-controlled, blinded, randomized clinical trial being conducted in the United States to provide high-quality evidence on the efficacy of COVID-19 convalescent plasma as a treatment for adults hospitalized with symptomatic disease. Adults hospitalized with COVID-19 with respiratory symptoms for less than 14 days are eligible. Enrolled patients are randomized in a 1:1 ratio to 1 unit (200-399 mL) of COVID-19 convalescent plasma that has demonstrated neutralizing function using a SARS-CoV-2 chimeric virus neutralization assay. Study treatments are administered in a blinded fashion and patients are followed for 28 days. The primary outcome is clinical status 14 days after study treatment as measured on a 7-category ordinal scale assessing mortality, respiratory support, and return to normal activities of daily living. Key secondary outcomes include mortality and oxygen-free days. The trial is projected to enroll 1000 patients and is designed to detect an odds ratio ≤ 0.73 for the primary outcome. Discussion: This trial will provide the most robust data available to date on the efficacy of COVID-19 convalescent plasma for the treatment of adults hospitalized with acute moderate to severe COVID-19. These data will be useful to guide the treatment of COVID-19 patients in the current pandemic and for informing decisions about whether developing a standardized infrastructure for collecting and disseminating convalescent plasma to prepare for future viral pandemics is indicated. Trial Registration: ClinicalTrials.gov: NCT04362176. Date of trial registration: April 24, 2020, https://clinicaltrials.gov/ct2/show/NCT04362176.

Mucosal-associated invariant T (MAIT) cells mediate protective host responses in sepsis

Sepsis is a systemic inflammatory response to infection and a leading cause of death. Mucosal-associated invariant T (MAIT) cells are innate-like T cells enriched in mucosal tissues that recognize bacterial ligands. We investigated MAIT cells during clinical and experimental sepsis, and their contribution to host responses. In experimental sepsis, MAIT-deficient mice had significantly increased mortality and bacterial load, and reduced tissue-specific cytokine responses. MAIT cells of WT mice expressed lower levels of IFN-γ and IL-17a during sepsis compared to sham surgery, changes not seen in non-MAIT T cells. MAIT cells of patients at sepsis presentation were significantly reduced in frequency compared to healthy donors, and were more activated, with decreased IFN-γ production, compared to both healthy donors and paired 90-day samples. Our data suggest that MAIT cells are highly activated and become dysfunctional during clinical sepsis, and contribute to tissue-specific cytokine responses that are protective against mortality during experimental sepsis.

SARS-CoV-2 Innate Effector Associations and Viral Load in Early Nasopharyngeal Infection

To examine innate immune responses in early SARS-CoV-2 infection that may change clinical outcomes, we compared nasopharyngeal swab data from 20 virus-positive and 20 virus-negative individuals. Multiple innate immune-related and ACE-2 transcripts increased with infection and were strongly associated with increasing viral load. We found widespread discrepancies between transcription and translation. Interferon proteins were unchanged or decreased in infected samples suggesting virally-induced shut-off of host anti-viral protein responses. However, IP-10 and several interferon-stimulated gene proteins increased with viral load. Older age was associated with modifications of some effects. Our findings may characterize the disrupted immune landscape of early disease.

COVID-19 patients exhibit reduced procoagulant platelet responses

BACKGROUND

Emerging evidence implicates dysfunctional platelet responses in thrombotic complications in COVID-19 patients. Platelets are important players in inflammation-induced thrombosis. In particular, procoagulant platelets support thrombin generation and mediate thromboinflammation.

OBJECTIVES

To examine if procoagulant platelet formation is altered in COVID-19 patients and if procoagulant platelets contribute to pulmonary thrombosis.

PATIENTS/METHODS

Healthy donors and COVID-19 patients were recruited from the University of Utah Hospital System. Platelets were isolated and procoagulant platelet formation measured by annexin V binding as well as mitochondrial function were examined. We utilized mice lacking the ability to form procoagulant platelets (CypDplt-/- ) to examine the role of procoagulant platelets in pulmonary thrombosis.

RESULTS AND CONCLUSIONS

We observed that platelets isolated from COVID-19 patients had a reduced ability to become procoagulant compared to those from matched healthy donors, as evidenced by reduced mitochondrial depolarization and phosphatidylserine exposure following dual stimulation with thrombin and convulxin. To understand what impact reduced procoagulant platelet responses might have in vivo, we subjected mice with a platelet-specific deletion of cyclophilin D, which are deficient in procoagulant platelet formation, to a model of pulmonary microvascular thrombosis. Mice with platelets lacking cyclophilin D died significantly faster from pulmonary microvascular thrombosis compared to littermate wild-type controls. These results suggest dysregulated procoagulant platelet responses may contribute to thrombotic complications during SARS-CoV-2 infection.

Cytokine release syndrome in COVID-19: Innate immune, vascular, and platelet pathogenic factors differ in severity of disease and sex

COVID-19 rapidly emerged as a crippling public health crisis in the last few months, which has presented a series health risk. Understanding of the immune response and biomarker analysis is needed to progress toward understanding disease pathology and developing improved treatment options. The goal of this study is to identify pathogenic factors that are linked to disease severity and patient characteristics. Patients with COVID-19 who were hospitalized from March 17 to June 5, 2020 were analyzed for clinical features of disease and soluble plasma cytokines in association with disease severity and sex. Data from COVID-19 patients with acute illness were examined along with an age- and gender-matched control cohort. We identified a group of 16 soluble factors that were found to be increased in COVID-19 patients compared to controls, whereas 2 factors were decreased. In addition to inflammatory cytokines, we found significant increases in factors known to mediate vasculitis and vascular remodeling (PDGF-AA, PDGF-AB-BB, soluble CD40L (sCD40L), FGF, and IP10). Four factors such as platelet-derived growth factors, fibroblast growth factor-2, and IFN-γ-inducible protein 10 were strongly associated with severe disease and ICU admission. Th2-related factors (IL-4 and IL-13) were increased with IL-4 and sCD40L present at increased levels in males compared with females. Our analysis revealed networking clusters of cytokines and growth factors, including previously unknown roles of vascular and stromal remodeling, activation of the innate immunity, as well activation of type 2 immune responses in the immunopathogenesis of COVID-19. These data highlight biomarker associations with disease severity and sex in COVID-19 patients.

Phospho-inositide-dependent kinase 1 regulates signal dependent translation in megakaryocytes and platelets

BACKGROUND

Regulated protein synthesis is essential for megakaryocyte (MK) and platelet functions, including platelet production and activation. PDK1 (phosphoinositide-dependent kinase 1) regulates platelet functional responses and has been associated with circulating platelet counts. Whether PDK1 also directly regulates protein synthetic responses in MKs and platelets, and platelet production by MKs, remains unknown.

OBJECTIVE

To determine if PDK1 regulates protein synthesis in MKs and platelets.

METHODS

Pharmacologic PDK1 inhibitors (BX-795) and mice where PDK1 was selectively ablated in MKs and platelets (PDK1-/- ) were used. PDK1 signaling in MKs and platelets (human and murine) were assessed by immunoblots. Activation-dependent translation initiation and protein synthesis in MKs and platelets was assessed by probing for dissociation of eIF4E from 4EBP1, and using m7-GTP pulldowns and S35 methionine incorporation assays. Proplatelet formation by MKs, synthesis of Bcl-3 and MARCKs protein, and clot retraction were employed for functional assays.

RESULTS

Inhibiting or ablating PDK1 in MKs and platelets abolished the phosphorylation of 4EBP1 and eIF4E by preventing activation of the PI3K and MAPK pathways. Inhibiting PDK1 also prevented dissociation of eIF4E from 4EBP1, decreased binding of eIF4E to m7GTP (required for translation initiation), and significantly reduced de novo protein synthesis. Inhibiting PDK1 reduced proplatelet formation by human MKs and blocked MARCKs protein synthesis. In both human and murine platelets, PDK1 controlled Bcl-3 synthesis. Inhibition of PDK1 led to complete failure of clot retraction in vitro.

CONCLUSIONS

PDK1 is a previously unidentified translational regulator in MKs and platelets, controlling protein synthetic responses, proplatelet formation, and clot retraction.

Glucose Metabolism Is Required for Platelet Hyperactivation in a Murine Model of Type 1 Diabetes

Patients with type 1 diabetes mellitus (T1DM) have increased thrombosis and platelet activation. The mechanisms for platelet hyperactivation in diabetes are incompletely understood. T1DM is accompanied by hyperglycemia, dyslipidemia, and increased inflammation in addition to an altered hormonal milieu. In vitro analysis of platelets revealed that normal glucose reduces platelet activation whereas hyperglycemic conditions increase platelet activation. We therefore hypothesized that hyperglycemia increases platelet glucose utilization, which increases platelet activation to promote thrombosis. Glucose uptake and glycolysis were increased in platelets isolated from mice given streptozotocin (STZ) to induce T1DM in concert with induction of GLUT3. Platelets from STZ-induced diabetic mice exhibited increased activation after administration of protease-activated receptor 4 peptide and convulxin. In contrast, platelets isolated from GLUT1 and GLUT3 double-knockout (DKO) mice, which lack the ability to use glucose, failed to increase activation in hyperglycemic mice. Diabetic mice displayed decreased survival in a collagen/epinephrine-induced pulmonary embolism model of in vivo platelet activation relative to nondiabetic controls. Survival after pulmonary embolism was increased in diabetic DKO mice relative to nondiabetic controls. These data reveal that increased platelet glucose metabolism in vivo contributes to increased platelet activation and thrombosis in a model of T1DM.

Amicus or Adversary Revisited: Platelets in Acute Lung Injury and Acute Respiratory Distress Syndrome

Platelets are essential cellular effectors of hemostasis and contribute to disease as circulating effectors of pathologic thrombosis. These are their most widely known biologic activities. Nevertheless, recent observations demonstrate that platelets have a much more intricate repertoire beyond these traditional functions and that they are specialized for contributions to vascular barrier integrity, organ repair, antimicrobial host defense, inflammation, and activities across the immune continuum. Paradoxically, on the basis of clinical investigations and animal models of disease, some of these newly discovered activities of platelets appear to contribute to tissue injury. Studies in the last decade indicate unique interactions of platelets and their precursor, the megakaryocyte, in the lung and implicate platelets as essential effectors in experimental acute lung injury and clinical acute respiratory distress syndrome. Additional discoveries derived from evolving work will be required to precisely define the contributions of platelets to complex subphenotypes of acute lung injury and to determine if these remarkable and versatile blood cells are therapeutic targets in acute respiratory distress syndrome.

Deletion of GLUT1 and GLUT3 Reveals Multiple Roles for Glucose Metabolism in Platelet and Megakaryocyte Function

Anucleate platelets circulate in the blood to facilitate thrombosis and diverse immune functions. Platelet activation leading to clot formation correlates with increased glycogenolysis, glucose uptake, glucose oxidation, and lactic acid production. Simultaneous deletion of glucose transporter (GLUT) 1 and GLUT3 (double knockout [DKO]) specifically in platelets completely abolished glucose uptake. In DKO platelets, mitochondrial oxidative metabolism of non-glycolytic substrates, such as glutamate, increased. Thrombosis and platelet activation were decreased through impairment at multiple activation nodes, including Ca²⁺ signaling, degranulation, and integrin activation. DKO mice developed thrombocytopenia, secondary to impaired pro-platelet formation from megakaryocytes, and increased platelet clearance resulting from cytosolic calcium overload and calpain activation. Systemic treatment with oligomycin, inhibiting mitochondrial metabolism, induced rapid clearance of platelets, with circulating counts dropping to zero in DKO mice, but not wild-type mice, demonstrating an essential role for energy metabolism in platelet viability. Thus, substrate metabolism is essential for platelet production, activation, and survival.

Glucose Transporter 3 Potentiates Degranulation and Is Required for Platelet Activation

OBJECTIVE

On activation, platelets increase glucose uptake, glycolysis, and glucose oxidation and consume stored glycogen. This correlation between glucose metabolism and platelet function is not well understood and even less is known about the role of glucose metabolism on platelet function in vivo. For glucose to enter a cell, it must be transported through glucose transporters. Here we evaluate the contribution of GLUT3 (glucose transporter 3) to platelet function to better understand glucose metabolism in platelets.

APPROACH AND RESULTS

Platelet-specific knockout of GLUT3 was generated by crossing mice harboring GLUT3 floxed allele to a PF4 (platelet factor 4)-driven Cre recombinase. In platelets, GLUT3 is localized primarily on α-granule membranes and under basal conditions facilitates glucose uptake into α-granules to be used for glycolysis. After activation, platelets degranulate and GLUT3 translocates to the plasma membrane, which is responsible for activation-mediated increased glucose uptake. In vivo, loss of GLUT3 in platelets increased survival in a collagen/epinephrine model of pulmonary embolism, and in a K/BxN model of autoimmune inflammatory disease, platelet-specific GLUT3 knockout mice display decreased disease progression. Mechanistically, loss of GLUT3 decreased platelet degranulation, spreading, and clot retraction. Decreased α-granule degranulation is due in part to an impaired ability of GLUT3 to potentiate exocytosis.

CONCLUSIONS

GLUT3-mediated glucose utilization and glycogenolysis in platelets promotes α-granule release, platelet activation, and postactivation functions.

Platelets in Pulmonary Immune Responses and Inflammatory Lung Diseases

Platelets are essential for physiological hemostasis and are central in pathological thrombosis. These are their traditional and best known activities in health and disease. In addition, however, platelets have specializations that broaden their functional repertoire considerably. These functional capabilities, some of which are recently discovered, include the ability to sense and respond to infectious and immune signals and to act as inflammatory effector cells. Human platelets and platelets from mice and other experimental animals can link the innate and adaptive limbs of the immune system and act across the immune continuum, often also linking immune and hemostatic functions. Traditional and newly recognized facets of the biology of platelets are relevant to defensive, physiological immune responses of the lungs and to inflammatory lung diseases. The emerging view of platelets as blood cells that are much more diverse and versatile than previously thought further predicts that additional features of the biology of platelets and of megakaryocytes, the precursors of platelets, will be discovered and that some of these will also influence pulmonary immune defenses and inflammatory injury.

The role of rigid and hinged polypropylene ankle-foot-orthoses in the management of cerebral palsy: a case study

Ankle-foot orthoses are commonly used in the treatment of spastic cerebral palsy to hold the foot in a position conductive to a more functional gait. This study, utilizing quantitative biomechanical techniques, evaluates the effects of a rigid ankle-foot orthosis and a hinged ankle-foot orthosis on spastic cerebral palsy gait. The subject was a 4.5 year old female diagnosed as spastic diplegic cerebral palsied shortly after birth. Testing involved collection of kinematic coordinate data employing a WATSMART video system and ground reaction force data using a Kistler force plate. Jensen's (1978) photogrammetric method was used to estimate body segment inertial parameters. The hinged ankle-foot orthosis was found to be more effective than the rigid ankle-foot orthosis. The subject exhibited a more natural ankle motion during the stance phase of gait, greater symmetry of segmental lower extremity motion, and decreased knee moments during stance while wearing a hinged ankle-foot orthosis.