Arginase 1 (Arg1) as an Up-Regulated Gene in COVID-19 Patients: A Promising Marker in COVID-19 Immunopathy

Investigating the Hepcidin Gene Polymorphisms in COVID-19-Associated Mucormycosis Susceptibility: A Clinical-Laboratory Study

Background

Following the coronavirus disease 2019 outbreak (COVID-19), it became a worrisome health burden worldwide. COVID-19-associated mucormycosis emergence, characterized by dysregulated inflammation and iron metabolism, exacerbated the prognosis of affected patients. Given the significance of hepcidin in regulating inflammation and iron metabolism, this study investigated the significance of hepcidin single nucleotide polymorphisms (SNP) in COVID-19-associated mucormycosis development, along with the association between the clinical and laboratory factors and COVID-19-associated mucormycosis.

Methods

From September 2021 to November 2021, COVID-19 patients with and without mucormycosis were enrolled in this cross-sectional study. Their medical records and laboratory results were investigated. SNP genotyping was performed using Sanger sequencing. Hardy-Weinberg Equilibrium, Pearson's Chi square, and student t test were used for analyzing the data using SPSS software version 25. P<0.05 was regarded as statistically significant.

Results

Here, 110 COVID-19 patients with and without mucormycosis were investigated. Elevated levels of urea, aspartate aminotransferase, lactate dehydrogenase, and increased ratio of polymorphonuclear neutrophil to lymphocytes were associated with decreased risk of COVID-19-associated mucormycosis in patients (all P<0.05). Moreover, diabetes mellitus increased the risk of mucormycosis (P=0.028). In contrast to patients without mucormycosis, patients with mucormycosis did not display 442 GA and SNP335 GT genotypes. Unlike patients without mucormycosis, none of the patients with mucormycosis had SNP442 GA and SNP335 GT genotypes. Regarding SNP 443 C>T, and the combination of SNPs 582 A>G and 443 C>T, CC genotype and AA+CC genotypes were associated with increased lactate dehydrogenase levels in COVID-19 patients, respectively.

Conclusion

Regarding SNP 443 C>T, the CC genotype was associated with increased lactate dehydrogenase levels in COVID-19 patients. In terms of SNP 582 A>G and SNP 443 C>T, COVID-19 patients with AA+CC genotypes had higher levels of LDH. None of the patients with mucormycosis had SNP442 GA and SNP335 GT genotypes.

Unveiling the metabolic and coagulation disruptions in SARS-CoV-2-associated acute macular neuroretinopathy: A case-control study

SARS-CoV-2 infection has been associated with the increased incidence of acute macular neuroretinopathy (AMN), an infrequent ocular disorder. However, the precise mechanisms underpinning AMN in the context of SARS-CoV-2 infection (AMN-SARS-CoV-2) remain elusive. In this case-control study, 14 patients diagnosed with AMN-SARS-CoV-2 between 2022/12 and 2023/3 were enrolled and compared with 14 SARS-CoV-2-infected individuals without AMN, who served as controls (SARS-CoV-2-no AMN). Metabolomic profiling using ultrahigh-performance liquid chromatography-online electrospray mass spectrometry revealed significant alterations in serum metabolites in AMN-SARS-CoV-2 patients. Coagulation abnormalities were observed in AMN-SARS-CoV-2 patients, and their relationship with metabolic disorders was studied. Finally, a predictive model for AMN-SARS-CoV-2 was established. Seventy-six upregulated and 42 downregulated metabolites were identified in AMN-SARS-CoV-2 cases. Notably, arginine metabolism within the urea cycle was significantly altered, evidenced by variations in ornithine, citrulline,  l-proline, and ADAM levels, correlating with abnormal coagulation markers like platelet crit, fibrinogen degradation product, and fibrinogen. Additionally, increased arginase 1 (AGR1) activity within the urea cycle and reduced nitric oxide synthase activity were observed in AMN-SARS-CoV-2. The integration of urea cycle metabolite levels with coagulation parameters yielded a robust discriminatory model for AMN-SARS-CoV-2, as evidenced by an area under the curve of 0.96. The findings of the present study enhance our comprehension of the underlying metabolic mechanisms associated with AMN-SARS-CoV-2 and offer potential diagnostic markers for this uncommon ocular disorder within the context of SARS-CoV-2 infection.

Increase in venous thromboembolism in SARS-CoV-2 infected lung tissue: proteome analysis of lung parenchyma, isolated endothelium, and thrombi

AIMS

COVID-19 pneumonia is characterized by an increased rate of deep venous thrombosis and pulmonary embolism. To better understand the pathophysiology behind thrombosis in COVID-19, we performed proteomics analysis on SARS-CoV-2 infected lung tissue.

METHODS

Liquid chromatography mass spectrometry was performed on SARS-CoV-2 infected postmortem lung tissue samples. Five protein profiling analyses were performed: whole slide lung parenchyma analysis, followed by analysis of isolated thrombi and endothelium, both stratified by disease (COVID-19 versus influenza) and thrombus morphology (embolism versus in situ). Influenza autopsy cases with pulmonary thrombi were used as controls.

RESULTS

Compared to influenza controls, both analyses of COVID-19 whole-tissue and isolated endothelium showed upregulation of proteins and pathways related to liver metabolism including urea cycle activation, with arginase being among the top upregulated proteins in COVID-19 lung tissue. Analysis of isolated COVID-19 thrombi showed significant downregulation of pathways related to platelet activation compared to influenza thrombi. Analysis of isolated thrombi based on histomorphology shows that in situ thrombi have significant upregulation of coronavirus pathogenesis proteins.

CONCLUSIONS

The decrease in platelet activation pathways in severe COVID-19 thrombi suggests a relative increase in venous thromboembolism, as thrombi from venous origin tend to contain fewer platelets than arterial thrombi. Based on histomorphology, in situ thrombi show upregulation of various proteins related to SARS-CoV-2 pathogenesis compared to thromboemboli, which may indicate increased in situ pulmonary thrombosis in COVID-19. Therefore, this study supports the increase of venous thromboembolism without undercutting the involvement of in situ thrombosis in severe COVID-19.

Plasma Protein Biomarkers Distinguish Multisystem Inflammatory Syndrome in Children From Other Pediatric Infectious and Inflammatory Diseases

BACKGROUND

Multisystem inflammatory syndrome in children (MIS-C) is a rare but serious hyperinflammatory complication following infection with severe acute respiratory syndrome coronavirus 2. The mechanisms underpinning the pathophysiology of MIS-C are poorly understood. Moreover, clinically distinguishing MIS-C from other childhood infectious and inflammatory conditions, such as Kawasaki disease or severe bacterial and viral infections, is challenging due to overlapping clinical and laboratory features. We aimed to determine a set of plasma protein biomarkers that could discriminate MIS-C from those other diseases.

METHODS

Seven candidate protein biomarkers for MIS-C were selected based on literature and from whole blood RNA sequencing data from patients with MIS-C and other diseases. Plasma concentrations of ARG1, CCL20, CD163, CORIN, CXCL9, PCSK9 and ADAMTS2 were quantified in MIS-C (n = 22), Kawasaki disease (n = 23), definite bacterial (n = 28) and viral (n = 27) disease and healthy controls (n = 8). Logistic regression models were used to determine the discriminatory ability of individual proteins and protein combinations to identify MIS-C and association with severity of illness.

RESULTS

Plasma levels of CD163, CXCL9 and PCSK9 were significantly elevated in MIS-C with a combined area under the receiver operating characteristic curve of 85.7% (95% confidence interval: 76.6%-94.8%) for discriminating MIS-C from other childhood diseases. Lower ARG1 and CORIN plasma levels were significantly associated with severe MIS-C cases requiring inotropes, pediatric intensive care unit admission or with shock.

CONCLUSION

Our findings demonstrate the feasibility of a host protein biomarker signature for MIS-C and may provide new insight into its pathophysiology.

Arginase is upregulated in healthy women infected by oncogenic HPV types

INTRODUCTION

The implication of arginase enzyme in Human Papillomavirus (HPV) infections has not been clearly elucidated. The present study investigates whether HPV infection is correlated with changes in plasmatic arginase activity and cervical ARG1 and ARG2 mRNA expression among infected women negative for intraepithelial lesions (NIL).

MATERIEL AND METHODS

The present study included 300 women. The plasmatic arginase activity was evaluated by a colorimetric assay. Cervical HPV was detected by real-time PCR. The circulating viral load and ARG1 and ARG2 mRNA expression quantification were performed by quantitative real-time PCR.

RESULTS

A significant increase in plasma arginase activity and ARG1 and ARG2 mRNA expression levels in cervical cells was observed among HPV-positive women compared to the HPV-negative group. The highest levels were significantly associated with oncogenic HPV, and increased arginase activity was associated with a high HPV circulating viral load. Moreover, the highest levels of arginase activity were observed in oncogenic HPV-positive inflammatory smears.

DISCUSSION

These data suggest that HPV could modulate arginase activity and expression, which may restrict arginine bioavailability and inhibit this amino acid's antiviral properties.

CONCLUSION

Our findings revealed that arginase activity and isoform gene expression were upregulated in women with HPV infection, particularly the oncogenic HPV types.

N-Acetylglucosamine mitigates lung injury and pulmonary fibrosis induced by bleomycin

Lung injury and pulmonary fibrosis contribute to morbidity and mortality, and, in particular, are characterized as leading cause on confirmed COVID-19 death. To date, efficient therapeutic approach for such lung diseases is lacking. N-Acetylglucosamine (NAG), an acetylated derivative of glucosamine, has been proposed as a potential protector of lung function in several types of lung diseases. The mechanism by which NAG protects against lung injury, however, remains unclear. Here, we show that NAG treatment improves pulmonary function in bleomycin (BLM)-induced lung injury model measured by flexiVent system. At early phase of lung injury, NAG treatment results in silenced immune response by targeting ARG1+ macrophages activation, and, consequently, blocks KRT8+ transitional stem cell in the alveolar region to stimulate PDGF Rβ+ fibroblasts hyperproliferation, thereby attenuating the pulmonary fibrosis. This combinational depression of immune response and extracellular matrix deposition within the lung mitigates lung injury and pulmonary fibrosis induced by BLM. Our findings provide novel insight into the protective role of NAG in lung injury.

Exploring dysregulated immune response genes and endothelial dysfunction biomarkers as predictors of severe COVID-19

Identifying individuals and factors associated with severe cases of COVID-19 is crucial as the pandemic continues to spread globally. Effective biomarkers for predicting severe cases are essential for optimizing clinical management, therapy, and preventing unfavorable outcomes. This exploratory observational study aimed to investigate the expression of dysregulated immune response genes (ARG1, NOS2, ITGA4, and SELPLG) in total leukocytes, plasmatic levels of P-selectin and PSGL-1, and their clinical associations in patients with mild and severe COVID-19. Data from 117 confirmed COVID-19 patients (severe = 58, mild = 59) were collected upon admission. Gene expression was measured using RT-qPCR, and plasma protein levels assessed with ELISA assay. The severe COVID-19 patient group had a higher median age of 62.0 (p = 0.0001), a higher proportion of black individuals (86.2%, p < 0.0001), and more males (65.5%, p = 0.007). The neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR) were significantly higher in the severe COVID-19 patient group (p < 0.0001), indicating ongoing systemic inflammation. Severe COVID-19 patients also exhibited increased expression of ARG1 (p < 0.05) and SELPLG (p < 0.0001) genes, as well as higher concentrations of soluble P-selectin (p < 0.005) and PSGL-1 (p < 0.05) proteins. Multivariate analysis revealed that NLR, PLR, the expression of SELPLG and sPSGL-1 were independent predictors of COVID-19 severity. In conclusion, this study suggests that biomarkers of endothelial dysfunction and dysregulated leukocyte responses are associated with COVID-19 severity, serving as promising predictive tools for optimizing clinical management and patient monitoring.

Optimization of the arginase activity assay micromethod for macrophages and sera

OBJECTIVE

We optimized the spectrophotometric micromethod for the determination of arginase activity based on the Corraliza et al. modification of Schimke's method. Arginase activity in sera from patients suffering from human African trypanosomiasis, in macrophage lysates from trypanosome-infected mice, and in purified bovine liver arginase was compared using the conventional and optimized micromethods.

RESULTS

The sensitivity of both micromethods was comparable. However, our optimized method has the following advantages: it uses small sample volumes (6 µl per assay vs. 50 µl) and reagent volumes (200 µl vs. 400 µl), it can be carried out in a single microplate well, thereby minimizing handling, and it requires fewer materials and utilizes readily available equipment. Our optimized method proved to be applicable and well suited for small-volume samples and resource-poor laboratories.

Hydroxytyrosol and Arginine as Antioxidant, Anti-Inflammatory and Immunostimulant Dietary Supplements for COVID-19 and Long COVID

Phytochemicals from plant extracts are becoming increasingly popular in the world of food science and technology because they have positive effects on human health. In particular, several bioactive foods and dietary supplements are being investigated as potential treatments for chronic COVID. Hydroxytyrosol (HXT) is a natural antioxidant, found in olive oil, with antioxidant anti-inflammatory properties that has been consumed by humans for centuries without reported adverse effects. Its use was approved by the European Food Safety Authority as a protective agent for the cardiovascular system. Similarly, arginine is a natural amino acid with anti-inflammatory properties that can modulate the activity of immune cells, reducing the production of pro-inflammatory cytokines such as IL-6 and TNF-α. The properties of both substances may be particularly beneficial in the context of COVID-19 and long COVID, which are characterised by inflammation and oxidative stress. While l-arginine promotes the formation of ^•NO, HXT prevents oxidative stress and inflammation in infected cells. This combination could prevent the formation of harmful peroxynitrite, a potent pro-inflammatory substance implicated in pneumonia and COVID-19-associated organ dysfunction, as well as reduce inflammation, improve immune function, protect against free radical damage and prevent blood vessel injury. Further research is needed to fully understand the potential benefits of HXT and arginine in the context of COVID-19.

Bacterial Brain Abscess and Life-Threatening Intracranial Hypertension Requiring Emergent Decompressive Craniectomy After SARS-CoV-2 Infection in a Healthy Adolescent

Acute coronavirus 2 (SARS-CoV-2) infection usually results in mild symptoms, but secondary infections after SARS-CoV-2 infection can occur, particularly with comorbid conditions. We present the clinical course of a healthy adolescent with a brain abscess and life-threatening intracranial hypertension requiring emergent decompressive craniectomy after a SARS-CoV-2 infection. A 13-year-old healthy immunized male presented with invasive frontal, ethmoid, and maxillary sinusitis and symptoms of lethargy, nausea, headache, and photophobia due to a frontal brain abscess diagnosed three weeks after symptoms and 11 days of oral amoxicillin treatment. Coronavirus disease 2019 (COVID-19) reverse transcription-polymerase chain reaction (RT-PCR) was negative twice but then positive on amoxicillin day 11 (symptom day 21), when magnetic resonance imaging revealed a 2.5-cm right frontal brain abscess with a 10-mm midline shift. The patient underwent emergent craniotomy for right frontal epidural abscess washout and functional endoscopic sinus surgery with ethmoidectomy. On a postoperative day one, his neurological condition showed new right-sided pupillary dilation and decreased responsiveness. His vital signs showed bradycardia and systolic hypertension. He underwent an emergent decompressive craniectomy for signs of brain herniation. Bacterial PCR was positive for Streptococcus intermedius, for which he received intravenous vancomycin and metronidazole. He was discharged home on hospital day 14 without neurological sequelae and future bone flap replacement. Our case highlights the importance of timely recognition and treatment of brain abscess and brain herniation in patients with neurological symptoms after SARS-CoV-2 infection, even in otherwise healthy patients.

Diagnostic, Prognostic and Mechanistic Biomarkers of COVID-19 Identified by Mass Spectrometric Metabolomics

A number of studies have assessed the impact of SARS-CoV-2 infection and COVID-19 severity on the metabolome of exhaled air, saliva, plasma, and urine to identify diagnostic and prognostic biomarkers. In spite of the richness of the literature, there is no consensus about the utility of metabolomic analyses for the management of COVID-19, calling for a critical assessment of the literature. We identified mass spectrometric metabolomic studies on specimens from SARS-CoV2-infected patients and subjected them to a cross-study comparison. We compared the clinical design, technical aspects, and statistical analyses of published studies with the purpose to identify the most relevant biomarkers. Several among the metabolites that are under- or overrepresented in the plasma from patients with COVID-19 may directly contribute to excessive inflammatory reactions and deficient immune control of SARS-CoV2, hence unraveling important mechanistic connections between whole-body metabolism and the course of the disease. Altogether, it appears that mass spectrometric approaches have a high potential for biomarker discovery, especially if they are subjected to methodological standardization.

An untargeted metabolomic approach to investigate antiviral defence mechanisms in memory leukocytes secreting anti-SARS-CoV-2 IgG in vitro

Evidence shows that individuals infected by SARS-CoV-2 experience an altered metabolic state in multiple organs. Metabolic activities are directly involved in modulating immune responses against infectious diseases, yet our understanding of how host metabolism relates to inflammatory responses remains limited. To better elucidate the underlying biochemistry of the leukocyte response, we focused our analysis on possible relationships between SARS-CoV-2 post-infection stages and distinct metabolic pathways. Indeed, we observed a significant altered metabolism of tryptophan and urea cycle pathways in cultures of peripheral blood mononuclear cells obtained 60-90 days after infection and showing in vitro IgG antibody memory for spike-S1 antigen (n = 17). This work, for the first time, identifies metabolic routes in cell metabolism possibly related to later stages of immune defence against SARS-CoV-2 infection, namely, when circulating antibodies may be absent but an antibody memory is present. The results suggest reprogramming of leukocyte metabolism after viral pathogenesis through activation of specific amino acid pathways possibly related to protective immunity against SARS-CoV-2.

Genetic regulation of iron homeostasis in sideropenic patients with mild COVID-19 disease under a new oral iron formulation: Lessons from a different perspective

Background

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) needs iron to replicate itself. Coronaviruses are able to upregulate Chop/Gadd153 and Arg1 genes, consequently leading to CD8 lymphocytes decrease, degradation of asparagine and decreased nitric oxide (NO), thus impairing immune response and antithrombotic functions. Little is known about regulation of genes involved in iron metabolism in paucisymptomatic patients with COVID-19 disease or in patients with iron deficiency treated with sucrosomial iron.

Methods

Whole blood was taken from the COVID-19 patients and from patients with sideropenic anemia, treated or not (control group) with iron supplementations. Enrolled patients were: affected by COVID19 under sucrosomal iron support (group A), affected by COVID-19 not under oral iron support (group B), iron deficiency not under treatment, not affected by COVID19 (control group). After RNA extraction and complementary DNA (cDNA) synthesis of Arg1, Hepcidin and Chop/Gadd153, gene expression from the 3 groups was measured by qRT-PCR. M2 macrophages were detected by cytofluorimetry using CD163 and CD14 markers.

Results

Forty patients with COVID-19 (group A), 20 patients with iron deficiency treated with sucrosomial iron (group B) and 20 patients with iron deficiency not under treatment (control group) were enrolled. In all the patients supported with oral sucrosomial iron, the gene expression of Chop, Arg1 and Hepcidin genes was lower than in sideropenic patients not supported with iron, M1 macrophages polarization and functional iron deficiency was also lower in group A and B, than observed in the control group.

Conclusions

New oral iron formulations, as sucrosomial iron, are able to influence the expression of genes like Chop and Arg1 and to influence M2 macrophage polarization mainly in the early phase of COVID-19 disease.

Analysis and identification of potential type II helper T cell (Th2)-Related key genes and therapeutic agents for COVID-19

COVID-19 pandemic poses a severe threat to public health. However, so far, there are no effective drugs for COVID-19. Transcriptomic changes and key genes related to Th2 cells in COVID-19 have not been reported. These genes play an important role in host interactions with SARS-COV-2 and may be used as promising target. We analyzed five COVID-19-associated GEO datasets (GSE157103, GSE152641, GSE171110, GSE152418, and GSE179627) using the xCell algorithm and weighted gene co-expression network analysis (WGCNA). Results showed that 5 closely correlated modular genes to COVID-19 and Th2 cell enrichment levels, including purple, blue, pink, tan and turquoise, were intersected with differentially expressed genes (DEGs) and 648 shared genes were obtained. GO and KEGG pathway enrichment analyses revealed that they were enriched in cell proliferation, differentiation, and immune responses after virus infection. The most significantly enriched pathway involved the regulation of viral life cycle. Three key genes, namely CCNB1, BUB1, and UBE2C, may clarify the pathogenesis of COVID-19 associated with Th2 cells. 11 drug candidates were identified that could down-regulate three key genes using the cMAP database and demonstrated strong drugs binding energies aganist the three keygenes using molecular docking methods. BUB1, CCNB1 and UBE2C were identified key genes for COVID-19 and could be promising therapeutic targets.

Comprehensive bioinformatics analysis reveals common potential mechanisms, progression markers, and immune cells of coronary virus disease 2019 and atrial fibrillation

OBJECTIVES

Atrial fibrillation (AF) is the most common arrhythmia in coronary virus disease 2019 (COVID-19) patients, especially in severe patients. A history of AF can exacerbate COVID-19 symptoms. COVID-19 Patients with new-onset AF have prolonged hospital stays and increased death risk. However, the mechanisms and targets of the interaction between COVID-19 and AF have not been elucidated.

MATERIALS AND METHODS

We used a series of bioinformatics analyses to understand biological pathways, protein-protein interaction (PPI) networks, gene regulatory networks (GRNs), and protein-chemical interactions between COVID-19 and AF and constructed an AF-related gene signature to assess COVID-19 severity and prognosis.

RESULTS

We found folate and one-carbon metabolism, calcium regulation, and TFG-β signaling pathway as potential mechanisms linking COVID-19 and AF, which may be involved in alterations in neutrophil metabolism, inflammation, and endothelial cell function. We identified hug genes and found that NF-κb, hsa-miR-1-3p, hsa-miR-124-3p, valproic acid, and quercetin may be key regulatory molecules. We constructed a 3-gene signature consisting of ARG1, GIMAP7, and RFX2 models for the assessment of COVID-19 severity and prognosis, and found that they are associated with neutrophils, T cells, and hematopoietic stem cells, respectively.

CONCLUSION

Our study reveals a dysregulation of metabolism, inflammation, and immunity between COVID-19 and AF, and identified several therapeutic targets and progression markers. We hope that the results will reveal important insights into the complex interactions between COVID-19 and AF that will drive novel drug development and help in severity assessment.

Arginase: shedding light on the mechanisms and opportunities in cardiovascular diseases

Arginase, a binuclear manganese metalloenzyme in the urea, catalyzes the hydrolysis of L-arginine to urea and L-ornithine. Both isoforms, arginase 1 and arginase 2 perform significant roles in the regulation of cellular functions in cardiovascular system, such as senescence, apoptosis, proliferation, inflammation, and autophagy, via a variety of mechanisms, including regulating L-arginine metabolism and activating multiple signal pathways. Furthermore, abnormal arginase activity contributes to the initiation and progression of a variety of CVDs. Therefore, targeting arginase may be a novel and promising approach for CVDs treatment. In this review, we give a comprehensive overview of the physiological and biological roles of arginase in a variety of CVDs, revealing the underlying mechanisms of arginase mediating vascular and cardiac function, as well as shedding light on the novel and promising therapeutic approaches for CVDs therapy in individuals.

Characterization of Altered Gene Expression and Histone Methylation in Peripheral Blood Mononuclear Cells Regulating Inflammation in COVID-19 Patients

The pandemic of COVID-19 has caused >5 million deaths in the world. One of the leading causes of the severe form of COVID-19 is the production of massive amounts of proinflammatory cytokines. Epigenetic mechanisms, such as histone/DNA methylation, miRNA, and long noncoding RNA, are known to play important roles in the regulation of inflammation. In this study, we investigated if hospitalized COVID-19 patients exhibit alterations in epigenetic pathways in their PBMCs. We also compared gene expression profiles between healthy controls and COVID-19 patients. Despite individual variations, the expressions of many inflammation-related genes, such as arginase 1 and IL-1 receptor 2, were significantly upregulated in COVID-19 patients. We also found the expressions of coagulation-related genes Von Willebrand factor and protein S were altered in COVID-19 patients. The expression patterns of some genes, such as IL-1 receptor 2, correlated with their histone methylation marks. Pathway analysis indicated that most of those dysregulated genes were in the TGF-β, IL-1b, IL-6, and IL-17 pathways. A targeting pathway revealed that the majority of those altered genes were targets of dexamethasone, which is an approved drug for COVID-19 treatment. We also found that the expression of bone marrow kinase on chromosome X, a member of TEC family kinases, was increased in the PBMCs of COVID-19 patients. Interestingly, some inhibitors of TEC family kinases have been used to treat COVID-19. Overall, this study provides important information toward identifying potential biomarkers and therapeutic targets for COVID-19 disease.

Virus-Induced Membrane Fusion in Neurodegenerative Disorders

A growing body of epidemiological and research data has associated neurotropic viruses with accelerated brain aging and increased risk of neurodegenerative disorders. Many viruses replicate optimally in senescent cells, as they offer a hospitable microenvironment with persistently elevated cytosolic calcium, abundant intracellular iron, and low interferon type I. As cell-cell fusion is a major driver of cellular senescence, many viruses have developed the ability to promote this phenotype by forming syncytia. Cell-cell fusion is associated with immunosuppression mediated by phosphatidylserine externalization that enable viruses to evade host defenses. In hosts, virus-induced immune dysfunction and premature cellular senescence may predispose to neurodegenerative disorders. This concept is supported by novel studies that found postinfectious cognitive dysfunction in several viral illnesses, including human immunodeficiency virus-1, herpes simplex virus-1, and SARS-CoV-2. Virus-induced pathological syncytia may provide a unified framework for conceptualizing neuronal cell cycle reentry, aneuploidy, somatic mosaicism, viral spreading of pathological Tau and elimination of viable synapses and neurons by neurotoxic astrocytes and microglia. In this narrative review, we take a closer look at cell-cell fusion and vesicular merger in the pathogenesis of neurodegenerative disorders. We present a "decentralized" information processing model that conceptualizes neurodegeneration as a systemic illness, triggered by cytoskeletal pathology. We also discuss strategies for reversing cell-cell fusion, including, TMEM16F inhibitors, calcium channel blockers, senolytics, and tubulin stabilizing agents. Finally, going beyond neurodegeneration, we examine the potential benefit of harnessing fusion as a therapeutic strategy in regenerative medicine.

Targeting Arginine in COVID-19-Induced Immunopathology and Vasculopathy

Coronavirus disease 2019 (COVID-19) represents a major public health crisis that has caused the death of nearly six million people worldwide. Emerging data have identified a deficiency of circulating arginine in patients with COVID-19. Arginine is a semi-essential amino acid that serves as key regulator of immune and vascular cell function. Arginine is metabolized by nitric oxide (NO) synthase to NO which plays a pivotal role in host defense and vascular health, whereas the catabolism of arginine by arginase to ornithine contributes to immune suppression and vascular disease. Notably, arginase activity is upregulated in COVID-19 patients in a disease-dependent fashion, favoring the production of ornithine and its metabolites from arginine over the synthesis of NO. This rewiring of arginine metabolism in COVID-19 promotes immune and endothelial cell dysfunction, vascular smooth muscle cell proliferation and migration, inflammation, vasoconstriction, thrombosis, and arterial thickening, fibrosis, and stiffening, which can lead to vascular occlusion, muti-organ failure, and death. Strategies that restore the plasma concentration of arginine, inhibit arginase activity, and/or enhance the bioavailability and potency of NO represent promising therapeutic approaches that may preserve immune function and prevent the development of severe vascular disease in patients with COVID-19.

Severe COVID-19 Shares a Common Neutrophil Activation Signature with Other Acute Inflammatory States

Severe COVID-19 patients present a clinical and laboratory overlap with other hyperinflammatory conditions such as hemophagocytic lymphohistiocytosis (HLH). However, the underlying mechanisms of these conditions remain to be explored. Here, we investigated the transcriptome of 1596 individuals, including patients with COVID-19 in comparison to healthy controls, other acute inflammatory states (HLH, multisystem inflammatory syndrome in children [MIS-C], Kawasaki disease [KD]), and different respiratory infections (seasonal coronavirus, influenza, bacterial pneumonia). We observed that COVID-19 and HLH share immunological pathways (cytokine/chemokine signaling and neutrophil-mediated immune responses), including gene signatures that stratify COVID-19 patients admitted to the intensive care unit (ICU) and COVID-19_nonICU patients. Of note, among the common differentially expressed genes (DEG), there is a cluster of neutrophil-associated genes that reflects a generalized hyperinflammatory state since it is also dysregulated in patients with KD and bacterial pneumonia. These genes are dysregulated at the protein level across several COVID-19 studies and form an interconnected network with differentially expressed plasma proteins that point to neutrophil hyperactivation in COVID-19 patients admitted to the intensive care unit. scRNAseq analysis indicated that these genes are specifically upregulated across different leukocyte populations, including lymphocyte subsets and immature neutrophils. Artificial intelligence modeling confirmed the strong association of these genes with COVID-19 severity. Thus, our work indicates putative therapeutic pathways for intervention.

Dexamethasone modulates immature neutrophils and interferon programming in severe COVID-19

Although critical for host defense, innate immune cells are also pathologic drivers of acute respiratory distress syndrome (ARDS). Innate immune dynamics during Coronavirus Disease 2019 (COVID-19) ARDS, compared to ARDS from other respiratory pathogens, is unclear. Moreover, mechanisms underlying the beneficial effects of dexamethasone during severe COVID-19 remain elusive. Using single-cell RNA sequencing and plasma proteomics, we discovered that, compared to bacterial ARDS, COVID-19 was associated with expansion of distinct neutrophil states characterized by interferon (IFN) and prostaglandin signaling. Dexamethasone during severe COVID-19 affected circulating neutrophils, altered IFNactive neutrophils, downregulated interferon-stimulated genes and activated IL-1R2+ neutrophils. Dexamethasone also expanded immunosuppressive immature neutrophils and remodeled cellular interactions by changing neutrophils from information receivers into information providers. Male patients had higher proportions of IFNactive neutrophils and preferential steroid-induced immature neutrophil expansion, potentially affecting outcomes. Our single-cell atlas (see 'Data availability' section) defines COVID-19-enriched neutrophil states and molecular mechanisms of dexamethasone action to develop targeted immunotherapies for severe COVID-19.

l-Arginine and COVID-19: An Update

l-Arginine is involved in many different biological processes and recent reports indicate that it could also play a crucial role in the coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Herein, we present an updated systematic overview of the current evidence on the functional contribution of L-Arginine in COVID-19, describing its actions on endothelial cells and the immune system and discussing its potential as a therapeutic tool, emerged from recent clinical experimentations.

Severe COVID-19 Is Characterized by an Impaired Type I Interferon Response and Elevated Levels of Arginase Producing Granulocytic Myeloid Derived Suppressor Cells

COVID-19 ranges from asymptomatic in 35% of cases to severe in 20% of patients. Differences in the type and degree of inflammation appear to determine the severity of the disease. Recent reports show an increase in circulating monocytic-myeloid-derived suppressor cells (M-MDSC) in severe COVID 19 that deplete arginine but are not associated with respiratory complications. Our data shows that differences in the type, function and transcriptome of granulocytic-MDSC (G-MDSC) may in part explain the severity COVID-19, in particular the association with pulmonary complications. Large infiltrates by Arginase 1+ G-MDSC (Arg+G-MDSC), expressing NOX-1 and NOX-2 (important for production of reactive oxygen species) were found in the lungs of patients who died from COVID-19 complications. Increased circulating Arg+G-MDSC depleted arginine, which impaired T cell receptor and endothelial cell function. Transcriptomic signatures of G-MDSC from patients with different stages of COVID-19, revealed that asymptomatic patients had increased expression of pathways and genes associated with type I interferon (IFN), while patients with severe COVID-19 had increased expression of genes associated with arginase production, and granulocyte degranulation and function. These results suggest that asymptomatic patients develop a protective type I IFN response, while patients with severe COVID-19 have an increased inflammatory response that depletes arginine, impairs T cell and endothelial cell function, and causes extensive pulmonary damage. Therefore, inhibition of arginase-1 and/or replenishment of arginine may be important in preventing/treating severe COVID-19.

Genome-wide screening of SARS-CoV-2 infection-related genes based on the blood leukocytes sequencing data set of patients with COVID-19

Coronavirus disease 2019 (COVID‐19) is a global epidemic disease caused by a novel virus, severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), causing serious adverse effects on human health. In this study, we obtained a blood leukocytes sequencing data set of COVID‐19 patients from the GEO database and obtained differentially expressed genes (DEGs). We further analyzed these DEGs by protein–protein interaction analysis and Gene Ontology enrichment analysis and identified the DEGs closely related to SARS‐CoV‐2 infection. Then, we constructed a six‐gene model (comprising IFIT3, OASL, USP18, XAF1, IFI27, and EPSTI1) by logistic regression analysis and calculated the area under the ROC curve (AUC) for the diagnosis of COVID‐19. The AUC values of the training group, testing group, and entire group were 0.930, 0.914, and 0.921, respectively. The six genes were highly expressed in patients with COVID‐19 and positively correlated with the expression of SARS‐CoV‐2 invasion‐related genes (ACE2, TMPRSS2, CTSB, and CTSL). The risk score calculated by this model was also positively correlated with the expression of TMPRSS2, CTSB, and CTSL, indicating that the six genes were closely related to SARS‐CoV‐2 infection. In conclusion, we comprehensively analyzed the functions of DEGs in the blood leukocytes of patients with COVID‐19 and constructed a six‐gene model that may contribute to the development of new diagnostic and therapeutic ideas for COVID‐19. Moreover, these six genes may be therapeutic targets for COVID‐19.

COVID‐19 is a global epidemic and poses a serious risk to human health.

The differentially expressed genes related to SARS‐CoV‐2 infection in leukocytes of patients with COVD‐19 were screened.

A 6‐gene model for COVID‐19 diagnosis and treatment was constructed by logistic regression analysis.

The role and mechanism of these six genes (IFIT3, OASL, USP18, XAF1, IFI27, and EPSTI1) in COVID‐19 were preliminarily analyzed.