Plasma N-Cleaved Galectin-9 Is a Surrogate Marker for Determining the Severity of COVID-19 and Monitoring the Therapeutic Effects of Tocilizumab

PLSCR1 suppresses SARS-CoV-2 infection by downregulating cell surface ACE2

Type I interferons exert their antiviral effects against SARS-CoV-2 by inducing the expression of interferon-stimulated genes (ISGs), including but not limited to LY6E, CH25H, IFITM2/3, and IFIH1. However, the antiviral effect and underlying mechanisms of action of most ISGs in SARS-CoV-2 infection are not yet fully understood. By screening 109 ISG-knockout cell lines, we identify that phospholipid scramblase 1 (PLSCR1), an interferon-inducible protein, acts as a crucial restriction factor against SARS-CoV-2 infection. Cells lacking PLSCR1 are highly susceptible to SARS-CoV-2 infection. Conversely, overexpression of PLSCR1 inhibits SARS-CoV-2 infection. Depletion of PLSCR1 enhances cellular entry of both pseudotyped and authentic SARS-CoV-2. Mechanistically, PLSCR1 inhibits SARS-CoV-2 entry by specifically downregulating plasma membrane expression of ACE2, the virus's receptor, without affecting the overall levels of ACE2 within the cell. As such, we unraveled previously unappreciated mechanisms by which PLSCR1 exerts its restrictive effect on SARS-CoV-2. These data provide new insights into the interplay between host innate antiviral immunity and SARS-CoV-2 and shed light on novel antiviral therapeutics.

IMPORTANCE

Phospholipid scramblase 1 (PLSCR1) has been identified as a critical host restriction factor against SARS-CoV-2 infection. In this study, we demonstrated that PLSCR1 inhibited SARS-CoV-2 entry by downregulating the plasma membrane expression of ACE2, the primary receptor for viral entry. Our findings elucidate a novel host-pathogen interaction that not only deepens our understanding of the innate immune response to SARS-CoV-2 but offers potential strategies for therapeutic interventions against COVID-19.

Virus-Induced Host Chemokine CCL2 in COVID-19 Pathogenesis: Potential Prognostic Marker and Target of Anti-Inflammatory Strategy

A wide variety of inflammatory mediators, mainly cytokines and chemokines, are induced during SARS CoV-2 infection. Among these proinflammatory mediators, chemokines tend to play a pivotal role in virus-mediated immunopathology. The C-C chemokine ligand 2 (CCL2), also known as monocyte chemoattractant protein-1 (MCP-1) is a potent proinflammatory cytokine and strong chemoattractant of monocytes, macrophages and CD4+ T cells bearing C-C chemokine receptor type-2 (CCR2). Besides controlling immune cell trafficking, CCL2 is also involved in multiple pathophysiological processes including systemic hyperinflammation associated cytokine release syndrome (CRS), organ fibrosis and blood coagulation. These pathological features are commonly manifested in severe and fatal cases of COVID-19. Given the crucial role of CCL2 in COVID-19 pathogenesis, the CCL2:CCR2 axis may constitute a potential therapeutic target to control virus-induced hyperinflammation and multi-organ dysfunction. Herein we describe recent advances on elucidating the role of CCL2 in COVID-19 pathogenesis, prognosis, and a potential target of anti-inflammatory interventions.

Galectin-9 in cancer therapy: from immune checkpoint ligand to promising therapeutic target

Galectin-9 (Gal-9) is a vital member of the galectin family, functioning as a multi-subtype galactose lectin with diverse biological roles. Recent research has revealed that Gal-9's interaction with tumors is an independent factor that influences tumor progression. Furthermore, Gal-9 in the immune microenvironment cross-talks with tumor-associated immune cells, informing the clarification of Gal-9's identity as an immune checkpoint. A thorough investigation into Gal-9's role in various cancer types and its interaction with the immune microenvironment could yield novel strategies for subsequent targeted immunotherapy. This review focuses on the latest advances in understanding the direct and indirect cross-talk between Gal-9 and hematologic malignancies, in addition to solid tumors. In addition, we discuss the prospects of Gal-9 in tumor immunotherapy, including its cross-talk with the ligand TIM-3 and its potential in immune-combination therapy.

Elevated matrix metalloproteinase‑9 expression is associated with COVID‑19 severity: A meta‑analysis

The present meta-analysis investigated the clinical value of serum matrix metalloproteinase (MMP)-9 levels in Coronavirus Disease 2019 (COVID-19) patients. Studies assessing the outcomes of patients with COVID-19 in correlation with the MMP-9 levels were retrieved from PubMed, Web of Science, EMBASE, Cochrane, WANFANG, and CNKI. A meta-analysis was performed to compare the serum MMP-9 levels between different patient groups: Severe vs. non-severe; acute respiratory distress syndrome (ARDS) vs. non-ARDS; non-survivors vs. survivors; neurologic syndrome vs. non-neurologic syndrome; and obese diabetic vs. non-obese diabetic. A total of 2,062 COVID-19-confirmed patients from 12 studies were included in this meta-analysis. The serum MMP-9 levels were significantly higher in patients with severe COVID-19 than in those with non-severe COVID-19 [weighted mean difference (WMD) 246.61 (95% confidence interval (CI), 115.86-377.36), P<0.001]. Patients with ARDS exhibited significantly higher MMP-9 levels than those without ARDS [WMD 248.55 (95% CI, 63.84-433.25), P<0.001]. The MMP-9 levels in the non-survivors did not significantly differ from those in the survivors [WMD 37.79 (95% CI, -18.08-93.65), P=0.185]. Patients with comorbidities, including neurological syndromes, and obese diabetic patients had significantly higher MMP-9 levels than those without comorbidities [WMD 170.73 (95% CI, 95.61-245.85), P<0.001]. Serum MMP-9 levels were associated with COVID-19 severity and may serve as a therapeutic target for improving the prognosis of patients with COVID-19.