Rapid Reversible Osmoregulation of Cytoplasmic Biomolecular Condensates of Human Interferon-α-Induced Antiviral MxA GTPase.

We previously discovered that exogenously expressed GFP-tagged cytoplasmic human myxovirus resistance protein (MxA), a major antiviral effector of Type I and III interferons (IFNs) against several RNA- and DNA-containing viruses, existed in the cytoplasm in phase-separated membraneless biomolecular condensates of varying sizes and shapes with osmotically regulated disassembly and reassembly. In this study we investigated whether cytoplasmic IFN-α-induced endogenous human MxA structures were also biomolecular condensates, displayed hypotonic osmoregulation and the mechanisms involved. Both IFN-α-induced endogenous MxA and exogenously expressed GFP-MxA formed cytoplasmic condensates in A549 lung and Huh7 hepatoma cells which rapidly disassembled within 1-2 min when cells were exposed to 1,6-hexanediol or to hypotonic buffer (~40-50 mOsm). Both reassembled into new structures within 1-2 min of shifting cells to isotonic culture medium (~330 mOsm). Strikingly, MxA condensates in cells continuously exposed to culture medium of moderate hypotonicity (in the range one-fourth, one-third or one-half isotonicity; range 90-175 mOsm) first rapidly disassembled within 1-3 min, and then, in most cells, spontaneously reassembled 7-15 min later into new structures. This spontaneous reassembly was inhibited by 2-deoxyglucose (thus, was ATP-dependent) and by dynasore (thus, required membrane internalization). Indeed, condensate reassembly was preceded by crowding of the cytosolic space by large vacuole-like dilations (VLDs) derived from internalized plasma membrane. Remarkably, the antiviral activity of GFP-MxA against vesicular stomatitis virus survived hypoosmolar disassembly and subsequent reassembly. The data highlight the exquisite osmosensitivity of MxA condensates, and the preservation of antiviral activity in the face of hypotonic stress.

Association of human myxovirus resistance protein A with severity of COVID-19.

BACKGROUND: In this retrospective cohort study, we explored the correlation of blood human myxovirus resistance protein A (MxA) level with severity of disease in hospitalized COVID-19 patients. METHODS: All 304 patients admitted for COVID-19 in our hospital until 30th of April 2021 were included in this study. MxA was measured from peripheral blood samples in 268 cases. Patients were divided into groups based on their level of MxA on admission. We studied baseline characteristics and severity of disease on admission based on clinical parameters and inflammatory biomarker levels in each group. Severity of disease during hospitalization was determined by the applied level of respiratory support, by the usage of corticosteroids and by the duration of hospitalization. RESULTS: Higher MxA levels on admission were associated with a shorter duration of symptoms before admission, and with more severe disease. Adjusted Odds Ratios for any respiratory support were 9.92 (95%CI 2.11-46.58; p = 0.004) in patients with MxA between 400 µg/L and 799 µg/L (p = 0.004) and 20.08 (95%CI 4.51-89.44; p < 0.001) in patients with MxA ≥ 800 µg/L in comparison with patients with initial MxA < 400 µg/L. The usage of corticosteroids was significantly higher in the high-MxA group (77%) in comparison with the intermediate-MxA group (62%, p = 0.013) and low-MxA group (47%, p < 0.001). CONCLUSIONS: Higher initial levels of MxA were associated with more severe COVID-19. MxA may be a helpful additional biomarker to predict the severity of the disease.

SARS-CoV-2 Interference of Influenza Virus Replication in Syrian Hamsters.

In hamsters, SARS-CoV-2 infection at the same time as or before H3N2 influenza virus infection resulted in significantly reduced influenza virus titers in the lungs and nasal turbinates. This interference may be correlated with SARS-CoV-2-induced expression of MX1.

Developing a Virus-Binding Bacterium Expressing Mx Protein on the Bacterial Surface to Prevent Grouper Nervous Necrosis Virus Infection.

Grouper nervous necrosis virus (GNNV) infection causes mass grouper mortality, leading to substantial economic loss in Taiwan. Traditional methods of controlling GNNV infections involve the challenge of controlling disinfectant doses; low doses are ineffective, whereas high doses may cause environmental damage. Identifying potential methods to safely control GNNV infection to prevent viral outbreaks is essential. We engineered a virus-binding bacterium expressing a myxovirus resistance (Mx) protein on its surface for GNNV removal from phosphate-buffered saline (PBS), thus increasing the survival of grouper fin (GF-1) cells. We fused the grouper Mx protein (which recognizes and binds to the coat protein of GNNV) to the C-terminus of outer membrane lipoprotein A (lpp-Mx) and to the N-terminus of a bacterial autotransporter adhesin (Mx-AIDA); these constructs were expressed on the surfaces of Escherichia coli BL21 (BL21/lpp-Mx and BL21/Mx-AIDA). We examined bacterial surface expression capacity and GNNV binding activity through enzyme-linked immunosorbent assay; we also evaluated the GNNV removal efficacy of the bacteria and viral cytotoxicity after bacterial adsorption treatment. Although both constructs were successfully expressed, only BL21/lpp-Mx exhibited GNNV binding activity; BL21/lpp-Mx cells removed GNNV and protected GF-1 cells from GNNV infection more efficiently. Moreover, salinity affected the GNNV removal efficacy of BL21/lpp-Mx. Thus, our GNNV-binding bacterium is an efficient microparticle for removing GNNV from 10‰ brackish water and for preventing GNNV infection in groupers.

The differing pathophysiologies that underlie COVID-19-associated perniosis and thrombotic retiform purpura: a case series.

BACKGROUND: There are two distinctive acral manifestations of COVID-19 embodying disparate clinical phenotypes. One is perniosis occurring in mildly symptomatic patients, typically children and young adults; the second is the thrombotic retiform purpura of critically ill adults with COVID-19. OBJECTIVES: To compare the clinical and pathological profiles of these two different cutaneous manifestations of COVID-19. METHODS: We compared the light microscopic, phenotypic, cytokine and SARS-CoV-2 protein and RNA profiles of COVID-19-associated perniosis with that of thrombotic retiform purpura in critical patients with COVID-19. RESULTS: Biopsies of COVID-19-associated perniosis exhibited vasocentric and eccrinotropic T-cell- and monocyte-derived CD11c+ , CD14+ and CD123+ dendritic cell infiltrates. Both COVID-associated and idiopathic perniosis showed striking expression of the type I interferon-inducible myxovirus resistance protein A (MXA), an established marker for type I interferon signalling in tissue. SARS-CoV-2 RNA, interleukin-6 and caspase 3 were minimally expressed and confined to mononuclear inflammatory cells. The biopsies from livedo/retiform purpura showed pauci-inflammatory vascular thrombosis without any MXA decoration. Blood vessels exhibited extensive complement deposition with endothelial cell localization of SARS-CoV-2 protein, interleukin-6 and caspase 3; SARS-CoV-2 RNA was not seen. CONCLUSIONS: COVID-19-associated perniosis represents a virally triggered exaggerated immune reaction with significant type I interferon signaling. This is important to SARS-CoV-2 eradication and has implications in regards to a more generalized highly inflammatory response. We hypothesize that in the thrombotic retiform purpura of critically ill patients with COVID-19, the vascular thrombosis in the skin and other organ systems is associated with a minimal interferon response. This allows excessive viral replication with release of viral proteins that localize to extrapulmonary endothelium and trigger extensive complement activation.