Participação da ubiquitina-ligase Smurf1 na modulação da imunopatologia causada pela infecção por Betacoronavirus

Abstract

COVID-19 is a disease caused by SARS-CoV-2, belonging to the Betacoronavirus genus, and is characterized by intense systemic inflammation associated with elevated production of cytokines and chemokines. Betacoronaviruses can trigger an exacerbated inflammatory response, which the host must regulate to prevent excessive damage. One of the main mechanisms involved in this regulation is ubiquitination, a post-translational process in which ubiquitin molecules are covalently attached to target proteins, promoting their degradation or functional modification to adjust the immune response. Among the proteins involved in ubiquitination, Smurf1 stands out as an E3 ubiquitin ligase that catalyzes the ubiquitination and proteasomal degradation of various protein substrates related to inflammatory responses and antiviral signaling. Recent data indicate that Smurf1 mRNA is highly expressed in nasopharyngeal and oropharyngeal swabs from COVID-19 patients, suggesting that Smurf1 may regulate immune responses during Betacoronavirus infection. This study investigated the importance of Smurf1 in antiviral immunity and its regulation of the inflammatory response using infection models with the murine coronaviruses MHV-3 and MHV-A59, which exhibit different degrees of pathogenicity. In vitro experiments showed that in macrophage infection with MHV-3, Smurf1 negatively regulated CXCL1 production without affecting viral titers or cell viability. In contrast, during MHV-A59 infection, Smurf1 reduced the production of pro-inflammatory cytokines such as TNF and CXCL1, controlled viral replication, and preserved cell viability. In vivo evaluation also revealed important differences. Wild-type or Smurf1−/− mice infected intranasally with MHV-3 showed no differences in survival between groups. In hematological parameters, Smurf1−/− mice exhibited increased granulocytes and lymphopenia, leading to a higher granulocyte-to-lymphocyte ratio. However, no significant differences were observed in viral titers, tissue damage, or inflammatory mediator production in the lungs. Nevertheless, the absence of Smurf1 led to a slight increase in necrotic regions in the liver. In MHV-A59 infection, Smurf1−/− mice showed increased susceptibility, with early death in lethal infections and signs of exacerbated systemic inflammation. Smurf1 expression in the lungs was essential for controlling viral replication by negatively regulating IFN-β mRNA and modulating the inflammatory profile of macrophages and neutrophils. Smurf1 did not directly influence IFN-β mRNA expression in the liver but increased TNF and iNOS in neutrophils while reducing TNF in macrophages. Additionally, Smurf1−/− mice exhibited greater liver damage, evidenced by elevated alanine aminotransferase (ALT) levels and aspartate aminotransferase (AST), suggesting significant tissue injury. These findings highlight that Smurf1 exerts distinct functions depending on the viral context. While its role was modest in MHV-3 infection, Smurf1 was crucial in MHV-A59 infection for regulating the inflammatory response and protecting against systemic damage. The absence of Smurf1 led to uncontrolled inflammation, increased viral replication, and higher mortality, underscoring its critical role in antiviral immunity and inflammatory homeostasis. These results contribute to the understanding of Smurf1-mediated immune mechanisms and suggest that this protein may be a potential therapeutic target for combating Betacoronavirus infections.