Deciphering the role of viral glycoproteins in NLRP3 inflammasome activation and pyroptosis in THP-1 macrophages

Infections with viral pathogens are a major global health concern, as highlighted by the Coronavirus disease 2019 (COVID-19) pandemic. Understanding the mechanisms of viral pathogenesis, including how viruses modulate the immune response, is a crucial component in the fight against viral infections. Inflammasomes, particularly the nucleotide-binding oligomerization domain, leucine rich repeat and pyrin domain containing (NLRP) 3 inflammasome, play a pivotal role in innate immunity by detecting pathogens and initiating an immune response. Although multiple studies have shown that viruses can activate inflammasomes, the specific viral components responsible for this activation remain largely undefined. This study aimed to investigate the role of four viral glycoproteins, namely the spike protein (S-protein) of the severe acute respiratory syndrome coronavirus (SARS-CoV) 1 and SARS-CoV-2, glycoprotein B (gB) of the human cytomegalovirus (HCMV), and E2 of the hepatitis C virus (HCV), in triggering NLRP3 inflammasome activation and pyroptosis in THP-1 macrophages, thereby offering new insights into viral pathogenesis. Employing a range of methodologies, including enzyme-linked immunosorbent assays, western blots, and immunofluorescence, this research investigated the stimulatory effects of these viral glycoproteins on THP-1 macrophages. The study focused on measuring interleukin (IL)-1β secretion, on the analysis of the expression levels of NLRP3 and apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC) proteins, and on examining the formation of ASC specks, a critical step in inflammasome activation. Furthermore, the research utilized NLRP3 and Gasdermin D (GSDMD) knockout cells to validate the role of these proteins in the observed immune response. GSDMD mediated pyroptotic cell death, as a consequence of inflammasome activation following glycoprotein exposure, was assessed through lactase dehydrogenase release assays and flow cytometry. The findings revealed that stimulation with the selected viral glycoproteins led to increased IL-1β secretion, upregulation of NLRP3, and formation of ASC specks. Notably, the absence of NLRP3 or GSDMD significantly reduced IL-1β secretion. Additionally, exposure to viral glycoproteins resulted in enhanced cell death. This study contributes to the field by identifying specific viral glycoproteins that can trigger the NLRP3 inflammasome and pyroptosis in THP-1 macrophages, thereby advancing our understanding of the complex interactions between viral pathogens and the host immune system. The research underscores the need for further investigations into the cellular receptors that these glycoproteins bind to initiate inflammasome activation. Moreover, it highlights the importance of exploring whether other inflammasomes are involved in the immune response to viral infections. Future research should aim to confirm these findings in vivo to expand our knowledge of the molecular mechanisms underlying inflammasome activation by viral pathogens.