CASP4/11 contributes to pulmonary inflammation and disease exacerbation in COVID-19 (preprint)

Infection with SARS-CoV-2 induces COVID-19, an inflammatory disease that is usually self-limited, but depending on patient conditions may culminate with critical illness and patient death. The virus triggers activation of intracellular sensors, such as the NLRP3 inflammasome, which promotes inflammation and aggravates the disease. Thus, identification of host components associated with NLRP3 inflammasome is key for understanding the physiopathology of the disease. Here, we reported that SARS-CoV-2 induces upregulation and activation of human Caspase-4/CASP4 (mouse Caspase-11/CASP11) and this process contributes to inflammasome activation in response to SARS-CoV-2. CASP4 was expressed in lung autopsy of lethal cases of COVID-19 and CASP4 expression correlates with expression of inflammasome components and inflammatory mediators such as CASP1, IL1B, IL18 and IL6. In vivo infections performed in transgenic hACE2 humanized mouse, deficient or sufficient for Casp11, indicate that hACE2 Casp11-/- mice were protected from disease development, with reduced body weight loss, reduced temperature variation, increased pulmonary parenchymal area, reduced clinical score of the disease and reduced mortality. Collectively, our data establishes that CASP4/11 contributes to disease pathology and contributes for future immunomodulatory therapeutic interventions to COVID-19.

Inflammasome activation and pulmonary viral loads define two distinct clinical outcomes in COVID-19 (preprint)

Inflammasome activation is associated with disease severity in patients who are infected with SARS-CoV-2 and influenza viruses, but the specific cell types involved in inflammasome activation, as well as the balance of inflammasome activation versus viral replication in COVID-19 exacerbation and the induction of patient death, are unknown. In this study, we assessed lung autopsies of 47 COVID-19 and 12 influenza fatal cases and examined the inflammatory profiles and inflammasome activation; additionally, we correlated these factors with clinical and histopathological patient conditions. We observed an overall stronger inflammasome activation in lethal cases of SARS-CoV-2 compared to influenza and found a different profile of inflammasome-activating cells during these diseases. In COVID-19 patients, inflammasome activation is mostly mediated by macrophages and endothelial cells, whereas in influenza, type I and type II pneumocytes contribute more significantly. An analysis of gene expression allowed for the classification of COVID-19 patients into two different clusters. Cluster 1 (n=16 patients) died with higher viral loads and exhibited a reduced inflammatory profile than Cluster 2 (n=31 patients). Illness time, mechanical ventilation time, pulmonary fibrosis, respiratory functions, histopathological status, thrombosis, and inflammasome activation significantly differed between the two clusters. Our data demonstrated two distinct profiles in lethal cases of COVID-19, thus indicating that the balance of viral replication and inflammasome-mediated pulmonary inflammation may lead to different clinical conditions, yet both lead to patient death. An understanding of this process is critical for decisions between immune-mediated or antiviral-mediated therapies for the treatment of critical cases of COVID-19.

Efferocytosis of SARS-CoV-2-infected dying cells impairs macrophage anti-inflammatory programming and continual clearance of apoptotic cells (preprint)

COVID-19 is a disease of dysfunctional immune responses, but the mechanisms triggering immunopathogenesis are not established. The functional plasticity of macrophages allows this cell type to promote pathogen elimination and inflammation or suppress inflammation and promote tissue remodeling and injury repair. During an infection, the clearance of dead and dying cells, a process named efferocytosis, can modulate the interplay between these contrasting functions. Here, we show that engulfment of SARS-CoV2-infected apoptotic cells (AC) exacerbates inflammatory cytokine production, inhibits the expression of efferocytic receptors, and impairs continual efferocytosis by macrophages. We also provide evidence that monocytes from severe COVID-19 patients express reduced levels of efferocytic receptors and fail to uptake AC. Our findings reveal that dysfunctional efferocytosis of SARS-CoV-2-infected cell corpses suppress macrophage anti-inflammation and efficient tissue repair programs and provide mechanistic insights for the pathogenesis of the hyperinflammation and extensive tissue damage associated with COVID-19.

Inflammasome activation in COVID-19 patients (preprint)

Severe cases of COVID-19 are characterized by a strong inflammatory process that may ultimately lead to organ failure and patient death. The NLRP3 inflammasome is a molecular platform that promotes inflammation via cleavage and activation of key inflammatory molecules including active caspase-1 (Casp1p20), IL-1{beta} and IL-18. Although the participation of the inflammasome in COVID-19 has been highly speculated, the inflammasome activation and participation in the outcome of the disease is unknown. Here we demonstrate that the NLRP3 inflammasome is activated in response to SARS-CoV-2 infection and it is active in COVID-19, influencing the clinical outcome of the disease. Studying moderate and severe COVID-19 patients, we found active NLRP3 inflammasome in PBMCs and tissues of post-mortem patients upon autopsy. Inflammasome-derived products such as Casp1p20 and IL-18 in the sera correlated with the markers of COVID-19 severity, including IL-6 and LDH. Moreover, higher levels of IL-18 and Casp1p20 are associated with disease severity and poor clinical outcome. Our results suggest that the inflammasome is key in the pathophysiology of the disease, indicating this platform as a marker of disease severity and a potential therapeutic target for COVID-19.