Loss of Platelet 12-Lipoxygenase Aggravates the Severity of Sars-Cov-2 Infection

Uncontrolled inflammation and dysregulation of platelet activity, leading to venous thromboembolic events are hallmark pathological findings of severe COVID-19. Considering that 12-lipoxygenase (12-LOX) is a key enzyme regulating platelet activity, we investigated its contribution during SARS-CoV-2 infection.

To examine the role of platelet-type 12-LOX, we performed intranasal infections of angiotensin-converting enzyme 2 transgenic mice (K18-hACE2) and K18-hACE2 knockout mice for the Alox12 gene, which encodes the platelet 12-LOX enzyme, using 500 TCID50 of the SARS-CoV-2 Delta strain. Notably, Alox12 knockout mice exhibited more severe disease and higher lethality. To decipher the drivers of this increased severity, we evaluated pulmonary tissue inflammation in mice. The Alox12 knockout mice showed elevated levels of central inflammatory cytokines/chemokines such as IFN-α, IFN-γ, IL-6, CCL-3, CCL-2, CCL-4, CXCL-1, CXCL-9 measured by Luminex multiplex assays. These results were corroborated by histopathological analysis, indicating a higher inflammatory score on the third and fifth day post-infection. Despite 12-LOX's role in platelet activation, we found no signs of higher coagulation processes in the pulmonary tissues of knockout animals, as evidenced by histopathology and preliminary transcriptome analysis of lung tissue.

Furthermore, we investigated the effect of 12-LOX loss on whole blood leukocyte populations by flow cytometry throughout the infection. No significant differences in these populations were observed in the knockout animals relative to WT mice. To explore the impact of 12-LOX metabolites on pulmonary inflammation, we performed mass spectrometry analysis of the main biolipids. Our study unveiled a significant decrease in the levels of inflammatory mediators, namely 12-HETrE, PGE1, 12-HEPE, Maresin-2, 12-HETE, 15-HETE, 11-HETE, LTB4, and 12-KETE, in the lungs of Alox12 knockout mice.

Taken together, our results underscore the critical role of platelet 12-LOX in regulating pulmonary inflammation during SARS-CoV-2 infection. Loss of this enzyme disrupts even more the production of inflammatory mediators following infection, exacerbating disease severity. Our findings highlight the relevance of platelet 12-LOX activity in the regulation of pulmonary inflammation after SARS-CoV-2 infection, shedding light on potential therapeutic targets.