Growth Arrest-Specific Factor 6 (GAS6) Is Increased in COVID-19 Patients and Predicts Clinical Outcome
Background: Growth arrest-specific factor 6 (GAS6) and the Tyro3, AXL, and MERTK (TAM) receptors counterbalance pro-inflammatory responses. AXL is a candidate receptor for SARS-CoV-2, particularly in the respiratory system, and the GAS6/AXL axis is targeted in current clinical trials against COVID-19. However, GAS6 and TAMs have not been evaluated in COVID-19 patients at emergency admission. Methods: Plasma GAS6, AXL, and MERTK were analyzed in 132 patients consecutively admitted to the emergency ward during the first peak of COVID-19. Results: GAS6 levels were higher in the SARS-CoV-2-positive patients, increasing progressively with the severity of the disease. Patients with initial GAS6 at the highest quartile had the worst outcome, with a 3-month survival of 65%, compared to a 90% survival for the rest. Soluble AXL exhibited higher plasma concentration in deceased patients, without significant differences in MERTK among SARS-CoV-2-positive groups. GAS6 mRNA was mainly expressed in alveolar cells and AXL in airway macrophages. Remarkably, THP-1 human macrophage differentiation neatly induces AXL, and its inhibition (bemcentinib) reduced cytokine production in human macrophages after LPS challenge. Conclusions: Plasma GAS6 and AXL levels reflect COVID-19 severity and could be early markers of disease prognosis, supporting a relevant role of the GAS6/AXL system in the immune response in COVID-19. ; This research was funded by MINISTERIO DE CIENCIA E INNOVACIÓN (Project# RTI2018-095672-B-I00), Instituto de Salud Carlos III, Fondo de Investigación Sanitaria (grant numbers PI15/00531, PI19/01410), Fundació La Marató TV3 (grant numbers 20153030 and 20153031), and was co-funded by EUROPEAN UNION (ERDF "A way to make Europe"), Consejo Superior de Investigaciones Científicas (CSIC-COV19-016/202020E155), Proyectos COVID-19 de la Junta de Castilla y León (07.04.467B04.74011.0), AGAUR (2017_SGR_177), and CERCA Programme/Generalitat de Catalunya ; Peer reviewed