Abstract 419: Liberation Of Soluble Urokinase Plasminogen Receptor (supar) Occurs In Response To Coronavirus Infection But Not To Influenza Virus Infection

Abstract

Objectives: Urokinase (uPA), and its receptor, uPAR, mediate fibrinolysis and matrix remodeling. Liberation of monocyte/macrophage (MO/Mϕ) bound uPAR to yield soluble uPAR (suPAR) occurs after infection with coronaviruses (CoVs) such as SARS-CoV-2, and suPAR levels correlate with systemic inflammation and degree of end organ injury. How suPAR liberation from MO/Mϕs occurs after CoV infection, and whether suPAR induction occurs after pneumotropic viral infections such as influenza A (IAV) is unclear. Methods: Murine bone marrow derived Mϕs (BMDMs) and immortalized Mϕs (RAW264.7) were infected with CoV [MHVA59 (murine model for SARS-CoV-2 infection) or MHV1] or with IAV (A/PR/8/34) and levels of mRNA and protein were measured using qRT-PCR and ELISA, respectively. uPA activity of cell supernatants was quantitated using a commercially available assay. uPA knockdown of Mϕs was performed using siRNA transfection. C57BL6/J mice underwent intranasal inoculation of either 2x10 5 pfu of MHVA59, 25 pfu of IAV, or with PBS (sham). Plasma levels of suPAR and splenic Mϕ (surrogate for circulating MOs) levels of mRNA and protein were analyzed at post-infection day 3. Results: Though both CoV or IAV infection resulted in induction of mRNA and protein levels of cellular uPAR and uPA, and uPA activity, only CoV infection yielded liberation of suPAR from Mϕs (Fig. 1A-C). Indicating a functional role in suPAR liberation, infection of uPA-silenced Mϕs yielded a blunted induction of suPAR release despite not affecting mRNA levels of uPAR (Fig 1D). Finally, inoculation of mice with MHVA59, but not with IAV, resulted in elevated plasma levels of suPAR, despite inducing a robust induction of uPAR in splenic Mϕs (Fig. 1E). Conclusions: suPAR induction results after CoV infection, but not IAV infection, and occurs through a uPA-dependent pathway. Antagonism of co-regulators of uPAR and uPA may prove to be a therapeutic strategy to combat post-CoV tissue injury mediated by Mϕs.