Soluble Urokinase Plasminogen Activator Receptor (suPAR) Regulates Acute Immune Response and Inflammation

Background: suPAR is an immune mediated circulating factor. Its elevation has been implicated in acute kidney injury (AKI) in patients. While high levels of suPAR led to a decreased survival in mouse cecal slurry sepsis models, its underlying mechanism remains unclear. Methods: We created a folic acid (FA) kidney injury model in 3 strains of mice, carrying different levels of suPAR including none (uPAR knockout, uPARKO), regular (wildtype, WT) and elevated (suPAR-Tg). We collected samples to evaluate kidney function and structural changes. We extracted peripheral white blood cells, bone marrow and kidney cells for single cell RNA sequencing. Results: Within 3 days of FA standard dose injection, all suPAR-Tg mice died, while most WT and all uPARKO mice survived, confirming that high levels of suPAR contributes to increased mortality in mice. To explore the underlying molecular mechanisms, we employed a reduced dose of FA in both suPAR-Tg and uPARKO mice. Elevation of BUN demonstrated the efficacy of FA to induce AKI. 24 hours after FA injection, the differential expression gene analysis and KEGG pathway enrichment indicate the transcriptional changes in most cell types in peripheral blood, bone marrow and kidney. The common enriched pathways for both suPAR-Tg and uPARKO mouse cells include neuro-degeneration disease and viral infection, oxidative phosphorylation, non-alcoholic fatty liver disease, reactive oxygen species, suggesting the implication of FA toxicity in these cellular processes. FoxO signaling, cellular senescence related genes were enriched only in suPAR-Tg cells across the examined organs. While other pathways including C-type lectin receptor and TNF signaling are enriched specifically in suPAR-Tg in peripheral blood CD4 and CD8 T cells, they are detected in bone marrow and kidney cells in uPARKO mice, suggesting suPAR regulates immune response in an organ dependent manner. Conclusion: This study confirms that elevated suPAR contributes to decreased survival in mice, through mechanisms involving immune dysfunction. While some suPAR-associated signaling pathways seem consistently enriched across different tissues, others may be organ-specific. Additional studies are warranted to elucidate the temporal and spatial dynamics of suPAR in regulating immune responses associated with in enhanced susceptibility to mortality. Funding: NIDDK Support