Abstract Or141: Plasminogen small RNA cargo promotes immunogenicity and inhibits enzymatic activity.

Plasminogen (Plg), the pro-enzyme of the serine-protease plasmin, is known for its role in cleaving blood clots within the fibrinolytic pathway. More recently, Plg has been reported to associate with oxidized phospholipids and accept cholesterol from macrophages, two processes normally observed with lipoproteins. Other non-enzymatic functions of Plg include aiding monocyte migration, activation of immune cells, and angiogenesis. We have previously reported the biological functions of cell-free RNA circulating on lipoproteins. Based on these newly described functions of Plg as a lipoprotein-like particle, we hypothesized that Plg transports functional cell-free RNA. Moreover, we predicted that small RNA (sRNA) cargo regulates Plg’s classic enzymatic and alternative inflammatory capacities. Plg were isolated from plasma by lysine-slurry chromatography and checked for purity and quality by electrophoresis and endotoxin tests, respectively. Highly-pure human and bovine Plg samples were observed to dose-dependently transport RNAs in plasma, namely sRNAs (25-60nt in length). High-throughput small RNA sequencing analyses found that Plg carries both host and non-host (microbial) sRNA. Plg samples were observed to accept sRNAs from donor macrophages in efflux studies, and Plg were observed to have moderate affinity (Kd=nM-µM range) towards candidate host and microbial sRNAs, as quantified by microscale thermophoresis. We also observed that Plg samples were markedly pro-inflammatory towards primary macrophages; however, we demonstrated through PCR and bulk sequencing that sRNA cargo on Plg confers, in large part, Plg’s pro-inflammatory functions towards macrophages, as RNase treated Plg failed to activate cytokine expression in treated human and mouse primary macrophages. Most importantly, RNase treatments of both human and bovine PLG were found to significantly increase Plg’s enzymatic activity, as observed through activity assay and clot lysis assays. Overall, these results support a negative regulatory role for sRNA cargo on Plg’s enzymatic function and a positive role for sRNA cargo driving Plg’s inflammatory properties. Collectively, results from this study suggest that Plg is a novel circulating ribonucleoprotein and that sRNA cargo likely governs the enzymatic capacity and inflammation within the clot or wound microenvironment. Therefore, Plg-sRNA cargo and its receptors provide new therapeutic targets to control fibrinolysis and systemic inflammation.