Human heart explant-derived cell extracellular vesicles inhibit NLRP3 inflammasome activation in macrophages
Authors: Vaka Ramana , Parent Sandrine , Davis Darryl 
Published: May 2023

Background: Abnormal activation of NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome plays a crucial role in promoting myocardial inflammation and adverse remodeling. Extracellular vesicles (EVs) secreted by heart explant-derived cells (HDCs) have been shown to reduce inflammation and confer cardioprotection in animal models of myocardial infarction. These salutary effects are suggested to be mediated by antiinflammatory microRNA (miRNA) cargo found within the EVs. However, whether HDC EVs can modulate NLRP3 inflammasome activation is not known. Hypothesis & Study Objective: Given their antiinflammatory effects and abundantly enriched miRNA transcripts, we hypothesized that HDC EVs attenuate NLRP3 inflammasome activation. Therefore, the objective of this study was to assess the inhibitory effect of HDC EVs on NLRP3 inflammasome activation in macrophages-a major proinflammatory cell type recruited to myocardium after an ischemic insult. Methods: Human HDCs were cultured from cardiac biopsies in a clinical grade cell manufacturing facility. EVs were isolated from conditioned media (ultracentrifugation) and characterized for their identity (Nanosight & antibody array). Monocytes (THP-1) were differentiated into macrophages with phorbol-myristate acetate (PMA; 3 days) and treated with EVs (4E+10 EVs/mL; 20 hours) before priming (lipopolysaccharide; 4 hours) and activating (nigericin; 1 hour) NLRP3 inflammasome. Caspase-1 activity, IL-1β and IL-18 levels in the culture supernatants were measured using a Caspase-Glo® 1 assay and ELISA respectively. EV miRNA cargo was profiled using nCounter ® human miRNA expression assay. Functional enrichment analysis and miRNA target prediction were performed using bioinformatic tools (Tam 2.0 & miRWalk v3). Results: EV size (160±2 nm) and markers (ICAM, ALIX, CD81, CD63, EPCAM, ANXAS, TSG101, FLOT-1) confirmed EV identity. EV treatment significantly inhibited NLRP3 inflammasome induced caspase-1 activity (67% lower vs. no EV treated, n=4-6, p<0.0001). Further, EV treated macrophages showed a significant reduction in IL-18 (623±8 vs.1462±43 pg/mL, n=3, p=0.0025) and a trend towards reduction in IL-1β levels (1292±115 vs. 2535±115 pg/mL, n=3, p=0.08). MicroRNA set analysis revealed that EVs are enriched with 22 anti-inflammatory miRNAs and importantly 3 of the top 10 significantly enriched functional terms (overrepresentation, p<0.05) are found to be related to immunity and inflammation. Interestingly, EVs are enriched with 4 miRNAs (miR-100, miR-181a, miR-21, miR-22) predicted to inhibit NLRP3 inflammasome. Conclusion: Our findings show that human heart explant-derived cell EVs inhibit activation of NLRP3 inflammasome in macrophages and this effect in part is possibly mediated via transfer of their anti-inflammatory miRNA cargo. These preliminary findings encourage a preclinical investigation to assess EV modulatory effect on NLRP3 inflammasome in models of ischemic heart disease. Canadian Institutes of Health Research Project Grant 410103 (DRD) and University of Ottawa Heart Institute Strategic Research Endowed Fellowship (RV) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.