Monocytes promote pyroptosis of endothelial cells during lung ischemia-reperfusion via IL-1R/NF-κB/NLRP3 signaling.

In our previous study, we observed that donor pulmonary intravascular nonclassical monocytes play a major role in early PGF, but the specific mechanism remained unclear. In this study, we investigated the mechanistic role of monocytes in inducing pyroptosis of human pulmonary microvascular endothelial cells (HPMECs) during IRI. A murine hilar ligation model of IRI was utilized whereby left lungs underwent 1 h of ischemia and 23 h of reperfusion. Monocyte depletion by intraperitoneal clodronate-liposome treatment on pulmonary edema and pyroptosis activation were determined. In vitro experiments, we performed the co-culture experiments under hypoxia-reoxygenation (H/R) conditions to mimic the IRI environment. We monitored the expression of NLRP3, caspase-1 and IL-1β in co-cultures of monocytes (U937 cells) and HPMECs under H/R conditions. NLRP3, IL-1β and IL-1R siRNA knockdown, caspase-1 and NF-κB pathway inhibitors were employed to elucidate the mechanism modulating HPMEC pyroptosis during H/R. Treatment of mice with clodronate-liposome attenuated IR-induced pulmonary edema, cytokine production and pyroptosis activation. In vitro, NLRP3 knockdown in monocytes reduced caspase-1 and IL-1β secretion in co-cultures of monocytes and HPMECs. Reduced HPMEC pyroptosis was also observed either containing HPMECs with genetically engineered IL-1R knockdown or in co-culture treated with a Triplotide inhibitor that disrupts NF-κB signaling. Monocytes play a vital role in the development of transplant-associated ischemia-reperfusion injury. A potential role is that monocytes secrete IL-1β to induce HPMEC pyroptosis via the IL-1R/NF-κB/NLRP3 pathway.