Small extracellular vesicles from HO-1 modified BMMSCs alleviate steatotic liver grafts ischemia-reperfusion injury by delivering PDIA4 to promote reparative macrophage polarization.

Utilizing steatotic liver donors presents a viable strategy to mitigate the donor shortage in liver transplantation. However, severe steatosis increases the susceptibility of livers to ischemia-reperfusion injury (IRI) during transplantation, and regulating hepatic macrophage polarization can suppress liver inflammation and alleviate IRI. This study investigates the effects of small extracellular vesicles (sEVs) from heme oxygenase-1 (HO-1) modified bone marrow mesenchymal stem cells (BMMSCs), termed HM-sEVs, on IRI and macrophage polarization in steatotic liver grafts. We found that HM-sEVs significantly alleviated steatotic liver grafts IRI compared to sEVs from BMMSCs (M-sEVs). Further experiments have demonstrated that HM-sEVs can be internalized by macrophages and possess a greater capacity to promote reparative macrophage polarization and inhibit inflammatory responses, compared to M-sEVs. Mechanistically, protein disulfide-isomerase A4 (PDIA4) was found to be highly enriched in HM-sEVs. HM-sEVs can deliver PDIA4 to macrophages, activating the PDIA4/HSP90/MYC axis. This activation inhibits MYC ubiquitination and degradation, thereby promoting reparative macrophage polarization. In summary, our results indicated HM-sEVs can promote hepatic reparative macrophage polarization by activating the PDIA4/HSP90/MYC axis, providing a theoretical foundation for the application of HM-sEVs in alleviating steatotic liver grafts IRI and mitigating donor liver shortages.