Research Associate Professor NYU Grossman School of Medicine
Introduction: Ferroptosis is a recently discovered programmed cell death involved in disorders including infectious disease, autoimmune disease, and cancer. It is characterized by iron accumulation and reactive oxygen species (ROS)-induced lipid peroxidation. Neutrophils are the first line of innate defense against urinary tract infection (UTI), and their interaction with uropathogenic E.coli (UPEC) triggers generation of ROS and leads to cell death. However, whether UPECs induce ferroptosis in neutrophils remains elusive. This study aims to elucidate the role of ferroptosis in neutrophils-mediated host defense against UTI. Methods: Human myeloblastic cells HL-60 were induced to terminally differentiated neutrophils by 1.5% DMSO for 72 hours. The differentiated cells were challenged by type 1 piliated UPEC strains (UTI89, NU14), isogenic FimH adhesin deletion strain (NU14-1), or non-fimbriated laboratory strain (HB101) at a multiplicity of infection of 40. ROS level was examined by H2DCFDA cellular ROS assay. Iron level was measured by Phen Green FL diacetate assay. Cell membrane integrity was checked by DiO cell labeling. Lipid peroxidation was detected by cell-based lipid peroxidation assay. The cells were exposed to UPEC virulent factors lipopolysaccharide (LPS) and flagellin. HL-60 cells pretreated with or without the ferroptosis inhibitor ferrostatin-1 were infected, and cell suspensions were lysed, diluted, and plated to assess viable UPECs. Results: Type 1 piliated UPEC strains UTI89 and NU14 induced a rapid elevation in ROS and iron accumulation in differentiated HL-60 cells in a dose- and time-dependent manner and accompanied by lipid peroxidation with multiple perforations on the membrane, all of which are hallmarks of ferroptosis. On the contrary, pretreatment of HL-60 cells with ferroptosis inhibitor ferrostatin-1 reduced 20% of UPEC-induced ROS production, alleviated lipid peroxidation, and led to a 36% higher number of viable UPECs compared to the controls. Furthermore, FimH deletion isogenic strain NU14-1 and non-fimbriated laboratory strain HB101 did not elicit activation of ferroptosis in HL-60 cells, indicating FimH-mediated adherence is required for inducing ferroptosis. Lastly, UPEC virulent factors LPS or flagellin alone did not evoke ferroptosis. Conclusions: Our data demonstrate for the first time that UPECs induce ferroptosis in neutrophils, and the induction depends on the adhesion of UPECs to the cell surface. The results also suggest that enhancing ferroptosis holds the therapeutic potential for improved clearance of UPECs. SOURCE OF Funding: None
