Gram-negative bacteria-driven increase of cytosolic phospholipase A2 leads to activation of Kupffer cells

Bacterial infections are prevalent and the major cause of morbidity and mortality in cirrhosis. Activation of human Kupffer cells (HKCs) from livers is essential for human innate immunity. Cytosolic phospholipase A2 (cPLA2) plays a crucial role in the control and balance of innate immune and inflammatory reactions. Uncharacterized is the role of cPLA2 in HKC activation by bacterial infection. This work aimed to determine the function and mechanism of cPLA2 in gram-negative bacteria (GNB)-induced HKC activation. In this study, we found that Escherichia coli (E. coli)-induced activation of HKCs led to a rise in cPLA2 mRNA and protein expression, where the ERK and NF-κB pathways were concurrently triggered. Luciferase activity of cPLA2' promoters, PLA2G4A promoters, was enhanced with the stimulation of E. coli or co-transfection with STAT3 or RelB in HKCs. E. coli massively boosted the binding activity of STAT3 and RelB to the specific regions of the PLA2G4A promoter as measured by ChIP-qPCR. The E. coli-ERK-STAT3 and E. coli-non-canonical NF-κB-RelB signaling axes were then identified using pathway inhibitors and transcription factors in the rescue experiments during E. coli-induced HKC activation. In conclusion, we discovered that cPLA2 is necessary for E. coli-induced HKC activation, and the underlying mechanism could be the transcriptional regulation of STAT3 and RelB on the PLA2G4A promoter following the ERK and non-canonical NF-κB signaling activation, implying that the regulation of cPLA2 expression via the E. coli-ERK/non-canonical NF-κB-STAT3/RelB signaling axis could be effective for controlling GNB-induced HKC activation in cirrhotic patients.