Abstract
Secondary infections cause sepsis that lead to patient disability or death. Contact of macrophages with bacterial components (such as lipopolysaccharide—LPS) activates the intracellular signaling pathway downstream of Toll-like receptors (TLR), which initiate an immune proinflammatory response. However, the expression of nuclear factor-kappa B (NF-κB)-dependent proinflammatory cytokines significantly decreases after single high or multiple LPS stimulations. Knowing that poly(ADP-ribose) polymerase-1 (PARP1) serves as a cofactor of NF-κB, we aimed to verify a hypothesis of the possible contribution of PARP1 to the development of LPS-induced tolerance in human macrophages. Using TNF-α mRNA expression as a readout, we demonstrate that PARP1 interaction with the TNF-α promoter, controls macrophage immunoparalysis. We confirm that PARP1 is extruded from the gene promoter, whereas cell pretreatment with Olaparib maintains macrophage responsiveness to another LPS treatment. Furthermore, cell pretreatment with proteasome inhibitor MG132 completely abrogates the effect of Olaparib, suggesting that PARP1 acts with NF-κB in the same regulatory pathway, which controls pro-inflammatory cytokine transcription. Mechanistically, PARP1 trapping allows for the re-rebinding of p65 to the TNF-α promoter in LPS-stimulated cells. In conclusion, PARP traps prevent PARP1 extrusion from the TNF-α promoter upon macrophage stimulation, thereby maintaining chromatin responsiveness of TLR activation, allowing for the re-binding of p65 and TNF-α transcription.
Highlights
Accepted: 20 February 2021Sepsis-induced immunoparalysis is a complication of secondary infections that compromises the immune response [1]
To test the possible contribution of poly(ADP-ribose) polymerase-1 (PARP1) to the development of endotoxin-induced tolerance of human macrophages, we first optimized the doses of LPS, which paralyze the pro-inflammatory response of considered phagocytes
The extent of p65 enrichment in cells tolerized in the presence of olaparib was comparable to that of intact cells challenged for the first time with bacterial endotoxin. These results suggest that PARP1 extrusion from the gene promoter during the first contact of cells with LPS allows for chromatin remodeling, which impedes further recruitment of p65
Summary
Sepsis-induced immunoparalysis is a complication of secondary infections that compromises the immune response [1]. It is a life-threatening dysfunction caused by a dysregulation of the host response to infection. It leads to death or disability of patients and costs to the healthcare system [2,3]. Many models, including in vitro macrophage cultures, reveal that multiple LPS stimulation induces attenuation of pro-inflammatory response. This phenomenon is known as “endotoxin tolerance” [2,4]. The contact of bacterial LPS with the Toll-like receptor 4 (TLR4) on the macrophage cell surface induces secretion of numerous proinflammatory cytokines and factors, such as tumor necrosis factor-α (TNFα); interleukins IL-1β, IL-6, and IL-8; macrophage inflammatory protein 2 (MIP2); and cyclooxygenase-2 (COX2) [5,6]
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