Periodontitis is a widely spread chronic inflammatory disease caused by a changed oral microbiome. Although multiple species and risk factors have been associated with periodontitis, Porphyromonas gingivalis undoubtedly stands in the center as a keystone pathogen. The immune-modulatory function of P. gingivalis has been well characterized, but the mechanism by which peptidyl arginine deiminase (PPAD), a citrullinating enzyme, contributes to the infinite loop of inflammation is not fully understood. To determine the functional role of hypercitrullination in the context of periodontitis, we performed a comparative analysis on neutrophils stimulated by the wild type and the PPAD mutant strain that lacks an active enzyme. Our flow cytometric analysis revealed that PPAD contributes to the prolonged neutrophil survival upon bacteria stimulation, which was accompanied by aberrant IL-6 and TNF-α secretion in the experimental environment. To further elaborate on the complex mechanism by which citrullination sustains the chronic inflammatory state, we assessed the ROS production and phagocytic activity of neutrophils. Flow cytometry and colony formation assay demonstrated that PPAD obstructs the resolution of inflammation by promoting neutrophil survival and the release of pro-inflammatory cytokines while making the bacteria itself more resilient to phagocytosis.

The evolution of release factors catalyzing the hydrolysis of the final peptidyl-tRNA bond and the release of the polypeptide from the ribosome has been a longstanding paradox. While the components of the translation apparatus are generally well-conserved across extant life, structurally-unrelated release factor peptidyl hydrolases (RF-PHs) emerged in the stems of the bacterial and archaeo-eukaryotic lineages. We analyze the diversification of RF-PH domains within the broader evolutionary framework of the translation apparatus. Thus, we reconstruct the possible state of translation termination in the Last Universal Common Ancestor with possible tRNA-like terminators. Further, evolutionary trajectories of the several auxiliary release factors in ribosome quality control (RQC) and rescue pathways point to multiple independent solutions to this problem and frequent transfers between superkingdoms including the recently-characterized ArfT, which is more widely-distributed across life than previously appreciated. The eukaryotic RQC system was pieced together from components with disparate provenance, which include the long-sought Vms1/ANKZF1 RF-PH of bacterial origin. We also uncover an under-appreciated evolutionary driver of innovation in rescue pathways: effectors deployed in biological conflicts that target the ribosome. At least three rescue pathways (centered on the prfH/RFH, baeRF-1, and C12orf65 RF-PH domains), were likely innovated in response to such conflicts.

The peptidyl-prolyl isomerases of the cyclophilin type are distributed throughout human cells, including eight found solely in the nucleus. Nuclear cyclophilins are involved in complexes that regulate chromatin modification, transcription, and pre-mRNA splicing. This review collects what is known about the eight human nuclear cyclophilins: PPIH, PPIE, PPIL1, PPIL2, PPIL3, PPIG, CWC27, and PPWD1. Each “spliceophilin” is evaluated in relation to the spliceosomal complex in which it has been studied, and current work studying the biological roles of these cyclophilins in the nucleus are discussed. All eight of the human splicing complexes available in the PDB are analyzed from the viewpoint of the human spliceophilins. Future directions in structural and cellular biology, and the importance of developing spliceophilin-specific inhibitors, are considered.

Neutrophil extracellular trap formation has been identified as a new cell death mediator, termed NETosis, which is distinct from apoptosis and necrosis. NETs capture foreign substances, such as bacteria, by releasing DNA into the extracellular environment, and have been associated with inflammatory diseases and altered immune responses. Short-chain fatty acids, such as acetate, are produced by the gut microbiota and reportedly enhance innate immune responses; however, the underlying molecular mechanisms remain unclear. Here, we investigated the effects of sodium acetate, which has the highest SCFA concentration in the blood and gastrointestinal tract, on NETosis by focusing on the mechanisms associated with histone acetylation in neutrophil-like HL-60 cells. Sodium acetate enhanced NETosis as shown by fluorescence staining with SYTOX green, and the effect was directly proportional to the treatment duration (16–24 h). Moreover, the addition of sodium acetate significantly enhanced the acetylation of Ace-H3, H3K9ace, H3K14ace, and H3K27ace. Sodium acetate-induced histone acetylation rapidly decreased upon stimulation with the calcium ionophore A23187, whereas histone citrullination markedly increased. These results demonstrate that sodium acetate induces NETosis via histone acetylation in neutrophil-like HL-60 cells, providing new insights into the therapeutic effects based on the innate immunity-enhancing effect of dietary fiber.