PADI4 mediates autophagy and participates in the role of ganoderic acid A monomers in delaying the senescence of Alzheimer's cells through the Akt/mTOR pathway.

The effects of PADI4 and GAA on the senescence of Alzheimer's cells were explored in the present work. HT22 cells were treated with Aß25-35 to establish an Alzheimer's model and were then treated with different concentrations of GAA and transfected with a siPADI4 lentiviral vector. GAA could reverse the effects of Aß25-35 on inhibiting cell viability and promoting apoptosis and senescence. siPADI4 reduced Aß25-35-induced cell viability and upregulated Aß25-35-induced cell apoptosis and senescence, as well as partially reversed the effect of GAA on cells, and these results were confirmed by detecting the expressions of senescence- and apoptosis-related proteins. In addition, siPADI4 was found to promote the phosphorylation of Akt and mTOR, which was partially reversed by GAA. In conclusion, PADI4 mediates autophagy and participates in the role of GAA monomers in delaying the senescence of Alzheimer's cells through the Akt/mTOR pathway.

Frontline Science: Anthrax lethal toxin-induced, NLRP1-mediated IL-1ß release is a neutrophil and PAD4-dependent event.

Anthrax lethal toxin (LT) is a protease that activates the NLRP1b inflammasome sensor in certain rodent strains. Unlike better-studied sensors, relatively little is known about the priming requirements for NLRP1b. In this study, we investigate the rapid and striking priming-independent LT-induced release of IL-1ß in mice within hours of toxin challenge. We find IL-1ß release to be a NLRP1b- and caspase-1-dependent, NLRP3 and caspase-11-independent event that requires both neutrophils and peptidyl arginine deiminiase-4 (PAD4) activity. The simultaneous LT-induced IL-18 response is neutrophil-independent. Bone marrow reconstitution experiments in mice show toxin-induced IL-1ß originates from hematopoietic cells. LT treatment of neutrophils in vitro did not induce IL-1ß, neutrophil extracellular traps (NETs), or pyroptosis. Although platelets interact closely with neutrophils and are also a potential source of IL-1ß, they were unable to bind or endocytose LT and did not secrete IL-1ß in response to the toxin. LT-treated mice had higher levels of cell-free DNA and HMGB1 in circulation than PBS-treated controls, and treatment of mice with recombinant DNase reduced the neutrophil- and NLRP1-dependent IL-1ß release. DNA sensor AIM2 deficiency, however, did not impact IL-1ß release. These data, in combination with the findings on PAD4, suggest a possible role for in vivo NETs or cell-free DNA in cytokine induction in response to LT challenge. Our findings suggest a complex interaction of events and/or mediators in LT-treated mice with the neutrophil as a central player in induction of a profound and rapid inflammatory response to toxin.

Mitochondrial DNA Stimulates TLR9-Dependent Neutrophil Extracellular Trap Formation in Primary Graft Dysfunction.

The immune system is designed to robustly respond to pathogenic stimuli but to be tolerant to endogenous ligands to not trigger autoimmunity. Here, we studied an endogenous damage-associated molecular pattern, mitochondrial DNA (mtDNA), during primary graft dysfunction (PGD) after lung transplantation. We hypothesized that cell-free mtDNA released during lung ischemia-reperfusion triggers neutrophil extracellular trap (NET) formation via TLR9 signaling. We found that mtDNA increases in the BAL fluid of experimental PGD (prolonged cold ischemia followed by orthotopic lung transplantation) and not in control transplants with minimal warm ischemia. The adoptive transfer of mtDNA into the minimal warm ischemia graft immediately before lung anastomosis induces NET formation and lung injury. TLR9 deficiency in neutrophils prevents mtDNA-induced NETs, and TLR9 deficiency in either the lung donor or recipient decreases NET formation and lung injury in the PGD model. Compared with human lung transplant recipients without PGD, severe PGD was associated with high levels of BAL mtDNA and NETs, with evidence of relative deficiency in DNaseI. We conclude that mtDNA released during lung ischemia-reperfusion triggers TLR9-dependent NET formation and drives lung injury. In PGD, DNaseI therapy has a potential dual benefit of neutralizing a major NET trigger (mtDNA) in addition to dismantling pathogenic NETs.

Autoantibodies to protein-arginine deiminase (PAD) 4 in rheumatoid arthritis: immunological and clinical significance, and potential for precision medicine.

Introduction: The protein-arginine deiminase (PAD) 4 enzyme plays an important role in the pathogenesis of rheumatoid arthritis (RA) and also represents an antigenic target. Anti-PAD4 antibodies can be present in RA and are associated with specific clinical features. Areas covered: This review aims to analyze the current knowledge and recent findings on anti-PAD4 antibodies in RA and their clinical and immunological significance. Expert opinion: Anti-PAD4 antibodies are not currently used in clinical practice for the management of RA. Nevertheless, there is growing evidence of their relevance in RA, and of their potential utility to improve diagnosis, patient stratification, and prognosis.