Leishmania donovani mevalonate kinase regulates host actin for inducing phagocytosis

Despite the well-established role of macrophages in phagocytosing Leishmania, the contribution of the parasite to this process is not well understood. Present study provides insights into the mechanism underlying the MVK-induced entry of L. donovani and improve our knowledge of host-pathogen interactions. We have discussed Mevalonate kinase (MVK)-induced actin reorganization, modulation of signaling pathways and host cell functions. Our results show that LdMVK gains access to macrophage cytosol and induces actin assembly modulation through the activation of actin-related proteins: VASP, Src and ERM. We have also demonstrated that LdMVK induces Ca2+ signaling and Akt pathway in macrophages, which are critical components of Leishmania survival and proliferation. Interestingly, we found that antibodies against LdMVK can kill Leishmania-infected macrophages in culture by forming extracellular traps, highlighting the potential of LdMVK in inhibiting parasite death. Overall, LdMVK is a virulent factor in Leishmania that mediates parasite internalization and host modulation by targeting host proteins phosphorylation and calcium homeostasis having significant implications in disease progression.

Impact of endogenous and exogenous nitrogen species on macrophage extracellular trap (MET) formation by bone marrow-derived macrophages

Macrophage extracellular traps (METs) represent a novel defense mechanism in the antimicrobial arsenal of macrophages. However, mechanisms of MET formation are still poorly understood and this is at least partially due to the lack of reliable and reproducible models. Thus, we aimed at establishing a protocol of MET induction by bone marrow-derived macrophages (BMDMs) obtained from cryopreserved and then thawed bone marrow (BM) mouse cells. We report that BMDMs obtained in this way were morphologically (F4/80+) and functionally (expression of inducible nitric oxide (NO) synthase and NO production) differentiated and responded to various stimuli of bacterial (lipopolysaccharide, LPS), fungal (zymosan) and chemical (PMA) origin. Importantly, BMDMs were successfully casting METs composed of extracellular DNA (extDNA) serving as their backbone to which proteins such as H2A.X histones and matrix metalloproteinase 9 (MMP-9) were attached. In rendered 3D structure of METs, extDNA and protein components were embedded in each other. Since studies had shown the involvement of oxygen species in MET release, we aimed at studying if reactive nitrogen species (RNS) such as NO are also involved in MET formation. By application of NOS inhibitor - L-NAME or nitric oxide donor (SNAP), we studied the involvement of endogenous and exogenous RNS in traps release. We demonstrated that L-NAME halted MET formation upon stimulation with LPS while SNAP alone induced it. The latter phenomenon was further enhanced in the presence of LPS. Taken together, our findings demonstrate that BMDMs obtained from cryopreserved BM cells are capable of forming METs in an RNS-dependent manner.

Polystyrene microplastics promote liver inflammation by inducing the formation of macrophages extracellular traps

Microplastics (MPs), a new and increasing environmental pollutant, can cause ongoing damage to organisms. Although recent studies have revealed mechanisms of action for some of the hepatotoxicity caused by MPs, the role-played by cellular interactions, particularly immune cells, in the process of liver injury has not been elucidated. In the present study, 5-μm polystyrene microplastics (PS-MPs) induced liver inflammation as well as the formation of Macrophage extracellular traps (METs). Macrophage and LMH cell co-culture systems confirmed that PS-MPs-induced METs promote inflammation in hepatocytes. Mechanistically, macrophages actively phagocytose particles after 4 h of exposure to PS-MPs. Subsequently PS-MPs elevated ROS levels and disrupt mitochondrial kinetic homeostasis. Further activation of mitochondrial autophagy and lysosomes. After phagocytosis of PS-MPs by macrophages for 12 h, continued autophagy and lysosome activation eventually lead to lysosome rupture and release of calcium ions to induce the formation of METs. Blocking ROS (NAC) and autophagy (3MA) partially alleviated mitochondrial and lysosomal damage and thus inhibited the formation of METs induced by PS-MPs. NAC also delayed the onset of respiratory burst to alleviate METs formation. In conclusion, our study reveals the mechanism of METs formation in liver inflammation induced by PS-MPs exposure and suggests that lysosomal damage may be one of the key players in the formation of METs induced by PS-MPs.

Polystyrene microplastics-induced macrophage extracellular traps contributes to liver fibrotic injury by activating ROS/TGF-β/Smad2/3 signaling axis

Microplastics (MPs) are a type of emerging pollutant, posing a great threat to human and animal health. While recent studies have revealed the link between MPs exposure and liver injury of organisms, the effect of particle size on the level of MPs-induced hepatotoxicity and the intrinsic mechanism remain to be explored. Here, we established a mouse model exposed to two-diameter polystyrene MPs (PS-MPs, 1-10 μm or 50-100 μm) for 30 days. The in vivo results revealed that PS-MPs caused liver fibrotic injury in mice, accompanied with macrophages recruitment and macrophage extracellular traps (METs) formation, which were negatively correlated with particle size. The data in vitro showed that PS-MPs treatment could induce macrophages to release METs in a reactive oxygen species (ROS)-independent manner, and the METs formation level caused by large-size particles was higher than small-size particles. Further mechanistic analysis of a cell co-culture system revealed that PS-MPs-induced METs release led to a hepatocellular inflammatory response and epithelial-mesenchymal transition (EMT) via activating the ROS/TGF-β/Smad2/3 signaling axis, and this biological crosstalk could be relieved by DNase I. Overall, this findings demonstrates the key role of the action mechanism of METs in aggravating MPs-caused liver injury.

5'-Nucleotidase is dispensable for the growth of Salmonella Typhimurium but inhibits the bactericidal activity of macrophage extracellular traps

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a zoonotic pathogen that causes severe gastroenteritis. The 5'-nucleotidases of pathogens can dephosphorylate adenosine phosphates, boost adenosine levels and suppress the pro-inflammatory immune response. In our previous study, an extracellular nuclease, 5'-nucleotidase, was identified in the extracellular proteins of S. Typhimurium. However, the nuclease activity and the function of the 5'-nucleotidase of S. Typhimurium have not been explored. In the present study, deletion of the 5'-nucleotidase gene is dispensable for S. Typhimurium growth, even under environmental stress. Fluorescence microscopy revealed that the 5'-nucleotidase mutant induced more macrophage extracellular traps (METs) than the wild type did. Furthermore, recombinant 5'-nucleotidase protein (r5Nuc) could degrade λDNA, and the nuclease activity of r5Nuc was optimum at 37 °C and pH 6.0-7.0. The Mg²⁺ enhanced the nuclease activity of r5Nuc, whereas Zn²⁺ inhibited it. Meanwhile, deletion of the 5'-nucleotidase gene increased the bactericidal activity of METs, and r5Nuc could degrade METs and inhibit the bactericidal activity of METs. In conclusion, S. Typhimurium growth was independent of 5'-nucleotidase, but the nuclease activity of 5'-nucleotidase assisted S. Typhimurium to evade macrophage-mediated extracellular killing through degrading METs.

Hepcidin gene silencing ameliorated inflammation and insulin resistance in adipose tissue of db/db mice via inhibiting METs formation

As a major feature of diabetes, inflammation is closely related to macrophage extracellular traps and the expression of hepcidin upregulated by diabetes is reportedly involved in chronic inflammation. Therefore, we aimed to explore whether hepcidin could be implicated in inflammation and macrophage extracellular traps (METs) formation. The diabetic db/db mouse model was established exhibiting insulin resistance (IR), inflammation, macrophages infiltration and higher expression of hepcidin, where samples were obtained from epididymal adipose tissue. We observed that inflammation and IR improved in adipose tissue of mice treated with hepcidin gene silencing. Furthermore, METs formation could be markedly inhibited via hepcidin gene silencing followed by attenuated inflammatory response due to METs, indicating hepcidin gene silencing played a key role in anti-inflammation by inhibiting METs formation. So, we concluded that hepcidin gene silencing has a potential for treatment of diabetes due to its ability to ameliorate inflammation via inhibiting METs formation.

Extracellular traps and PAD4 released by macrophages induce citrullination and auto-antibody production in autoimmune arthritis

The mechanisms underlying the transition of rheumatoid arthritis (RA) systemic autoimmunity to the joints remain largely unknown. Here, we demonstrate that macrophages in the secondary lymphoid organs (SLOs) and synovial ectopic lymphoid-like structures (ELSs) express peptidylarginine deiminase 4 (PAD4) in murine collagen induced arthritis (CIA) and synovial biopsies from RA patients. Moreover, peptidyl citrulline colocalized with macrophages in SLOs and ELSs, and depletion of macrophages in CIA decreased lymphoid tissue citrullination and serum anti-citrullinated protein/peptide antibody (ACPA) levels. Furthermore, PAD was released from activated murine and RA synovial tissue and fluid (SF) macrophages which functionally deiminated extracellular proteins/peptides in vitro. Additionally, activated murine and SF macrophages displayed macrophage extracellular trap formation (METosis) and release of intracellular citrullinated histones. Moreover, presentation of citrullinated proteins induced ACPA production in vitro. Thus, lymphoid tissue macrophages contribute to self-antigen citrullination and ACPA production, indicating that their selective targeting would potentially ameliorate citrullination-dependent autoimmune disorders.