Midkine drives cardiac inflammation by promoting neutrophil trafficking and NETosis in myocarditis.

Heart failure due to dilated cardiomyopathy is frequently caused by myocarditis. However, the pathogenesis of myocarditis remains incompletely understood. Here, we report the presence of neutrophil extracellular traps (NETs) in cardiac tissue of patients and mice with myocarditis. Inhibition of NET formation in experimental autoimmune myocarditis (EAM) of mice substantially reduces inflammation in the acute phase of the disease. Targeting the cytokine midkine (MK), which mediates NET formation in vitro, not only attenuates NET formation in vivo and the infiltration of polymorphonuclear neutrophils (PMNs) but also reduces fibrosis and preserves systolic function during EAM. Low-density lipoprotein receptor-related protein 1 (LRP1) acts as the functionally relevant receptor for MK-induced PMN recruitment as well as NET formation. In summary, NETosis substantially contributes to the pathogenesis of myocarditis and drives cardiac inflammation, probably via MK, which promotes PMN trafficking and NETosis. Thus, MK as well as NETs may represent novel therapeutic targets for the treatment of cardiac inflammation.

Identification and functional characterization of amphioxus Miple, ancestral type of vertebrate midkine/pleiotrophin homologues.

Midkine (MK) and pleiotrophin (PTN) are the only two members of heparin-binding growth factor family. MK/PTN homologues found from Drosophila to humans are shown to have antibacterial activities and their antibacterial domains are conserved during evolution. However, little is known about MK/PTN homologue in the basal chordate amphioxus, and overall, information regarding MK/PTN homologues is rather limited in invertebrates. In this study, we identified a single MK/PTN homologue in Branchiostoma japonicum, termed BjMiple, which has a novel domain structure of PTN-PTNr1-PTNr2, and represents the ancestral form of vertebrate MK/PTN family proteins. BjMiple was expressed mainly in the ovary in a tissue-dependent fashion, and its expression was remarkably up-regulated following challenge with bacteria or their signature molecules LPS and LTA, suggesting its involvement in antibacterial responses. Functional assays revealed that BjMiple had strong antimicrobial activity, capable of killing a panel of Gram-negative and Gram-positive bacteria via a membranolytic mechanism, including interaction with bacterial membrane via LPS and LTA, membrane depolarization and high intracellular levels of ROS. Importantly, strong antibacterial activity was localized in PTN42-61 and PTNr142-66. Additionally, BjMiple and its derived peptides PTN42-61 and PTNr142-66 were not cytotoxic to human RBCs and mammalian cells. Taken together, our study suggests that amphioxus Miple is the ancestral type of vertebrate MK/PTN family homologues, and can play important roles as innate peptide antibiotics, which renders it a promising template for the design of novel peptide antibiotics against multi-drug resistant bacteria.

[Investigation of cytokine and midkine responses of human THP-1 leukemia cells induced by phorbol-12-Myristate-13-Acetate (PMA) at different concentrations and times]. / Degisik konsantrasyonlarda ve sürelerde Phorbol-12-Myristate-13-Acetate ile uyarilan insan THP-1 lösemi hücrelerinin sitokin ve midkin yanitlarinin arastirilmasi.

Macrophages are accepted as cells that initially contact with the pathogens and initiate the innate immune response. They play effective roles in innate immune and inflammatory responses by intercellular relations and inflammatory mediator secretion. Human THP-1 leukemia cells are frequently used for the in vitro determination of the signal pathways, and the functions of macrophages. Phorbol-12-Myristate-13-Acetate (PMA) is commonly used to induce macrophage differentiation of monocytic cell lines but the extent of differentiation in comparison to primary tissue macrophages is unclear. Midkine acts as a cytokine and growth factor which organizes proliferation, differentiation, survival, adhesion and migration of immune cells. The aim of this study was to observe the differences in the secretion of midkine, TNF-α, IL-10 and IFN-γ of macrophages differentiated from monocytes when stimulated with different doses of PMA for different durations. For this purpose, THP-1 monocytic cells were proliferated by PMA at 24, 48 and 72 hours by using the concentrations of 10 ng/ml, 20 ng/ml, 40 ng/ml and 60 ng/ ml. Midkine, TNF-α, IL-10 and IFN-γ cytokine levels were determined by ELISA in the supernatants of the cells collected at the end of incubation times. PMA stimuli initiated changes that were indicative of differentiation in the cell morphology. Differentiation of cells by PMA induced midkine, TNF-α, IL-10 and IFN-γ secretions in monocytic cells even at the lowest dosage (10 ng/ml). PMA caused cytotoxicity in the cells when the dosages were increased (> 20 ng/ml). THP-1 cells have a basal secretion of midkine and are increased by dosage dependent with PMA stimulation. Midkine secretion has shown changes dependent with dosage and time. A difference was also observed in the cytokine profile of PMA stimulated cells at different doses. The results indicated that the differentiation of THP-1 monocytes to macrophages requires optimization to ensure that this in vitro macrophage model more precisely reflects real in vivo physiologic conditions. As a conclusion the results have shown that a modified PMA differentiation protocol (20 ng/ml and 48 hours incubation) might enhance macrophage differentiation of THP-1 cells without induced cell death (viability 92.2%) and cytokine secretion and midkine responses were the important discriminators of the level of macrophage differentiation.