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

Large-scale exome-wide association analysis identifies loci for White Blood Cell Traits and Pleiotropy with Immune-Mediated Diseases

White blood cells play diverse roles in innate and adaptive immunity. Genetic association analyses of phenotypic variation in circulating white blood cell (WBC) counts from large samples of otherwise healthy individuals can provide insights into genes and biologic pathways involved in production, differentiation, or clearance of particular WBC lineages (myeloid, lymphoid) and also potentially inform the genetic basis of autoimmune, allergic, and blood diseases. We performed an exome array-based meta-analysis of total WBC and subtype counts (neutrophils, monocytes, lymphocytes, basophils, and eosinophils) in a multi-ancestry discovery and replication sample of ∼157,622 individuals from 25 studies. We identified 16 common variants (8 of which were coding variants) associated with one or more WBC traits, the majority of which are pleiotropically associated with autoimmune diseases. Based on functional annotation, these loci included genes encoding surface markers of myeloid, lymphoid, or hematopoietic stem cell differentiation (CD69, CD33, CD87), transcription factors regulating lineage specification during hematopoiesis (ASXL1, IRF8, IKZF1, JMJD1C, ETS2-PSMG1), and molecules involved in neutrophil clearance/apoptosis (C10orf54, LTA), adhesion (TNXB), or centrosome and microtubule structure/function (KIF9, TUBD1). Together with recent reports of somatic ASXL1 mutations among individuals with idiopathic cytopenias or clonal hematopoiesis of undetermined significance, the identification of a common regulatory 3 UTR variant of ASXL1 suggests that both germline and somatic ASXL1 mutations contribute to lower blood counts in otherwise asymptomatic individuals. These association results shed light on genetic mechanisms that regulate circulating WBC counts and suggest a prominent shared genetic architecture with inflammatory and autoimmune diseases

Macrophage LRP1 Promotes Diet-Induced Hepatic Inflammation and Metabolic Dysfunction by Modulating Wnt Signaling

Hepatic inflammation is associated with the development of insulin resistance, which can perpetuate the disease state and may increase the risk of metabolic syndrome and diabetes. Despite recent advances, mechanisms linking hepatic inflammation and insulin resistance are still unclear. The low-density lipoprotein receptor-related protein 1 (LRP1) is a large endocytic and signaling receptor that is highly expressed in macrophages, adipocytes, hepatocytes, and vascular smooth muscle cells. To investigate the potential role of macrophage LRP1 in hepatic inflammation and insulin resistance, we conducted experiments using macrophage-specific LRP1-deficient mice (macLRP1−/−) generated on a low-density lipoprotein receptor knockout (LDLR−/−) background and fed a Western diet. LDLR−/−; macLRP1−/− mice gained less body weight and had improved glucose tolerance compared to LDLR−/− mice. Livers from LDLR−/−; macLRP1−/− mice displayed lower levels of gene expression for several inflammatory cytokines, including Ccl3, Ccl4, Ccl8, Ccr1, Ccr2, Cxcl9, and Tnf, and reduced phosphorylation of GSK3α and p38 MAPK proteins. Furthermore, LRP1-deficient peritoneal macrophages displayed altered cholesterol metabolism. Finally, circulating levels of sFRP-5, a potent anti-inflammatory adipokine that functions as a decoy receptor for Wnt5a, were elevated in LDLR−/−; macLRP1−/− mice. Surface plasmon resonance experiments revealed that sFRP-5 is a novel high affinity ligand for LRP1, revealing that LRP1 regulates levels of this inhibitor of Wnt5a-mediated signaling. Collectively, our results suggest that LRP1 expression in macrophages promotes hepatic inflammation and the development of glucose intolerance and insulin resistance by modulating Wnt signaling

High-affinity binding of plasminogen-activator inhibitor 1 complexes to LDL receptor-related protein 1 requires lysines 80, 88, and 207

© 2020 Migliorini et al. It is well-established that complexes of plasminogen-activator inhibitor 1 (PAI-1) with its target enzymes bind tightly to low-density lipoprotein (LDL) receptor-related protein 1 (LRP1), but the molecular details of this interaction are not well-defined. Furthermore, considerable controversy exists in the literature regarding the nature of the interaction of free PAI-1 with LRP1. In this study, we examined the binding of free PAI-1 and complexes of PAI-1 with low-molecular-weight urokinase-type plasminogen activator to LRP1. Our results confirmed that uPA:PAI-1 complexes bind LRP1 with ∼100-fold increased affinity over PAI-1 alone. Chemical modification of PAI-1 confirmed an essential requirement of lysine residues in PAI-1 for the interactions of both PAI-1 and uPA: PAI-1 complexes with LRP1. Results of surface plasmon resonance measurements supported a bivalent binding model in which multiple sites on PAI-1 and uPA:PAI-1 complexes interact with complementary sites on LRP1. An ionic-strength dependence of binding suggested the critical involvement of two charged residues for the interaction of PAI-1 with LRP1 and three charged residues for the interaction of uPA:PAI-1 complexes with LRP1. An enhanced affinity resulting from the interaction of three regions of the uPA: PAI-1 complex with LDLa repeats on LRP1 provided an explanation for the increased affinity of uPA:PAI-1 complexes for LRP1. MutationalanalysisrevealedanoverlapbetweenLRP1bindingand binding of a small-molecule inhibitor of PAI-1, CDE-096, confirming an important role for Lys-207 in the interaction of PAI-1 with LRP1 and of the orientations of Lys-207, -88, and -80 for the interaction of uPA:PAI-1 complexes with LRP1

Phosphorylated LRP1-ICD interacts with SHP-2 with high affinity.

<p>(a) Cell lysates from NRK fibroblasts were incubated with phosphorylated GST:LRP1-ICD (<i>lane 1</i>), unphosphorylated GST:LRP1-ICD (<i>lane 3</i>), GST and src (<i>lane 2</i>) or GST alone (<i>lane 4</i>) all bound to Glutathione-Sepharose. Following incubation and washing, eluted proteins were separated by SDS-PAGE and analyzed by immunoblot analysis for SHP-2 (<i>upper panel</i>), for tyrosine phosphorylation (<i>middle panel</i>) and for total protein by Ponseau stain (<i>lower panel</i>). (b) Increasing concentrations of phosphorylated (circles) or unphosporylated (squares) GST:LRP1-ICD were incubated with microtiter wells coated with SHP-2 (closed symbols) or BSA (open symbols). Bound GST:LRP1-ICD was detected with anti-GST antibodies. Curve shows the best fit to a single class of sites using non-linear regression analysis. *, absorbance values for pLRP1-ICD are significantly different from those of LRP1-ICD (p<0.0001, Students t test) (c) SPR analysis confirms binding of SHP-2 (1 µM) to immobilized phosphorylated GST:LRP1-ICD but not to immobilized unphosphorylated GST:LRP1-ICD.</p

SHP-2 and LRP1 co-immunoprecipitate and co-localize in fibroblasts following PDGF stimulation.

<p>(a) WI38 fibroblasts were serum starved overnight and stimulated with PDGF (30 ng/mL) for 2, 5, 10 and 15 minutes at 37°C. Cells were treated with DSP crosslinker for 30 minutes on ice prior to lysis. Lysates were immunoprecipitated with a SHP-2 antibody (sc-280) and western blot analysis was performed using a monoclonal antibody to LRP1, 11H4 (top panel). Loading was controlled by using anti-SHP-2 IgG (bottom panel). As a control, non-immune IgG (IgG) was employed for immunoprecipitation (15 min stimulation with 30 ng/ml PDGF). (b) Immunflourescence studies reveal colocalization of LRP1 and phospho-SHP-2 in fibroblasts stimulated with PDGF-BB. WI38 cells were cultured on glass cover slips, fixed with formaldehyde, and processed for immunofluorescent microscopy as described in “Methods”. The confocal image was taken using 60X oil immersion objective. Box 1 is a representative section from the ‘trailing’ edge of this migrating cell and box 2 is a representative area of the ‘leading’ edge of the cell. (c–e) represent a 3 fold enlarged area from box 2, at the ‘leading’ edge of the cell; (c) <i>green</i> LRP1 staining, (d) <i>red</i> phospho-SHP-2 staining, (e) <i>yellow</i> colocalization of LRP1 and phospho-SHP-2.</p

pPDGFRβ kinase domain and pLRP1-ICD compete for SHP-2 binding.

<p>(a,b) Increasing concentrations of GST:pLRP1-ICD were incubated with microtiter wells coated with SHP-2 in the presence of 0, 20, 60 and 180 nM pPDGFRβ KD (a) or sPDGFr (b). Bound GST:pLRP1-ICD was detected with anti-GST antibody. Curves in (a) show best fits to a single class of sites using non-linear regression analysis. The K_D values at each concentration are significantly different (p = 0.0007, Students t test). (c) Percent binding, normalized to 0 nM pPDGFRβ, of GST:pLRP1-ICD (100 nM) binding to SHP-2 in the presence of 20, 60 and 180 nM pPDGFRβ KD. (*, p = 0.0024; **p<0.0001, Students t test).</p

Quantitative analysis of interaction of the PDGFRβ kinase domain with SHP-2.

<p>Increasing concentrations of phosphorylated (closed squares) or unphosphorylated PDGFRβ KD (closed circles) were incubated with microtiter wells coated with SHP-2. Bound PDGFRβ KD was detected using an anti-PDGFRβ antibody. As a control, the binding of phosphorylated PDGFRβ KD to BSA (open triangles) was also measured. Curves show the best fit to a single class of sites using non-linear regression analysis. The binding of pPDGFRβ to SHP-2 is significantly different from the binding of PDGFRβ to SHP-2 (p = 0.0002, Students t test).</p