The multifaceted role of plasminogen in inflammation

A fine-tuned activation and deactivation of proteases and their inhibitors are involved in the execution of the inflammatory response. The zymogen/proenzyme plasminogen is converted to the serine protease plasmin, a key fibrinolytic factor by plasminogen activators including tissue-type plasminogen activator (tPA). Plasmin is part of an intricate protease network controlling proteins of initial hemostasis/coagulation, fibrinolytic and complement system. Activation of these protease cascades is required to mount a proper inflammatory response. Although best known for its ability to dissolve clots and cleave fibrin, recent studies point to the importance of fibrin-independent functions of plasmin during acute inflammation and inflammation resolution. In this review, we provide an up-to-date overview of the current knowledge of the enzymatic and cytokine-like effects of tPA and describe the role of tPA and plasminogen receptors in the regulation of the inflammatory response with emphasis on the cytokine storm syndrome such as observed during coronavirus disease 2019 or macrophage activation syndrome. We discuss tPA as a modulator of Toll like receptor signaling, plasmin as an activator of NFkB signaling, and summarize recent studies on the role of plasminogen receptors as controllers of the macrophage conversion into the M2 type and as mediators of efferocytosis during inflammation resolution.

Heat-Shock Proteins 70 Induce Pro-Inflammatory Maturation Program in Decidual CD1a(+) Dendritic Cells

PROBLEM

The aim of the study was to assess possible binding of a mixture of constitutive Hsc70 and inducible Hsp70 forms (HSP70) to Toll-like receptor (TLR) 4 and CD91 receptors on decidual CD1a(+) dendritic cells (DCs) and their influence on DCs maturation status.

METHOD OF STUDY

Immunohistology and immunofluorescence of paraffin-embedded first trimetester and term pregnancy decidua were performed together with flow cytometry detection of antigens in DCs after stimulation of decidual mononuclear cells with HSP70.

RESULTS

Hsc70 and Hsp70 labeling revealed intracellular and nuclear staining in trophoblast cells. The numbers of Hsc70(+) and Hsp70(+) cells of decidual tissue were higher in early pregnancy decidua than in decidua at term. HSP70 binds CD91 and TLR4 receptors on CD1a(+) DCs and increased the expression of CD83, HLA-DR, CD80, and CD86, but decreased CC receptor (CCR) 5. HSP70 increased CC ligand (CCL) 3 and CCL22. HSP70 in the concentration of 1 μg/mL increased the percentage of interferon-γ and interleukin (IL)-15-expressing cells over the cells expressing IL-4.

CONCLUSION

HSP70 binds CD91 and TLR4 on decidual CD1a(+) DCs, causes their maturation, and increases IL-15 in the context of Th1 cytokine/chemokine domination, which could support immune response harmful for ongoing pregnancy.

[Protein components of innate immunity in protection from pathogenic invasion (literature review)]

System of innate immunity is a set of effector molecules and cells counteracting invasion of pathogens and their products. Alpha-2-macroglobulin (a2-MG) and lactoferrin (LF) play a significant role in primary protection of organism. A wide spectrum of transport and regulatory functions, high affinity to endocytosis receptor as well as structural features of these proteins allow them not only to effectively protect the organism during direct contact with pathogen but also to have an immunomodulatory impact on immunocompetent cells of adaptive immunity. However despite a common receptor and a number of ligands, mechanisms of realization of protective functions ofa2-MG and LF differ significantly. The aim of this review is to systemize knowledge on means and mechanisms of protection of a 2-MG and LF against invasion.

High efficiency CD91- and LOX-1-mediated re-presentation of gp96-chaperoned peptides by MHC II molecules

Exogenous antigens enter antigen-presenting cells through non-specific mechanisms and are presented by the MHC II molecules. We show here that antigens chaperoned by the heat shock protein gp96 enter dendritic cells and B cells through a specific, CD91- and LOX-1-mediated mechanism, and are presented by MHC II molecules, in addition to MHC I molecules as previously demonstrated. Receptor utilization results in high efficiency uptake such that antigen concentrations as low as 10(-9) M, if chaperoned by gp96, lead to productive antigen presentation. Chaperoning by gp96 increases the efficiency of uptake over un-chaperoned peptides by up to two orders of magnitude. Consistent with these studies in vitro, immunization of mice with gp96-peptide complexes (containing 5 ng peptide) results in generation of a peptide-specific CD4+ T cell response. The high efficiency suggests a mechanism in which dendritic cells, exposed in vivo to heat shock protein-chaperoned peptides liberated by virus-infected host cells or by the lysis of infecting bacteria, may prime and expand specific CD4+ responses.

Participation of the lipoprotein receptor LRP1 in hypoxia-HSP90alpha autocrine signaling to promote keratinocyte migration

Hypoxia is a microenvironmental stress in many pathological conditions, including wound healing and tumor invasion. Under hypoxia, the cells are forced to adapt alternative and self-supporting mechanisms. Understanding these mechanisms may lead to new insights into human disorders. We report here a novel autocrine signaling mechanism by which hypoxia promotes human keratinocyte (HK) migration. First, hypoxia triggers HKs to secrete heat shock protein 90-alpha (HSP90alpha) via a HIF1-dependent pathway. The secreted HSP90alpha in turn promotes migration, but not proliferation, of the cells. Disruption of the secretion or extracellular function of HSP90alpha blocked hypoxia-stimulated HK migration. The ubiquitously expressed surface receptor, LRP1 (LDL-receptor-related protein 1), mediates the HSP90alpha signaling. Inhibition of LRP1 binding to extracellular HSP90alpha by neutralizing antibodies or genetic silencing of the LRP1 receptor by RNAi completely nullified hypoxia-driven HK migration. Finally, re-introducing a RNAi-resistant LRP1 cDNA into LRP1-downregulated HKs rescued the motogenic response of the cells to hypoxia. We propose that the hypoxia-HSP90alpha-LRP1 autocrine loop provides previously unrecognized therapeutic targets for human disorders such as chronic wounds and cancer invasion.

Tissue factor induction by aggregated LDL depends on LDL receptor-related protein expression (LRP1) and Rho A translocation in human vascular smooth muscle cells

OBJECTIVE

Low density lipoprotein (LDL) internalized in the vascular wall and modified by binding to extracellular matrix-proteoglycans (ECM) becomes aggregated (agLDL). AgLDL induces tissue factor (TF) expression and activity in human vascular smooth muscle cells (VSMC). TF expression in vascular cells promotes the prothrombotic transformation of the vascular wall. However, the mechanisms by which agLDL induces TF are not known. The aim of this study was to investigate the mechanisms involved in TF activation by extracellular matrix-modified LDL in human VSMC.

METHODS AND RESULTS

AgLDL significantly induces TF expression (real time PCR and Western blot analysis) and procoagulant activity (factor Xa generation test) in human VSMC. HMG-CoA reductase inhibition completely prevents agLDL-induced TF expression and partially inhibits agLDL-TF activation. These effects are reverted by geranylgeranyl pyrophosphate (GGPP) but not by farnesyl pyrophosphate (FPP), suggesting the involvement of a geranylated protein in agLDL-TF induction. AgLDL increases Rho A translocation (2-fold) from the cytoplasm to the cell membrane in control but not in simvastatin-treated VSMC. Exoenzyme C3, a specific Rho A inhibitor, completely prevents agLDL-induced TF overexpression and partially agLDL-TF activation. Blocking LRP1, the receptor of agLDL, with anti-LRP1 antibodies or inhibiting LRP1 expression by small interference RNA treatment (siRNA-LRP1) impairs agLDL-induced TF overexpression and activation.

CONCLUSIONS

These results demonstrate that TF induction by agLDL depends on LRP1 expression and requires Rho A translocation to the cellular membrane.

Soluble alpha2-macroglobulin receptor is increased in endotracheal aspirates from infants and children after cardiopulmonary bypass

OBJECTIVE

Cytokine dysregulation contributes to the systemic inflammatory response after cardiopulmonary bypass. Clearance of cytokine binding proteins may be important in the resolution of inflammation. Our aim was to determine whether the cytokine binding protein alpha 2 -macroglobulin and its soluble receptor were upregulated in endotracheal aspirates from infants and children undergoing cardiopulmonary bypass.

METHODS

Seventy tracheal aspirates were collected before and after cardiopulmonary bypass from 35 infants and children undergoing surgical correction of congenital heart defects. alpha 2 -Macroglobulin and the soluble alpha 2 -macroglobulin receptor were identified by Western blot. With the use of multi-analyte cytokine profiling, pro-inflammatory and anti-inflammatory cytokines were quantified, normalized to total protein, and expressed as ratios. Paired t tests and Wilcoxon signed-rank tests were performed between prebypass and postbypass samples. Correlations were examined among alpha 2 -macroglobulin, soluble alpha 2 -macroglobulin receptor, cytokine ratios, and the clinical variables of cardiopulmonary bypass, aortic crossclamp, and circulatory arrest times.

RESULTS

alpha 2 -Macroglobulin increased by 50% (mean densitometry increase 82,683 +/- 184,594, P = .012), and soluble alpha 2 -macroglobulin receptor increased by 17% (mean densitometry increase 506,148 +/- 687,037, P = .0001) after cardiopulmonary bypass. The ratio of interleukin-8/interleukin-4 increased by 136% ( P = .0001), and interleukin-8/interleukin-10 increased by 102% ( P = .001). The increase in soluble alpha 2 -macroglobulin receptor was positively correlated with the ratios of interleukin-8/interleukin-4 and interleukin-8/interleukin-10. There were no statistically significant positive correlations between the increase in alpha 2 -macroglobulin or soluble alpha 2 -macroglobulin receptor and measured clinical variables.

CONCLUSIONS

We report for the first time the upregulation of alpha 2 -macroglobulin and soluble alpha 2 -macroglobulin receptor in tracheal aspirates after cardiopulmonary bypass in infants and children. Soluble alpha 2 -macroglobulin receptor correlates with increased alpha 2 -macroglobulin and a disproportionate increase in pro-inflammatory to anti-inflammatory cytokine ratios.

All three LDL receptor homology regions of the LDL receptor-related protein bind multiple ligands

The three complete human LDL receptor homology regions of the LDL receptor-related protein (sLRP2, sLRP3, and sLRP4) have been expressed in Pichia pastoris SMD1168 with constitutive coexpression of the receptor-associated protein (RAP). Each sLRP was purified to homogeneity after deglycosylation using a combination of anion-exchange and size exclusion chromatography. Mass spectrometry and N-terminal sequencing confirmed the identity of each fragment at purified yields of several milligrams per liter. Despite the large number of disulfide linkages and glycosylation sites in each LDL receptor homology region (sLRP), all were shown to be competent for binding to several LRP1 ligands. Each sLRP also bound human RAP, which is thought to be a generalized receptor antagonist, in solution-binding experiments. As expected, sLRP2 bound the receptor-binding domain of alpha(2)-macroglobulin (residues 1304-1451). All three sLRPs bound human apolipoprotein-enriched beta very low density lipoprotein, the canonical ligand for this receptor. All three sLRPs also bound lactoferrin and thrombin-protease nexin 1 complexes. Only sLRP4 bound thrombin-antithrombin III complexes. The results show that binding-competent LDL receptor homology regions (sLRPs) can be produced in high yield in P. pastoris and readily purified. Each sLRP has binding sites for multiple ligands, but not all ligand binding could be competed by RAP.

Naturally formed or artificially reconstituted non-covalent alpha2-macroglobulin-peptide complexes elicit CD91-dependent cellular immunity

Immunization of mice with in vitro reconstituted alpha2-macroglobulin-peptide complexes primes peptide-specific CTL responses. We show here using the H-Y antigenic system that naturally produced, immunogenic alpha2-macroglobulin-peptide complexes can be isolated from the sera of normal male mice. As an application of these ideas to cancer immunity, we show that the immunity evoked by alpha2-macroglobulin-peptide complexes reconstituted in vitro is effective in prophylaxis against tumors. Furthermore, complex peptide mixtures isolated from tumor lysates can be reconstituted non-covalently with alpha2-macroglobulin and such complexes elicit potent protective tumor immunity. This approach circumvents the need for prior knowledge of the identity of the immunogenic peptides. The heat shock protein/alpha2-macroglobulin receptor CD91 is shown to be involved in the ability of heat shock proteins or alpha2-macroglobulin to elicit an anti-tumor immune response.