Targeting glycosaminoglycans in the lung by an engineered CXCL8 as a novel therapeutic approach to lung inflammation

G-CSFR-induced leukocyte transendothelial migration during the inflammatory response is regulated by the ICAM1-PKCa axis: based on multiomics integration analysis

As an indispensable inflammatory mediator during sepsis, granulocyte colony-stimulating factor (G-CSF) facilitates neutrophil production by activating G-CSFR. However, little is known about the role of intracellular downstream signalling pathways in the induction of inflammation. To explore the functions of molecules in regulating G-CSFR signalling, RNA sequencing and integrated proteomic and phosphoproteomic analyses were conducted to predict the differentially expressed molecules in modulating the inflammatory response after G-CSFR expression was either up- or downregulated, in addition to the confirmation of their biological function by diverse experimental methods. In the integrated bioinformatic analysis, 3190 differentially expressed genes (DEGs) and 1559 differentially expressed proteins (DEPs) were identified in multiple-group comparisons (p < 0.05, FC >  ± 1.5) using enrichment analyses, as well as those classic pathways such as the TNF, NFkappaB, IL-17, and TLR signalling pathways. Among them, 201 proteins, especillay intercellular cell adhesion molecule-1 (ICAM1) and PKCa, were identified as potential molecules involved in inflammation according to the protein-protein interaction (PPI) analysis, and the leukocyte transendothelial migration (TEM) pathway was attributed to the intervention of G-CSFR. Compared with the control and TNF-a treatment, the G-CSFR (G-CSFROE)-overexpressing led to an obvious increase in the number of leukocytes with the TEM phenotype. Mechanically, the expression of ICAM1 and PKCa was significantly up- and downregulated by G-CSFROE, which directly led to increased TEM; moreover, PKCa expression was negatively regulated by ICAM1 expression, leading to aberrant leukocyte TEM. Altogether, the ICAM1‒PKCa axis was found a meaningful target in the leukocyte TEM induced by G-CSFR upregulation.

Syndecan-4 is the key proteoglycan involved in mediating sepsis-associated lung injury

Vascular endothelial cell dysfunction involving syndecan (SDC) proteoglycans contributes to acute sepsis-associated lung injury (ALI), but the exact SDC isoform involved is unclear. We aimed to clarify which SDCs are involved in ALI. A relevant gene expression dataset (GSE5883) was analysed for differentially expressed genes (DEGs) between lipopolysaccharide (LPS)-treated and control lung endothelial cells and for SDC isoform expression. Bioinformatic analyses to predict DEG function were conducted using R language, Gene Ontology, and the Kyoto Encyclopedia of Genes and Genomes. SDC2 and SDC4 expression profiles were examined under inflammatory conditions in human lung vascular endothelial cell and mouse sepsis-associated ALI models. Transcription factors regulating SDC2/4 were predicted to indirectly assess SDC involvement in septic inflammation. Of the DEGs, 224 and 102 genes were up- and downregulated, respectively. Functional analysis indicated that DEGs were involved in modulating receptor ligand and signalling receptor activator activities, cytokine receptor binding, responses to LPS and molecules of bacterial origin, regulation of cell adhesion, tumour necrosis factor signalling, and other functions. DEGs were also enriched for cytoplasmic ribonucleoprotein granules, transcription regulator complexes, and membrane raft cellular components. SDC4 gene expression was 4.5-fold higher in the LPS group than in the control group, while SDC2 levels were similar in both groups. SDC4 mRNA and protein expression was markedly upregulated in response to inflammatory injury, and SDC4 downregulation severely exacerbated inflammatory responses in both in vivo and in vitro models. Overall, our data demonstrate that SDC4, rather than SDC2, is involved in LPS-induced sepsis-associated ALI.

Comparing the Cytokine Storms of COVID-19 and Pandemic Influenza

Emerging respiratory viruses are major health threats due to their potential to cause massive outbreaks. Over the past 2 years, the coronavirus disease 2019 (COVID-19) pandemic has caused millions of cases of severe infection and deaths worldwide. Although natural and vaccine-induced protective immune mechanisms against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been increasingly identified, the factors that determine morbimortality are less clear. Comparing the immune signatures of COVID-19 and other severe respiratory infections such as the pandemic influenza might help dissipate current controversies about the origin of their severe manifestations. As such, identifying homologies in the immunopathology of both diseases could provide targets for immunotherapy directed to block shared pathogenic mechanisms. Meanwhile, finding unique characteristics that differentiate each infection could shed light on specific immune alterations exploitable for diagnostic and individualized therapeutics for each case. In this study, we summarize immunopathological aspects of COVID-19 and pandemic influenza from the perspective of cytokine storms as the driving force underlying morbidity. Thereby, we analyze similarities and differences in the cytokine profiles of both infections, aiming to bring forward those molecules more attractive for translational medicine and drug development.

Targeting Chemokine-Glycosaminoglycan Interactions to Inhibit Inflammation

Leukocyte migration into tissues depends on the activity of chemokines that form concentration gradients to guide leukocytes to a specific site. Interaction of chemokines with their specific G protein-coupled receptors (GPCRs) on leukocytes induces leukocyte adhesion to the endothelial cells, followed by extravasation of the leukocytes and subsequent directed migration along the chemotactic gradient. Interaction of chemokines with glycosaminoglycans (GAGs) is crucial for extravasation in vivo. Chemokines need to interact with GAGs on endothelial cells and in the extracellular matrix in tissues in order to be presented on the endothelium of blood vessels and to create a concentration gradient. Local chemokine retention establishes a chemokine gradient and prevents diffusion and degradation. During the last two decades, research aiming at reducing chemokine activity mainly focused on the identification of inhibitors of the interaction between chemokines and their cognate GPCRs. This approach only resulted in limited success. However, an alternative strategy, targeting chemokine-GAG interactions, may be a promising approach to inhibit chemokine activity and inflammation. On this line, proteins derived from viruses and parasites that bind chemokines or GAGs may have the potential to interfere with chemokine-GAG interactions. Alternatively, chemokine mimetics, including truncated chemokines and mutant chemokines, can compete with chemokines for binding to GAGs. Such truncated or mutated chemokines are characterized by a strong binding affinity for GAGs and abrogated binding to their chemokine receptors. Finally, Spiegelmers that mask the GAG-binding site on chemokines, thereby preventing chemokine-GAG interactions, were developed. In this review, the importance of GAGs for chemokine activity in vivo and strategies that could be employed to target chemokine-GAG interactions will be discussed in the context of inflammation.

A C-terminal CXCL8 peptide based on chemokine-glycosaminoglycan interactions reduces neutrophil adhesion and migration during inflammation

Leucocyte recruitment is critical during many acute and chronic inflammatory diseases. Chemokines are key mediators of leucocyte recruitment during the inflammatory response, by signalling through specific chemokine G-protein-coupled receptors (GPCRs). In addition, chemokines interact with cell-surface glycosaminoglycans (GAGs) to generate a chemotactic gradient. The chemokine interleukin-8/CXCL8, a prototypical neutrophil chemoattractant, is characterized by a long, highly positively charged GAG-binding C-terminal region, absent in most other chemokines. To examine whether the CXCL8 C-terminal peptide has a modulatory role in GAG binding during neutrophil recruitment, we synthesized the wild-type CXCL8 C-terminal [CXCL8 (54-72)] (Peptide 1), a peptide with a substitution of glutamic acid (E) 70 with lysine (K) (Peptide 2) to increase positive charge; and also, a scrambled sequence peptide (Peptide 3). Surface plasmon resonance showed that Peptide 1, corresponding to the core CXCL8 GAG-binding region, binds to GAG but Peptide 2 binding was detected at lower concentrations. In the absence of cellular GAG, the peptides did not affect CXCL8-induced calcium signalling or neutrophil chemotaxis along a diffusion gradient, suggesting no effect on GPCR binding. All peptides equally inhibited neutrophil adhesion to endothelial cells under physiological flow conditions. Peptide 2, with its greater positive charge and binding to polyanionic GAG, inhibited CXCL8-induced neutrophil transendothelial migration. Our studies suggest that the E70K CXCL8 peptide, may serve as a lead molecule for further development of therapeutic inhibitors of neutrophil-mediated inflammation based on modulation of chemokine-GAG binding.

Heparin Binding Proteins as Therapeutic Target: An Historical Account and Current Trends

The polyanionic nature and the ability to interact with proteins with different affinities are properties of sulfated glycosaminoglycans (GAGs) that determine their biological function. In designing drugs affecting the interaction of proteins with GAGs the challenge has been to generate agents with high binding specificity. The example to emulated has been a heparin-derived pentasaccharide that binds to antithrombin-III with high affinity. However, the portability of this model to other biological situations is questioned on several accounts. Because of their structural flexibility, oligosaccharides with different sulfation and uronic acid conformation can display the same binding proficiency to different proteins and produce comparable biological effects. This circumstance represents a formidable obstacle to the design of drugs based on the heparin scaffold. The conceptual framework discussed in this article is that through a direct intervention on the heparin-binding functionality of proteins is possible to achieve a high degree of action specificity. This objective is currently pursued through two strategies. The first makes use of small molecules for which in the text we provide examples from past and present literature concerning angiogenic factors and enzymes. The second approach entails the mutagenesis of the GAG-binding site of proteins as a means to generate a new class of biologics of therapeutic interest.

Glycosaminoglycan-Mediated Downstream Signaling of CXCL8 Binding to Endothelial Cells

The recruitment of leukocytes, mediated by endothelium bound chemokine gradients, is a vital process in inflammation. The highly negatively charged, unbranched polysaccharide family of glycosaminoglycans (GAGs), such as heparan sulfate and chondroitin sulfate mediate chemokine immobilization. Specifically the binding of CXCL8 (interleukin 8) to GAGs on endothelial cell surfaces is known to regulate neutrophil recruitment. Currently, it is not clear if binding of CXCL8 to GAGs leads to endothelial downstream signaling in addition to the typical CXCR1/CXCR2 (C-X-C motif chemokine receptor 1 and 2)-mediated signaling which activates neutrophils. Here we have investigated the changes in protein expression of human microvascular endothelial cells induced by CXCL8. Tumor necrosis factor alpha (TNFα) stimulation was used to mimic an inflammatory state which allowed us to identify syndecan-4 (SDC4) as the potential proteoglycan co-receptor of CXCL8 by gene array, real-time PCR and flow cytometry experiments. Enzymatic GAG depolymerization via heparinase III and chondroitinase ABC was used to emulate the effect of glycocalyx remodeling on CXCL8-induced endothelial downstream signaling. Proteomic analyses showed changes in the expression pattern of a number of endothelial proteins such as Zyxin and Caldesmon involved in cytoskeletal organization, cell adhesion and cell mobility. These results demonstrate for the first time a potential role of GAG-mediated endothelial downstream signaling in addition to the well-known CXCL8-CXCR1/CXCR2 signaling pathways in neutrophils.

Regulation of Chemokine Activity - A Focus on the Role of Dipeptidyl Peptidase IV/CD26

Chemokines are small, chemotactic proteins that play a crucial role in leukocyte migration and are, therefore, essential for proper functioning of the immune system. Chemokines exert their chemotactic effect by activation of chemokine receptors, which are G protein-coupled receptors (GPCRs), and interaction with glycosaminoglycans (GAGs). Furthermore, the exact chemokine function is modulated at the level of posttranslational modifications. Among the different types of posttranslational modifications that were found to occur in vitro and in vivo, i.e., proteolysis, citrullination, glycosylation, and nitration, NH₂-terminal proteolysis of chemokines has been described most intensively. Since the NH₂-terminal chemokine domain mediates receptor interaction, NH₂-terminal modification by limited proteolysis or amino acid side chain modification can drastically affect their biological activity. An enzyme that has been shown to provoke NH₂-terminal proteolysis of various chemokines is dipeptidyl peptidase IV or CD26. This multifunctional protein is a serine protease that preferably cleaves dipeptides from the NH₂-terminal region of peptides and proteins with a proline or alanine residue in the penultimate position. Various chemokines possess such a proline or alanine residue, and CD26-truncated forms of these chemokines have been identified in cell culture supernatant as well as in body fluids. The effects of CD26-mediated proteolysis in the context of chemokines turned out to be highly complex. Depending on the chemokine ligand, loss of these two NH₂-terminal amino acids can result in either an increased or a decreased biological activity, enhanced receptor specificity, inactivation of the chemokine ligand, or generation of receptor antagonists. Since chemokines direct leukocyte migration in homeostatic as well as pathophysiologic conditions, CD26-mediated proteolytic processing of these chemotactic proteins may have significant consequences for appropriate functioning of the immune system. After introducing the chemokine family together with the GPCRs and GAGs, as main interaction partners of chemokines, and discussing the different forms of posttranslational modifications, this review will focus on the intriguing relationship of chemokines with the serine protease CD26.

Modulation of Chemokine Responses: Synergy and Cooperativity

Chemokine biology is mediated by more complex interactions than simple monomolecular ligand–receptor interactions, as chemokines can form higher order quaternary structures, which can also be formed after binding to glycosaminoglycans (GAGs) on endothelial cells, and their receptors are found as dimers and/or oligomers at the cell surface. Due to the complexity of the chemokine binding and signaling system, several mechanisms have been proposed to provide an explanation for the synergy observed between chemokines in leukocyte migration. Pioneering studies on interactions between different chemokines have revealed that they can act as antagonists, or synergize with other chemokines. The synergism can occur at different levels, involving either two chemokine receptors triggered simultaneously or sequentially exposed to their agonists, or the activation of one type of chemokine receptor triggered by chemokine heterocomplexes. In addition to the several chemokines that, by forming a heterocomplex with chemokine receptor agonists, act as enhancers of molecules of the same family, we have recently identified HMGB1, an endogenous damage-associated molecular patterns (DAMPs) molecule, as an enhancer of the activity of CXCL12. It is now evident that synergism between chemokines is crucial at the very early stage of inflammation. In addition, the low-affinity interaction with GAGs has recently been shown to induce cooperativity allowing synergy or inhibition of activity by displacement of other ligands.

PA401, a novel CXCL8-based biologic therapeutic with increased glycosaminoglycan binding, reduces bronchoalveolar lavage neutrophils and systemic inflammatory markers in a murine model of LPS-induced lung inflammation

RATIONALE

Neutrophils play a fundamental role in a number of chronic lung diseases. Among the mediators of their recruitment to the lung, CXCL8 (IL-8) is considered to be one of the major players. CXCL8 exerts its chemotactic activity by binding to its GPCR receptors (CXCR1/R2) located on neutrophils, as well as through interactions with glycosaminoglycans (GAGs) on cell surfaces including those of the microvascular endothelium. Binding to GAG co-receptors is required to generate a solid-phase haptotactic gradient and to present IL-8/CXCL8 in a proper conformation to its receptors on circulating neutrophils.

METHODS

We have engineered increased GAG-binding affinity into human CXCL8, thereby obtaining a competitive inhibitor that displaces wild-type IL-8/CXCL8 from GAGs. By additionally knocking-out the GPCR binding domain of the chemokine, we generated a dominant negative protein (dnCXCL8; PA401) with potent anti-inflammatory characteristics proven in vivo in a murine model of LPS-induced lung inflammation (Adage et al., 2015). Here we have further investigated PA401 activity in this pulmonary model by evaluating plasma changes induced by LPS on white blood cells (WBC) and a broad range of inflammatory markers, especially chemokines, by addressing immediate effects of PA401 on these parameters in healthy and LPS exposed mice.

RESULTS

Aerosolized LPS induced a significant increase in bronchoalveolar lavage (BAL) neutrophils after 3 and 7h, as well as an increase in total WBC and changes in 21 of the 59 measured plasma markers, mostly belonging to the chemokine family. PA401 treatment in saline exposed mice didn't induce major changes in any of the measured parameters. When administered to LPS aerosolized mice, PA401 caused a significant normalization of KC/mCXCL1 and other inflammatory markers, as well as of blood WBC count. In addition, BAL neutrophils were significantly reduced, confirming the previously observed lung anti-inflammatory activity of PA401 in this experiment.

CONCLUSIONS

PA401 is a new promising biologic therapeutic with a novel and unique mechanism of action for interfering with neutrophilic lung inflammation, that also normalizes plasma inflammatory markers.