Inter-α inhibitor proteins maintain neutrophils in a resting state by regulating shape and reducing ROS production

Major endothelial damage markers identified from hemadsorption filters derived from treated patients with septic shock - endoplasmic reticulum stress and bikunin may play a role

Introduction

In septic patients the damage of the endothelial barrier is decisive leading to circulatory septic shock with disseminated vascular coagulation, edema and multiorgan failure. Hemadsorption therapy leads to rapid resolution of clinical symptoms. We propose that the isolation of proteins adsorbed to hemadsorption devices contributes to the identification of mediators responsible for endothelial barrier dysfunction.

Material and methods

Plasma materials enriched to hemadsorption filters (CytoSorb®) after therapy of patients in septic shock were fractionated and functionally characterized for their effect on cell integrity, viability, proliferation and ROS formation by human endothelial cells. Fractions were further studied for their contents of oxidized nucleic acids as well as peptides and proteins by mass spectrometry.

Results

Individual fractions exhibited a strong effect on endothelial cell viability, the endothelial layer morphology, and ROS formation. Fractions with high amounts of DNA and oxidized DNA correlated with ROS formation in the target endothelium. In addition, defined proteins such as defensins (HNP-1), SAA1, CXCL7, and the peptide bikunin were linked to the strongest additive effects in endothelial damage.

Conclusion

Our results indicate that hemadsorption is efficient to transiently remove strong endothelial damage mediators from the blood of patients with septic shock, which explains a rapid clinical improvement of inflammation and endothelial function. The current work indicates that a combination of stressors leads to the most detrimental effects. Oxidized ssDNA, likely derived from mitochondria, SAA1, the chemokine CXCL7 and the human neutrophil peptide alpha-defensin 1 (HNP-1) were unique for their significant negative effect on endothelial cell viability. However, the strongest damage effect occurred, when, bikunin - cleaved off from alpha-1-microglobulin was present in high relative amounts (>65%) of protein contents in the most active fraction. Thus, a relevant combination of stressors appears to be removed by hemadsorption therapy which results in fulminant and rapid, though only transient, clinical restitution.

Neuroprotective efficacy of hypothermia and Inter-alpha Inhibitor Proteins after hypoxic ischemic brain injury in neonatal rats

Therapeutic hypothermia is the standard of care for hypoxic-ischemic (HI) encephalopathy. Inter-alpha Inhibitor Proteins (IAIPs) attenuate brain injury after HI in neonatal rats. Human (h) IAIPs (60 ​mg/kg) or placebo (PL) were given 15 ​min, 24 and 48 ​h to postnatal (P) day-7 rats after carotid ligation and 8% oxygen for 90 ​min with (30 ​°C) and without (36 ​°C) exposure to hypothermia 1.5 ​h after HI for 3 ​h. Hemispheric volume atrophy (P14) and neurobehavioral tests including righting reflex (P8-P10), small open field (P13-P14), and negative geotaxis (P14) were determined. Hemispheric volume atrophy in males was reduced (P ​< ​0.05) by 41.9% in the normothermic-IAIP and 28.1% in the hypothermic-IAIP compared with the normothermic-PL group, and in females reduced (P ​< ​0.05) by 30.3% in the normothermic-IAIP, 45.7% in hypothermic-PL, and 55.2% in hypothermic-IAIP compared with the normothermic-PL group after HI. Hypothermia improved (P ​< ​0.05) the neuroprotective effects of hIAIPs in females. The neuroprotective efficacy of hIAIPs was comparable to hypothermia in female rats (P ​= ​0.183). Treatment with hIAIPs, hypothermia, and hIAIPs with hypothermia decreased (P ​< ​0.05) the latency to enter the peripheral zone in the small open field test in males. We conclude that hIAIPs provide neuroprotection from HI brain injury that is comparable to the protection by hypothermia, hypothermia increases the effects of hIAIPs in females, and hIAIPs and hypothermia exhibit some sex-related differential effects.

[The plasma protein HRG is an important factor for preventing sepsis and maintaining homeostatic response]

Acute phase proteins such as CRP, amyloid protein A, and α1-antitrypsin are produced in the liver and their plasma levels are increased during the acute inflammatory response. In contrast, there are plasma proteins whose dynamics are opposite to acute phase proteins. This group includes histidine-rich glycoprotein (HRG), inter-α-inhibitor proteins, albumin, and transthyretin. HRG binds to a variety of factors and regulates the fundamental processes; the blood coagulation, the clearance of apoptotic cells, and tumor growth. In the present review, we focus on the anti-septic effects of HRG in mice model, the actions of HRG on human blood cells/vascular endothelial cells, and the identification of a novel receptor CLEC1A for HRG, based on our recent findings. HRG appears to maintain the quiescence of neutrophils; a round shape, the low levels of spontaneous release of ROS, the ease passage through artificial microcapillaries, and prevention of adhesion to vascular endothelial cells. HRG also inhibited activation of vascular endothelial cells; the suppression of adhesion molecules and the inhibition of HMGB1 mobilization and cytokine secretion. It was shown that plasma HRG level was an excellent biomarker of septic patients in ICU for the evaluation of severity and prognosis. So far little attention has been paid to HRG in terms of a functional role in sepsis and ARDS, however, it is strongly suggested that HRG may be an important plasma factor that prevents a progress in the septic cascade and maintains the homeostasis of blood cells and vascular endothelial cells.

Inter-alpha inhibitor proteins attenuate lipopolysaccharide-induced blood-brain barrier disruption in neonatal mice

There is a paucity of information regarding efficacious pharmacological neuroprotective strategies to attenuate or reduce brain injury in neonates. Lipopolysaccharide (LPS) disrupts blood-brain barrier (BBB) function in adult rodents and increases inflammation in adults and neonates. Human blood-derived Inter-alpha Inhibitor Proteins (IAIPs) are neuroprotective, improve neonatal survival after LPS, and attenuate LPS-induced disruption of the BBB in adult male mice. We hypothesized that LPS also disrupts the function of the BBB in neonatal mice and that IAIPs attenuate the LPS-induced BBB disruption in male and female neonatal mice. IAIPs were administered to neonatal mice after LPS and BBB permeability quantified with intravenous 14C-sucrose and 99mTc-albumin. Although repeated high doses (3 mg/kg) of LPS in neonates resulted in high mortality rates and a robust increase in BBB permeability, repeated lower doses (1 mg/kg) of LPS resulted in lower mortality rates and disruption of the BBB in both male and female neonates. IAIP treatment attenuated disruption of the BBB similarly to sucrose and albumin after exposure to low-dose LPS in neonatal mice. Exposure to low-dose LPS elevated IAIP concentrations in blood, but it did not appear to increase the systemic levels of Pre-alpha inhibitor (PaI), one of the family members of the IAIPs that contains heavy chain 3. We conclude that IAIPs attenuate LPS-related disruption of the BBB in both male and female neonatal mice.

GZMKhigh CD8+ T effector memory cells are associated with CD15high neutrophil abundance in non-metastatic colorectal tumors and predict poor clinical outcome

CD8⁺ T cells are a major prognostic determinant in solid tumors, including colorectal cancer (CRC). However, understanding how the interplay between different immune cells impacts on clinical outcome is still in its infancy. Here, we describe that the interaction of tumor infiltrating neutrophils expressing high levels of CD15 with CD8⁺ T effector memory cells (T_EM) correlates with tumor progression. Mechanistically, stromal cell-derived factor-1 (CXCL12/SDF-1) promotes the retention of neutrophils within tumors, increasing the crosstalk with CD8⁺ T cells. As a consequence of the contact-mediated interaction with neutrophils, CD8⁺ T cells are skewed to produce high levels of GZMK, which in turn decreases E-cadherin on the intestinal epithelium and favors tumor progression. Overall, our results highlight the emergence of GZMK^high CD8⁺ T_EM in non-metastatic CRC tumors as a hallmark driven by the interaction with neutrophils, which could implement current patient stratification and be targeted by novel therapeutics.

Novel aspects of sepsis pathophysiology: NETs, plasma glycoproteins, endotheliopathy and COVID-19

In 2016, sepsis was newly defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Sepsis remains one of the crucial medical problems to be solved worldwide. Although the world health organization has made sepsis a global health priority, there remain no specific and effective therapy for sepsis so far. Indeed, over the previous decades almost all attempts to develop novel drugs have failed. This may be partly ascribable to the multifactorial complexity of the septic cascade and the resultant difficulties of identifying drug targets. In addition, there might still be missing links among dysregulated host responses in vital organs. In this review article, recent advances in understanding of the complex pathophysiology of sepsis are summarized, with a focus on neutrophil extracellular traps (NETs), the significant role of NETs in thrombosis/embolism, and the functional roles of plasma proteins, histidine-rich glycoprotein (HRG) and inter-alpha-inhibitor proteins (IAIPs). The specific plasma proteins that are markedly decreased in the acute phase of sepsis may play important roles in the regulation of blood cells, vascular endothelial cells and coagulation. The accumulating evidence may provide us with insights into a novel aspect of the pathophysiology of sepsis and septic ARDS, including that in COVID-19.

Exogenous inter-α inhibitor proteins prevent cell death and improve ischemic stroke outcomes in mice

Inter-α inhibitor proteins (IAIPs) are a family of endogenous plasma and extracellular matrix molecules. IAIPs suppress proinflammatory cytokines, limit excess complement activation, and bind extracellular histones to form IAIP-histone complexes, leading to neutralization of histone-associated cytotoxicity in models of sepsis. Many of these detrimental processes also play critical roles in the pathophysiology of ischemic stroke. In this study, we first assessed the clinical relevance of IAIPs in stroke and then tested the therapeutic efficacy of exogenous IAIPs in several experimental stroke models. IAIP levels were reduced in both ischemic stroke patients and in mice subjected to experimental ischemic stroke when compared with controls. Post-stroke administration of IAIP significantly improved stroke outcomes across multiple stroke models, even when given 6 hours after stroke onset. Importantly, the beneficial effects of delayed IAIP treatment were observed in both young and aged mice. Using targeted gene expression analysis, we identified a receptor for complement activation, C5aR1, that was highly suppressed in both the blood and brain of IAIP-treated animals. Subsequent experiments using C5aR1-knockout mice demonstrated that the beneficial effects of IAIPs are mediated in part by C5aR1. These results indicate that IAIP is a potential therapeutic candidate for the treatment of ischemic stroke.

High-mobility group box-1 and inter-alpha inhibitor proteins: In vitro binding and co-localization in cerebral cortex after hypoxic-ischemic injury

The high-mobility group box-1 (HMGB1) protein is a transcription-regulating protein located in the nucleus. However, it serves as a damage-associated molecular pattern protein that activates immune cells and stimulates inflammatory cytokines to accentuate neuroinflammation after release from damaged cells. In contrast, Inter-alpha Inhibitor Proteins (IAIPs) are proteins with immunomodulatory effects including inhibition of pro-inflammatory cytokines. We have demonstrated that IAIPs exhibit neuroprotective properties in neonatal rats exposed to hypoxic-ischemic (HI) brain injury. In addition, previous studies have suggested that the light chain of IAIPs, bikunin, may exert its anti-inflammatory effects by inhibiting HMGB1 in a variety of different injury models in adult subjects. The objectives of the current study were to confirm whether HMGB1 is a target of IAIPs by investigating the potential binding characteristics of HMGB1 and IAIPs in vitro, and co-localization in vivo in cerebral cortices after exposure to HI injury. Solid-phase binding assays and surface plasmon resonance (SPR) were used to determine the physical binding characteristics between IAIPs and HMGB1. Cellular localizations of IAIPs-HMGB1 in neonatal rat cortex were visualized by double labeling with anti-IAIPs and anti-HMGB1 antibodies. Solid-phase binding and SPR demonstrated specific binding between IAIPs and HMGB1 in vitro. Cortical cytoplasmic and nuclear co-localization of IAIPs and HMGB1 were detected by immunofluorescent staining in control and rats immediately and 3 hours after HI. In conclusion, HMGB1 and IAIPs exhibit direct binding in vitro and co-localization in vivo in neonatal rats exposed to HI brain injury suggesting HMGB1 could be a target of IAIPs.

Citrullinated inter-alpha-trypsin inhibitor heavy chain 4 in arthritic joints and its potential effect in the neutrophil migration

The citrullinated inter-alpha-trypsin inhibitor heavy chain 4 (cit-ITIH4) was identified as its blood level was associated with the arthritis score in peptide glucose-6-phosphate-isomerase-induced arthritis (pGIA) mice and the disease activity in patients with rheumatoid arthritis (RA). This study aimed to clarify its citrullination pathway and function as related to neutrophils. In pGIA-afflicted joints, ITIH4 and cit-ITIH4 levels were examined by immunohistochemistry (IHC), immunoprecipitation (IP) and Western blotting (WB), while peptidylarginine deiminase (PAD) expression was measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), IHC and immunofluorescent methods. The pGIA mice received anti-lymphocyte antigen 6 complex locus G6D (Ly6G) antibodies to deplete neutrophils and the expression of cit-ITIH4 was investigated by WB. The amounts of ITIH4 and cit-ITIH4 in synovial fluid (SF) from RA and osteoarthritis (OA) patients were examined by I.P. and W.B. Recombinant ITIH4 and cit-ITIH4 were incubated with sera from healthy volunteers before its chemotactic ability and C5a level were evaluated using Boyden's chamber assay and enzyme-linked immunosorbent assay (ELISA). During peak arthritic phase, ITIH4 and cit-ITIH4 were increased in joints while PAD4 was over-expressed, especially in the infiltrating neutrophils of pGIA mice. Levels of cit-ITIH4 in plasma and joints significantly decreased upon neutrophil depletion. ITIH4 was specifically citrullinated in SF from RA patients compared with OA patients. Native ITIH4 inhibited neutrophilic migration and decreased C5a levels, while cit-ITIH4 increased its migration and C5a levels significantly. Cit-ITIH4 is generated mainly in inflamed joints by neutrophils via PAD4. Citrullination of ITIH4 may change its function to up-regulate neutrophilic migration by activating the complement cascade, exacerbating arthritis.

Histidine-Rich Glycoprotein Stimulates Human Neutrophil Phagocytosis and Prolongs Survival through CLEC1A

Histidine-rich glycoprotein (HRG) is a multifunctional plasma protein and maintains the homeostasis of blood cells and vascular endothelial cells. In the current study, we demonstrate that HRG and recombinant HRG concentration dependently induced the phagocytic activity of isolated human neutrophils against fluorescence-labeled Escherichia coli and Staphylococcus aureus through the stimulation of CLEC1A receptors, maintaining their spherical round shape. The phagocytosis-inducing effects of HRG were inhibited by a specific anti-HRG Ab and enhanced by opsonization of bacteria with diluted serum. HRG and C5a prolonged the survival time of isolated human neutrophils, in association with a reduction in the spontaneous production of extracellular ROS. In contrast, HRG maintained the responsiveness of neutrophils to TNF-α, zymosan, and E. coli with regard to reactive oxygen species production. The blocking Ab for CLEC1A and recombinant CLEC1A-Fc fusion protein significantly inhibited the HRG-induced neutrophil rounding, phagocytic activity, and prolongation of survival time, suggesting the involvement of the CLEC1A receptor in the action of HRG on human neutrophils. These results as a whole indicated that HRG facilitated the clearance of E. coli and S. aureus by maintaining the neutrophil morphology and phagocytosis, contributing to the antiseptic effects of HRG in vivo.

Bioactive proteins in bovine colostrum and effects of heating, drying and irradiation

Bovine colostrum (BC) contains bioactive proteins, such as immunoglobulin G (IgG), lactoferrin (LF) and lactoperoxidase (LP). BC was subjected to low-temperature, long-time pasteurization (LTLT, 63 °C, 30 min) or high-temperature, short-time pasteurization (HTST, 72 °C, 15 s) and spray-drying (SD), with or without γ-irradiation (GI, ∼14 kGy) to remove microbial contamination. Relative to unpasteurized liquid BC, SD plus GI increased protein denaturation by 6 and 11%, respectively, increasing to 19 and 27% after LTLT and to 48% after HTST, with no further effects after GI (all P < 0.05). LTLT, without or with GI, resulted in 15 or 29% denaturation of IgG, compared with non-pasteurized BC, and 34 or 58% for HTST treatment (all P < 0.05, except LTLT without GI). For IgG, only GI, not SD or LTLT, increased denaturation (30-38%, P < 0.05) but HTST increased denaturation to 40%, with further increases after GI (60%, P < 0.05). LTLT and HTST reduced LP levels (56 and 81% respectively) and LTLT reduced LF levels (21%), especially together with GI (47%, P < 0.05). Denaturation of BSA, β-LgA, β-LgB and α-La were similar to IgG. Methionine, a protective amino acid against free oxygen radicals, was oxidised by LTLT + GI (P < 0.05) while LTLT and HTST had no effect. Many anti-inflammatory proteins, including serpin anti-proteinases were highly sensitive to HTST and GI but preserved after LTLT pasteurization. LTLT, followed by SD is an optimal processing technique preserving bioactive proteins when powdered BC is used as a diet supplement for sensitive patients.

Novel Neuroprotective Agents to Treat Neonatal Hypoxic-Ischemic Encephalopathy: Inter-Alpha Inhibitor Proteins

Perinatal hypoxia-ischemia (HI) is a major cause of brain injury and mortality in neonates. Hypoxic-ischemic encephalopathy (HIE) predisposes infants to long-term cognitive deficits that influence their quality of life and place a large burden on society. The only approved treatment to protect the brain after HI is therapeutic hypothermia, which has limited effectiveness, a narrow therapeutic time window, and is not considered safe for treatment of premature infants. Alternative or adjunctive therapies are needed to improve outcomes of full-term and premature infants after exposure to HI. Inter-alpha inhibitor proteins (IAIPs) are immunomodulatory molecules that are proposed to limit the progression of neonatal inflammatory conditions, such as sepsis. Inflammation exacerbates neonatal HIE and suggests that IAIPs could attenuate HI-related brain injury and improve cognitive outcomes associated with HIE. Recent studies have shown that intraperitoneal treatment with IAIPs can decrease neuronal and non-neuronal cell death, attenuate glial responses and leukocyte invasion, and provide long-term behavioral benefits in neonatal rat models of HI-related brain injury. The present review summarizes these findings and outlines the remaining experimental analyses necessary to determine the clinical applicability of this promising neuroprotective treatment for neonatal HI-related brain injury.

Effects of inter-alpha inhibitor proteins on brain injury after exposure of neonatal rats to severe hypoxia-ischemia

Hypoxic-ischemic (HI) brain injury is one of the most common neurological problems occurring in premature and full-term infants after perinatal complications. Hypothermia is the only treatment approved for HI encephalopathy in newborns. However, this treatment is only partially protective, cannot be used to treat premature infants, and has limited efficacy to treat severe HI encephalopathy. Inflammation contributes to the evolution of HI brain injury in neonates. Inter-alpha Inhibitor Proteins (IAIPs) are immunomodulatory proteins that have neuroprotective properties after exposure to moderate HI in neonatal rats. The objective of the current study was to determine the neuroprotective efficacy of treatment with IAIPs starting immediately after or with a delay of one hour after exposure to severe HI of 120 min duration. One hundred and forty-six 7-day-old rat pups were randomized to sham control, HI and immediate treatment with IAIPs (60 mg/kg) or placebo (PL), and sham, HI and delayed treatment with IAIPs or PL. IAIPs or PL were given at zero, 24, and 48 h after HI or 1, 24 and 48 h after HI. Total brain infarct volume was determined 72 h after exposure to HI. Treatment with IAIPs immediately after HI decreased (P < 0.05) infarct volumes by 58.0% and 44.5% in male and female neonatal rats, respectively. Delayed treatment with IAIPs after HI decreased (P < 0.05) infarct volumes by 23.7% in male, but not in female rats. We conclude that IAIPs exert neuroprotective effects even after exposure to severe HI in neonatal rats and appear to exhibit some sex-related differential effects.

The Inter-α-Trypsin Inhibitor Family: Versatile Molecules in Biology and Pathology

Inter-α-trypsin inhibitor (IαI) family members are ancient and unique molecules that have evolved over several hundred million years of vertebrate evolution. IαI is a complex containing the proteoglycan bikunin to which heavy chain proteins are covalently attached to the chondroitin sulfate chain. Besides its matrix protective activity through protease inhibitory action, IαI family members interact with extracellular matrix molecules and most notably hyaluronan, inhibit complement, and provide cell regulatory functions. Recent evidence for the diverse roles of the IαI family in both biology and pathology is reviewed and gives insight into their pivotal roles in tissue homeostasis. In addition, the clinical uses of these molecules are explored, such as in the treatment of inflammatory conditions including sepsis and Kawasaki disease, which has recently been associated with severe acute respiratory syndrome coronavirus 2 infection in children.

Significant Remodeling Affects the Circulating Glycosaminoglycan Profile in Adult Patients with both Severe and Mild Forms of Acute Pancreatitis

Acute pancreatitis (AP) manifests itself either as a mild, self-limiting inflammation or a severe, systemic inflammatory process that is associated with various complications and a high mortality rate. It is unknown whether these two forms of the disease can differ in the profile of circulating glycosaminoglycans, which are molecules with huge biological reactivity due to a high density of negative electric charge. Plasma glycosaminoglycans were characterized/quantified in 23 healthy controls, 32 patients with mild AP, and 15 individuals with severe disease using electrophoresis with enzymatic identification (chondroitin sulfate and heparan sulfate) or an ELISA-based test (hyaluronan). Moreover, the correlations between the glycosaminoglycan levels and clinical parameters were evaluated. Both forms of AP showed similar remodeling of the plasma profile of the sulfated glycosaminoglycans. In contrast, only in the patients with mild AP was the level of circulating hyaluronan significantly decreased as compared to the healthy controls. Both forms of AP are associated with systemic changes in the metabolism of glycosaminoglycans. However, the alterations in hyaluronan metabolism may contribute to the disease evolution. The circulating hyaluronan may have some clinical value to predict the severity of AP and to evaluate the clinical status of patients with severe AP.

Inter-alpha inhibitor proteins attenuate lipopolysaccharide-induced blood-brain barrier disruption and downregulate circulating interleukin 6 in mice

Circulating levels of inter-alpha inhibitor proteins change dramatically in acute inflammatory disorders, which suggest an important contribution to the immunomodulatory system. Human blood-derived inter-alpha inhibitor proteins are neuroprotective and improve survival of neonatal mice exposed to lipopolysaccharide. Lipopolysaccharide augments inflammatory conditions and disrupts the blood-brain barrier. There is a paucity of therapeutic strategies to treat blood-brain barrier dysfunction, and the neuroprotective effects of human blood-derived inter-alpha inhibitor proteins are not fully understood. To examine the therapeutic potential of inter-alpha inhibitor proteins, we administered human blood-derived inter-alpha inhibitor proteins to male and female CD-1 mice after lipopolysaccharide exposure and quantified blood-brain barrier permeability of intravenously injected ¹⁴C-sucrose and ^99mTc-albumin. We hypothesized that human blood-derived inter-alpha inhibitor protein treatment would attenuate lipopolysaccharide-induced blood-brain barrier disruption and associated inflammation. Lipopolysaccharide increased blood-brain barrier permeability to both ¹⁴C-sucrose and ^99mTc-albumin, but human blood-derived inter-alpha inhibitor protein treatment only attenuated increases in ¹⁴C-sucrose blood-brain barrier permeability in male mice. Lipopolysaccharide stimulated a more robust elevation of male serum inter-alpha inhibitor protein concentration compared to the elevation measured in female serum. Lipopolysaccharide administration also increased multiple inflammatory factors in serum and brain tissue, including interleukin 6. Human blood-derived inter-alpha inhibitor protein treatment downregulated serum interleukin 6 levels, which were inversely correlated with serum inter-alpha inhibitor protein concentration. We conclude that inter-alpha inhibitor proteins may be neuroprotective through mechanisms of blood-brain barrier disruption associated with systemic inflammation.

Inter-α-inhibitor heavy chain-1 has an integrin-like 3D structure mediating immune regulatory activities and matrix stabilization during ovulation

Inter-α-inhibitor is a proteoglycan essential for mammalian reproduction and also plays a less well-characterized role in inflammation. It comprises two homologous "heavy chains" (HC1 and HC2) covalently attached to chondroitin sulfate on the bikunin core protein. Before ovulation, HCs are transferred onto the polysaccharide hyaluronan (HA) to form covalent HC·HA complexes, thereby stabilizing an extracellular matrix around the oocyte required for fertilization. Additionally, such complexes form during inflammatory processes and mediate leukocyte adhesion in the synovial fluids of arthritis patients and protect against sepsis. Here using X-ray crystallography, we show that human HC1 has a structure similar to integrin β-chains, with a von Willebrand factor A domain containing a functional metal ion-dependent adhesion site (MIDAS) and an associated hybrid domain. A comparison of the WT protein and a variant with an impaired MIDAS (but otherwise structurally identical) by small-angle X-ray scattering and analytical ultracentrifugation revealed that HC1 self-associates in a cation-dependent manner, providing a mechanism for HC·HA cross-linking and matrix stabilization. Surprisingly, unlike integrins, HC1 interacted with RGD-containing ligands, such as fibronectin, vitronectin, and the latency-associated peptides of transforming growth factor β, in a MIDAS/cation-independent manner. However, HC1 utilizes its MIDAS motif to bind to and inhibit the cleavage of complement C3, and small-angle X-ray scattering-based modeling indicates that this occurs through the inhibition of the alternative pathway C3 convertase. These findings provide detailed structural and functional insights into HC1 as a regulator of innate immunity and further elucidate the role of HC·HA complexes in inflammation and ovulation.

Protein Deimination and Extracellular Vesicle Profiles in Antarctic Seabirds

Pelagic seabirds are amongst the most threatened of all avian groups. They face a range of immunological challenges which seem destined to increase due to environmental changes in their breeding and foraging habitats, affecting prey resources and exposure to pollution and pathogens. Therefore, the identification of biomarkers for the assessment of their health status is of considerable importance. Peptidylarginine deiminases (PADs) post-translationally convert arginine into citrulline in target proteins in an irreversible manner. PAD-mediated deimination can cause structural and functional changes in target proteins, allowing for protein moonlighting in physiological and pathophysiological processes. PADs furthermore contribute to the release of extracellular vesicles (EVs), which play important roles in cellular communication. In the present study, post-translationally deiminated protein and EV profiles of plasma were assessed in eight seabird species from the Antarctic, representing two avian orders: Procellariiformes (albatrosses and petrels) and Charadriiformes (waders, auks, gulls and skuas). We report some differences between the species assessed, with the narrowest EV profiles of 50-200 nm in the northern giant petrel Macronectes halli, and the highest abundance of larger 250-500 nm EVs in the brown skua Stercorarius antarcticus. The seabird EVs were positive for phylogenetically conserved EV markers and showed characteristic EV morphology. Post-translational deimination was identified in a range of key plasma proteins critical for immune response and metabolic pathways in three of the bird species under study; the wandering albatross Diomedea exulans, south polar skua Stercorarius maccormicki and northern giant petrel. Some differences in Gene Ontology (GO) biological and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways for deiminated proteins were observed between these three species. This indicates that target proteins for deimination may differ, potentially contributing to a range of physiological functions relating to metabolism and immune response, as well as to key defence mechanisms. PAD protein homologues were identified in the seabird plasma by Western blotting via cross-reaction with human PAD antibodies, at an expected 75 kDa size. This is the first study to profile EVs and to identify deiminated proteins as putative novel plasma biomarkers in Antarctic seabirds. These biomarkers may be further refined to become useful indicators of physiological and immunological status in seabirds-many of which are globally threatened.

Inter-alpha Inhibitor Proteins Modulate Neuroinflammatory Biomarkers After Hypoxia-Ischemia in Neonatal Rats

Neuroinflammation contributes to hypoxic-ischemic (HI) brain injury. Inter-alpha inhibitor proteins (IAIPs) have important immunomodulatory properties. Human (h) plasma-derived IAIPs reduce brain injury and improve neurobehavioral outcomes after HI. However, the effects of hIAIPs on neuroinflammatory biomarkers after HI have not been examined. We determined whether hIAIPs attenuated HI-related neuroinflammation. Postnatal day-7 rats exposed to sham-placebo, or right carotid ligation and 8% oxygen for 90 minutes with placebo, and hIAIP treatment were studied. hIAIPs (30 mg/kg) or PL was injected intraperitoneally immediately, 24, and 48 hours after HI. Rat complete blood counts and sex were determined. Brain tissue and peripheral blood were prepared for analysis 72 hours after HI. The effects of hIAIPs on HI-induced neuroinflammation were quantified by image analysis of positively stained astrocytic (glial fibrillary acid protein [GFAP]), microglial (ionized calcium binding adaptor molecule-1 [Iba-1]), neutrophilic (myeloperoxidase [MPO]), matrix metalloproteinase-9 (MMP9), and MMP9-MPO cellular markers in brain regions. hIAIPs reduced quantities of cortical GFAP, hippocampal Iba-1-positive microglia, corpus callosum MPO, and cortical MMP9-MPO cells and the percent of neutrophils in peripheral blood after HI in male, but not female rats. hIAIPs modulate neuroinflammatory biomarkers in the neonatal brain after HI and may exhibit sex-related differential effects.

Intravascular heavy chain-modification of hyaluronan during endotoxic shock

During inflammation, the covalent linking of the ubiquitous extracellular polysaccharide hyaluronan (HA) with the heavy chains (HC) of the serum protein inter alpha inhibitor (IαI) is exclusively mediated by the enzyme tumor necrosis factor α (TNFα)-stimulated-gene-6 (TSG-6). While significant advances have been made regarding how HC-modified HA (HC-HA) is an important regulator of inflammation, it remains unclear why HC-HA plays a critical role in promoting survival in intraperitoneal lipopolysaccharide (LPS)-induced endotoxemia while exerting only a modest role in the outcomes following intratracheal exposure to LPS. To address this gap, the two models of intraperitoneal LPS-induced endotoxic shock and intratracheal LPS-induced acute lung injury were directly compared in TSG-6 knockout mice and littermate controls. HC-HA formation, endogenous TSG-6 activity, and inflammatory markers were assessed in plasma and lung tissue. TSG-6 knockout mice exhibited accelerated mortality during endotoxic shock. While both intraperitoneal and intratracheal LPS induced HC-HA formation in lung parenchyma, only systemically-induced endotoxemia increased plasma TSG-6 levels and intravascular HC-HA formation. Cultured human lung microvascular endothelial cells secreted TSG-6 in response to both TNFα and IL1β stimulation, indicating that, in addition to inflammatory cells, the endothelium may secrete TSG-6 into circulation during systemic inflammation. These data show for the first time that LPS-induced systemic inflammation is uniquely characterized by significant vascular induction of TSG-6 and HC-HA, which may contribute to improved outcomes of endotoxemia.

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HC-HA deficiency accelerated mortality after IP LPS, but only modestly affected IT LPS outcomes.

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Both intratracheal (IT) and intraperitoneal (IP) LPS triggered lung HC-HA formation.

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IP LPS, but not IT LPS instillation induced intravascular TSG-6 and HC-HA.

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Intravascular HC-HA formation may be protective against LPS-induced injury.