G-CSF induces membrane expression of a myeloperoxidase glycovariant that operates as an E-selectin ligand on human myeloid cells

Hyper-truncated Asn355- and Asn391-glycans modulate the activity of neutrophil granule myeloperoxidase

Myeloperoxidase (MPO) plays essential roles in neutrophil-mediated immunity via the generation of reactive oxidation products. Complex carbohydrates decorate MPO at discrete sites, but their functional relevance remains elusive. To this end, we have characterised the structure-biosynthesis-activity relationship of neutrophil MPO (nMPO). Mass spectrometry demonstrated that nMPO carries both characteristic under-processed and hyper-truncated glycans. Occlusion of the Asn355/Asn391-glycosylation sites and the Asn323-/Asn483-glycans, located in the MPO dimerisation zone, was found to affect the local glycan processing, thereby providing a molecular basis of the site-specific nMPO glycosylation. Native mass spectrometry, mass photometry and glycopeptide profiling revealed significant molecular complexity of diprotomeric nMPO arising from heterogeneous glycosylation, oxidation, chlorination and polypeptide truncation variants and a previously unreported low-abundance monoprotomer. Longitudinal profiling of maturing, mature, granule-separated and pathogen-stimulated neutrophils demonstrated that nMPO is dynamically expressed during granulopoiesis, unevenly distributed across granules and degranulated upon activation. We also show that proMPO-to-MPO maturation occurs during early/mid-stage granulopoiesis. While similar global MPO glycosylation was observed across conditions, the conserved Asn355-/Asn391-sites displayed elevated glycan hyper-truncation, which correlated with higher enzyme activities of MPO in distinct granule populations. Enzymatic trimming of the Asn355-/Asn391-glycans recapitulated the activity gain and showed that nMPO carrying hyper-truncated glycans at these positions exhibits increased thermal stability, polypeptide accessibility and ceruloplasmin-mediated inhibition potential relative to native nMPO. Finally, molecular modelling revealed that hyper-truncated Asn355-glycans positioned in the MPO-ceruloplasmin interface are critical for uninterrupted inhibition. Here, through an innovative and comprehensive approach, we report novel functional roles of MPO glycans, providing new insight into neutrophil-mediated immunity.

Case report: characterization of a persistent, treatment-resistant, novel Staphylococcus aureus infection causing chronic mastitis in a Holstein dairy cow

Background

Mastitis is the most common health concern plaguing the modern dairy cow and costs dairy producers estimates of two billion dollars annually. Staphylococcus aureus infections are prevalent, displaying varied disease presentation and markedly low cure rates. Neutrophils are considered the first line of defense against mastitis causing bacteria and are frequently targeted in the development of treatment and prevention technologies. We describe a case of naturally occurring, chronic mastitis in a Holstein cow (1428), caused by a novel strain of S. aureus that was not able to be cleared by antibiotic treatment.

Case presentation

The infection was identified in a single quarter, 2 months into the cow’s first lactation. The infection persisted for the following 20 months, including through dry off, and a second calving and lactation. This case of mastitis was associated with a consistently high somatic cell count, however presented with no other clinical signs. This cow was unsuccessfully treated with antibiotics commonly used to treat mastitis, consisting of two rounds of treatment during lactation and an additional round at the beginning of dry off. The chronic infection was also unchanged through an experimental mid-lactation treatment with pegylated granulocyte-colony stimulating factor (PEG-gCSF) and an additional periparturient treatment with PEG-gCSF. We isolated milk neutrophils from 1428 and compared them to two cows challenged with experimental S. aureus, strain Newbould 305. Neutrophils from 1428’s milk had higher surface expression of myeloperoxidase compared to experimental Newbould challenged animals, as well as increased presence of Neutrophil Extracellular Traps. This suggests a heightened activation state of neutrophils sourced from 1428’s naturally occurring infection. Upon postmortem examination, the affected quarter revealed multifocal abscesses separated by fibrous connective tissues. Abscesses were most common in the gland cistern and collecting duct region. Microscopically, the inflammatory reaction was pyogranulomatous to granulomatous and consistent with botryomycosis. Colonies of Gram-positive cocci were found within the eosinophilic matrix of the Splendore-Hoeppli reaction within granulomas and intracellularly within the acinar epithelium.

Conclusions

Collectively, we describe a unique case of chronic mastitis, the characterization of which provides valuable insight into the mechanics of S. aureus treatment resistance and immune escape.

Shuxuening injection facilitates neurofunctional recovery via down-regulation of G-CSF-mediated granulocyte adhesion and diapedesis pathway in a subacute stroke mouse model

Post-stroke neural damage is a serious health concern which does not yet have an effective treatment. We have shown previously that Shuxuening injection (SXNI), a Ginkgo biloba extract-based natural medicine, protects brain after an acute ischemic stroke, but its efficacy for post-stroke recovery is not known. This study was to investigate whether SXNI can improve the prognosis of stroke at a subacute phase. Mice with cerebral ischemia-reperfusion injury (CIRI) were established by middle cerebral artery occlusion (MCAO), and drugs or saline were injected by the tail vein every 12 h after reperfusion. The therapeutic effect of SXNI was evaluated by survival rate, modified neurologic severity scores (mNSS), open-field test, locomotive gait patterns, cerebral infarction volume, brain edema and histopathological changes. Subsequently, a combined method of RNA-seq and Ingenuity® Pathway Analysis (IPA) was performed to identify key targets and pathways of SXNI facilitating the prognosis of stroke in mouse brain. The results of the transcriptome analysis were verified by real time reverse transcription-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), western blot (WB) and immunohistochemistry (IHC). The experimental results showed that in the new subacute stroke model, SXNI markedly improves the survival rate, neurological and motor functions and histopathological changes, and significantly reduces cerebral infarction and edema volume. RNA-seq analysis of subacute stroke mice with or without SXNI (3 mL/kg) indicated 963 differentially expressed genes (DEGs) with a fold change ≥ 1.5 and a P-value ≤ 0.01. IPA analysis of DEGs showed that granulocyte adhesion and diapedesis ranked first in the pathway ranking, and the most critical gene regulated by SXNI was G-csf. Simultaneously, RT-PCR, ELISA, WB and IHC results demonstrated that SXNI not only obviously reduced the mRNA expression levels of key genes G-csf, Sele and Mac-1 in this pathway, but also significantly decreased the protein expression levels of G-CSF in serum and E-selectin and MAC-1 in brain tissues. In summary, our research suggested that SXNI can exert a remarkable neurofunctional therapeutic effect on stroke mice via down-regulating G-CSF to inhibit granulocyte adhesion and diapedesis. This study provides experimental evidence that SXNI may fulfill the need for stroke medicine targeting specifically at the recovery stage.

Differential phenotype of immune cells in blood and milk following pegylated granulocyte colony-stimulating factor therapy during a chronic Staphylococcus aureus infection in lactating Holsteins

Neutrophils are principal host innate immune cell responders to mastitis infections. Thus, therapies have been developed that target neutrophil expansion. This includes the neutrophil-stimulating cytokine granulocyte colony-stimulating factor (gCSF). Pegylated gCSF (PEG-gCSF; Imrestor, Elanco Animal Health, Greenfield, IN) has been shown to reduce the natural incidence of mastitis in periparturient cows in commercial settings and reduce severity of disease against experimental mastitis challenge. Pegylated gCSF stimulates neutrophil expansion but also induces changes in monocyte and lymphocyte circulating numbers, surface protein expression changes, or both. We hypothesized that PEG-gCSF modulates surface expression of monocytes and neutrophils and facilitates their migration to the mammary gland. We challenged 8 mid-lactation Holsteins with approximately 150 cfu of Staphylococcus aureus (Newbould 305) in a single quarter via intramammary infusion. All animals developed chronic infections as assessed by bacteria counts and somatic cell counts (SCC). Ten to 16 wk postchallenge, 4 of the animals were treated with 2 subcutaneous injections of PEG-gCSF 7 d apart. Complete blood counts, SCC, bacterial counts, milk yield, feed intake, neutrophils extracellular trap analysis, and flow cytometric analyses of milk and blood samples were performed at indicated time points for 14 d after the first PEG-gCSF injection. The PEG-gCSF-treated cows had significantly increased numbers of blood neutrophils and lymphocytes compared with control cows. Flow cytometric analyses revealed increased surface expression of myeloperoxidase (MPO) on neutrophils and macrophages in milk but not in blood of treated cows. Neutrophils isolated from blood of PEG-gCSF-treated cows had decreased surface expression of CD62L (L-selectin) in blood, consistent with cell activation. Surprisingly, CD62L cell surface expression was increased on neutrophils and macrophages sourced from milk from treated animals compared with cells isolated from controls. The PEG-gCSF-treated cows did not clear the S. aureus infection, nor did they significantly differ in SCC from controls. These findings provide evidence that PEG-gCSF therapy modifies cell surface expression of neutrophils and monocytes. However, although surface MPO⁺ cells accumulate in the mammary gland, the lack of bacterial control from these milk-derived cells suggests an incomplete role for PEG-gCSF treatment against chronic S. aureus infection and possibly chronic mammary infections in general.

Targeting Myeloperoxidase Disrupts Mitochondrial Redox Balance and Overcomes Cytarabine Resistance in Human Acute Myeloid Leukemia

Chemotherapies alter cellular redox balance and reactive oxygen species (ROS) content. Recent studies have reported that chemoresistant cells have an increased oxidative state in hematologic malignancies. In this study, we demonstrated that chemoresistant acute myeloid leukemia (AML) cells had a lower level of mitochondrial and cytosolic ROS in response to cytarabine (AraC) and overexpressed myeloperoxidase (MPO), a heme protein that converts hydrogen peroxide to hypochlorous acid (HOCl), compared with sensitive AML cells. High MPO-expressing AML cells were less sensitive to AraC in vitro and in vivo. They also produced higher levels of HOCl and exhibited an increased rate of mitochondrial oxygen consumption when compared with low MPO-expressing AML cells. Targeting MPO expression or enzyme activity sensitized AML cells to AraC treatment by triggering oxidative damage and sustaining oxidative stress, particularly in high MPO-expressing AML cells. This sensitization stemmed from mitochondrial superoxide accumulation, which impaired oxidative phosphorylation and cellular energetic balance, driving apoptotic death and selective eradication of chemoresistant AML cells in vitro and in vivo. Altogether, this study uncovers a noncanonical function of MPO enzyme in maintaining redox balance and mitochondrial energetic metabolism, therefore affecting downstream pathways involved in AML chemoresistance. SIGNIFICANCE: These findings demonstrate the role of myeloperoxidase in the regulation of ROS levels and sensitivity of AML cells to cytarabine, an essential chemotherapeutic backbone in the therapy of AML.

Surface Engineering of Pancreatic Islets with a Heparinized StarPEG Nanocoating

Cell surface engineering can protect implanted cells from host immune attack. It can also reshape cellular landscape to improve graft function and survival post-transplantation. This protocol aims to achieve surface engineering of pancreatic islets using an ultrathin heparin-incorporated starPEG (Hep-PEG) nanocoating. To generate the Hep-PEG nanocoating for pancreatic islet surface engineering, heparin succinimidyl succinate (Heparin-NHS) was first synthesized by modification of its carboxylate groups using N-(3-dimethylamino propyl)-N'-ethyl carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). The Hep-PEG mixture was then formed by crosslinking of the amino end-functionalized eight-armed starPEG (starPEG-(NH2)8) and Heparin-NHS. For islet surface coating, mouse islets were isolated via collagenase digestion and gradient purification using Histopaque. Isolated islets were then treated with ice cold Hep-PEG solution for 10 min to allow covalent binding between NHS and the amine groups of islet cell membrane. Nanocoating with the Hep-PEG incurs minimal alteration to islet size and volume and heparinization of the islets with Hep-PEG may also reduce instant blood-mediated inflammatory reaction during islet transplantation. This "easy-to-adopt" approach is mild enough for surface engineering of living cells without compromising cell viability. Considering that heparin has shown binding affinity to multiple cytokines, the Hep-PEG nanocoating also provides an open platform that enables incorporation of unlimited functional biological mediators and multi-layered surfaces for living cell surface bioengineering.

The effect of pegylated granulocyte colony-stimulating factor treatment prior to experimental mastitis in lactating Holsteins

Neutrophils are the first-acting and most prominent cellular defense against mastitis-causing pathogens. This makes neutrophil activation and expansion obvious candidates for targeted therapeutics. The granulocyte colony-stimulating factor (G-CSF) cytokine stimulates the bone marrow to produce granulocytes and stem cells and release them into the bloodstream, which results in neutrophilia as well as increasing the presence of other progenitor cells in the bloodstream. A pegylated form of G-CSF (PEG-gCSF) has been shown to significantly decrease naturally occurring mastitis rates in cows postpartum. The use of PEG-gCSF had not been evaluated in response to an experimental mastitis challenge. In an effort to examine the effect and mechanism of PEG-gCSF treatment, we challenged 11 mid-lactation Holsteins with ∼400 cfu Escherichia coli P4 by intramammary infusion. Five cows received 2 PEG-gCSF injections, one at 14 d and the other at 7 d before disease challenge, and 6 cows remained untreated. To evaluate the response of cows to the PEG-gCSF treatment, we measured complete blood counts, somatic cell counts, bacterial counts, milk yield, and feed intake data. The PEG-gCSF-treated cows had significantly increased circulating levels of neutrophils and lymphocytes after each PEG-gCSF injection, as well as following mastitis challenge. The PEG-gCSF-treated cows had significantly lower bacterial counts and lower milk BSA levels at the peak of infection. In addition, control cows had significant decreases in milk yield postinfection and significantly reduced feed intake postinfection compared with PEG-gCSF-treated cows. Collectively, PEG-gCSF treatment resulted in reduced disease severity when administered before a bacterial challenge. Mechanistically, we show that G-CSF treatment increases cell surface expression of an E-selectin ligand before infection on neutrophils and monocytes found in the blood. These cells quickly disappear from the blood shortly after infection, suggesting a mechanism for the reduced mastitis severity by priming immune cells for quick targeting to the site of infection.

The other myeloperoxidase: Emerging functions

Myeloperoxidase (MPO) is a member of the mammalian peroxidase family. It is mainly expressed in neutrophils, monocytes and macrophages. As a catalyzer of reactive oxidative species and radical species formation, it contributes to neutrophil bactericidal activity. Nevertheless MPO invalidation does not seem to have major health consequences in affected individuals. This suggests that MPO might have alternative functions supporting its conservation during evolution. We will review the available data supporting these non-canonical functions in terms of tissue specific expression, function and enzymatic activity. Thus, we discuss its cell type specific expression. We review in between others its roles in angiogenesis, endothelial (dys-) function, immune reaction, and inflammation. We summarize its pathological actions in clinical conditions such as cardiovascular disease and cancer.

Pancreatic islet surface bioengineering with a heparin-incorporated starPEG nanofilm

Cell surface engineering could protect implanted cells from host immune rejections while modify the cellular landscape for better post-transplantation graft function and survival. Islet transplantation is considered the most promising therapeutic option with the potential to cure diabetes. Current approach to improve clinical efficacy of pancreatic islet transplantation is alginate encapsulation. However, disappointing outcomes have been reported in clinical trials due to larger islet size resulted by encapsulation and alginate-elicited host immune responses. We have developed an ultrathin nanofilm of starPEG with incorporated heparin (Hep-PEG) that binds covalently to the amine groups of islet surface membrane via its N-hydroxysuccinimide groups. The Hep-PEG nanocoating elicited minimal alteration on islet volume in culture. Hep-PEG-coated islets exhibited robust islet viability accompanied by uncompromised islet insulin secretory function. Instant blood-mediated inflammatory reaction was also reduced by Hep-PEG islet coating, accompanied by enhanced intra-islet revascularization. In addition, despite its semi-permeability, Hep-PEG islet coating promoted the survival of islets exposed to pro-inflammatory cytokines. Considering that inflammation and hypoxia are primary causes of immediate cell loss for cell therapy, the Hep-PEG nanofilm represents a viable approach for cell surface engineering which would improve the clinical outcome of cell therapies.

Cell-Specific Variation in E-Selectin Ligand Expression among Human Peripheral Blood Mononuclear Cells: Implications for Immunosurveillance and Pathobiology

Both host defense and immunopathology are shaped by the ordered recruitment of circulating leukocytes to affected sites, a process initiated by binding of blood-borne cells to E-selectin displayed at target endothelial beds. Accordingly, knowledge of the expression and function of leukocyte E-selectin ligands is key to understanding the tempo and specificity of immunoreactivity. In this study, we performed E-selectin adherence assays under hemodynamic flow conditions coupled with flow cytometry and Western blot analysis to elucidate the function and structural biology of glycoprotein E-selectin ligands expressed on human PBMCs. Circulating monocytes uniformly express high levels of the canonical E-selectin binding determinant sialyl Lewis X (sLe^X) and display markedly greater adhesive interactions with E-selectin than do circulating lymphocytes, which exhibit variable E-selectin binding among CD4⁺ and CD8⁺ T cells but no binding by B cells. Monocytes prominently present sLe^X decorations on an array of protein scaffolds, including P-selectin glycoprotein ligand-1, CD43, and CD44 (rendering the E-selectin ligands cutaneous lymphocyte Ag, CD43E, and hematopoietic cell E-selectin/L-selectin ligand, respectively), and B cells altogether lack E-selectin ligands. Quantitative PCR gene expression studies of glycosyltransferases that regulate display of sLe^X reveal high transcript levels among circulating monocytes and low levels among circulating B cells, and, commensurately, cell surface α(1,3)-fucosylation reveals that acceptor sialyllactosaminyl glycans convertible into sLe^X are abundantly expressed on human monocytes yet are relatively deficient on B cells. Collectively, these findings unveil distinct cell-specific patterns of E-selectin ligand expression among human PBMCs, indicating that circulating monocytes are specialized to engage E-selectin and providing key insights into the molecular effectors mediating recruitment of these cells at inflammatory sites.

Immune Complex-Induced, Nitric Oxide-Mediated Vascular Endothelial Cell Death by Phagocytes Is Prevented with Decoy FcγReceptors

Autoimmune vasculitis is an endothelial inflammatory disease that results from the deposition of immune-complexes (ICs) in blood vessels. The interaction between Fcgamma receptors (FcγRs) expressed on inflammatory cells with ICs is known to cause blood vessel damage. Hence, blocking the interaction of ICs and inflammatory cells is essential to prevent the IC-mediated blood vessel damage. Thus we tested if uncoupling the interaction of FcγRs and ICs prevents endothelium damage. Herein, we demonstrate that dimeric FcγR-Igs prevented nitric oxide (NO) mediated apoptosis of human umbilical vein endothelial cells (HUVECs) in an in vitro vasculitis model. Dimeric FcγR-Igs significantly inhibited the IC-induced upregulation of inducible nitric oxide synthase (iNOS) and nitric oxide (NO) release by murine monocytic cell line. However, FcγR-Igs did not affect the exogenously added NO-induced upregulation of pro-apoptotic genes such as Bax (15 fold), Bak (35 fold), cytochrome-C (11 fold) and caspase-3 (30 fold) in HUVECs. In conclusion, these data suggest that IC-induced NO could be one of the major inflammatory mediator promoting blood vessel inflammation and endothelial cell death during IC-mediated vasculitis which can be effectively blocked by dimeric decoy FcγRs.

S100A8/A9 is an important host defence mediator in neuropathic foot ulcers in patients with type 2 diabetes mellitus

Chronic wounds and in particular diabetic foot ulcers (DFUs) are a growing clinical challenge, but the underlying molecular pathophysiological mechanisms are unclear. Recently, we reported reduced levels of the immunomodulating and antimicrobial S100A8/A9 in non-healing venous leg ulcers (VLUs), while another study found increased S100A8/A9 in DFUs. To clarify these apparently contradictory findings, we compared S100A8/A9 as well as an inducer, lipopolysaccharide (LPS) and selected innate immune response mediators in wound fluids from non-healing DFUs and VLUs with healing wounds. Wound fluids were collected from neuropathic DFUs (n = 6) and VLUs (n = 9) of median 2-year duration, and split-thickness skin graft donor site wounds (n = 10) by standardized method. None of the patients had ischaemic extremities or clinically infected wounds. LPS was determined by limulus amoebocyte lysate test, and S100A8/A9, granulocyte colony-stimulating factor (G-CSF), interleukin (IL)-10 and vascular endothelial growth factor (VEGF) by immunospecific quantitative assays. LPS levels were median 8.7 (interquartile range 5.4-21.2) ng/ml in DFUs compared with 121 (22-2000) ng/ml in VLUs. S100A8/A9 was higher (p = 0.020) in DFUs [718 (634-811) µg/ml] than in VLUs [303 (252-533) µg/ml]. Neither G-CSF nor IL-10 wound fluid levels differed significantly between the chronic wound groups. VEGF levels correlated with LPS (r = 0.758, p = 0.011, n = 10) and were higher (p = 0.024) in VLU wound fluids. LPS (p < 0.0001), S100A8/A9 (p = 0.005), G-CSF (p = 0.003), IL-10 (p = 0.003) and VEGF (p = 0.005) were increased in chronic wound fluids combined compared with the sterile donor site wound fluids. The protein alterations in the wounds were not reflected in the patients' sera. Low S100A8/A9 levels may contribute to poor wound healing in colonized chronic wounds with striking difference between DFUs and VLUs.

The glycobiology of the CD system: a dictionary for translating marker designations into glycan/lectin structure and function

The profile of cell surface molecules, the biochemical platform for cellular communication, can be likened to a molecular fingerprint. Historically, raising monoclonal antibodies by immunization with cells has been instrumental in obtaining tools suited for phenotyping and functional analysis. Initially for leukocyte antigens, the resulting cluster of differentiation (CD) nomenclature has become a popular system for classification. Glycans presented on proteins or lipids and receptors for carbohydrate structures (lectins) are part of the CD list. Our review presents biochemical and biomedical highlights of the respective CD entries.