The CD177 c.1291A Allele Leads to a Loss of Membrane Expression and Mimics a CD177-Null Phenotype.

CD177 is a glycosyl phosphatidyl inositol (GPI)-linked, neutrophil-specific glycoprotein that in 3-5% of normal individuals is absent from all neutrophils. The molecular mechanism behind the absence of CD177 has not been unravelled completely. Here, we analyse the impact of the recently described CD177 c.1291G>A variant on CD177 expression. Recombinant CD177 c.1291G>A was expressed in HEK293F cells and its expression on the cell surface, inside the cell, and in the culture supernatant was investigated. The CD177 c.1291G>A protein was characterised serologically and its interaction with proteinase 3 (PR3) was demonstrated by confocal laser scanning microscopy. Our experiments show that CD177 c.1291G>A does not interfere with CD177 protein biosynthesis but affects the membrane expression of CD177, leading to very low copy numbers of the protein on the cellular surface. The mutation does not interfere with the ability of the protein to bind PR3 or human polyclonal antibodies against wild-type CD177. Carriers of the c.1291G>A allele are supposed to be phenotyped as CD177-negative, but the protein is present in soluble form. The presence of CD177 c.1291A leads to the production of an unstable CD177 protein and an apparent "CD177-null" phenotype.

Hepatocyte integrity depends on c-Jun-controlled proliferation in Schistosoma mansoni infected mice.

Schistosomiasis is a parasitic disease affecting more than 250 million people worldwide. The transcription factor c-Jun, which is induced in S. mansoni infection-associated liver disease, can promote hepatocyte survival but can also trigger hepatocellular carcinogenesis. We aimed to analyze the hepatic role of c-Jun following S. mansoni infection. We adopted a hepatocyte-specific c-Jun knockout mouse model (Alb-Cre/c-Jun loxP) and analyzed liver tissue and serum samples by quantitative real-time PCR array, western blotting, immunohistochemistry, hydroxyproline quantification, and functional analyses. Hepatocyte-specific c-Jun knockout (c-JunΔli) was confirmed by immunohistochemistry and western blotting. Infection with S. mansoni induced elevated aminotransferase-serum levels in c-JunΔli mice. Of note, hepatic Cyclin D1 expression was induced in infected c-Junf/f control mice but to a lower extent in c-JunΔli mice. S. mansoni soluble egg antigen-induced proliferation in a human hepatoma cell line was diminished by inhibition of c-Jun signaling. Markers for apoptosis, oxidative stress, ER stress, inflammation, autophagy, DNA-damage, and fibrosis were not altered in S. mansoni infected c-JunΔli mice compared to infected c-Junf/f controls. Enhanced liver damage in c-JunΔli mice suggested a protective role of c-Jun. A reduced Cyclin D1 expression and reduced hepatic regeneration could be the reason. In addition, it seems likely that the trends in pathological changes in c-JunΔli mice cumulatively led to a loss of the protective potential being responsible for the increased hepatocyte damage and loss of regenerative ability.

The Avidity of Autoreactive Alpha-Synuclein Antibodies in Leucine-Rich Repeat Kinase 2 Mutation Carriers Is Not Altered Compared to Healthy Controls or Patients with Parkinson's Disease.

The accumulation and aggregation of alpha-synuclein (α-Syn) are pathological processes associated with Parkinson's disease, indicating that the regulation of protein is a crucial etiopathological mechanism. Interestingly, human serum and cerebrospinal fluid contain autoantibodies that recognize α-Syn. This potentially demonstrates an already existing, naturally decomposing, and protective system. Thus, quantitative or qualitative alterations, such as the modified antigen binding of so-called naturally occurring autoantibodies against α-Syn (nAbs-α-Syn), may induce disease onset and/or progression. We investigated the serum titers and binding characteristics of nAbs-α-Syn in patients suffering from sporadic Parkinson's disease (n = 38), LRRK2 mutation carriers (n = 25), and healthy controls (n = 22). METHODS: Titers of nAbs-α-Syn were assessed with ELISA and binding affinities and kinetics with SPR. Within the patient cohort, we discriminated between idiopathic and genetic (LRRK2-mutated) variants. RESULTS: ELISA experiments revealed no significant differences in nAbs-α-Syn serum titers among the three cohorts. Moreover, the α-Syn avidity of nAbs-α-Syn was also unchanged. CONCLUSIONS: Our findings indicate that nAbs-α-Syn concentrations or affinities in healthy and diseased persons do not differ, independent of mutations in LRRK2.

Circulating Adipokines and Hepatokines Serve as Diagnostic Markers during Obesity Therapy.

Allocation of morbidly obese patients to either conservative therapy options-such as lifestyle intervention and/or low-calorie diet (LCD)-or to bariatric surgery-preferably sleeve gastrectomy or Roux-en-Y gastric bypass (RYGB)-represents a crucial decision in order to obtain sustainable metabolic improvement and weight loss. The present study encompasses 160 severely obese patients, 81 of whom participated in an LCD program, whereas 79 underwent RYGB surgery. The post-interventional dynamics of physiologically relevant adipokines and hepatokines (ANGPTL4, CCL5, GDF15, GPNMB, IGFBP6), as well as their correlation with fat mass reduction and improvement of liver fibrosis, were analyzed. Systemic GDF15 was characterized as an excellent predictive marker for hepatic fibrosis as well as type 2 diabetes mellitus. Of note, baseline GDF15 serum concentrations were positively correlated with NFS and HbA1c levels after correction for BMI, suggesting GDF15 as a BMI-independent marker of hepatic fibrosis and T2D in obese individuals. Specific GDF15 cut-off values for both diseases were calculated. Overall, the present data demonstrate that circulating levels of specific adipokines and hepatokines are regulated with therapy-induced fat loss and metabolic improvement and might, therefore, serve as biomarkers for the success of obesity therapy strategies.

Efficacy of Chondroprotective Food Supplements Based on Collagen Hydrolysate and Compounds Isolated from Marine Organisms.

Osteoarthritis belongs to the most common joint diseases in humans and animals and shows increased incidence in older patients. The bioactivities of collagen hydrolysates, sulfated glucosamine and a special fatty acid enriched dog-food were tested in a dog patient study of 52 dogs as potential therapeutic treatment options in early osteoarthritis. Biophysical, biochemical, cell biological and molecular modeling methods support that these well-defined substances may act as effective nutraceuticals. Importantly, the applied collagen hydrolysates as well as sulfated glucosamine residues from marine organisms were strongly supported by both an animal model and molecular modeling of intermolecular interactions. Molecular modeling of predicted interaction dynamics was evaluated for the receptor proteins MMP-3 and ADAMTS-5. These proteins play a prominent role in the maintenance of cartilage health as well as innate and adapted immunity. Nutraceutical data were generated in a veterinary clinical study focusing on mobility and agility. Specifically, key clinical parameter (MMP-3 and TIMP-1) were obtained from blood probes of German shepherd dogs with early osteoarthritis symptoms fed with collagen hydrolysates. Collagen hydrolysate, a chondroprotective food supplement was examined by high resolution NMR experiments. Molecular modeling simulations were used to further characterize the interaction potency of collagen fragments and glucosamines with protein receptor structures. Potential beneficial effects of collagen hydrolysates, sulfated glycans (i.e., sulfated glucosamine from crabs and mussels) and lipids, especially, eicosapentaenoic acid (extracted from fish oil) on biochemical and physiological processes are discussed here in the context of human and veterinary medicine.

Transfusion of target antigens to preimmunized recipients: a new mechanism in transfusion-related acute lung injury.

Transfusion-related lung injury (TRALI) is a serious side effect of blood transfusion. Exclusion of antibody carriers from the donor pool has significantly decreased the number of cases, but TRALI remains the leading cause of transfusion-related morbidity and mortality in industrialized countries. Here, we show that proteins released from donor cells during processing of blood components are capable of inducing a new type of reverse TRALI when transfused to preimmunized recipients. First, we show that soluble neutrophil surface protein CD177 in complex with proteinase 3 (sCD177/PR3) is not only present in human plasma but also in packed red blood cell (PRBC) supernatant. Filtration or storage enhances the concentration of sCD177/PR3 in PRBCs. Second, we show that sCD177/PR3 specifically binds to PECAM-1 on stimulated (but not on unstimulated) endothelial cells (ECs). Third, we provide evidence that the sCD177/PR3/PECAM-1 complex is functional. In the presence of monoclonal or human antibodies against CD177 or PR3, ECs produce reactive oxygen species and become apoptotic. Albumin flux through an EC monolayer increases significantly whenever antibodies and the cognate antigens are present. Finally, we describe a clinical case in which anti-CD177 present in a transfusion recipient precipitated TRALI after the transfusion of CD177-positive, but not CD177-negative, PRBCs. In conclusion, we introduce a new TRALI mechanism based on the specific binding of transfused, soluble antigens to activated ECs in preimmunized recipients. We suggest that further studies and clinical work-up of TRALI should also include antibody investigation of the recipient.

Glycoprotein V is a relevant immune target in patients with immune thrombocytopenia.

Platelet autoantibody-induced platelet clearance represents a major pathomechanism in immune thrombocytopenia (ITP). There is growing evidence for clinical differences between anti-glycoprotein IIb/IIIa and anti-glycoprotein Ib/IX mediated ITP. Glycoprotein V is a well characterized target antigen in Varicella-associated and drug-induced thrombocytopenia. We conducted a systematic study assessing the prevalence and functional capacity of autoantibodies against glycoprotein V. A total of 1140 patients were included. In one-third of patients, platelet-bound autoantibodies against glycoproteins Ib/IX, IIb/IIIa, or V were detected in a monoclonal antibody immobilization of platelet antigen assay; platelet-bound autoantiglycoprotein V was present in the majority of samples (222 out of 343, 64.7%). Investigation of patient sera revealed the presence of free autoantibodies against glycoprotein V in 13.5% of these patients by an indirect monoclonal antibody immobilization of platelet antigen assay, but in 39.6% by surface plasmon resonance technology. These antibodies showed significantly lower avidity (association/dissociation ratio 0.32±0.13 vs 0.73±0.14; P<0.001). High- and low-avidity antibodies induced comparable amounts of platelet uptake in a phagocytosis assay using CD14+ positively-selected human macrophages [mean phagocytic index, 6.81 (range, 4.75-9.86) vs 6.01 (range, 5.00-6.98); P=0.954]. In a NOD/SCID mouse model, IgG prepared from both types of anti-glycoprotein V autoantibodies eliminated human platelets with no detectable difference between the groups from the murine circulation [mean platelet survival at 300 minutes, 40% (range, 27-55) vs 35% (16-46); P=0.025]. Our data establish glycoprotein V as a relevant immune target in immune thrombocytopenia. We would suggest that further studies including glycoprotein V will be required before ITP treatment can be tailored according to platelet autoantibody specificity.

Extending the functional characteristics of naturally occurring autoantibodies against ß-Amyloid, Prion Protein and α-Synuclein.

BACKGROUND: Abnormal aggregation of proteins induces neuronal cell loss in neurodegenerative disorders such as Alzheimer's Disease, Creutzfeldt-Jakob Disease and Parkinson's Disease. Specific stimuli initialize conformational changes in physiological proteins, causing intra- or extracellular protein aggregation. We and other groups have identified naturally occurring autoantibodies (nAbs) as part of the human antibody pool that are able to prevent peptide fibrillation. These nAbs show a rescue effect following exposure of toxic aggregates on neurons, and they support microglial uptake of aggregated peptides. OBJECTIVE: Identification of a putative common epitope among the relevant proteins ß-Amyloid, α-Synuclein and Prion Protein for the respective nAbs. MATERIAL AND METHODS: Binding affinity between the aforementioned proteins and nAbs was tested by Dot Blot, ELISA and SPR-technology. Furthermore, the functionality of the protein-nAbs-complexes was studied in Thioflavin-T assays and microglial uptake experiments to study dependent inhibition of protein aggregation and enhancement of Fcγ mediated uptake by microglial cells. RESULTS: ß-Amyloid and Prion Protein fragment showed considerable binding affinity and functional efficacy for all applied nAbs. Thereby, no significant difference within the different nAbs was detected. In contrast, α-Synuclein was bound exclusively by nAbs-α-Synuclein, which was reproduced in all binding studies. Surprisingly, functional assays with α-Synuclein revealed no significant effect of nAbs in comparison to IVIg treatment. However, all applied nAbs as well as IVIg show a minimal functionality on the microglial uptake of α-Synuclein. CONCLUSION: nAbs-Aß, nAbs-PrP possibly display comparable affinity to the same structural epitope within Aß and PrP106-126 A117V whereas the epitope recognized by nAbs-α-Syn is only present in α-Syn. The structural similarity of Aß and PrP fragment promotes the outline for an efficient antibody for the treatment of several neurodegenerative disorders and extend the functional characteristics of the investigated nAbs.

Molecular and Functional Characterization of Fcγ Receptor IIIb-Ligand Interaction: Implications for Neutrophil-Mediated Immune Mechanisms in Malaria.

The Fcγ receptor IIIb (FcγRIIIb) is a low-affinity receptor of IgG and is essential in neutrophil-mediated effector functions. Different allelic forms of FcγRIIIb carrying human neutrophil antigen (HNA-1a, -1b, -1c, and -1d) have been identified. Here, we have generated stable transfected HEK293 cell lines expressing HNA-1aa, -1bb, and -1bc. Of these, cells expressing HNA-1bc interacted significantly stronger (binding affinities, 2.277 versus 0.743) with human IgG than cells expressing the HNA-1aa or -1bb alloforms. The higher affinity of IgG toward the HNA-1c alloform was confirmed using neutrophils derived from German blood donors. Neutrophils from HNA-1abc-phenotyped individuals bound IgG significantly stronger (1.825 versus 0.903) than did neutrophils from HNA-1ab-typed individuals. These findings were confirmed by surface plasmon resonance (SPR) analysis demonstrating that recombinant HNA-1bc had a higher affinity (dissociation constant [Kd ], 7.24 × 10-6 M) than recombinant HNA-1bb (Kd , 1.15 × 10-5 M) against normal IgG. Finally, we demonstrated that Plasmodium falciparum merozoites opsonized with human IgG affinity purified against P. falciparum glutamate-rich protein (GLURP) enhanced stronger reactive oxygen species (ROS) emission in neutrophils obtained from HNA-1abc donors than in neutrophils from HNA-1ab donors. Collectively, these results indicate that the amino acid substitution Ala78Asp resulting in the HNA-1c allotype leads to higher affinity toward human IgG, enhancement of neutrophil activation, and possibly effective clearance of malaria by intracellular ROS.

Lysozyme's lectin-like characteristics facilitates its immune defense function.

Interactions between human lysozyme (HL) and the lipopolysaccharide (LPS) of Klebsiella pneumoniae O1, a causative agent of lung infection, were identified by surface plasmon resonance. To characterize the molecular mechanism of this interaction, HL binding to synthetic disaccharides and tetrasaccharides representing one and two repeating units, respectively, of the O-chain of this LPS were studied. pH-dependent structural rearrangements of HL after interaction with the disaccharide were observed through nuclear magnetic resonance. The crystal structure of the HL-tetrasaccharide complex revealed carbohydrate chain packing into the A, B, C, and D binding sites of HL, which primarily occurred through residue-specific, direct or water-mediated hydrogen bonds and hydrophobic contacts. Overall, these results support a crucial role of the Glu35/Asp53/Trp63/Asp102 residues in HL binding to the tetrasaccharide. These observations suggest an unknown glycan-guided mechanism that underlies recognition of the bacterial cell wall by lysozyme and may complement the HL immune defense function.

PECAM-1-dependent heme oxygenase-1 regulation via an Nrf2-mediated pathway in endothelial cells.

The antioxidant enzyme heme oxygenase (HO)-1, which catalyses the first and rate-limiting step of heme degradation, has major anti-inflammatory and immunomodulatory effects via its cell-type-specific functions in the endothelium. In the current study, we investigated whether the key endothelial adhesion and signalling receptor PECAM-1 (CD31) might be involved in the regulation of HO-1 gene expression in human endothelial cells (ECs). To this end PECAM-1 expression was down-regulated in human umbilical vein ECs (HUVECs) by an adenoviral vector-based knockdown approach. PECAM-1 knockdown markedly induced HO-1, but not the constitutive HO isoform HO-2. Nuclear translocation of the transcription factor NF-E2-related factor-2 (Nrf2), which is a master regulator of the inducible antioxidant cell response, and intracellular levels of reactive oxygen species (ROS) were increased in PECAM-1-deficient HUVECs, respectively. PECAM-1-dependent HO-1 regulation was also examined in PECAM-1 over-expressing Chinese hamster ovary and murine L-cells. Endogenous HO-1 gene expression and reporter gene activity of transiently transfected luciferase HO-1 promoter constructs with Nrf2 target sequences were decreased in PECAM-1 over-expressing cells. Moreover, a regulatory role of ROS for HO-1 regulation in these cells is demonstrated by studies with the antioxidant N-acetylcysteine and exogenous hydrogenperoxide. Finally, direct interaction of PECAM-1 with a native complex of its binding partner NB1 (CD177) and serine proteinase 3 (PR3) from human neutrophils, markedly induced HO-1 expression in HUVECs. Taken together, we demonstrate a functional link between HO-1 gene expression and PECAM-1 in human ECs, which might play a critical role in the regulation of inflammation.

Molecular organization of various collagen fragments as revealed by atomic force microscopy and diffusion-ordered NMR spectroscopy.

Heterogeneous mixtures of collagen fragments can be used as nutrition supplement or as key ingredients for ointments with therapeutic relevance in wound healing. Some mixtures of collagen fragments are referred to as collagen hydrolysates owing to the production process with hydrolytic enzymes. Since the precise composition of collagen hydrolysates is generally unknown, it is of interest to analyze samples containing various collagen fragments with appropriate biophysical methods. Any product optimization without a profound knowledge concerning the size and the molecular weight distribution of its components is nearly impossible. It turned out that a combination of AFM methods with NMR techniques is exceptionally suited to examine the size range and the aggregation behavior of the collagen fragments in the hydrolysates of fish, jellyfish, chicken, porcine and bovine collagen. Supported by molecular modeling calculations, the AFM and NMR experiments provide a detailed knowledge about the composition of collagen hydrolysates and collagen ointments. Furthermore, the data allow a correlation between the size of the fragments and their potential bioactivity.

Synthesis and molecular recognition studies of the HNK-1 trisaccharide and related oligosaccharides. The specificity of monoclonal anti-HNK-1 antibodies as assessed by surface plasmon resonance and STD NMR.

The human natural killer cell carbohydrate, HNK-1, plays function-conducive roles in peripheral nerve regeneration and synaptic plasticity. It is also the target of autoantibodies in polyneuropathies. It is thus important to synthesize structurally related HNK-1 carbohydrates for optimizing its function-conducive roles, and for diagnosis and neutralization of autoantibodies in the fatal Guillain-Barré syndrome. As a first step toward these goals, we have synthesized several HNK-1 carbohydrate derivatives to assess the specificity of monoclonal HNK-1 antibodies from rodents: 2-aminoethyl glycosides of selectively O-sulfated trisaccharide corresponding to the HNK-1 antigen, its nonsulfated analogue, and modified structures containing 3-O-fucosyl or 6-O-sulfo substituents in the N-acetylglucosamine residues. These were converted, together with several related oligosaccharides, into biotin-tagged probes to analyze the precise carbohydrate specificity of two anti-HNK-1 antibodies by surface plasmon resonance that revealed a crucial role of the glucuronic acid in antibody binding. The contribution of the different oligosaccharide moieties in the interaction was shown by saturation transfer difference (STD) NMR of the complex consisting of the HNK-1 pentasaccharide and the HNK-1 412 antibody.

Interaction of the α2A domain of integrin with small collagen fragments.

We here present a detailed study of the ligand-receptor interactions between single and triple-helical strands of collagen and the α2A domain of integrin (α2A), providing valuable new insights into the mechanisms and dynamics of collagen-integrin binding at a sub-molecular level. The occurrence of single and triple-helical strands of the collagen fragments was scrutinized with atom force microscopy (AFM) techniques. Strong interactions of the triple-stranded fragments comparable to those of collagen can only be detected for the 42mer triple-helical collagen-like peptide under study (which contains 42 amino acid residues per strand) by solid phase assays as well as by surface plasmon resonance (SPR) measurements. However, changes in NMR signals during titration and characteristic saturation transfer difference (STD) NMR signals are also detectable when α2A is added to a solution of the 21mer single-stranded collagen fragment. Molecular dynamics (MD) simulations employing different sets of force field parameters were applied to study the interaction between triple-helical or single-stranded collagen fragments with α2A. It is remarkable that even single-stranded collagen fragments can form various complexes with α2A showing significant differences in the complex stability with identical ligands. The results of MD simulations are in agreement with the signal alterations in our NMR experiments, which are indicative of the formation of weak complexes between single-stranded collagen and α2A in solution. These results provide useful information concerning possible interactions of α2A with small collagen fragments that are of relevance to the design of novel therapeutic A-domain inhibitors.

Why structurally different cyclic peptides can be glycomimetics of the HNK-1 carbohydrate antigen.

The cyclic peptides c-(LSETTl) and c-(RTLPFS) are of potential clinical interest--they stimulate neurite outgrowth in a way that is similar to the effects of the HNK-1 (human natural killer cell-1) antigenic carbohydrate chains, which are terminated by 3'-sulfated glucuronic acid attached to an N-acetyllactosamine unit. To investigate the structure-activity relationships of the ability of the cyclic peptides to mimic HNK-1 carbohydrates, conformational analysis and examination of hydrophobic and hydrophilic patterns were performed and compared with the characteristics of a synthetic HNK-1 trisaccharide derivative. Data obtained demonstrate that both the trisaccharide and the glycomimetic peptide c-(LSETTl) exhibit a similar relationship between their hydrophobic moieties and their negatively charged sites. However, the second cyclic glycomimetic peptide investigated here, c-(RTLPFS), has a positively charged group as a potential contact point due to its Arg residue. Therefore, we studied the amino acid composition of all known receptor structures in the Protein Data Bank that are in contact with uronic acid and/or sulfated glycans. Interactions of the HNK-1 trisaccharide, c-(LSETTl), and c-(RTLPFS) with a laminin fragment involved in HNK-1 carbohydrate binding (i.e., the 21mer peptide: KGVSSRSYVGCIKNLEISRST) were also analyzed. Because the structure of the HNK-1-binding laminin domain is not available in the Protein Data Bank, we used the HNK-1-binding 21mer peptide fragment of laminin for the construction of a model receptor that enabled us to compare the molecular interplay of the HNK-1 trisaccharide and the two cyclopeptides c-(LSETTl) and c-(RTLPFS) with a reliable receptor structure in considerable detail.