ORCID Profile
0000-0002-3154-1040
Current Organisation
University of Aberdeen
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Publisher: Wiley
Date: 12-04-2022
DOI: 10.1111/BJH.18164
Abstract: Red blood cells (RBCs) lose plasma membrane in the spleen as they age, but the cells and molecules involved are yet to be identified. Sickle cell disease and infection by Plasmodium falciparum cause oxidative stress that induces aggregates of cross‐linked proteins with N‐linked high‐mannose glycans (HMGs). These glycans can be recognised by mannose‐binding lectins, including the mannose receptor (CD206), expressed on macrophages and specialised phagocytic endothelial cells in the spleen to mediate the extravascular haemolysis characteristic of these diseases. We postulated this system might also mediate removal of molecules and membrane in healthy in iduals. Surface expression of HMGs on RBCs from patients who had previously undergone splenectomy was therefore assessed: high levels were indeed observable as large membrane aggregates. Glycomic analysis by mass spectrometry identified a mixture of Man 5‐9 GlcNAc 2 structures. HMG levels correlated well with manual pit counts ( r = 0.75–0.85). To assess further whether HMGs might act as a splenic reticuloendothelial function test, we measured levels on RBCs from patients with potential functional hyposplenism, some of whom exhibited high levels that may indicate risk of complications.
Publisher: Wiley
Date: 26-07-2014
DOI: 10.1111/BJH.13051
Publisher: Elsevier BV
Date: 08-2007
DOI: 10.1111/J.1538-7836.2007.02626.X
Abstract: Patients with myeloproliferative disease (MPD) have an increased risk of thrombosis. We studied markers of platelet and coagulation activation in a large cohort of patients with MPD (n = 118) and related this to Janus Kinase 2 (JAK2) V617 F mutation status, a marker of clonality, and the presence of antiphospholipid antibodies (APA), all of which have been associated with thrombosis in MPD. D-dimer, thrombin-antithrombin complexes (TAT), prothrombin fragments 1 + 2 (F(1+2)), soluble E-selectin (sE-selectin), and soluble P-selectin (sP-selectin) levels were compared between patients and hypertensive controls (n = 127). Assays for lupus anticoagulant (LA), anticardiolipin antibodies (ACA), antibeta2 glycoprotein 1 antibodies (anti-beta(2)GP1), and antiprothrombin antibodies (alpha-Pro) were also performed. The JAK2 V617F mutation status was determined in the cohort using lification refractory mutation system (ARMS) polymerase chain reaction. Disease clonality was determined in 54 patients using the HUMARA assay. sP-selectin was significantly increased in patients with MPD (P <or= 0.001). sP-selectin levels were significantly elevated in JAK2 V617F-positive patients compared to wild-type (P = 0.006), or controls (P < 0.001). There was no correlation between proportion clonality and any activation marker. We found no significant difference in the incidence of APA between patients and controls (11% vs. 14%, P = 0.46), and no significant association between APA status and any activation marker. The JAK2 V617F mutation is associated with platelet activation, as measured by elevated sP-selectin levels, in MPD. In contrast to previous reports, we found no excess of APA in patients with MPD.
Publisher: Springer Science and Business Media LLC
Date: 19-03-2021
DOI: 10.1038/S41467-021-21814-Z
Abstract: In both sickle cell disease and malaria, red blood cells (RBCs) are phagocytosed in the spleen, but receptor-ligand pairs mediating uptake have not been identified. Here, we report that patches of high mannose N-glycans (Man 5-9 GlcNAc 2 ), expressed on diseased or oxidized RBC surfaces, bind the mannose receptor (CD206) on phagocytes to mediate clearance. We find that extravascular hemolysis in sickle cell disease correlates with high mannose glycan levels on RBCs. Furthermore, Plasmodium falciparum -infected RBCs expose surface mannose N-glycans, which occur at significantly higher levels on infected RBCs from sickle cell trait subjects compared to those lacking hemoglobin S. The glycans are associated with high molecular weight complexes and protease-resistant, lower molecular weight fragments containing spectrin. Recognition of surface N-linked high mannose glycans as a response to cellular stress is a molecular mechanism common to both the pathogenesis of sickle cell disease and resistance to severe malaria in sickle cell trait.
Publisher: Cold Spring Harbor Laboratory
Date: 27-11-2020
DOI: 10.1101/2020.11.26.399402
Abstract: In both sickle cell disease (SCD) and malaria, red blood cells (RBCs) are phagocytosed in the spleen, but receptor-ligand pairs mediating uptake have not been identified. Here, we report that patches of high mannose N-glycans (Man 5-9 GlcNAc 2 ), expressed on diseased or oxidized RBC surfaces, bind the mannose receptor (CD206) on phagocytes to mediate clearance. Extravascular haemolysis in SCD correlates with high mannose glycan levels on RBCs. Infection of RBCs with Plasmodium falciparum expose surface mannose N-glycans on healthy RBCs, which occurred at significantly higher levels on RBCs from subjects with sickle cell trait compared to those lacking haemoglobin S. The glycans were associated with high molecular weight complexes and protease-resistant, lower molecular weight fragments containing spectrin. Recognition of surface N-linked high mannose glycans, a novel response to cellular stress, is the first molecular mechanism common to both the pathogenesis of SCD and resistance to severe malaria in sickle cell trait.
Publisher: American Society of Hematology
Date: 29-11-2018
DOI: 10.1182/BLOOD-2018-99-117290
Abstract: Heterozygosity for Hemoglobin (Hb) S, sickle cell trait (SCT), affects over 40 million people and confers resistance to severe infection by Plasmodium falciparum. Homozygosity for HbS, or compound heterozygosity with certain other alleles of Hb, affects over 4 million in iduals and causes sickle cell disease (SCD). Hemolytic anaemia is a prominent feature of SCD and is mainly extravascular, mediated by hepatic and splenic macrophages. No ligands for this process have been identified. As many macrophage phagocytic receptors recognise carbohydrates, we surveyed surface glycan expression by sickle cells using a panel of 8 lectins and flow cytometry. Most glycans were similar to those of healthy red blood cells (RBC), except much higher expression of terminal mannose. We investigated the structural basis for these residues using glycomic mass spectroscopy, which showed them to be N-linked high (Man5-9GlcNAc2) mannoses, a surprising conclusion as these are usually intermediates in the formation of complex glycans and not displayed on cell surfaces. High resolution microscopy revealed the mannose residues to be carried in discrete microdomains on the surfaces of sickle cells. These structures were absent on the surfaces of healthy RBC, instead being present in the membrane skeleton under the cell surface. Lectin blots and immunoprecipitation showed the mannoses to co-migrate predominantly with spectrin. We showed these mannose-bearing structures were able to stimulate phagocytosis of RBC by using a peripheral blood derived macrophage uptake assay. Sickle RBC were taken up at high rates compared to healthy RBC and this could be inhibited by congeners of mannose. We identified the importance of a cognate ligand (CD206: the mannose receptor) using blocking antibodies and knockdown of CD206 expression using siRNA. The in vivo and pathogenic relevance of mannose exposure was investigated by taking advantage of the heterogeneity of hemolysis in SCD. RBC with SCD (n=94), SCT (n=57) and healthy in iduals (n=54) were assayed for mannose exposure by flow cytometry. SCT and healthy RBC showed no mannose exposure but high levels were found on HbSS RBC (p .0001). Co-incident inheritance of HbSS with higher HbF values and alleles encoding alpha-thalassaemia resulted in lower surface mannose values. Overall, markers of hemolysis (RBC count, haemoglobin, reticulocyte count) correlated well with mannose exposure (Spearman correlation coefficients -0.68, -0.40, 0.37 p=0.0001, 0.0032, 0.0063 respectively). Plasma LDH is a marker of intravascular hemolysis and correlated with overall hemolysis within SCD (r=-0.25, p=0.016), but not mannose exposure (r=0.14, p=0.19). Thus mannose exposure correlated only with extravascular hemolysis. Identification of a ligand pair mediating rapid clearance of sickle cells raised the possibility that they also mediate enhanced clearance of SCT RBC infected by malarial parasites. Indeed, P. falciparum cultures induced mannose expression at the pigmented trophozoite and schizont stages in infected HbAA RBCs, at levels corresponding to mild hemolysis in SCD. Mannose expression in infected HbAS RBCs was even higher, with levels corresponding to severe hemolysis in SCD. Infection with P. falciparum and selection for HbS arose only recently in human evolution, raising the question of what the physiological triggers for this mechanism are. Infection with malarial parasites causes oxidative stress. We therefore subjected healthy RBC to copper sulphate, which resulted in surface mannose exposure as well as uptake by macrophages. Oxidized SCT RBC displayed more mannose than oxidized healthy RBC. Thus, we have identified a new cell surface 'eat me' signalling mechanism that allows inspecting macrophages to engage with the rigid membrane skeleton and phagocytose the mannose displaying cell. The mechanism is stimulated by HbS: when present in high concentrations, the mechanism is activated constitutively, resulting in sickle cell anaemia. Heterozygosity for HbS is insufficient by itself to trigger mannose exposure. However, the mechanism is primed so that oxidative stress associated with infection by P. falciparum causes greater mannose display, increased parasitized cell clearance and protection against severe malaria. These findings should allow the design of inhibitors of sickle cell haemolysis and inducers of protection against malaria. Cao: University of Aberdeen: Patents & Royalties. Barker:University of Aberdeen: Patents & Royalties. Vickers:University of Aberdeen: Patents & Royalties GSK: Equity Ownership.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Mark Vickers.