PhD student, Radboud University Medical center
Describes how pathogen sialidase affect platelet sialic acid leading to vascular complications.
Platelets are blood cells that regulate blood clotting. They containing molecules on their surfaces known as sialic acid. Cleaving off sialic acid from platelet membrane affects platelet function. Some pathogens like Streptococcus pneumoniae bacteria produce sialidase, an enzyme that can cut off sialic acid (a process known as desialylation). When platelets are desialylated they become hyper-reactive. During bloodstream infection, platelet hyper-reactivity contributes to microvascular obstruction and multi-organ failure. My research analyzed the capability and mechanisms at which streptococcus sialidase is able to desialylate platelets. Furthermore, it explores whether sialidase inhibitors (medical intervention) can reverse sialidase-mediated platelet hyper-reactivity. Results from my research work pose a new therapeutic strategy of preventing vascular complications of pneumococcal bloodstream infections.
Abstract: Prolonged isolated thrombocytopenia (PT) is a frequent complication in patients who undergo allogeneic hematopoietic stem cell transplantation (allo-HSCT), and it is associated with an adverse prognosis. In this study, we hypothesized that desialylation on platelet surfaces was associated with PT after allo-HSCT. The mechanisms participating in this process may include NEU1 translocation, platelet apoptosis, and phagocytosis by macrophages.PT was defined as a peripheral platelet count less than 100 × 10(9)/L without sustained anemia or leukopenia for more than 3 months after allo-HSCT. 34 patients were identified consecutively from a cohort of 255 patients who underwent allo-HSCT for hematologic malignancies between May and October 2014 at Peking University Institute of Hematology. Desialylation, enzyme expression, and phagocytosis were detected using flow cytometry, immunofluorescence, RT-PCR, Western blot, and so on.Platelets from the PT patients had significantly fewer sialic acids (P = .001) and increased β-galactose exposure indicative of desialylation on the surface (P = .042), and serum from the PT patients showed a higher sialic acid concentration (8.400 ± 0.2209 μmol/L, P < .001). The sialidase NEU1 was over-expressed from mRNA to protein levels, and its catalytic activity was increased in platelets from the PT patients. Desialylation of GPIbα in the PT patients was correlated with changes in 14-3-3ζ distribution, which, relative to Bad activation, modulated the expression of Bcl-2 family proteins, depolarized the inner membrane of the mitochondria, and initiated the intrinsic mitochondria-dependent pathway of apoptosis. Macrophages derived from the THP-1 cell line preferred to phagocytize desialylated platelets from the PT patients in vitro. We also revealed that oseltamivir (400 μmol/L) could inhibit 50 % of the sialidase activity on platelets and could protect 20 % of platelets from phagocytosis in vitro.Desialylation of platelets was associated with platelet apoptosis and phagocytosis, whereas oseltamivir could reduce platelet destruction in the periphery, indicating a potential novel treatment for PT after allo-HSCT.
Pub.: 27 Oct '15, Pinned: 12 Sep '17
Abstract: Although surface sialic acid is considered a key determinant for the survival of circulating blood cells and glycoproteins, its role in platelet circulation lifetime is not fully clarified. We show that thrombocytopenia in mice deficient in the St3gal4 sialyltransferase gene (St3Gal-IV(-/-) mice) is caused by the recognition of terminal galactose residues exposed on the platelet surface in the absence of sialylation. This results in accelerated platelet clearance by asialoglycoprotein receptor-expressing scavenger cells, a mechanism that was recently shown to induce thrombocytopenia during Streptococcus pneumoniae sepsis. We now identify platelet GPIbalpha as a major counterreceptor on ST3Gal-IV(-/-) platelets for asialoglycoprotein receptors. Moreover, we report data that establish the importance of sialylation of the von Willebrand factor in its function.
Pub.: 13 Jun '09, Pinned: 12 Sep '17
Abstract: The endocytic Ashwell-Morell receptor (AMR) of hepatocytes detects pathogen remodeling of host glycoproteins by neuraminidase in the bloodstream and mitigates the lethal coagulopathy of sepsis. We have investigated the mechanism of host protection by the AMR during the onset of sepsis and in response to the desialylation of blood glycoproteins by the NanA neuraminidase of Streptococcus pneumoniae. We find that the AMR selects among potential glycoprotein ligands unmasked by microbial neuraminidase activity in pneumococcal sepsis to eliminate from blood circulation host factors that contribute to coagulation and thrombosis. This protection is attributable in large part to the rapid induction of a moderate thrombocytopenia by the AMR. We further show that neuraminidase activity in the blood can be manipulated to induce the clearance of AMR ligands including platelets, thereby preactivating a protective response in pneumococcal sepsis that moderates the severity of disseminated intravascular coagulation and enables host survival.
Pub.: 29 Nov '13, Pinned: 12 Sep '17