Autoantibody-Mediated Changes in Platelets Sialic Pattern: Potential Impact on Platelet Functionality and Lifespan in Immune Thrombocytopenia

Introduction Immune thrombocytopenia (ITP) is a bleeding disorder mediated by autoantibodies (AAbs) that are targeting different glycoproteins (GPs) on the platelet (PLT) surface. Desialylation, the loss of sialic acid from PLT GPs, has been reported to contribute to the increased PLT destruction in ITP. In this work, we investigated the impact of AAb-mediated desialylation on the function as well as apoptotic status of human platelets.

Methods AAbs from well-characterized ITP patients were first screened for desialylation ability using the lectin binding assay. After incubation of PLTs with ITP or control sera, glycan changes were analyzed by flow cytometry (FC). To investigate the impact of desialylation on PLTs life-span, the NOD/SCID animal model was used. The activation of the apoptotic pathway was analyzed measuring changes in the inner mitochondrial membrane potential (TMRE assay), by FC. To evaluate the impact of desialylation on PLT function, an adhesion assay with different surface coatings was performed.

Results A total of 100 ITP sera were investigated in this study. 28 sera induced a significant increase in the exposure of ß-galactose on the PLT surface compared to control sera (mean fold increase (FI): 3.50, range: 1.79–13.61, p = 0.0001). In addition, 21 sera caused higher exposure of N-acetylglucosamine on the surface of PLTs (FI: 2.41, range: 1.54–5.47, p = 0.0001). Injection of desialylating AAbs resulted in accelerated clearance of human PLTs from the mouse circulation which was significantly reduced by a specific neuraminidase inhibitor that prevents desialylation on the PLT surface (survival of human PLTs after 5 hours: 28 ± 5%, range: 20–46% vs. 45 ± 3%, range: 36–54%, p = 0.019, respectively). Moreover, ITP AAbs-induced desialylation led to impaired PLT adherence on fibrinogen and von Willebrand factor, compared to non-desialylating AAbs (34 ± 7% vs. 74 ± 8%, p = 0.002; 26 ± 2% vs. 67 ± 5%, p = 0.003, respectively). No correlation between the increased exposure of ß-galactose as well as N-acetylglucosamine and the induction of PLT apoptosis was observed (r = −0.33, p = 0.351; r = −0.344, p = 0.331, respectively).

Conclusion Our findings suggest that desialylating ITP AAbs are able to affect human PLT survival in an apoptosis-independent way. Most importantly, our data suggest that AAb-mediated desialylation seems to contribute to the pathophysiology of ITP beyond thrombocytopenia, namely, to the bleeding tendency.

Publication History

Article published online:
13 November 2020