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    Poster Networking

    Platelets and Megakaryocytes

    Poster Networking Session

    PB0867 - Alpha-2-macroglobulin precludes platelet aggregation in response to the Brain-Derived Neurotrophic Factor (BDNF)

    Monday, June 26, 2023
    18:30 – 19:30 ET
    Room: Exhibition
    Background: The brain-derived neurotrophic factor (BDNF) induces platelet activation, secretion and aggregation in isolated platelets. However, BDNF is readily detectable in plasma, thus a mechanism to preclude constant activation of platelets appears necessary.

    Aims: We investigated the mechanism regulating the bioavailability of BDNF in blood.

    Methods: To assess protein-protein interactions, we used molecular docking and immunoprecipitation. Platelet aggregation was assessed using light transmission aggregometry with washed platelets from healthy volunteers in response to classical agonists (collagen, ADP, TRAP6 and arachidonic acid) or BDNF, in the absence or presence of alpha-2-macroglobulin (α2M), and in platelet-rich plasma. Signaling downstream of BDNF was assessed with phospho-blots.

    Results: As little as 25% autologous plasma was sufficient to completely abolish platelet aggregation in response to BDNF. In silico modeling showed that BDNF could bind to both the native and the activated α2M in mainly 2 different ways, parallel and perpendicular arrangements; no stable binding of the high-affinity BDNF receptor, the tropomyosin receptor kinase B (TrkB), to the complex formed by BDNF-α2M appeared possible. Both the native and activated forms of α2M formed stable complexes with BDNF experimentally. The BDNF-α2M complex prevented TrkB activation in contrast to BDNF alone which induced strong downstream phosphorylation of the signal transducer and activator of transcription 3 (STAT3) protein. Both native and activated α2M inhibited BDNF-induced platelet aggregation in a concentration-dependent manner with comparable half maximal inhibitory concentrations (IC50≈125-150 nM). This inhibitory effect was specific to BDNF, as neither native nor activated α2M altered platelet responses to classical agonists.

    Conclusion(s): We show α2M to be a potential physiological regulator of BDNF bioavailability in blood, limiting platelet activation by BDNF to the site of vascular injury.