PB0409 - Inhibition of the p75 pan neurotrophic receptor partly inhibits BDNF-induced platelet aggregation

Background: The Brain-Derived Neurotrophic Factor (BDNF) promotes neuronal growth and survival, acting through the tropomyosin receptor kinase B (TrkB) and the 75 kDa pan-neurotrophic receptor (p75NTR). This effect is amplified by receptor heterodimerization. BDNF is widely expressed outside of the central nervous system (CNS), with levels in platelets up to 1000-fold greater than in the CNS. We have shown that isolated platelets aggregate in response to BDNF via the activation of a truncated form of the TrkB receptor. Whether p75NTR is involved in BDNF-induced platelet aggregation remains unknown.

Aims: To investigate the role of p75NTR in BDNF-induced platelet aggregation.

Methods: Washed platelets were prepared from whole blood of healthy volunteers by sequential centrifugation. Platelets were activated using classical agonists (ADP, collagen, thrombin receptor activating peptide [TRAP]) and BDNF, in the absence or presence of 2 p75NTR inhibitors, THX-B and TAT-Pep 5. Aggregation was measured by light transmission aggregometry. Signaling pathways downstream of BDNF activation were assessed by anti-phosphoprotein immunoblots. Platelet p75NTR levels were quantified by ELISA.

Results: p75NTR immunoreactivity was detected on the surface (28.3±19.4%) and within (56.4±18.4%) platelets. Its levels were highly variable, with a 10-fold difference between highest (382 pg/ml) and lowest (38 pg/ml) values. Collagen-, ADP-, and TRAP-induced aggregation was not affected by the p75NTR inhibitors. Furthermore, inhibition of p75NTR showed high interindividual variation, with responses ranging from no effect to a complete abrogation of platelet activation and aggregation in response to BDNF. Signaling downstream of p75NTR activation showed similar variability in response to p75NTR inhibitors.

Conclusion(s): Pharmacological inhibition of p75NTR abrogated BDNF-induced platelet aggregation in some but not all healthy volunteers, suggesting a modest role of p75NTR in BDNF-induced platelet aggregation. Whether this variability in aggregation is related to the high interindividual variation in platelet p75NTR levels remains to be established.