Faculty of Pharmacy, Université de Montréal, Montréal, QC, Canada.
Research Center, Montreal Heart Institute, Montréal, QC, Canada.
Front Immunol. 2020 Nov 25;11:575607. doi: 10.3389/fimmu.2020.575607. eCollection 2020.
Brain-derived neurotrophic factor (BDNF) plays a role in synaptic plasticity and neuroprotection. BDNF has well-established pro-survival effects, whereas its precursor protein, proBDNF, induces apoptosis. Thus, it has been suggested that the proBDNF/BDNF ratio could be an indicator of neuronal health. Access to neurons is, understandably, limited. Because of their similarities, platelets have been put forward as a non-invasive biomarker of neuronal health; indeed, they store large quantities of BDNF and can release it into circulation upon activation, similarly to neurons. However, whether platelets also express the precursor proBDNF protein remains unknown. We therefore sought to characterize proBDNF levels in human platelets and plasma.
The presence of proBDNF was assessed by immunoblotting, cell fractionation, flow cytometry, and confocal microscopy in washed platelets from 10 healthy volunteers. Platelets from 20 independent healthy volunteers were activated with several classical agonists and the release of BDNF and proBDNF into plasma was quantified by ELISA.
Platelets expressed detectable levels of proBDNF (21 ± 13 fmol/250 x 10 platelets). ProBDNF expression was mainly localized in the intracellular compartment. The proBDNF to BDNF molar ratio was ~1:5 in platelets and 10:1 in plasma. In stark contrast to the release of BDNF during platelet activation, intraplatelet and plasma concentrations of proBDNF remained stable following stimulation with classical platelet agonists, consistent with non-granular expression.
Platelets express both the mature and the precursor form of BDNF. Whether the intraplatelet proBDNF to BDNF ratio could be used as a non-invasive biomarker of cognitive health warrants further investigation.
脑源性神经营养因子（BDNF）在突触可塑性和神经保护中发挥作用。BDNF 具有明确的促生存作用，而其前体蛋白 proBDNF 则诱导细胞凋亡。因此，有人提出 proBDNF/BDNF 比值可能是神经元健康的一个指标。由于神经元的可及性有限，因此可以理解。由于它们的相似性，血小板被提出作为神经元健康的非侵入性生物标志物；事实上，它们储存大量的 BDNF，并且可以在激活时将其释放到循环中，类似于神经元。然而，血小板是否也表达前体 proBDNF 蛋白仍然未知。因此，我们试图描述人类血小板和血浆中的 proBDNF 水平。
通过免疫印迹、细胞分级分离、流式细胞术和共聚焦显微镜评估 10 名健康志愿者的洗涤血小板中 proBDNF 的存在。使用几种经典激动剂激活来自 20 名独立健康志愿者的血小板，并通过 ELISA 定量测量 BDNF 和 proBDNF 释放到血浆中。
血小板表达可检测水平的 proBDNF（21 ± 13 fmol/250 x 10 血小板）。proBDNF 表达主要定位于细胞内隔室。血小板中 proBDNF 与 BDNF 的摩尔比约为 1:5，而在血浆中为 10:1。与血小板激活过程中 BDNF 的释放形成鲜明对比的是，经典血小板激动剂刺激后，血小板内和血浆中 proBDNF 的浓度保持稳定，这与非颗粒表达一致。
血小板表达成熟和前体形式的 BDNF。血小板内 proBDNF 与 BDNF 的比值是否可作为认知健康的非侵入性生物标志物，尚需进一步研究。
