Tissue-type plasminogen activator induces synaptic vesicle endocytosis in cerebral cortical neurons

• Authors: Manuel Yepes, Emory University; Fang Wu, Emory University; Enrique Torre, Emory University; David Cuellar-Giraldo, Emory University; Dingwu Jia, Emory University; Lihong Cheng, Emory University
• Journal Title: Neuroscience
• Volume: Volume 319
• Publisher: Elsevier | 2016-04, Pages 69-78
• Type of Work: Article | Post-print: After Peer Review
• Publisher DOI: http://doi.org/10.1016/j.neuroscience.2016.01.046
• Subjects: Biology, Neuroscience
• Keywords: tissue-type plasminogen activator; Plasminogen; Plasmin; synaptic vesicle; endocytosis

Abstract

The release of the serine proteinase tissue-type plasminogen activator (tPA) from the presynaptic terminal of cerebral cortical neurons plays a central role in the development of synaptic plasticity, adaptation to metabolic stress and neuronal survival. Our earlier studies indicate that by inducing the recruitment of the cytoskeletal protein βII-spectrin and voltage-gated calcium channels to the active zone (AZ), tPA promotes Ca2+-dependent translocation of synaptic vesicles (SVs) to the synaptic release site where they release their load of neurotransmitters into the synaptic cleft. Here we used a combination of in vivo and in vitro experiments to investigate whether this effect leads to depletion of SVs in the presynaptic terminal. Our data indicate that tPA promotes SVs endocytosis via a mechanism that does not require the conversion of plasminogen into plasmin. Instead, we show that tPA induces calcineurin (CaN) - mediated dynamin I dephosphorylation, which is followed by dynamin I-induced recruitment of the actin binding protein profilin II to the presynaptic membrane, and profilin II-induced F-actin formation. We report that this tPA-induced sequence of events leads to the association of newly formed SVs with F-actin clusters in the endocytic zone. In summary, the data presented here indicate that following the exocytotic release of neurotransmitters tPA activates the mechanism whereby SVs are retrieved from the presynaptic membrane and endocytosed to replenish the pool of vesicles available for a new cycle of exocytosis. Together, these results indicate that in cerebral cortical neurons tPA plays a central role coupling SVs exocytosis and endocytosis.