Rapid Increases in proBDNF after Pilocarpine-Induced Status Epilepticus in Mice Are Associated with Reduced proBDNF Cleavage Machinery

Ajay X Thomas,Marco I Gonzalez,Amy R Brooks-Kayal,Yasmin Cruz Del Angel,Philip M Lam,Barbara L Hempstead,Andrew J Carrel,Shelley J Russek,Jessica Carlsen

doi:10.1523/eneuro.0020-15.2016

Abstract

Brain-derived neurotrophic factor (BDNF) levels are elevated after status epilepticus (SE), leading to activation of multiple signaling pathways, including the janus kinase/signal transducer and activator of transcription pathway that mediates a decrease in GABAA receptor α1 subunits in the hippocampus (Lund et al., 2008). While BDNF can signal via its pro or mature form, the relative contribution of these forms to signaling after SE is not fully known. In the current study, we investigate changes in proBDNF levels acutely after SE in C57BL/6J mice. In contrast to previous reports (Unsain et al., 2008; Volosin et al., 2008; VonDran et al., 2014), our studies found that levels of proBDNF in the hippocampus are markedly elevated as early as 3 h after SE onset and remain elevated for 7 d. Immunohistochemistry studies indicate that seizure-induced BDNF localizes to all hippocampal subfields, predominantly in principal neurons and also in astrocytes. Analysis of the proteolytic machinery that cleaves proBDNF to produce mature BDNF demonstrates that acutely after SE there is a decrease in tissue plasminogen activator and an increase in plasminogen activator inhibitor-1 (PAI-1), an inhibitor of extracellular and intracellular cleavage, which normalizes over the first week after SE. In vitro treatment of hippocampal slices from animals 24 h after SE with a PAI-1 inhibitor reduces proBDNF levels. These findings suggest that rapid proBDNF increases following SE are due in part to reduced cleavage, and that proBDNF may be part of the initial neurotrophin response driving intracellular signaling during the acute phase of epileptogenesis.

Highlights

Brain-derived neurotrophic factor (BDNF) promotes growth and differentiation of neurons during development and plays an important role in many physiological processes, such as learning and memory, as well as various pathological processes, such as epileptogenesis (Lu et al, 2014)
BDNF knock-in C57BL/6J mice, there is an increase in proBDNF as early as 3 h after status epilepticus (SE) onset, with levels remaining elevated at 24 h and peaking at 3 d post-SE
We demonstrated that acute increases in proBDNF after SE are associated with changes in the enzymes involved in the proteolytic processing of proBDNF, and that enhancing proBDNF cleavage by inhibiting Plasminogen activator inhibitor-1 (PAI-1) reduces proBDNF levels in hippocampal slices from animals 24 h after SE

Summary

Introduction

Brain-derived neurotrophic factor (BDNF) promotes growth and differentiation of neurons during development and plays an important role in many physiological processes, such as learning and memory, as well as various pathological processes, such as epileptogenesis (Lu et al, 2014). ProBDNF can be cleaved extracellularly by matrix metalloproteinases (MMPs; Ϫ3, Ϫ7, or 9), or by components of the tissue plasminogen activator/ plasmin (tPA/plasmin) proteolytic cascade (Lee et al, 2001; Pang et al, 2004). The activity of these proteases is tightly regulated. Plasminogen activator inhibitor-1 (PAI-1) inhibits both tPA and furin, inhibiting both extracellular and intracellular cleavage (Binder et al, 2002; Dupont et al, 2009; Bernot et al, 2011; Fig. 1). Tissue inhibitor of metalloproteinases (TIMPs) inhibit MMPs, while neuroserpin and ␣2 antiplasmin (A2AP) inhibit the tPA/plasmin proteolytic cascade (Hastings et al, 1997; Krueger et al, 1997; Brew et al, 2000; Yepes and Lawrence, 2004; Coughlin, 2005)

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