Bcl-xL Is Required by Primary Hippocampal Neurons during Development to Support Local Energy Metabolism at Neurites

Joseph Jansen,Madison Scott,Emma Amjad,Han-A Park,Allison Stumpf,Kim Caldwell,Kimberly Lackey

doi:10.3390/biology10080772

Abstract

Simple SummaryB-cell lymphoma-extra large (Bcl-xL) is an anti-apoptotic protein that regulates energy metabolism in neurons. In this study, we found that primary hippocampal neurons transduced with Bcl-xL shRNA or treated with a pharmacological inhibitor of Bxl-xL had a decrease in the population of motile mitochondria. Primary hippocampal neurons lacking Bcl-xL failed to retain ATP at their neurites, which hindered the formation of complex neurite arbors, and ultimately had enhanced vulnerability to excitotoxic challenge.B-cell lymphoma-extra large (Bcl-xL) is a mitochondrial protein known to inhibit mitochondria-dependent intrinsic apoptotic pathways. An increasing number of studies have demonstrated that Bcl-xL is critical in regulating neuronal energy metabolism and has a protective role in pathologies associated with an energy deficit. However, it is less known how Bcl-xL regulates physiological processes of the brain. In this study, we hypothesize that Bcl-xL is required for neurite branching and maturation during neuronal development by improving local energy metabolism. We found that the absence of Bcl-xL in rat primary hippocampal neurons resulted in mitochondrial dysfunction. Specifically, the ATP/ADP ratio was significantly decreased in the neurites of Bcl-xL depleted neurons. We further found that neurons transduced with Bcl-xL shRNA or neurons treated with ABT-263, a pharmacological inhibitor of Bcl-xL, showed impaired mitochondrial motility. Neurons lacking Bcl-xL had significantly decreased anterograde and retrograde movement of mitochondria and an increased stationary mitochondrial population when Bcl-xL was depleted by either means. These mitochondrial defects, including loss of ATP, impaired normal neurite development. Neurons lacking Bcl-xL showed significantly decreased neurite arborization, growth and complexity. Bcl-xL depleted neurons also showed impaired synapse formation. These neurons showed increased intracellular calcium concentration and were more susceptible to excitotoxic challenge. Bcl-xL may support positioning of mitochondria at metabolically demanding regions of neurites like branching points. Our findings suggest a role for Bcl-xL in physiological regulation of neuronal growth and development.

Highlights

B-cell lymphoma-extra large (Bcl-xL) is an anti-apoptotic member of the Bcl2 protein family [1]
In order to investigate the roles of Bcl-xL on local ATP levels, primary hippocampal neurons isolated from E18 rats were transduced with either Bcl-xL shRNA or control shRNA at days in vitro 7 (DIV7) (Figure 1A; Supplementary Figure S1)
Depletion of Bcl-xL significantly decreased the population of motile mitochondria in primary hippocampal neurons, and this may hinder the delivery of mitochondria, impairing local energy metabolism at neurites

Summary

Introduction

B-cell lymphoma-extra large (Bcl-xL) is an anti-apoptotic member of the Bcl protein family [1]. Bcl-xL prevents oligomerization of pro-apoptotic Bcl family members such as Bax and Bak and loss of mitochondrial membrane integrity, inhibiting apoptotic cell death [2,3,4]. In addition to its role as an anti-apoptotic protein, Bcl-xL is critical in mitochondrial function regulating neuronal bioenergetics and synaptic plasticity in the brain [9,10]. Bcl-xL closes a mitochondrial inner membrane leak channel, thereby enhancing neuronal energy metabolism with greater ATP production without requiring excess oxygen uptake [11,12,13]. The Bcl-xL-Drp complex promotes clathrin-mediated endocytosis and enhances the synaptic vesicle pool [15]

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