Bcl‐xl is required by primary hippocampal neurons during development to support local energy metabolism at neurites

Abstract

B‐cell lymphoma‐extra large (Bcl‐xL) is a mitochondrial protein known to inhibit mito-chondria‐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 mi-tochondria and an increased stationary mitochondrial population when Bcl‐xL was depleted by either means. These mitochondrial defects, including loss of ATP, impaired normal neurite develop-ment. 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 chal-lenge. Bcl‐xL may support positioning of mitochondria at metabolically demanding regions of neu-rites like branching points. Our findings suggest a role for Bcl‐xL in physiological regulation of neuronal growth and development.