Nerve growth factor signaling regulates motility and docking of axonal mitochondria

Axonal transport is thought to distribute mitochondria to regions of the neuron where their functions are required [1]. In cultured neurons, mitochondrial transport responds to growth cone activity, and this involves both a transition between motile and stationary states of mitochondria and modulation of their anterograde transport activity [2]. Although the exact cellular signals responsible for this regulation remain unknown, we recently showed that mitochondria accumulate in sensory neurons at regions of focal stimulation with NGF and suggested that this involves downstream kinase signaling [3]. Here, we demonstrate that NGF regulation of axonal organelle transport is specific to mitochondria. Quantitative analyses of motility show that the accumulation of axonal mitochondria near a focus of NGF stimulation is due to increased movement into bead regions followed by inhibition of movement out of these regions and that anterograde and retrograde movement are differentially affected. In axons made devoid of F-actin by latrunculin B treatment, bidirectional transport of mitochondria continues, but they can no longer accumulate in the region of NGF stimulation. These results indicate that intracellular signaling can specifically regulate mitochondrial transport in neurons, and they suggest that axonal mitochondria can respond to signals by locally altering their transport behavior and by undergoing docking interactions with the actin cytoskeleton.