A new method for quantifying mitochondrial axonal transport

Abstract

Axonal transport of mitochondria is critical for neuronal survival and function. Automatically quantifying and analyzing mitochondrial movement in a large quantity remain challenging. Here, we report an efficient method for imaging and quantifying axonal mitochondrial transport using microfluidic-chamber-cultured neurons together with a newly developed analysis package named “MitoQuant”. This tool-kit consists of an automated program for tracking mitochondrial movement inside live neuronal axons and a transient-velocity analysis program for analyzing dynamic movement patterns of mitochondria. Using this method, we examined axonal mitochondrial movement both in cultured mammalian neurons and in motor neuron axons of Drosophila in vivo. In 3 different paradigms (temperature changes, drug treatment and genetic manipulation) that affect mitochondria, we have shown that this new method is highly efficient and sensitive for detecting changes in mitochondrial movement. The method significantly enhanced our ability to quantitatively analyze axonal mitochondrial movement and allowed us to detect dynamic changes in axonal mitochondrial transport that were not detected by traditional kymographic analyses.Electronic supplementary materialThe online version of this article (doi:10.1007/s13238-016-0268-3) contains supplementary material, which is available to authorized users.

Connecting mitochondrial dynamics and life-or-death events via Bcl-2 family proteins

“…Using cultured neurons as a model system, mitochondria were found to move at speeds ranging from 0.05 μm/s (representing a possible threshold to define motile mitochondria (Chen et al, 2016) to 1–1.5 μm/s (Stepkowski et al, 2016), consistent with previous studies (Ashrafi et al, 2014; Wang and Schwarz, 2009). Therefore, observed average velocities vary across a wide range.…”

“…Interestingly, non-neuronal tumor cells might exploit this molecular ‘brake’ system by silencing SNPH expression, which translates into enhanced mitochondrial movements and targeting of ATP-producing mitochondria to the peripheral cytoskeleton of the tumor cells to fuel cell motility and invasion (Caino et al, 2016). Still, regulation of SNPH recruitment and activity remains elusive, as do the molecular pathways controlling the duration of mitochondrial retention at specific sites and the frequent reversal of motion direction following the pausing events (Bertholet et al, 2016; Chen et al, 2016; Ligon and Steward, 2000). …”

Regulated distribution of mitochondria in touch receptor neurons of C. elegans influences touch response

“…Bi-directional transport mitochondria is correlated with axonal outgrowth and the mitochondrial motility is maintained throughout the axonal development (Morris and Hollenbeck, 1993;Ruthel and Hollenbeck, 2003). Mitochondria are found to be predominantly stationary in the axon and tends to present or accumulate, enriched/present in energy demanding areas (Chen et al, 2016). These regions include growth cones (Morris and Hollenbeck, 1993;Smith and Gallo, 2018), synaptic boutons (Levy et al, 2003), nodes of Ranvier (Zhang et al, 2010), axonal branches and dendritic shafts (Li et al, 2004;Ruthel and Hollenbeck, 2003).…”

The role of mitochondria in axon development and regeneration

“…A shows the summary of the types of mitochondrial motility), and mitochondria can undergo switches in the directionality of transport while moving. Another form of mitochondrial behavior within the axon has been described as “dynamic pausing” (Chen et al, ), reflecting repeated cycles of minor anterograde and retrograde displacements in the position of the mitochondrion without net movement. Mitochondria in the dynamic pausing state have a greater propensity to subsequently engage in long duration directed movement (Chen et al, ).…”