Nano-positioning and tubulin conformation contribute to axonal transport regulation of mitochondria along microtubules

Abstract

Correct spatiotemporal distribution of organelles and vesicles is crucial for healthy cell functioning and is regulated by intracellular transport mechanisms. Controlled transport of bulky mitochondria is especially important in polarized cells such as neurons that rely on these organelles to locally produce energy and buffer calcium. Mitochondrial transport requires and depends on microtubules that fill much of the available axonal space. How mitochondrial transport is affected by their position within the microtubule bundles is not known. Here, we found that anterograde transport, driven by kinesin motors, is susceptible to the molecular conformation of tubulin in neurons both in vitro and in vivo. Anterograde velocities negatively correlate with the density of elongated tubulin dimers like guanosine triphosphate (GTP)-tubulin. The impact of the tubulin conformation depends primarily on where a mitochondrion is positioned, either within or at the rim of microtubule bundle. Increasing elongated tubulin levels lowers the number of motile anterograde mitochondria within the microtubule bundle and increases anterograde transport speed at the microtubule bundle rim. We demonstrate that the increased kinesin velocity and density on microtubules consisting of elongated dimers add to the increased mitochondrial dynamics. Our work indicates that the molecular conformation of tubulin contributes to the regulation of mitochondrial motility and as such to the local distribution of mitochondria along axons.

Common mechanisms underlying axonal transport deficits in neurodegenerative diseases: a mini review

“…Similarly, an exome sequencing study confirmed that overexpression of α-tubulin with W407X mutation severely affect inter-microtubule aggregation and track formation ( Smith et al, 2014 ). These results suggest that a normal structure of microtubule is important for neuronal axonal transport ( Van Steenbergen et al, 2022 ). Further, mutations in TUBA4A might result in defective microtubule tracks and possibly contribute to the pathogenesis of ALS.…”

Highly Specialized Mechanisms for Mitochondrial Transport in Neurons: From Intracellular Mobility to Intercellular Transfer of Mitochondria

“…Microtubules polymerize at the plus-end via the incorporation of fresh guanosine triphosphate (GTP) to β-tubulin, which is hydrolyzed to guanosine diphosphate (GDP) in already incorporated tubulin dimers. However, GTP-bound tubulin dimers have also been described in the stable microtubule lattice [ 15 , 16 , 17 ] and are more enriched in axons than dendrites [ 17 , 18 ]. These so-named GTP islands protect microtubule depolymerization and promote self-repair [ 19 , 20 ] but also regulate the local conformation of tubulin to modulate the transport of mitochondria [ 18 ].…”

“…However, GTP-bound tubulin dimers have also been described in the stable microtubule lattice [ 15 , 16 , 17 ] and are more enriched in axons than dendrites [ 17 , 18 ]. These so-named GTP islands protect microtubule depolymerization and promote self-repair [ 19 , 20 ] but also regulate the local conformation of tubulin to modulate the transport of mitochondria [ 18 ]. A recent study showed that anterograde mitochondria halt along GTP-bound elongated dimers within the microtubule bundle but they remain motile at the rim of the microtubule bundle [ 18 ].…”

Characterizing the blood–brain barrier and gut barrier with super-resolution imaging: opportunities and challenges

“…tools have been developed to study neuron properties, functions, and interactions with other cells, [6][7][8] much less attention has been given to the brain vascular and glial cells, particularly at high resolutions. 9 In fact, the visualization of these cells was mostly performed with diffraction-limited optical techniques, such as epifluorescence and confocal microscopy.…”

“… 5 Researchers are thus turning their attention to super-resolution microscopy techniques to complement traditional approaches and gain mechanistic insights. 4 Although a lot of neurophotonic tools have been developed to study neuron properties, functions, and interactions with other cells, 6 – 8 much less attention has been given to the brain vascular and glial cells, particularly at high resolutions. 9 In fact, the visualization of these cells was mostly performed with diffraction-limited optical techniques, such as epifluorescence and confocal microscopy.…”