This proposal focuses on the dynamic behavior of mitochondria in cells. In particular, it examines two pathways that control that behavior via different posttranslational modifications of the motor-adaptor protein milton/TRAK1/2. The movement of mitochondria is driven by two microtubule-based motors, Kinesin-1 and Dynein, and these motors are bound to the mitochondrial surface by a motor/adaptor complex consisting of the proteins milton and Miro (also called TRAK1/2 and RhoT1/2). The first regulatory pathway we here investigate involves the enzyme O-GlcNAc Transferase (OGT), an enzyme that catalyzes the addition of the sugar residue N-Acetyl Glucosamine to serine and threonine residues on proteins. We and others have found that this enzyme GlcNAcylates milton. We also find that expression of OGT in neurons arrests the movement of the mitochondria and that this occurs directly through its substrate milton. Because OGT is thought to be a nutrient sensor that is more active when glucose levels are high, we hypothesized that the OGT pathway will stop mitochondria under conditions of high extracellular glucose and indeed we observe that mitochondrial movement is decreased in axons via this pathway when glucose levels are raised. We propose to examine the mechanism by which OGT halts mitochondria and also the significance of OGT and milton GlcNAcylation for the distribution of mitochondria in axons. The second regulatory pathway that is examined in this grant also concerns mitochondrial/cytoskeletal interactions and their regulation by a posttranslational modification, in this case phosphorylation of milton. Through the motors that move mitochondria and also additional likely anchoring proteins, mitochondria normally exist in a close relationship with microtubules. We find that this situation is very different in dividing cells. When a cell enters mitosis, the microtubules are dismantled and reform as the spindle apparatus. During mitosis, mitochondria are excluded from the regions of the cell that contain microtubules. We have found that milton becomes phosphorylated during the cell cycle, probably by cdk1. We will investigate the significance of this phosphorylation for the state of the motor/adaptor complex and its significance for the mitotic redistribution of mitochondria.

Public Health Relevance

Mitochondria and their dynamics are crucial to the survival of many cell types, but especially neurons. The present proposal examines two pathways regulating their dynamics: one that may help neurons cope with a changing nutrient environment and another that may be crucial during the division of non-neuronal cells. Defects in controlling mitochondrial dynamics are likely to cause neurodegeneration and may also impair proper inheritance of chromosomes by daughter cells.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Synapses, Cytoskeleton and Trafficking Study Section (SYN)
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Gindhart, Joseph G
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Boston Children's Hospital
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Misgeld, Thomas; Schwarz, Thomas L (2017) Mitostasis in Neurons: Maintaining Mitochondria in an Extended Cellular Architecture. Neuron 96:651-666
Gornstein, Erica L; Schwarz, Thomas L (2017) Neurotoxic mechanisms of paclitaxel are local to the distal axon and independent of transport defects. Exp Neurol 288:153-166
Cartoni, Romain; Pekkurnaz, Gulcin; Wang, Chen et al. (2017) A high mitochondrial transport rate characterizes CNS neurons with high axonal regeneration capacity. PLoS One 12:e0184672
Su, Cathy; Schwarz, Thomas L (2017) O-GlcNAc Transferase Is Essential for Sensory Neuron Survival and Maintenance. J Neurosci 37:2125-2136
Shlevkov, Evgeny; Kramer, Tal; Schapansky, Jason et al. (2016) Miro phosphorylation sites regulate Parkin recruitment and mitochondrial motility. Proc Natl Acad Sci U S A 113:E6097-E6106
Cartoni, Romain; Norsworthy, Michael W; Bei, Fengfeng et al. (2016) The Mammalian-Specific Protein Armcx1 Regulates Mitochondrial Transport during Axon Regeneration. Neuron 92:1294-1307
Chung, Jarom Yan-Ming; Steen, Judith Arunodhaya; Schwarz, Thomas Lewis (2016) Phosphorylation-Induced Motor Shedding Is Required at Mitosis for Proper Distribution and Passive Inheritance of Mitochondria. Cell Rep 16:2142-2155
Ashrafi, Ghazaleh; Schwarz, Thomas L (2015) PINK1- and PARK2-mediated local mitophagy in distal neuronal axons. Autophagy 11:187-9
Gornstein, Erica; Schwarz, Thomas L (2014) The paradox of paclitaxel neurotoxicity: Mechanisms and unanswered questions. Neuropharmacology 76 Pt A:175-83
Ashrafi, Ghazaleh; Schlehe, Julia S; LaVoie, Matthew J et al. (2014) Mitophagy of damaged mitochondria occurs locally in distal neuronal axons and requires PINK1 and Parkin. J Cell Biol 206:655-70

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