# Energy stress activates AMPK to arrest mitochondria via phosphorylation of TRAK1

## TL;DR

This paper explains how cells stop mitochondria from moving when energy is low, helping to keep energy production where it's most needed.

## Contribution

The study identifies a novel mechanism where AMPK phosphorylates TRAK1 to arrest mitochondria during energy stress.

## Key findings

- AMPK phosphorylates TRAK1 to arrest mitochondria when ATP levels are low.
- Mitochondrial arrest occurs without triggering mitophagy in response to antimycin A.
- Actin fibers accumulate near mitochondria to anchor them during energy stress.

## Abstract

Falk et al. identify a mechanism coupling mitochondrial movement to energy demand. When energy levels are low, the energy-sensing kinase AMPK phosphorylates the motor/adaptor protein TRAK1, arresting mitochondria via the actin cytoskeleton. This mechanism likely helps to position mitochondria where they are most needed.

Neuronal signaling requires large amounts of ATP, making neurons particularly sensitive to defects in energy homeostasis. Mitochondrial movement and energy production are therefore regulated to align local demands with mitochondrial output. Here, we report a pathway that arrests mitochondria in response to decreases in the ATP-to-AMP ratio, an indication that ATP consumption exceeds supply. In neurons and cell lines, low concentrations of the electron transport chain inhibitor antimycin A decrease the production of ATP and concomitantly arrest mitochondrial movement without triggering mitophagy. This arrest is accompanied by the accumulation of actin fibers adjacent to the mitochondria, which serve as an anchor that resists the associated motors. This arrest is mediated by activation of the energy-sensing kinase AMPK, which phosphorylates TRAK1. This mechanism likely helps maintain cellular energy homeostasis by anchoring energy-producing mitochondria in places where they are most needed.