TSG101 negatively regulates mitochondrial biogenesis in axons

Abstract

There is a tight association between mitochondrial dysfunction and neurodegenerative diseases and axons that are particularly vulnerable to degeneration, but how mitochondria are maintained in axons to support their physiology remains poorly defined. In an in vivo forward genetic screen for mutants altering axonal mitochondria, we identified tsg101. Neurons mutant for tsg101 exhibited an increase in mitochondrial number and decrease in mitochondrial size. TSG101 is best known as a component of the endosomal sorting complexes required for transport (ESCRT) complexes; however, loss of most other ESCRT components did not affect mitochondrial numbers or size, suggesting TSG101 regulates mitochondrial biology in a noncanonical, ESCRT-independent manner. The TSG101-mutant phenotype was not caused by lack of mitophagy, and we found that autophagy blockade was detrimental only to the mitochondria in the cell bodies, arguing mitophagy and autophagy are dispensable for the regulation of mitochondria number in axons. Interestingly, TSG101 mitochondrial phenotypes were instead caused by activation of PGC-1ɑ/Nrf2-dependent mitochondrial biogenesis, which was mTOR independent and TFEB dependent and required the mitochondrial fission–fusion machinery. Our work identifies a role for TSG101 in inhibiting mitochondrial biogenesis, which is essential for the maintenance of mitochondrial numbers and sizes, in the axonal compartment.

Hallmarks and Molecular Tools for the Study of Mitophagy in Parkinson’s Disease

“…Another controversial concept in the field of mitophagy, which has been analyzed with the mito-QC and mtKeima reporters, revolves around soma-localized and axonal mitochondria. In particular, whether mitochondria in these compartments are differentially susceptible to mitophagy is still incompletely understood [180][181][182]. A sophisticated study by Harbauer et al has begun to address this issue, demonstrating that axonal mitochondria undergo local PINK1/Parkin-mediated mitophagy [183].…”

Crosstalk of organelles in Parkinson’s disease – MiT family transcription factors as central players in signaling pathways connecting mitochondria and lysosomes

“…A recent genetic screen in Drosophila identified TSG101 (tumor susceptibility gene 101) as regulator of mitochondrial number and size in fly neuronal axons. Mitochondrial biogenesis in neuronal axons in a TSG101 mutant background was independent of PGC-1ɑ, NRF2, and mTOR but required TFEB and the mitochondrial fission–fusion machinery [ 184 ].…”

Analysis of Mitochondrial Dynamics in AdultDrosophilaAxons

“…We introduce two methodological approaches for the in-depth study of mitochondrial morphology and dynamics in adult axons in vivo (see Protocol: Clonal Imaging of Mitochondria in the Dissected Fly Wing [Maddison et al 2022]; Protocol: Live Imaging of Mitochondria in the Intact Fly Wing [Mattedi et al 2022]). These are useful both for hypothesis-driven approaches Vagnoni and Bullock 2018) and for discovering new modulators of mitochondrial function through completely unbiased genetic screening (Smith et al 2019b;Lin et al 2021). For the latter, male flies can be fed ethyl methanesulfonate and crossed with females containing mosaic analysis with a repressible cell marker (MARCM) machinery.…”

“…One wing can then be dissected from F 1 males and used to screen for axon or mitochondrial phenotypes resulting from the random mutagenesis specifically in clones. Isolated males with interesting phenotypes are saved and bred to recover the mutation of interest, which can be found using whole-genome sequencing and deficiency mapping if lethal (Neukomm et al 2014(Neukomm et al , 2017Smith et al 2019b;Lin et al 2021). These protocols are useful for independent evaluations of mitochondrial morphology and trafficking, respectively, to gain further knowledge of mitochondrion-neuron cross talk.…”