Restricted mitochondrial protein acetylation initiates mitochondrial autophagy

Abstract

SummaryBecause nutrient-sensing nuclear and cytosolic acetylation mediates cellular autophagy, we investigated whether mitochondrial acetylation modulates mitochondrial autophagy (mitophagy). Knockdown of GCN5L1, a component of the mitochondrial acetyltransferase machinery, diminished mitochondrial protein acetylation and augmented mitochondrial enrichment of autophagy mediators. This program was disrupted by SIRT3 knockdown. Chronic GCN5L1 depletion increased mitochondrial turnover and reduced mitochondrial protein content and/or mass. In parallel, mitochondria showed blunted respiration and enhanced 'stressresilience'. Genetic disruption of autophagy mediators Atg5 and p62 (also known as SQSTM1), as well as GCN5L1 reconstitution, abolished deacetylation-induced mitochondrial autophagy. Interestingly, this program is independent of the mitophagy E3-ligase Parkin (also known as PARK2). Taken together, these data suggest that deacetylation of mitochondrial proteins initiates mitochondrial autophagy in a canonical autophagy-mediator-dependent program and shows that modulation of this regulatory program has ameliorative mitochondrial homeostatic effects.

SirT3 Regulates the Mitochondrial Unfolded Protein Response

“…2I), suggesting a parkin-independent mechanism of mitophagy. In agreement with this possibility, mitophagy induced by restricted mitochondrial protein acetylation has also been found to be independent of parkin (34).…”

GCN5-like Protein 1 (GCN5L1) Controls Mitochondrial Content through Coordinated Regulation of Mitochondrial Biogenesis and Mitophagy

“…Here it was shown that the expression of GCN5L1 led to an increase in lysine acetylation in the mitochondria, and that this worked in opposition to the mitochondrial deacetylase SIRT3 (16). We then found that a decrease in acetylation caused by GCN5L1 shRNA knockdown in HepG2 cells acted as a molecular marker of mitochondrial nutrient depletion, and that this resulted in an increase in mitophagy (14). These findings were in agreement with previous studies that suggested GCN5L1 (also known as BLOC1S1) may be involved in the formation of lysosome-related organelles (22), and that its loss was associated with an increase in mitophagy in a unbiased genetic siRNA library screen (23).…”

“…2, B and C). The presence of elevated p62 levels have variously been ascribed to either an increase in autophagic activity (14) or a block in autophagic flux (18). While the increased transcript levels (Fig.…”

“…Ϫ/Ϫ MEFs Are Not Deficient in Mitochondrial Content-We previously demonstrated that HepG2 liver cells with shRNA-depleted GCN5L1 levels were deficient in mitochondrial content, and that this led to a reduction in their oxidative respiration capacity (14). We therefore examined whether MEF KO cells that are completely deficient in GCN5L1 exhibited a similar phenotype.…”

“…Given the importance of mitochondria to the survival of the cell, it is expected that there is a high degree of regulation and coordination between these two opposing pathways. We therefore resolved to investigate these dual mechanisms in the context of General Control of Amino Acid Synthesis 5-like 1 (GCN5L1), 2 a mitochondrial protein that we recently reported as controlling organelle clearance by mitophagy (14). Here we show that genetic deletion of GCN5L1 leads to an up-regulation of Transcription Factor EB (TFEB), a transcription factor which acts as a master regulator of autophagy (15).…”