Temporal landscape of mitochondrial proteostasis governed by the UPR.

Breakdown of mitochondrial proteostasis activates quality control pathways including the mitochondrial unfolded protein response (UPR) and PINK1/Parkin mitophagy. However, beyond the up-regulation of chaperones and proteases, we have a limited understanding of how the UPR remodels and restores damaged mitochondrial proteomes. Here, we have developed a functional proteomics framework, termed MitoPQ (Mitochondrial Proteostasis Quantification), to dissect the UPR's role in maintaining proteostasis during stress.

Mitochondrial degradation: Mitophagy and beyond.

Mitochondria are central hubs of cellular metabolism that also play key roles in signaling and disease. It is therefore fundamentally important that mitochondrial quality and activity are tightly regulated. Mitochondrial degradation pathways contribute to quality control of mitochondrial networks and can also regulate the metabolic profile of mitochondria to ensure cellular homeostasis.

ATG4 family proteins drive phagophore growth independently of the LC3/GABARAP lipidation system.

The sequestration of damaged mitochondria within double-membrane structures termed autophagosomes is a key step of PINK1/Parkin mitophagy. The ATG4 family of proteases are thought to regulate autophagosome formation exclusively by processing the ubiquitin-like ATG8 family (LC3/GABARAPs). We discover that human ATG4s promote autophagosome formation independently of their protease activity and of ATG8 family processing.

LC3/GABARAPs drive ubiquitin-independent recruitment of Optineurin and NDP52 to amplify mitophagy.

Current models of selective autophagy dictate that autophagy receptors, including Optineurin and NDP52, link cargo to autophagosomal membranes. This is thought to occur via autophagy receptor binding to Atg8 homologs (LC3/GABARAPs) through an LC3 interacting region (LIR). The LIR motif within autophagy receptors is therefore widely recognised as being essential for selective sequestration of cargo.