Local ROS and inefficient autophagosome formation limit Optineurin-mediated mitophagy in neurons.

Mitophagy is a quality control mechanism that maintains neuronal health by removing damaged mitochondria. In neurons, mitophagy can be driven by Optineurin (OPTN), a selective autophagy receptor recruited in response to oxidative stress. However, mechanistic studies of mitophagy have relied mainly on non-neuronal cell lines and acute damage paradigms. It remains unknown whether these findings translate to neurons under physiological stress conditions. Here, we investigated the temporal dynamics of OPTN-dependent mitophagy under mild oxidative stress using live-cell imaging in primary rat hippocampal neurons. We found that autophagosomes failed to readily engulf OPTN-positive (OPTN+) mitochondria, revealing a previously unidentified rate-limiting step in neuronal OPTN-mediated mitophagy. Additionally, OPTN+ mitochondria colocalized with acidified lysosomes over timescales significantly longer than previously reported. These OPTN+ mitochondria displayed locally elevated reactive oxygen species (ROS). Scavenging mitochondrial ROS increased lysosomal colocalization with damaged mitochondria and accelerated mitophagy progression. Together, these findings indicate that redox signaling contributes to the slow timescale of OPTN-mediated mitophagy in neurons.