**TL;DR** Damaged mitochondria in distal hippocampal axons recruit Parkin, LC3-positive autophagosomes, and lysosomes locally, allowing mitophagy without retrograde transport to the soma. This axonal mitophagy requires both PINK1 and Parkin. **Key findings** - Local mt-KR activation damaged only irradiated axonal mitochondria: fragmented/rounded morphology arose in 22% of illuminated mitochondria vs 4% outside the region (P < 0.0001). Antimycin A locally reduced TMRM intensity to 57% of initial within 8 min in the perfusion chamber. - Damaged axonal mitochondria recruited autophagosomes and lysosomes locally: Antimycin A increased GFP-LC3–positive mitochondria from 5% to 20% (P < 0.05), LAMP1-YFP colocalization from 9% to 28% (P < 0.01), and dual RFP-LC3/LAMP1-YFP colocalization from 5% to 19% (P < 0.05); with lysosomal inhibitors, 60% of mitochondria became LAMP1-YFP–positive (P < 0.05). - Parkin was recruited to damaged axonal mitochondria: mt-KR activation recruited YFP-Parkin to 10% of targeted mitochondria vs 3% with mt-DsRed (P < 0.01); Antimycin A increased Parkin-positive mitochondria from 5% to 40% (P < 0.05), and Veratridine recruited Parkin to 39% (P < 0.05). - Axonal mitophagy required PINK1 and Parkin: in Parkin+/+ axons, LC3 colocalization increased from 4% to 33% after Antimycin A (P < 0.05), but not in Parkin−/− axons (P = 1); in PINK1+/+ axons, LC3 colocalization increased from 3% to 18% (P < 0.01), whereas PINK1−/− axons showed only 3% to 8% (P = 0.09), rescued by PINK1-FLAG to 6% to 16% (P < 0.05). **Methods** - Rat and mouse hippocampal neurons were cultured, transfected with fluorescent markers, and imaged live in microfluidic devices allowing local perfusion of axons with Antimycin A or Veratridine; mt-KR was activated locally with a 555-nm laser to damage a small subset of axonal mitochondria. - Mitochondrial membrane potential was measured with TMRM; Parkin and LC3 recruitment were quantified by line-scan fluorescence intensity along axons, with Parkin-positive mitochondria scored as YFP-Parkin peaks at least twice neighboring background. - Genetic requirements were tested using Parkin−/− mice and PINK1−/− rats, with rescue by mCherry-Parkin or PINK1-FLAG; statistical comparisons used Mann–Whitney U tests, with P < 0.05 considered significant. **Limitations** - The paper states that antibodies were not available to detect endogenous Parkin recruitment in axons, so YFP-Parkin overexpression could be argued as a caveat; however, failure of mitophagy in PINK1−/− rats and Parkin−/− mice indicates endogenous proteins are necessary. - The paper notes that not all damaged mitochondria recruited Parkin or LC3; only 40% of Antimycin A–depolarized mitochondria were Parkin positive and 20% were engulfed in autophagosomes, likely underestimates because mitoautophagosomes are transient, and other mitochondrial changes, stochastic onset, or limiting PINK1/Parkin/autophagosomal machinery may be required. - The paper states it cannot exclude that some damaged mitochondria return to the soma, particularly from proximal axons/dendrites, and that how PINK1 is activated in axons is unknown; evident limitations include the in vitro cultured hippocampal neuron system and acute pharmacological/photosensitizer damage rather than in vivo physiological damage.

Mitophagy of damaged mitochondria occurs locally in distal neuronal axons and requires PINK1 and Parkin

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