Mitochondrial Microautophagy: An Emerging Pathway in Maintaining Mitochondrial Homeostasis

Background:Mitochondrial quality control has traditionally been attributed to mitophagy. However, emerging evidence indicates that mitochondrial microautophagy represents a distinct quality control pathway. This pathway enables selective removal of damaged mitochondrial subdomains while preserving overall organelle integrity. Therefore, mitochondrial microautophagy can be viewed as a redox-adaptive, sub-organelle quality control system that responds to localized mitochondrial stress.Scope of Review: In this review, we integrate recent mechanistic, imaging, and molecular studies to establish an updated framework of mitochondrial microautophagy. We describe this process as a sequential pathway involving damage sensing, mitochondria-lysosome contact formation, lysosomal membrane remodeling, selective degradation, and metabolic recycling. Localized reactive oxygen species (ROS) serve as important signals during this process. ROS define specific damage microdomains and facilitate selective mitochondrial component recognition. Subsequent cargo delivery and degradation are regulated by multiple molecular modules. These modules include the ubiquitin-autophagy-related protein 8 system, vacuolar-type H⁺-ATPase-dependent membrane remodeling, Ras-related in brain-endosomal sorting complexes required for transport signaling, the spermatogenesis-associated 18/mitochondria-eating protein pathway, and the mechanistic target of rapamycin complex 1-transcription factor EB and nuclear factor erythroid 2-related factor 2 stress-response networks.Outstanding Questions: Despite substantial progress, several fundamental questions remain unresolved. The mechanisms underlying cargo recognition require further clarification. The existence of specific redox-sensitive receptors remains to be determined. In addition, future technological advances will provide deeper insights into this pathway.Conclusions: Understanding mitochondrial microautophagy may reveal new therapeutic opportunities for mitochondrial dysfunction-associated disorders, including neurodegeneration, ischemic injury, metabolic disorders, and aging. Antioxid. Redox Signal. 00, 000-000.