Autophagy is a conserved cellular recycling system in which cells break down their own components to maintain balance, adapt to stress and survive nutrient shortages. Material destined for degradation is enclosed in double membrane vesicles called autophagosomes, which then fuse with lysosomes where enzymes digest the contents. The resulting building blocks are reused for energy production and new synthesis.

Research shows autophagy operates at several levels. Basal autophagy runs continuously to remove damaged proteins and organelles, especially in long lived cells like neurons. Stress induced autophagy is triggered by starvation, oxidative stress, infection and other challenges. Selective forms target specific structures, such as mitophagy for mitochondria, aggrephagy for protein aggregates and xenophagy for invading microbes.

Key regulators include nutrient sensing pathways centered on mTOR and AMPK, which integrate information about energy and amino acid availability. Transcription factors like TFEB control lysosome and autophagy gene expression. Genetic studies in yeast, animals and humans have identified many core autophagy genes and linked their disruption to disease.

Impaired or misregulated autophagy is associated with neurodegenerative disorders, cancer, metabolic disease, infections and aging. In neurodegeneration, defective clearance of protein aggregates and damaged mitochondria is a major theme. In cancer, autophagy may suppress tumor initiation by limiting damage, yet later support tumor growth by supplying nutrients. During infection, autophagy can either help eliminate pathogens or be subverted by them.

Because autophagy influences longevity, metabolism, immunity and cell survival, it is an active therapeutic target. Approaches include pharmacological activation or inhibition, dietary interventions such as fasting and modulation of specific selective autophagy pathways.