Figure 1. Main functions of the lysosome and their relationship with key cellular processes.

Lysosomes are involved in the degradation and recycling of extracellular material, via endocytosis, and intracellular material, via autophagy. In these processes lysosomes fuse with late endosomes and with autophagosomes, respectively. The resulting breakdown products are used to generate new cellular components and energy in response to the nutritional needs of the cell. Lysosomes also undergo Ca²⁺ regulated exocytosis to secrete their content into the extracellular space and to repair damaged plasma membrane. Upon plasma membrane injury, lysosomes rapidly migrate to the damaged site and fuse with the plasma membrane to allow efficient resealing. More recently, lysosomes have been identified as signaling organelles that can sense nutrient availability and activate a lysosome-to-nucleus signaling pathway that mediates the starvation response and regulates energy metabolism.