Mechanisms of amine accumulation in, and egress from, lysosomes

The human body is continuously exposed to small organic molecules containing one or more basic nitrogen atoms. Many of these are endogenous (i.e., neurotransmitters, polyamines and biogenic amines), while others are exogenously supplied in the form of drugs, foods and pollutants. It is well-known that many amines have a strong propensity to specifically and substantially accumulate in highly acidic intracellular compartments, such as lysosomes, through a mechanism referred to as ion trapping. It is also known that cells have acquired the unique ability to sense and respond to amine accumulation in lysosomes in an effort to prevent potential negative consequences associated with hyperaccumulation. We describe here methods that are used to evaluate the dynamics of amine accumulation in, and egress from, lysosomes. Moreover, we highlight specific proteins that are thought to play important roles in these pathways. A theoretical model describing lysosomal amine dynamics is described and shown to adequately fit experimental kinetic data. The implications of this research in understanding and treating disease are discussed.