Calpain Hydrolysis of α- and β2-Adaptins Decreases Clathrin-dependent Endocytosis and May Promote Neurodegeneration

Abstract

Clathrin-dependent endocytosis is mediated by a tightly regulated network of molecular interactions that provides essential protein-protein and protein-lipid binding activities. Here we report the hydrolysis of the ␣-and ␤2-subunits of the tetrameric adaptor protein complex 2 by calpain. Calcium-dependent ␣-and ␤2-adaptin hydrolysis was observed in several rat tissues, including brain and primary neuronal cultures. Neuronal ␣-and ␤2-adaptin cleavage was inducible by glutamate stimulation and was accompanied by the decreased endocytosis of transferrin. Heterologous expression of truncated forms of the ␤2-adaptin subunit significantly decreased the membrane recruitment of clathrin and inhibited clathrin-mediated receptor endocytosis. Moreover, the presence of truncated ␤2-adaptin sensitized neurons to glutamate receptor-mediated excitotoxicity. Proteolysis of ␣-and ␤2-adaptins, as well as the accessory clathrin adaptors epsin 1, adaptor protein 180, and the clathrin assembly lymphoid myeloid leukemia protein, was detected in brain tissues after experimentally induced ischemia and in cases of human Alzheimer disease. The present study further clarifies the central role of calpain in regulating clathrin-dependent endocytosis and provides evidence for a novel mechanism through which calpain activation may promote neurodegeneration: the sensitization of cells to glutamate-mediated excitotoxicity via the decreased internalization of surface receptors.

Slow Excitotoxicity in Alzheimer's Disease

“…Recent studies using yeast have indicated a role of PICALM in A␤ toxicity [113,114]. Changes in adaptor proteins decrease clathin mediated receptor endocytosis and sensitizes neurons to glutamate receptor excitotoxicity [115]. Together, these findings suggest that alterations in PICALM may affect iron metabolism, processing of A␤PP, endocytosis of receptors or exocytosis of neurotransmitters, with effects on neuronal excitation and excitotoxicity.…”

Role of Phosphatidylinositol Clathrin Assembly Lymphoid-Myeloid Leukemia (PICALM) in Intracellular Amyloid Precursor Protein (APP) Processing and Amyloid Plaque Pathogenesis

“…The transferrin receptor is ubiquitously expressed and is known to undergo clathrin-mediated endocytosis with rapid recycling to the cell surface (26). PICALM, however, can selectively internalize some cargoes over others (20,27).…”

Reply to Valenza and Cattaneo: SIRT2-mediated neuroprotection and cholesterol dyshomeostasis in Huntington’s disease

“…The absence of changes in sterol biosynthesis gene expression in primary striatal neurons exposed to mutant huntingtin fragments replicates previous data in this system and also concurs with previous microarray studies of human and mouse HD brains and microdissected neuronal samples (3). Our study used two different models with different time courses (3,4), and thus, the two different endpoints were reported. The observations of increased sterol accumulation through an apparently sterol regulatory element binding proteinindependent mechanism are also consistent with those of another independent study (5).…”