Membrane trafficking and transport

Abstract

ALS= : amyotrophic lateral sclerosis; BMP= : bone morphogenic protein; CMT= : Charcot-Marie-Tooth; CMT2= : Charcot-Marie-Tooth type II; COP= : coat complex; dHMN= : distal hereditary motor neuronopathy; ER= : endoplasmic reticulum; ERGIC= : endoplasmic reticulum–Golgi complex intermediate compartment; ESCRT= : endosomal sorting complex required for transport; GTPase= : guanidine triphosphatase; HAP= : huntingtin-associated protein; HSAN= : hereditary sensory and autonomic neuropathy; HSP= : hereditary spastic paraplegia; MFN2= : mitofusin 2; MVB= : multivesicular body; PI= : phosphoinositide; REEP= : receptor-expression-enhancing protein; RTN= : reticulon; SNARE= : soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor; TGN= : trans-Golgi network; VAMP= : vesicle associated membrane protein; VAPB= : vesicle-associated membrane protein-associated protein B. Normal neural function depends on the appropriate delivery and removal of proteins and lipids at pre-, post- or extrasynaptic membranes. The membrane transport system comprises the endoplasmic reticulum (ER), the Golgi complex, secretory vesicles, endosomes, and lysosomes. This system is involved in 2 fundamental cellular pathways, the secretory and the endocytic pathway. The secretory pathway transports most of the transmembrane and secreted proteins from their site of synthesis in the ER to their final destinations, including the presynaptic membrane. Endocytosis participates in control of the composition of the plasma membrane, intra- and intercellular signaling, and uptake of essential nutrients. Vesicular trafficking along the secretory and endocytic pathways depends on interactions of several membrane proteins with the cytoskeleton. The directionality and specificity of membrane trafficking depends on a large number of transmembrane, cytoskeletal, and adaptor proteins that are involved in membrane shaping and remodeling, and in vesicular trafficking along microtubules. Mutations affecting many of these proteins manifest with different phenotypes, including hereditary spastic paraplegia (HSP), distal hereditary motor neuronopathy (dHMN), Charcot-Marie-Tooth type II (CMT2) neuropathy, and hereditary sensory and autonomic neuropathy (HSAN). The mechanisms of membrane trafficking, secretory pathways, and endocytosis, and their clinical correlations have been recently reviewed.1,–,13 Membrane trafficking involves several common mechanisms, including vesicular biogenesis, transport along microtubules, and tethering and fusion of the vesicle membrane with the recipient compartment (figure). Figure Mechanisms involved in the secretory and endocytic pathways in neurons The secretory pathway proteins from their site of synthesis in the endoplasmic reticulum (ER) to the Golgi complex and from there to their final destinations in the membrane or synaptic vesicles. ER structure depends of interactions of several interacting membrane proteins, including atlastatin-1, receptor-expression-enhancing protein1 (REEP), and spastin, which also …