title: Expression of axonal protein degradation machinery in sympathetic neurons is regulated by nerve growth factor.
abstract: Deficiencies in protein degradation and proteolytic function within neurons are linked to a number of neurodegenerative diseases and developmental disorders. Compartmentalized cultures of peripheral neurons were used to investigate the properties and relative abundance of the proteolytic machinery in the axons and cell bodies of sympathetic and sensory neurons. Immunoblotting of axonal proteins demonstrated that LAMP2, LC3, and PSMA2 were abundant in axons, suggesting that lysosomes, autophagosomes and proteasomes were located in axons. Interestingly, the expression of proteins associated with lysosomes and proteasomes were upregulated selectively in axons by NGF stimulation of the distal axons of sympathetic neurons, suggesting that axonal growth and maintenance requires local protein turnover. The regulation of the abundance of both proteasomes and lysosomes in axons by NGF provides a link between protein degradation and the trophic status of peripheral neurons. Inhibition of proteasomes located in axons resulted in an accumulation of ubiquitinated proteins in these axons. In contrast, lysosome inhibition in axons did not result in an accumulation of ubiquitinated proteins or the transferrin receptor, a transmembrane protein degraded by lysosomes. Interestingly, lysosomes were transported both retrogradely and anterogradely, so it is likely that ubiquitinated proteins that are normally destined for degradation by lysosomes in axons can be transported to the cell bodies for degradation. In summary, proteasomal degradation occurs locally, whereas proteins degraded by lysosomes can most likely either be degraded locally in axons or be transported to cell bodies for degradation.
authors.affiliation: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan 48109, USA.
authors.forename: John P
authors.initials: JP
authors.lastname: Frampton
authors.forename: Chong
authors.initials: C
authors.lastname: Guo
authors.forename: Brian A
authors.initials: BA
authors.lastname: Pierchala
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism*; D002478:Cells, Cultured; D007150:Immunohistochemistry; D008247:Lysosomes / Q000378:metabolism; D020932:Nerve Growth Factor / Q000378:metabolism*; D009475:Neurons, Afferent / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D059748:Proteolysis; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D020932:Nerve Growth Factor; D046988:Proteasome Endopeptidase Complex