Activity-dependent trafficking of lysosomes in dendrites and dendritic spines.

In neurons, lysosomes, which degrade membrane and cytoplasmic components, are thought to primarily reside in somatic and axonal compartments, but there is little understanding of their distribution and function in dendrites. Here, we used conventional and two-photon imaging and electron microscopy to show that lysosomes traffic bidirectionally in dendrites and are present in dendritic spines. We find that lysosome inhibition alters their mobility and also decreases dendritic spine number. Furthermore, perturbing microtubule and actin cytoskeletal dynamics has an inverse relationship on the distribution and motility of lysosomes in dendrites. We also find trafficking of lysosomes is correlated with synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors. Strikingly, lysosomes traffic to dendritic spines in an activity-dependent manner and can be recruited to individual spines in response to local activation. These data indicate the position of lysosomes is regulated by synaptic activity and thus plays an instructive role in the turnover of synaptic membrane proteins

Activity- and ubiquitin-dependent turnover of AMPA receptors and the trafficking of lysosomes in dendrites and dendritic spines

Changes in synaptic strength underlie the basis of learning and memory and are controlled, in part, by the insertion and removal of AMPA-type glutamate receptors. Once internalized, these receptors maybe recycled back to the plasma membrane by subunit-specific interactions with other proteins or by post-translational modifications such as phosphorylation. Ubiquitination, another post-translational modification, has recently emerged as a key signal that regulates the recycling and trafficking of glutamate receptors. However, the activity-dependent rules that govern internalization and degradation have not been fully elucidated.This dissertation was designed in two parts; (1) to investigate the molecular specificity and activity-dependent rules of AMPAR ubiquitination via a deubiquinating enzyme, USP8 and (2) to determine how the lysosome, an organelle that degrades AMPARs, may also respond to synaptic cues to coordinate degradation of membrane proteins such as AMAPRs. We approached the first part of this study by evaluating the distribution and activation of USP8 and how neuronal activity alters USP8 distribution and activation. Using mainly biochemical techniques such as western blot and immunopreciptation as well as immunostaining, we showed that NMDAR signaling is required to spare AMPARs from ubiquitin-dependent internalization and degradation. To elucidate activity-dependent trafficking of lysosomes, we utilized electron microscopy and confocal live imaging of neurons and 2-photon imaging of organotypic hippocampal slices to visualize lysosomes. We found that lysosomes are positioned locally at dendritic spines and can be recruited do a dendritic spine in an activity-dependent manner. These findings provide evidence for activity-dependent control of a DUB, USP8, and an organelle, the lysosome, at synapses. We showed the dynamic regulation of USP8 is critical in maintaining synapses and scaling during homeostatic plasticity and that neuronal activity can signal to the lysosome to locally degrade membrane proteins. These studies suggest that localized degradation can play an active role in remodeling synapses to facilitate plastic events and help locally maintain cellular homeostasis

Activity- and ubiquitin-dependent turnover of AMPA receptors and the trafficking of lysosomes in dendrites and dendritic spines

Changes in synaptic strength underlie the basis of learning and memory and are controlled, in part, by the insertion and removal of AMPA-type glutamate receptors. Once internalized, these receptors maybe recycled back to the plasma membrane by subunit-specific interactions with other proteins or by post-translational modifications such as phosphorylation. Ubiquitination, another post-translational modification, has recently emerged as a key signal that regulates the recycling and trafficking of glutamate receptors. However, the activity-dependent rules that govern internalization and degradation have not been fully elucidated.This dissertation was designed in two parts; (1) to investigate the molecular specificity and activity-dependent rules of AMPAR ubiquitination via a deubiquinating enzyme, USP8 and (2) to determine how the lysosome, an organelle that degrades AMPARs, may also respond to synaptic cues to coordinate degradation of membrane proteins such as AMAPRs. We approached the first part of this study by evaluating the distribution and activation of USP8 and how neuronal activity alters USP8 distribution and activation. Using mainly biochemical techniques such as western blot and immunopreciptation as well as immunostaining, we showed that NMDAR signaling is required to spare AMPARs from ubiquitin-dependent internalization and degradation. To elucidate activity-dependent trafficking of lysosomes, we utilized electron microscopy and confocal live imaging of neurons and 2-photon imaging of organotypic hippocampal slices to visualize lysosomes. We found that lysosomes are positioned locally at dendritic spines and can be recruited do a dendritic spine in an activity-dependent manner. These findings provide evidence for activity-dependent control of a DUB, USP8, and an organelle, the lysosome, at synapses. We showed the dynamic regulation of USP8 is critical in maintaining synapses and scaling during homeostatic plasticity and that neuronal activity can signal to the lysosome to locally degrade membrane proteins. These studies suggest that localized degradation can play an active role in remodeling synapses to facilitate plastic events and help locally maintain cellular homeostasis

Ubiquitin-dependent trafficking and turnover of ionotropic glutamate receptors

Changes in synaptic strength underlie the basis of learning and memory and are controlled, in part, by the insertion or removal of AMPA-type glutamate receptors at the postsynaptic membrane of excitatory synapses. Once internalized, these receptors may be recycled back to the plasma membrane by subunit-specific interactions with other proteins or by post-translational modifications such as phosphorylation. Alternatively, these receptors may be targeted for destruction by multiple degradation pathways in the cell. Ubiquitination, another post-translational modification, has recently emerged as a key signal that regulates the recycling and trafficking of glutamate receptors. In this review, we will discuss recent findings on the role of ubiquitination in the trafficking and turnover of ionotropic glutamate receptors and plasticity of excitatory synapses

Activity-dependent trafficking of lysosomes in dendrites and dendritic spines.

In neurons, lysosomes, which degrade membrane and cytoplasmic components, are thought to primarily reside in somatic and axonal compartments, but there is little understanding of their distribution and function in dendrites. Here, we used conventional and two-photon imaging and electron microscopy to show that lysosomes traffic bidirectionally in dendrites and are present in dendritic spines. We find that lysosome inhibition alters their mobility and also decreases dendritic spine number. Furthermore, perturbing microtubule and actin cytoskeletal dynamics has an inverse relationship on the distribution and motility of lysosomes in dendrites. We also find trafficking of lysosomes is correlated with synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors. Strikingly, lysosomes traffic to dendritic spines in an activity-dependent manner and can be recruited to individual spines in response to local activation. These data indicate the position of lysosomes is regulated by synaptic activity and thus plays an instructive role in the turnover of synaptic membrane proteins