Dynamic bi-directional phosphorylation events associated with the reciprocal regulation of synapses during homeostatic up- and down-scaling

Abstract

Homeostatic synaptic scaling allows for bi-directional adjustment of the strength of synaptic connections in response to changes in their input. Protein phosphorylation modulates many neuronal and synaptic processes, but it has not been studied on a global, proteome-wide scale during synaptic scaling. To examine this, we used LC-MS/MS analyses to measure changes in the phosphoproteome in response to up- or down-scaling in cultured cortical neurons over minutes to 24 hours. Out of 45,000 phosphorylation events measured, ~3,300 (associated with 1,280 phospho-proteins) were regulated by homeostatic scaling. The activity-sensitive phosphoproteins were predominantly located at synapses and involved in cytoskeletal reorganization. We identified many early transient phosphorylation events which could serve as sensors for the activity offset as well as late and/or persistent phosphoregulation that could represent effector mechanisms driving the homeostatic response. Much of the persistent phosphorylation was reciprocally regulated by up- or down-scaling, suggesting that the mechanisms underlying these two poles of synaptic regulation make use of a common signaling axis.

Autophagy regulates neuronal excitability by controlling cAMP/Protein Kinase A signaling

“…One of the most intriguing finding in our study is that the autophagy-mediated PKA signaling primarily regulates the phosphorylation state of cytoskeletal scaffolding proteins confined to the postsynaptic density of excitatory synapses, whereas its contribution to the regulation of presynaptic and/or mitochondrial proteins is minor. Intriguingly, the majority of candidates identified in our global phosphoproteomics analysis (including LRRC7, DLGAP4, DLGAP2, SHANK3, STXBP5, SYNGAP1, EPB4.1L1) have been recently described to be essential for PKA-dependent synaptic downscaling of glutamatergic neurons ( 62 ). Homeostatic synaptic scaling defines a negative regulation of postsynaptic strength due to increased or decreased neuronal activity and is crucial to prevent runaway excitation and maintain circuit stability in the neocortex.…”

Microglial TNFα orchestrates brain phosphorylation during the sleep period and controls homeostatic sleep

“…Notably, many of these substrates change in phosphorylation upon induction of homeostatic downscaling (fig. S7) ( 75 ), a form of synaptic plasticity believed to occur during sleep to weaken excitatory synapses ( 8 , 73 ). Furthermore, predictive and experimental validation of microglial TNFα-targeted kinases allowed identification of PKCs and MAPKs (fig.…”

Proteostatic regulation in neuronal compartments

“…For example, phosphorylation of tau regulates its solubility, which in turn is linked to its aggregation and formation of the neurofibrillary tangles found in Alzheimer's disease [93]. PTMs are also essential for the modulation of activity-dependent processes related to learning and memory [94,95]. Despite an increasing understanding of UPS regulation, many open questions remain, especially in the context of neurons, and little is known about local PTMs of ribosomes or UPS components, which likely play an important role in targeted protein synthesis and degradation.…”