Neuronal membrane proteasomes homeostatically regulate neural circuit activity in vivo and are required for learning-induced behavioral plasticity

Abstract

Protein degradation is critical for brain function through processes that remain poorly understood. Here we investigated the in vivo function of a recently reported neuronal membrane-associated proteasome (NMP) in the brain of Xenopus laevis tadpoles. We demonstrated that NMPs are present in the tadpole brain with biochemistry and electron microscopy, and showed that they actively degrade neuronal activity-induced nascent proteins. Using in vivo calcium imaging in the optic tectum, we showed that acute inhibition of NMP function rapidly increased spontaneous neuronal activity, resulting in hyper-synchronization among tectal neurons. At the circuit level, inhibiting NMPs abolished learning-dependent improvement in a visuomotor behavior paradigm in live animals. Our data provide the first in vivo characterization of NMP functions in the vertebrate nervous system and suggest that NMP-mediated degradation of activity-induced nascent proteins may serve as a homeostatic modulatory mechanism in neurons that is critical for regulating neuronal activity and experience-dependent circuit plasticity.

Activity-Induced Cortical Glutamatergic Neuron Nascent Proteins

“…Decreased NSPs may arise by decreasing transcript levels ( Raab-Graham and Niere, 2017 ; Dong et al, 2020 ), for instance, downstream of activity-induced expression of transcriptional repressors ( Ashok et al, 2020 ; Dong et al, 2020 ), by miRNA-mediated mechanisms ( Henshall et al, 2016 ; Bencurova et al, 2021 ; Zolboot et al, 2021 ) or by activity-induced degradation of NSPs. Recent studies identified a neuronal membrane-associated proteosome that degrades activity-induced NSPs ( Ramachandran and Margolis, 2017 ; Ramachandran et al, 2018 ; He et al, 2022 ) and is required for behavioral plasticity ( He et al, 2022 ). Although proteomic analysis of human brain samples indicates that seizure can increase and decrease proteins ( Xiao et al, 2020 ), our data specifically show that activity-induced decreases in NSPs contribute to this outcome.…”