The Nedd8 pathway controls dendritic spine maturation and stability: critical role of PSD-95 neddylation

VOGL AM; BROCKMANN MM; GIUSTI SA; MACCARRONE G; MOEBUS AJ; RICHTER JS; VERCELLI CA; ROSELLI F; RAMMES G; VOGT-WEISENHORN DM; TURCK CW; STEIN V; DEUSSING JM; REFOJO D

Trieste

Conferencia; European Science Foundation (ESF) & Federation of European Neuroscience Societies (FENS) Conference. The Neurobiology of Synapses and their dysfunction; 2013

Neddylation deficiency in pyramidal neurons alters NMDAR function, LTD, spine stability and learning and memory. In recent years, the importance of Ubiquitylation and SUMOylation, an ubiquitin-like pathway, as posttranslational modifications controlling different aspects of synapse development and plasticity has been well established. However, the role of other ubiquitin-like proteins (UBLs) in neuronal development and synaptic function remains virtually unknown. This is particularly surprising in the case of Nedd8. Although it was originally discovered in embryonic brain tissue, the best-documented function of Nedd8 is to control the cell cycle and cellular proliferation in peripheral cells by targeting Cullin-RING ligases (CRLs). However, recent reports indicate additional functions of neddylation beyond CRLs. In this line, we collected evidence indicating that neddylation increases during neuronal development, is an active posttranslational modification within mature synapses and controls dendritic spine maturation and stability. We now report that Nedd8 conjugation is regulated by neuronal activity and that neddylation is required for synaptic NMDAR function. Stimulation of synaptic NMDA receptors leads to a transient increase in neddylated substrates. Pharmacological inhibition of neddylation via the specific Nedd8 inhibitor MLN-4924 blocks the NMDA-induced phosphorylation of CaMKIIa and ERK1/2. Furthermore, electrophysiological experiments revealed that inhibition of neddylation diminishes evoked NMDAR-dependent currents and that neddylation is necessary to sustain LTD. To dissect the role of neddylation on synapse stability and complex behaviors in vivo, we generated the first conditional KO mouse line of the Nedd8 pathway. The inducible deletion of the Nedd8-activating enzyme subunit Nae1 in pyramidal neurons of the forebrain, results in a gradual decrease of neddylated substrates and a concomitant loss of spines and excitatory synapses. Interestingly, Nae1 ?KO (CaMKIIa-CreERT2) mice show distinct and temporally increasing impairments in specific behaviors. During the first two weeks after the induction of the KO and prior to any structural changes, Nae1-KO mice show a marked increase in anxiety-related behavior in emotional tests. At the same time points short-term object recognition memory was also impaired. These results suggest that neddylation controls functional properties of spines or synapses in vivo. Later on, beginning with the onset of morphological changes of spines and synapses, 3-4 weeks after the KO was induced, Nae1-KO mice show severe impairments in short- and long-term spatial-, object and social memory tests and they are unable to form fear memories. Other behaviors, including working-memory and stress-coping were still intact at the same experimental time points. In summary our results place neddylation as a critical regulator of synapse stability, function and brain plasticity as well as complex behaviors.