Identification of synaptoneurosomal transcriptome engaged into translation in response to NMDA-R stimulation

Synapses are the regions of the neuron that enable the transmission and propagation of action potentials on the cost of high energy consumption and elevated demand for mitochondrial ATP production. The rapid changes in local energetic requirements at dendritic spines implies the role of mitochondria in the maintenance of their homeostasis. We have employed quantitative mass spectrometry and in vitro stimulation of isolated mouse synaptoneurosomes to create a comprehensive view of local protein synthesis in neurons. Strikingly, the second most numerus group of proteins synthetized in the synapses represented ones imported into the mitochondria. The proteomic data were further supported by sequencing of mRNAs bound with actively translating polyribosomes. Our results show that an important pool of mitochondrial proteins is locally produced at the synapse indicting that mitochondrial biogenesis take place locally in order to maintain the pool of functional mitochondria in axons and dendrites. We further show that stimulation of synaptoneurosomes induce the local synthesis of mitochondrial proteins that are transported to the mitochondria and incorporated into the protein supercomplexes of respiratory chain. This contributes to mitochondrial biogenesis in neurons and a logical consequence of this fact would be a dysregulation of mitochondrial function in the conditions that deal with dysregulated synaptic translation, such as fragile X syndrome. Indeed, we have shown mitochondrial dysfunction in synapses of Fmr1 KO mice. Overall design: Examination of synaptoneurosomal transcriptome in comparison to polyribosomal fractions after NMDA-R stimulation, performed in three replicates.