Alterations in the proteome of developing neocortical synaptosomes in the absence of MET signaling revealed by comparative proteomics

Alterations in the expression of genes encoding proteins involved in synapse formation, maturation and function are a hallmark of many neurodevelopmental and psychiatric disorders. For example, there is reduced neocortical expression of the MET receptor tyrosine kinase (MET) transcript and protein in autism spectrum disorder and Rett syndrome. Preclinical in vivo and in vitro models manipulating MET signaling reveal that the receptor modulates excitatory synapse development and maturation in select forebrain circuits. The molecular adaptations underlying the altered synaptic development remain unknown. We performed a comparative mass spectrometry analysis of synaptosomes generated from the neocortex of wild type and Met null mice during the peak of synaptogenesis (postnatal day 14; data are available from ProteomeXchange with identifier PXD033204). The analyses revealed broad disruption of the developing synaptic proteome in the absence of MET, consistent with the localization of MET protein in pre- and postsynaptic compartments, including proteins associated with the neocortical synaptic MET interactome and those encoded by syndromic and ASD risk genes. In addition to an overrepresentation of altered proteins associated with the SNARE complex, multiple proteins in the ubiquitin-proteasome system and associated with the synaptic vesicle, as well as proteins that regulate actin filament organization and synaptic vesicle exocytosis/endocytosis, were disrupted. Taken together, the proteomic changes are consistent with structural and functional changes observed following alterations in MET signaling. We hypothesize that the molecular adaptations following Met deletion may reflect a general mechanism that produces circuit-specific molecular changes due to loss or reduction of synaptic signaling proteins.

Automated summary

Alterations in gene expression affecting synapse formation, maturation, and function are characteristic of neurodevelopmental and psychiatric disorders. The MET receptor tyrosine kinase (MET) has reduced expression in the neocortex of individuals with autism spectrum disorder and Rett syndrome, and preclinical models suggest that MET modulates the development of excitatory synapses. Proteomic analysis of synaptosomes from the neocortex of Met knockout mice revealed widespread disruption of the synaptic proteome, including proteins associated with the MET interactome, syndromic and ASD risk genes, the SNARE complex, ubiquitin-proteasome system, and actin filament organization. The findings suggest that the molecular adaptations following MET deletion may contribute to circuit-specific changes in synaptic proteins.