Distinct intracellular signaling mediates C‐MET regulation of dendritic growth and synaptogenesis

Abstract

Hepatocyte growth factor (HGF) activation of the MET receptor tyrosine kinase influences multiple neurodevelopmental processes. Evidence from human imaging and mouse models shows that, in the forebrain, disruptions in MET signaling alter circuit formation and function. One likely means of modulation is by controlling neuron maturation. Here, we examined the signaling mechanisms through which MET exerts developmental effects in the neocortex. In situ hybridization revealed that hgf is located near MET-expressing neurons, including deep neocortical layers and periventricular zones. Western blot analyses of neocortical crude membranes demonstrated that HGF-induced MET autophosphorylation peaks during synaptogenesis, with a striking reduction in activation between P14 and P17 just prior to pruning. In vitro analysis of postnatal neocortical neurons assessed the roles of intracellular signaling following MET activation. There is rapid, HGF-induced phosphorylation of MET, ERK1/2 and Akt that is accompanied by two major morphological changes increases in total dendritic growth and synapse density. Selective inhibition of each signaling pathway altered only one of the two distinct events. MAPK/ERK pathway inhibition significantly reduced the HGF-induced increase in dendritic length, but had no effect on synapse density. In contrast, inhibition of the PI-3K/Akt pathway reduced HGF-induced increases in synapse density, with no effect on dendritic length. The data reveal a key role for MET activation during the period of neocortical neuron growth and synaptogenesis, with distinct biological outcomes mediated via discrete MET-linked intracellular signaling pathways in the same neurons.

Receptor Tyrosine Kinase MET Interactome and Neurodevelopmental Disorder Partners at the Developing Synapse

“…However, the present proteomics data, together with functional neuroimaging (42) and postmortem human brain studies (13, 29, 30), and behavioral (43, 44), electrophysiology and morphological analyses of synapse development (20, 38–40) in mutant mice, suggest that the MET interactome contributes to NDD expression. This does not mean that disrupting MET alone is causal for NDDs.…”

“…Based on morphology and other criteria used in our laboratory, neurons at this time were healthy and fully capable of responding to HGF by increasing dendritic growth and synaptogenesis (Fig. S2A) (38). Experiments were performed using an antibody directed against MET in combination with antibodies specifically recognizing NTRK3, SYNGAP1, SHANK3, GRIN2B or GRM5.…”

“…The synaptosomes were treated with HGF for 5 minutes, as this time frame results in an abundant amount of phospho-MET receptor (38). Using Co-IP/MS, we identified 72 putative MET-interacting proteins.…”

“…In contrast, cortical areal expression patterns vary significantly between rodent and primate (32, 34, 35). MET is expressed in excitatory neocortical neurons and enriched in growing forebrain axons and synapses (36, 37), with phosphorylation occurring mostly in the neuropil and not in axon tracts (38). Accumulating human and animal model data demonstrate an important role for MET in circuit development.…”

The Pleiotropic MET Receptor Network: Circuit Development and the Neural-Medical Interface of Autism

“…Further, MET protein expression is robust in neuropil, with an enrichment in pre- and post-synaptic compartments, and developing axon tracts, reflecting active transport to the synapse (36, 54). Strikingly, localization of endogenously-activated MET (pMET) in the developing forebrain reveals enriched receptor activation in the neuropil, with an absence from axon tracts (55). …”