Polysialylated NCAM and EphrinA/EphA Regulate Synaptic Development of GABAergic Interneurons in Prefrontal Cortex

Abstract

A novel function for the neural cell adhesion molecule (NCAM) was identified in ephrinA/EphA-mediated repulsion as an important regulatory mechanism for development of GABAergic inhibitory synaptic connections in mouse prefrontal cortex. Deletion of NCAM, EphA3, or ephrinA2/3/5 in null mutant mice increased the numbers and size of perisomatic synapses between GABAergic basket interneurons and pyramidal cells in the developing cingulate cortex (layers II/III). A functional consequence of NCAM loss was increased amplitudes and faster kinetics of miniature inhibitory postsynaptic currents in NCAM null cingulate cortex. NCAM and EphA3 formed a molecular complex and colocalized with the inhibitory presynaptic marker vesicular GABA transporter (VGAT) in perisomatic puncta and neuropil in the cingulate cortex. EphrinA5 treatment promoted axon remodeling of enhanced green fluorescent protein-labeled basket interneurons in cortical slice cultures and induced growth cone collapse in wild-type but not NCAM null mutant neurons. NCAM modified with polysialic acid (PSA) was required to promote ephrinA5-induced axon remodeling of basket interneurons in cortical slices, likely by providing a permissive environment for ephrinA5/EphA3 signaling. These results reveal a new mechanism in which NCAM and ephrinAs/EphA3 coordinate to constrain GABAergic interneuronal arborization and perisomatic innervation, potentially contributing to excitatory/inhibitory balance in prefrontal cortical circuitry.

The Neural Cell Adhesion Molecule (NCAM) Promotes Clustering and Activation of EphA3 Receptors in GABAergic Interneurons to Induce Ras Homolog Gene Family, Member A (RhoA)/Rho-associated protein kinase (ROCK)-mediated Growth Cone Collapse

“…NCAM also plays a critical role in the regulation of perisomatic synapses in the developing prefrontal cortex (2). For information to be transmitted effectively within the brain, an intricate balance of excitation and inhibition in the cortical circuitry must be established.…”

“…Previous work identified a novel role for the neural adhesion molecule NCAM as an obligate component of a receptor complex that acts in the early postnatal mouse medial frontal cortex to constrain basket interneuron connectivity with pyramidal neuron soma (2). Deletion of NCAM, EphA3, or ephrin-A2/ A3/A5 in mice increases the number of perisomatic basket cell synaptic terminals in the mPFC (2).…”

“…Deletion of NCAM, EphA3, or ephrin-A2/ A3/A5 in mice increases the number of perisomatic basket cell synaptic terminals in the mPFC (2). NCAM associates with EphA3 tyrosine kinase, an ephrin-A5 receptor, and mediates growth cone collapse of GABAergic interneuron terminals in cortical neuron cultures (2). Furthermore, ephrin-A5 treatment of cortical slices promotes loss of perisomatic basket cell synaptic puncta, and this loss is NCAM-dependent (2).…”

“…NCAM associates with EphA3 tyrosine kinase, an ephrin-A5 receptor, and mediates growth cone collapse of GABAergic interneuron terminals in cortical neuron cultures (2). Furthermore, ephrin-A5 treatment of cortical slices promotes loss of perisomatic basket cell synaptic puncta, and this loss is NCAM-dependent (2). Although NCAM and EphA3 co-localize in vivo at perisomatic synapses (2), the significance and mechanism of NCAM/EphA3 binding and clustering are not understood.…”

“…Furthermore, ephrin-A5 treatment of cortical slices promotes loss of perisomatic basket cell synaptic puncta, and this loss is NCAM-dependent (2). Although NCAM and EphA3 co-localize in vivo at perisomatic synapses (2), the significance and mechanism of NCAM/EphA3 binding and clustering are not understood. Highlighting the importance of NCAM and ephrinA/EphA signaling in human cortical circuitry, genetic polymorphisms and dysregulation of NCAM (19 -25) or EphA/ephrinA (26 -28) are associated with schizophrenia, autism, and bipolar disorder.…”