Modulation of cortical GABAergic currents by anti-neuroligin 2 (scFvNLG2-645)

The efficiency of synaptic transmission relies on the temporally and spatially regulated expression of postsynaptic receptors localized in precise apposition to presynaptic release sites. At synapses, receptors are organized in clusters which are formed by highly regulated events, dynamically controlled by a number of proteins including scaffolds, adhesion molecules and active transport processes along the cytoskeleton (Kneussel and Loebrich, 2007). Neuroligins (NLGNs) are adhesion molecules which together with neurexins (NRXNs) provide a direct link between the pre and the postsynaptic sites by bridging the cleft (Lisé and El-Husseini, Cell Mol Life Sci 2006). The binding between NRXNs and NLGNs represents not only a structural but also a functional link between pre- and postsynaptic elements. The bidirectional signaling through the NLGN- NRXNs pathway is crucial for synapse development and stabilization (Levinson and El-Husseini, Neuron 2005; Craig and Kang, Curr Opin Neurobiol 2007). In particular, the neuroligin type 2 (NLGN2) is preferentially associated with GABAergic synapses ( Varoqueaux et al., Eur J Cell Biol 2004). By regulating signaling between pre and postsynaptic specializations these proteins play a key role in information processing and contribute to maintain the excitatory (E) /inhibitory (I) balance. This represents a critical condition for the correct functioning of neuronal networks and requires precise connections through dynamic processes involving neurotransmitter receptors, transporters, scaffolding proteins and the cytoskeleton. In physiological conditions the E/I balance is kept constant by a homeostatic feedback mechanism (Turrigiano and Nelson, Nat Rev Neurosci 2004). An incorrect E/I balance at the level of cortical microcircuits may underlie several forms of neuropsychiatric disorders including Autism Spectrum Disorders, Schizophrenia and Depression (Nelson SB and Valakh V, Neuron 2015). In cortical cultures, action potential independent spontaneous inhibitory postsynaptic currents (miniature IPSCs) were recorded from pyramidal neurons infected with a lentivirus vector driving the expression of EGFP or EGFP fused with the intrabody against the cytoplasmic domain of NLG2 (scFvNLG2-645). This intrabody is made against NLG2 complete cytoplasmatic domain containing both gephyrin binding and collybistin binding domains. The scFv NLG2-645 significantly impaired inhibitory neurotransmission, altering the frequency of GABAergic postsynaptic currents. These data support the hypothesis that NLG2 regulates the presynaptic organization of GABAergic synapse. Craig AM1, Kang Y (2007) Neurexin-neuroligin signaling in synapse development. Curr Opin Neurobiol.;17(1):43-52. Kneussel M, Loebrich S (2007) Trafficking and synaptic anchoring of ionotropic inhibitory neurotransmitter receptors. Biol Cell 99: 297-309. Levinson JN ,El-Husseini A (2005) Building excitatory and inhibitory synapses: balancing neuroligin partnerships. Neuron 20;48(2):171-4. Lisé MF, aEl-Husseini A (2006) The neuroligin and neurexin families: from structure to function at the synapse. Cell Mol Life Sci 63(16):1833-49. Nelson SB, Valakh V (2015) Excitatory/Inhibitory Balance and Circuit Homeostasis in Autism Spectrum Disorders. Neuron 87: 684-698 Turrigiano GG, Nelson SB (2004) Homeostatic plasticity in the developing nervous system. Nat Rev Neurosci;5(2):97-107. Varoqueaux F, Jamain S, Brose N (2004) Neuroligin 2 is exclusively localized to inhibitory synapses. Eur J Cell Biol ;83(9):449-56.