Neuregulin/Alpha7nAChR Signaling, the GABAergic Switch and Neurodevelopmental Risk: Mechanisms of Gestational Choline Supplementation.

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Project Summary During early brain development, GABA is the main excitatory neurotransmitter due to a reverse chloride gradient mediated via the chloride co-transporter genes NKCC1 and KCC2. Signaling via the nicotinic receptor, a7nAChR, is a key driver of the GABA excitatory/inhibitory [E/I] shift necessary for normative neurodevelopment. Dysfunctional maturation of GABAergic neurotransmission and E/I balance in the brain is implicated in the pathogenesis of several neurodevelopmental disorders (NDDs), including autism spectrum disorder (ASDs). Recently, our studies have identified a functional polymorphism in the Neuregulin 1 gene promoter, rs6994992, which is associated with elevated brain transcription of a novel NRG1 isoform, (NRG1-IV) and more critically lower levels of α7nAChR in the human brain. Signaling via the α7nAChR is a critical driver of the GABA excitatory/inhibitory (E/I) shift, mediated via the chloride transporters, NKCC1 and KCC2 and is also a known genetic risk factor for several NDDs, especially ASD, in the form of 15q13.3 microdeletion syndrome. In rodents, α7nAChR knockdown prevents the switch, resulting in aberrant maturation of GABAergic hyperpolarization and NRG1 is a key regulator of α7nAChRs; the specific role of NRG1-IV is unknown. In human studies, rs6994992 is associated with human cognition, sensory processing and anxiety behaviors, and data from our lab suggest attenuated sensory processing in babies carrying the T allele, and an interaction with maternal gestational dietary choline supplementation. Choline is a α7nAChR agonist, and a novel prenatal nutrient supplementation strategy shown to improve childhood behaviors and early brain development. In summary, the objective of this multidisciplinary proposal is the developmental characterization of a novel biological pathway linking NRG1, α7nAChR and NKCC1/KCC2 with regulation of E/I balance maturation, using a novel transgenic mouse (NRG1- IVtgNSE-tTA) genetically modified to express human NRG1-IV in brain and cutting-edge experimental approaches. We will test two main hypotheses.1). NRG1-IV overexpression contributes to atypical maturation of neocortical GABAergic signaling and E/I cortical balance, mediated via reduced α7nAChR and developmental expression of the chloride co-transporters NKCC1 and KCC2 and 2). Prenatal stimulation of α7nAChR, via dietary choline supplementation, will correct development of the switch, improve adult E/I cortical imbalance and neurobehavioral outcomes relevant to several NDDs, mechanistically via a7nAChR. This research will improve our knowledge of basic mechanisms of typical and atypical development related to a key signaling pathways involved in several NDDs, especially ASD, and identify new treatment/intervention approaches for people with developmental disabilities.