Mutations in Na+/H+ exchanger NHE6 (SLC9A6) underlie several X-linked developmental brain disorders including the neurodegenerative disease Christianson Syndrome (CS). Symptoms include cerebellar atrophy, non-verbal status, seizures and severe cognitive disabilities. NHE6 deletion or loss-of-function mutations lead to attenuated endosomal signaling, dysregulated synaptic transmission and abnormal dendritic branching in vitro and in vivo [1]. In this project, we aim to investigate the localization of wildtype- and CS-associated NHE6 variants in primary neurons, the importance of NHE6 in receptor-recycling pathways and cellular signaling, and its role in regulating neuronal metabolism. Cerebellar, cortical, and hippocampal primary neurons were isolated from NMRI mice, and NHE6 localized using immunofluorescence and confocal microscopy. NHE6 localization was similar between primary neuron types, however NHE6 localization to early and recycling endosomes was greater in neuronal outgrowths compared to soma of cerebellar and hippocampal neurons. Treatment of primary neurons with brain-derived neurotrophic factor (BDNF) resulted in rapid activation of its receptor TrkB, and downstream Akt, ERK, and CREB activation in cerebellar and hippocampal neurons. Strikingly, NHE6 knockdown decreased the long-term activation of CREB and attenuated Akt activation.In conclusion, our results suggest that NHE6 is highly localized to early and recycling endosomes in neuronal outgrowths and regulates signaling pathways important for neuronal proliferation and plasticity, possibly via regulation of TrkB recycling. In ongoing work, we investigate how NHE6 KO affects neuronal metabolism, in particular iron homeostasis and mitochondrial health.The project is supported by Independent Research Fund Denmark (grant 3103-00217B).[1] Ouyang Q et al. Neuron. 2013;80(1):97-112. doi: 10.1016/j.neuron.2013.07.043