CHRISTIANSON SYNDROME PROTEIN NHE6 (SLC9A6) DRIVES METABOLIC SHIFT IN CORTICAL ASTROCYTES

Mutations in endosomal Sodium-Hydrogen Exchanger NHE6 (SLC9A6) lead to the devastating neurodevelopmental disease Christianson Syndrome (CS), symptoms including severe seizures, microcephaly and the attenuation of weight and growth gain. Ex vivo research found that loss of NHE6 in primary neurons leads to disrupted synaptic transmission, reduced axonal and dendritic branching and diminished long-term potentiation. However, effects on glial cells are essentially unstudied.
Here, we hypothesized that loss of NHE6 in cortical astrocytes contributes to the CS phenotype through changes in astrocyte metabolism that limit their support of neuronal function. We used primary cultures of wild type (WT) and NHE6 knockout (KO) cortical astrocytes to study the effect of NHE6 loss on glucose and lipid metabolism. Using techniques such as proteomics, isotope tracing and confocal imaging we investigated different metabolic pathways including glycolysis, oxidative phosphorylation and fatty acid oxidation.
NHE6 KO led to substantial metabolic reprogramming in cortical astrocytes. Glycolytic proteins were downregulated in NHE6 KO cells while proteins involved in tricarboxylic acid cycle regulation, electron transport chain, and beta-oxidation were significantly upregulated. Strikingly, oxidative phosphorylation in NHE6 KO astrocytes, but not in WT astrocytes, was significantly increased during fatty acids (FA) supplementation, suggesting increased reliance on FAs. Inhibiting endocytosis completely abolished this response.
We identified significant proteomic changes in NHE6 KO astrocytes all linked to metabolism. While further mechanistic insight is needed, our results are consistent with the notion that NHE6 loss rewires cortical astrocyte metabolism and impacts their ability to sufficiently support neurons metabolically, potentially contributing to CS pathology.