Arfgef1 haploinsufficiency in mice alters neuronal endosome composition and decreases membrane surface postsynaptic GABA A receptors

ARFGEF1 encodes a guanine exchange factor involved in intracellular vesicle trafficking, and is a candidate gene for childhood genetic epilepsies. To model ARFGEF1 haploinsufficiency observed in a recent Lennox Gastaut Syndrome patient, we studied a frameshift mutation (Arfgef1 ) in mice. Arfgef1 pups exhibit signs of developmental delay, and Arfgef1 adults have a significantly decreased threshold to induced seizures but do not experience spontaneous seizures. Histologically, the Arfgef1 brain exhibits a disruption in the apical lining of the dentate gyrus and altered spine morphology of deep layer neurons. In primary hippocampal neuron culture, dendritic surface and synaptic but not total GABA receptors (GABA R) are reduced in Arfgef1 neurons with an accompanying decrease in the number of GABA R-containing recycling endosomes in cell body. Arfgef1 neurons also display differences in the relative ratio of Arf6 :Rab11 :TrfR recycling endosomes. Although the GABA R-containing early endosomes in Arfgef1 neurons are comparable to wildtype, Arfgef1 neurons show an increase in the number of GABA R-containing lysosomes in dendrite and cell body. Together, the altered endosome composition and decreased neuronal surface GABA R results suggests a mechanism whereby impaired neuronal inhibition leads to seizure susceptibility.