Unveiling the crucial role of betaine: Modulation of GABA homeostasis via SLC6A1 transporter (GAT1)

Betaine is an endogenous osmolyte that exhibits therapeutic potential by mitigating various neurological disorders. However, the underlying cellular and molecular mechanisms responsible for its neuroprotective effects remain puzzling. In this study, we describe a possible mechanism behind the positive impact of betaine in preserving neurons from excitotoxicity. Using electrophysiology, mass spectroscopy, radiolabelled cellular assay, and molecular dynamics simulation we demonstrate that betaine at mM concentration acts as a slow substrate of GAT1 (slc6a1), the predominant GABA transporter in the central nervous system. Intriguingly, when betaine is present at low concentration (0.01-3 mM) with GABA (at concentration <K0.5), it blocks the GABA reuptake. This GAT1 modulation occurs through the temporal inhibition of the transporter, i.e., the prolonged occupancy by betaine impedes the rapid transition of the transporter to the inward conformation. The temporal inhibition results in a crucial regulatory mechanism contributing to the maintenance of GABA homeostasis, preserving neurons from excitotoxicity.