O-GlcNac Modulation of GABAergic Transmission

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Changes in the strength of GABAergic transmission is heavily influenced by posttranslational modifications and allosteric modulators like benzodiazepines and neurosteroids. O-GlcNAcylation (O- GlcNAc) is a post- translational modification that is tightly regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which add or remove the O-GlcNAc moiety of β–N-acetylglucosamine to Ser/Thr residues on proteins, respectively. Various neurodegenerative diseases like Alzheimer's disease (AD), and metabolic disorders like, diabetes exhibit dysregulated O-GlcNAc levels. Published reports from our lab have demonstrated that an acute increase in O-GlcNAcylation induces a long-term depression of evoked GABAAR mediated IPSCs (eIPSCs) and reduces the amplitude and frequency of spontaneous IPSC (sIPSC) in hippocampal principal cells, however the mechanism in which this occurs is unknown. Numerous studies have shown that serine phosphorylation of GABAAR can increase or decrease GABAAR currents depending on the neuron type and specific subunit. While O-GlcNAcylation modulates inhibitory GABA-gated currents, no studies have examined its interplay with serine phosphorylation on GABAergic transmission. Because the crosstalk between O-GlcNAcylation and phosphorylation affects the regulation of various proteins, the potential exists that O-OglcNAcylation and phosphorylation will interaction in the modulation of GABAAR function and the strength of inhibitory transmission. Furthermore, a potential interaction could impact how allosteric modulators effect GABAARs, since serine phosphorylation can either increase or decrease efficacy of these modulators. Studies proposed will investigate these hypotheses and will also test whether disease conditions where O- GlcNAc levels are chronically elevated lead to depressed GABAAR function that can be rescued via pharmacological inhibition of OGT. To determine O-GlcNAcylation's effect on GABAergic transmission in the presence of phosphorylation and allosteric modulators, I will use electrophysiological techniques, immunoblotting assays and mass spectrometry. Results will show whether the modulation of GABAAR function by PKA and allosteric modulators are shaped by the presence or absence of a co-occurring O- GlcNAc modification and if the restoration of O-GlcNAcylation levels in a disease models can restore the E/I balance.