Loss of O-GlcNAcylation is fatal for survival and physiological functions of dopamine neurons

Abstract

The dopamine system in the midbrain is important for volitional movement, action selection, and reward-related behaviors. Although the dopamine systemmediates versatile functions, it contains only a small set of neurons in the midbrain. Moreover, these dopamine neurons are highly susceptible to Parkinson’sdisease (PD), and prematurely degenerate during disease progression. O-GlcNAcylation is one of the post-translational modifications modulating manyfundamental cellular processes, including transcription, translation, and signal transduction. It attaches O-linked N-acetylglucosamine (O-GlcNAc) moieties toserine, threonine residues of cytoplasmic, nuclear, and mitochondrial proteins. Interestingly, O-GlcNAc modification and two enzymes governing O-GlcNAcylation, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), are abundant in the mammalian brain, while our understanding of the physiological role ofO-GlcNAcylation remains rudimentary in the brain. In this study, we aim to elucidate the role of O-GlcNAcylation in dopamine neurons by utilizing whole-cellpatch clamp recording, optogenetics, fast-scanning cyclic voltammetry (FSCV), and immunohistochemistry. Notably, dopamine neuron-specific OGT conditionalknockout (cKO) mice exhibited markedly reduced survival and body weight. Furthermore, down-regulation of O-GlcNAc in dopamine neurons caused severe celldeath and dysfunction, implying the critical role of O-GlcNAcylation in dopamine neurons. Juvenile OGT cKO mice showed alterations in physiological functionsincluding reduced input resistance, increased action potential firing, attenuated Ih current, and enhanced inhibitory synaptic transmission in dopamine neurons.Pharmacological down-regulation of O-GlcNAcylation using an OGT inhibitor was also able to change the synaptic transmission of dopamine neurons.Importantly, adeno-associated virus-mediated knockout of OGT in adult midbrain dopamine neurons led to significant neuronal death, potentially excluding thedevelopmental impact of OGT in dopamine neurons. Moreover, 2 weeks of knockout induction by AAV was enough to alter the intrinsic properties of dopamineneurons, further emphasizing the importance of O-GlcNAcylation in the maintenance of dopamine neurons. Together, our data clearly demonstrate that O-GlcNAcylation is vital for survival, maintenance, and physiological functions of dopamine neurons.