Enhancing protein O-GlcNAcylation in down syndrome mice mitigates memory dysfunctions through the rescue of mitochondrial bioenergetics, stress responses and pathological markers

Disturbances of the single sugar modification of proteins, O-GlcNAc, have been identified as a potential connection between disrupted brain metabolism and intellectual decay. In Alzheimer disease (AD), the reduced uptake of glucose in the brain results in aberrant O-GlcNAc cycling contributing to redox imbalance and neurodegeneration. Notably, alterations of O-GlcNAc homeostasis, associated with impaired O-GlcNAc transferase (OGT)/O-GlcNAcase (OGA) regulation, foster neuropathological mechanisms characterized by the presence of AD hallmarks in Down syndrome (DS) models. In the present study we examined the ability of Thiamet G (TMG), a well-known OGA inhibitor, in improving bio-energetic processes, inducing stress responses, reducing AD-related signatures and ameliorating cognition in a murine model of DS. Our data demonstrate that short-term intranasal administration of TMG restored OGA activity and normalized the global O-GlcNAc profile in mouse cortices. By a proteomic approach we identified protein components whose increased O-GlcNAc levels rescue, resulted to brain molecular and cognitive improvements. Remarkably, these included elements involved in energy production, neuronal architecture, antioxidant and stress response mechanisms. The ability of TMG in rescuing O-GlcNAc cycle and metabolic changes, associated with improved mitochondrial activity in cortical tissue, was further accompanied by changes in the O-GlcNAc/phospho ratio of APP and Tau. Functional improvements translated in enhanced recognition memory in Ts2Cje mice. Our study highlights the pivotal role of altered protein O-GlcNAcylation in DS neuropathology and establishes the molecular basis to envision the O-GlcNAc process as a promising therapeutic target to mitigate genetic- and metabolism-driven brain alterations linked to redox imbalance, mitochondrial failure and the development of AD features.