567. cGAS–STING Pathway Activation in Microglia in a Mouse Model of GLUT1 Deficiency Syndrome: Cognitive Improvement with STING Inhibition and a Ketogenic Diet

Abstract

Abstract Background Glucose transporter type 1 deficiency syndrome (GLUT1-DS) is an inherited metabolic encephalopathy primarily caused by reduced expression and/or function of the GLUT1 protein. A wide range of neurological symptoms, including epilepsy and cognitive impairment, have been reported in affected individuals. Currently, no established therapy is available for GLUT1-DS, and ketogenic diet therapy is applied as a symptomatic treatment. Previous studies using GLUT1-DS model mice have reported aberrant activation of microglia. Microglia are known to directly participate in neuronal activity through processes such as synaptic pruning; however, the relationship between microglial activation and clinical manifestations remains unclear in this disease. Aims & Objectives The present study aimed to elucidate the molecular mechanisms underlying microglial activation in a GLUT1-DS mouse model and to clarify its association with disease pathology. Method Glut1 heterozygous knockout mice (Glut1 del/+) were used as a model of GLUT1-DS. Microglial activation states and double-stranded DNA (dsDNA) accumulation were evaluated using immunohistochemistry. Western blotting was performed to assess the activation status of the cGAS–STING pathway in the brains of model mice. To investigate the effects of cGAS–STING pathway inhibition, the STING inhibitor H-151 was administered to model mice. In addition, ketogenic diet therapy was applied. To assess intervention-induced changes in cognitive function, the object location test and novel object recognition test (OLT/NORT) were performed. Results We found that microglial activation was particularly pronounced in the thalamus of GLUT1-DS model mice. In the thalamus, phosphorylation of TBK1, a key marker of cGAS–STING pathway activation, was significantly increased, and abnormal accumulation of dsDNA, an activating ligand of the pathway, was observed within microglia. Based on these findings, we evaluated inhibition of the cGAS–STING pathway as a novel therapeutic strategy. Administration of the STING inhibitor H-151 to GLUT1-DS model mice led to improvements in cognitive function. Furthermore, H-151 treatment significantly reduced dsDNA accumulation in microglia and microglia activation. Ketogenic diet therapy also resulted in cognitive improvement in model mice, consistent with clinical observations in patients. Moreover, ketogenic diet therapy improved cognitive function in model mice, consistent with the effects observed in patients, and was accompanied by normalization of microglial inflammatory phenotypes, reduced accumulation of dsDNA in microglia, and suppression of the activated cGAS–STING pathway in this model mice. Discussion & Conclusions Because inhibition of the cGAS–STING pathway led to an improvement in symptoms, these findings suggest that microglial activation in this disease is associated with excessive activation of the cGAS–STING pathway, which in turn contributes to cognitive impairment. Moreover, findings from ketogenic diet therapy suggest that the ketogenic diet may not only improve metabolic dysfunction by supplying ketone bodies as an alternative energy source to glucose, but also by suppressing excessive activation of the cGAS–STING pathway, thereby improving cognitive function.