Stage- and Region-Dependent Proteomic Alterations in a Mouse Model of Creatine Transporter Deficiency

SLC6A8 encodes the creatine transporter (CRT), which mediates creatine transport across the plasma membrane in the brain, including the blood–brain barrier and neurons. Creatine transporter deficiency (CTD), caused by pathogenic variants in SLC6A8 , leads to cerebral creatine depletion and cognitive impairment. Here, we investigated the developmental molecular mechanisms underlying CTD using the pathogenic c.1681G>C (G561R) variant of Slc6a8 , which corresponds to a variant identified in SLC6A8 in a patient with CTD. In vitro analyses using HEK293 cells expressing mutant mouse CRT carrying the G561R variant demonstrated impaired N-glycan maturation and plasma membrane localization of the transporter, resulting in markedly reduced creatine uptake, consistent with previous reports on the corresponding human CRT variant. To investigate the in vivo effects of this pathogenic variant, we generated CRT-G561R knock-in mice by introducing the c.1681G>C point mutation into the mouse Slc6a8 gene using the CRISPR/Cas9 system. These male mice exhibited severe reductions in brain creatine levels, postnatal growth retardation, and impaired spatial memory, despite preserved gross brain morphology. Quantitative proteomic analyses of the hippocampus and cerebral cortex during postnatal development revealed region-dependent protein alterations in CTD. The hippocampus showed pronounced early postnatal remodeling involving proteins related to actin cytoskeleton organization and vesicle-mediated membrane trafficking, whereas the cerebral cortex exhibited a more gradual response involving creatine biosynthesis-related enzymes and later-emerging mitochondrial pathways, including the mitochondrial translation machinery. These findings demonstrate stage- and region-dependent proteomic remodeling during postnatal brain development in CTD. Significance Statement Creatine transporter deficiency (CTD) causes cerebral creatine depletion and intellectual disability; however, the developmental mechanisms linking creatine loss to brain dysfunction remain unclear. We performed developmental proteomic profiling of the hippocampus and cerebral cortex using a mouse model carrying a pathogenic Slc6a8 variant identified in patients with CTD. Creatine transporter dysfunction induces distinct region- and stage-dependent molecular responses during postnatal brain maturation. The hippocampus shows early alterations in cytoskeleton-dependent membrane trafficking pathways, consistent with impaired synaptic and circuit maturation, whereas the cerebral cortex exhibits progressive metabolic and mitochondrial adaptations. These findings suggest that impaired creatine-dependent energy buffering disrupts distinct developmental programs across brain regions, potentially contributing to cognitive dysfunction by hindering early hippocampal circuit maturation.