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RAB GDP dissociation inhibitor-1 gene (GDI1) encodes for αGDI, a protein controlling the cycling of small GTPases orchestrating intracellular vesicular trafficking. Mutations in human GDI1 are responsible for X-linked intellectual disability (XLID). Adult mice lacking Gdi1 gene (Gdi1 KO), a model of XLID, showed working and associative memory deficits. The cognitive phenotype was explained by a large decrease in the reserve pool of synaptic vesicles (SVs) at the hippocampal synapses, resulting in a slow SV recovery after SV depletion. Thus, cognitive deficits may reflect the temporary depletion of the immediately available SVs. Because Gdi1 is ubiquitously expressed in neurons and in astrocytes, GDI1 mutations could affect trafficking of both cell types impairing astrocyte-neuron cross talk, leading to cognitive defects. To dissect the role of αGDI in neurons and in astrocytes, two conditional models in which Gdi1 is deleted respectively in neurons (CamkII-Cre+-Gdi1flox/Y) or in astrocytes (Glast-CreERT2+-Gdi1flox/Y) were generated. The CamkII-Cre+-Gdi1flox/Y mice phenocopied the Gdi1 KO mouse instead, Glast-CreERT2+-Gdi1flox/Y mice have a selective impairment in working memory which was rescued by inhibiting glycolysis by 2-deoxy-D-glucose administration. Proteomic analysis showed significant changes in astrocyte-resident glucose handling enzymes. Imaging with [18F]-fluoro-2-deoxy-D-glucose revealed an increased D-glucose uptake in Gdi1-null brain, consistent with the facilitated D-glucose utilisation. These results support a new astrocyte-based mechanism in XLID, opening a novel therapeutic opportunity of targeting aerobic glycolysis, advocating a change in clinical practice. Gen za inhibitor disociacije GDP-1 (GDI1) RAB kodira beljakovino αGDI, ki nadzoruje kroženje majhnih GTPaz, ki uravnavajo znotrajcelični transport mešičkov. Mutacije v človeškem GDI1 so odgovorne za od X-kromosoma odvisno nespecifično umsko manjzmožnost (XLID). Odrasle miši brez gena Gdi1 (Gdi1-null), model XLID, imajo oslabljeno tvorbo delovnega in asociativnega spomina. Kognitivni fenotip je bil pojasnjen z zmanjšanjem rezervnega bazena sinaptičnih mešičkov (SV) v hipokampalnih sinapsah, zaradi česar se SV po izpraznitvi prepočasi nadomeščajo. Pomanjkanje takoj razpoložljivih SV se lahko odraža kot kognitivni primanjkljaj. Zaradi izražanja Gdi1 tako v nevronih kot astrocitih, bi lahko mutacije v Gdi1 vplivale na transport mešičkov v obeh tipih celic, kar lahko ovira navzkrižno komunikacijo med astrociti in nevroni in s tem povzroča kognitivne okvare. Da bi bolje razumeli vlogo αGDI v nevronih in astrocitih, sta bila ustvarjena dva pogojna modela miši, v katerih je Gdi1 izbrisan v nevronih (CamkII-Cre+-Gdi1flox/Y) ali v astrocitih (GLAST-CreERT2+-Gdi1flox/Y). Miši CamkII-Cre+-Gdi1flox/Y so imele enak fenotip kot miši Gdi1-null, medtem ko so imele miši GLAST-CreERT2+-Gdi1flox/Y selektivno okvaro delovnega spomina, ki je bil obnovljen z inhibicijo glikolize z intraperitonealnim vnosom 2-deoksi-D-glukoze. Proteomska analiza astrocitov je pokazala spremembe v encimih, ki uravnavajo presnovo glukoze. Slikanje s [18F]-fluoro-2-deoksi-D-glukozo je razkrilo zvečan privzem D-glukoze v možganih miši Gdi1-null. Rezultati razkrivajo nov mehanizem pri XLID, ki temelji na astrocitih in uravnavanju aerobne glikolize. Predstavljajo novo terapevtsko priložnost, kar je relevantno za spremembo klinične prakse. |
