7,8-Dihydroxyflavone Induces Synapse Expression Of AMPA Glua1 And Ameliorates Cognitive And Spine Abnormalities In A Mouse Model Of Fragile X Syndrome

Objective Fragile X syndrome(FXS)is the most common cause of intellectual disability in males and the most common single gene cause of autism.Dendrite and spine abnormalities have been correlated with impaired cognitive abilities in FXS,where neurons show a high density of long,thin,and immature dendritic spines.However,to date,there is no effective pharmacotherapeutic agent available.7,8-Dihydroxyflavone(7,8-DHF)has recently been identified as a high affinity tropomyosin receptor kinase B(TrkB)agonist.The purpose of this paper was to examine the utility of 7,8-DHF as an effective pharmacotherapeutic agent that targets dendritic pathology and cognitive impairments in FXS mutant.Method Fmr1(fragile X mental retardation 1)knock out(KO)(FVB 129 P2-Pde6b+Tyrc-ch-Fmr1tm1Cgr/J)and control(FVB.129P2-Pde6bTyrc-ch/Ant J),here-after referred to as wild-type(WT)strain mice were used as the animal model of FXS.Sixty four Fmr1 KO and WT male mice were divided into four groups respectively,namely 7,8-DHF-KO,vehicle-KO,7,8-DHF-WT,and vehicle-WT,16 mice in each group.Treatment group were fed with 7,8-DHF(5mg/kg),and vehicle group were fed with the same concentration of dimethy sulfoxide(DMSO)without7,8-DHF.Conditional fear test and Morris water maze test were used to examine the effects of 7,8-DHF on spatial and fear memory functions in in Fmr1 KO mice after 4weeks treatment.And then we measured dendritic spine number and density using Golgi staining kits in the hippocampal CA1 and lateral amygdala.The protein expression and phosphorylation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid(AMPA)receptor GluA1-4 subunits,tyrosine kinase B,calcium/calmodulin-dependent protein kinase II,and protein kinase C were determined by western blot analysis.Results(1)The study found that 4 weeks 7,8-DHF treatment affected behavioral performance,especially improved spatial and fear memory of Fmr1 KO mice.(2)7,8-DHF ameliorated morphological spine abnormalities including the number and elongation of spines in the hippocampus and amygdala of Fmr1 KO mice.(3)7,8-DHF enhanced the expression of AMPA GluA1 receptor,but reduced the normal levels of Glu A2 at the synapses in Fmr1 KO mice.(4)Potentially related to drug-induced changes in AMPA receptor subunits,7,8-DHF at the synapses led to phosphorylation of specific serine sites on subunits Ser818 and Ser813 of GluA1,and Ser880 of GluA2,as well as phosphorylation of TrkB,calcium/calmodulin-dependent protein kinase II,and protein kinase C.However,7,8-DHF neither affected behavioral performance nor increased TrkB phosphorylation in WT mice,which suggests that it had FXS-specific correcting effect.Conclusion These results demonstrated that 7,8-DHF improved learning and memory,and reduced abnormalities in spine morphology,thus providing a potential pharmacotherapeutic strategy for FXS.