Reduced Calsyntenin-1 Interaction With ICAM5 Implicated In Dendritic Spine Abnormalities In Fragile X Syndrome

Objective:The present study is to explore the role of calsyntenin-1（Clstn1）,type-1transmembrane proteins of the cadherin superfamily,in spine maturation in FXS neurons,and whether it mediates intracellular transportation and redistribution of Intercellular adhesion molecule-5（ICAM5）Methods:Fmr1 knock out（KO）(FVB.129P2-Pde6b⁺Tyr^c-ch-ch Fmr1^tm1Cgr/J)and control(FVB.129P2-Pde6b⁺Tyr^c-ch/AntJ),were used as the animal model of FXS.Western blotting and Golgi staining were used to observe the changes of the expression of CLSTN1 and ICAM5 proteins in the WT and Fmr1KO mice and the changes of the dendritic spines in a day-dependent manner.Primary mouse neuronal cultures were separated from prefrontal cerebral cortex of WT or Fmr1 KO mouse.The interaction between CLSTN1 and ICAM5 was identified by immunocytochemistry and colocalization,Co-Immunoprecipitation,live cell imaging and time-lapse analysis.Dil staining was used to observe the effect on spine development when changing the CLSTN1 protein in cultured neurons.Results:（1）Excessive filopodia-like spines are presented in developmental medial prefrontal cortex of Fmr1 KO mice.（2）CLSTN1 is reduced while ICAM5 is overexpressed in postnatal medial prefrontal cortex of Fmr1 KO mice.（3）ICAM5 and CLSTN1 are interacted in cultured WT dendrites of neurons,Transfected overexpressed proteins also present a common transport phenomenon（4）In mouse prefrontal cortex neurons interfered CLSTN1 expression,the co-localization of ICAM5 and PSD95 was significantly increased and resulting in ICAM5 accumulation on the cell surface,and then affects dendritic morphology.（6）The overexpression of CLSTN1 can improve abnormalities of dendritic spine morphology in cultured neurons of Fmr1 KO mice.Conclusion:This study demonstrates that CLSTN1 plays a critical role in dendritic spine formation and maturation through regulating ICAM5 redistribution in neurons.In Fmr1 KO mice,CLSTN1 dysregulation contributes to the excessive dendritic ICAM5 distribution and further the abnormality of spine formation and maturation.Thus,CLSTN1 may serve as a potential biomarker as well as a therapeutic target for FXS.