The Mechanism Of Mitophagy Disorder Caused By The Deletion Of Fragile X Messenger Ribonucleoprotein

Background Fragile X Messenger Ribonucleoprotein(FMRP)is the expression product of Fragile X Messenger Ribonucleoprotein 1(Fmr1).As an RNA binding protein,FMRP is involved in synaptic plasticity and function,synaptic connections,and regulates the development of neural circuits.The lack of FMRP will damage the neural circuits and cognitive functions.Deletion of FMRP leads to Fragile X syndrome(FXS),an inherited intellectual disability and the most common single gene disorder in autism spectrum disorders.Mitochondria,as dynamic organelles,generate cellular energy through peroxidation osorylation in eukaryotic cells.Neurons in the development mainly rely on this biological energy to maintain synaptic formation,protein synthesis and dendritic spine development.Mitochondrial dysfunction in developing brain can disrupt neural development.Studies have shown that brain metabolism of FMRP-deficient mice is abnormal,with increased oxidative stress and ROS,leading to mitochondrial dysfunction.Mitoagy may degrade damaged mitochondria for mitochondrial quality control and maintain cell homeostasis.However,the effect and mechanism of FMRP deletion on mitoagy remain unclear.Objective The purpose of this study was to investigate the mechanism of mitoagy disorder caused by the deletion of FMRP.Methods WT and Fmr1 KO mice were used as FXS models to detect mitochondrial morology in hippocampus by electron microscopy.Mitochondrial function in hippocampus was detected by ATP kit.The expression levels of mitoagy related proteins in hippocampus were detected by western blotting and q RT-PCR.The subcellular distribution of mitoagy related proteins was detected by subcellular component separation and western blotting.The co-localization of mitochondriaassociated proteins and autoagy associated proteins were detected by immunofluorescence.In the primary neurons of Fmr1 KO mice,the co-localization of mitochondria-associated proteins and autophagy associated proteins were detected by immunofluorescence to determine the mitophagy.Results Hippocampal mitochondrial marker TOM20 was increased and ATP levels were decreased in Fmr1 KO mice.The expression of mitochondrial dynamics related protein MFN1 decreased and DRP1 increased.The expressions of MFN1,MFN2,DRP1 and FIS1 were increased,while the expressions of OPA1 were decreased.The expressions of mitophagy related proteins PINK1,P62 and ATG5 decreased,while the expressions of Parkin and p-Parkin increased.The expressions of mitophagy related genes PINK1,Parkin,LC3 and P62 were increased.TOM20 colocalized with PINK1 increased and TOM20 colocalized with Parkin decreased.PINK1 accumulates in the mitochondrial outer membrane and Parkin is reduced in the mitochondrial outer membrane.In Fmr1 KO mice hippocampal neurons,the spherical and damaged mitochondria were increased,the mitochondrial swelling was obvious,the ridge disappeared,and the volume decreased.The colocalization of mitochondria and LC3 were increased and mitochondria and lysosome were decreased.Conclusion The absence of FMRP leads to the abnormal morphology and function of mitochondria,the increased mitochondria autophagosomes and the impaired function of mitochondria autophagosomes.The transfer process from mitochondria autophagosomes to lysosomes is blocked,and the absence of FMRP activates the PINK1/Parkin-dependent mitophagy pathway.This study helps to deepen the regulatory mechanism of FMRP and provide insight into and targets for the treatment of FXS.