The Regulatory Mechanism Of YTHDF Aggregates In Brain Aging

YTHDF proteins widely exist in eukaryotes and their YTH domain on the C-terminus binds to single strand RNA.The role of YTHDF1 and YTHDF2,both are widely accepted readers for m6 A modified RNAs,in RNA metabolism has been recognized under physiological conditions.However,their function during aging,especially brain aging,remains largely elusive.The major phenotype of brain aging is progressive cognitive decline,which is accompanied by changes in mitochondrial morphology and function.The primary function of mitochondira is to generate energy in form of ATP to accommodate high energy demand of neuronal function.However,how aging induces changes in mitochondrial morphology and function and the contribution to brain aging remain unknown.The proteolytic capacity is decreased with aging,leading to difficulty to remove misfolded proteins and formation of protein aggregates.YTHDF proteins contain a low complexity domain(LCD),which is a typical domain that mediates phase-phase separation of proteins.Thus,YTHDF proteins have a potential to form aggregates.Whether aging could induce the formation of YTHDF protein aggregates is unknown.Here,we demonstrate that YTHDF1 and YTHDF2 proteins form insoluble aggregates(YTHDF1-YTHDF2 aggregates)in the cytoplasm during brain aging,and these aggregates are detergent-insoluble.The formation of these aggregates is dependent on phosphorylation modification on LCD and phase-phase separation properties of YTHDF proteins.YTHDF2 bound m RNAs,especially a subset of nucleus-encoded mitochondrial m RNAs,form cytoplasmic inclusions with YTHDF1-YTHDF2 aggregates,leading to translation suppression of these m RNAs.Consequently,mitochondrial biogenesis,dynamics,and respiratory function are impaired.In addition,mice with forced expression of Ythdf1 and Ythdf2 in the mPFCs mimic phenotypes and gene expression profiles observed in aged mice.Overexpression of Ythdf1 and Ythdf2 induces the formation of RNA-protein inclusions,leading to impairment in mitochondrial biogenesis,dynamics,and respiratory function.Phenotypes of these mice are highly similar to that of aged mice.Behaviorally,mice with Ythdf overexpression show impaired spatial,contextual,and fear memory.Moreover,simultaneous expression of Ythdf1 and Ythdf2 leads to more severe impairment in memory than single Ythdf expression.Thus,through illustrating a role for YTHDF aggregates in disrupting mitochondrial function during brain aging,our study defines YTHDF aggregates as a potential hallmark and therapeutic target for brain aging.