Abstract
BackgroundAberrant alternative splicing plays critical role in aging and age-related diseases. Heterogeneous nuclear ribonucleoproteins (hnRNPs) reportedly regulate RNA splicing process. Whether and how hnRNPs contribute to age-related neurodegenerative diseases, especially Alzheimer’s disease (AD), remain elusive.MethodsImmunoblotting and immunostaining were performed to determine expression patterns and cellular/subcellular localization of the long isoform of hnRNP D-like (L-DL), which is a hnRNP family member, in mouse hippocampus. Downregulation of L-DL in WT mice was achieved by AAV-mediated shRNA delivery, followed by memory-related behavioural tests. L-DL interactome was analysed by affinity-precipitation and mass spectrometry. Alternative RNA splicing was measured by RNA-seq and analyzed by bioinformatics-based approaches. Downregulation and upregulation of L-DL in APP/PS1 mice were performed using AAV-mediated transduction.ResultsWe show that L-DL is specifically localized to nuclear speckles. L-DL levels are decreased in the hippocampus of aged mouse brains and downregulation of L-DL impairs cognition in mice. L-DL serves as a structural component to recruit other speckle proteins, and regulates cytoskeleton- and synapse-related gene expression by altering RNA splicing. Mechanistically, these splicing changes are modulated via L-DL-mediated interaction of SF3B3, a core component of U2 snRNP, and U2AF65, a U2 spliceosome protein that guides U2 snRNP’s binding to RNA. In addition, L-DL levels are decreased in APP/PS1 mouse brains. While downregulation of L-DL deteriorates memory deficits and overexpression of L-DL improves cognitive function in AD mice, by regulating the alternative splicing and expression of synaptic gene CAMKV.ConclusionsOur findings define a molecular mechanism by which hnRNP L-DL regulates alternative RNA splicing, and establish a direct role for L-DL in AD-related synaptic dysfunction and memory decline.
Highlights
Aberrant alternative splicing plays critical role in aging and age-related diseases
L-Heterogeneous nuclear ribonucleoprotein D-like (DL) shows an age-dependent decrease in the brain Heterogeneous nuclear ribonucleoproteins (hnRNPs) DL (DL) is a highly conserved nuclear RNA binding protein located in the genomic position 4q21 [40]
These findings suggest that long isoform of hnRNP D-like (L-DL) is predominantly localized to neuronal nuclei and displays an age-dependent reduction in the hippocampus of mouse brain
Summary
Aberrant alternative splicing plays critical role in aging and age-related diseases. Heterogeneous nuclear ribonucleoproteins (hnRNPs) reportedly regulate RNA splicing process. Exon 18 skipping of postsynaptic density protein 95 (PSD95) results in generation of a splicing variant with premature translational termination, and this splicing variant is prone to degradation through nonsense-mediated decay (NMD) pathway, resulting in reduced levels of PSD95 [9] This splicing change of PSD95 is promoted by polypyrimidine tract binding protein 1 (PTBP1), whose levels are significantly increased upon aging progression [10]. Fulllength BACE1 shows an age-dependent increase, resulting in a rise in BACE1 level and a consequent accumulation of Aβ in the brain [13] This leads to age-related cognitive impairment and AD progression [14,15,16]. A mutation in intron 4 of presenilin 1 (PS1) leads to production of an aberrant transcript and a full-length PS1 with insertion of an extra threonine, promoting Aβ42 production and AD pathology [17, 18]
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