Nuclear speckle specific hnRNP D-like prevents age- and AD-related cognitive decline by modulating RNA splicing

Background: Aberrant 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.
Methods: Immunoblotting 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.
Results: We 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.
Conclusions: Our 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.
Keywords: hnRNP DL, Aging, Alzheimer’s disease (AD), Cognition, Nuclear speckles, Alternative splicing