Targeting synaptic dysfunction using antisense RNA enhancers in neurodegenerative diseases

Synaptic transmission is of critical importance for the neurons to communicate, and abnormalities are observed in neurodegenerative diseases, psychiatric disorders, and intellectual disability. Loss of the synaptic vesicle proteins is shared among these disorders and is being noted as one of the earliest hallmarks of neurogenerative diseases. Therefore, novel therapeutics targeting synapses are fundamental to improve brain plasticity and maintain a healthy brain function. 

Here, we propose to normalize synaptic protein levels by targeting unstable synaptic mRNAs using antisense RNA enhancer molecules with the ‘long-term goal’ of developing a therapy for patients with synaptic dysfunction, specifically in Alzheimer’s Disease (AD) and Amyotrophic Lateral Sclerosis (ALS). Our ‘hypothesis’ is that stabilization of unstable synaptic mRNA’s by antisense RNA molecules will be effective in enhancing and restore the levels of downregulated synaptic proteins in AD and ALS. As a ‘proof of concept’ antisense RNA molecules targeting 5’UTR regions of unstable synaptic genes (synapsin and synaptophysin) fused to enhancer elements such as SINE and/or CSE replicase recognition sites were designed. To explore the efficacy and specificity, three different binding domains that span the 5’UTR region and transcription start sites (-40/+32, -40/+4, -14/+4) per gene were prepared and screened in a cell line that endogenously expresses the target genes. Our preliminary results show that SINEUP elements enhanced protein translation of the synapsin dimer by 80% and the monomers by 40%, while the CSE elements in combination with the replicase increased translation of the monomers by 50-80%. This significant enhancement can stimulate synaptogenesis, synaptic vesicle recruitment, and maintain the mature synapses. An increase in synaptophysin was also observed. Ex vivo studies using a diseased cell model are in progress to assess phenotype and function. This is a promising step toward targeting synapses in neurodegenerative diseases.