Site-directed A → I RNA editing as a therapeutic tool: moving beyond genetic mutations

Abstract

Adenosine deamination by the ADAR family of enzymes is a natural process that edits genetic information as it passes through messenger RNA. Adenosine is converted to inosine in mRNAs, and this base is interpreted as guanosine during translation. Realizing the potential of this activity for therapeutics, a number of researchers have developed systems that redirect ADAR activity to new targets, ones that aren’t normally edited. These site-directed RNA editing (SDRE) systems can be broadly classified into two categories: ones that deliver an antisense RNA oligonucleotide to bind opposite a target adenosine, creating an editable structure that endogenously expressed ADARs recognize, and ones that tether the catalytic domain of recombinant ADAR to an antisense RNA oligonucleotide that serves as a targeting mechanism, much like with CRISPR-Cas or RNAi. To date, SDRE has been used mostly to try and correct genetic mutations. Here we argue that these applications are not ideal SDRE, mostly because RNA edits are transient and genetic mutations are not. Instead, we suggest that SDRE could be used to tune cell physiology to achieve temporary outcomes that are therapeutically advantageous, particularly in the nervous system. These include manipulating excitability in nociceptive neural circuits, abolishing specific phosphorylation events to reduce protein aggregation related to neurodegeneration or reduce the glial scarring that inhibits nerve regeneration, or enhancing G protein-coupled receptor signaling to increase nerve proliferation for the treatment of sensory disorders like blindness and deafness.

Unveiling the A-to-I mRNA editing machinery and its regulation and evolution in fungi

“…A-to-I RNA editing systems have recently gained attention for their ability to recode genetic information at the mRNA level. This allows for the correction of pathogenic mutations and the reprogramming of genetic information, which is particularly relevant as C:G to T:A genetic mutations account for approximately half of all known pathogenic point mutations in humans ( 17, 18 ). Site-directed RNA editing systems have been developed using ADARs to target disease-causing point mutations ( 19, 20 ).…”

Structural and functional effects of inosine modification in mRNA

“…Precise inhibition of specific A-to-I editing events has also been observed with the use of antisense oligonucleotides (ASOs) that specifically bind to ADAR transcript targets, effecting a change in RNA structure that prevents ADAR recognition and subsequent editing ( Mizrahi et al 2013 ; Tay et al 2021 ). ADARs are also currently being utilized to implement specific A-to-I editing events at specific locations in the transcript via the process called site-directed RNA editing (SDRE) ( Khosravi and Jantsch 2021 ; Diaz Quiroz et al 2023 ; Pfeiffer and Stafforst 2023 ). SDRE uses antisense oligonucleotides complementary to therapeutically relevant target sites to form the duplex structure required for ADAR recruitment and editing.…”

The role of ADAR1 through and beyond its editing activity in cancer

“…However, the strategies of targeted RNA A-to-I editing by using endogenous or exogenous ADARs are both limited. For example, endogenous ADARs expression levels are insufficient, and delivered exogenous ADARs reduce their substrate activity [ 134 ]. Therefore, detailed understanding the factors that influence ADARs editing activity is essential to enhance their activity.…”