Circular RNAs (circRNAs) have emerged as significant players in gene regulation and therapeutic applications. Unlike linear RNAs, circRNAs form covalently closed loop structures without 5′ and 3′ ends, making them highly stable and resistant to exonuclease degradation. Their unique properties make them promising tools in RNA interference (RNAi) and gene silencing therapies.

CircRNAs are derived from precursor mRNAs (pre-mRNAs) through a process called back-splicing. They are highly expressed in eukaryotic cells and exhibit tissue-specific and developmental stage-specific expression patterns. Due to their circular structure, they have longer half-lives compared to linear RNAs, making them ideal candidates for RNA-based therapeutics. Discover more

RNAi is a natural gene silencing mechanism that involves small RNA molecules, such as small interfering RNAs (siRNAs) and microRNAs (miRNAs), in post-transcriptional regulation. These small RNAs bind to the RNA-induced silencing complex (RISC), which facilitates the degradation or translational repression of target mRNAs. CircRNAs can serve as miRNA sponges, siRNA precursors, or even directly participate in gene regulation by encoding functional peptides.

One of the most well-studied roles of circRNAs is their function as competing endogenous RNAs (ceRNAs) or miRNA sponges. By sequestering specific miRNAs, circRNAs prevent them from binding to their target mRNAs, thereby modulating gene expression. For example, CDR1as (ciRS-7) acts as a sponge for miR-7, influencing several signaling pathways associated with neurological diseases and cancer.

CircRNAs can be engineered to produce siRNAs through enzymatic processing. Synthetic circRNAs containing specific siRNA sequences can be introduced into cells, where they are processed into functional siRNAs by Dicer. This strategy allows for sustained and efficient gene silencing with reduced off-target effects. For more

• Cancer Therapy : CircRNAs can be designed to suppress oncogene expression by acting as miRNA sponges or siRNA precursors. They can also deliver tumor-suppressor miRNAs to downregulate cancer-promoting genes.
• Neurodegenerative Diseases : CircRNAs like CDR1as regulate neuronal miRNAs, offering potential therapeutic strategies for Alzheimer’s and Parkinson’s disease.
• Viral Infections : CircRNA-based RNAi can target viral RNAs, providing an innovative approach to antiviral therapy against hepatitis, HIV, and SARS-CoV-2.
• Genetic Disorders: CircRNA-mediated RNAi can silence disease-causing genes in monogenic disorders such as Duchenne muscular dystrophy and Huntington’s disease.

Challenges and Future Directions

Despite their potential, several challenges remain in utilizing circRNAs for gene silencing :

• Delivery Efficiency: Effective and targeted delivery of synthetic circRNAs remains a major hurdle.
• Immunogenicity: Engineered circRNAs must be optimized to minimize immune responses.
• Off-Target Effects: Ensuring specificity and reducing unintended gene silencing is critical for clinical applications.

Ongoing research focuses on improving circRNA engineering, optimizing delivery methods, and understanding their interactions with cellular components to advance their use in RNAi-based therapies.

Circular RNAs represent a novel and promising tool for RNAi and gene silencing therapies. Their stability, ability to function as miRNA sponges, and potential as siRNA precursors offer exciting opportunities for treating various diseases. Further research and technological advancements will pave the way for their successful clinical application in precision medicine.

https://pmc.ncbi.nlm.nih.gov/articles/PMC8632079/