Chen Lingling's group discovered the immunogenic mechanism and potential applications of in vitro synthesis of circular RNA

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Most circular RNAs come from reverse splicing of exons to form a closed loop structure with covalent bonds
.

Studies have found that this type of molecule has a unique production and processing process, which is different from the folded conformation of linear RNA, and has high stability

It should be pointed out that there are two important issues that need to be paid attention to when studying the potential applications of circular RNA synthesized in vitro, one is how to improve the efficiency of synthesizing circular RNA in vitro, and the other is whether the synthesized circular RNA is immunogenic
.

On the one hand, recent research reports indicate that the circular RNA synthesized in vitro can be recognized by the innate immune receptor RIG-I, and then cause the innate immune response in the cell (Chen et al.

To clarify these important issues, Chen Lingling's team first compared the efficiency and immunogenicity of different methods of in vitro synthesis of circular RNA
.

At present, there are two main ways to synthesize circular RNA in vitro: direct intramolecular linking based on the catalysis of T4 RNA ligase, and self-splicing loop based on type I intron ribozyme

Further comparison and analysis of the sequence and secondary structure of circular RNA synthesized by different circularization methods found that the circular RNA synthesized based on T4 RNA ligase only introduced 1 to 3 exogenous nucleotides, but the two types of I contained The circular RNA formed by self-splicing in vitro will introduce 74 or 186 exogenous nucleotides, respectively
.

Researchers used the improved circSHAPE-MaP technology (Liu et al.

The previous work of Chen Lingling's research group found that overexpression of endogenous circular RNA containing 16-26bp short double-stranded structure in PBMC or T cells derived from patients with systemic lupus erythematosus (SLE) can inhibit the abnormal activation of PKR and disease marker genes ( Liu et al.
, Cell 2019), suggesting that in vitro synthesis of non-immunogenic circular RNA containing a short double-stranded structure is expected to become a new method for the treatment of autoimmune diseases
.

The small molecule compounds that have been reported to inhibit abnormal phosphorylation activation of PKR, such as 2-Aminopurine (2-AP), oxindole/imidazole derivative compound 16 (C16), etc.

　　In summary, this research lays an important foundation for the further application of circular RNA synthesized in vitro, and also brings promising prospects for the further development of nucleic acid aptamers and gene therapy based on circular RNA technology
.

　　Dr.
Chuxiao Liu, a postdoctoral fellow in Lingling Research Group of the Center for Molecular Cellular Excellence, and Sikun Guo, a doctoral student, are the co-first authors of the paper, and Researcher Chen Lingling is the corresponding author of the paper
.

This work was supported by researcher Yang Li from the Shanghai Institute of Nutrition and Health of the Chinese Academy of Sciences, PhD student Xu Yifeng in the Chen Lingling group, and Dr.

　　Article link: https:// 

The immunogenic mechanism and potential applications of in vitro synthesis of circular RNA