Muscle Regeneration and RNA: New Perspectives for Ancient Molecules

Abstract

The ability of the ribonucleic acid (RNA) to self-replicate, combined with a unique cocktail of chemical properties, suggested the existence of an RNA world at the origin of life. Nowadays, this hypothesis is supported by innovative high-throughput and biochemical approaches, which definitively revealed the essential contribution of RNA-mediated mechanisms to the regulation of fundamental processes of life. With the recent development of SARS-CoV-2 mRNA-based vaccines, the potential of RNA as a therapeutic tool has received public attention. Due to its intrinsic single-stranded nature and the ease with which it is synthesized in vitro, RNA indeed represents the most suitable tool for the development of drugs encompassing every type of human pathology. The maximum effectiveness and biochemical versatility is achieved in the guise of non-coding RNAs (ncRNAs), which are emerging as multifaceted regulators of tissue specification and homeostasis. Here, we report examples of coding and ncRNAs involved in muscle regeneration and discuss their potential as therapeutic tools. Small ncRNAs, such as miRNA and siRNA, have been successfully applied in the treatment of several diseases. The use of longer molecules, such as lncRNA and circRNA, is less advanced. However, based on the peculiar properties discussed below, they represent an innovative pool of RNA biomarkers and possible targets of clinical value.

Keywords: RNA therapeutics; cardiac regeneration; noncoding RNAs (ncRNAs); skeletal muscle regeneration.

Figure 1

Chemical and structural properties of RNA that are usable for therapeutics. Different RNA types are shown as follow: (A) mRNA/modRNA. The uridine into pseudouridine substitution in modRNAs is represented by the greek Ψ symbol (red); (B) lncRNA; (C) circRNA. Locket (yellow) represents the covalently closed structure which makes circRNA resistant to exonucleases (RNases); (D) miRNA. See text for further details.

Figure 2

RNA-based drugs in muscular and cardiovascular pathologies. (A) “Mimics” and siRNAs act by targeting specific mRNAs to inhibit their translation. Examples include the TQJ230 siRNAs, which specifically recognize and induce the degradation of ApoA mRNA in patients with pre-existing cardiovascular diseases [91]; (B) “AntagomiRs” act by sponging endogenous miRNAs, thus preventing their translational repression. MRG-110 was used to block miR-92a activity on pro-angiogenic genes to induce wound healing [92]; (C) ASO can be used to modify the splicing of precursor mRNAs (pre-mRNA). The exon-skipping strategy applied to dystrophin exon 51 is shown as an example. In DMD patients (-ASO), genetic mutations lead to the formation of a premature stop codon (STOP symbol) in the mature transcript that causes the lack of protein translation. The use of ASO base-pairing with dystrophin exon 51 (+ASO) promotes its exclusion from the mature mRNA and leads to the translation of a shorter (but functional) protein. For each targeted exon, the ASO approved by the FDA (Food and Drug Administration) are indicated [93,94,95,96,97]; (D) VEGF modRNA used in MI patients [98]. The uridine into pseudouridine substitution is represented by the greek Ψ symbol (red). Grey line: DNA; black line: RNA; red line: Therapeutic RNA.

Figure 3

Examples of lncRNA circuitries in muscle regeneration. (A) In the cytoplasm, lncRNAs and circRNAs can act as competing endogenous RNAs (ceRNA) to interfere with miRNA binding to their targets. Examples include CAREL/mir-296 [161], MIAT/miR-24 [162], LncMUMA/miR-762 [163], Lnc-Mg/miR-125b [164], CircHipk3/miR-133a [165], CircNfix/miR-214 [166], HRCR/miR-233 [167], and Circ-miR/miR-132/212 [168]. In the nucleus, lncRNAs can influence gene expression at the epigenetic level through several mechanisms [65]. Examples in the figure include (B) lncRNA decoys: LncMAAT impedes SOX6 binding on the promoter of miR-29b to repress its transcription [169], Linc-YY1 binds YY1 and blocks its interaction with the PRC2 complex [170]; (C) lncRNA guides: CPR [171] and Lnc-Rewind [172] respectively interact with the DNMT3A and G9a repressive complexes and guide them on specific promoters. Dashed grey lines represent the loss of interaction and regulation. TF = Transcription Factor. See text for further details.