circSP199a, a circularized RNA sponge targeting miR-199a-5p and -3p, mitigates mouse cardiac hypertrophy and fibrosis

Increasing evidence shows that microRNAs (miRNAs) are functionally associated with cardiac remodeling. Functionally, some cytoplasmic circRNAs may act as miRNA sponges to inhibit functions of the combined miRNAs. Our previous study showed that miR-199a-5p and -3p promote cardiac hypertrophy and fibrosis. In this study, we designed and synthesized a novel circularized RNA sponge, circSP199a, and evaluated the therapeutic effects of circSP199a against cardiac hypertrophy and fibrosis. The synthesized circSP199a included 6 repeats of reverse complements of seed sequences of miR-199a-5p and -3p with 515 nt in length. We showed that the synthesized circSP199a and expression vector-mediated circSP199a expression inhibited cardiomyocyte hypertrophy and mitigated the fibrotic phenotypes in neonatal mouse cardiac fibroblasts and human cardiac organoid fibrosis via the combination of miR-199a-5p and -3p. Furthermore, intravenous injection of AAV9-circSP199a for 21 days in advance significantly ameliorated transverse aortic constriction-induced cardiac injury and remodeling in mice. We demonstrated that circSP199a blocked the functions of miR-199a-5p and -3p to enhance the expression of target genes of PGC-1α, Rb1, Sirt1 and Smad1 both in vitro and in vivo. These results provide new insights into the development of RNA sponge-based therapies for cardiac hypertrophy and fibrosis. The artificial circSP199a functions as a novel inhibitor of miR-199a-5p and -3p, exogenous provision of circSP199a specifically sponges miR-199a-5p and -3p to block their functions with subsequent upregulations of the target genes, including PGC-1α, Rb1, SIRT1 and Smad1, to mitigate the pathological cardiac hypertrophy and fibrosis.