Worldwide millions of patients suffer from cardiovascular diseases, which can lead to life-threatening conditions. Besides improvements in diagnosing and treating those patients, regenerative treatments are still limited. Therefore novel curative strategies are urgently needed. Long non-coding RNAs (lncRNAs) emerged as druggable molecules, but due to their relatively recent discovery their exploration as therapeutic targets is still in its infancy. LncRNAs arecharacterized by a length of more than 200 nucleotides and modulate gene expression on a transcriptional and posttranslational level via various mechanisms. Another advantage of targeting lncRNAs is their specific expression during diseases or different developmental stages reducing potential adverse effects. 

After a cardiac injury cardiomyocytes are lost irreversibly due to the limited regenerative capacity of the heart. Besides exogenously applied cell therapy, the stimulation of the low but existing intrinsic proliferative potential of cardiomyocytes is pursued. In this regard we aimed to identify novel lncRNAs as potential regulators in cardiac regeneration.

One of the promising candidates is the lncRNA Cyrano, which we found by analyzing publicly available RNA sequencing data sets of regenerating and non-regenerating hearts. Cyrano shows a remarkable sequence conservation from fish to humans, which is rare for lncRNAs and suggests an important regulatory role across the evolution. Cyrano is enriched in the brain and the heart; in the latter Cyrano is highly expressed in cardiomyocytes compared to cardiac fibroblasts and endothelial cells.

To modulate Cyrano in human iPSC-derived cardiomyocytes in vitro specific siRNAs were applied. Global transcriptomic alterations were analyzed by total RNA sequencing in Cyrano depleted cardiomyocytes and revealed an impact of the Cyrano knockdown on the cell cycle and cell cycle-associated pathways. Indeed we observed an enhanced Ki67 expression in cardiomyocytes after Cyrano knockdown. Also the total number of cardiomyocytes increased after silencing. To more specifically assess proliferation in cardiomyocytes, a cyclin B1 reporter cell line was applied. In line, also here the knockdown of Cyrano induced the number of proliferating cardiomyocytes.

Besides the pro-proliferative effect of silencing Cyrano we also focused on the potentially cardioprotective role of Cyrano focusing on pathological cardiac hypertrophy. We observed a dysregulation in cardiac tissue from patients suffering from hypertrophic diseases. Therefore, Cyrano knockout and control mice were subjected to a transverse aortic constriction, resulted in a pressure overload-induced cardiac hypertrophy, subsequently leading to heart failure. Echocardiographic analysis of cardiac parameters elucidated a partial rescue of the hypertrophic phenotype in Cyrano knockout animals. In depth investigation of the underlying mechanisms are ongoing. 

In conclusion, the modulation of the highly conserved lncRNA Cyrano represents an interesting strategy for cardiac regeneration in terms of boosting cardiomyocytes proliferation. Additionally also the reduction of Cyrano expression in cardiac hypertrophy is beneficial for cardiac performance. New therapeutic options for cardiovascular diseases are urgently needed and the modulating of lncRNAs might play a crucial role in future therapeutic strategies.