Cardiovascular diseases (CVDs) remain the leading cause of death worldwide. Current treatments for CVDs only alleviate the patient´s symptoms but they do not cure the underlying causes of the diseases. Therefore, there is an urgent need for novel therapeutic approaches. In recent years, non-coding RNAs (ncRNAs) have emerged as promising new therapeutic targets. Among them are long non-coding RNAs (lncRNAs), which are defined as transcripts longer than 200 base pairs. They play key roles in regulating gene expression at transcriptional, post-transcriptional, and translational levels. They are often expressed in cell type and disease-specific manner, highlighting their potential as powerful therapeutic targets.
Through initial sequencing analysis in mice, we identified that the lncRNA Foxo6os is downregulated in various heart disease conditions. After observing promising initial results showing that the overexpression of murine Foxo6os had beneficial treatment effects in different disease settings, we aimed to translate the results into a human context. Interestingly, we discovered a locus conserved lncRNA annotated as SCMH1-DT (ENST00000425554.2).
Owing to translational relevance, we focused on investigating SCMH1-DT, which is similarly downregulated in human heart failure samples. LncRNA SCMH1-DT is primarily expressed in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and endothelial cells, with minimal expression in fibroblasts. In vitro, the downregulation was further validated in human iPSC-derived cardiomyocytes either cultivated under hypoxic conditions or treated with doxorubicin to mimic cardiotoxicity. Importantly, the modulation of SCMH1-DT was possible using an siRNA approach for downregulation as well as different overexpression methods including adeno-associated viruses (AAVs) and in vitro-transcribed RNA encapsulated in lipid nanoparticles (LNPs).
Initial gain-of-function experiments in hiPSC-CMs using AAV6-mediated overexpression increased cell viability and decreased apoptosis after incubation in a hypoxic environment whereas the downregulation exhibited contrary effects. However, tracking cell division using an hiPSC-CM cyclin B1 reporter cell line for following cell division showed that SCMH1-DT overexpression does not induce cardiomyocyte proliferation.
To further evaluate the therapeutic potential in a human disease setting, we overexpressed SCMH1-DT in an ex vivo system of living myocardial slices (LMS) and assessed the contractile function and hypertrophic gene expression. Treatment of hypertrophic LMS with AAV6-SCMH1-DT improved contractile function and decreased hypertrophic gene expression.
In conclusion, our findings suggest an important role of SCMH1-DT in the health and survival of cardiomyocytes warranting further investigation into the regulatory functions of SCMH1-DT.
