AAV9-mediated TNPO3 overexpression in the heart rescues RBM20 cardiomyopathy in mice

The RBM20 gene encodes for an alternative splicing regulator which, when mutated, can cause an aggressive form of DCM. The majority of RBM20 mutations identified in patients are found in the RS-domain, and lead to cytoplasmic mislocalization of the protein. In our previous work (Kornienko et al., Nat Commun, 2023), we identified TNPO3 as a direct nuclear importer of RBM20, and showed that restoring nuclear localization of mislocalizing variants rescues splicing dysfunction in iPSC-CMs. Here, we used our two recently published mouse models with patient-relevant RBM20 variants (Grosch et al., Nat Commun, 2023) to test whether nuclear relocalization could restore the alternative splicing and cardiac dysfunction in vivo. We used AAV9 vectors to overexpress TNPO3 in murine hearts and thereby facilitate nuclear import of RBM20 variants. We show that TNPO3 overexpression could rescue ejection fraction, cardiac volume, and alternative splicing, without having any detectable adverse effects on wild type animals. These results provide the first in vivo evidence that restoring RBM20 localization can significantly improve cardiac function and correct for splicing errors.