iPSC-based Models of Genetic Dilated Cardiomyopathy: from Mechanisms to Personalized Therapies

Dilated cardiomyopathy (DCM) is a primary disease of the heart muscle, characterized by enlargement of the left ventricle and systolic dysfunction, which results in progressive heart failure. Approximately 30-50% of cases are familial and are caused by mutations in more than 50 different genes. Among these, sarcomeric protein Titin is the most frequently associated with DCM, accounting for 25% of familiar cases. Although less frequent in DCM cases (4-7%), mutations in LMNA gene, encoding the nuclear envelope component Lamin A/C, lead to a more aggressive phenotype characterized by occurrence of conduction system disorders and arrhythmia. DCM patients usually show a heterogeneous spectrum of symptoms, that manifest with variable penetrance; response to Optimal Medical Therapy, which is still based on symptomatic and non-personalized treatments, is also poorly predictable. Based on these premises, the main aim of this work was to establish whether cellular models based on patient-specific pluripotent stem cells may provide a valuable platform to determine clearer genotype/phenotype correlations and to test patient-specific response to therapies. To this end, we employed cardiomyocytes (CMs) differentiated from induced Pluripotent Stem Cells (iPSC) generated from DCM patients, bearing different mutations in TTN or LMNA genes. In detail, two iPSC lines carrying LMNA mutations (LMNA K219T and LMNA R190W ) were previously generated by our group, while 4 iPSC lines (TTN01, TTN02, TTN03 and TTN04) derived from TTN-mutated patients were newly reprogrammed. We assessed the specific alterations of TTN-CMs and LMNA-CMs by measuring their electrical and mechanical properties by patch clamp and Ion Optix system. Results showed signs of contractile dysfunction in TTN-CMs, with a significant reduction of shortening and relaxation velocity and a consequent increase of the time to peak and time to baseline compared to control CMs; this was associated to a faster calcium transient dynamics, suggesting a possible compensatory mechanism for impaired contraction. The treatment with ACE inhibitor Ramipril was sufficient to rescues these alterations in TTN03-CMs, but not in TTN02-CMs, reflecting the different response that these two patients displayed in vivo (TTN03 being a responder, TTN02 being a non-responder to Optimal Medical Therapy). As previously described by our group, LMNA-CMs were instead characterized by reduced sodium current density which resulted in altered excitability of these cells and slower impulse propagation velocity. Here, we found that junctional conductance is also significantly reduced, further sustaining the implication of the investigated LMNA mutations in conduction defects typically occurring in patients with LMNA-DCM. Coherently, plasmatic membrane expression of both the sodium channel protein Nav1.5 and the gap junction component Connexin 43 were significantly reduced in LMNA- CMs. Interestingly, when LMNA-CMs were treated with Remodelin, a N-acetyltransferase 10 inhibitor previously demonstrated to be effective in improving survival of progeric mice and restoring nuclear abnormalities of Lamin A/C-depleted cells, Nav1.5 and Connexin 43 localization at the plasma membrane was significantly enhanced, and the electrical phenotype LMNA-CMs was restored. In conclusion, while completing the functional characterization for all the patient’s lines, our results identify iPSC-models as a reliable tool to discriminate the diverse DCM manifestations as well as to test drug response in vitro. Once completed, our study should contribute to improve DCM patients’ risks stratification and help developing personalized therapeutic approaches.