Digital Theses Archive


Tesi etd-03302023-173049

Type of thesis
Delayed administration of pro-regenerative miR-199a after myocardial infarction: efficacy versus untoward effects
Scientific disciplinary sector
Istituto di Scienze della Vita - PHD IN MEDICINA TRASLAZIONALE
  • cardiomyocyte proliferation
  • gene therapy
  • miRNA-199a
  • myocardial infarction
Exam session start date
Acute loss of a major amount of cardiac tissue following myocardial infarction frequently leads to heart failure, an illness with a low quality of life and a high death rate. Because the prevalence of heart failure is rising, the development of an effective and safe cardio-reparative therapy could mark a significant milestone in cardiovascular medicine. Our team recently demonstrated in a pig model that intramyocardial injection of miRNA-199a genes delivered by adeno-associated viral vectors (AAV) shortly after the induction of acute myocardial infarction (MI) resulted in nearly complete recovery of cardiac morpho-functional parameters. However, 6-7 weeks following miRNA-199a delivery, the majority of the animals died suddenly, most likely due to lethal arrhythmias.<br>The overarching goal of this study was to investigate the hypothesis that delaying AAV6-miR199a treatment during the healing phase of MI had therapeutic effects without inducing long-term lethal arrhythmias.<br>The first goal was to investigate whether the therapeutic efficacy of AAV6-miR-199a delivery is time-dependent. MI was caused by placing a balloon-tipped catheter into the left anterior descending coronary artery and occluding it for 90 minutes under X-ray fluoroscopic monitoring. To evaluate baseline cardiac morpho-functional features and scar diameters, all pigs underwent baseline cardiac MRI evaluation on day 5 (Protocol 1) or day 12 (Protocol 2) post-MI. Two days after MRI, animals underwent open-chest surgery and were randomly assigned to receive 2 x 1013 of AAV6-miR-199a or empty AAV6 (AAV-control) injected in multiple places along the infarct border zone. The animals had a second cardiac MRI one month after receiving AAV. Scar mass and global and regional contractile performance parameters were not significantly different between AAV6-miR-199a and AAV-control MI in either of the Protocols. <br>Despite the lack of significant morpho-functional changes, the majority of pigs in both protocols died of abrupt cardiac death 6-8 weeks after AAV6-miR-199a administration. We were able to record ECG tracings in several cases that indicated ventricular fibrillation as the cause of death.<br>Our second goal was to see if infarcted hearts treated with miR-199a have a decreased threshold for ventricular arrhythmias in response to aberrant electrical stimuli. In infarcted hearts, electrophysiology tests were performed six weeks following AAV6-miR-199a or AAV6-control administration. While all AAV6-control animals developed ventricular arrhythmias, AAV6-miR-199a-treated pigs exhibited unexpected resistance to external extra stimuli, even with the most intense stimulation pattern.<br>In conclusion, our findings suggest that gene therapy using miR-199a for cardiac repair loses efficacy when delivered 7 or more days after MI, while the propensity for deadly arrhythmias remains in treated hearts. Surprisingly, the infarcted hearts treated with miR-199a, have a higher threshold for ventricular arrhythmias in response to aberrant electrical stimuli. These data provide support for the idea that delivering miR-199a via AAV vectors, which results in long-term expression, is not the best approach. Future studies will examine different types of vectors for short-term expression of miR-199a, such as synthetic nanoparticles that can only be administered during the acute phase of MI.<br>