A novel gene therapy for familial dilated cardiomyopathy based upon disruption of PP2A-- mAKAP-beta signalosomes

Familial Dilated Cardiomyopathy (DCM) is a common inherited cause of heart failure characterized by progressive left ventricular dilatation and systolic dysfunction. Despite the discovery of novel genetic mutations causing DCM, the downstream mechanisms resulting in heart failure are still unclear, and there remains a great unmet clinical need. Contributing to the phenotype of ventricular dilatation in DCM is the lengthening of cardiac myocytes, which exhibit increased overall length to width ratio. We have shown that increasing the phosphorylation of the transcription factor serine response factor (SRF) at serine residue 103 by displacement of protein phosphatase 2A (PP2A) from the perinuclear scaffold protein muscle A-kinase anchoring protein β (mAKAPβ) can inhibit myocyte lengthening and improve cardiac function following myocardial infarction. Notably, SRF S103 phosphorylation is decreased in both human heart failure and in the hearts of transgenic mice expressing the human DCM α-tropomyosin Glu54Lys (Tm-E54K) mutant allele. We now show that, accordingly, targeting of mAKAPβ-PP2A signalosomes constitutes a new therapeutic strategy for DCM. A self-complementary serotype 9 adeno-associated virus (AAV9sc) conferring cardiac-specific expression of a mAKAPβ fragment comprising the PP2A binding domain (PBD) was used to target the signalosomes in mice. AAV9sc.PBD administration into neonatal Tm-E54K mice provided long term preservation of cardiac function and prevented ventricular dilatation. At 16 weeks of age, ejection fraction was significantly improved 14%[MK1], and wall thickness was increased for AAV9sc.PBD TM-E54K mice when compared with control AAV9sc.GFP treated TM-E54K mice. Morphometry of acutely dissociated adult mouse myocytes showed that AAV9sc.PBD treatment restored myocyte length to width ratio to that of non-transgenic animals, while western blots showed increased SRF S103 phosphorylation. The results in mice have been corroborated by PBD expression in engineered heart tissues (EHT) generated from an induced pluripotent stem cell (iPSC) line for a DCM phospholamban R14del patient. PBD expression increased SRF S103 phosphorylation and improved tissue contractility. Taken together, this study suggests that increasing SRF S103 phosphorylation by disruption of mAKAPβ-PP2A signalosomes can constitute a novel therapeutic strategy for DCM. Funded by Department of NIH Grant R01HL146111 (Dr. Kapiloff), R01 HL139679 and Leducq Foundation CurePlan (Dr. Karakikes), and the NHLBI Gene Therapy Resource Program. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.