Restoration of full length filamin C is sufficient to prevent FLNC deficient cardiomyopathy in mice.

Filamin C (FLNC) is an essential cytoskeletal protein required for cardiomyocyte structural integrity and mechanotransduction. Truncating FLNC variants cause haploinsufficiency associated with dilated and arrhythmogenic cardiomyopathies, yet no therapies currently address the underlying defect of FLNC deficiency. Gene replacement is challenging because the approximately 8.2-kb FLNC coding sequence exceeds the packaging capacity of conventional adeno-associated virus (AAV) vectors. Here, we engineered a triple-AAV strategy optimized for full-length FLNC reconstitution in the heart. Screening in HEK293 cells identified GP41-1 and IMPDH as a compatible orthogonal pair for efficient full-length FLNC reconstitution. In tamoxifen-inducible, cardiomyocyte-specific Flnc knockout mice, systemic delivery of optimized MyoAAV2A vectors restored full-length FLNC expression and re-established sarcomeric localization following cardiomyocyte FLNC depletion. A total vector dose of 1 × 10¹³ genome copies/kg restored FLNC to approximately endogenous abundance, preserved systolic function and ventricular dimensions, limited cardiac enlargement, attenuated fibrotic remodeling and prevented premature death. FLNC replacement also attenuated pathological transcriptional remodeling and compensatory changes in cytoskeletal and junction-associated proteins. These findings demonstrate that systemic split-intein-mediated reconstitution of full-length FLNC can preserve cardiac structure and function in vivo, providing preclinical support for a mutation-independent therapeutic strategy for FLNC-associated cardiomyopathy.