FHOD3 deficiency disrupts sarcomere organization and activates CaMKII signaling in human stem cell-derived cardiomyocytes
Background Inherited cardiomyopathy (ICM) is a genetic disorder characterized by abnormal myocardial structure and function, often progressing to heart failure. FHOD3, a member of the Formin gene family, plays a crucial role in cardiomyocyte cytoskeletal organization. Mutations in FHOD3 have been associated with various cardiomyopathies, including hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM) and left ventricular noncompaction (LVNC). However, the molecular mechanisms underlying FHOD3 deficiency-induced cardiomyopathy remain elusive. Methods A FHOD3 knockout (FHOD3-/-) human embryonic stem cell (hESC) line was generated using the CRISPR/Cas9 system and subsequently differentiated into cardiomyocytes (hESC-CMs). Sarcomere structure, calcium handling, mitochondrial function, and contractility were evaluated via immunofluorescence, electron microscopy, Seahorse metabolic analysis, and high-definition video analysis, respectively. Transcriptomic sequencing was performed to identify differentially expressed genes and enriched pathways. Results FHOD3-deficient hESC-CMs exhibited marked sarcomere disorganization and degradation, impaired calcium handling and compromised mitochondrial function, ultimately leading to reduced contractility. Transcriptomic analysis revealed significant downregulation of sarcomere-related genes and calcium-handling genes, with enrichment in pathways associated with cardiomyopathy and calcium signaling. Furthermore, FHOD3 deficiency triggered the phosphorylation of CaMKII (Thr286), a key regulator of cardiac hypertrophy and remodeling, contributing to the progression of heart failure. Treatment with the myosin activator Omecamtiv mecarbil (OM) partially restored contractility without affecting calcium handling, highlighting its potential as a therapeutic strategy.