An Alternative Mechanism of Subcellular Iron Uptake Deficiency in Cardiomyocytes

Abstract

Background: Systemic defects in intestinal iron absorption, circulation, and retention cause iron deficiency in 50% of patients with heart failure. Defective subcellular iron uptake mechanisms that are independent of systemic absorption are incompletely understood. The main intracellular route for iron uptake in cardiomyocytes is clathrin-mediated endocytosis. Methods: We investigated subcellular iron uptake mechanisms in patient-derived and CRISPR/Cas–edited induced pluripotent stem cell–derived cardiomyocytes as well as patient-derived heart tissue. We used an integrated platform of MS-DIA–based proteomics and signaling pathway interrogation. We employed a genetic iPSC model of 2 inherited mutations (TnT [troponin T]-R141W and TPM1 [tropomyosin 1]-L185F) that lead to dilated cardiomyopathy (DCM), a frequent cause of heart failure, to study the underlying molecular dysfunctions of DCM mutations. Results: We identified a druggable molecular pathomechanism of impaired subcellular iron deficiency that is independent of systemic iron metabolism. Clathrin-mediated endocytosis defects as well as impaired endosome distribution and cargo transfer were identified as a basis for subcellular iron deficiency in DCM-induced pluripotent stem cell–derived cardiomyocytes. The clathrin-mediated endocytosis defects were also confirmed in the hearts of patients with DCM with end-stage heart failure. Correction of the TPM1-L185F mutation in DCM patient–derived induced pluripotent stem cells, treatment with a small compound, RhoA activator II, or iron supplementation rescued the molecular disease pathway and recovered contractility. Phenocopying the effects of the TPM1-L185F mutation into WT induced pluripotent stem cell–derived cardiomyocytes could be ameliorated by iron supplementation. Conclusions: Our findings suggest that impaired endocytosis and cargo transport resulting in subcellular iron deficiency could be a relevant pathomechanism for patients with DCM carrying inherited mutations. Insight into this molecular mechanism may contribute to the development of treatment strategies and risk management in heart failure.