Rationale: LMNA (Lamin A/C) is a nuclear membrane protein that interacts with the genome and regulates gene expression. Mutations in the LMNA gene cause several distinct diseases, referred to as laminopathies. Cardiac involvement, typically manifesting with heart failure and conduction defects, is a common cause of death in laminopathies.
Objective: To delineate the mechanism(s) responsible for heart failure in laminopathies.
Methods and Results: Whole heart RNA sequencing was performed in 2-week old wild type and LMNA-deficient (Lmna-/-) mice. Transcriptomes were analyzed to identify the differentially expressed genes and their upstream regulators. Gene expression was also analyzed qPCR and protein levels were confirmed by immunoblotting. Apoptosis was assessed by TUNEL assay, histology by Masson trichrome and PicroSirius Red staining, and cardiac function by echocardiography. At 2 weeks of age, Lmna-/- mice had normal survival, cardiac function, and myocardial collagen volume fraction but were smaller in size. A total of 809 transcripts (~10%) were dysregulated (q<0.05), comprised of 576 upregulated and 233 downregulated transcripts in the Lmna-/- mouse hearts, as compared to WT. Pathway analysis identified FOXO and E2F transcription factors (TFs) as the most activated and suppressed upstream regulators, respectively. Levels of FOXO targets were also increased in the human heart failure samples. Gene ontology Gene Set Enrichment Analysis identified inflammation, apoptosis, and hypoxia as the most activated, and cell cycle, adipogenesis, and oxidative phosphorylation as the most suppressed biological functions. Activation of FOXO1 and FOXO3 TFs were validated by increased nuclear localization and increased levels of its downstream targets. Knockdown of FOXO 1 and FOXO3 by recombinant AAV9 vectors expressing a sequence-specific shRNA, partially rescued the target transcripts and apoptosis and prolonged the median survival by 2-fold.
Conclusions: FOXO TFs are activated in the heart and contribute to the pathogenesis of cardiac phenotype in the LMNA-deficient mice. Targeting of the FOXO TFs in the heart improves cardiac phenotype and survival. Thus, FOXO TFs are potential therapeutic targets in heart failure caused in laminopathies.