Cardiomyocyte-Specific Nucleolin Deficiency Induces Progressive Heart Failure in Adult Mice

Background: Nucleolin (NCL) is a multifunctional nucleolar phosphoprotein involved in ribosome biogenesis, RNA metabolism, transcriptional regulation, and cellular stress responses. Although NCL has been studied in diverse biological contexts, its role in maintaining adult cardiomyocyte homeostasis and cardiac function remains poorly defined. Methods: To determine whether loss of Ncl in cardiomyocytes is sufficient to induce cardiac dysfunction in vivo, we generated a tamoxifen-inducible cardiomyocyte-specific Ncl knockout mouse model ( Ncl ^fl/fl ;Myh6-Cre). Cardiac function, myocardial remodeling, mitochondrial ultrastructure, energy and lipid metabolism, and transcriptomic alterations were systematically evaluated. Results: Following tamoxifen induction, Ncl ^ΔCM mice developed progressive cardiac dysfunction characterized by reduced survival, impaired systolic function, and elevated serum CK-MB and LDH1 levels. Histological analysis revealed myocardial disorganization and increased collagen deposition. Transmission electron microscopy demonstrated mitochondrial swelling, fragmentation, and cristae disruption, accompanied by reduced myocardial ATP content. Ncl ^ΔCM mice also exhibited disturbed lipid homeostasis, with reduced myocardial free fatty acid and triglyceride levels and increased circulating lipid levels. Transcriptomic analysis revealed marked alterations in metabolic pathways, particularly fatty acid metabolism-related programs. Consistent with these findings, expression of fatty acid metabolism-related genes, including Fasn, Cd36, Cpt1b, Cact, Acat1, and Acot1 , was significantly reduced. Gene set enrichment analysis further demonstrated enrichment of the p53 pathway in Ncl ^ΔCM hearts. Expression of the p53/senescence-associated genes Trp53, Cdkn1a, and Cdkn2a was increased at the mRNA level, while increased P53 and P21 protein expression was confirmed by Western blotting. Immunofluorescence staining further demonstrated increased P21 expression in cardiomyocytes of Ncl ^ΔCM hearts. Conclusions: Cardiomyocyte-specific deletion of Ncl is sufficient to induce progressive heart failure in adult mice. This phenotype is associated with myocardial remodeling, mitochondrial injury, impaired energy metabolism, disrupted lipid metabolic homeostasis, and activation of a p53–P21-associated senescence program. These findings identify NCL as an important regulator of adult cardiac structural and metabolic homeostasis and establish a useful genetic model for investigating cardiomyocyte-intrinsic mechanisms underlying heart failure.