Abstract 17345: Dysregulated Phenylalanine Catabolism is a Key Determinant of Cardiac Aging

Introduction: Cardiac aging is characterized by cardiomyocyte hypertrophy and myocardial interstitial fibrosis with impaired contractility and relaxation. Recent metabolomics studies revealed an age-dependent increase in the plasma levels of essential amino acid phenylalanine (Phe), which is predictive of heart failure hospitalization. The present study aimed to dissect 1) the basis for increased Phe levels with age and 2) how Phe may promote age-related cardiac dysfunction. Methods: To establish a role for Phe in driving cardiac aging, wild-type (WT) male mice were treated twice a day with Phe (200 mg/kg) for a month. The impact of Phe on cellular senescence, redox biology and epigenetics were explored in cultured cardiomyocytes (primary adult rat and AC-16 human cardiomyocytes) treated with Phe. In vivo cardiac structure and function, together with Phe catabolism were monitored in WT and in p21 -/- mice (in pursuit of p21 induction with Phe and age) up to 24 months of age. Finally, we treated aged WT mice with tetrahydrobiopterin (BH4; 10 mg/kg), the essential cofactor for Phe-degrading enzyme phenylalanine hydroxylase (Pah). The effect of aging and Phe treatment on hepatic Phe catabolism was explored in vivo and vitro in AML-12 hepatocytes. Results: Natural aging induced a progressive increase in plasma Phe levels concomitant with cardiac dysfunction, whilst p21 deficiency prevented these changes. Phe treatment triggered cellular senescence, along with complex redox and epigenetic changes in vitro and induced an age-mimicking cardiac deterioration in young WT mice in vivo . Pharmacological restoration of Phe catabolism with BH4 reversed the rise in plasma Phe and senescent cardiac alterations in aged WT mice without affecting myocardial NOS activity. Key observations were reproduced in corresponding human samples and collectively they pointed to hepatic Phe catabolic decline with ensuing elevated plasma Phe levels compromising cardiac integrity. Conclusions: Our findings established a pathogenic role for increased Phe levels in cardiac aging, highlighting modulation of Phe catabolism as a potential therapeutic target for age-associated cardiac impairment.