Question: Cysteine is metabolized in endothelial cells by the enzyme cystathionine gamma lyase (CSE) which also generates the H ₂ S, a potential angiocrine factor. H ₂ S generation and cysteine catabolism regulate endothelial cell activation and mechanosensing. This project set out to characterize the effects of reduced endothelial cell cysteine catabolism (inducible endothelial cell-specific CSE knockout mice / CSE ^iΔEC mice) and to identify potential CSE-associated angiocrine effects on cardiomyocytes.

Methods and results: Analysis of CSE activity and H ₂ S levels (HPLC-MS / MS) in endothelial cells from 1, 3, 6 and 18 month old mice revealed a gradual decrease in H ₂ S production. This decrease was associated with the enhanced phosphorylation of CSE on Ser377, which inhibits its activity. To determine whether the deletion of endothelial cell CSE impacts on cardiac function, CSE ^iΔEC and wild type littermates were studied. Cardiac echocardiography and μCT analyzes revealed an age dependent systolic and diastolic dysfunction, which was enhanced in 18 month old CSE ^iΔEC mice - based on left ventricle posterior wall thickness. In addition, pulsed-wave Doppler recording showed severe right ventricular dysfunction, with significantly shorter pulmonary acceleration time and tricuspid annular plane systolic excursion measures. Histopathological characterization of hearts confirmed severe hypertrophy without signs of inflammation in hearts from CSE ^iΔEC mice compared to their wild type littermates. Mechanistically, endothelial CSE deletion impacted on the cardiomyocyte transcriptional program. RNA sequencing of cardiomyocytes isolated from 18 month old wild type and CSE ^iΔECmice, revealed changes in hypertrophic (ie myosin heavy chain 6 and 7) and metabolic related transcripts (ie carbonic anhydrase 3, fatty acid synthase). Validation of the most upregulated transcripts confirmed these observations, while treatment with the sulfur donor (sodium polysulthionate) reversed this effect. The most altered gene was cytochrome P450 2E1 (CYP2E1), and its upregulation could be confirmed at the protein level.

Conclusions : Age-related alterations in the endothelial cysteine catabolism impact on cardiac function and cardiomyocyte transcriptional program. Studies are ongoing to investigate the link between CSE and CYP2E1 as well as the impact of cardiomyocyte CYP2E1 on heart function.