Metallothionein Abrogates GTP Cyclohydrolase I Inhibition–Induced Cardiac Contractile and Morphological Defects: Role of Mitochondrial Biogenesis

• Published in: Hypertension (Dallas, Tex. 1979) Vol. 53; no. 6; pp. 1023 - 1031
• Main Authors: Ceylan-Isik, Asli F, Guo, Kelly K, Carlson, Edward C, Privratsky, Jamie R, Liao, Song-Jie, Cai, Lu, Chen, Alex F, Ren, Jun
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD American Heart Association, Inc 01.06.2009; Lippincott Williams & Wilkins
• Subjects: Analysis of Variance; Animals; Arterial hypertension. Arterial hypotension; Biological and medical sciences; Biopterins - analogs & derivatives; Biopterins - blood; Biopterins - metabolism; Blood and lymphatic vessels; Blotting, Western; Cardiology. Vascular system; Chromatography, High Pressure Liquid; Clinical manifestations. Epidemiology. Investigative techniques. Etiology; Disease Models, Animal; Echocardiography; GTP Cyclohydrolase - metabolism; Male; Medical sciences; Metallothionein - drug effects; Metallothionein - metabolism; Mice; Mice, Transgenic; Mitochondria, Heart - metabolism; Myocardial Contraction - drug effects; Myocardial Contraction - physiology; Myocytes, Cardiac - cytology; Myocytes, Cardiac - metabolism; Nitric Oxide - biosynthesis; Oxygen Consumption - physiology; Probability; Random Allocation; Reverse Transcriptase Polymerase Chain Reaction; RNA - analysis; Sensitivity and Specificity; Sugar Acids - pharmacology; Hypertension; GTP; Hyperoxides; Cardiovascular disease; cardiomyocyte mechanics; metallothionein; superoxide; BH4; eNOS uncoupling
• ISSN: 0194-911X; 1524-4563
• DOI: 10.1161/HYPERTENSIONAHA.108.123422

One key mechanism for endothelial dysfunction is endothelial NO synthase (eNOS) uncoupling, whereby eNOS generates O2 rather than NO because of deficient eNOS cofactor tetrahydrobiopterin (BH4). This study was designed to examine the effect of BH4 deficiency on cardiac morphology and function, as well as the impact of metallothionein (MT) on BH4 deficiency–induced abnormalities, if any. Friend virus B (FVB) and cardiac-specific MT transgenic mice were exposed to 2,4-diamino-6-hydroxy-pyrimidine (DAHP; 10 mmol/L, 3 weeks), an inhibitor of the BH4 synthetic enzyme GTP cyclohydrolase I. DAHP reduced plasma BH4 levels by 85% and elevated blood pressure in both FVB and MT mice. Echocardiography found decreased fractional shortening and increased end-systolic diameter in DAHP-treated FVB mice. Cardiomyocytes from DAHP-treated FVB mice displayed enhanced O2 production, contractile and intracellular Ca defects including depressed peak shortening and maximal velocity of shortening/relengthening, prolonged duration of relengthening, reduced intracellular Ca rise, and clearance. DAHP triggered mitochondrial swelling/myocardial filament aberrations and mitochondrial O2 accumulation, assessed by transmission electron microscopy and MitoSOX Red fluorescence, respectively. DAHP also promoted the N-nitro-l-arginine methyl ester–inhibitable O2 production and eNOS phosphorylation at Thr497. Although MT had little effect on cardiac mechanics and ultrastructure, it attenuated DAHP-induced defects in cardiac function, morphology, O2 production, and eNOS phosphorylation (Thr497). The DAHP-induced cardiomyocyte mechanical responses were alleviated by in vitro BH4 treatment. DAHP inhibited mitochondrial biogenesis, mitochondrial uncoupling protein 2, and chaperone heat shock protein 90, and all but uncoupling protein 2 were rescued by MT. Our data suggest a role for BH4 deficiency in cardiac dysfunction and the therapeutic potential of antioxidants against eNOS uncoupling in the heart.