TIGAR reduces smooth muscle cell autophagy to prevent pulmonary hypertension.

Yamanaka R, Hoshino A, Fukai K, Urata R, Minami Y, Honda S, Fushimura Y, Hato D, Iwai-Kanai E, Matoba S. TIGAR reduces smooth muscle cell autophagy to prevent pulmonary hypertension. Am J Physiol Heart Circ Physiol 319: H1087-H1096, 2020. First published September 18, 2020; doi:10.1152/ajpheart.00314.2020.-Pulmonary arterial hypertension (PAH) is a refractory disease. Its prognosis remains poor; hence, establishment of novel therapeutic targets is urgent. TP53-induced glycolysis and apoptosis regulator (TIGAR) is a downstream target of p53 and exhibits functions inhibiting autophagy and reactive oxygen species (ROS). Recently, p53 was shown to suppress PAH progression. Because inhibition of autophagy and ROS is known to improve PAH, we examined the effect of TIGAR on PAH progression. We compared pulmonary hypertension (PH) development between TIGAR-deficient knockout (KO) and wild-type (WT) mice using a hypoxia-induced PH model. Human pulmonary artery smooth muscle cells (PASMCs) were used for in vitro experiments with small interfering RNA (siRNA) to investigate the possible molecular mechanisms. From the analysis of right ventricular pressure, right ventricular weight, and mortality rate, we concluded that the hypoxia-induced PH development was remarkably higher in TIGAR KO than in WT mice. Pathological investigation revealed that medial thickening of the pulmonary arterioles and cell proliferation were increased in TIGAR KO mice. Autophagy and ROS activity were also increased in TIGAR KO mice. TIGAR knockdown by siRNA increased cell proliferation and migration, exacerbated autophagy, and increased ROS generation during hypoxia. Autophagy inhibition by chloroquine and ROS inhibition by N-acetylcysteine attenuated the proliferation and migration of PASMCs caused by TIGAR knockdown and hypoxia exposure. TIGAR suppressed the proliferation and migration of PASMCs via inhibiting autophagy and ROS and, therefore, improved hypoxia-induced PH. Thus, TIGAR might be a promising therapeutic target for PAH.NEW & NOTEWORTHY Pulmonary arterial hypertension is a refractory disease. TP53-induced glycolysis and apoptosis regulator (TIGAR) is a downstream target of p53 and exhibits functions inhibiting autophagy and reactive oxygen species (ROS). By using TIGAR-deficient knockout mice and human pulmonary artery smooth muscle cells, we found that TIGAR suppressed the proliferation and migration of PASMCs via inhibiting autophagy and ROS and, therefore, improved hypoxia-induced PH. TIGAR will be a promising therapeutic target for PAH.

Cardiac-Specific Bdh1 Overexpression Ameliorates Oxidative Stress and Cardiac Remodeling in Pressure Overload-Induced Heart Failure.

BACKGROUND: Energy starvation and the shift of energy substrate from fatty acids to glucose is the hallmark of metabolic remodeling during heart failure progression. However, ketone body metabolism in the failing heart has not been fully investigated. METHODS AND RESULTS: Microarray data analysis and mitochondrial isobaric tags for relative and absolute quantification proteomics revealed that the expression of D-ß-hydroxybutyrate dehydrogenase I (Bdh1), an enzyme that catalyzes the NAD+/NADH coupled interconversion of acetoacetate and ß-hydroxybutyrate, was increased 2.5- and 2.8-fold, respectively, in the heart after transverse aortic constriction. In addition, ketone body oxidation was upregulated 2.2-fold in transverse aortic constriction hearts, as determined by the amount of 14CO2 released from the metabolism of [1-14C] ß-hydroxybutyrate in isolated perfused hearts. To investigate the significance of this augmented ketone body oxidation, we generated heart-specific Bdh1-overexpressing transgenic mice to recapitulate the observed increase in basal ketone body oxidation. Bdh1 transgenic mice showed a 1.7-fold increase in ketone body oxidation but did not exhibit any differences in other baseline characteristics. When subjected to transverse aortic constriction, Bdh1 transgenic mice were resistant to fibrosis, contractile dysfunction, and oxidative damage, as determined by the immunochemical detection of carbonylated proteins and histone acetylation. Upregulation of Bdh1 enhanced antioxidant enzyme expression. In our in vitro study, flow cytometry revealed that rotenone-induced reactive oxygen species production was decreased by adenovirus-mediated Bdh1 overexpression. Furthermore, hydrogen peroxide-induced apoptosis was attenuated by Bdh1 overexpression. CONCLUSIONS: We demonstrated that ketone body oxidation increased in failing hearts, and increased ketone body utilization decreased oxidative stress and protected against heart failure.

D-Glutamate is metabolized in the heart mitochondria.

D-Amino acids are enantiomers of L-amino acids and have recently been recognized as biomarkers and bioactive substances in mammals, including humans. In the present study, we investigated functions of the novel mammalian mitochondrial protein 9030617O03Rik and showed decreased expression under conditions of heart failure. Genomic sequence analyses showed partial homology with a bacterial aspartate/glutamate/hydantoin racemase. Subsequent determinations of all free amino acid concentrations in 9030617O03Rik-deficient mice showed high accumulations of D-glutamate in heart tissues. This is the first time that a significant amount of D-glutamate was detected in mammalian tissue. Further analysis of D-glutamate metabolism indicated that 9030617O03Rik is a D-glutamate cyclase that converts D-glutamate to 5-oxo-D-proline. Hence, this protein is the first identified enzyme responsible for mammalian D-glutamate metabolism, as confirmed in cloning analyses. These findings suggest that D-glutamate and 5-oxo-D-proline have bioactivities in mammals through the metabolism by D-glutamate cyclase.