Saxagliptin restores vascular mitochondrial exercise response in the Goto-Kakizaki rat.

Cardiovascular disease risk and all-cause mortality are largely predicted by physical fitness. Exercise stimulates vascular mitochondrial biogenesis through endothelial nitric oxide synthase (eNOS), sirtuins, and PPARγ coactivator 1α (PGC-1α), a response absent in diabetes and hypertension. We hypothesized that an agent regulating eNOS in the context of diabetes could reconstitute exercise-mediated signaling to mitochondrial biogenesis. Glucagon-like peptide 1 (GLP-1) stimulates eNOS and blood flow; we used saxagliptin, an inhibitor of GLP-1 degradation, to test whether vascular mitochondrial adaptation to exercise in diabetes could be restored. Goto-Kakizaki (GK) rats, a nonobese, type 2 diabetes model, and Wistar controls were exposed to an 8-day exercise intervention with or without saxagliptin (10 mg·kg·d). We evaluated the impact of exercise and saxagliptin on mitochondrial proteins and signaling pathways in aorta. Mitochondrial protein expression increased with exercise in the Wistar aorta and decreased or remained unchanged in the GK animals. GK rats treated with saxagliptin plus exercise showed increased expression of mitochondrial complexes, cytochrome c, eNOS, nNOS, PGC-1α, and UCP3 proteins. Notably, a 3-week saxagliptin plus exercise intervention significantly increased running time in the GK rats. These data suggest that saxagliptin restores vascular mitochondrial adaptation to exercise in a diabetic rodent model and may augment the impact of exercise on the vasculature.

Selective class I histone deacetylase inhibition suppresses hypoxia-induced cardiopulmonary remodeling through an antiproliferative mechanism.

RATIONALE: Histone deacetylase (HDAC) inhibitors are efficacious in models of hypertension-induced left ventricular heart failure. The consequences of HDAC inhibition in the context of pulmonary hypertension with associated right ventricular cardiac remodeling are poorly understood. OBJECTIVE: This study was performed to assess the utility of selective small-molecule inhibitors of class I HDACs in a preclinical model of pulmonary hypertension. METHODS AND RESULTS: Rats were exposed to hypobaric hypoxia for 3 weeks in the absence or presence of a benzamide HDAC inhibitor, MGCD0103, which selectively inhibits class I HDACs 1, 2, and 3. The compound reduced pulmonary arterial pressure more dramatically than tadalafil, a standard-of-care therapy for human pulmonary hypertension that functions as a vasodilator. MGCD0103 improved pulmonary artery acceleration time and reduced systolic notching of the pulmonary artery flow envelope, which suggests a positive impact of the HDAC inhibitor on pulmonary vascular remodeling and stiffening. Similar results were obtained with an independent class I HDAC-selective inhibitor, MS-275. Reduced pulmonary arterial pressure in MGCD0103-treated animals was associated with blunted pulmonary arterial wall thickening because of suppression of smooth muscle cell proliferation. Right ventricular function was maintained in MGCD0103-treated animals. Although the class I HDAC inhibitor only modestly reduced right ventricular hypertrophy, it had multiple beneficial effects on the right ventricle, which included suppression of pathological gene expression, inhibition of proapoptotic caspase activity, and repression of proinflammatory protein expression. CONCLUSIONS: By targeting distinct pathogenic mechanisms, isoform-selective HDAC inhibitors have potential as novel therapeutics for pulmonary hypertension that will complement vasodilator standards of care.

Fatty liver is associated with reduced SIRT3 activity and mitochondrial protein hyperacetylation.

Acetylation has recently emerged as an important mechanism for controlling a broad array of proteins mediating cellular adaptation to metabolic fuels. Acetylation is governed, in part, by SIRTs (sirtuins), class III NAD(+)-dependent deacetylases that regulate lipid and glucose metabolism in liver during fasting and aging. However, the role of acetylation or SIRTs in pathogenic hepatic fuel metabolism under nutrient excess is unknown. In the present study, we isolated acetylated proteins from total liver proteome and observed 193 preferentially acetylated proteins in mice fed on an HFD (high-fat diet) compared with controls, including 11 proteins not previously identified in acetylation studies. Exposure to the HFD led to hyperacetylation of proteins involved in gluconeogenesis, mitochondrial oxidative metabolism, methionine metabolism, liver injury and the ER (endoplasmic reticulum) stress response. Livers of mice fed on the HFD had reduced SIRT3 activity, a 3-fold decrease in hepatic NAD(+) levels and increased mitochondrial protein oxidation. In contrast, neither SIRT1 nor histone acetyltransferase activities were altered, implicating SIRT3 as a dominant factor contributing to the observed phenotype. In Sirt3⁻(/)⁻ mice, exposure to the HFD further increased the acetylation status of liver proteins and reduced the activity of respiratory complexes III and IV. This is the first study to identify acetylation patterns in liver proteins of HFD-fed mice. Our results suggest that SIRT3 is an integral regulator of mitochondrial function and its depletion results in hyperacetylation of critical mitochondrial proteins that protect against hepatic lipotoxicity under conditions of nutrient excess.

Cardiac-specific overexpression of dominant-negative CREB leads to increased mortality and mitochondrial dysfunction in female mice.

Cardiac failure is associated with diminished activation of the transcription factor cyclic nucleotide regulatory element binding-protein (CREB), and heart-specific expression of a phosphorylation-deficient CREB mutant in transgenic mice [dominant negative CREB (dnCREB) mice] recapitulates the contractile phenotypes of cardiac failure (Fentzke RC, Korcarz CE, Lang RM, Lin H, Leiden JM. Dilated cardiomyopathy in transgenic mice expressing a dominant-negative CREB transcription factor in the heart. J Clin Invest 101: 2415-2426, 1998). In the present study, we demonstrated significantly elevated mortality and contractile dysfunction in female compared with male dnCREB mice. Female dnCREB mice demonstrated a 21-wk survival of only 17% compared with 67% in males (P < 0.05) and exclusively manifest decreased cardiac peroxisome proliferator-activated receptor-γ coactivator-1α and estrogen-related receptor-α content, suggesting sex-related effects on cardiac mitochondrial function. Hearts from 4-wk-old dnCREB mice of both sexes demonstrated diminished mitochondrial respiratory capacity compared with nontransgenic controls. However, by 12 wk of age, there was a significant decrease in mitochondrial density (citrate synthase activity) and deterioration of mitochondrial structure, as demonstrated by transmission electron microscopy, in female dnCREB mice, which were not found in male transgenic littermates. Subsarcolemmal mitochondria isolated from hearts of female, but not male, dnCREB mice demonstrated increased ROS accompanied by decreases in the expression/activity of the mitochondrial antioxidants MnSOD and glutathione peroxidase. These results demonstrate that heart-specific dnCREB expression results in mitochondrial respiratory dysfunction in both sexes; however, increased oxidant burden, reduced antioxidant expression, and disrupted mitochondrial structure are exacerbated by the female sex, preceding and contributing to the greater contractile morbidity and mortality. These results provide further support for the role of the CREB transcription factor in regulating mitochondrial integrity and identify a critical pathway that may contribute to sex differences in heart failure.

Impaired response to exercise intervention in the vasculature in metabolic syndrome.

Physical activity decreases risk for diabetes and cardiovascular disease morbidity and mortality; however, the specific impact of exercise on the diabetic vasculature is unexamined. We hypothesized that an acute, moderate exercise intervention in diabetic and hypertensive rats would induce mitochondrial biogenesis and mitochondrial antioxidant defence to improve vascular resilience. SHHF/Mcc-fa(cp) lean (hypertensive) and obese (hypertensive, insulin resistant), as well as Sprague Dawley (SD) control rats were run on a treadmill for 8 days. In aortic lysates from SD rats, we observed a significant increase in subunit proteins from oxidative phosphorylation (OxPhos) complexes I-III, with no changes in the lean or obese SHHF rats. Exercise also increased the expression of mitochondrial antioxidant defence uncoupling protein 3 (UCP3) (p < 0.05) in SHHF lean rats, whereas no changes were observed in the SD or SHHF obese rats with exercise. We evaluated upstream signalling pathways for mitochondrial biogenesis, and only peroxisome proliferators-activated receptor gamma coactivator 1α (PGC-1α) significantly decreased in SHHF lean rats (p < 0.05) with exercise. In these experiments, we demonstrate absent mitochondrial induction with exercise exposure in models of chronic vascular disease. These findings suggest that chronic vascular stress results in decreased sensitivity of vasculature to the adaptive mitochondrial responses normally induced by exercise.