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Chiung-Zuan Chiu, Bao-Wei Wang and Kou-Gi Shyu

Cardiomyocyte hypoxia causes cardiac hypertrophy through cardiac-restricted gene expression. Urotensin II (UII) cooperates with activating protein 1 (AP1) to regulate cardiomyocyte growth in response to myocardial injuries. Angiotensin II (AngII) stimulates UII expression, reactive oxygen species (ROS) production, and cardiac hypertrophy. This study aimed to evaluate the expression of UII, ROS, and AngII as well as their genetic transcription after hypoxia treatment in neonatal cardiomyocytes. Cultured neonatal rat cardiomyocytes were subjected to hypoxia for different time periods. UII (Uts2) protein levels increased after 2.5% hypoxia for 4 h with earlier expression of AngII and ROS. Both hypoxia and exogenously added AngII or Dp44mT under normoxia stimulated UII expression, whereas AngII receptor blockers, JNK inhibitors (SP600125), JNK siRNA, or N-acetyl-l-cysteine (NAC) suppressed UII expression. The gel shift assay indicated that hypoxia induced an increase in DNA–protein binding between UII and AP1. The luciferase assay confirmed an increase in transcription activity of AP1 to the UII promoter under hypoxia. After hypoxia, an increase in 3H-proline incorporation in the cardiomyocytes and expression of myosin heavy chain protein, indicative of cardiomyocyte hypertrophy, were observed. In addition, hypoxia increased collagen I expression, which was inhibited by SP600125, NAC, and UII siRNA. In summary, hypoxia in cardiomyocytes increases UII and collagen I expression through the induction of AngII, ROS, and the JNK pathway causing cardiomyocyte hypertrophy and fibrosis.

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Bao-Wei Wang, Hang Chang, Peiliang Kuan and Kou-Gi Shyu

Angiotensin II (AngII) plays a critical role in cardiac remodeling and promotes cardiac myocyte hypertrophy. Myostatin, a negative regulator of muscle growth, is increased in hypertrophied and infarcted heart. The direct effect of AngII on cardiac myocyte myostatin expression has not been previously investigated. We hypothesized that myostatin may act as a cardiac endocrine inhibitor for AngII. AngII-induced myostatin protein expression in cultured rat neonatal cardiomyocytes was dose-dependent. AngII significantly increased myostatin protein and mRNA expression in a time-dependent manner. Addition of losartan, SB203580, or p38 siRNA 30 min before AngII stimulation significantly blocked the increase of myostatin protein by AngII. AngII significantly increased phosphorylation of p38 while SB205380 and losartan attenuated the phosphorylation of p38 induced by AngII. AngII increased, while myostatin-Mut plasmid, SB203580, losartan, and myocyte enhance factor 2 (MEF-2) antibody abolished the myostatin promoter activity. Co-stimulation with myostatin and AngII significantly inhibited the protein synthesis induced by AngII. In conclusion, AngII enhances myostatin expression in cultured rat neonatal cardiomyocytes. The AngII-induced myostatin is mediated through p38 MAP kinase and MEF-2 pathway.

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Qiongge Zhang, Chaoqun Wang, Yehua Tang, Qiangqiang Zhu, Yongcheng Li, Haiyan Chen, Yi Bao, Song Xue, Liangliang Sun, Wei Tang, Xiangfang Chen, Yongquan Shi, Lefeng Qu, Bin Lu and Jiaoyang Zheng

Hyperglycemia plays a major role in the development of diabetic macrovascular complications, including atherosclerosis and restenosis, which are responsible for the most of disability and mortality in diabetic patients. Osteopontin (OPN) is an important factor involved in atherogenesis, and hyperglycemia enhances the transcriptional activity of FoxO1 which is closely association with insulin resistance and diabetes. Here, we showed that plasma OPN levels were significantly elevated in type 2 diabetic patients and positively correlated with glycated albumin (GA). The more atherosclerotic lesions were observed in the aorta of diabetic ApoE−/− mice analyzed by Sudan IV staining. High glucose increased both the mRNA and protein expression levels of OPN and inhibited the phosphorylation of FoxO1 in RAW 264.7 cells. Overexpression of WT or constitutively active mutant FoxO1 promoted the expression levels of OPN, while the dominant-negative mutant FoxO1 decreased slightly the expression of OPN. Conversely, knockdown of FoxO1 reduced the expression of OPN. Luciferase reporter assay revealed that high glucose and overexpression of FoxO1 enhanced the activities of the OPN promoter region nt −1918 ~ −713. Furthermore, the interactions between FoxO1 and the OPN promoter were confirmed by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation assay (ChIP). Our results suggest that high glucose upregulates OPN expression via FoxO1 activation, which would play a critical role in the development of diabetic atherogenesis.