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Dopamine receptors exist in many tissues, including rat cardiac tissue. However, the physiological importance of dopamine receptors in the homeostatic regulation of cardiac function is unclear. In this study, a model of ischaemia/reperfusion was established by culturing primary neonatal rat cardiomyocytes in ischaemia-mimetic solution for 2 hr, followed by incubation in normal culture medium for 24 hr. Lactate dehydrogenase activity, superoxide dismutase activity and malondialdehyde content were determined colorimetrically with a spectrophotometer. Apoptotic cell death was assayed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling staining and flow cytometry, and morphological alterations were observed with transmission electron microscopy. The intracellular free calcium concentration ([Ca2+]i) was measured by confocal laser scanning microscopy. Finally, the expression of dopamine receptor 1 (DR1), caspase-3, -8 and -9, Fas, Fas ligand and Bcl-2 and the release of cytochrome c were analysed by Western blot. The results showed that DR1 expression was increased markedly during ischaemia/reperfusion. Treatment with 10 µM SKF-38393 (DR1 agonist) significantly increased lactate dehydrogenase activity, decreased superoxide dismutase activity and increased malondialdehyde content in the culture medium. The DR1 agonist promoted the release of cytochrome c, accumulation of [Ca2+]i, and apoptosis induced by ischaemia/reperfusion. Furthermore, SKF-38393 up-regulated the expression of caspase-3, -8 and -9, Fas and Fas ligand, and down-regulated Bcl-2 expression. In contrast, 10 µM SCH-23390 (DR1 antagonist) had no significant effects on the above indicators. In conclusion, DR1 activation is involved in the apoptosis of cultured neonatal rat cardiomyocytes in simulated ischaemia/reperfusion through the mitochondrial and death receptor pathways. [ABSTRACT FROM AUTHOR]

Peritoneal dialysis (PD)-related peritoneal fibrosis (PF) is characterized by progressive extracellular matrix (ECM) accumulation in peritoneal mesothelial cells (PMCs) during long-term use of high glucose (HG)-based dialysates. Activation of the renin-angiotensin system (RAS) has been shown to be associated with PF. The aim of this study was to explore the underlying mechanism of the RAS in HG-induced PF. We treated C57BL/6 mice and a human PMC line with HG to induce a PF model and to stimulate ECM accumulation, respectively. RAS activity was blocked using valsartan or angiotensin II (ANGII) type 1 receptor siRNA. The major findings were as follows. First, mice in the HG group exhibited increased collagen deposition and expression of ECM proteins, including a-smooth muscle actin (a-SMA) and collagen type I in the peritoneum. Consistent with the in vivo data, HG upregulated a-SMA expression in human peritoneal mesothelial cells (HPMCs) in a time- and dose-dependent manner. Second, HG stimulation led to RAS activation in HPMCs, and inactivation of RAS decreased the expression of ECM proteins in vivo and in vitro, even during HG stimulation. Finally, RAS-mediated ECM production was associated with lipid accumulation in HPMCs and depended on the dysregulation of the low-density lipoprotein receptor (LDLr) pathway. HG-stimulated HPMCs showed increased coexpression of LDLr and α-SMA, whereas blockade of RAS activity reversed the effect. Furthermore, inhibition of LDLr signaling decreased α-SMA and collagen type I expression in HPMCs when treated with HG and ANG II. In conclusion, increased intracellular RAS activity impaired lipid homeostasis and induced ECM accumulation in HPMCs by disrupting the LDLr pathway, which contributed to PF. [ABSTRACT FROM AUTHOR]

The transcription factor, interferon regulatory factor 5 (IRF5), is important in the induction of type I interferon, proinflammatory cytokines and chemokines, and is involved in autoimmune diseases and tumourigenesis. However, the mechanisms underlying the transcriptional regulation of wild-type IRF5 remain to be fully elucidated. The present study was primarily designed to clarify whether specificity protein 1 (Sp1) was involved in the regulation of IRF5. Initially, the IRF5 promoter region was cloned and its promoter activity was examined using Hela and HEK 293 cells. Deletion analyses revealed that the region spanning -179 to +62 was the minimal promoter of IRF5. Bioinformatics analyses showed that this region contained three putative Sp1 binding sites, and mutational analyses revealed that all the Sp1 sites contributed to transcriptional activity. Secondly, the overexpression of Sp1 was found to increase the activity of the IRF5 promoter and the mRNA level of IRF5, determined using reporter gene assays and polymerase chain reaction analysis, respectively. By contrast, treatment with mithramycin and Sp1 small interfering RNA significantly reduced the activity of the IRF5 promoter and the mRNA level of IRF5. Finally, the results of an electrophoretic mobility shift assay and a chromatin immunoprecipitation assay demonstrated that Sp1 bound to the promoter region of IRF5 in vitro and in vivo. These results suggested that the Sp1 transcription factor is the primary determinant for activating the basal transcription of the IRF5. [ABSTRACT FROM AUTHOR]

Background: Myocardial ischemia/reperfusion injury is the major cause of morbidity and mortality for cardiovascular diseases. Dopamine D2 receptors are expressed in cardiac tissues. However, the roles of dopamine D2 receptors in myocardial ischemia/reperfusion injury and cardiomyocyte apoptosis are unclear. Here we investigated the effects of both dopamine D2 receptors agonist (bromocriptine) and antagonist (haloperidol) on apoptosis of cultured neonatal rat ventricular myocytes induced by ischemia/reperfusion injury. Methods: Myocardial ischemia/reperfusion injury was simulated by incubating primarily cultured neonatal rat cardiomyocytes in ischemic (hypoxic) buffer solution for 2 h. Thereafter, these cells were incubated for 24 h in normal culture medium. Results: Treatment of the cardiomyocytes with 10 μM bromocriptine significantly decreased lactate dehydrogenase activity, increased superoxide dismutase activity, and decreased malondialdehyde content in the culture medium. Bromocriptine significantly inhibited the release of cytochrome c, accumulation of [Ca2+]i, and apoptosis induced by ischemia/reperfusion injury. Bromocriptine also down-regulated the expression of caspase-3 and -9, Fas and Fas ligand, and up-regulated Bcl-2 expression. In contrast, haloperidol (10 μM) had no significant effects on the apoptosis of cultured cardiomyocytes under the aforementioned conditions. Conclusions: These data suggest that activation of dopamine D2 receptors can inhibit apoptosis of cardiomyocytes encountered during ischemia/reperfusion damage through various pathways. [ABSTRACT FROM AUTHOR]