Nitro-oleic acid inhibits angiotensin II-induced hypertension

RATIONALE

Nitro-oleic acid (OA-NO(2)) is a bioactive, nitric-oxide derived fatty acid with physiologically relevant vasculoprotective properties in vivo. OA-NO(2) exerts cell signaling actions as a result of its strong electrophilic nature and mediates pleiotropic cell responses in the vasculature.

OBJECTIVE

The present study sought to investigate the protective role of OA-NO(2) in angiotensin (Ang) II-induced hypertension.

METHODS AND RESULTS

We show that systemic administration of OA-NO(2) results in a sustained reduction of Ang II-induced hypertension in mice and exerts a significant blood pressure lowering effect on preexisting hypertension established by Ang II infusion. OA-NO(2) significantly inhibits Ang II contractile response as compared to oleic acid (OA) in mesenteric vessels. The improved vasoconstriction is specific for the Ang II type 1 receptor (AT(1)R)-mediated signaling because vascular contraction by other G-protein-coupled receptors is not altered in response to OA-NO(2) treatment. From the mechanistic viewpoint, OA-NO(2) lowers Ang II-induced hypertension independently of peroxisome proliferation-activated receptor (PPAR)gamma activation. Rather, OA-NO(2), but not OA, specifically binds to the AT(1)R, reduces heterotrimeric G-protein coupling, and inhibits IP(3) (inositol-1,4,5-trisphosphate) and calcium mobilization, without inhibiting Ang II binding to the receptor.

CONCLUSIONS

These results demonstrate that OA-NO(2) diminishes the pressor response to Ang II and inhibits AT(1)R-dependent vasoconstriction, revealing OA-NO(2) as a novel antagonist of Ang II-induced hypertension.

Involvement of inducible 6-phosphofructo-2-kinase in the anti-diabetic effect of peroxisome proliferator-activated receptor gamma activation in mice

PFKFB3 is the gene that codes for the inducible isoform of 6-phosphofructo-2-kinase (iPFK2), a key regulatory enzyme of glycolysis. As one of the targets of peroxisome proliferator-activated receptor gamma (PPARgamma), PFKFB3/iPFK2 is up-regulated by thiazolidinediones. In the present study, using PFKFB3/iPFK2-disrupted mice, the role of PFKFB3/iPFK2 in the anti-diabetic effect of PPARgamma activation was determined. In wild-type littermate mice, PPARgamma activation (i.e. treatment with rosiglitazone) restored euglycemia and reversed high fat diet-induced insulin resistance and glucose intolerance. In contrast, PPARgamma activation did not reduce high fat diet-induced hyperglycemia and failed to reverse insulin resistance and glucose intolerance in PFKFB3(+/-) mice. The lack of anti-diabetic effect in PFKFB3(+/-) mice was associated with the inability of PPARgamma activation to suppress adipose tissue lipolysis and proinflammatory cytokine production, stimulate visceral fat accumulation, enhance adipose tissue insulin signaling, and appropriately regulate adipokine expression. Similarly, in cultured 3T3-L1 adipocytes, knockdown of PFKFB3/iPFK2 lessened the effect of PPARgamma activation on stimulating lipid accumulation. Furthermore, PPARgamma activation did not suppress inflammatory signaling in PFKFB3/iPFK2-knockdown adipocytes as it did in control adipocytes. Upon inhibition of excessive fatty acid oxidation in PFKFB3/iPFK2-knockdown adipocytes, PPARgamma activation was able to significantly reverse inflammatory signaling and proinflammatory cytokine expression and restore insulin signaling. Together, these data demonstrate that PFKFB3/iPFK2 is critically involved in the anti-diabetic effect of PPARgamma activation.

Smooth and cardiac muscle-selective knock-out of Kruppel-like factor 4 causes postnatal death and growth retardation

Krüppel-like factor 4 (Klf4) is a transcription factor involved in differentiation and proliferation in multiple tissues. We demonstrated previously that tamoxifen-induced deletion of the Klf4 gene in mice accelerated neointimal formation but delayed down-regulation of smooth muscle cell differentiation markers in carotid arteries following injury. To further determine the role of Klf4 in the cardiovascular system, we herein derived mice deficient for the Klf4 gene in smooth and cardiac muscle using the SM22alpha promoter (SM22alpha-CreKI(+)/Klf4(loxP/loxP) mice). SM22alpha-CreKI(+)/Klf4(loxP/loxP) mice were born at the expected Mendelian ratio, but they gradually died after birth. Although approximately 40% of SM22alpha-CreKI(+)/Klf4(loxP/loxP) mice survived beyond postnatal day 28, they exhibited marked growth retardation. In wild-type mice, Klf4 was expressed in the heart from late embryonic development through adulthood, whereas it was not expressed in smooth muscle. No changes were observed in morphology or expression of smooth muscle cell differentiation markers in vessels of SM22alpha-CreKI(+)/Klf4(loxP/loxP) mice. Of interest, cardiac output was significantly decreased in SM22alpha-CreKI(+)/Klf4(loxP/loxP) mice, as determined by magnetic resonance imaging. Moreover, a lack of Klf4 in the heart resulted in the reduction in expression of multiple cardiac genes, including Gata4. In vivo chromatin immunoprecipitation assays on the heart revealed that Klf4 bound to the promoter region of the Gata4 gene. Results provide novel evidence that Klf4 plays a key role in late fetal and/or postnatal cardiac development.

miR-10a contributes to retinoid acid-induced smooth muscle cell differentiation

MicroRNAs (miRs) have been reported to play a critical role in muscle differentiation and function. The purpose of this study is to determine the role of miRs during smooth muscle cell (SMC) differentiation from embryonic stem cells (ESCs). MicroRNA profiling showed that miR-10a expression is steadily increased during in vitro differentiation of mouse ESCs into SMCs. Loss-of-function approaches using miR-10a inhibitors uncovered that miR-10a is a critical mediator for SMC lineage determination in our retinoic acid-induced ESC/SMC differentiation system. In addition, we have documented for the first time that histone deacetylase 4 is a novel target of miR-10a and mediates miR-10a function during ESC/SMC differentiation. To determine the molecular mechanism through which retinoic acid induced miR-10a expression, a consensus NF-kappaB element was identified in the miR-10a gene promoter by bioinformatics analysis, and chromatin immunoprecipitation assay confirmed that NF-kappaB could bind to this element. Finally, inhibition of NF-kappaB nuclear translocation repressed miR-10a expression and decreased SMC differentiation from ESCs. Our data demonstrate for the first time that miR-10a is a novel regulator in SMC differentiation from ESCs. These studies suggest that miR-10a may play important roles in vascular biology and have implications for the diagnosis and treatment of vascular diseases.

Covalent peroxisome proliferator-activated receptor gamma adduction by nitro-fatty acids: selective ligand activity and anti-diabetic signaling actions

The peroxisome proliferator-activated receptor-gamma (PPARgamma) binds diverse ligands to transcriptionally regulate metabolism and inflammation. Activators of PPARgamma include lipids and anti-hyperglycemic drugs such as thiazolidinediones (TZDs). Recently, TZDs have raised concern after being linked with increased risk of peripheral edema, weight gain, and adverse cardiovascular events. Most reported endogenous PPARgamma ligands are intermediates of lipid metabolism and oxidation that bind PPARgamma with very low affinity. In contrast, nitro derivatives of unsaturated fatty acids (NO(2)-FA) are endogenous products of nitric oxide ((*)NO) and nitrite (NO(2)(-))-mediated redox reactions that activate PPARgamma at nanomolar concentrations. We report that NO(2)-FA act as partial agonists of PPARgamma and covalently bind PPARgamma at Cys-285 via Michael addition. NO(2)-FA show selective PPARgamma modulator characteristics by inducing coregulator protein interactions, PPARgamma-dependent expression of key target genes, and lipid accumulation is distinctively different from responses induced by the TZD rosiglitazone. Administration of this class of signaling mediators to ob/ob mice revealed that NO(2)-FA lower insulin and glucose levels without inducing adverse side effects such as the increased weight gain induced by TZDs.

miR-497 regulates neuronal death in mouse brain after transient focal cerebral ischemia

Dysfunction of the microRNA (miR) network has been emerging as a major regulator in neurological diseases. However, little is known about the functional significance of unique miRs in ischemic brain damage. Here, we found that miR-497 is induced in mouse brain after transient middle cerebral artery occlusion (MCAO) and mouse N2A neuroblastoma (N2A) cells after oxygen-glucose deprivation (OGD). Loss-of-miR-497 function significantly suppresses OGD-induced N2A cell death, whereas gain-of-miR-497 function aggravates OGD-induced neuronal loss. Moreover, miR-497 directly binds to the predicted 3'-UTR target sites of bcl-2/-w genes. Furthermore, knockdown of cerebral miR-497 effectively enhances bcl-2/-w protein levels in the ischemic region, attenuates ischemic brain infarction, and improves neurological outcomes in mice after focal cerebral ischemia. Taken together, our data suggest that miR-497 promotes ischemic neuronal death by negatively regulating antiapoptotic proteins, bcl-2 and bcl-w. We raise the possibility that this pathway may contribute to the pathogenesis of the ischemic brain injury in stroke.

Disruption of inducible 6-phosphofructo-2-kinase ameliorates diet-induced adiposity but exacerbates systemic insulin resistance and adipose tissue inflammatory response

Adiposity is commonly associated with adipose tissue dysfunction and many overnutrition-related metabolic diseases including type 2 diabetes. Much attention has been paid to reducing adiposity as a way to improve adipose tissue function and systemic insulin sensitivity. PFKFB3/iPFK2 is a master regulator of adipocyte nutrient metabolism. Using PFKFB3(+/-) mice, the present study investigated the role of PFKFB3/iPFK2 in regulating diet-induced adiposity and systemic insulin resistance. On a high-fat diet (HFD), PFKFB3(+/-) mice gained much less body weight than did wild-type littermates. This was attributed to a smaller increase in adiposity in PFKFB3(+/-) mice than in wild-type controls. However, HFD-induced systemic insulin resistance was more severe in PFKFB3(+/-) mice than in wild-type littermates. Compared with wild-type littermates, PFKFB3(+/-) mice exhibited increased severity of HFD-induced adipose tissue dysfunction, as evidenced by increased adipose tissue lipolysis, inappropriate adipokine expression, and decreased insulin signaling, as well as increased levels of proinflammatory cytokines in both isolated adipose tissue macrophages and adipocytes. In an in vitro system, knockdown of PFKFB3/iPFK2 in 3T3-L1 adipocytes caused a decrease in the rate of glucose incorporation into lipid but an increase in the production of reactive oxygen species. Furthermore, knockdown of PFKFB3/iPFK2 in 3T3-L1 adipocytes inappropriately altered the expression of adipokines, decreased insulin signaling, increased the phosphorylation states of JNK and NFkappaB p65, and enhanced the production of proinflammatory cytokines. Together, these data suggest that PFKFB3/iPFK2, although contributing to adiposity, protects against diet-induced insulin resistance and adipose tissue inflammatory response.

Human C-reactive protein does not promote atherosclerosis in transgenic rabbits

BACKGROUND

Although there is a statistically significant association between modestly raised baseline plasma C-reactive protein (CRP) values and future cardiovascular events, the debate is still unsettled in regard to whether CRP plays a causal role in the pathogenesis of atherosclerosis.

METHODS AND RESULTS

We generated 2 lines of transgenic (Tg) rabbits expressing human CRP (hCRP). The plasma levels of hCRP in hCRP-Tg-1 and hCRP-Tg-2 rabbits were 0.4+/-0.13 (n=14) and 57.8+/-20.6 mg/L (n=12), respectively. In addition, hCRP isolated from Tg rabbit plasma exhibited the ability to activate the rabbit complement. To define the role of hCRP in atherosclerosis, we compared the susceptibility of hCRP-Tg rabbits to cholesterol-rich diet-induced aortic and coronary atherosclerosis with that of non-Tg rabbits. After being fed with a cholesterol-rich diet for 16 weeks, Tg and non-Tg rabbits developed similar hypercholesterolemia and lesion sizes in both aortic and coronary arteries. Immunohistochemical staining and Western blotting revealed that hCRP was indeed present in the lesions but did not affect macrophage accumulation and smooth muscle cell proliferation of the lesions.

CONCLUSIONS

Neither high nor low plasma concentrations of hCRP affected aortic or coronary atherosclerosis lesion formation in hCRP-Tg rabbits.

Nitro-fatty acid inhibition of neointima formation after endoluminal vessel injury

RATIONALE

Fatty acid nitroalkenes are endogenously generated electrophilic byproducts of nitric oxide and nitrite-dependent oxidative inflammatory reactions. Existing evidence indicates nitroalkenes support posttranslational protein modifications and transcriptional activation that promote the resolution of inflammation.

OBJECTIVE

The aim of this study was to assess whether in vivo administration of a synthetic nitroalkene could elicit antiinflammatory actions in vivo using a murine model of vascular injury.

METHODS AND RESULTS

The in vivo administration (21 days) of nitro-oleic acid (OA-NO(2)) inhibited neointimal hyperplasia after wire injury of the femoral artery in a murine model (OA-NO(2) treatment resulted in reduced intimal area and intima to media ratio versus vehicle- or oleic acid (OA)-treated animals,P<0.0001). Increased heme oxygenase (HO)-1 expression accounted for much of the vascular protection induced by OA-NO(2) in both cultured aortic smooth muscle cells and in vivo. Inhibition of HO by Sn(IV)-protoporphyrin or HO-1 small interfering RNA reversed OA-NO(2)-induced inhibition of platelet-derived growth factor-stimulated rat aortic smooth muscle cell migration. The upregulation of HO-1 expression also accounted for the antistenotic actions of OA-NO(2) in vivo, because inhibition of neointimal hyperplasia following femoral artery injury was abolished in HO-1(-/-) mice (OA-NO(2)-treated wild-type versus HO-1(-/-) mice, P=0.016).

CONCLUSIONS

In summary, electrophilic nitro-fatty acids induce salutary gene expression and cell functional responses that are manifested by a clinically significant outcome, inhibition of neointimal hyperplasia induced by arterial injury.

A comparison of murine smooth muscle cells generated from embryonic versus induced pluripotent stem cells

Smooth muscle cell (SMC) differentiation and dedifferentiation play a critical role in the pathogenesis of cardiovascular diseases. The lack of a good and simple in vitro SMC differentiation system has hampered the progress of SMC field for years. The generation of such an in vitro system would be invaluable for exploring molecular mechanisms of SMC differentiation and dedifferentiation. Recently, the establishment of induced pluripotent stem (iPS) cells has offered a novel therapeutic strategy to generate patient-specific stem cell lines. Here we have investigated whether iPS cells are able to differentiate into SMCs in vitro. Mouse iPS cell (O9 and TT025) monolayers were treated with 10(-5) mol/L all-trans retinoid acid (RA). After 8 days of RA treatment, we found that >40% of the O9 iPS cells expressed the SMC-markers including SMalpha-actin and SM myosin heavy chain. Also, we documented that iPS-derived SMCs acquired SMC functional characteristics including contraction and calcium influx in response to stimuli. Moreover, our results indicated that there were differences in SMC-specific gene expression patterns between SMCs derived from O9 and TT025 iPS as well as normal embryonic stem cells. These differences might be due to disparity in the current iPS technology. Taken together, our data have established a simple iPS-SMC system to generate SMCs in vitro, which has tremendous potential to generate individualized SMCs for vascular tissue engineering and personalized drug screening.

PPARs and the cardiovascular system

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone-receptor superfamily. Originally cloned in 1990, PPARs were found to be mediators of pharmacologic agents that induce hepatocyte peroxisome proliferation. PPARs also are expressed in cells of the cardiovascular system. PPAR gamma appears to be highly expressed during atherosclerotic lesion formation, suggesting that increased PPAR gamma expression may be a vascular compensatory response. Also, ligand-activated PPAR gamma decreases the inflammatory response in cardiovascular cells, particularly in endothelial cells. PPAR alpha, similar to PPAR gamma, also has pleiotropic effects in the cardiovascular system, including antiinflammatory and antiatherosclerotic properties. PPAR alpha activation inhibits vascular smooth muscle proinflammatory responses, attenuating the development of atherosclerosis. However, PPAR delta overexpression may lead to elevated macrophage inflammation and atherosclerosis. Conversely, PPAR delta ligands are shown to attenuate the pathogenesis of atherosclerosis by improving endothelial cell proliferation and survival while decreasing endothelial cell inflammation and vascular smooth muscle cell proliferation. Furthermore, the administration of PPAR ligands in the form of TZDs and fibrates has been disappointing in terms of markedly reducing cardiovascular events in the clinical setting. Therefore, a better understanding of PPAR-dependent and -independent signaling will provide the foundation for future research on the role of PPARs in human cardiovascular biology.

Beneficial effect of young oocytes for rabbit somatic cell nuclear transfer

This study was designed to examine the effect of the age of rabbit oocytes on the developmental potential of cloned embryos. The metaphase II oocytes used for nuclear transfer (NT) were collected at 10, 12, 14, and 16 h post-hCG injection (hpi). The total number of oocytes collected per donor (21.4-23.7) at 12 to 16 hpi was similar, but significantly higher than that collected at 10 hpi (16.2). Additionally, a significant improvement in blastocyst development was achieved with embryos generated by electrically mediated cell fusion (56.0%), compared to those from nuclear injection (13.1 %) (Experiment 1). Markedly higher blastocyst development (45.8-54.5%) was also achieved with oocytes collected at 10-12 hpi than from those collected 14-16 hpi (8.3-14.3%) (Experiment 2). In Experiment 3, the blastocyst rates of NT embryos derived from oocytes harvested 12 hpi (39.2-42.8 %) were significantly higher than from those collected at 16 hpi (6.8-8.4 %) (p < 0.05), regardless of the donor cell age. Kinase activity assays showed variable changes of activity in rabbit oocytes over the period of 10-16 hpi; however, there was no correlation with preimplantational development (blastocyst rate vs. MPF, R = 0.326; blastocyst rate vs. MAPK, R = -0.131). Embryo transfer of NT embryos utilizing 12 hpi oocytes resulted in one full-term but stillborn, and one live cloned rabbit; thus, an efficiency of 1.7 % (n = 117) (Experiment 4). These results demonstrated that NT utilizing relatively young rabbit oocytes, harvested at 10-12 h after hCG injection, was beneficial for the development of NT embryos.

Vascular smooth muscle cell-selective peroxisome proliferator-activated receptor-gamma deletion leads to hypotension

BACKGROUND

Peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists are commonly used to treat diabetes, although their PPARgamma-dependent effects transcend their role as insulin sensitizers. Thiazolidinediones lower blood pressure (BP) in diabetic patients, whereas results from conventional/tissue-specific PPARgamma experimental models suggest an important pleiotropic role for PPARgamma in BP control. Little evidence is available on the molecular mechanisms underlying the role of vascular smooth muscle cell-specific PPARgamma in basal vascular tone.

METHODS AND RESULTS

We show that vascular smooth muscle cell-selective deletion of PPARgamma impairs vasoactivity with an overall reduction in BP. Aortic contraction in response to norepinephrine is reduced and vasorelaxation is enhanced in response to beta-adrenergic receptor (beta-AdR) agonists in vitro. Similarly, vascular smooth muscle cell-selective PPARgamma knockout mice display a biphasic response to norepinephrine in BP, reversible on administration of beta-AdR blocker, and enhanced BP reduction on treatment with beta-AdR agonists. Consistent with enhanced beta2-AdR responsiveness, we found that the absence of PPARgamma in vascular smooth muscle cells increased beta2-AdR expression, possibly leading to the hypotensive phenotype during the rest phase.

CONCLUSIONS

These data uncovered the beta2-AdR as a novel target of PPARgamma transcriptional repression in vascular smooth muscle cells and indicate that PPARgamma regulation of beta2-adrenergic signaling is important in the modulation of BP.

Ligand-activated peroxisome proliferator-activated receptor-gamma protects against ischemic cerebral infarction and neuronal apoptosis by 14-3-3 epsilon upregulation

BACKGROUND

Thiazolidinediones have been reported to protect against ischemia-reperfusion injury. Their protective actions are considered to be peroxisome proliferator-activated receptor-gamma (PPAR-gamma)-dependent; however, it is unclear how PPAR-gamma activation confers resistance to ischemia-reperfusion injury.

METHODS AND RESULTS

We evaluated the effects of rosiglitazone or PPAR-gamma overexpression on cerebral infarction in a rat model and investigated the antiapoptotic actions in the N2-A neuroblastoma cell model. Rosiglitazone or PPAR-gamma overexpression significantly reduced infarct volume. The protective effect was abrogated by PPAR-gamma small interfering RNA. In mice with knock-in of a PPAR-gamma dominant-negative mutant, infarct volume was enhanced. Proteomic analysis revealed that brain 14-3-3epsilon was highly upregulated in rats treated with rosiglitazone. Upregulation of 14-3-3epsilon was abrogated by PPAR-gamma small interfering RNA or antagonist. Promoter analysis and chromatin immunoprecipitation revealed that rosiglitazone induced PPAR-gamma binding to specific regulatory elements on the 14-3-3epsilon promoter and thereby increased 14-3-3epsilon transcription. 14-3-3epsilon Small interfering RNA abrogated the antiapoptotic actions of rosiglitazone or PPAR-gamma overexpression, whereas 14-3-3epsilon recombinant proteins rescued brain tissues and N2-A cells from ischemia-induced damage and apoptosis. Elevated 14-3-3epsilon enhanced binding of phosphorylated Bad and protected mitochondrial membrane potential.

CONCLUSIONS

Ligand-activated PPAR-gamma confers resistance to neuronal apoptosis and cerebral infarction by driving 14-3-3epsilon transcription. 14-3-3epsilon Upregulation enhances sequestration of phosphorylated Bad and thereby suppresses apoptosis.

Expression profiling of nuclear receptors in human and mouse embryonic stem cells

Nuclear receptors (NRs) regulate gene expression in essential biological processes including differentiation and development. Here we report the systematic profiling of NRs in human and mouse embryonic stem cell (ESC) lines and during their early differentiation into embryoid bodies. Expression of the 48 human and mouse NRs was assessed by quantitative real-time PCR. In general, expression of NRs between the two human cell lines was highly concordant, whereas in contrast, expression of NRs between human and mouse ESCs differed significantly. In particular, a number of NRs that have been implicated previously as crucial regulators of mouse ESC biology, including ERRbeta, DAX-1, and LRH-1, exhibited diametric patterns of expression, suggesting they may have distinct species-specific functions. Taken together, these results highlight the complexity of the transcriptional hierarchy that exists between species and governs early development. These data should provide a unique resource for further exploration of the species-specific roles of NRs in ESC self-renewal and differentiation.

Gene expression module-based chemical function similarity search

Investigation of biological processes using selective chemical interventions is generally applied in biomedical research and drug discovery. Many studies of this kind make use of gene expression experiments to explore cellular responses to chemical interventions. Recently, some research groups constructed libraries of chemical related expression profiles, and introduced similarity comparison into chemical induced transcriptome analysis. Resembling sequence similarity alignment, expression pattern comparison among chemical intervention related expression profiles provides a new way for chemical function prediction and chemical–gene relation investigation. However, existing methods place more emphasis on comparing profile patterns globally, which ignore noises and marginal effects. At the same time, though the whole information of expression profiles has been used, it is difficult to uncover the underlying mechanisms that lead to the functional similarity between two molecules. Here a new approach is presented to perform biological effects similarity comparison within small biologically meaningful gene categories. Regarding gene categories as units, a reduced similarity matrix is generated for measuring the biological distances between query and profiles in library and pointing out in which modules do chemical pairs resemble. Through the modularization of expression patterns, this method reduces experimental noises and marginal effects and directly correlates chemical molecules with gene function modules.

Rad GTPase deficiency leads to cardiac hypertrophy

BACKGROUND

Rad (Ras associated with diabetes) GTPase is the prototypic member of a subfamily of Ras-related small G proteins. The aim of the present study was to define whether Rad plays an important role in mediating cardiac hypertrophy.

METHODS AND RESULTS

We document for the first time that levels of Rad mRNA and protein were decreased significantly in human failing hearts (n=10) compared with normal hearts (n=3; P<0.01). Similarly, Rad expression was decreased significantly in cardiac hypertrophy induced by pressure overload and in cultured cardiomyocytes with hypertrophy induced by 10 micromol/L phenylephrine. Gain and loss of Rad function in cardiomyocytes significantly inhibited and increased phenylephrine-induced hypertrophy, respectively. In addition, activation of calcium-calmodulin-dependent kinase II (CaMKII), a strong inducer of cardiac hypertrophy, was significantly inhibited by Rad overexpression. Conversely, downregulation of CaMKIIdelta by RNA interference technology attenuated the phenylephrine-induced hypertrophic response in cardiomyocytes in which Rad was also knocked down. To further elucidate the potential role of Rad in vivo, we generated Rad-deficient mice and demonstrated that they were more susceptible to cardiac hypertrophy associated with increased CaMKII phosphorylation than wild-type littermate controls.

CONCLUSIONS

The present data document for the first time that Rad is a novel mediator that inhibits cardiac hypertrophy through the CaMKII pathway. The present study will have significant implications for understanding the mechanisms of cardiac hypertrophy and setting the basis for the development of new strategies for treatment of cardiac hypertrophy.

Intussusception and rotavirus associated hospitalisation in New Zealand

AIMS

To describe the epidemiology of intussusception and its relation to rotavirus associated hospitalisation in New Zealand.

METHODS

National hospital discharge data between January 1998 and June 2003 for all children younger than 3 years of age with intussusception were reviewed. Independently, children from the same age group, admitted to eight paediatric units with rotavirus gastroenteritis between May 1998 and May 2000, were identified prospectively. Epidemiological characteristics of cases with intussusception were compared with those of hospitalised rotavirus disease.

RESULTS

During the 5.5 year study period, there were 277 cases of intussusception and no deaths. Most (72%) occurred in the first year of life (age adjusted incident rate 65 per 100,000 child-years, 95% CI 56 to 74). Risk of intussusception was less in females (risk ratio 0.58; 95% CI 0.43 to 0.78) and for Maori (risk ratio 0.52; 95% CI 0.35 to 0.77) when compared with European infants. In contrast to hospitalised rotavirus cases, intussusception peaked at a younger age and lacked seasonality.

CONCLUSIONS

This study provides national baseline data on intussusception for future rotavirus vaccine programmes in New Zealand. Wild-type rotaviruses do not appear to have a major role in triggering intussusception. Prospective surveillance systems, using standardised case definitions and nested case-control methodology, are needed to further our understanding of the aetiology and epidemiology of intussusception.

Peroxisome proliferator-activated receptor gamma inhibits transforming growth factor beta-induced connective tissue growth factor expression in human aortic smooth muscle cells by interfering with Smad3

Activation of peroxisome proliferator-activated receptor gamma (PPAR gamma) after balloon injury significantly inhibits VSMC proliferation and neointima formation. However, the precise mechanisms of this inhibition have not been determined. We hypothesized that activation of PPAR gamma in vascular injury could attenuate VSMC growth and matrix production during vascular lesion formation. Since connective tissue growth factor (CTGF) is a key factor regulating extracellular matrix production, abrogation of transforming growth factor beta (TGF-beta)-induced CTGF production by PPAR gamma activation may be one of the mechanisms through which PPAR gamma agonists inhibit neointima formation after vascular injury. In this study, we demonstrate that the PPAR gamma natural ligand (15-deoxyprostaglandin J(2)) and a synthetic ligand (GW7845) significantly inhibit TGF-beta-induced CTGF production in a dose-dependent manner in HASMCs. In addition, suppression of CTGF mRNA expression is relieved by pretreatment with an antagonist of PPAR gamma (GW9662), suggesting that the inhibition of CTGF expression is mediated by PPAR gamma. To elucidate further the molecular mechanism by which PPAR gamma inhibits CTGF expression, an approximately 2-kilobase pair CTGF promoter was cloned. We found that PPAR gamma activation inhibits TGF-beta-induced CTGF promoter activity in a dose-dependent manner, and suppression of CTGF promoter activity by PPAR gamma activation is completely rescued by overexpression of Smad3, but not by Smad4. Furthermore, PPAR gamma physically interacts with Smad3 but not Smad4 in vitro in glutathione S-transferase pull-down experiments. Taken together, the data suggest that PPAR gamma inhibits TGF-beta-induced CTGF expression in HASMCs by directly interfering with the Smad3 signaling pathway.

Platelet-derived growth factor promotes the expression of peroxisome proliferator-activated receptor gamma in vascular smooth muscle cells by a phosphatidylinositol 3-kinase/Akt signaling pathway

Vascular diseases such as atherosclerosis are characterized by abnormal accumulation of vascular smooth muscle cells (VSMCs) within the intimal lining. The intimal VSMCs exhibit an increased expression of peroxisome proliferator-activated receptor gamma (PPARgamma), and the administration of pharmacological PPARgamma agonists attenuates vascular lesion formation. The factors that regulate PPARgamma expression in the vasculature are poorly defined. Here we report that platelet-derived growth factor (PDGF) upregulates PPARgamma by the phosphatidylinositol 3-kinase (PI3-kinase)/Akt signaling pathway. Using Northern-blotting and Western-blotting analyses, we observed that the levels of PPARgamma mRNA and protein were increased by 2- to 3.5-fold in human aortic smooth muscle cells (HASMCs) treated with PDGF (20 ng/mL). This was abolished by preincubation of HASMCs with a PI3-kinase inhibitor (LY294002, 50 micromol/L), and partially inhibited by a MEK1 inhibitor (U0126, 10 micromol/L), but not affected by a p38 kinase inhibitor (SB202190, 10 micromol/L). In addition, overexpression of the dominant-negative p85 subunit of PI3-kinase or Akt proteins blocked the PDGF-induced PPARgamma expression. Taken together, our results suggest that PDGF induces PPARgamma expression in VSMCs by a PI3-kinase/Akt signaling pathway. The characterization of factors and signaling pathways that modulate PPARgamma expression in VSMCs may have important implications for understanding the pathogenesis of vascular diseases.

Molecular mechanism of fibronectin gene activation by cyclic stretch in vascular smooth muscle cells

Fibronectin plays an important role in vascular remodeling. A functional interaction between mechanical stimuli and locally produced vasoactive agents is suggested to be crucial for vascular remodeling. We examined the effect of mechanical stretch on fibronectin gene expression in vascular smooth muscle cells and the role of vascular angiotensin II in the regulation of the fibronectin gene in response to stretch. Cyclic stretch induced an increase in vascular fibronectin mRNA levels that was inhibited by actinomycin D and CV11974, an angiotensin II type 1 receptor antagonist; cycloheximide and PD123319, an angiotensin II type 2 receptor antagonist, did not affect the induction. In transfection experiments, fibronectin promoter activity was stimulated by stretch and inhibited by CV11974 but not by PD123319. DNA-protein binding experiments revealed that cyclic stretch enhanced nuclear binding to the AP-1 site, which was partially supershifted by antibody to c-Jun. Site-directed mutation of the AP-1 site significantly decreased the cyclic stretch-mediated activation of fibronectin promoter. Furthermore, antisense c-jun oligonucleotides decreased the stretch-induced stimulation of the fibronectin promoter activity and the mRNA expression. These results suggest that cyclic stretch stimulates vascular fibronectin gene expression mainly via the activation of AP-1 through the angiotensin II type 1 receptor.

Expression of renin-angiotensin system and extracellular matrix genes in cardiovascular cells and its regulation through AT1 receptor

Angiotensinogen (AGT) is a unique substrate of the renin-angiotensin system and fibronectin (FN) is an important component of the extracellular matrix. These play critical roles in the pathophysiological changes including cardiovascular remodeling and hypertrophy in response to hypertension. This study was performed to examine the regulation of AGT and FN gene in cardiac myocytes (CMs) and vascular smooth muscle cells (VSMCs) in response to mechanical stretch. Mechanical stretch significantly increased the AGT mRNA expression in CMs, while these stimuli did not affect FN mRNA levels. On the other hand, mechanical stretch upregulated FN mRNA levels in VSMCs, whereas no increase in AGT mRNA levels was observed in response to stretch stimuli. An angiotensin II type 1 (AT1) receptor antagonist (CV11974) significantly decreased these stretch-mediated increases in mRNA level and promoter activity of the AGT and FN gene, whereas angiotensin II type 2 (AT2) receptor antagonist (PD 123319) did not affect the induction. These results indicate that mechanical stretch activates transcription of the AGT and FN gene mainly via AT1 receptor-pathway in CMs and VSMCs. Furthermore, mechanisms regulating AGT and FN gene seem to be different between CMs and VSMCs.

LXRalpha functions as a cAMP-responsive transcriptional regulator of gene expression

LXRalpha is a member of a nuclear receptor superfamily that regulates transcription. LXRalpha forms a heterodimer with RXRalpha, another member of this family, to regulate the expression of cholesterol 7alpha-hydroxylase by means of binding to the DR4-type cis-element. Here, we describe a function for LXRalpha as a cAMP-responsive regulator of renin and c-myc gene transcriptions by the interaction with a specific cis-acting DNA element, CNRE (an overlapping cAMP response element and a negative response element). Our previous studies showed that renin gene expression is regulated by cAMP, at least partly, through the CNRE sequence in its 5'-flanking region. This sequence is also found in c-myc and several other genes. Based on our cloning results using the yeast one-hybrid system, we discovered that the mouse homologue of human LXRalpha binds to the CNRE and demonstrated that it binds as a monomer. To define the function of LXRalpha on gene expression, we transfected the renin-producing renal As4.1 cells with LXRalpha expression plasmid. Overexpression of LXRalpha in As4.1 cells confers cAMP inducibility to reporter constructs containing the renin CNRE. After stable transfection of LXRalpha, As4.1 cells show a cAMP-inducible up-regulation of renin mRNA expression. In parallel experiments, we demonstrated that LXRalpha can also bind to the homologous CNRE in the c-myc promoter. cAMP promotes transcription through c-myc/CNRE:LXRalpha interaction in LXRalpha transiently transfected cells and increases c-myc mRNA expression in stably transfected cells. Identification of LXRalpha as a cAMP-responsive nuclear modulator of renin and c-myc expression not only has cardiovascular significance but may have generalized implication in the regulation of gene transcription.

Interferon-gamma induces AT(2) receptor expression in fibroblasts by Jak/STAT pathway and interferon regulatory factor-1

The expression of angiotensin II type 2 (AT(2)) receptor is closely associated with cell growth, differentiation, and/or injury. We examined the effect of interferon (IFN)-gamma on AT(2) receptor expression in mouse fibroblast R3T3 cells and demonstrated that IFN-gamma treatment increased the expression of AT(2) receptor mRNA as well as its binding. Interferon regulatory factor (IRF)-1 was induced in mouse fibroblast R3T3 cells after IFN-gamma stimulation, and electrophoretic mobility shift assay showed an increase in IRF-1 binding with the IRF-specific binding sequence in the AT(2) receptor gene promoter region after IFN-gamma stimulation. The IRF-1 gene promoter contains an IFN-gamma-activated sequence (GAS) motif for possible binding of signal transducer(s) and activator(s) of transcription (STAT). Indeed, in R3T3 cells, IFN-gamma treatment resulted in rapid activation of Janus kinase (Jak) 1, Jak2, and STAT1 via tyrosine phosphorylation. Electrophoretic mobility shift assay with the GAS probe revealed increased STAT1 binding to the IRF-1 gene promoter in response to IFN-gamma stimulation. Transfection of GAS-binding oligonucleotides inhibited the effect of IFN-gamma on IRF-1 production, resulting in the AT(2) receptor trans-activation. Taken together, our data show that IFN-gamma upregulates AT(2) receptor expression in R3T3 cells via the activation of the intracellular Jak/STAT pathway and production of IRF-1.