PPARγ Regulates Mitochondrial Structure and Function and Human Pulmonary Artery Smooth Muscle Cell Proliferation

Pulmonary hypertension (PH) is a progressive disorder that causes significant morbidity and mortality despite existing therapies. PH pathogenesis is characterized by metabolic derangements that increase pulmonary artery smooth muscle cell (PASMC) proliferation and vascular remodeling. PH-associated decreases in peroxisome proliferator-activated receptor γ (PPARγ) stimulate PASMC proliferation, and PPARγ in coordination with PPARγ coactivator 1α (PGC1α) regulates mitochondrial gene expression and biogenesis. To further examine the impact of decreases in PPARγ expression on human PASMC (HPASMC) mitochondrial function, we hypothesized that depletion of either PPARγ or PGC1α perturbs mitochondrial structure and function to stimulate PASMC proliferation. To test this hypothesis, HPASMCs were exposed to hypoxia and treated pharmacologically with the PPARγ antagonist GW9662 or with siRNA against PPARγ or PGC1α for 72 hours. HPASMC proliferation (cell counting), target mRNA levels (qRT-PCR), target protein levels (Western blotting), mitochondria-derived H₂O₂ (confocal immunofluorescence), mitochondrial mass and fragmentation, and mitochondrial bioenergetic profiling were determined. Hypoxia or knockdown of either PPARγ or PGC1α increased HPASMC proliferation, enhanced mitochondria-derived H₂O₂, decreased mitochondrial mass, stimulated mitochondrial fragmentation, and impaired mitochondrial bioenergetics. Taken together, these findings provide novel evidence that loss of PPARγ diminishes PGC1α and stimulates derangements in mitochondrial structure and function that cause PASMC proliferation. Overexpression of PGC1α reversed hypoxia-induced HPASMC derangements. This study identifies additional mechanistic underpinnings of PH, and provides support for the notion of activating PPARγ as a novel therapeutic strategy in PH.

Peroxisome Proliferator-Activated Receptor γ Regulates the V-Ets Avian Erythroblastosis Virus E26 Oncogene Homolog 1/microRNA-27a Axis to Reduce Endothelin-1 and Endothelial Dysfunction in the Sickle Cell Mouse Lung

Pulmonary hypertension (PH), a serious complication of sickle cell disease (SCD), causes significant morbidity and mortality. Although a recent study determined that hemin release during hemolysis triggers endothelial dysfunction in SCD, the pathogenesis of SCD-PH remains incompletely defined. This study examines peroxisome proliferator-activated receptor γ (PPARγ) regulation in SCD-PH and endothelial dysfunction. PH and right ventricular hypertrophy were studied in Townes humanized sickle cell (SS) and littermate control (AA) mice. In parallel studies, SS or AA mice were gavaged with the PPARγ agonist, rosiglitazone (RSG), 10 mg/kg/day, or vehicle for 10 days. In vitro, human pulmonary artery endothelial cells (HPAECs) were treated with vehicle or hemin for 72 hours, and selected HPAECs were treated with RSG. SS mice developed PH and right ventricular hypertrophy associated with reduced lung levels of PPARγ and increased levels of microRNA-27a (miR-27a), v-ets avian erythroblastosis virus E26 oncogene homolog 1 (ETS1), endothelin-1 (ET-1), and markers of endothelial dysfunction (platelet/endothelial cell adhesion molecule 1 and E selectin). HPAECs treated with hemin had increased ETS1, miR-27a, ET-1, and endothelial dysfunction and decreased PPARγ levels. These derangements were attenuated by ETS1 knockdown, inhibition of miR-27a, or PPARγ overexpression. In SS mouse lung or in hemin-treated HPAECs, activation of PPARγ with RSG attenuated reductions in PPARγ and increases in miR-27a, ET-1, and markers of endothelial dysfunction. In SCD-PH pathogenesis, ETS1 stimulates increases in miR-27a levels that reduce PPARγ and increase ET-1 and endothelial dysfunction. PPARγ activation attenuated SCD-associated signaling derangements, suggesting a novel therapeutic approach to attenuate SCD-PH pathogenesis.

Peroxisome proliferator-activated receptor-γ enhances human pulmonary artery smooth muscle cell apoptosis through microRNA-21 and programmed cell death 4

Pulmonary hypertension (PH) is a progressive disorder whose cellular pathogenesis involves enhanced smooth muscle cell (SMC) proliferation and resistance to apoptosis signals. Existing evidence demonstrates that the tumor suppressor programmed cell death 4 (PDCD4) affects patterns of cell growth and repair responses in the systemic vasculature following experimental injury. In the current study, the regulation PDCD4 and its functional effects on growth and apoptosis susceptibility in pulmonary artery smooth muscle cells were explored. We previously demonstrated that pharmacological activation of the nuclear transcription factor peroxisome proliferator-activated receptor-γ (PPARγ) attenuated hypoxia-induced proliferation of human pulmonary artery smooth muscle cells (HPASMCs) by inhibiting the expression and mitogenic functions of microRNA-21 (miR-21). In the current study, we hypothesize that PPARγ stimulates PDCD4 expression and HPASMC apoptosis by inhibiting miR-21. Our findings demonstrate that PDCD4 is reduced in the mouse lung upon exposure to chronic hypoxia (10% O₂ for 3 wk) and in hypoxia-exposed HPASMCs (1% O₂). HPASMC apoptosis was reduced by hypoxia, by miR-21 overexpression, or by siRNA-mediated PPARγ and PDCD4 depletion. Activation of PPARγ inhibited miR-21 expression and resultant proliferation, while restoring PDCD4 levels and apoptosis to baseline. Additionally, pharmacological activation of PPARγ with rosiglitazone enhanced PDCD4 protein expression and apoptosis in a dose-dependent manner as demonstrated by increased annexin V detection by flow cytometry. Collectively, these findings demonstrate that PPARγ confers growth-inhibitory signals in hypoxia-exposed HPASMCs through suppression of miR-21 and the accompanying derepression of PDCD4 that augments HPASMC susceptibility to undergo apoptosis.

Peroxisome Proliferator-Activated Receptor γ and microRNA 98 in Hypoxia-Induced Endothelin-1 Signaling

Endothelin-1 (ET-1) plays a critical role in endothelial dysfunction and contributes to the pathogenesis of pulmonary hypertension (PH). We hypothesized that peroxisome proliferator-activated receptor γ (PPARγ) stimulates microRNAs that inhibit ET-1 and pulmonary artery endothelial cell (PAEC) proliferation. The objective of this study was to clarify molecular mechanisms by which PPARγ regulates ET-1 expression in vitro and in vivo. In PAECs isolated from patients with pulmonary arterial hypertension, microRNA (miR)-98 expression was reduced, and ET-1 protein levels and proliferation were increased. Similarly, hypoxia reduced miR-98 and increased ET-1 levels and PAEC proliferation in vitro. In vivo, hypoxia reduced miR-98 expression and increased ET-1 and proliferating cell nuclear antigen (PCNA) levels in mouse lung, derangements that were aggravated by treatment with the vascular endothelial growth factor receptor antagonist Sugen5416. Reporter assays confirmed that miR-98 binds directly to the ET-1 3'-untranslated region. Compared with littermate control mice, miR-98 levels were reduced and ET-1 and PCNA expression were increased in lungs from endothelial-targeted PPARγ knockout mice, whereas miR-98 levels were increased and ET-1 and PCNA expression was reduced in lungs from endothelial-targeted PPARγ-overexpression mice. Gain or loss of PPARγ function in PAECs in vitro confirmed that alterations in PPARγ were sufficient to regulate miR-98, ET-1, and PCNA expression. Finally, PPARγ activation with rosiglitazone regimens that attenuated hypoxia-induced PH in vivo and human PAEC proliferation in vitro restored miR-98 levels. The results of this study show that PPARγ regulates miR-98 to modulate ET-1 expression and PAEC proliferation. These results further clarify molecular mechanisms by which PPARγ participates in PH pathogenesis and therapy.

Time-dependent PPARγ Modulation of HIF-1α Signaling in Hypoxic Pulmonary Artery Smooth Muscle Cells

BACKGROUND

Pathogenesis of pulmonary hypertension is complex and involves activation of the transcription factor, hypoxia-inducible factor-1 (HIF-1) that shifts cellular metabolism from aerobic respiration to glycolysis, in part, by increasing the expression of its downstream target pyruvate dehydrogenase kinase-1 (PDK-1), thereby promoting a proliferative, apoptosis-resistant phenotype in pulmonary vascular cells. Activation of the nuclear hormone transcription factor, peroxisome proliferator-activated receptor gamma (PPARγ), attenuates pulmonary hypertension and pulmonary artery smooth muscle cell (PASMC) proliferation. In the current study, we determined whether PPARγ inhibits HIF-1α and PDK-1 expression in human PASMCs.

METHODS

HPASMCs were exposed to normoxia (21% O2) or hypoxia (1% O2) for 2-72 hours ± treatment with the PPARγ-ligand, rosiglitazone (RSG, 10μM).

RESULTS

Compared to normoxia, HIF-1α mRNA levels were elevated in HPASMC at 2 hours hypoxia and reduced to baseline levels by 24-72 hours. HIF-1α protein levels increased following 4 and 8 hours of hypoxia and returned to baseline levels by 24 and 72 hours. PDK-1 protein levels increased following 24 hours hypoxia and remained elevated by 72 hours. RSG treatment at the onset of hypoxia attenuated HIF-1α protein and PDK-1 mRNA and protein levels at 4, 8 and 24 hours of hypoxia, respectively. However, RSG treatment during final 24 hours of 72-hour hypoxia, an intervention that inhibits HPASMC proliferation, failed to prevent hypoxia-induced PDK-1 expression.

CONCLUSION

Hypoxia causes transient activation of HPASMC HIF-1α that is attenuated by RSG treatment initiated at hypoxia onset. These findings provide novel evidence that PPARγ modulates fundamental and acute cellular responses to hypoxia through both HIF-1-dependent and HIF-1-independent mechanisms.

Smooth Muscle-Targeted Overexpression of Peroxisome Proliferator Activated Receptor-γ Disrupts Vascular Wall Structure and Function

Activation of the nuclear hormone receptor, PPARγ, with pharmacological agonists promotes a contractile vascular smooth muscle cell phenotype and reduces oxidative stress and cell proliferation, particularly under pathological conditions including vascular injury, restenosis, and atherosclerosis. However, pharmacological agonists activate both PPARγ-dependent and -independent mechanisms in multiple cell types confounding efforts to clarify the precise role of PPARγ in smooth muscle cell structure and function in vivo. We, therefore, designed and characterized a mouse model with smooth muscle cell-targeted PPARγ overexpression (smPPARγOE). Our results demonstrate that smPPARγOE attenuated contractile responses in aortic rings, increased aortic compliance, caused aortic dilatation, and reduced mean arterial pressure. Molecular characterization revealed that compared to littermate control mice, aortas from smPPARγOE mice expressed lower levels of contractile proteins and increased levels of adipocyte-specific transcripts. Morphological analysis demonstrated increased lipid deposition in the vascular media and in smooth muscle of extravascular tissues. In vitro adenoviral-mediated PPARγ overexpression in human aortic smooth muscle cells similarly increased adipocyte markers and lipid uptake. The findings demonstrate that smooth muscle PPARγ overexpression disrupts vascular wall structure and function, emphasizing that balanced PPARγ activity is essential for vascular smooth muscle homeostasis.

Targeting mitochondrial reactive oxygen species to modulate hypoxia-induced pulmonary hypertension

Pulmonary hypertension (PH) is characterized by increased pulmonary vascular remodeling, resistance, and pressures. Reactive oxygen species (ROS) contribute to PH-associated vascular dysfunction. NADPH oxidases (Nox) and mitochondria are major sources of superoxide (O(2)(•-)) and hydrogen peroxide (H(2)O(2)) in pulmonary vascular cells. Hypoxia, a common stimulus of PH, increases Nox expression and mitochondrial ROS (mtROS) production. The interactions between these two sources of ROS generation continue to be defined. We hypothesized that mitochondria-derived O(2)(•-) (mtO(2)(•-)) and H(2)O(2) (mtH(2)O(2)) increase Nox expression to promote PH pathogenesis and that mitochondria-targeted antioxidants can reduce mtROS, Nox expression, and hypoxia-induced PH. Exposure of human pulmonary artery endothelial cells to hypoxia for 72 h increased mtO(2)(•-) and mtH(2)O(2). To assess the contribution of mtO(2)(•-) and mtH(2)O(2) to hypoxia-induced PH, mice that overexpress superoxide dismutase 2 (Tg(hSOD2)) or mitochondria-targeted catalase (MCAT) were exposed to normoxia (21% O(2)) or hypoxia (10% O(2)) for three weeks. Compared with hypoxic control mice, MCAT mice developed smaller hypoxia-induced increases in RVSP, α-SMA staining, extracellular H(2)O(2) (Amplex Red), Nox2 and Nox4 (qRT-PCR and Western blot), or cyclinD1 and PCNA (Western blot). In contrast, Tg(hSOD2) mice experienced exacerbated responses to hypoxia. These studies demonstrate that hypoxia increases mtO(2)(•-) and mtH(2)O(2). Targeting mtH(2)O(2) attenuates PH pathogenesis, whereas targeting mtO(2)(•-) exacerbates PH. These differences in PH pathogenesis were mirrored by RVSP, vessel muscularization, levels of Nox2 and Nox4, proliferation, and H(2)O(2) release. These studies suggest that targeted reductions in mtH(2)O(2) generation may be particularly effective in preventing hypoxia-induced PH.

PPARγ Ligands Attenuate Hypoxia-Induced Proliferation in Human Pulmonary Artery Smooth Muscle Cells through Modulation of MicroRNA-21

Pulmonary hypertension (PH) is a progressive and often fatal disorder whose pathogenesis involves pulmonary artery smooth muscle cell (PASMC) proliferation. Although modern PH therapies have significantly improved survival, continued progress rests on the discovery of novel therapies and molecular targets. MicroRNA (miR)-21 has emerged as an important non-coding RNA that contributes to PH pathogenesis by enhancing vascular cell proliferation, however little is known about available therapies that modulate its expression. We previously demonstrated that peroxisome proliferator-activated receptor gamma (PPARγ) agonists attenuated hypoxia-induced HPASMC proliferation, vascular remodeling and PH through pleiotropic actions on multiple targets, including transforming growth factor (TGF)-β1 and phosphatase and tensin homolog deleted on chromosome 10 (PTEN). PTEN is a validated target of miR-21. We therefore hypothesized that antiproliferative effects conferred by PPARγ activation are mediated through inhibition of hypoxia-induced miR-21 expression. Human PASMC monolayers were exposed to hypoxia then treated with the PPARγ agonist, rosiglitazone (RSG,10 μM), or in parallel, C57Bl/6J mice were exposed to hypoxia then treated with RSG. RSG attenuated hypoxic increases in miR-21 expression in vitro and in vivo and abrogated reductions in PTEN and PASMC proliferation. Antiproliferative effects of RSG were lost following siRNA-mediated PTEN depletion. Furthermore, miR-21 mimic decreased PTEN and stimulated PASMC proliferation, whereas miR-21 inhibition increased PTEN and attenuated hypoxia-induced HPASMC proliferation. Collectively, these results demonstrate that PPARγ ligands regulate proliferative responses to hypoxia by preventing hypoxic increases in miR-21 and reductions in PTEN. These findings further clarify molecular mechanisms that support targeting PPARγ to attenuate pathogenic derangements in PH.

Peroxisome proliferator-activated receptor gamma depletion stimulates Nox4 expression and human pulmonary artery smooth muscle cell proliferation

Hypoxia stimulates pulmonary hypertension (PH) in part by increasing the proliferation of pulmonary vascular wall cells. Recent evidence suggests that signaling events involved in hypoxia-induced cell proliferation include sustained nuclear factor-kappaB (NF-κB) activation, increased NADPH oxidase 4 (Nox4) expression, and downregulation of peroxisome proliferator-activated receptor gamma (PPARγ) levels. To further understand the role of reduced PPARγ levels associated with PH pathobiology, siRNA was employed to reduce PPARγ levels in human pulmonary artery smooth muscle cells (HPASMC) in vitro under normoxic conditions. PPARγ protein levels were reduced to levels comparable to those observed under hypoxic conditions. Depletion of PPARγ for 24-72 h activated mitogen-activated protein kinase, ERK 1/2, and NF-κB. Inhibition of ERK 1/2 prevented NF-κB activation caused by PPARγ depletion, indicating that ERK 1/2 lies upstream of NF-κB activation. Depletion of PPARγ for 72 h increased NF-κB-dependent Nox4 expression and H2O2 production. Inhibition of NF-κB or Nox4 attenuated PPARγ depletion-induced HPASMC proliferation. Degradation of PPARγ depletion-induced H2O2 by PEG-catalase prevented HPASMC proliferation and also ERK 1/2 and NF-κB activation and Nox4 expression, indicating that H2O2 participates in feed-forward activation of the above signaling events. Contrary to the effects of PPARγ depletion, HPASMC PPARγ overexpression reduced ERK 1/2 and NF-κB activation, Nox4 expression, and cell proliferation. Taken together these findings provide novel evidence that PPARγ plays a central role in the regulation of the ERK1/2-NF-κB-Nox4-H2O2 signaling axis in HPASMC. These results indicate that reductions in PPARγ caused by pathophysiological stimuli such as prolonged hypoxia exposure are sufficient to promote the proliferation of pulmonary vascular smooth muscle cells observed in PH pathobiology.

Chronic hypoxia promotes pulmonary artery endothelial cell proliferation through H2O2-induced 5-lipoxygenase

Pulmonary Hypertension (PH) is a progressive disorder characterized by endothelial dysfunction and proliferation. Hypoxia induces PH by increasing vascular remodeling. A potential mediator in hypoxia-induced PH development is arachidonate 5-Lipoxygenase (ALOX5). While ALOX5 metabolites have been shown to promote pulmonary vasoconstriction and endothelial cell proliferation, the contribution of ALOX5 to hypoxia-induced proliferation remains unknown. We hypothesize that hypoxia exposure stimulates HPAEC proliferation by increasing ALOX5 expression and activity. To test this, human pulmonary artery endothelial cells (HPAEC) were cultured under normoxic (21% O2) or hypoxic (1% O2) conditions for 24-, 48-, or 72 hours. In a subset of cells, the ALOX5 inhibitor, zileuton, or the 5-lipoxygenase activating protein inhibitor, MK-886, was administered during hypoxia exposure. ALOX5 expression was measured by qRT-PCR and western blot and HPAEC proliferation was assessed. Our results demonstrate that 24 and 48 hours of hypoxia exposure have no effect on HPAEC proliferation or ALOX5 expression. Seventy two hours of hypoxia significantly increases HPAEC ALOX5 expression, hydrogen peroxide (H2O2) release, and HPAEC proliferation. We also demonstrate that targeted ALOX5 gene silencing or inhibition of the ALOX5 pathway by pharmacological blockade attenuates hypoxia-induced HPAEC proliferation. Furthermore, our findings indicate that hypoxia-induced increases in cell proliferation and ALOX5 expression are dependent on H2O2 production, as administration of the antioxidant PEG-catalase blocks these effects and addition of H2O2 to HPAEC promotes proliferation. Overall, these studies indicate that hypoxia exposure induces HPAEC proliferation by activating the ALOX5 pathway via the generation of H2O2.

Hypoxia downregulates PPARγ via an ERK1/2-NF-κB-Nox4-dependent mechanism in human pulmonary artery smooth muscle cells

The ligand-activated transcription factor peroxisome proliferator-activated receptor γ (PPARγ) regulates metabolism, cell proliferation, and inflammation. Pulmonary hypertension (PH) is associated with reduced PPARγ expression, and hypoxia exposure regimens that cause PH reduce PPARγ expression. This study examines mechanisms of hypoxia-induced PPARγ downregulation in vitro and in vivo. Hypoxia reduced PPARγ mRNA and protein levels, PPARγ activity, and the expression of PPARγ-regulated genes in human pulmonary artery smooth muscle cells (HPASMCs) exposed to 1% oxygen for 72 h. Similarly, exposure of mice to hypoxia (10% O₂) for 3 weeks reduced PPARγ mRNA and protein in mouse lung. Inhibiting ERK1/2 with PD98059 or treatment with siRNA directed against either NF-κB p65 or Nox4 attenuated hypoxic reductions in PPARγ expression and activity. Furthermore, degradation of H₂O₂ using PEG-catalase prevented hypoxia-induced ERK1/2 phosphorylation and Nox4 expression, suggesting sustained ERK1/2-mediated signaling and Nox4 expression in this response. Mammalian two-hybrid assays demonstrated that PPARγ and p65 bind directly to each other in a mutually repressive fashion. We conclude from these results that hypoxic regimens that promote PH pathogenesis and HPASMC proliferation reduce PPARγ expression and activity through ERK1/2-, p65-, and Nox4-dependent pathways. These findings provide novel insights into mechanisms by which pathophysiological stimuli such as hypoxia cause loss of PPARγ activity and pulmonary vascular cell proliferation, pulmonary vascular remodeling, and PH. These results also indicate that restoration of PPARγ activity with pharmacological ligands may provide a novel therapeutic approach in selected forms of PH.

Peroxisome proliferator-activated receptor gamma (PPARγ) regulates thrombospondin-1 and Nox4 expression in hypoxia-induced human pulmonary artery smooth muscle cell proliferation

Transforming growth factor-β1 (TGF- β1) and thrombospondin-1 (TSP-1) are hypoxia-responsive mitogens that promote vascular smooth muscle cell (SMC) proliferation, a critical event in the pathogenesis of pulmonary hypertension (PH). We previously demonstrated that hypoxia-induced human pulmonary artery smooth muscle (HPASMC) cell proliferation and expression of the NADPH oxidase subunit, Nox4, were attenuated by the peroxisome proliferator-activated receptor γ (PPARγ) agonist, rosiglitazone. The current study examines the hypothesis that rosiglitazone regulates Nox4 expression and HPASMC proliferation by attenuating TSP-1 signaling. Selected HPASMC were exposed to normoxic or hypoxic (1% O₂) environments or TSP-1 (0-1 μg/ ml) for 72 hours ± administration of rosiglitazone (10 μM). Cellular proliferation, Nox4, TSP-1, and TGF-β1 expression and reactive oxygen species generation were measured. Mice exposed to hypoxia (10% O₂) for three weeks were treated with rosiglitazone (10 mg/kg/day) for the final 10 days, and lung TSP-1 expression was examined. Hypoxia increased TSP-1 and TGF-β1 expression and HPASMC proliferation, and neutralizing antibodies to TSP-1 or TGF-β1 attenuated proliferation. Rosiglitazone attenuated hypoxia-induced HPASMC proliferation and increases in mouse lung and HPASMC TSP-1 expression, but failed to reduce increases in TGF-β1 expression or Nox4 expression and activity caused by direct TSP-1 stimulation. Transfecting HPASMC with siRNA to Nox4 attenuated hypoxia- or TSP-1-stimulated HPASMC proliferation. These findings provide novel evidence that TSP-1-mediated Nox4 expression plays a critical role in hypoxia-induced HPASMC proliferation. PPARγ activation with exogenous ligands attenuates TSP-1 expression to reduce Nox4 expression. These results clarify mechanisms of hypoxia-induced SMC proliferation and suggest additional pathways by which PPARγ agonists may regulate critical steps in the pathobiology of PH.

The Nox4 inhibitor GKT137831 attenuates hypoxia-induced pulmonary vascular cell proliferation

Increased NADP reduced (NADPH) oxidase 4 (Nox4) and reduced expression of the nuclear hormone receptor peroxisome proliferator-activated receptor γ (PPARγ) contribute to hypoxia-induced pulmonary hypertension (PH). To examine the role of Nox4 activity in pulmonary vascular cell proliferation and PH, the current study used a novel Nox4 inhibitor, GKT137831, in hypoxia-exposed human pulmonary artery endothelial or smooth muscle cells (HPAECs or HPASMCs) in vitro and in hypoxia-treated mice in vivo. HPAECs or HPASMCs were exposed to normoxia or hypoxia (1% O(2)) for 72 hours with or without GKT137831. Cell proliferation and Nox4, PPARγ, and transforming growth factor (TGF)β1 expression were measured. C57Bl/6 mice were exposed to normoxia or hypoxia (10% O(2)) for 3 weeks with or without GKT137831 treatment during the final 10 days of exposure. Lung PPARγ and TGF-β1 expression, right ventricular hypertrophy (RVH), right ventricular systolic pressure (RVSP), and pulmonary vascular remodeling were measured. GKT137831 attenuated hypoxia-induced H(2)O(2) release, proliferation, and TGF-β1 expression and blunted reductions in PPARγ in HPAECs and HPASMCs in vitro. In vivo GKT137831 inhibited hypoxia-induced increases in TGF-β1 and reductions in PPARγ expression and attenuated RVH and pulmonary artery wall thickness but not increases in RVSP or muscularization of small arterioles. This study shows that Nox4 plays a critical role in modulating proliferative responses of pulmonary vascular wall cells. Targeting Nox4 with GKT137831 provides a novel strategy to attenuate hypoxia-induced alterations in pulmonary vascular wall cells that contribute to vascular remodeling and RVH, key features involved in PH pathogenesis.

The PPARγ ligand rosiglitazone attenuates hypoxia-induced endothelin signaling in vitro and in vivo

Peroxisome proliferator-activated receptor (PPAR) γ activation attenuates hypoxia-induced pulmonary hypertension (PH) in mice. The current study examined the hypothesis that PPARγ attenuates hypoxia-induced endothelin-1 (ET-1) signaling to mediate these therapeutic effects. To test this hypothesis, human pulmonary artery endothelial cells (HPAECs) were exposed to normoxia or hypoxia (1% O(2)) for 72 h and treated with or without the PPARγ ligand rosiglitazone (RSG, 10 μM) during the final 24 h of exposure. HPAEC proliferation was measured with MTT assays or cell counting, and mRNA and protein levels of ET-1 signaling components were determined. To explore the role of hypoxia-activated transcription factors, selected HPAECs were treated with inhibitors of hypoxia-inducible factor (HIF)-1α (chetomin) or nuclear factor (NF)-κB (caffeic acid phenethyl ester, CAPE). In parallel studies, male C57BL/6 mice were exposed to normoxia (21% O(2)) or hypoxia (10% O(2)) for 3 wk with or without gavage with RSG (10 mg·kg(-1)·day(-1)) for the final 10 days of exposure. Hypoxia increased ET-1, endothelin-converting enzyme-1, and endothelin receptor A and B levels in mouse lung and in HPAECs and increased HPAEC proliferation. Treatment with RSG attenuated hypoxia-induced activation of HIF-1α, NF-κB activation, and ET-1 signaling pathway components. Similarly, treatment with chetomin or CAPE prevented hypoxia-induced increases in HPAEC ET-1 mRNA and protein levels. These findings indicate that PPARγ activation attenuates a program of hypoxia-induced ET-1 signaling by inhibiting activation of hypoxia-responsive transcription factors. Targeting PPARγ represents a novel therapeutic strategy to inhibit enhanced ET-1 signaling in PH pathogenesis.

PPAR{gamma} regulates hypoxia-induced Nox4 expression in human pulmonary artery smooth muscle cells through NF-{kappa}B

NADPH oxidases are a major source of superoxide production in the vasculature. The constitutively active Nox4 subunit, which is selectively upregulated in the lungs of human subjects and experimental animals with pulmonary hypertension, is highly expressed in vascular wall cells. We demonstrated that rosiglitazone, a synthetic agonist of the peroxisome proliferator-activated receptor-γ (PPARγ), attenuated hypoxia-induced pulmonary hypertension, vascular remodeling, Nox4 induction, and reactive oxygen species generation in the mouse lung. The current study examined the molecular mechanisms involved in PPARγ-regulated, hypoxia-induced Nox4 expression in human pulmonary artery smooth muscle cells (HPASMC). Exposing HPASMC to 1% oxygen for 72 h increased Nox4 gene expression and H(2)O(2) production, both of which were reduced by treatment with rosiglitazone during the last 24 h of hypoxia exposure or by treatment with small interfering RNA (siRNA) to Nox4. Hypoxia also increased HPASMC proliferation as well as the activity of a Nox4 promoter luciferase reporter, and these increases were attenuated by rosiglitazone. Chromatin immunoprecipitation assays demonstrated that hypoxia increased binding of the NF-κB subunit, p65, to the Nox4 promoter and that binding was attenuated by rosiglitazone treatment. The role of NF-κB in Nox4 regulation was further supported by demonstrating that overexpression of p65 stimulated Nox4 promoter activity, whereas siRNA to p50 or p65 attenuated hypoxic stimulation of Nox4 promoter activity. These results provide novel evidence for NF-κB-mediated stimulation of Nox4 expression in HPASMC that can be negatively regulated by PPARγ. These data provide new insights into potential mechanisms by which PPARγ activation inhibits Nox4 upregulation and the proliferation of cells in the pulmonary vascular wall to ameliorate pulmonary hypertension and vascular remodeling in response to hypoxia.

Broiler performance and in vivo viscosity as influenced by a range of xylanases, varying in ability to effect wheat in vitro viscosity

1. Exogenous enzymes such as xylanase are used in diets for broilers to eliminate anti-nutritive effects caused by the presence of non-starch polysaccharides (NSP). It has been proposed that the mechanism by which xylanases exert their effect is through reducing in vivo viscosity within the broiler digestive tract. Previous research has reported that in vitro viscosity was a reasonable predictor of in vivo viscosity and that this method could be used to assess the efficacy of xylanases. 2. The objective of this study was to examine the response of broilers offered a wheat-based diet supplemented with a range of xylanases, varying in ability to reduce in vitro viscosity. 3. A total of 18 xylanases (Syngenta Animal Nutrition) were used to investigate the effect of xylanase on wheat in vitro viscosity. For the in vitro viscosity assay, pepsin was dissolved in either 005 or 01 M hydrochloric acid (HCl). 4. A wheat-based diet was formulated, produced and split into 7 batches; xylanase (500 U/kg) was sprayed onto 6 of the batches and the 7th was the control. This was repeated three times to produce a total of 21 diets, 18 of which contained xylanase. 5. The experiment was conducted in three consecutive trials. Each trial utilised 63 male, Ross broilers from 7 to 28 d of age. Dry matter intake (DMI), liveweight gain (LWG) and gain:feed were determined weekly. Excreta were collected from d 14 to 21 for determination of apparent metabolisable energy (AME). Oil and neutral detergent fibre (NDF) digestibility and ileal digestibility of dry matter (DM) and starch were determined. 6. Regression analyses were applied to the mean intestinal viscosity against DMI, LWG, gain:feed and the ratio of metabolisable energy to gross energy (ME:GE). To compare xylanases across the three trials, the data were subjected to REML analysis (Genstat 5). 7. When 01 M HCl was used for dissolution of pepsin, considerable reductions in in vitro viscosity were achieved for the majority of the xylanases-to values less than 12% of the control treatment. When 005 M HCl was used for the dissolution of pepsin, initial viscosity values were lower and the reduction in in vitro viscosity less dramatic than that observed with 01 M HCl. 8. With the exception of diets containing xylanases 9003 and 7162, significant reductions in in vivo viscosity were observed for diets containing xylanase in comparison to the control diet. 9. In terms of gain:feed, ME:GE and AME the xylanases ranked best were 2230 and 9003. Xylanase 2230 also resulted in the highest values for ileal DM and starch digestibility. 10. There were weak but significant relationships between in vitro viscosity and in vivo jenjunal digesta viscosity when in vitro viscosity was determined using either 01 or 005 M HCl (r(2)= 0287 and 0240, respectively). 11. The relationship between jejunal viscosity and DMI was significant (P < 005) but relatively poor (r(2)= 023). There were also significant (P < 005) relationships between jejunal digestal viscosity and gain:feed and ME:GE (r(2)= 034 and 028, respectively). 12. In conclusion, in vitro viscosity may be of some use in predicating xylanase response in vivo.

The role of nitric oxide in the mechanical repression of RANKL in bone stromal cells

Both mechanical loading and nitric oxide (NO) have positive influences on bone mass. NO production is induced by mechanical strain via upregulation of eNOS mRNA and protein, the predominant NOS in adult bone. At the same time, strain causes decreased expression of RANKL, a factor critical for osteoclastogenesis. In this study, we harvested primary stromal cells from wild-type (WT) and eNOS(-/-) mice to test whether induction of NO by mechanical strain was necessary for transducing mechanical inhibition of RANKL. We found that strain inhibition of RANKL expression was prevented by NOS inhibitors (L-NAME and L-NMMA) in WT stromal cells. Surprisingly, stromal cells from eNOS(-/-) mice showed significant mechanical repression of RANKL expression (p<0.05). Mechanical strain still increased NO production in the absence of eNOS, and was abolished by SMTC, a specific nNOS inhibitor. nNOS mRNA and protein expression were increased by strain in eNOS(-/-) but not in WT cells, revealing that nNOS was mechanically sensitive. When NO synthesis was blocked with either SMTC or siRNA targeting nNOS in eNOS(-/-) cells however, strain still was able to suppress RANKL expression by 34%. This indicated that strain suppression of RANKL can also occur through non-NO dependent pathways. While our results confirm the importance of NO in the mechanical control of skeletal remodeling, they also suggest alternative signaling pathways by which mechanical force can produce anti-catabolic effects on the skeleton.

Fumaric and sorbic acid as additives in broiler feed

The aim of the experiment was to study the effect of dietary organic acids, fumaric and sorbic, on nitrogen corrected apparent metabolisable energy (AME(N)), metabolisability of nutrients, endogenous losses and performance on young broiler chickens. A total of 56 male Ross broilers were used in a growing experiment from 14 to 30d age. Seven experimental wheat-based (655g/kg) diets were formulated. The control diet did not contain organic acids. The other six diets were produced with the addition of fumaric or sorbic acids, replacing 0.5% , 1.0% or 1.5% of the wheat. The organic acid supplemented diets contained higher levels of AME(N) compared to the control diet. Overall, birds offered organic acids had lower feed intake. Dietary organic acids did not significantly affect weight gain or feed efficiency, however, birds offered supplemented diets had lower numbers of Lactic acid bacteria and Coliforms in the ileum and caeca. Birds offered organic acids had lower levels of endogenous losses compared to control fed birds. There was a negative relationship between AME(N) of the diets and excreted endogenous losses, measured as sialic acid. It can be concluded that the decrease in secretions from the gastrointestinal tract in the presence of fumaric and sorbic acids may be a mechanism involved in the mode of action of dietary organic acids.

The feminisation of the orthodontic workforce

OBJECTIVE

To describe the status and activity of women in the UK orthodontic workforce.

DESIGN AND SETTING

Postal questionnaire based on the UK orthodontic workforce.

SUBJECTS

All orthodontic providers in the UK.

MATERIALS AND METHODS

A questionnaire was circulated to the total study population. The variables studied relating to sex were numbers, age, number of sessions worked, productivity, professional status and retirement intentions.

RESULTS

The response rate was 72.7%. 31.4% of the participants were female. The average age of female providers was 42.7 (SE 0.48) years, who were on average 4 years younger than males. Sixty-six percent of specialist trainees are women and 34% men. 41.5% of male providers and 31.6% of female providers plan to retire in the next 15 years. The mean number of sessions worked by women was 7.2 (SE 0.1) and men 8.2 (SE 0.1). Women completed 24.2 (SE 1.9) cases per session and men 25.6 (SE 1.3).

CONCLUSIONS

The orthodontic workforce is becoming increasingly feminised. The cumulative effect of more women completing fewer cases will mean that workforce planners will need to consider increasing numbers to allow for this feminisation.

Response to mechanical strain in an immortalized pre-osteoblast cell is dependent on ERK1/2

Mechanical strain inhibits osteoclastogenesis by regulating osteoblast functions: We have shown that strain inhibits receptor activator of NF-kappaB ligand (RANKL) expression and increases endothelial nitric oxide synthase (eNOS) and nitric oxide levels through ERK1/2 signaling in primary bone stromal cells. The primary stromal culture system, while contributing greatly to understanding of how the microenvironment regulates bone remodeling is limited in use for biochemical assays and studies of other osteoprogenitor cell responses to mechanical strain: Stromal cells proliferate poorly and lose aspects of the strain response after a relatively short time in culture. In this study, we used the established mouse osteoblast cell line, conditionally immortalized murine calvarial (CIMC-4), harvested from mouse calvariae conditionally immortalized by insertion of the gene coding for a temperature-sensitive mutant of SV40 large T antigen (TAg) and support osteoclastogenesis. Mechanical strain (0.5-2%, 10 cycles per min, equibiaxial) caused magnitude-dependent decreases in RANKL expression to less than 50% those of unstrained cultures. Overnight strains of 2% also increased osterix (OSX) and RUNX2 expression by nearly twofold as measured by RT-PCR. Importantly, the ERK1/2 inhibitor, PD98059, completely abrogated the strain effects bringing RANKL, OSX, and RUNX2 gene expression completely back to control levels. These data indicate that the strain effects on CIMC-4 cells require activation of ERK1/2 pathway. Therefore, the CIMC-4 cell line is a useful alternative in vitro model which effectively recapitulates aspects of the primary stromal cells and adds an extended capacity to study osteoblast control of bone remodeling in a mechanically active environment.

IGF-I secretion by prostate carcinoma cells does not alter tumor-bone cell interactions in vitro or in vivo

BACKGROUND

IGF-I is an important growth and differentiative factor for osteoblasts and may have a role in defining prostate cancer risk and skeletal metastases.

METHODS

Conditioned media (CM) from human prostate cancer (PC), C4-2 and C4-2B, which produce osteoblastic lesions, and PC-3, which causes osteolysis, was added to MC3T3-E1 bone cultures. SCID mice were injected intratibially with these engineered cells. Tumor bearing tibiae were analyzed by microCT and pQCT.

RESULTS

CM from PC cells increased osteoblast proliferation and differentiation and was unaltered by the type of PC cell, IGF-I antibodies, or exogenous IGF-I and IGFBP2. Study of intratibial PC tumors in SCID mice showed that C4-2 cells grew slowly preserving bone structure, while PC-3 tumors caused rapid osteolysis. Overexpression of IGF-I did not change either tumor progression or skeletal response.

CONCLUSIONS

IGF-I is neither necessary nor sufficient for the osteoblastic response to PC metastases.

Mechanical inhibition of RANKL expression is regulated by H-Ras-GTPase

Mechanical input is known to regulate bone remodeling, yet the molecular events involved in mechanical signal transduction are poorly understood. We here investigate proximal events leading to the ERK1/2 activation that is required for mechanical repression of RANKL (receptor activator of NF-kappaB ligand) expression, the factor that controls local recruitment of osteoclasts. Using primary murine bone stromal cells we show that dynamic mechanical strain via substrate deformation activates Ras-GTPase, in particular the H-Ras isoform. Pharmacological inhibition of H-Ras function prevents strain activation of H-Ras as well as the downstream mechanical repression of RANKL. Furthermore, small interfering RNA silencing of H-Ras, but not K-Ras, abrogates mechanical strain repression of RANKL. H-Ras-specific inhibition of mechanorepression of RANKL was also demonstrated in a murine pre-osteoblast cell line (CIMC-4). The requirement of cholesterol for H-Ras activation was probed; cholesterol depletion of rafts using methyl-betacyclodextrin prevented mechanical H-Ras activation. That the mechanical repression of RANKL requires activation of H-Ras, a specific isoform of Ras-GTP that is known to reside in the lipid raft microdomain, suggests that spatial arrangements are critical for generation of specific downstream events in response to mechanical signals. By partitioning signals this way, cells may be able to generate different downstream responses through seemingly similar signaling cascades.

Regulation of RANKL promoter activity is associated with histone remodeling in murine bone stromal cells

Receptor activator of NFkappa-B ligand (RANKL) is essential for osteoclast formation, function, and survival. Although RANKL mRNA and protein levels are modulated by 1,25(OH)2D3 and other osteoactive factors, regulatory mechanisms remain unclear. In this study, we show that 2 kb or 2 kb plus exon 1 of a RANKL promoter sequence conferred neither 1,25(OH)2D3 response nor tissue specificity. The histone deacetylase inhibitors trichostatin A (TSA) and sodium butyrate (SB), however, strongly increased RANKL promoter activity. A series of 5'-deleted RANKL promoter constructs from 2,020 to 110 bp showed fourfold increased activity after TSA treatment. TSA also dose dependently enhanced endogenous RANKL mRNA expression with 50 microM of TSA treatment causing equivalent RANKL expression to that seen with 1 nM 1,25(OH)2D3. Using a chromatin immunoprecipitation (ChIP) assay we showed that TSA significantly enhanced association of both acetylated histone H3 and H4 on the RANKL promoter, with H4 > H3. A similar increase in acetylated histone H4 on the RANKL gene locus was seen after 1,25(OH)2D3 treatment, but ChIP assay did not reveal localization of VDR/RXR heterodimers on the putative VDRE of the RANKL promoter. To explore the role of H4 acetylation of 1,25(OH)2D3 stimulated RANKL, we added both TSA and 1,25(OH)2D3 together. While the combination further increased acetylation of H4 on the RANKL locus, surprisingly, TSA inhibited 1,25(OH)2D3-induced RANKL mRNA expression by 70% at all doses of 1 ,25(OH)2D3 studied. These results suggest that TSA increases of endogenous expression of RANKL involve enhanced acetylation of histones on the proximal RANKL promoter. Preventing deacetylation, however, blocks 1,25(OH)2D3 action on this gene. Chromatin remodeling is therefore involved in RANKL expression.

Anti-proliferative effect of estrogen in breast cancer cells that re-express ERalpha is mediated by aberrant regulation of cell cycle genes

Estrogen receptor (ER)-negative breast carcinomas do not respond to hormone therapy, making their effective treatment very difficult. The re-expression of ERalpha in ER-negative MDA-MB-231 breast cancer cells has been used as a model system, in which hormone-dependent responses can be restored. Paradoxically, in contrast to the mitogenic activity of 17beta-estradiol (E2) in ER-positive breast cancer cells, E2 suppresses proliferation in ER-negative breast cancer cells in which ERalpha has been re-expressed. We have used global gene expression profiling to investigate the mechanism by which E2 suppresses proliferation in MDA-MB-231 cells that express ERalpha through adenoviral infection. We show that a number of genes known to promote cell proliferation and survival are repressed by E2 in these cells. These include genes encoding the anti-apoptosis factor SURVIVIN, positive cell cycle regulators (CDC2, CYCLIN B1, CYCLIN B2, CYCLIN G1, CHK1, BUB3, STK6, SKB1, CSE1 L) and chromosome replication proteins (MCM2, MCM3, FEN1, RRM2, TOP2A, RFC1). In parallel, E2-induced the expression of the negative cell cycle regulators KIP2 and QUIESCIN Q6, and the tumour-suppressor genes E-CADHERIN and NBL1. Strikingly, the expression of several of these genes is regulated in the opposite direction by E2 compared with their regulation in ER-positive MCF-7 cells. Together, these data suggest a mechanism for the E2-dependent suppression of proliferation in ER-negative breast cancer cells into which ERalpha has been reintroduced.

Essential structural and functional determinants within the forkhead domain of FOXC1

The forkhead domain (FHD)-containing developmental transcription factor FOXC1 is mutated in patients presenting with Axenfeld-Rieger malformations. In this paper, we report the introduction of positive, negative or neutral charged amino acids into critical positions within the forkhead domain of FOXC1 in an effort to better understand the essential structural and functional determinants within the FHD. We found that FOXC1 is intolerant of mutations at I87. Additionally, alterations of amino acids within alpha-helix 1 of the FOXC1 FHD affected both nuclear localization and transactivation. Amino acids within alpha-helix 3 were also found to be necessary for transactivation and can have roles in correct localization. Interestingly, changing amino acids within alpha-helix 3, particularly R127, resulted in altered DNA-binding specificity and granted FOXC1 the ability to bind to a novel DNA sequence. Given the limited topological variation of FHDs, due to the high conservation of residues, we anticipate that models of forkhead domain function derived from these data will be relevant to other members of the FOX family of transcription factors.

Nitric oxide regulates receptor activator of nuclear factor-kappaB ligand and osteoprotegerin expression in bone marrow stromal cells

Bone remodeling reflects an equilibrium between bone resorption and formation. The local expression of receptor activator of nuclear factor-kappaB ligand (RANKL) and osteoprotegerin (OPG) in bone determines the entry of monoblastic precursors into the osteoclast lineage and subsequent bone resorption. Nitric oxide (NO) inhibits osteoclastic bone resorption in vitro and regulates bone remodeling in vivo. An interaction of NO with RANKL and OPG has not been studied. Here, we show that treatment of ST-2 murine stromal cells with the NO donor sodium nitroprusside (100 microm) for 24 h inhibited 1,25 dihydroxyvitamin D(3)-induced RANKL mRNA to less than 33 +/- 7% of control level, whereas OPG mRNA increased to 204 +/- 19% of control. NOR-4 replicated these NO effects. The effects of NO were dose dependent and associated with changes in protein levels: RANKL protein decreased and OPG protein increased after treatment with NO. PTH-induced RANKL expression in primary stromal cells was inhibited by sodium nitroprusside, indicating that the NO effect did not require vitamin D. NO donor did not change the stability of RANKL or OPG mRNAs, suggesting that NO affected transcription. Finally, cGMP, which can function as a second messenger for NO, did not reproduce the NO effect, nor did inhibition of endogenous guanylate cyclase prevent the NO effect on these osteoactive genes. The effect of NO to decrease the RANKL/OPG equilibrium should lead to decreased recruitment of osteoclasts and positive bone formation. Thus, drugs and conditions that cause local increase in NO formation in bone may have positive effects on bone remodeling.

Prostate carcinoma cells that have resided in bone have an upregulated IGF-I axis

BACKGROUND

Prostate cancer (PC) has a propensity to metastasize to the skeleton, inducing an osteoblastic response in the host. Recent epidemiological studies have suggested that circulating IGF-I may be important for both the pathogenesis and dissemination of PC. We have postulated that tumor secreted IGF-I in conjunction with endogenous IGF-I contributes to the osteoblastic phenotype characteristic of metastatic PC.

METHODS

To test this thesis we studied the established LNCaP PC progression model consisting of three genetically related human PC cell lines.

RESULTS

Using RIA, we found serum-free conditioned media (CM) of LNCaP and C4-2 had no measurable IGF-I, whereas IGF-I was easily detected in CM from C4-2B cells at 24 hr (i.e., 1.8 +/- 0.53 ng/mg cell protein). Real-time PCR of IGF-I mRNA showed that C4-2B expressed 100-fold more IGF-I mRNA than LNCaP cells. In addition, C4-2B expression of IGF-I mRNA was substantially increased in the presence of exogenous IGF-I to nearly twofold. While IGFBP-3 and IGFBP-1 were not detectable in the CM of any PC line, all cells secreted IGFBP-2. C4-2B cells produced 40% more IGFBP-2 than LNCaP or C4-2 cells (C4-2B at 167 +/- 43 ng/mg cell protein). RANKL, a product of bone stromal cells, was also differentially expressed: LNCaP had threefold higher RANKL mRNA compared to C4-2 and C4-2B and at least equivalent protein expression.

CONCLUSIONS

Our results suggest that PC cells that have metastasized to bone have an upregulated IGF-I regulatory system. This suggests an activated IGF-I axis contributes to the host-PC interaction in promoting osteoblastic metastases.

Mechanical strain differentially regulates endothelial nitric-oxide synthase and receptor activator of nuclear kappa B ligand expression via ERK1/2 MAPK

Exercise promotes positive bone remodeling through controlling cellular processes in bone. Nitric oxide (NO), generated from endothelial nitric-oxide synthase (eNOS), prevents resorption, whereas receptor activator of nuclear kappa B ligand (RANKL) promotes resorption through regulating osteoclast activity. Here we show that mechanical strain differentially regulates eNOS and RANKL expression from osteoprogenitor stromal cells in a magnitude-dependent fashion. Strain (0.25-2%) induction of eNOS expression was magnitude-dependent, reaching a plateau at 218 +/- 36% of control eNOS. This was accompanied by increases in eNOS protein and a doubling of NO production. Concurrently, 0.25% strain inhibited RANKL expression with increasing response up to 1% strain (44 +/- 3% of control RANKL). These differential responses to mechanical input were blocked when an ERK1/2 inhibitor was present during strain application. Inhibition of NO generation did not prevent strain-activated ERK1/2. To confirm the role of ERK1/2, cells were treated with an adenovirus encoding a constitutively activated MEK; Ad.caMEK significantly increased eNOS expression and NO production by more than 4-fold and decreased RANKL expression by half. In contrast, inhibition of strain-activated c-Jun kinase failed to prevent strain effects on either eNOS or RANKL. Our data suggest that physiologic levels of mechanical strain utilize ERK1/2 kinase to coordinately regulate eNOS and RANKL in a manner leading to positive bone remodeling.

Nitric oxide donors inhibit luciferase expression in a promoter-independent fashion

Nitric oxide (NO) is an important molecule with diverse bio-messenger functions including regulation of gene expression. Transcriptional studies using sensitive luciferase reporter systems have suggested that NO inhibits the promoter activity of a variety of genes. Here we report that NO donors (sodium nitroprusside, 2',2'-(hydroxynitrosohydrazono)bis-ethanimine, and (+/-)-(E)-4-ethyl-2-[(Z)-hydroxyimino]-5-nitro-3-hexen-1-yl-nicotinamide) decrease luciferase activity in a promoter-independent fashion in both viral and eukaryotic promoters, with a reduction to nearly 50% in the presence of 100 microm NO donor. Addition of an SV40 enhancer downstream of the luciferase coding region shifted NO donor inhibition to the right, with inhibition at approximately 300 microm. In contrast, when studied in a chloramphenicol acetyltransferase reporter, two promoters indicating inhibition by NO were unaffected. The decrease in luciferase activity was not caused by NO suppression of the luciferase enzyme. Real-time PCR data showed that luciferase mRNA half-life decreased by nearly half in the presence of NO donor (from 75 to 45 min). The SV40 enhancer prolonged luciferase mRNA half-life and somewhat blunted the NO effect. Our data suggest that exogenous NO inhibits luciferase activity in a dose-dependent manner through decreasing luciferase mRNA stability. Thus, the use of luciferase reporter systems to study transcriptional regulation by NO should be attempted with caution.

IGF-I regulates osteoprotegerin (OPG) and receptor activator of nuclear factor-kappaB ligand in vitro and OPG in vivo

IGF-I, a ubiquitous polypeptide, plays a key role in longitudinal bone growth and acquisition. The most predominant effect of skeletal IGF-I is acceleration of the differentiation program for osteoblasts. However, in vivo studies using recombinant human (rh) IGF-I and/or rhGH have demonstrated stimulation of both bone formation and resorption, thereby potentially limiting the usefulness of these peptides in the treatment of osteoporosis. In this study, we hypothesized that IGF-I modulates bone resorption by regulating expression of osteoprotegerin (OPG) and receptor activator of nuclear factor-kappaB (RANK) ligand (RANKL) in bone cells. Using Northern analysis in ST2 cells, we found that human IGF-I suppressed OPG mRNA in a time- and dose-dependent manner: 100 micro g/LIGF-I (13 nM) decreased OPG expression by 37.0 +/- 1.8% (P < 0.002). The half maximal inhibitory dose of IGF-I was reached at 50 micro g/liter ( approximately 6.5 nM) with no effect of IGF-I on OPG message stability. Conditioned media from ST2 cells confirmed that IGF-I decreased secreted OPG, reducing levels by 42%, from 12.1-7 ng/ml at 48 h (P < 0.05). Similarly, IGF-I at 100 micro g/liter (13 nM) increased RANKL mRNA expression to 353 +/- 74% above untreated cells as assessed by real-time PCR. In vivo, low doses of rhGH when administered to elderly postmenopausal women only modestly raised serum IGF-I (to concentrations of 18-26 nM) and did not affect circulating OPG concentrations; however, administration of rhIGF-I (30 micro g/kg.d) for 1 yr to older women resulted in a significant increase in serum IGF-I (to concentrations of 39-45 nM) and a 20% reduction in serum OPG (P < 0.05). In summary, we conclude that IGF-I in a dose- and time-dependent manner regulates OPG and RANKL in vitro and in vivo. These data suggest IGF-I may act as a coupling factor in bone remodeling by activating both bone formation and bone resorption; the latter effect appears to be mediated through the OPG/RANKL system in bone.

Activation of extracellular signal-regulated kinase is involved in mechanical strain inhibition of RANKL expression in bone stromal cells

Mechanical input is known to regulate skeletal mass. In vitro, application of strain inhibits osteoclast formation by decreasing expression of the ligand RANKL in bone stromal cells, but the mechanism responsible for this down-regulation is unknown. In experiments here, application of 1.8% equibiaxial strain for 6 h reduced vitamin D-stimulated RANKL mRNA expression by nearly one-half in primary bone stromal cells. Application of strain caused a rapid activation of ERK1/2, which returned to baseline by 60 minutes. Adding the ERK1/2 inhibitor PD98059 30 minutes before strain delivery prevented the strain effect on RANKL mRNA expression, suggesting that activation of ERK1/2 was required for transduction of the mechanical force. Mechanical strain also activated N-terminal Jun kinase (JNK) that, in contrast, did not return to baseline during 24 h of continuous strain. This suggests that JNK may represent an accessory pathway for mechanical transduction in bone cells. Our data indicate that strain modulation of RANKL expression involves activation of MAPK pathways.

Expression of the transcription factor GADD153 is an indicator of apoptosis for recombinant chinese hamster ovary (CHO) cells

Loss of cell viability, through engagement of apoptotic cell death, represents a limitation to maintenance of high levels of productivity of recombinant animal cells in culture. The ability to monitor the status of recombinant cells, and to define indicators of their "well-being," would present a valuable approach to permit a rational intervention at appropriate times during culture. Growth arrest and DNA damage gene 153 (GADD153) is a member of the CCAAT/enhancer-binding protein (C/EBP) family of transcription factors and has been associated with apoptosis. We have examined the expression of GADD153 in conditions associated with apoptosis of recombinant CHO cells in batch culture. GADD153 expression is very low in CHO cells growing in the exponential phase of batch culture but is activated as cells enter the decline phase. Depletion of nutrients (glucose or glutamine) causes activation of GADD153 expression as does the imposition of endoplasmic reticulum stress. In all cases, there is a good relationship between the extent of apoptosis that occurs in response to each stress and the degree of GADD153 expression. In addition, nutrient refeeding or reversal of stress produces a concomitant decrease in expression of GADD153 and the susceptibility to apoptosis. Thus, GADD153 appears to offer a valid indicator of apoptosis and illustrates the potential for definition of monitors of cellular status related to the likelihood of apoptosis of cell populations.

A novel action of the newly described prolactin-releasing peptides: cardiovascular regulation

The physiological relevance of the recently described prolactin-releasing peptides (PrRPs) has yet to be established. Here, we demonstrate the low potency of the PrRPs (minimum effective dose: 100 nM), compared to that observed for thyrotropin-releasing hormone (TRH, minimum effective dose: 1.0 nM), to stimulate prolactin (PRL) release from cultured pituitary cells harvested from lactating female rats. Anatomic studies question the role of these peptides in neuroendocrine control of lactotroph function. Instead, peptide and peptide receptor mapping studies suggest potential actions in hypothalamus and brainstem unrelated to the control of anterior pituitary hormone secretion. Intracerebroventricular (i.c.v. ) administration of both PrRP-20 and PrRP-31 (0.4 and 4.0 nmol) resulted in significantly increased mean arterial blood pressure in conscious, unrestrained rats [peak elevations vs. baseline: PrRP-20, 10% and 16%, low and high dose peptide; PrRP-31, 7% and 10%; compared to the response to 0.1 nmol angiotensin II (A II), 15-17%]. Similar doses of peptide did not significantly alter water drinking in response to overnight fluid deprivation, or thirst or salt appetite in response to an isotonic hypovolemic challenge. Thus, the effect on blood pressure appeared relatively specific. We suggest that these peptides, identified originally as ligands for a receptor found in abundance in pituitary gland, play a broader role in brain function and that the ability of them to stimulate PRL release may not represent their primary biologic function.

Transcriptional regulation of the expression of macrophage colony stimulating factor

The regulatory regions for transcriptional control of the MCSF gene are unknown. We examined regulatory control in a 774-bp murine MCSF promoter transfected into MC3T3-E1 osteoblast-like and COS-7 cells. Deletion of upstream sequence from -635 increased basal activity of the promoter by at least four-fold, an increase that was maintained when PU.1, NFkappaB and Egr1/Sp1 consensus sequences were subsequently removed. Mutagenesis identified a suppressor element between -635 and -642 from the transcriptional start site and an oligonucleotide representing this sequence was retarded by nuclear cell protein. TNFalpha (1 ng/ml), PTH (5x10(-8) M), and IL-1alpha (100 pg/ml), which increased MCSF protein secretion, failed to enhance the transcriptional rate of the full-length promoter. TNFalpha was able to stimulate transcription of a heterologous reporter transfected into COS-7 containing multiple copies of the murine MCSF NFkappaB site inserted before a minimal promoter. In contrast, deletion of the same NFkappaB response element increased basal activity in the native promoter. Thus, the NFkappaB sequence may act as a negative regulator in the context of the endogenous promoter. Our results indicate that constitutive transcriptional activity conferred by the MCSF promoter may be damped by a suppressor protein. Transcriptional regulation, however, does not appear to be a major stimulatory mechanism for MCSF secretion.

Cardiovascular regulatory actions of the hypocretins in brain

The hypocretins, also known as the orexins, are alternate translation products of a single gene. The recognition of their production in neurons of the rostral diencephalon, and their axonal localization in brain sites known to be important in the control of appetite, led to the demonstration of their orexogenic actions. However, these peptides are not as potent as other appetite stimulating neuropeptides and they have been localized in areas of brain more related to cardiovascular function. We verified the orexogenic actions of hypocretin-1 (Hcrt-1) and hypocretin-2 (Hcrt-2) in an ad libitum feeding model and identified the threshold dose to be 1 nmol when given into the lateral cerebroventricle (i.c. v.). Even at threshold doses for feeding, both Hcrt-1 and Hcrt-2 given i.c.v. into conscious, unrestrained rats stimulated significant elevations in mean arterial blood pressure, that appeared dose related. These elevations were relatively long lasting, mirroring the time course of a pressor dose of angiotensin II (0.1 nmol i.c.v.); however, the magnitude of blood pressure elevation to hypocretin did not equal that of A II. These data suggest an additional, non-appetitive action of the hypocretins and indicate that the peptide and receptor mapping studies may have predicted important roles for the peptides in the central nervous system control of cardiovascular function.

Role of NFkappaB in the regulation of macrophage colony stimulating factor by tumor necrosis factor-alpha in ST2 bone stromal cells

Expression of MCSF in bone is important to the regulation of osteoclastogenesis. We show here that tumor necrosis factor-alpha (TNFalpha) increases the production of both soluble (sMCSF) and membrane-bound (mMCSF) macrophage colony stimulating factor by ST2 bone stromal cells. Treatment of ST2 cells with TNFalpha caused sMCSF levels to increase by 394+/-5% from basal; mMCSF rose by 316+/-66% from 30+/-10 per 100,000 cells in the same time. These increases were consistent with increased expression of mRNAs encoding both isoforms. Increases in MCSF mRNA are also seen after stimulation with dexamethasone. To investigate the potential role of NFkappaB in this TNFalpha effect, we treated cells with sodium salicylate (NaS), an inhibitor of NFkappaB translocation. NaS decreased TNFalpha-stimulated NFkappaB activation by 50% as assessed by EMSA. Despite inhibition of NFkappaB signaling, NaS enhanced TNFalpha-stimulated MCSF secretion and did not prevent TNFalpha-stimulated increases in sMCSF mRNA, suggesting that NFkappaB was not involved in TNFalpha effect on the gene. TNFalpha failed to stimulate transcription of a 774 nucleotide MCSF promoter-luciferase reporter transfected into ST2 cells which contained the NFkappaB consensus sequence. Deletion of the seven nucleotides containing the NFkappaB homology response sequence from the MCSF promoter increased basal gene transcription by twofold. TNFalpha thus contributes to an osteoclastogenic environment through upregulation of bone expression of both MCSF isoforms. Our data suggests that NFkappaB is not the major signaling pathway through which this occurs.

Antisense oligonucleotide treatment reveals a physiologically relevant role for adrenomedullin gene products in sodium intake

Adrenomedullin (AM), a potent hypotensive peptide, is produced in numerous tissues including adrenal gland, kidney, brain and pituitary gland, where it acts to modify sodium homeostasis. Central AM administration dose-dependently inhibits sodium appetite. AM antisense oligonucleotide treatment significantly lowered peptide content in the hypothalamic paraventricular (PVN) nucleus and exaggerated the consumption of sodium. These results support a physiologic role for adrenomedullin gene products in the central regulation of sodium homeostasis.

Gender-biased activity of the novel prolactin releasing peptides: comparison with thyrotropin releasing hormone reveals only pharmacologic effects

The prolactin- (PRL) releasing activities of the newly described PRL-releasing peptides (PrRPs) were compared to that of thyrotropin-releasing hormone (TRH) in dispersed, rat anterior pituitary cell cultures. A dose-related stimulation of PRL release by TRH was observed in cells harvested from both intact male and random cycle female pituitary donors. The minimum effective dose of TRH ranged from 1 to 10 nM. Neither PrRP-20 nor PrRP-31 significantly altered PRL secretion in cells from male donors even at doses as high as 1 microM. In cells harvested from females, only the highest doses of PrRP-20 and PrRP-31 tested (0.1 and 1.0 microM) significantly stimulated PRL secretion. The PRL-releasing action of TRH was observed already at 15 min of incubation, whereas those of PrRP-20 and PrRP-31 appeared only after 1 and 2 h of incubation, and the magnitude of PRL release in the presence of 1 microM PrRPs was significantly less than that of a similar dose of TRH. These data do not suggest a physiologically relevant role for the PrRPs in the neuroendocrine regulation of PRL secretion in intact male and nonlactating, random-cycle female rats.

Proadrenomedullin N-terminal 20 peptide inhibits adrenocorticotropin secretion from cultured pituitary cells, possibly via activation of a potassium channel

Preproadrenomedullin is processed into at least two biologically active peptides, adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP). Both peptides are hypotensive; however, they exert this action via differing mechanisms. In pituitary cells in culture, both basal and releasing factor-stimulated adrenocorticotropin (ACTH) secretion is inhibited by AM. Here we report that basal, but not stimulated, ACTH secretion from cultured rat pituitary cells is also inhibited by PAMP. The effect is dose-related, occurs in a physiologically relevant dose range that is similar to that of AM, and is blocked by the potassium channel blocker, glybenclamide. The failure of glybenclamide to inhibit AM's effects on ACTH secretion indicates that in pituitary, as in other tissues, these two products of the same prohormone can exert similar biologic activity, although via differing mechanisms.

Central mechanisms for the hypertensive effects of preproadrenomedullin-derived peptides in conscious rats

Peptides derived from postranslational processing of preproadrenomedullin exert potent hypotensive effects in the periphery. One of those peptides, adrenomedullin (AM) also has been demonstrated to act centrally in conscious rats to inhibit water drinking and salt appetite and, in anesthetized rats, surprisingly to increase blood pressure. We examined the effects of AM and the other postranslational product, proadrenomedullin NH2-terminal 20 peptide (PAMP), on blood pressure in conscious rats. Both AM and PAMP elicited dose-related increases in mean arterial pressure after cerebroventricular administration. The hypertensive effects of both AM and PAMP and of ANG II were blocked by peripheral administration of phentolamine, indicating actions of the peptides in brain to stimulate sympathetic nervous system function. Blockade of central ANG II receptors with saralasin prevented the hypertensive effects of both ANG II and PAMP, suggesting recruitment of endogenous angiotensinergic systems by central PAMP. The structural homolog of AM, calcitonin gene-related peptide (CGRP), at similar doses did nto significantly affect blood pressure. Furthermore, the hypertensive effects of ANG II, AM, and PAMP were not abrogated by prior administration of the CGRP antagonist. We hypothesize that AM and PAMP exert cardioprotective effects in brain, which may counterbalance the volume-unloading actions of the peptides in the periphery.

Adrenomedullin inhibits salt appetite

Adrenomedullin (AM) exerts profound natriuretic and vasodilatory effects in conscious animals. This newly discovered hormone also acts in the central nervous system to inhibit water drinking and in the pituitary gland to reduce basal and stimulated ACTH release. We investigated whether the natriuretic action of AM in kidney was matched by a central nervous system action to decrease salt intake. Isotonic hypovolemia induced in male rats by pretreatment with polyethylene glycol potently stimulates both water and salt water (0.3 mol/liter NaCl) drinking. Saline drinking was significantly inhibited when AM was administered into the lateral cerebroventricle before the drinking interval. The effect was dose related (dose range, 44-88 pmol), long lasting (> 5 h), and reversible (resolved at 24 h). When hypovolemic rats were administered antiserum to AM (intracerebroventricular administration) before the drinking interval, a significant 2-fold augmentation of saline drinking was observed. These data suggest that in addition to peripheral actions on cardiovascular and renal function and pituitary actions to inhibit ACTH release, AM may act within the central nervous system to determine fluid and electrolyte balance and, ultimately, blood pressure.

A 35 amino acid fragment of leptin inhibits feeding in the rat

Peptide fragments of the larger 167 amino acid obesity gene related peptide (OBGRP), leptin, were tested for their ability to inhibit feeding in the rat. The C-terminal fragment, OBGRP 116-167 exerted only minimal inhibition of feeding when administered into the lateral cerebroventricle. No alteration in feeding was observed following administration of OBGRP 57-92. We hypothesized that the satiety effects of leptin reside in the N-terminal region of the peptide sequence. Significant, dose-related, and reversible inhibition of food intake was observed following central administration of the 35 amino acid fragment OBGRP 22-56. These results suggest that a small, readily synthesized fragment of the 167 amino acid peptide leptin may exert physiologically relevant satiety effects in brain revealing an endocrine feedback mechanism by which the adipocyte may modulate hypothalamic function.

The novel vasoactive hormone, adrenomedullin, inhibits water drinking in the rat

The novel hormone, adrenomedullin (AdM), which exerts potent hypotensive effects in the periphery and natriuretic actions in the kidney, was found to be antidipsogenic. Cerebroventricular injection of AdM (22, 44, and 88 pmol) resulted in a dose-related diminution of water drinking in response to subsequent central administration of 100 pmol angiotensin II. Additionally, 88 pmol AdM significantly inhibited the drinking response to overnight water deprivation and hyperosmotic challenge. No significant effects of AdM in the doses tested were observed on blood pressure, heart rate, or motor activity. These results suggest that this novel hormone can act within the nervous system to complement its peripheral actions on fluid and electrolyte homeostasis, independent of a central action on cardiovascular function or locomotion.

Antidipsogenic actions of endothelins are exerted via the endothelin-A receptor in the brain

The receptor subtype mediating the antidipsogenic effects of the endothelins (ETs) was determined in conscious, unrestrained, normally hydrated rats. Intracerebroventricular injection of 6, 12, and 20 ng ET-2 resulted in a significant, dose-related inhibition of water drinking in response to subsequent injection of 100 pmol angiotensin II (ANG II). Pretreatment with 50 or 100 ng ET-B receptor agonist failed to alter the subsequent drinking response to ANG II. Drinking in response to ANG II was significantly accentuated in rats pretreated with 50, 100, and 200 ng of the selective ET-A receptor antagonist BQ-123. These data indicate that the antidipsogenic effects of the ETs are mediated via the ET-A receptor subtype and further suggest that endogenous ET plays a physiologically relevant role in the central nervous system control of fluid and electrolyte homeostasis.