Xiao-Lu Tang

Progesterone receptors A and B differentially modulate corticotropin-releasing hormone gene expression through a cAMP regulatory element

Corticotrophin-releasing hormone (CRH) plays a major role in mechanisms controlling human pregnancy and parturition. Gene regulation by progesterone may be a key point in the control of placental CRH production. Studies in primary placental cells show that antagonism of progesterone activity or production by RU486 or trilostane leads to an increase in CRH promoter activity. This effect can be reversed by the addition of progesterone. Overexpression of progesterone receptorA (PR-A) or glucocorticoid receptor resulted in a decrease in CRH promoter activity following progesterone treatment, whereas an increase in promoter activity was observed with overexpressed PR-B. Studies including mutation of the cAMP regulatory element (CRE) confirm this site to be essential for the progesterone-mediated effects. In summary, our results demonstrate that progesterone regulates CRH gene transcription via a CRE in the CRH promoter and that PR-A and PR-B exhibit different actions in the regulation of CRH gene expression.

H2S Attenuates LPS-Induced Acute Lung Injury by Reducing Oxidative/Nitrative Stress and Inflammation.

Background: Hydrogen sulfide (H2S), known as the third endogenous gaseous transmitter, has received increasing attention because of its diverse effects, including angiogenesis, vascular relaxation and myocardial protection.We aimed to investigate the role of H2S in oxidative/nitrative stress and inflammation in acute lung injury (ALI) induced by endotoxemia. Methods: Male ICR mice were divided in six groups: (1) Control group; (2) GYY4137treatment group; (3) L-NAME treatment group; (4) lipopolysaccharide (LPS) treatment group; (5) LPS with GYY4137 treatment group; and (6) LPS with L-NAME treatment group. The lungs were analysed by histology, NO production in the mouse lungs determined by modified Griess (Sigma-Aldrich) reaction, cytokine levels utilizing commercialkits, and protein abundance by Western blotting. Results: GYY4137, a slowly-releasing H2S donor, improved the histopathological changes in the lungs of endotoxemic mice. Treatment with NG-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, increased anti-oxidant biomarkers such as thetotal antioxidant capacity (T-AOC) and theactivities of catalase (CAT) and superoxide dismutase (SOD) but decreased a marker of peroxynitrite (ONOO-) action and 3-nitrotyrosine (3-NT) in endotoxemic lung. L-NAME administration also suppressed inflammation in endotoxemic lung, as evidenced by the decreased pulmonary levels of interleukin (IL)-6, IL-8, and myeloperoxidase (MPO) and the increased level of anti-inflammatory cytokine IL-10. GYY4137 treatment reversed endotoxin-induced oxidative/nitrative stress, as evidenced by a decrease in malondialdehyde (MDA), hydrogenperoxide (H2O2) and 3-NT and an increase in the antioxidant biomarker ratio of reduced/oxidized glutathione(GSH/GSSG ratio) and T-AOC, CAT and SOD activity. GYY4137 also attenuated endotoxin-induced lung inflammation. Moreover, treatment with GYY4137 inhibited inducible NOS (iNOS) expression and nitric oxide (NO) production in the endotoxemia lung. Conclusions: GYY4137 conferred protection against acute endotoxemia-associated lung injury, which may have beendue to the anti-oxidant, anti-nitrative and anti-inflammatory properties of GYY4137. The present findings warrant further exploration of the clinical applicability of H2S in the prevention and treatment of ALI.

Upregulation of microRNA-22 contributes to myocardial ischemia-reperfusion injury by interfering with the mitochondrial function

Mitochondrial oxidative damage is critically involved in cardiac ischemia reperfusion (I/R) injury. MicroRNA-22 (miR-22) has been predicted to potentially target sirtuin-1 (Sirt1) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α), both of which are known to provide protection against mitochondrial oxidative injury. The present study aims to investigate whether miR-22 is involved in the regulation of cardiac I/R injury by regulation of mitochondrial function. We found that miR-22 level was significantly increased in rat hearts subjected to I/R injury, as compared with the sham group. Intra-myocardial injection of 20 ug miR-22 inhibitor reduced I/R injury as evidenced by significant decreases in cardiac infarct size, serum lactate dehydrogenase (LDH) and creatine kinase (CK) levels and the number of apoptotic cardiomyocytes. H9c2 cardiomyocytes exposed to hypoxia/reoxygenation (H/R) insult exhibited an increase in miR-22 expression, which was blocked by reactive oxygen species (ROS) scavenger and p53 inhibitor. In addition, miR-22 inhibitor attenuated, whereas miR-22 mimic aggravated H/R-induced injury in H9c2 cardiomyocytes. MiR-22 inhibitor per se had no significant effect on cardiac mitochondrial function. Mitochondria from rat receiving miR-22 inhibitor 48h before ischemia were found to have a significantly less mitochondrial superoxide production and greater mitochondrial membrane potential and ATP production as compared with rat receiving miR control. In H9c2 cardiomyocyte, it was found that miR-22 mimic aggravated, whilst miR-22 inhibitor significantly attenuated H/R-induced mitochondrial damage. By using real time PCR, western blot and dual-luciferase reporter gene analyses, we identified Sirt1 and PGC1α as miR-22 targets in cardiomyocytes. It was found that silencing of Sirt1 abolished the protective effect of miR-22 inhibitor against H/R-induced mitochondrial dysfunction and cell injury in cardiomyocytes. Taken together, our findings reveal a novel molecular mechanism for cardiac mitochondrial dysfunction during myocardial I/R injury at the miRNA level and demonstrate the therapeutic potential of miR-22 inhibition for acute myocardial I/R injury by maintaining cardiac mitochondrial function.

Overproduction of nitric oxide by endothelial cells and macrophages contributes to mitochondrial oxidative stress in adrenocortical cells and adrenal insufficiency during endotoxemia.

We have recently demonstrated that lipopolysaccharide (LPS) causes mitochondrial oxidative stress and dysfunction in adrenal glands, thereby leading to adrenocortical insufficiency. Since nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) leads to mitochondrial damage in various tissues, the present study aims to investigate whether NO contributes to mitochondrial oxidative stress in adrenal cortex and adrenocortical insufficiency during endotoxemia. Systemic administration of LPS increased iNOS expression and NO production in adrenal glands of mice. The specific iNOS inhibitor 1400 W significantly attenuated the LPS-induced mitochondrial superoxide production and dysfunction in adrenal glands, and reversed the LPS-induced adrenocortical hyporesponsiveness to adrenocorticotropic hormone (ACTH). In contrast, administration of the NO donor sodium nitroprusside (SNP) led to mitochondrial oxidative stress and dysfunction in adrenal glands, which resulted in a blunted corticosterone response to ACTH. Using double immunofluorescence staining for iNOS with the vascular endothelial cell marker CD31 or the macrophage marker CD68, we found that increased iNOS expression was found in vascular endothelial cells and macrophages, but not adrenocortical cells in the adrenal gland during endotoxemia. Administration of the hydrogen sulfide (H2S) donor GYY4137 inhibited NO production and reversed LPS-induced adrenocortical hyporesponsiveness. Our data suggest that overproduction of NO, which is mainly generated by endothelial cells and macrophages during endotoxemia, contributes to mitochondrial oxidative stress in adrenocortical cells and subsequently leads to adrenal insufficiency.

Endotoxin tolerance of adrenal gland: attenuation of corticosterone production in response to lipopolysaccharide and adrenocorticotropic hormone.

Objectives:Reversible adrenal insufficiency frequently has been diagnosed in critically ill patients with sepsis who have either low basal cortisol levels or low cortisol responses to adrenocorticotropic hormone (ACTH) stimulation. It is generally accepted that a phenomenon called “endotoxin tolerance” contributes to immunosuppression during sepsis. The present study was to investigate whether endotoxin tolerance occurs in the adrenal gland, leading to hyporesponsiveness of adrenal gland during sepsis. Design:Controlled laboratory experiment. Setting:University research laboratory. Subjects:Sprague-Dawley male rats 200–250 g and primary isolated adrenal fasciculata-reticularis cells. Interventions:Rats received intra-arterial injection of purified lipopolysaccharide (0.5 mg/kg) through indwelling femoral arterial catheters, and 24 hrs later the adrenocortical sensitivity to exogenous ACTH (10 ng/kg) was detected. Primary fasciculata-reticularis cells were pretreated with lipopolysaccharide at 0.1–100 ng/mL or with ACTH at 0.01–10 ng/mL and then challenged, in fresh media, with 1 &mgr;g/mL lipopolysaccharide or 10 ng/mL ACTH. Measurements and Main Results:Toll-like receptor 4 was expressed in adrenal gland and primary fasciculata-reticularis cells. Plasma corticosterone response to ACTH was decreased in rats receiving preinjection of lipopolysaccharide. Lipopolysaccharide pretreatment caused a significant decrease in corticosterone production in response to subsequent ACTH and lipopolysaccharide stimulation in primary fasciculata-reticularis cells. Lipopolysaccharide pretreatment inhibited ACTH- and lipopolysaccharide-induced expression of steroid metabolizing enzymes. Lipopolysaccharide significantly decreased Toll-like receptor 4 and ACTH receptor expression. Conclusions:Pre-exposure to lipopolysaccharide resulted in hyporesponsiveness to ACTH stimulation in rats. In vitro, lipopolysaccharide pretreatment impaired corticosterone production of fasciculata-reticularis cells in response to ACTH and lipopolysaccharide, which was associated with decreased expression of synthetic enzymes required for corticosterone production. Our results indicate that endotoxin tolerance of adrenal gland is one of the mechanisms for adrenocortical insufficiency during sepsis.

Isoflavones suppress cyclic adenosine 3′,5′-monophosphate regulatory element-mediated transcription in osteoblastic cell line

Soy isoflavones have been implicated to exert benefit on bone loss in postmenopausal women. Isoflavones can induce estrogen response element-mediated transcription in osteoblastic cells. In the present study, we investigate whether isoflavones genistein and daidzein regulate target gene transcription through cAMP regulatory element (CRE) in osteoblastic cells. It was found that 17β-estradiol (E(2)), genistein and daidzein suppressed the transcriptional activity of CRE-luciferase reporter gene in human osteoblastic cell line MG-63 cells. E(2) and genistein but not daidzein inhibited the cAMP analogue 8-Br cAMP-induced transcription of CRE reporter gene. Both genistein and E(2) inhibited basal and cAMP-induced mRNA levels of endogenous estrogen responsive genes containing CRE/CRE-like elements in their promoter regions, including interleukin (IL) 8 and serum- and glucocorticoid-inducible kinase 1 (SGK1). Daidzein inhibited basal and cAMP-induced IL-8, but not SGK1 mRNA expression. The inhibitory effects of E(2), genistein and daidzein on CRE-mediated transcription activity were enhanced by estrogen receptor (ER) α overexpression in MG-63 cells, which could be blocked by nonselective ER antagonists ICI182780, 4-OH tamoxifen and specific ERα antagonist MPP. Genistein and daidzein, but not E(2) treatment, caused a significant decrease in CRE-mediated transcription activity in ERβ-transfected MG-63 cells, which could be blocked by ICI182780, 4-OH tamoxifen and the selective ERβ antagonist (R,R)-5,11-diethyl-5.6,11,12-tetradro-2,8-chrysenediol. Our results indicate that isoflavones genistein and daidzein might modulate bone remodeling through ERs by regulating target gene expression through the CRE motifs.

Rosiglitazone inhibition of calvaria-derived osteoblast differentiation is through both of PPARγ and GPR40 and GSK3β-dependent pathway

Rosiglitazone (RSG) can cause bone loss, however the mechanisms remain largely unknown. This study aims to investigate the effects of RSG on differentiation and mineralization of osteoblasts using primary cultured mouse fetal calvaria-derived osteoblasts as a model, and elucidate the receptor and signaling pathways responsible for these effects. We found that RSG suppressed the differentiation and mineralization of calvaria-derived osteoblasts. Peroxisome proliferators-activated receptor γ (PPARγ) siRNA significantly reversed the inhibitory effect of RSG on osteogenic differentiation. The expression of G protein-coupled receptor (GPR) 40 was suppressed during differentiation, but was increased by RSG treatment. GPR40 siRNA significantly reversed the inhibitory effect of RSG on osteogenesis. RSG activated glycogen synthase kinase (GSK)-3β, which in turn decreased β-catenin expression. RSG-induced GSK3β activation was mediated through both PPARγ and GPR40. These results suggest that both PPARγ and GRP40 are required for RSG-induced inhibition of mouse calvaria osteoblast differentiation, which is mediated through GSK3β-dependent pathway.

Resveratrol alleviates endotoxemia-associated adrenal insufficiency by suppressing oxidative/nitrative stress.

We have recently demonstrated that endotoxin causes oxidative stress and overproduction of nitric oxide in adrenal glands, thereby leading to adrenocortical insufficiency. The aim of this study is to investigate the effects of resveratrol, a natural plant polyphenol with anti-oxidant and anti-nitrative properties, on endotoxemia-associated adrenocortical insufficiency. Resveratrol was administered immediately before injection of lipopolysaccharide (LPS). Twenty four hours later, the adrenocorticotropic hormone (ACTH) stimulation tests was been performed to measure the plasma corticosterone level and the adrenal gland tissues were collected for histopathologic examination, and determination of malondialdehyde (MDA), total antioxidant capacity (T-AOC), superoxide dismutase (SOD) activity, catalase (CAT) activity, inducible nitric oxide synthase (iNOS) expression, nitric oxide (NO) and peroxynitrite production. Treatment with resveratrol significantly inhibited endotoxemia-induced iNOS expression, NO production, and peroxynitrite formation and also attenuated LPS-induced oxidative stress in the adrenal gland, as evidenced by the decrease of pro-oxidant biomarker (MDA), and the increases of anti-oxidant biomarkers (T-AOC, CAT and SOD activity). H&E staining demonstrated that administration of LPS resulted in increased into the adrenal gland. H&E-stained sections of adrenal glands demonstrated signs of leukocyte infiltration and hemorrhage during endotoxemia, which were significantly improved by resveratrol treatment. In addition, resveratrol reversed the LPS-induced downregulation of ACTH receptor and silent information regulator 1 (SIRT1) in adrenal gland, as well as adrenocortical hyporesponsiveness to ACTH. Resveratrol exerts protective effects against endotoxemia-associated adrenocortical insufficiency by suppressing oxidative/nitrative stress. These findings support the potential for resveratrol as a possible pharmacological agent to improve adrenocortical insufficiency resulting from oxidative/nitrative damage.

Phorbol ester stimulates corticotropin-releasing hormone gene promoter activity through a cAMP regulatory element in primary placental cells

Placental corticotropin-releasing hormone (CRH) plays an important role in the mechanisms controlling human pregnancy and parturition, and several endogenous factors are known to regulate placental CRH gene expression. In this article, the authors investigate the regulation of the CRH genes promoter activity by a protein kinase C (PKC) activator, phorbol-12-myristate-13-acetate (PMA), in primary cultures of placental cells. The PMA stimulation of the CRH gene promoter activity was dose dependent, and further studies, including progressive deletion and mutation analysis of the CRH promoter, localized the region essential for PMA responsiveness to a consensus cyclic adenosine monophosphate regulatory element (CRE). Furthermore, estradiol treatment resulted in decreases of both basal and PMA-stimulated promoter activity when the CRE element was present but had no effect when the CRE element was absent. Thus, PMA stimulates CRH gene transcriptional activity through the CRE, suggesting that cross-talk between PKC and protein kinase A signaling pathways targets this regulatory element in placental cells.

Protein tyrosine phosphatase SHP-1 modulates osteoblast differentiation through direct association with and dephosphorylation of GSK3β

SHP-1, the Src homology-2 (SH2) domain-containing phosphatase 1, is a cytosolic protein-tyrosine phosphatase (PTP) predominantly expressed in hematopoietic-derived cells. Previous studies have focused on the involvement of SHP-1 in osteoclastogenesis. Using primary cultured mouse fetal calvaria-derived osteoblasts as a model, this study aims to investigate the effects of SHP-1 on differentiation and mineralization of osteoblasts and elucidate the signaling pathways responsible for these effects. We found that osteoblasts treated by osteogenic media showed significant increase in SHP-1 expression, which contributed to osteoblastic differentiation and mineralization. Using immunoprecipitation assay, we found that a direct association between SHP-1 and glycogen synthase kinase (GSK)-3β could be detected in differentiated osteoblasts and was significantly inhibited by SHP-1 inhibitor NSC87877. Inhibition of SHP-1 activated GSK3β, thereby leading to suppression of osteoblast differentiation and mineralization, which could be rescued by the inhibitor of GSK3β. In addition, we found that rosiglitazone (RSG) treatment led to significant decrease in SHP-1 expression. Overexpression of SHP-1 reversed RSG-induced GSK3β activation, thus rescuing the inhibitory effect of RSG on osteoblast differentiation and mineralization. These findings suggest that protein tyrosine phosphatase SHP-1 may act as a positive regulator of osteoblast differentiation through direct association with and dephosphorylation of GSK3β. Downregulation of SHP-1 may contribute to RSG-induced inhibition of mouse calvaria osteoblast differentiation by activating GSK3β-dependent pathway.