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C Klett, M Bader, M Schwemmle, D Ganten and E Hackenthal

ABSTRACT

Several authors have shown that angiotensin II stimulates hepatic angiotensinogen synthesis in vivo, ex vivo and in vitro. In previous studies we have demonstrated that this effect of angiotensin II depends mainly on a transient inhibition of adenylyl cyclase and is the consequence of a stabilization of angiotensinogen mRNA. In the present study we describe the isolation of a polysomal 12 kDa protein which, in band shift and cross link assays, shows a specific affinity to the 3′ untranslated region (3′ UTR) of angiotensinogen mRNA and prevents enzymatic degradation of angiotensinogen mRNA in a cell-free incubation system. [32P]UTP-labelled or unlabelled 3′ fragments of angiotensinogen mRNA were synthesized on a transcription vector (pGEM5zf+) into which the corresponding DNA sequence was cloned after restriction from vector pRAG 16. Binding of the 12 kDa protein to the radioactively labelled 3′ UTR of angiotensinogen mRNA could be displaced by unlabelled 3′ UTR mRNA fragments but not by a renin mRNA of comparable length derived from the coding region, The RNA-binding protein appears to be derived from a higher molecular mass precursor (45 kDa) which is preferentially present under reducing conditions in vitro; the active low molecular mass form is evident in the absence of reducing agents. In a cross link experiment we established that a band shift signal which was obtained in the presence of the 45 kDa protein preparation exclusively depends on RNA binding of the active 12 kDa protein. In addition, a phosphorylation step may be involved in the activation of the 12 kDa protein, since its molecular mass and isoelectric point correlate with proteins which were phosphorylated in response to transient decreases of cAMP (induced by guanfacine or angiotensin II) or in response to a direct inhibition of protein kinase A by the cAMP antagonist Rp-cAMP. The importance of phosphorylation reactions for the stabilization of angiotensinogen mRNA was further assessed in a cell-free incubation system of rat liver parenchymal cells. These studies demonstrated that in the presence of acid phosphatase (1 U/ml) the half-life of angiotensinogen was significantly decreased. In the same incubation system the 12 kDa protein increased the half-life of endogenous as well as of exogenous angiotensinogen mRNA three- to fourfold, while no stabilizing effect was apparent when exogenous angiotensinogen mRNA from which the 3′ tail had been deleted was added. We concluded that an intracellular 12 kDa protein may play a crucial role in the angiotensin Il-induced stabilization of hepatic angiotensinogen mRNA and further suggest that this protein exerts its effect via binding to the 3′ UTR of angiotensinogen mRNA in response to a cAMP-dependent activation step.

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M Shimojo, C B Whorwood and P M Stewart

ABSTRACT

11β-Hydroxysteroid dehydrogenase (11β-HSD) catalyses the interconversion of biologically active cortisol to inactive cortisone in man, and corticosterone to 11-dehydrocorticosterone in rodents. As such, this enzyme has been shown to confer aldosterone-selectivity on the mineralocorticoid receptor and to modulate cortisol/corticosterone access to the glucocorticoid receptor (GR). Two kinetically distinct isoforms of this enzyme have been characterized in both rodents and man; a low-affinity NADP(H)-dependent enzyme (11β-HSD1) which predominantly acts as an oxo-reductase and, more recently, a high-affinity NAD-dependent uni-directional dehydrogenase (11β-HSD2). In this study we have analysed the expression of both 11β-HSD1 and 11β-HSD2 isoforms in rat adrenal cortex and medulla and have investigated their possible roles with respect to glucocorticoid-regulated enzymes mediating catecholamine biosynthesis in adrenal medullary chromaffin cells.

Using a rat 11β-HSD1 probe and a recently cloned in-house mouse 11β-HSD2 cDNA probe, Northern blot analyses revealed expression of mRNA species encoding both 11β-HSD1 (1·4kb) and 11β-HSD2 (1·9kb) in the whole adrenal. Consistent with this, 11β-dehydrogenase activity (pmol 11-dehydrocorticosterone formed/mg protein per h, mean ± s.e.m.) in adrenal homogenates, when incubated with 50 nm corticosterone in the presence of 200 μm NAD, was 97·0 ± 9·0 and with 500 nm corticosterone in the presence of 200 μm NADP, was 98·0 ± 1·4 11-Oxoreductase activity (pmol corticosterone formed/mg protein per h) with 500 nm 11-dehydrocorticosterone in the presence of 200 μm NADPH, was 187·7 ± 31·2. In situ hybridization studies of rat adrenal cortex and medulla using 35S-labelled antisense 11β-HSD1 cRNA probe revealed specific localization of 11β-HSD1 mRNA expression predominantly to cells at the corticomedullary junction, most likely within the inner cortex. In contrast, 11β-HSD2 mRNA was more abundant in cortex versus medulla, and was more uniformly distributed over the adrenal gland. Negligible staining was detected using control sense probes.

Ingestion of the 11β-HSD inhibitor, glycyrrhizic acid (>100mg/kg body weight per day for 4 days) resulted in significant inhibition of adrenal NADP-dependent (98·0 ± 1·4 vs 42·5 ± 0·4) and NAD-dependent (97·0 ± 9·0 vs 73·2 ± 6·7) 11β-dehydrogenase activity and 11-oxoreductase activity (187·7 ± 31·2 vs 67·7 ± 15·3). However, while levels of 11β-HSD1 mRNA were similarly reduced (0·85 ± 0·07 vs 0·50 ± 0·05 arbitrary units), those for 11β-HSD2 remained unchanged (0·44 ± 0·03 vs 0·38 ± 0·01). Levels of mRNA encoding the glucocorticoid-dependent enzyme phenylethanolamine N-methyltransferase which catalyses the conversion of noradrenaline to adrenaline, were also significantly reduced in those rats given glycyrrhizic acid (1·12 ± 0·04 vs 0·78 ± 0·04), while those for the glucocorticoid-independent enzyme tyrosine hydroxylase (1·9 kb), which catalyses the conversion of tyrosine to DOPA, were unchanged (0·64 ± 0·04 vs 0·61 ± 0·04).

In conclusion, the rat adrenal gland expresses both 11β-HSD1 and 11β-HSD2 isoforms. 11β-HSDl gene expression is localized to the adrenal cortico-medullary junction, where it is ideally placed to regulate the supply of cortex-derived corticosterone to the medullary chromaffin cells. This, together with our in vivo studies, suggests that 11β-HSD1 may play an important role with respect to adrenocorticosteroid regulation of adrenaline biosynthesis. The role of 11β-HSD2 in the adrenal remains to be elucidated.

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Feng Wang, Lu Wang, Yifeng Wang, Dai Li, Tianpeng Hu, Manyi Sun and Ping Lei

Insulin-like growth factor-1 (IGF-1) improves cognitive function, but its mechanism has not been elucidated. The aim of the study was to explore whether IGF-1 exerted its protective effect on cognitive function and anxiety behavior through the activation of PI3K/Akt/CREB pathway in high-fat diet rats. Neuronal cells HT22 were treated with nothing, IGF-1, IGF-1 + LY294002 or IGF-1 + 666-15. Expressions of p-PI3K, p-Akt and p-CREB were measured using Western blot analysis. Thirty C57BL/6J rats were used. After feeding with high-fat diet, normal saline, PEG-IGF-1, PEG-IGF-1 + LY294002 or PEG-IGF-1 + 666-15 was treated. Cognitive function and anxiety behavior were assessed by Morris water maze and open field test. Several inflammation and oxidative stress biomarkers were measured using recognized methods. Expressions of p-PI3K and p-CREB were also measured using Western blot analysis. After IGF-1 treatment in cells, expressions of p-PI3K, p-Akt and p-CREB were increased. Furthermore, LY294002 downregulated the expressions of these three proteins, but 666-15 only inhibited the expression of CREB in the cells. Compared with the control rats, we found abnormalities of cognitive function and anxiety behavior, inhibition of PI3K/Akt/CREB pathway and increase of oxidative stress and inflammation in high-fat diet rats. After PEG-IGF-1 treatment, the changes in high-fat diet rats were reversed. Then, we blocked the pathway and found that these blockers attenuated the protective effects of PEG-IGF-1. In conclusion, IGF-1 improved cognitive function and anxiety behavior in high-fat diet rats and inhibited inflammation and oxidative stress in hippocampus tissue through the activation of PI3K/Akt/CREB pathway.

Free access

Yi Lu, Wang-sheng Wang, Yi-kai Lin, Jiang-wen Lu, Wen-jiao Li, Chu-yue Zhang and Kang Sun

Our previous studies have demonstrated that human fetal membranes are capable of de novo synthesis of serum amyloid A1 (SAA1), an acute phase protein of inflammation, wherein SAA1 may participate in parturition by inducing a number of inflammation mediators including interleukine-1β, interleukine-6 and prostaglandin E2. However, the regulation of SAA1 expression in the fetal membranes remains largely unknown. In the current study, we examined the regulation of SAA1 expression by cortisol, a crucial steroid produced locally in the fetal membranes at parturition, and the interaction between cortisol and SAA1 in the feed-forward induction of SAA1 expression in human amnion fibroblasts. Results showed that cortisol-induced SAA1 expression in a concentration-dependent manner, which was greatly enhanced by SAA1 despite modest induction of SAA1 expression by itself. Mechanism studies revealed that the induction of SAA1 expression by cortisol and SAA1 was blocked by either the transcription factor STAT3 antagonist AZD0530 or siRNA-mediated knockdown of STAT3. Furthermore, cortisol- and SAA1-induced STAT3 phosphorylation in a sequential order with the induction by SAA1 preceding the induction by cortisol. However, combination of cortisol and SAA1 failed to further intensify the phosphorylation of STAT3. Consistently, cortisol and SAA1 increased the enrichment of STAT3 at the SAA1 promoter. Taking together, this study has demonstrated that cortisol and SAA1 can reinforce each other in the induction of SAA1 expression through sequential phosphorylation of STAT3. The enhancement of cortisol-induced SAA1 expression by SAA1 may lead to excessive SAA1 accumulation resulting in parturition-associated inflammation in the fetal membranes.

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Rosalia C M Simmen and Angela S Kelley

Enhanced inflammation and reduced apoptosis sustain the growth of endometriotic lesions. Alterations in the expression of estrogen receptor-alpha (ERα) and estrogen receptor-beta (ERβ) accompany the conversion of resident endometrial cells within the normal uterine environment to ectopic lesions located in extrauterine sites. Recent studies highlighted in this focused review linked ERβ to dysregulation of apoptotic and inflammatory networks involving novel interacting partners in endometriosis. The elucidation of these nongenomic actions of ERβ using human cells and mouse models is an important step in understanding key regulatory pathways that are disrupted leading to disease establishment and progression.

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Carla Caruso, Lila Carniglia, Daniela Durand, Teresa N Scimonelli and Mercedes Lasaga

Astrocytes exert a wide variety of functions with paramount importance in brain physiology. After injury or infection, astrocytes become reactive and they respond by producing a variety of inflammatory mediators that help maintain brain homeostasis. Loss of astrocyte functions as well as their excessive activation can contribute to disease processes; thus, it is important to modulate reactive astrocyte response. Melanocortins are peptides with well-recognized anti-inflammatory and neuroprotective activity. Although melanocortin efficacy was shown in systemic models of inflammatory disease, mechanisms involved in their effects have not yet been fully elucidated. Central anti-inflammatory effects of melanocortins and their mechanisms are even less well known, and, in particular, the effects of melanocortins in glial cells are poorly understood. Of the five known melanocortin receptors (MCRs), only subtype 4 is present in astrocytes. MC4R has been shown to mediate melanocortin effects on energy homeostasis, reproduction, inflammation, and neuroprotection and, recently, to modulate astrocyte functions. In this review, we will describe MC4R involvement in anti-inflammatory, anorexigenic, and anti-apoptotic effects of melanocortins in the brain. We will highlight MC4R action in astrocytes and discuss their possible mechanisms of action. Melanocortin effects on astrocytes provide a new means of treating inflammation, obesity, and neurodegeneration, making them attractive targets for therapeutic interventions in the CNS.

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Huixia Li, Zhuanmin Zhang, Dongxu Feng, Lin Xu, Fang Li, Jiali Liu, Xinxin Jin, Zhuang Qian, Xiaomin Kang and Hongzhi Sun

Progranulin (PGRN), a multifunctional protein implicated in embryonic development and immune response, was recently introduced as a novel marker of chronic inflammation related with insulin resistance in obesity and type 2 diabetes mellitus. However, the potential mechanisms of PGRN on insulin signaling pathways are poorly understood. In this study, PGRN mediated the chemotaxis of RAW264.7, impaired insulin action and stimulated production of inflammatory factors in adipocytes, which was accompanied by increased c-Jun N-terminal kinase (JNK) activation and serine phosphorylation of insulin receptor substrate-1. PGRN knockdown partially led to an increase in insulin action as well as a decrease in the JNK activation and extracellular signal-regulated kinase phosphorylation in cells exposed to tumor-necrosis factor-α (TNF-α). Meanwhile, PGRN treatment resulted in an elevation of transcription factor nuclear factor κB (NF-κB) nuclear translocation and acetylation, and increased Il-1b, Il6, Tnf-a expression, whereas NF-κB inhibition reversed PGRN-induced insulin action impairment and inflammatory gene expression. Finally, we showed that sirtuin 1 (SIRT1) expression was downregulated by PGRN treatment, whereas SIRT1 overexpression improved PGRN-induced insulin resistance, NF-κB activation, and inflammatory gene expression. Our results suggest that PGRN regulates adipose tissue inflammation possibly by controlling the gain of proinflammatory transcription in a SIRT1-NF-κB dependent manner in response to inducers such as fatty acids and endoplasmic reticulum stress.

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Ying Li, Fuzhe Ma, Huimin Li, Yuguo Song, Huan Zhang, Ziping Jiang and Hao Wu

Impaired wound healing is a common complication among patients with diabetes mellitus (DM), resulting in high rates of disability and mortality. Recent findings highlighted the critical role of nuclear factor erythroid 2-related factor 2 (NRF2) – a master of cellular antioxidants scavenging excessive DM-induced free radicals – in accelerating diabetic wound healing. Dimethyl fumarate (DMF) is a potent NRF2 activator used for the treatment of multiple sclerosis. However, the effect of DMF on wound healing has not been determined. The present study investigated the effect of DMF on the diabetic and the non-diabetic wound healing in streptozotocin-induced diabetic mice and non-diabetic control mice. DMF activated NRF2 signaling under both conditions. Interestingly, DMF attenuated oxidative damage and inflammation and accelerated wound closure in diabetic mice. However, this effect was not observed in non-diabetic mice. Keratinocytes were treated with normal glucose (NG), high glucose (HG) or hydrogen peroxide (H2O2), in the presence or absence of DMF to assess the role of reactive oxygen species (ROS) – inducible in DM – in mediating DMF-induced protection. Both HG and H2O2 elevated ROS, oxidative damage and inflammation, the effects of which were similarly blunted by DMF. However, in spite of the activation of NRF2, DMF lost this capability under the NG condition. The findings of this study demonstrate that ROS activate the protective effect of DMF on the diabetic wound healing.

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Caitlyn Nguyen-Ngo, Nanthini Jayabalan, Carlos Salomon and Martha Lappas

Gestational diabetes mellitus (GDM) imposes serious short- and long-term health problems for mother and baby. An effective therapeutic that can reduce the incidence of GDM and improve long-term maternal and fetal outcomes is a major research priority, crucially important for public health. A lack of knowledge about the underlying pathophysiology of GDM has hampered the development of such therapeutics. What we do know, however, is that maternal insulin resistance, low-grade inflammation and endothelial cell dysfunction are three central features of pregnancies complicated by GDM. Indeed, data generated over the past decade have implicated a number of candidate regulators of insulin resistance, inflammation and endothelial cell dysfunction in placenta, maternal adipose tissue and skeletal muscle. These include nuclear factor-κB (NF-κB), peroxisome proliferator-activated receptors (PPARs), sirtuins (SIRTs), 5′ AMP-activated protein kinase (AMPK), glycogen synthase kinase 3 (GSK3), PI3K/mTOR, inflammasome and endoplasmic reticulum (ER) stress. In this review, the identification of these as key modulators of GDM will be discussed. The biochemical pathways involved in the formation of these may represent potential sites for intervention that may translate to therapeutic interventions to prevent the development of GDM.

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Bettina Sederquist, Paola Fernandez-Vojvodich, Farasat Zaman and Lars Sävendahl

Children with inflammatory diseases usually display abnormal growth patterns as well as delayed puberty. This is a result of several factors related to the disease itself, such as malnutrition, hypercortisolism, and elevated levels of pro-inflammatory cytokines. These factors in combination with glucocorticoid treatment contribute to growth retardation during chronic inflammation by systemically affecting the major regulator of growth, the GH/IGF1 axis. However, recent studies have also shown evidence of a direct effect of these factors at the growth plate level. In conditions of chronic inflammation, pro-inflammatory cytokines are upregulated and released into the circulation. The most abundant of these, tumor necrosis factor α, interleukin 1β (IL1β), and IL6, are all known to directly act on growth plate cartilage to induce apoptosis and thereby suppress bone growth. Both clinical and experimental studies have shown that growth retardation can partly be rescued when these cytokines are blocked. Therefore, therapy modulating the local actions of these cytokines may be effective for preventing growth failure in patients with chronic inflammatory disorders. In this review, we report the current knowledge of inflammatory cytokines and their role in regulating bone growth.