非诺贝特对脂多糖诱导的心肌细胞肿瘤坏死因子—α表达的影响

目的 探讨过氧化体增殖物激活型受体α(PPARα)激活剂对新生大鼠心肌细胞肿瘤坏死因子-α(TNF-α)和PPARα自身表达水平的影响。方法 体外原代培养新生Wistar大鼠心肌细胞，给予不同浓度的非诺贝特(PPARα激活剂)刺激，并辅加脂多糖诱导TNF-α表达。采用半定量逆转录．聚合酶链反应法检测TNF-α和PPARα mRNA的表达，酶联免疫吸附测定法检测TNF-α的蛋白水平，Western印迹法检测PPARα蛋白表达。结果与对照组相比，非诺贝特组的TNF-α mRNA及蛋白表达水平明显降低，且呈剂量依赖性。而相应的PPARα mRNA及蛋白水平则无显变化。结论 PPARα激活剂可显抑制新生大鼠心肌细胞中脂多糖诱导的TNF-α表达，PPARα活化后发挥抗炎作用，但PPARα本身的表达水平可能并没有改变。     

Platelet Toll-like receptor expression modulates lipopolysaccharide-induced thrombocytopenia and tumor necrosis factor-alpha production in vivo

Toll-like receptors (TLRs) play a critical role in stimulating innate immunity by recognizing pathogen-associated molecular patterns (PAMPs) on invading microorganisms. Platelets also play a role in innate immunity, and we studied whether they express TLR. Results show that human and murine platelets variably expressed TLR2, TLR4, and TLR9 by flow cytometry and Western blotting. TLR4 expression was confirmed by demonstrating murine platelet binding to lipopolysaccharide (LPS). Thrombin activation of the platelets significantly enhanced the expression of TLR9, suggesting that at least some TLRs may derive from intracellular compartments. When LPS was administered to LPS-sensitive C3H/HeN and LPS-resistant C3H/HeJ mice, functional TLR4 expression in vivo was shown to be responsible for LPS-induced thrombocytopenia. However, when the C3H/HeN mice were first rendered thrombocytopenic by an antiplatelet antibody and then administered LPS, a significant reduction occurred in their ability to produce TNF-alpha. The decreased cytokine production in the thrombocytopenic mice was restored with platelet transfusion. These results suggest that platelets express various TLRs and that the functional significance of one of these, TLR4, appears to be a role in the modulation of LPS-induced thrombocytopenia and TNF-alpha production. This work implicates platelets as important mediators of innate immune responses against invading microorganisms.     

Role of neuronal nitric oxide synthase in lipopolysaccharide-induced tumor necrosis factor-alpha expression in neonatal mouse cardiomyocytes

OBJECTIVE: Neuronal nitric oxide synthase (nNOS) has been shown to regulate intracellular calcium in cardiomyocytes. Calcium in turn modulates extracellular signal-related kinase (ERK) signaling, which is important in tumor necrosis factor-alpha (TNF-alpha) expression during lipopolysaccharide (LPS) stimulation. However, the role of nNOS in LPS-induced TNF-alpha expression is not known. We hypothesized that nNOS suppresses LPS-induced TNF-alpha expression by inhibiting the calcium/ERK signaling pathway. METHODS AND RESULTS: Cultured neonatal mouse cardiomyocytes were challenged with LPS for 4 h. While there was no change in the basal Ca(2+) concentration, LPS increased peak Ca(2+) levels. LPS stimulation increased TNF-alpha mRNA and protein levels in wild-type cells however, the responses were enhanced in nNOS(-/-) cardiomyocytes. Treatment with an antisense oligonucleotide against nNOS also significantly enhanced TNF-alpha expression during LPS stimulation. Furthermore, LPS-induced ERK phosphorylation was significantly increased in the nNOS(-/-) compared to wild-type cardiomyocytes. The enhanced TNF-alpha expression in nNOS(-/-) cardiomyocytes was abrogated by an L-type calcium channel blocker verapamil or ERK1 siRNA. Finally, myocardial ERK phosphorylation and TNF-alpha expression were increased while cardiac function was decreased in endotoxemia in nNOS(-/-) compared to wild-type mice. CONCLUSIONS: nNOS inhibits LPS-induced TNF-alpha expression in cardiomyocytes and improves cardiac function in endotoxemia. The inhibitory role of nNOS is mediated by a reduction in L-type calcium channel-dependent ERK signaling in cardiomyocytes.     

Glucocorticoids inhibit lipopolysaccharide-induced production of tumor necrosis factor-alpha by human fetal Kupffer cells.

Inflammatory mediators, such as interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF alpha) are secreted by fixed tissue macrophages and exhibit local autocrine and paracrine effects as well as distant endocrine effects. Human fetal Kupffer cells, the fixed tissue macrophages of the liver, may play a role as modulators of immune and endocrine function in early embryonic and fetal development. In the present study we isolated human fetal Kupffer cells to greater than 90% purity and prepared short term cultures to investigate the effect of glucocorticoids on the secretion of the cytokine TNF alpha. Fetal Kupffer cells secreted TNF alpha and IL-1 beta after culture with bacterial lipopolysaccharide (LPS), indicating that these cells express mature macrophage function. Cortisol and dexamethasone dramatically suppressed the LPS-stimulated secretion of TNF alpha by fetal Kupffer cells. The inhibitory effects of glucocorticoids appeared to be specific, since estrogen, progesterone, and testosterone had no effect on LPS stimulation of TNF alpha production. None of the steroids tested altered basal production or enhanced the LPS-stimulated production of TNF alpha by fetal Kupffer cells. The inhibition by glucocorticoids could be reversed by the addition of RU 486, indicating that this effect was mediated by the glucocorticoid receptor. These results demonstrate that human fetal macrophages demonstrate mature macrophage function in early gestation; they can be activated to produce TNF alpha by a well characterized modulator of cellular function (LPS) and suppressed by glucocorticoids.     

Peroxisome proliferator-activated receptor-alpha and receptor-gamma activators prevent cardiac fibrosis in mineralocorticoid-dependent hypertension

Peroxisome proliferator-activated receptor (PPAR) activation may prevent cardiac hypertrophy and inhibit production of endothelin-1 (ET-1), a hypertrophic agent. The aim of this in vivo study was to investigate the effects of PPAR activators on cardiac remodeling in DOCA-salt rats, a model overexpressing ET-1. Unilaterally nephrectomized 16-week-old Sprague-Dawley rats (Uni-Nx) were randomly divided into 4 groups: control rats, DOCA-salt, DOCA-salt+rosiglitazone (PPAR-gamma activator, 5 mg/kg per day), and DOCA-salt+fenofibrate (PPAR-alpha activator, 100 mg/kg per day). After 3 weeks of treatment, mean arterial blood pressure was significantly increased in DOCA-salt by 36 mm Hg. Mean arterial blood pressure was normalized by coadministration of rosiglitazone but not by fenofibrate. Both PPAR activators prevented cardiac fibrosis and abrogated the increase in prepro-ET-1 mRNA content in the left ventricle of DOCA-salt rats. Coadministration of rosiglitazone or fenofibrate failed to prevent thickening of left ventricle (LV) walls as measured by echocardiography and the increase in atrial natriuretic peptide mRNA levels. However, rosiglitazone and fenofibrate prevented the decrease in LV internal diameter and thus concentric remodeling of the LV found in DOCA-salt rats. Taken together, these data indicate a modulatory role of PPAR activators on cardiac remodeling in mineralocorticoid-induced hypertension, in part associated with decreased ET-1 production.     

Tumor necrosis factor-alpha decreases the phosphorylation levels of phospholamban and troponin I in spontaneously beating rat neonatal cardiac myocytes

The tumor necrosis factor (TNF) alpha level is elevated in patients with advanced heart failure, and the phosphorylation of contractile regulatory proteins is reduced in the human heart. We hypothesized that TNFalpha affects the phosphorylation of proteins involved in regulating contraction; phospholamban (PLB), myosin light chain 2 (MLC2) and troponin I (TnI). Spontaneously beating rat neonatal cardiac myocytes, prelabelled with [32P]orthophosphate, were treated with TNFalpha for 30 min, and stimulated with isoproterenol for 5 min. 32P-labelled myofibrillar proteins were isolated by 15% SDS-PAGE. Baseline phosphorylation levels of PLB, TnI and an unknown 23kDa phosphoprotein were decreased by TNFalpha in a dose-dependent manner. Moreover, TNFalpha attenuated the phosphorylation levels of PLB and TnI increased by a concentration of 0.01 microM isoproterenol, but not by 1 microM of isoproterenol. Although TNFalpha had no effect on the cAMP content or cAMP-dependent protein kinase activity in the presence or absence of isoproterenol, an inverse relationship was observed between the concentration of TNFalpha and the cGMP content in cardiac myocytes, and treatment with TNFalpha resulted in a concentration-dependent increase in type 2A protein phosphatase activity. The observation that TNFalpha decreases phosphorylation levels of PLB and TnI in cardiac myocytes suggests that the reduction of these protein phosphorylation levels is partially responsible for alterations of intracellular Ca2+-cycling and the force of contraction in TNF alpha-treated cardiac myocytes. Furthermore, TNFalpha reduces myocyte contraction and protein phosphorylation states possibly via cAMP-independent mechanisms, at least in part, by the activation of type 2A protein phosphatase.     

Hypoxia-induced Haem Oxygenase-1 gene expression in neonatal rat cardiac myocytes

Background: Haem oxygenase (HO-1), a heat shock or stress protein, is a rate-limiting enzyme in the conversion of pro-oxidant haem to biliverdin and carbon monoxide (CO). The products of haem catabolism serve regulatory and protective functions. Previous studies have shown that hypoxia induces HO-1 expression in cardiac myocytes. Accordingly, we investigated whether hypoxia-induced HO-1 expression is accompanied by increased CO production in cultured neonatal rat cardiac myocytes, and whether protein kinase C (PKC) is involved in hypoxia induced HO-1 gene expression.

Methods and Results: Expression of HO-1 in hypoxia-treated cells was examined by using northern and western blotting, and immunofluorescent staining. The level of HO-1 mRNA at 24 and 48 h was increased after the onset of hypoxia, with corresponding increase in the HO-1 protein level (6.7- and 8.7-fold at 24 and 48 h of hypoxia, respectively). HO-1 protein was colocalised with sarcomeric -actin in hypoxic myocytes. Hypoxia also significantly increased the production of CO by 2.5- and 8-fold at 24 and 48 h, respectively. Under normoxic conditions, activation of PKC by phorbol-12-myristate-13-acetate (PMA; 100 nmol/L) markedly increased HO-1 gene expression, while inhibition of PKC activity by calphostin C (100 nmol/L) blocked hypoxia-induced HO-1 gene expression in cardiac myocytes.

Conclusions: These results demonstrate that hypoxia markedly induces HO-1 expression and increases the production of CO in cardiac myocytes. This hypoxic response is attributed, at least in part, to activation of PKC. Increased HO-1 expression and resultant CO production may be beneficial with respect to protection of cardiac myocytes under hypoxic conditions.     

EDG1 receptor stimulation leads to cardiac hypertrophy in rat neonatal myocytes

Sphingosine 1 phosphate (S1P), an aminophospholipid, acts extracellularly as a ligand via the specific G protein-coupled receptors of the endothelial differentiation gene (EDG) 1, 3, 5, 6 and 8 receptors family and intracellularly as a second messenger in various cellular types. The aim of this work was to investigate biological activity of S1P in cardiomyocytes with respect to related sphingolipids. S1P was applied for 48 h on rat neonatal cardiomyocytes at 10 nM, 100 nM and 1 microM. S1P induced a concentration-dependent cellular hypertrophy evidenced by an increase in cell size, [3H]-phenylalanine incorporation, protein content and Brain Natriuretic Peptide (BNP) secretion. Among the lipids tested S1P exhibits the lower EC50 (67 nM) followed by dihydro-S1P (107 nM) and sphingosylphosphorylcholine (1.6 microM). The effect of S1P could be related to a stimulation of the EDG1 receptor since we showed that the EDG1 receptor is predominantly expressed at the mRNA and protein levels in rat cardiomyocytes and that specific anti-EDG1 antibodies inhibited the hypertrophic effect induced by S1P. Furthermore the expression level of most other EDG receptors for S1P appeared very low in cardiac myocytes. S1P (100 nM) increased the phosphorylation of p42/44MAPK, p38MAPK, JNK, Akt and p70(S6K), this effect being reversed by inhibitors of their respective phosphorylation which also rescue the hypertrophic phenotype. Finally, S1P stimulated actin stress fibre formation reverted by the Rho inhibitor, the C3 exoenzyme. Altogether, our results show that S1P induces cardiomyocyte hypertrophy mainly via the EDG1 receptor and subsequently via Gi through ERKs, p38 MAPK, JNK, PI3K and via Rho pathway.     

过氧化物酶体增殖物激活受体与肝病的关系

过氧化物酶体增殖物激活受体(peroxisome proliferator-activated receptor,PPAR)是一类由配体激活的核转录因子,属Ⅱ型核受体超家族成员,存在3种亚型,即PPARα、PPARδ、PPARγ,这三种亚型在结构上有一定的相似性,均含DNA结合区和配体结合区等。肝组织大量表达PPARα和少量的PPARδ、PPARγ。肝脏库普弗细胞和其他巨噬细胞一样可以表达PPARα、PPARγ,肝星状细胞表达PPARγ。本文重点综述PPARα、PPARγ在肝脏疾病中的作用机制。