Corticotropin-releasing hormone induces Fas ligand production and apoptosis in PC12 cells via activation of p38 mitogen-activated protein kinase

Induction of microglial apoptosis by corticotropin-releasing hormone

Neuropeptides are short-chain peptides found in brain tissue, some of which function as neurotransmitters and others as hormones. Neuropeptides may directly or indirectly modulate glial functions in the CNS. In the present study, effects of various neuropeptides on the viability and inflammatory activation of cultured microglia were investigated. Vasoactive intestinal peptide, substance P, cholecystokinin and neuropeptide Y did not affect microglial cell viability, whereas corticotropin-releasing hormone (CRH) induced a classical apoptosis of mouse microglia in culture as shown by nuclear condensation and fragmentation, terminal deoxynucleotidyl transferase dUTP nick-end labeling, and cleavage of caspase 3 and poly(ADP-ribose) polymerase protein. CRH, however, did not influence nitric oxide production or expression of inflammatory genes including those encoding cytokines and chemokines, indicating that CRH did not affect the inflammatory activation of microglia. The CRH-induced microglial apoptosis appeared to involve a mitochondrial pathway and reactive oxygen species, based on the mitochondrial membrane potential change, caspase 9 activation and sensitivity to antioxidants. Taken together, our results indicate that the stress neuropeptide CRH may regulate neuroinflammation by inducing the apoptosis of microglia, the major cellular source of inflammatory mediators in the CNS.

The molecular mechanisms underlying the regulation of the biological activity of corticotropin-releasing hormone receptors: implications for physiology and pathophysiology

The CRH receptor (CRH-R) is a member of the secretin family of G protein-coupled receptors. Wide expression of CRH-Rs in the central nervous system and periphery ensures that their cognate agonists, the family of CRH-like peptides, are capable of exerting a wide spectrum of actions that underpin their critical role in integrating the stress response and coordinating the activity of fundamental physiological functions, such as the regulation of the cardiovascular system, energy balance, and homeostasis. Two types of mammal CRH-R exist, CRH-R1 and CRH-R2, each with unique splicing patterns and remarkably distinct pharmacological properties, but similar signaling properties, probably reflecting their distinct and sometimes contrasting biological functions. The regulation of CRH-R expression and activity is not fully elucidated, and we only now begin to fully understand the impact on mammalian pathophysiology. The focus of this review is the current and evolving understanding of the molecular mechanisms controlling CRH-R biological activity and functional flexibility. This shows notable tissue-specific characteristics, highlighted by their ability to couple to distinct G proteins and activate tissue-specific signaling cascades. The type of activating agonist, receptor, and target cell appears to play a major role in determining the overall signaling and biological responses in health and disease.

Activation of membrane estrogen receptors induce pro-survival kinases

Experimental and epidemiological data suggest a neuroprotective role for estrogen (E(2)). We have recently shown that, in PC12 cells, non-permeable estradiol conjugated to bovine serum albumin (BSA) prevent serum-deprivation induced apoptosis through activation of specific membrane estrogen receptors (mER). In the present study, we explored in detail the early signaling events involved in this anti-apoptotic action, downstream to activation of mER. Our findings suggest that mER is associated to G-proteins, and its activation with non-permeable E(2)-BSA results in the activation of the following downstream pro-survival kinases pathways: (1) the PKB/Akt pathway, (2) the Src-->MEK-->ERK kinases and finally (3) the MAPK-->ERK kinases. Activation of these pro-survival signals leads to CREB phosphorylation and NFkappaB nuclear translocation, two transcription factors controlling the expression of anti-apoptotic Bcl-2 proteins. These data suggest that major pro-survival kinases are involved in the mER-mediated anti-apoptotic effects of estrogen. This is further supported by experiments with specific kinases inhibitors, which partially but significantly reversed the mER-mediated anti-apoptotic effect of E(2)-BSA. Our findings suggest that estrogen act via mER as potent cytoprotective factors, downstream activating pro-survival kinases, assuring thus an efficient and multipotent activation of the anti-apoptotic machinery.

Corticotropin-Releasing Factor and the Urocortins Induce the Expression of TLR4 in Macrophages via Activation of the Transcription Factors PU.1 and AP-1

Corticotropin-releasing factor (CRF) augments LPS-induced proinflammatory cytokine production from macrophages. The aim of the present study was to determine the mechanism by which CRF and its related peptides urocortins (UCN) 1 and 2 affect LPS-induced cytokine production. We examined their role on TLR4 expression, the signal-transducing receptor of LPS. For this purpose, the murine macrophage cell line RAW 264.7 and primary murine peritoneal macrophages were used. Exposure of peritoneal macrophages and RAW 264.7 cells to CRF, UCN1, or UCN2 up-regulated TLR4 mRNA and protein levels. To study whether that effect occurred at the transcriptional level, RAW 264.7 cells were transfected with a construct containing the proximal region of the TLR4 promoter linked to the luciferase gene. CRF peptides induced activation of the TLR4 promoter, an effect abolished upon mutation of a proximal PU.1-binding consensus or upon mutation of an AP-1-binding element. Indeed, all three peptides promoted PU.1 binding to the proximal PU.1 site and increased DNA-binding activity to the AP-1 site. The effects of CRF peptides were inhibited by the CRF2 antagonist anti-sauvagine-30, but not by the CRF1 antagonist antalarmin, suggesting that CRF peptides mediated the up-regulation of TLR4 via the CRF2 receptor. Finally, CRF peptides blocked the inhibitory effect of LPS on TLR4 expression. In conclusion, our data suggest that CRF peptides play an important role on macrophage function. They augment the effect of LPS by inducing Tlr4 gene expression, through CRF2, via activation of the transcription factors PU.1 and AP-1.

G protein-associated, specific membrane binding sites mediate the neuroprotective effect of dehydroepiandrosterone

The neurosteroid dehydroepiandrosterone (DHEA) at 1 nM protects NMDA-/GABAA-receptor negative neural crest-derived PC12 cells from apoptosis. We now report that membrane-impermeable DHEA-BSA conjugate replaces unconjugated DHEA in protecting serum-deprived PC12 cells from apoptosis (IC50=1.5 nM). Protection involves phosphorylation of the prosurvival factor Src and induction of the anti-apoptotic protein Bcl-2 and is sensitive to pertussis toxin. Binding assays of [3H]DHEA on isolated PC12 cell membranes revealed saturation within 30 min and binding of DHEA with a Kd of 0.9 nM. A similar binding activity was detectable in isolated membranes from rat hippocampus and from normal human adrenal chromaffin cells. The presence of DHEA-specific membrane binding sites was confirmed by flow cytometry and confocal laser microscopy of DHEA-BSA-FITC stained cells. In contrast to estrogens and progestins, glucocorticoids and androgens displaced DHEA from its membrane binding sites but with a 10-fold lower affinity than DHEA (IC50=9.3 and 13.6 nM, respectively). These agents acted as pure antagonists, blocking the antiapoptotic effect of DHEA as well as the induction of Bcl-2 proteins and Src kinase activation. In conclusion, our findings suggest that neural crest-derived cells possess specific DHEA membrane binding sites coupled to G proteins. Binding to these sites confers neuroprotection.

Corticotropin-releasing hormone induces vascular endothelial growth factor release from human mast cells via the cAMP/protein kinase A/p38 mitogen-activated protein kinase pathway

Mast cells are involved in allergic reactions but also in innate immunity and inflammation. Corticotropin-releasing hormone (CRH), the key regulator of the hypothalamic-pituitary-adrenal axis, also has proinflammatory effects, apparently through mast cells. We showed recently that CRH selectively stimulates human leukemic mast cells and human umbilical cord blood-derived mast cells to release newly synthesized vascular endothelial growth factor (VEGF) without release of either preformed mediators or cytokines. This effect was mediated through the activation of CRH receptor-1 and adenylate cyclase with increased intracellular cAMP. However, the precise mechanism by which CRH induces VEGF secretion has not yet been defined. Here, we show that CRH-induced VEGF release was dose-dependently inhibited by the specific protein kinase A inhibitor N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H89) or the p38 mitogen-activated protein kinase (MAPK) inhibitor 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580) but not by the specific inhibitor 2'-amino-3'-methoxyflavone (PD98059) of mitogen-activated protein kinase kinase, the upstream kinase of the extracellular signal-regulated protein kinase (ERK) or the c-Jun N-terminal kinase (JNK) inhibitor 1,9-pyrazoloanthrone anthra-(1,9-cd)pyrazol-6(2H)-one (SP600125). Furthermore, CRH significantly increased protein kinase A activity, which could be mimicked by the cell-permeable cAMP analog 8-bromo-cAMP, and was blocked by H89 or the adenylate cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ22536). CRH also induced rapid phosphorylation of p38 MAPK, which was mimicked by 8-bromo-cAMP and was inhibited by H89 or SB203580. CRH did not stimulate ERK or JNK phosphorylation and did not increase intracellular calcium levels. These results indicate that CRH induces VEGF release in human mast cells via selective activation of the cAMP/protein kinase A/p38 MAPK signaling pathway, thereby providing further insight into the molecular mechanism of how CRH affects the release of a key proinflammatory mediator.

Human lactoferrin exerts bi-directional actions on PC12 cell survival via ERK1/2 pathway

Human lactoferrin (hLF) is a member of the transferrin family and is found in most body fluids of human. Recent study showed that hLF played some roles in the regulation of cell growth. However, the biological function of hLF in the central nervous system and neuronal cells is still unclear. The MTT was used to assay cell viability, ELISA tests were used to assay caspase activities, and TUNEL staining was used to test the cytotoxicity of hLF to the cells. Our result showed that 700 microg/ml hLF significantly reduced the cell viability and increased the caspase 3 and 8 activities in PC12 neuronal cells. TUNEL staining further showed that 700 microg/ml hLF was cytotoxic to the PC12 through apoptosis-mediated pathway. In addition, 700 microg/ml hLF significantly decreased the protein expressions of phosphorylated extracellular-signal-regulated kinase 1/2 (ERK1/2) and Bcl-2 in PC12 cells, whereas 50 microg/ml hLF significantly increased the phosphorylation of ERK1/2 which could be specifically inhibited by PD98059. Furthermore, 50 microg/ml hLF could not only up-regulate the Bcl-2 expression but also protect PC12 cells from FasL-induced apoptosis. In conclusion, hLF plays a crucial role in the regulation of apoptosis and anti-apoptosis in PC12 neuronal cells via ERK1/2 phosphorylation pathway.

Adiponectin induces TNF-alpha and IL-6 in macrophages and promotes tolerance to itself and other pro-inflammatory stimuli

Adiponectin exerts anti-inflammatory effects via macrophages, suppressing the production of pro-inflammatory cytokines in response to bacterial lipopolysaccharide (LPS). Here, we provide experimental evidence that the "anti-inflammatory" effect of adiponectin may be due to an induction of macrophage tolerance: globular adiponectin (gAd) is a powerful inducer of TNF-alpha and IL-6 secretion in primary human peripheral macrophages, in the THP-1 human macrophage cell line, and in primary mouse peritoneal macrophages. Pre-exposure of macrophages to 10 microg/ml gAd rendered them tolerant to further gAd exposure or to other pro-inflammatory stimuli such as TLR3 ligand polyI:C and TLR4 ligand LPS, while pre-exposure to 1 microg/ml of and re-exposure to 10 microg/ml gAd unmasked its pro-inflammatory properties. GAd induced NF-kappaB activation and tolerance to further gAd or LPS exposure. Our data suggest that adiponectin constant presence in the circulation in high levels (in lean subjects) renders macrophages resistant to pro-inflammatory stimuli, including its own.

Urocortin 1 and Urocortin 2 induce macrophage apoptosis via CRFR2

Macrophages undergo apoptosis as a mechanism of regulating their activation and the inflammatory reaction. Macrophages express the Corticotropin-Releasing Factor Receptor-2 (CRFR2) the endogenous agonists of which, the urocortins, are also present at the site of inflammation. We have found that urocortins induced macrophage apoptosis in a dose- and time-dependent manner via CRFR2. In contrast to lipopolysaccharide (LPS)-induced apoptosis, the pro-apoptosis pathway activated by urocortins involved the pro-apoptotic Bax and Bad proteins and not nitric oxide, JNK and p38MAPK characteristic of LPS. In conclusion, our data suggest that endogenous CRFR2 ligands exert an anti-inflammatory effect via induction of macrophage apoptosis.

Dissecting the genetic effect of the CRH system on anxiety and stress-related behaviour

Corticotropin-releasing hormone (CRH) plays a central role in the adaptation of the body to stress. CRH integrates the endocrine, autonomic and behavioural responses to stress acting as a secretagogue within the line of the hypothalamic pituitary adrenocortical (HPA) system and as a neurotransmitter modulating synaptic transmission in the central nervous system. Accumulating evidence suggests that the neuroendocrine and behavioural symptoms observed in patients suffering from major depression are at least in part linked to a hyperactivity of the CRH system. Genetic modifications of the CRH system by conventional and conditional gene targeting strategies in the mouse allowed us to study the endogenous mechanisms underlying HPA system regulation and CRH-related neuronal circuitries involved in pathways mediating anxiety and stress-related behaviour.

Corticotropin-Releasing Hormone (CRH) Downregulates Interleukin-18 Expression in Human HaCaT Keratinocytes by Activation of p38 Mitogen-Activated Protein Kinase (MAPK) Pathway

It is generally accepted that corticotropin-releasing hormone (CRH) acts as the main coordinator of the central response to stress. Stress or an abnormal response to stressors has been found to modify the evolution of skin disorders, including psoriasis and atopic dermatitis. Nevertheless, the specific pathogenic role of stress remains unknown in skin diseases. Interleukin (IL)-18, a member of the IL-1 family, is a key mediator of peripheral inflammation and host defense responses, and is secreted by human keratinocytes. Here, we investigated the regulatory effect of CRH on expression of IL-18 in skin keratinocytes. Exposure of HaCaT cells to CRH resulted in a reduction of IL-18 mRNA transcripts and its production was in a concentration-dependent manner. In order to investigate whether the mitogen-activated protein kinase (MAPK) signaling pathway is involved in the downregulation of IL-18 production, cells were pre-treated with SB203580, an inhibitor of p38 MAPK, prior to the addition of CRH. This pre-treatment blocked the decrease in IL-18 production. In addition, CRH treatment induced rapid phosphorylation of p38 MAPK. SB203580 were able to inhibit CRH-induced p38 MAPK phosphorylation. CRH also inhibited production of IL-18 in human primary keratinocytes. These results suggest that CRH regulates IL-18 production through the MAPK signaling pathway in human keratinocytes.

Characterization of monochloramine toxicity on PC12 cells and protective effect of tocopherol via antioxidative function

Monochloramine (NH(2)Cl) is a physiological oxidant produced by activated neutrophils. In the present work, we studied the underlying mechanism of cytotoxic effects of NH(2)Cl on an undifferentiated rat pheochromocytoma PC12 cell line and the protective effects of antioxidants. The cells treated with 100 microM NH(2)Cl exhibited signs of apoptotic cell death such as phosphatidylserine exposure and caspase activation. To understand the mechanism of NH(2)Cl cytotoxicity, we examined the effect of various kinds of antioxidants including alpha-tocopherol (alpha-Toc) and beta-tocopherol (beta-Toc). These antioxidants exerted a protective effect against NH(2)Cl-induced cell death, and alpha-Toc exhibited the most potent inhibitory effect among the antioxidants used. A loss of cellular glutathione was observed in the cells treated with 100 microM NH(2)Cl. The formation of reactive oxygen species (ROS) was also measured using the fluorescent probe dichlorofluorescin diacetate. The fluorescence intensity increased prior to cell death and an antioxidant, such as alpha-Toc, suppressed the increase in ROS. Interestingly, beta-Toc also exerted similar inhibitory effects on cytotoxicity and caspase activation. These results suggest that free radical mediated process is involved in NH(2)Cl-induced PC12 cell death and that tocopherols inhibit this cell death via antioxidative function.

Corticotropin-releasing hormone activates protein kinase C in an isoenzyme-specific manner

Protein kinase C (PKC) has recently emerged as mediator of corticotropin-releasing hormone (CRH) effects. Aim of the present study was to study the effects of CRH on each PKC isoenzyme. As a model we have used the PC12 rat pheochromocytoma cell line, expressing the CRH type 1 receptor (CRHR1). Our data were as follows: (a) CRH-induced rapid phosphorylation of conventional PKCalpha and PKCbeta, accompanied by parallel increase of their concentration within nucleus. (b) CRH suppressed the phosphorylation of novel PKCdelta and PKCtheta;, which remained in the cytosol. (c) CRH-induced transient phosphorylation of atypical PKClambda and had no effect on PKCmu. (d) The effect of CRH on each PKC isoenzyme was blocked by a CRHR1 antagonist. (e) Blockade of conventional PKC phosphorylation inhibited CRH-induced calcium ion mobilization from intracellular stores as well as the CRH-induced apoptosis and Fas ligand production. In conclusion, our findings suggest that CRH via its CRHR1 receptor differentially regulates PKC-isoenzyme phosphorylation, an apparently physiologically relevant effect since blockade of conventional PKC phosphorylation abolished the biological effect of CRH.

Corticotropin-releasing hormone potentiates neural injury induced by oxygen-glucose deprivation: a possible involvement of microglia

While corticotropin-releasing hormone (CRH) has been implicated in a variety of brain disorders such as ischemic injury, the molecular mechanism by which CRH elicits its activities is largely unclear. In the present study, we have determined the effect of CRH on oxygen-glucose deprivation (OGD) induced apoptosis in fetal hippocampal neurons. CRH alone at concentrations of 10-200 nM had no effect on neuronal apoptosis. However, when neurons were co-cultured with microglia, CRH alone at concentrations greater than 100 nM induced neuronal apoptosis and CRH potentiated significant neuronal apoptosis following exposure to OGD. The effect of CRH on neuronal apoptosis was inhibited in the presence of the CRH antagonist astressin. Real-time RT-PCR revealed an increase in mRNA levels of Fas ligand (Fas-L), a membrane protein related to the TNF family, in cultured microglia following OGD exposure. In the presence of CRH, OGD-induced Fas-L expression was significantly increased. The effect of CRH on Fas-L expression was inhibited by specific inhibitors of the extracellular signal-regulated protein kinase (PD98059) and p38 mitogen-activated protein kinase (SB203580). These results suggest that CRH potentiates neuronal apoptosis induced by OGD in the presence of microglia and that this effect may be mediated through the induction of proinflammatory mediators in microglia.

Control of programmed cell death by neurotransmitters and neuropeptides in the developing mammalian retina

It has long been known that a barrage of signals from neighboring and connecting cells, as well as components of the extracellular matrix, control cell survival. Given the extensive repertoire of retinal neurotransmitters, neuromodulators and neurotrophic factors, and the exhuberant interconnectivity of retinal interneurons, it is likely that various classes of released neuroactive substances may be involved in the control of sensitivity to retinal cell death. The aim of this article is to review evidence that neurotransmitters and neuropeptides control the sensitivity to programmed cell death in the developing retina. Whereas the best understood mechanism of execution of cell death is that of caspase-mediated apoptosis, current evidence shows that not only there are many parallel pathways to apoptotic cell death, but non-apoptotic programs of execution of cell death are also available, and may be triggered either in isolation or combined with apoptosis. The experimental data show that many upstream signaling pathways can modulate cell death, including those dependent on the second messengers cAMP-PKA, calcium and nitric oxide. Evidence for anterograde neurotrophic control is provided by a variety of models of the central nervous system, and the data reviewed here indicate that an early function of certain neurotransmitters, such as glutamate and dopamine, as well as neuropeptides such as pituitary adenylyl cyclase-activating polypeptide and vasoactive intestinal peptide is the trophic support of cell populations in the developing retina. This may have implications both regarding the mechanisms of retinal organogenesis, as well as pathological conditions leading to retinal dystrophies and to dysfunctional cellular behavior.

Heat shock induces neurite outgrowth in PC12m3 cells via the p38 mitogen-activated protein kinase pathway

We investigated the role of the p38 mitogen-activated protein kinase (MAPK) pathway in heat-shock-induced neurite outgrowth of PC12 mutant cells in which nerve growth factor (NGF)-induced neurite outgrowth is impaired. When cultures of the PC12 mutant (PC12m3) cells were exposed to heat stress at 44 degrees C for 10 min, activity of p38 MAPK increased and neurite outgrowth was greatly enhanced. The neurite extension was inhibited by the p38 MAPK inhibitor BS203580. Longer heat treatment of PC12m3 cells provoked cell death, which was enhanced by SB203580. These findings suggest that heat-induced activation of p38 MAPK is responsible for the neurite outgrowth and survival of PC12m3 cells.

Estrogen exerts neuroprotective effects via membrane estrogen receptors and rapid Akt/NOS activation

The neuroprotective role of estrogen (E2) is supported by a multitude of experimental and epidemiological data, although its mode of action is not fully understood. The present work was conducted to study the underlying mechanisms of its neuroprotective action, using the rat cell line PC12, an established model for neuronal cell apoptosis and survival. Our results show that E2 (but not androgens or progestins) prevent growth inhibition and apoptosis of PC12 cells, induced by serum deprivation. Several mechanisms of action were investigated: 1) intracellular estrogen receptors (ERs) have been identified but do not appear to mediate the protective effect of E2. 2) The antioxidant properties of E2 cannot explain their protective actions at the concentrations used (10(-12)-10(-6) M). 3) Finally, membrane sites for E2 have been identified, and the underlying initial signaling cascade (2-30 min after E2) has been tested, showing Ca(2+) mobilization-->PI3K activation-->Akt phosporylation-->NOS activation. Inhibition of PI3K or NOS completely reversed the anti-apoptotic effect of E2. These results suggest a new mechanism of neuroprotective action of estrogen.

Transcriptional Response to Corticotropin-Releasing Factor in AtT-20 Cells

Corticotropin-releasing factor (CRF) plays a central role in the regulation of the hypothalamic-pituitary-adrenal axis, mediating endocrine and behavioral responses to various stressors. Two high-affinity receptors for CRF have been described. Although many of the intracellular signaling pathways activated by CRF have been studied extensively, our knowledge of transcriptional responses downstream of the CRF receptor 1 (CRFR1) is still limited. To elucidate gene networks regulated by CRF and CRFR1, we applied microarray technology to explore transcriptional response to CRF stimulation. Therefore, mouse pituitary-derived AtT-20 cells were exposed continuously to CRF either in the presence or absence of the specific CRFR1 antagonist R121919. Transcriptional responses to different treatments were studied in a time course ranging from 0.5 to 24 h. Microarray data were analyzed using classic microarray data analysis tools such as correspondence factor analysis, cluster analysis, and fold-change filtering. Furthermore, spectral map analysis was applied, a recently introduced unsupervised multivariate analysis method. A broad and transient transcriptional response to CRF was identified that could be blocked by the antagonist. This way, several known CRF-induced target genes and novel CRF responsive genes were identified. These include transcription factors such as cAMP-responsive element modulator (7x increased), secreted peptides such as cholecystokinin (1.5x), and proteins involved in modulating intracellular signaling, such as regulator of G-protein signaling 2 (11x). Up-regulation of many of these genes can be explained as negative feedback, attenuating CRF-activated pathways. In addition, spectral map analysis proved to be a promising new tool for microarray data analysis.

Dehydroepiandrosterone and allopregnanolone protect sympathoadrenal medulla cells against apoptosis via antiapoptotic Bcl-2 proteins

The neuroactive steroids dehydroepiandrosterone (DHEA), its sulfate ester DHEA sulfate (DHEAS), and allopregnanolone (Allo), produced by the CNS and the adrenals, appear to exert a protective effect in hippocampal and cortical neuron ischemia- and excitotoxicity-induced injury. We hypothesized that they may also play a protective role on the adrenal medulla, an important part of the sympathetic nervous system, and the tissue adjacent to their primary site of production. DHEA, DHEAS, and Allo protected rat chromaffin cells and the rat pheochromocytoma PC12 cell line, an established model for the study of adrenomedullary cell apoptosis and survival, against serum deprivation-induced apoptosis. Their effects were time- and dose-dependent, with EC50 1.8, 1.1, and 1.5 nM, respectively. The antiapoptotic effect of DHEA DHEAS and Allo was compared to that of a long list of structurally related compounds and was found to be structure-specific, confined mainly to conformation 3beta-OH-Delta5 for androstenes and 3alpha-OH for pregnanes. Indeed, 3-keto, Delta4, or C7 hydroxylated androstenes and 3beta pregnanes were ineffective. The prosurvival effect of DHEA(S) and Allo was N-methyl-D-aspartate-, GABAA-, sigma1-, or estrogen receptor-independent. It involved the antiapoptotic Bcl-2 proteins, their role being sine qua non for their action because Bcl-2 antisense oligonucleotides reversed their effects. Finally, DHEA(S) and Allo activated cAMP response element-binding protein and NF-kappaB, upstream effectors of antiapoptotic Bcl-2 protein expression. They also activated the antiapoptotic kinase PKCalpha/beta, a posttranslational activator of Bcl-2 protein. Our findings suggest that decline of DHEA(S) and Allo during aging or stress may leave the adrenal medulla unprotected against proapoptotic challenges.

Induction of p38 mitogen-activated protein kinase-mediated apoptosis is involved in outgrowth of trophoblast cells on endometrial epithelial cells in a model of human trophoblast-endometrial interactions

During embryo implantation in species with hemochorial placentation, such as the mouse and human, trophoblast cells of the attached blastocyst penetrate the luminal epithelium of the endometrium before invasion into the endometrial stroma. Signs of apoptosis were demonstrated in luminal endometrial epithelial cells (EEC) adjacent to the trophoblast cells; however, the signaling mechanisms leading to apoptosis in EEC remain unclear. Because mitogen-activated protein kinases (MAPK) were shown to mediate apoptosis in several model systems and found to be activated in the uterus during decidualization, the possible involvement of MAPK during trophoblast-EEC interactions was studied. By coculturing BeWo human trophoblast spheroids with RL95-2 human EEC monolayers to mimic the blastocyst-endometrial interaction, we found that most spheroids rapidly attached to EEC monolayers and then progressively expanded, with marked dislodgment of EEC adjacent to the spreading trophoblast cells. Immunoblotting analysis showed that both p38 MAPK and extracellular signal-regulated kinase (ERK) were activated in EEC after coculture. However, only SB203580 (a p38 MAPK inhibitor), but not PD98059 (an ERK inhibitor), inhibited trophoblast outgrowth on EEC monolayers through the suppression of p38 MAPK activation in EEC. Furthermore, trophoblast expansion caused prominent EEC apoptosis at the spheroid-EEC interface, as detected by annexin V labeling and valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (which binds activated caspases) staining, and SB203580 significantly decreased the percentage of apoptotic cells. Our results, based on a model of human trophoblast-EEC interactions, establish that trophoblast cells cause activation of p38 MAPK in EEC and, consequently, induce apoptosis and displacement of EEC, a process that may facilitate implantation.

The pharmacology of CP-154,526, a non-peptide antagonist of the CRH1 receptor: a review

Since CRH has been shown to mediate stress-induced physiological and behavioral changes, it has been hypothesized that CRH receptor antagonists may have therapeutic potential in disorders that involve excessive CRH activity. CP-154,526 and its close analog antalarmin are potent, brain-penetrable, selective nonpeptide CRH1 receptor antagonists that were discovered in an effort to develop compounds with efficacy in CNS disorders precipitated by stress. Since its discovery many investigators have used CP-154,526 as a tool to study the pharmacology of CRH and its receptors and to evaluate its therapeutic potential in a variety of CNS and peripheral disorders. Systemically-administered CP-154,526 has been demonstrated to antagonize CRH- and stress-induced neuroendocrine, neurochemical, electrophysiological, and behavioral effects. These findings support the hypothesis that CRH1 receptor antagonists may have therapeutic utility in a number of neuropsychiatric disorders. CP-154,526, as well as other CRH1 receptor antagonists that have since been discovered, have also shown activity in several preclinical models of anxiety, depression, and substance abuse, while having little effect on locomotor activity and motor function. Although these effects are on occasion inconsistent among different laboratories, clinical evaluation of CRH1 antagonists appears justified on the basis of these and clinical data implicating the involvement of CRH in several CNS disorders. The effects of CRH1 antagonists on cognition, neurodegeneration, inflammation, and the gastrointestinal system have not been as extensively characterized and additional studies will be necessary to evaluate their therapeutic potential in these areas.

Corticotropin-releasing factor (CRF) rapidly suppresses apoptosis by acting upstream of the activation of caspases

The physiological role of the corticotropin-releasing factor (CRF) family of peptides has recently been extended by emerging evidence of their cytoprotective effects. To determine whether CRF-mediated cytoprotection is linked to caspase-dependent apoptosis, the effect of CRF on the activation of caspases was investigated in detail in Y79 human retinoblastoma cells. The results presented here demonstrate that the cytoprotective effect of CRF against the actions of camptothecin (CT) was mediated by CRF receptor subtype 1, but not subtype 2. The observed CRF-mediated cytoprotection involved rapid and pronounced suppression of proteolytic processing and activation of procaspase-3, exerted even when CRF was added hours after the application of the cytotoxic agent. Surprisingly, activation of procaspase-3 preceded activation of the initiator procaspases 2, 8, 9 and 10 during CT-induced apoptosis of Y79 cells. The mechanism of the effect of CRF was examined using inhibitors of signalling pathways such as Wortmannin (Akt), cyclic AMP-dependent protein kinase (PKA), extracellular signal-regulated kinase (ERK), protein kinase c (PKC), p38 mitogen-activated protein kinase (p38 MAPK), phospholipase c (PLC), nuclear factor-kappaB (NF-kappaBeta) and c-jun N-terminal kinase (JNK). The involvement of PKA in the mediation of the anti-apoptotic effect of CRF has been established. Taken together, these results demonstrate for the first time that the cytoprotective effect of CRF involved suppression of pro-apoptotic pathways at a site upstream of activation of procaspase-3.

Corticotropin-releasing hormone induces proliferation and TNF-alpha release in cultured rat microglia via MAP kinase signalling pathways

We have previously demonstrated that corticotropin-releasing hormone (CRH) receptor 1 (CRH-R1) is functionally expressed in rat microglia. In the present study, we show that CRH, acting on CRH-R1, promoted cell proliferation and tumour necrosis factor-alpha (TNF-alpha) release in cultured rat microglia. Exogenous CRH resulted in an increase in BrdU incorporation compared with control cells, which was observed in a range of concentrations of CRH between 10 and 500 nm, with a maximal response at 50 nm. The effect of CRH on BrdU incorporation was inhibited by a CRH antagonist astressin but not by a cAMP-dependent protein kinase inhibitor H89. Exposure of microglial cells to CRH resulted in a transient and rapid increase in TNF-alpha release in a dose-dependent manner. In the presence of astressin, the effects of CRH on TNF-alpha release were attenuated. CRH effects on TNF-alpha release were also inhibited by specific inhibitors of MEK, the upstream kinase of the extracellular signal-regulated protein kinase (ERK) (PD98059) or p38 mitogen-activated protein kinase (SB203580), but not by H89. Furthermore, CRH induced rapid phosphorylation of ERK and p38 kinases. Astressin, PD98059, and SB230580 were able to inhibit CRH-induced kinase phosphorylation. These results suggest that CRH induces cell proliferation and TNF-alpha release in cultured microglia via MAP kinase signalling pathways, thereby providing insight into the interactions between CRH and inflammatory mediators.

Functional characteristics of CRH receptors and potential clinical applications of CRH-receptor antagonists

Corticotropin-releasing hormone (CRH) plays a major role in coordinating the behavioral, endocrine, autonomic and immune responses to stress. CRH and CRH-related peptides and their receptors are present in the central nervous system and in a wide variety of peripheral tissues, including the immune, cardiovascular and reproductive systems, and have been associated with the pathophysiology of many disease states. These observations have led to the development of several CRH receptor type-selective antagonists, which have been used experimentally to elucidate the role of CRH and related peptides in physiological and disease processes, such as anxiety and depression, sleep disorders, addictive behavior, inflammatory and allergic disorders, neurological diseases and pre-term labor. Because of the complex network of multiple CRH receptor subtypes and their tissue- and agonist-specific signaling diversity, antagonists need to be developed that can target specific CRH receptor isoform-driven signaling pathways.

Cell detachment triggers p38 mitogen-activated protein kinase-dependent overexpression of Fas ligand. A novel mechanism of Anoikis of intestinal epithelial cells

Many cell types undergo apoptosis when they are detached from the extracellular matrix (ECM). This phenomenon has been termed anoikis. Most epithelial cells, which are normally attached to a type of ECM called basement membrane, are particularly sensitive to anoikis. Conversely, carcinoma cells tend to be resistant to anoikis, and this resistance plays a critical role in tumor invasion and metastasis. We reported previously that detachment-induced down-regulation of the anti-apoptotic molecule Bcl-X(L) makes a significant contribution to anoikis of intestinal epithelial cells. Here we demonstrate that exogenous Bcl-X(L), no matter how highly expressed in these cells, can significantly attenuate anoikis but cannot completely prevent it, suggesting that at least another pro-apoptotic event is activated by the loss of cell-ECM contacts. Indeed, in this study we identified a novel mechanism of anoikis in intestinal epithelial cells that involves detachment-induced overexpression of Fas ligand. We also demonstrated that this elevation in Fas ligand expression requires a detachment-induced increase of p38 mitogen-activated protein kinase activity. We conclude that the activation of at least two different pro-apoptotic events is required for anoikis of intestinal epithelial cells.

Corticotropin-releasing hormone augments proinflammatory cytokine production from macrophages in vitro and in lipopolysaccharide-induced endotoxin shock in mice

Corticotropin-releasing hormone (CRH) exerts an anti-inflammatory effect indirectly, via cortisole production, and a proinflammatory effect directly on immune cells. The aim of the present work was to examine the effect of CRH on macrophage-derived cytokines both in vitro and in vivo. For the in vitro experiments we used two types of macrophages: (i) the RAW264.7 monocyte/macrophage cell line and (ii) thioglycolate-elicited peritoneal macrophages from BALB/c mice. We have found that CRH enhanced lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6 production. For the in vivo experiments we have used the LPS-induced endotoxin shock model in BALB/c mice, an established model for systemic inflammation in which macrophages are the major source of the proinflammatory cytokines responsible for the development of the shock. Administration of antalarmin, a synthetic CRH receptor 1 (CRHR1) antagonist, prior to LPS prolonged survival in a statistically significant manner. The effect was more evident at the early stages of endotoxin shock. CRHR1 blockade suppressed LPS-induced elevation of the macrophage-derived cytokines TNF-alpha, IL-1beta, and IL-6, confirming the role of CRH signals in cytokine expression. In conclusion, our data suggest that CRH signals play an early and crucial role in augmenting LPS-induced proinflammatory cytokine production by macrophages. Our data suggest that the diffuse neuroendocrine system via CRH directly affects the immune system at the level of macrophage activation and cytokine production.