Mechanisms underlying growth hormone effects in augmenting nitric oxide production and protein tyrosine nitration during endotoxin challenge

Repurposed drug agomelatine is therapeutic against collagen-induced arthritis via iNOS targeting

BACKGROUND

The most promising biologics tumor necrosis factor α (TNFα) inhibitors are effective in treating rheumatoid arthritis (RA) in only 50-70 % of the cases; thus, new drugs targeting TNFα-mediated inflammation are required.

METHODS

Firstly, the drugs that could inhibit FLS proliferation and TNFα induced inflammatory cytokine production were screened. Secondly, treatment effects of the identified drugs were screened in collagen-induced arthritis (CIA) mouse model. Thirdly, the inhibitory effect of the identified drug, agomelatine (AOM), on TNFα induced inflammatory cytokine production and NF-κB activity were confirmed. Fourthly, bioinformatics was applied to predict the binding target of AOM and the binding was confirmed, and the already known inhibitor of target was used to test the treatment effect for CIA mouse model. Finally, the effect of AOM on signaling pathway was tested and on TNFα induced inflammatory cytokine production was observed after inhibiting the target.

RESULTS

AOM effectively inhibited TNFα-induced NF-κB activation, NF-κB p65 translocation, and inflammatory cytokines production in vitro and was therapeutic against CIA. The mechanistic study indicated inducible nitric oxide synthase (iNOS) as the binding target of AOM. 1400 W, a known inhibitor of iNOS, could effectively treat CIA by decreasing iNOS activity and the levels of inflammatory cytokines. The inhibitory effect of AOM on TNFα-induced inflammation was further elucidated by 1400 W, or NF-κB p65 inhibitor JSH-23, indicating that AOM is therapeutic against CIA via iNOS/ERK/p65 signaling pathway after binding with iNOS.

CONCLUSIONS

AOM is therapeutic against CIA via inhibition of the iNOS/ERK/p65 signaling pathway after binding with iNOS.

Breed-specific differences in the immune response to lipopolysaccharide in ewes

Innate immune response to a lipopolysaccharide (LPS) challenge varies among sheep breeds. How different breeds respond to bacterial infections impacts management practices of sheep producers. Hence, clinical response, acute-phase response, and gene expression of pro- and anti-inflammatory markers in peripheral white blood cells (WBCs) were examined after an LPS challenge in Dorset and Suffolk ewes. Ewes received either PBS or 2.5 µg/kg LPS (i.v.) 4 to 5 d after onset of synchronized estrus. Blood was collected via jugular venipuncture intermittently for 24 h to determine WBC counts. Rectal temperatures and observations of behavioral/physical appearances were recorded hourly. After LPS, WBCs decreased the first hour (P = 0.0001) and rectal temperatures (P < 0.0001) increased through 4 h; both returned toward normal 6 h after challenge. Suffolk ewes exhibited greater changes in temperature (P = 0.03) and behavioral/physical responses (P < 0.0001) than Dorset ewes and had an enhanced acute-phase response demonstrated by increased concentrations of plasma haptoglobin (P = 0.04), as well as cortisol concentrations (P = 0.03). Real-time PCR was completed on buffy coat homogenates for expression of pro-inflammatory [CXCL8, IL-6, interferon gamma (IFNG), complement component 3 (C3), toll-like receptor 4 (TLR4), prostaglandin synthase 2 (PTGS2)] and anti-inflammatory [IL-10, superoxide dismutase 2 (SOD2), forkhead box P3 (FOXP3), peroxisome proliferator-activated receptor gamma (PPARG), mannose receptor C type 1 (MRC1), transforming growth factor β (TGFβ)] genes. After LPS treatment, gene expressions increased for CXCL8 (P = 0.0003), TLR4 (P = 0.004), SOD2 (P < 0.0001), and C3 (P = 0.003), while PPARG (P = 0.006) and MRC1 (P = 0.003) decreased. Overall, Dorset ewes had greater expression of TLR4 (P = 0.003), IL-10 (P = 0.045), PPARG (P = 0.002), FOXP3 (P = 0.001), and SOD2 (P = 0.0002), whereas Suffolk ewes had greater expression of IL-6 (P = 0.0007), IFNG (P = 0.02), PTGS2 (P = 0.0002), and C3 (P = 0.008). Suffolk ewes also displayed greater expression of IL-6 (P = 0.002) and C3 (P = 0.0004) in response to LPS. In conclusion, differences in gene expression may explain the enhanced inflammatory response in Suffolk ewes and may predispose Suffolk ewes to be more responsive to bacterial infection than Dorset ewes.

Temporal pattern changes in duodenal protein tyrosine nitration events in response to Eimeria acervulina infection in chickens

Intracellular generation of nitric oxide (NO) and superoxide anion (SOA) can result in the formation of 3'-nitrotyrosine proteins (NTp). Nitrated proteins usually are associated with significant perturbation in protein function, apoptosis, autophagy, and cell death. We undertook the present study to establish the temporal dynamics of NTp generation in cytokeratin-18-positive epithelial cells (ETCs) of broiler chickens in response to infection with Eimeria acervulina. Duodenal tissue was harvested from noninfected (NOI) and infected (INF) broilers on days (d) 1, 3, 6, 7, and 10 postinfection (PI) and fixed, embedded, and sectioned for quantitative image analysis, immunohistochemistry with antibodies specific to NTp and the SOA-generating enzyme xanthine oxidase (XO). The pixel density characteristics for NTp and XO representative of ETCs demonstrated that NTp and XO increased in intestinal villi as early as d1 PI (P < 0.05 vs. NOI). Progressive increases in NTp were evident in ETCs through d6 PI. For XO, increases in cell content increased only through d3. On d6 and d7 PI, high levels of NTp were present in immune infiltrating cells (IIC) where no XO was detected. The increases in ETC NTp occurred in a defined pattern, significant by villus-to-crypt location for day of infection, initiating in the distal villus and progressing down into the crypts. Two NTp patterns were observed for ETCs: a high level associated with ETCs harboring parasites and a low-level increase in ETCs not containing Eimeria but in proximity to such. The data suggest that NTp and XO responses may mediate some of the processes through which ETCs respond to Eimeria to limit the extent of infection by this pathogen.

Stress-induced behavioral and metabolic adaptations lead to an obesity-prone phenotype in ewes with elevated cortisol responses

The underlying cause of predisposition to obesity is complex but one marker is cortisol responsiveness. Selection of sheep for high (HR) or low (LR) cortisol responses to adrenocorticotropin shows that HR are more likely to become obese. Increased propensity to obesity is associated with reduced skeletal muscle thermogenesis. We sought to determine whether metabolic or behavioral responses to stress also contribute to altered propensity to obesity in LR and HR. Animals (n=5-10/group) were exposed to 3 stressors and we measured food intake and thermogenesis (recorded with dataloggers implanted into muscle). Stressors were hypoglycaemia (0.125 units/kg insulin, IV), a barking dog and immune challenge (200 ng/kg lipopolysaccharide--LPS, IV). LR animals showed a greater catabolic state in response to both immune and psychosocial stressors. LPS reduced (P<0.01) food intake in both groups but LR showed a greater (P<0.05) reduction in food intake and a more substantial (P<0.05) rise in muscle temperature. Introduction of the barking dog reduced (P<0.05) food intake in LR only. These metabolic differences coincided with differences in cortisol responsiveness, where HR animals had increased (P<0.05) cortisol in response to both immune and psychosocial stressors. We also assessed behavior in the following paradigms: 1, isolation in the open field test; 2, response to a human intruder; and 3, food competition. LR had greater (P<0.05) activity, reduced fearfulness and displayed a proactive coping style of behavior. Thus we demonstrate that high cortisol responsiveness identifies animals with stress-induced metabolic and behavioral traits that may contribute to susceptibility to obesity.

Improvement of lipopolysaccharide-induced hepatic injuries and inflammation with mulberry extracts

BACKGROUND

Mulberry water extracts (MWEs), which contain polyphenols including anthocyanins, have been used in traditional Chinese edible food. The hepatoprotective effects and molecular mechanisms of MWEs on acute liver failure induced by lipopolysaccharides (LPS) were investigated in vivo.

RESULTS

Rats were administered different doses of MWEs (0.5 and 1 g kg(-1)) 1 h before injection of LPS (5 mg kg(-1)) and then sacrificed 10 h after treatment with LPS. Liver function, inflammatory factors, oxidative stress index and hepatic histopathological alteration were examined in the rats with and without MWE treatment. Pretreatment with MWEs prevented LPS-induced liver damage by preventing associated increases of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALKP), triglycerol (TG), cholesterol and low-density lipoprotein/high-density lipoprotein ratio. MWEs also suppressed oxidative stress to prevent the formation of hepatic malondialdehyde (MDA). Furthermore, the molecular mechanism involved in LPS-induced liver injury was associated with reducing the expression of COX-2, NF-κB and iNOS in liver tissues.

CONCLUSION

The results support the investigation of MWEs as a therapeutic candidate for liver injuries and indicate that MWEs exhibit hepatoprotective activities via NF-κB signaling.

Effects of stress on endocrine and metabolic processes and redirection: cross talk between subcellular compartments

Recent advances in genome analysis and biochemical pathway mapping have advanced our understanding of how biological systems have evolved over time. Protein and DNA marker comparisons suggest that several of these systems are both ancient in origin but highly conserved into today's evolved species. However, remnants of some of the more ancient functions of these chemical systems can run in conflict with the functions that those same pathways serve in complex organisms and tissue systems today. Relevant to the present topic, nitric oxide (NO) and superoxide anion (O(2)(•-)), ancient cellular molecules in evolutionary terms, are recognized today as both necessary for the well-being and stable health of cells but also injurious to cells as elaborated in conjunction with the cellular stress response. Why the dichotomy? This question underlies one of the basic issues challenging researchers as well as practitioners in their approach to disease management. The fundamental proinflammatory response of the innate immune system of the host is needed for pathogen control but can be injurious to tissues from "collateral damage" from NO- and O(2)(•-)-derived reactive molecules capable of affecting protein function via post-translational chemical modification. This review highlights newer aspects of the biochemistry of the NO- and O(2)(•-)-mediated innate proinflammatory response and further show how protein and tissue damage via overproduction of reactive nitrogen and oxygen intermediary molecules such as peroxynitrite (ONOO(-)) might be targeted to specific epitopes of proteins. Changes in the regulation of metabolism in response to proinflammatory disease states are discussed for GH signal transduction and tissue specificity.

Hormonal causes of male sexual dysfunctions and their management (hyperprolactinemia, thyroid disorders, GH disorders, and DHEA)

INTRODUCTION

Besides hypogonadism, other endocrine disorders have been associated with male sexual dysfunction (MSD).

AIM

To review the role of the pituitary hormone prolactin (PRL), growth hormone (GH), thyroid hormones, and adrenal androgens in MSD.

METHODS

A systematic search of published evidence was performed using Medline (1969 to September 2011). Oxford Centre for Evidence-Based Medicine-Levels of Evidence (March 2009) was applied when possible.

MAIN OUTCOME MEASURES

The most important evidence regarding the role played by PRL, GH, thyroid, and adrenal hormone was reviewed and discussed.

RESULTS

Only severe hyperprolactinemia (>35 ng/mL or 735 mU/L), often related to a pituitary tumor, has a negative impact on sexual function, impairing sexual desire, testosterone production, and, through the latter, erectile function due to a dual effect: mass effect and PRL-induced suppression on gonadotropin secretion. The latter is PRL-level dependent. Emerging evidence indicates that hyperthyroidism is associated with an increased risk of premature ejaculation and might also be associated with erectile dysfunction (ED), whereas hypothyroidism mainly affects sexual desire and impairs the ejaculatory reflex. However, the real incidence of thyroid dysfunction in subjects with sexual problems needs to be evaluated. Prevalence of ED and decreased libido increase in acromegalic patients; however, it is still a matter of debate whether GH excess (acromegaly) may create effects due to a direct overproduction of GH/insulin-like growth factor 1 or because of the pituitary mass effects on gonadotropic cells, resulting in hypogonadism. Finally, although dehydroepiandrosterone (DHEA) and its sulfate have been implicated in a broad range of biological derangements, controlled trials have shown that DHEA administration is not useful for improving male sexual function.

CONCLUSIONS

While the association between hyperprolactinemia and hypoactive sexual desire is well defined, more studies are needed to completely understand the role of other hormones in regulating male sexual functioning.

Lipopolysaccharide-induced hepatic oxidative injury is not potentiated by knockout of GPX1 and SOD1 in mice

Knockout of copper, zinc-superoxide dismutase (SOD1) and (or) cellular glutathione peroxidase (GPX1) has been reported to have dual impacts on coping with free radical-induced oxidative injury. Because bacterial endotoxin lipopolysaccharide (LPS) triggers inflammatory responses involving the release of cytokines, nitric oxide and superoxide in targeted organs such as liver, in this study we used SOD1 knockout (SOD1-/-), GPX1 knockout (GPX1-/-), GPX1 and SOD1 double-knockout (DKO) and their wild-type (WT) mice to investigate the role of these two antioxidant enzymes in LPS-induced oxidative injury in liver. Mice of the four genotypes (2 month old) were killed at 0, 3, 6 or 12 h after an i.p. injection of saline or 5 mg LPS/kg body weight. The LPS injection caused similar increase in plasma alanine aminotransferase among the four genotypes. Hepatic total glutathione (GSH) was decreased (P<0.05) compared with the initial values by the LPS injection at all time points in the WT mice, but only at 6 and 12 h in the other three genotypes. The GSH level in the DKO mice was higher (P<0.05) than in the WT at 6 h. Although the LPS injection resulted in substantial increases in plasma NO in a time-dependent manner in all genotypes, the NO level in the DKO mice was lower (P<0.05) at 3, 6 and 12 h than in the WT. The level in the GPX1-/- and SOD1-/- mice was also lower (P<0.05) than in the WT at 3 h. The LPS-mediated hepatic protein nitration was detected in the WT and GPX1-/- mice at 3, 6 or 12 h, but not in the SOD1-/-. In conclusion, knockout of SOD1 and (or) GPX1 did not potentiate the LPS-induced liver injury, but delayed the induced hepatic GSH depletion and plasma NO production.

AKT/eNOS signaling module functions as a potential feedback loop in the growth hormone signaling pathway

Background

While evidence suggested that the activity states of Protein kinase B (AKT/PKB) and endothelial nitric oxide synthase (eNOS) play an important role in the progression of the Growth Hormone (GH) signal cascade, the implication of the activation of AKT/PKB and eNOS in terms of their function in the signaling pathway was not clear.

Results

Using a specific AKT/PKB inhibitor and a functional proteomic approach, we were able to detect the activities of multiple signal transduction pathway elements, the downstream targets of the AKT/PKB pathway and the modification of those responses by treatment with GH. Inhibiting the AKT/PKB activity reduced or eliminated the activation (phosphorylation) of eNOS. We demonstrated that the progression of the GH signal cascade is influenced by the activity status of AKT and eNOS, wherein the suppression of AKT activity appears to augment the activity of extracellular signal-regulated kinases 1 and 2 (Erk1/2) and to antagonize the deactivation (phosphorylation) of cyclin-dependent kinase 2 (CDC2/Cdk1) induced by GH. Phosphorylation of GSK3a/b (glycogen synthase kinase 3), the downstream target of AKT/PKB, was inhibited by the AKT/PKB inhibitor. GH did not increase phosphorylation of ribosomal S6 kinase 1 (RSK1) in normal cells but increases phosphorylation of RSK1 in cells pre-treated with the AKT and eNOS inhibitors.

Conclusion

The MAP kinase and CDC2 kinase-dependent intracellular mechanisms are involved in or are the targets of the GH's action processes, and these activities are probably directly or indirectly modulated by AKT/PKB pathways. We propose that the AKT/PKB-eNOS module likely functions as a negative feedback mediator of GH actions.

Plasma 3-nitrotyrosine is a biomarker in animal models of arthritis: Pharmacological dissection of iNOS' role in disease

The contribution of inducible nitric oxide synthase (iNOS) to oxidative/nitrative stress is well-documented in inflammation, but difficult to quantify. Using a novel, recently developed assay for 3-nitrotyrosine (3-NT), we characterized iNOS activity and its inhibition in preclinical models of inflammation. In particular, we utilized the 3-NT assay to assess the role of iNOS in the disease pathology as well as for proof of pharmacology of iNOS inhibitors in an acute endotoxin challenge model, in models of rheumatoid arthritis (RA) such as rat adjuvant- and collagen-induced arthritis (AIA and CIA) and a model of osteoarthritis (OA) such as rat sodium monoiodoacetate-induced arthritis (MIA). Quantification of nitrotyrosine was performed using immuno-affinity 2-D LC-MS/MS assay. This assay is a very specific and reproducible and is amenable to a number of biological fluids. Plasma levels of 3-NT were significantly elevated in an acute model of inflammation (rat LPS) and in models of rheumatoid arthritis (adjuvant- and collagen-induced arthritis), and osteoarthritis (monoiodoacetate-induced arthritis). Plasma 3-NT correlated with the severity of the inflammatory response; thus, a 20-fold increase was observed in the rat LPS model, a 10-fold increase in AIA, and only a 2.5-fold elevation in CIA. Pharmacological intervention with iNOS inhibitors decreased 3-NT levels and associated pathology. 3-NT determination allowed for better elucidation of the role of iNOS in RA and OA disease pathology and provided proof of pharmacology for NOS inhibitors in animal models of RA and OA.

Comparative aspects of the endotoxin- and cytokine-induced endocrine cascade influencing neuroendocrine control of growth and reproduction in farm animals

Disease in animals is a well-known inhibitor of growth and reproduction. Earlier studies were initiated to determine the effects of endotoxin on pituitary hormone secretion. These studies found that in sheep, growth hormone (GH) concentration was elevated, whereas insulin-like growth factor-I (IGF-I) was inhibited, as was luteinizing hormone (LH). Examination of the site of action of endotoxin in sheep determined that somatotropes expressed the endotoxin receptor (CD14) and that both endotoxin and interleukin-I beta activated GH secretion directly from the pituitary. In the face of elevated GH, there is a reduction of IGF-I in all species examined. As GH cannot activate IGF-I release during disease, there appears to be a downregulation of GH signalling at the liver, perhaps related to altered nitration of Janus kinase (JAK). In contrast to GH downregulation, LH release is inhibited at the level of the hypothalamus. New insights have been gained in determining the mechanisms by which disease perturbs growth and reproduction, particularly with regard to nitration of critical control pathways, with this perhaps serving as a novel mechanism central to lipopolysaccharide suppression of all signalling pathways. This pathway-based analysis is critical to the developing novel strategies to reverse the detrimental effect of disease on animal production.

Role of copper,zinc-superoxide dismutase in catalyzing nitrotyrosine formation in murine liver

The only known function of Cu,Zn-superoxide dismutase (SOD1) is to catalyze the dismutation of superoxide anion into hydrogen peroxide. Our objective was to determine if SOD1 catalyzes murine liver protein nitration induced by acetaminophen (APAP) and lipopolysaccharide (LPS). Liver and plasma samples were collected from young adult SOD1 knockout mice (SOD1-/-) and wild-type (WT) mice at 5 or 6 h after an ip injection of saline, APAP, or LPS. Hepatic nitrotyrosine formation was induced by APAP and LPS only in the WT mice. The diminished hepatic protein nitration in the SOD1-/- mice was not directly related to plasma nitrite and nitrate concentrations. Similar genotype differences were seen in liver homogenates treated with a bolus of peroxynitrite. Adding only the holo-, and not the apo-, SOD1 enzyme into the liver homogenates enhanced the reaction in an activity-dependent fashion and nearly eliminated the genotype difference at the high doses. Mass spectrometry showed four more nitrotyrosine residues in bovine serum albumin and 10 more nitrated protein candidates in the SOD1-/- liver homogenates by peroxynitrite with added SOD1. In conclusion, the diminished hepatic protein nitration mediated by APAP or LPS in the SOD1-/- mice is due to the lack of SOD1 activity per se.

Modeling growth factor activity during proinflammatory stress: methodological considerations in assessing cytokine modulation of IGF binding proteins released by cultured bovine kidney epithelial cells

The present research was conducted to model potential mechanisms through which IGFBPs might be affected by a key proinflammatory response initiating cytokine tumor necrosis factor (TNF-)-alpha. Madin-Darby bovine kidney epithelial (MDBK) cells, known to release IGFBPs in response to several stimuli, were grown under several conditions and challenged with forskolin (F) or recombinant TNF-alpha for 24h. Forskolin increased IGFBP-3 gene expression and media content of BP-3 protein. TNF-alpha increased basal and augmented F-mediated IGFBP-3 gene expression. However, TNF-alpha effects on the measurable media content of IGFBPs were influenced by culture conditions; in the absence of added protease inhibitors (PIs) or sufficient media albumin concentration (high BSA, 1mg/ml), the effect of TNF-alpha was to decrease (P<0.02) measurable IGFBPs. In the presence of PI and high BSA, media IGFBP-3 levels were shown to be increased by TNF-alpha consistent with the gene expression data. Changes in media IGFBP-3 protease activity were examined further to explain the observed effects of TNF-alpha on production and destruction of IGFBPs in media. When recombinant human IGFBP-3 (500 ng/ml) was added to PI-free, low BSA 100 microg/ml) media from TNF-treated MDBK cells, less than 10% of the BP-3 was recognizable by Western blot in 30 min; conversely, inclusion of High BSA and PI in media resulted in attenuation of the protease effect on the IGFBPs. The data suggest that the MDBK model of cellular response to proinflammatory stimulus is affected by culture conditions and that TNF-alpha affects media content of IGFBPs through effects on IGFBP gene expression coupled with degradation of IGFBPs via enhanced proteolytic enzyme release.

Insulin-like growth factor type-1 receptor down-regulation associated with dwarfism in Holstein calves

Perturbations in endocrine functions can impact normal growth. Endocrine traits were studied in three dwarf calves exhibiting retarded but proportionate growth and four phenotypically normal half-siblings, sired by the same bull, and four unrelated control calves. Plasma 3,5,3'-triiodothyronine and thyroxine concentrations in dwarfs and half-siblings were in the physiological range and responded normally to injected thyroid-releasing hormone. Plasma glucagon concentrations were different (dwarfs, controls>half-siblings; P<0.05). Plasma growth hormone (GH), insulin-like growth factor-1 (IGF-1) and insulin concentrations in the three groups during an 8-h period were similar, but integrated GH concentrations (areas under concentration curves) were different (dwarfs>controls, P<0.02; half-siblings>controls, P=0.08). Responses of GH to xylazine and to a GH-releasing-factor analogue were similar in dwarfs and half-siblings. Relative gene expression of IGF-1, IGF-2, GH receptor (GHR), insulin receptor, IGF-1 type-1 and -2 receptors (IGF-1R, IGF-2R), and IGF binding proteins were measured in liver and anconeus muscle. GHR mRNA levels were different in liver (dwarfs<controls, P<0.002; dwarfs<half-siblings, P=0.06; half-siblings<controls, P=0.08) but not in muscle. IGF-1R mRNA abundance in liver in half-siblings and controls was 2.4- and 2.5-fold higher (P=0.003 and P=0.001, respectively) and in muscle tissue was 2.3- and 1.8-fold higher (P=0.01 and P=0.08, respectively) than in dwarfs. Hepatic IGF-1R protein levels (Western blots) in muscle were 2.5-fold higher (P<0.05) and in liver and muscle (quantitative immunohistochemistry) were higher (P<0.02 and P<0.07, respectively) in half-siblings than in dwarfs. The reduced presence of IGF-1R may have been the underlying cause of dwarfism in studied calves.

Morphometric analysis of proinflammatory cytokines in mammary glands of sows suggests an association between clinical mastitis and local production of IL-1beta, IL-6 and TNF-alpha

Twelve healthy primiparous sows received intramammary inoculation with Escherichia coli (serotype O127) during the 24-h period preceding parturition. Mammary gland biopsy samples were taken immediately before inoculation (0 h) and from the inoculated and the contralateral non-inoculated glands 24 h after inoculation. The analyses of interleukin-1 beta (IL-1beta), IL-6, IL-8, and tumor necrosis factor alpha (TNF-alpha) by immunohistochemistry revealed that the production of these proinflammatory cytokines significantly increased in the inoculated mammary glands of sows that developed clinical signs of mastitis (affected group, n=4) 24 h after inoculation. This was also true for IL-8 in the inoculated mammary glands of sows that did not develop clinical signs of mastitis (nonaffected group, n=8). Sows that developed clinical signs of mastitis displayed significantly lower constitutive production of IL-1beta than did sows that remained clinically healthy. The data indicate that the development of clinical symptoms of coliform mastitis in the sow is associated with a locally increased proinflammatory cytokine production in response to intramammary E. coli infection.

Growth hormone (GH)-associated nitration of Janus kinase-2 at the 1007Y-1008Y epitope impedes phosphorylation at this site: mechanism for and impact of a GH, AKT, and nitric oxide synthase axis on GH signal transduction

A generalized increase in liver protein tyrosine nitration (3'-nitrotyrosine, 3'-NT) occurs after GH injection in a time frame consistent with observed acute GH hyporesponsiveness. Here we investigated whether the GH-associated nitration process might be targeted to the (1007)Y-(1008)Y-phosphorylation epitope of Janus kinase (JAK)-2 because of its homology to a defined peptide nitration motif. Using antibodies we developed to the 3'NT-substituted peptide analog of the (1007)Y-(1008)Y-JAK2 site (nitro-JAK2), we demonstrated a rapid increase in membrane-associated nitro-JAK2 after GH. In vivo (bovine liver) and in vitro (porcine hepatocytes), GH-induced cellular levels of nitro-(1007)Y-(1008)Y-JAK2 persisted significantly longer after a stimulatory GH pulse than did levels of phospho-JAK2. Treatment of cultured cells with inhibitors of AKT or endothelial nitric oxide synthase prior to GH challenge attenuated the increases in nitro-JAK2 predominantly in the membrane subcellular fraction. In instances in which GH effected orthophosphorylation of (694)Y-signal transducer and activator of transcription (STAT)-5b, the addition of AKT and endothelial nitric oxide synthase inhibitors prior to GH significantly increased the levels of phospho-(694)Y-STAT5b and phospho-(1007)Y-JAK2 over those arising from GH alone. Nuclear magnetic resonance molecular modeling of natural and 3'-NT- and orthophosphate-substituted peptide analogs of the (1007)Y-(1008)Y site demonstrated significant effects of 3'-nitration on the planar orientation and intramolecular stabilizing points of the affected tyrosines. When these peptides were used as substrates for in vitro tyrosine kinase phosphorylation reactions, 3'-NT in the (1007)Y and/or (1008)Y positions blocked the generation of (1007)Y-phosphotyrosine. The data suggest that the nitration of JAK2 may act as an inhibitory counterpart to phosphorylation activation, reflecting a very localized break on the progression of GH signal transduction processes spanning JAK-STAT-AKT interactions.

Caveolae nitration of Janus kinase-2 at the 1007Y-1008Y site: coordinating inflammatory response and metabolic hormone readjustment within the somatotropic axis

Life-threatening proinflammatory response (PR) induces severe GH resistance. Although low-level PR is much more commonly encountered clinically, relatively few studies have investigated the accompanying change in GH signal transduction progression and, in particular, the impact of low-level PR on Janus kinase (JAK)-2. Using a low-level, in vivo endotoxin [lipopolysaccharide (LPS)] challenge protocol, we demonstrated that the liver tissue content of JAK2 declined 24 h (62%, P < 0.02) after LPS and that tyrosine-nitrated JAK2 could be immunoprecipitated from post-LPS liver biopsy homogenates. With antibodies developed to probe specifically for nitration at the (1007)Y-(1008)Y phosphorylation epitope of JAK2, we demonstrated that the nitrated (1007)Y-(1008)Y-JAK-2 (nitro-JAK2) coimmunoprecipitated with caveolin-1 and (1177)phospho-SER-endothelial nitric oxide synthase when post-LPS liver homogenates were treated with anticaveolin-1 and protein A/G. The magnitude of increase in nitro-JAK2 was attenuated in animals treated with vitamin E prior to LPS. The increase in nitro-JAK2 after LPS was greater in a line of experimental animals with a genetic propensity for higher PR at the given LPS dose than responses measured in their normal counterparts. The development and remission of nitro-JAK2 was temporally concordant with changes in plasma concentrations of IGF-I; hepatocellular IGF-I mRNA content was inversely proportional to nitro-JAK2 content. Localized changes in the state of nitration of regulatory phosphorylation domains of JAK2 in caveolar microenvironments and tissue content of JAK2 during PR suggest a unique mechanism through which discrete signal transduction switching might occur in the liver to fine tune cellular responses to the endocrine-immune signals that develop during low-level, transient proinflammatory stress.

Nitric oxide mediates prostaglandins' deleterious effect on lipopolysaccharide-triggered murine fetal resorption

Genital tract bacterial infections could induce abortion and are some of the most common complications of pregnancy; however, the mechanisms remain unclear. We investigated the role of prostaglandins (PGs) in the mechanism of bacterial lipopolysaccharide (LPS)-induced pregnancy loss in a mouse model, and we hypothesized that PGs might play a central role in this action. LPS increased PG production in the uterus and decidua from early pregnant mice and stimulated cyclooxygenase (COX)-II mRNA and protein expression in the decidua but not in the uterus. We also observed that COX inhibitors prevented embryonic resorption (ER). To study the possible interaction between nitric oxide (NO) and PGs, we administered aminoguanidine, an inducible NO synthase inhibitor. NO inhibited basal PGE and PGF(2alpha) production in the decidua but activated their uterine synthesis and COX-II mRNA expression under septic conditions. A NO donor (S-nitroso-N-acetylpenicillamine) produced 100% ER and increased PG levels in the uterus and decidua. LPS-stimulated protein nitration was higher in the uterus than in the decidua. Quercetin, a peroxynitrite scavenger, did not reverse LPS-induced ER. Our results suggest that in a model of septic abortion characterized by increased PG levels, NO might nitrate and thus inhibit COX catalytic activity. ER prevention by COX inhibitors adds a possible clinical application to early pregnancy complications due to infections.

Adrenomedullin (AM) and adrenomedullin binding protein (AM-BP) in the bovine mammary gland and milk: Effects of stage of lactation and experimental intramammary E. coli infection

Adrenomedullin (AM) has been characterized as an endogenous tissue survival factor and modulator of many inflammatory processes. Because of the increased susceptibility of the mammary gland to infection during the time surrounding parturition in the cow, we investigated how milk and tissue content of AM and its binding protein (AM-BP) might be affected by the stage of lactation and the udder health status. Milk and mammary biopsy samples were obtained from Holstein cows 21 days prior to and at various times after calving to represent the dry period and early and mid-stages of lactation. Additional cows received an intramammary challenge with Escherichia coli for immunohistochemical characterization of AM and AM-BP. Milk AM concentrations were relatively constant across the stages of lactation while AM-BP increased two-fold (P<0.04) between early and mid-lactation. Milk AM (P<0.04) and AM-BP (P<0.03) increased as somatic cell counts (SCCs) increased within a given stage of lactation. Tissue content of both (AM and AM-BP) were significantly affected by stage of lactation, lowest in the dry period and progressively increasing to peak at mid-lactation as well as increasing in association with higher levels of SCCs. Following E. coli challenge, AM increased in epithelial cells surrounding mammary alveoli presenting high levels of SCCs. The data suggest that AM and AM-BP are cooperatively regulated in the mammary gland during lactation; changes in localized tissue AM and AM-BP content reflect a dynamic regulation of these tissue factors in the bovine mammary gland consistent with their protective effects within inflamed tissue.

Temporal response of liver signal transduction elements during in vivo endotoxin challenge in cattle: effects of growth hormone treatment

We quantified the changes in abundance of inducible nitric oxide synthase (iNOS) and associated tissue signal transduction pathway elements (STPEs) in the bovine liver in response to lipopolysaccharide (LPS) challenge and further assessed the impact on the LPS-driven variable responses as affected by daily treatment with recombinant growth hormone (GH) prior to LPS challenge. Twenty-four cross-bred beef steers were divided into GH-treated (recombinant bovine GH, Monsanto Inc., St. Louis, MO; 0.1mg/kg BW, i.m., daily for 12 days) and non-GH-treatment (control) groups (n=12/group). Liver biopsy samples were obtained from all animals at 0, 3, 6, and 24h after LPS challenge (E. coli 055:B5, 2.5 microg/kg BW, i.v. bolus) for Western blot analyses of iNOS and STPEs. In response to LPS, tissue levels of iNOS increased significantly (P<0.001) in the first 3h and persisted at levels greater than those at time 0 until 24h. GH further augmented levels of iNOS at 0, 3, and 6h resulting in an overall significant increase in the iNOS protein level (P<0.01). AKT/protein kinase B (AKT/PKB) phosphorylation levels at time 0 were not different between GH-treated and control animals; LPS increased the phosphorylation of AKT/PKB with GH treatment stimulating a four-fold further increase of AKT/PKB phosphorylation. Effects similar to those on AKT/PKB were also observed on signal transducer and activator of transcription 5b (STAT5b). The family of mitogen-activated protein kinase (MAPK) showed different pattern of response. ERK1/2 phosphorylation increased 3h after LPS challenge but only in GH-treated group (P<0.01). Compared to 0 h, SAPK/JUN phosphorylation increased in both experimental groups 3, 6h (P<0.01), and 24h (P<0.05) after LPS. However, at 3h the increase was greater (P<0.01) in GH-treated than in control animals. No effect of LPS challenge or GH treatment on p38(MAPK) was observed. These results suggest that GH treatment has a significant impact on the differential activation of STPEs in the clinical response to LPS.

Interleukin-1beta and tumor necrosis factor-alpha mediation of endotoxin action on growth hormone

In humans and sheep, endotoxin (LPS) administration results in increased growth hormone (GH) concentrations. To determine the role of cytokines in the effect of LPS on GH, sheep were challenged with IL-1beta or TNF-alpha. GH data were compared with results with LH, where the major effects of LPS are known to act via the hypothalamus. Intracerebroventricular (icv) administration of IL-1beta or TNF-alpha did not alter plasma concentrations of GH. Endotoxin was then administered intravenously (iv) in combination with icv injection of IL-1 receptor antagonist (IL-1RA), TNF antagonist (sTNF-R1), or saline. Administration of LPS increased GH (P < 0.0001), although coadministration of IL-1ra or sTNF-R1 icv did not alter GH response to LPS. In contrast, plasma concentrations of LH were profoundly inhibited by icv administration of either cytokine (P < 0.03), but the LH response to LPS was not altered by cytokine antagonists. Intravenous administration of either IL-1beta or TNF-alpha increased plasma concentrations of GH (P < 0.0001). Administration of IL-1RA and sTNF-R1 iv prevented LPS-induced increases in GH. Although LH was suppressed by high iv doses of IL-1beta (P = 0.0063), the antagonists did not alter the LH response to LPS. To determine whether LPS might directly activate GH release, confocal microscopy revealed colocalization of CD14, the LPS receptor, with GH and, to a lesser extent, LH and some prolactin (PRL)-containing cells, but not ACTH or TSH. These data are consistent with the effects of LPS on GH secretion originating through peripheral cytokine presentation to the pituitary, as well as a potential to act directly on selective populations of pituitary cells via CD14.

Characterization of calves exhibiting a novel inheritable TNF-α hyperresponsiveness to endotoxin: associations with increased pathophysiological complications

A subpopulation of calves, herein termed “hyperresponders” (HPR), was identified and defined by the patterns of plasma TNF-α concentrations that developed following two challenges with endotoxin (LPS, 0.8 μg Escherichia coli 055:B5 LPS/kg0.75live body wt) separated by 5 days. The principle characteristic of HPR calves was a failure to develop tolerance to repeated LPS challenge that was evident in the magnitude of the TNF-α concentrations and prolonged severity of pathological sequellae. Whereas calves failing to develop LPS tolerance were identified on the basis of their excessive in vivo plasma TNF-α concentration responses, in vitro TNF-α responses of peripheral blood mononuclear cells isolated from each calf and challenged with LPS or PMA did not correlate or predict the magnitude of in vivo plasma TNF response of the calf. Intentional breeding to obtain calves from bulls and/or cows documented as HPR resulted in offspring displaying the HPR character when similar progeny calves were tested with LPS in vivo, with extensive controls in place to account for sources of variability in the general TNF-α response to LPS that might compromise interpretation of the data. Feed intake, clinical serology and hematology profiles, and acute-phase protein responses of HPR calves following LPS were significantly different from those of calves displaying tolerance. These results suggest that the pattern of plasma TNF-α changes that evolve from a low-level double LPS challenge effectively reveal the presence of a genetic potential for animals to display excessive or prolonged pathological response to LPS-related stress and compromised prognosis for recovery.