Tumor necrosis factor and interleukin-1 down-regulate receptors for substance P in human astrocytoma cells

TNF-α evokes blood-brain barrier dysfunction through activation of Rho-kinase and neurokinin 1 receptor

Ischaemic stroke, accompanied by neuroinflammation, impairs blood-brain barrier (BBB) integrity through a complex mechanism involving activation of both RhoA/Rho kinase/myosin light chain-2 and neurokinin 1 receptor (NK1R). Using an in vitro model of human BBB composed of brain microvascular endothelial cells (BMEC), astrocytes and pericytes, this study examined the potential contributions of these elements to BBB damage induced by elevated availability of pro-inflammatory cytokine, TNF-α. Treatment of human BMECs with TNF-α significantly enhanced RhoA activity and the protein expressions of Rho kinase and phosphorylated Ser19MLC-2 while decreasing that of NK1R. Pharmacological inhibition of Rho kinase by Y-27632 and NK1R by CP96345 neutralised the disruptive effects of TNF-α on BBB integrity and function as ascertained by reversal of decreases in transendothelial electrical resistance and increases in paracellular flux of low molecular weight permeability marker, sodium fluorescein, respectively. Suppression of RhoA activation, mitigation of actin stress fibre formation and restoration of plasma membrane localisation of tight junction protein zonula occludens-1 appeared to contribute to the barrier-protective effects of both Y-27632 and CP96345. Attenuation of TNF-α-mediated increases in NK1R protein expression in BMEC by Y-27632 suggests that RhoA/Rho kinase pathway acts upstream to NK1R. In conclusion, specific inhibition of Rho kinase in cerebrovascular conditions, accompanied by excessive release of pro-inflammatory cytokine TNF-α, helps preserve endothelial cell morphology and inter-endothelial cell barrier formation and may serve as an important therapeutic target.

Co-regulated decrease of Neurokinin-1 receptor and Hemokinin-1 gene expression in monocytes and macrophages after activation with pro-inflammatory cytokines

Hemokinin-1 (HK-1), a potent ligand for the Neurokinin-1 receptor (NK-1) is thought to play a role in the immune system. To investigate the regulation of this receptor-ligand pair, we examined the effects of pro-inflammatory cytokines on their expression in the monocyte/macrophage cell lines Wehi-3 and RAW264.7. We demonstrate co-expression of NK-1 and HK-1 mRNA in both lines, as well as functional NK-1 receptor protein in Wehi-3 cells. Stimulation with IFN-gamma, IL-1beta and TNF-alpha markedly decreased NK-1 and HK-1 mRNA as well as NK-1 receptor protein, which coincided with monocytic differentiation. A co-regulated decrease could also be observed in differentiating primary bone marrow macrophages, suggesting that this receptor-ligand pair may be controlled by cytokine networks and may serve a developmental role in the immune system.

Interleukin-1beta upregulates functional expression of neurokinin-1 receptor (NK-1R) via NF-kappaB in astrocytes

Cytokines and neuropeptides are modulators of neuroimmunoregulation in the central nervous system (CNS). The interaction of these modulators may have important implications in CNS diseases. We investigated whether interleukin-1beta (IL-1beta) modulates the expression of neurokinin-1 receptor (NK-1R), the primary receptor for substance P (SP), a potent neuropeptide in the CNS. IL-1beta upregulated NK-1R expression in human astroglioma cells (U87 MG) and primary rat astrocytes at both mRNA and protein levels. IL-1beta treatment of U87 MG cells and primary rat astrocytes led to an increase in cytosolic Ca(2+) in response to SP stimulation, indicating that IL-1beta-induced NK-1R is functional. CP-96,345, a specific non-peptide NK-1R antagonist, inhibited SP-induced rise of [Ca(2+)](i) in the astroglioma cells. Investigation of the mechanism responsible for IL-1beta action revealed that IL-1beta has the ability of activating nuclear factor-kappab (NF-kappaB). Caffeic acid phenethyl ester (CAPE), a specific inhibitor of NF-kappaB activation, not only abrogated IL-1beta-induced NF-kappaB promoter activation, but also blocked IL-1beta-mediated induction of NK-1R gene expression. These findings provide additional evidence that there is a biological interaction between IL-1beta and the neuropeptide SP in the CNS, which may have important implications in the inflammatory diseases in the CNS.

Decreases in neurokinin-3 tachykinin receptor-immunoreactive and -mRNA levels are associated with salt appetite in the deoxycorticosterone-treated rat

Tachykinins are a family of neuropeptides that inhibit salt appetite. Although decreased tachykinin-mRNA levels are observed in natriorexic sodium-deplete rats, no decrease is seen in natriorexic sodium-replete rats that are administered the aldosterone-mimetic deoxycorticosterone acetate (DOCA). Since reduced synthesis of tachykinins could not account for increased appetite, we hypothesized that increased salt appetite was due to a downregulation of tachykinin receptors. Thus, we injected rats with DOCA once daily for 11 days and analyzed tachykinin receptor subtype, neurokinin 3 (NK3r)-immunoreactivity by Western blot analysis since intracerebroventricular injection of senktide (NK3r agonist) attenuates salt intake in DOCA-treated animals. We examined NK3r-immunoreactivity in several brain regions thought to be associated with the control of water and electrolyte balance including the bed nucleus of the stria terminalis, central nucleus of the amygdala, diagonal band of Broca, hippocampus, nucleus tractus solitarius, parabrachial nucleus, paraventricular nucleus of the hypothalamus, and supraoptic nucleus. Consistent with our hypothesis, we found decreased NK3r-immunoreactivity in all brain regions analyzed except for increases in the amygdala and no changes in the paraventricular nucleus of the hypothalamus. To examine whether DOCA's effects on NK3r synthesis are direct, we used differentiated N1E-115 neuroblastoma cells that express NK3r and treated them with a range of concentrations of DOCA and found a dose-dependent decrease in NK3r-mRNA abundance via Northern blotting. The present results suggest that the tachykinin receptors are downregulated after subchronic DOCA treatment and this finding is consistent with the hypothesis that suppressed inhibition of salt appetite as mediated through the tachykininergic system.

Differential effects of tumor necrosis factor-alpha and interleukin-1 on 3 beta-hydroxysteroid dehydrogenase/delta 5-->delta 4 isomerase expression in mouse Leydig cells

Immune-endocrine interactions are important to the regulation of Leydig cell steroidogenesis. We have shown previously that both tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1-beta) inhibit 8-bromo-cAMP-(8-Br-cAMP)-stimulated steroidogenesis in mouse Leydig cells. TNF and IL-1 both inhibit cAMP-stimulated testosterone production as well as mRNA and protein levels of cholesterol side chain cleavage enzyme (P450scc) and 17 alpha-hydroxylase/C17,20 lyase (P450c17) in mouse Leydig cells. Neither TNF nor IL-1 affects basal levels of P450scc mRNA and protein. In the present study, we tested the effects of TNF and IL-1 on basal testosterone production and 8-Br-cAMP-stimulated 3 beta-hydroxysteroid dehydrogenase/delta 5-->delta 4 isomerase (3 beta HSD) expression in Leydig cells. Purified and macrophage-depleted Leydig cells were cultured for 5 d with daily changes of media, and then treated with increasing concentrations of recombinant mouse TNF or IL-1 in the presence or absence of 8-Br-cAMP (50 microM) for 24 h. The media were collected for testosterone RIA and RNA and protein were extracted from cells. Basal testosterone production was inhibited by TNF, but not IL-1. Treatment of Leydig cells with 8-Br-cAMP alone caused a marked increase in 3 beta HSD mRNA, and protein levels. Both TNF and IL-1 inhibited cAMP-stimulated 3 beta HSD mRNA and protein levels, but only TNF inhibited basal 3 beta HSD expression. These results demonstrate that TNF and IL-1 have different effects on basal steroidogenesis in Leydig cells and suggest that TNF-mediated inhibition of basal testosterone production may be owing to the inhibition of basal 3 beta-HSD expression in Leydig cells.

Autoradiographic mapping of pulmonary NK1 and NK2 tachykinin receptors and changes after repeated antigen challenge in guinea pigs

An autoradiographic technique was used to study the distribution of changes in pulmonary NK1 and NK2 receptors in guinea pig lung after repeated antigen challenge. Specific labeling of [3H]CP96345 (NK1 receptors) and [3H]SR48968 (NK2 receptors) was localized over the tracheal and bronchial smooth muscle; the density of binding increased towards smaller airways with a higher density for [3H]CP96345 binding. Bronchial epithelium and pulmonary blood vessels were also labeled densely with [3H]CP96345. No remarkable difference in the pattern of distribution of pulmonary NK1 and NK2 tachykinin receptors was observed between control, vehicle-challenged, and repeatedly antigen-challenged (weekly for three times) guinea pigs. A significant reduction in specific labeling of [3H]CP96345 (p < 0.01) and [3H]SR48968 (p < 0.05) over pulmonary structures was observed in antigen-challenged compared to control or vehicle-challenged animals. This study provides evidence that NK1 and NK2 tachykinin receptors are both localized to smooth muscle of all sizes in guinea pig airways and provides further evidence for a discrete distribution of NK1 and NK2 tachykinin receptors, consistent with their relative functional activities. In an established model of airway inflammation a decrease in the expression of NK1 and NK2 tachykinin receptors was evident on several different cell types within the lung, and this could influence airway and vascular reactivity.

An N-terminal fragment of substance P, substance P(1-7), down-regulates neurokinin-1 binding in the mouse spinal cord

Injected intrathecally, substance P (SP) down-regulates neurokinin-1 (NK-1) binding in the spinal cord and desensitizes rats to the behavioral effect of SP. N-terminal fragments of SP, such as SP(1-7), induce antinociception and play a role in desensitization to SP in mice. The goal of this study was to assess the abilities of N- and C-terminal fragments of SP to down-regulate NK-1 binding. Binding of [3H]SP to mouse spinal cord membranes was inhibited by SP, CP-96,345, and to a lesser extent by SP(5-11), but not SP(1-7), consistent with these binding sites being NK-1 receptors. Injection of SP(5-11) intrathecally did not affect the affinity (Kd) or concentration (Bmax) of [3H]SP binding. However, injection of 1 nmol of SP(1-7) decreased the Bmax of [3H]SP binding in the spinal cord at 6 h after its injection just as this dose of SP decreased the Bmax at 24 h. These data suggest that the N-terminus of SP is responsible for down-regulation of NK-1 binding. As SP(5-11) did not down-regulate NK-1 binding, activation of NK-1 sites does not appear necessary or sufficient for down-regulation of SP binding. In contrast, SP(1-7), in spite of its inability to interact with NK-1 sites, did down-regulate SP binding, suggesting an indirect mechanism dissociated from NK-1 receptors.

Parainfluenza virus type 3 induced alterations in tachykinin NK1 receptors, substance P levels and respiratory functions in guinea pig airways

We have investigated the effects of parainfluenza virus type 3 (PI-3) on sensory neuropeptide levels, tachykinin receptors and their functions in guinea pig airways during the course of respiratory viral infection. PI-3 infected guinea pigs were hyperresponsive to methacholine and substance P aerosols as determined by earlier onset of dyspnea in these animals as compared with control on post-inoculation day (PID) 7 but not 19. In addition, plasma protein extravasation produced in response to the tachykinin was increased in infected airways during the first week post inoculation. Infected guinea pig trachea did not respond any differently to methacholine when smooth muscle contraction and [3H]inositol phosphate accumulation were measured although the magnitude of substance P effects using in vitro tests was significantly greater than control on post-inoculation day 7 but not 19. Trachea from PI-3 infected animals were characterized by reductions in substance P-like immunoreactivity, tachykinin NK1 receptor number and agonist affinity during the first post-inoculation week. Substance P levels or tachykinin NK1 receptor numbers or affinity were not altered in trachea of guinea pigs 4 days after treatment with lipopolysaccharide. These data suggest substance P release occurs during critical periods of respiratory viral infection which are temporally correlated with airway hyperresponsiveness. Despite apparent down-regulation of tachykinin NK1 receptors, substance P-mediated functions remained enhanced suggesting some alterations in post-receptor mechanisms.

The effect of TNFa on bradykinin receptor binding, phosphatidylinositol turnover and cell growth in human A431 epidermoid carcinoma cells

In this study, we examined the effect of TNFa on bradykinin (BK) B2 receptor binding and function in human A431 epidermoid carcinoma cells. [3H]BK binds to a single class of receptors on A431 cells in a saturable and reversible manner. A binding affinity (KD) of 3.0 +/- 0.3 nM (n = 4) and a Bmax of 151 +/- 14 fmols/10(6) cells, representing approximately 90,000 BK receptors per cell, was observed. The rank order of potency for BK agonist peptides indicates that the A431 BK receptor appears to be of the B2 subtype. When A431 cells were incubated with TNFa (10 ng/ml) for 48 h prior to BK binding, a significant decrease in the number of BK receptors compared to control was observed. TNFa did not influence the affinity of BK binding to A431 cells and direct addition of TNFa to the binding assay did not effect BK binding. BK-stimulated IP1 formation appeared to be increased in TNFa treated cells compared to control whereas histamine-stimulated IP1 formation was not influenced. Both control and TNFa treated cells were greater than 95% viable. However, TNFa treated cells were blocked in the G1 phase of the cell cycle resulting in a decrease in DNA synthesis. This may be one mechanism for the TNFa-induced decrease in BK receptors in A431 cells.