Decreased expression and activity of G-protein-coupled receptor kinases in peripheral blood mononuclear cells of patients with rheumatoid arthritis

Hydrogen peroxide causes uncoupling of dopamine D1-like receptors from G proteins via a mechanism involving protein kinase C and G-protein-coupled receptor kinase 2

Dopamine, via activation of D1-like receptors, inhibits Na,K-ATPase and Na,H-exchanger in renal proximal tubules and promotes sodium excretion. This effect of dopamine is not seen in conditions associated with oxidative stress such as hypertension, diabetes, and aging due to uncoupling of D1-like receptors from G proteins. To identify the role of oxidative stress in uncoupling of the D1-like receptors, we utilized primary cultures from rat renal proximal tubules. Hydrogen peroxide (H2O2), an oxidant, treatment to the cell cultures increased the level of malondialdehyde, a marker of oxidative damage. Further, H2O2 decreased membranous D1-like receptor numbers and proteins, D1-like agonist (SKF 38393)-mediated [35S]GTPgammaS binding and SKF 38393-mediated inhibition of Na,K-ATPase. Moreover, H2O2 treatment to the cultures caused membranous translocation of G-protein-coupled receptor kinase 2 (GRK 2) and increased serine phosphorylation of D1A receptors accompanied by an increase in protein kinase C (PKC) activity. Interestingly, PKC inhibitors blocked the H2O2-mediated stimulation of GRK 2 and serine phosphorylation of D1A receptors. Further, GRK 2 antisense but not scrambled oligonucleotides attenuated the effect of H2O2 on membranous expression of GRK 2. Moreover, direct activation of PKC with phorbol ester (PMA) resulted in reduction of SKF 38393-mediated [35S]GTPgammaS binding. We conclude that H2O2 stimulates PKC leading to the activation of GRK 2, which causes serine phopshorylation of D1A receptors and receptor G-protein uncoupling in these cells, resulting in impairment in D1-like receptor function.

Tumor Necrosis Factor-α Prevents Desensitization of Gαs-Coupled Receptors by Regulating GRK2 Association with the Plasma Membrane

We have reported previously that interleukin-1 and tumor necrosis factor (TNF)-alpha increase expression and function of adenosine A2A receptors (A2ARs), although the increased function is disproportionate to the increment in expression. We therefore studied the effect of TNF-alpha on A2A R function and desensitization in human monocytoid THP-1 cells. We observed that TNF-alpha regulates activity of A2A Rs and other G protein-coupled receptors (GPCRs) by altering their ligand-mediated desensitization. Pretreatment of resting cells with the A2AR agonist 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosine (CGS 21680) or the pan-adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine quickly desensitized cAMP responses to CGS 21680 restimulation, but TNF-alpha treatment prevented A2AR desensitization. As expected, A2A R occupancy induced translocation of GPCR kinase-2 (GRK2) to the plasma membrane (PM). We were surprised to find that after TNF-alpha treatment, A2AR occupancy not only failed to induce GRK2 translocation to PM but also decreased GRK2 association with PM. TNF-alpha altered GRK2 translocation in response to the beta-adrenergic receptor agonist isoproterenol in a similar manner. Similar to GRK2, beta-arrestin associated with PM after A2A R stimulation in control cells but not in TNF-alpha-treated cells. C2-ceramide, a downstream mediator in the sphingomyelinase (SMase)-dependent pathway, mimicked the effect of TNF-alpha on GRK2 translocation. Moreover, inhibitors of the SMases and an inhibitor of c-Jun NH2-terminal kinase, also a downstream effector in the SMase pathway, reversed TNF-alpha-mediated effects on GRK2 translocation and A2A R desensitization. These results suggest a novel form of cross-talk between TNF-alpha receptors and GPCRs; TNF-alpha enhances GPCR function by preventing agonist-induced desensitization of GPCRs by diminishing agonist-dependent recruitment of GRK2 and beta-arrestin to PM by a SMase pathway-mediated mechanism.

Once and future signaling: G protein-coupled receptor kinase control of neuronal sensitivity

G protein-coupled receptors (GPCRs) are the most numerous class of cell surface receptor, and substances acting through GPCRs mediate many critical signaling events and physiological processes. GPCR sensitivity and signaling is dynamic, responding rapidly to adjust to changes in the ambient level of stimulation of target cells. One important mediator of such receptor sensitivity is the family of GPCR kinases (GRKs). Like heterotrimeric G proteins, GRKs recognize agonist-bound, activated receptors, and this recognition promotes catalytic activation of GRKs, resulting in the preferential phosphorylation of activated receptors. GRK-phosphorylated receptors are then targeted by arrestin proteins, which bind to phosphorylated receptors. Arrestin-bound receptors are uncoupled from heterotrimeric G proteins, resulting in decreased sensitivity to further receptor stimulation (desensitization). Arrestin-bound receptors are also accelerated into internalization pathways and linked to distinct arrestin-mediated signaling pathways. GRKs thus serve as gatekeepers for receptors, terminating some signaling pathways and initiating others. One major outstanding question concerning GRKs understanding the mechanisms by which any particular receptor subtype (of the 800 or so in the body) is regulated by a specific GRK(s), and the consequences of this specificity. An understanding of this regulatory specificity could allow targeting of GRK function to ameliorate diseases involving GPCR dysregulation.

G protein-coupled receptor kinase 2 negatively regulates chemokine signaling at a level downstream from G protein subunits

The G protein-coupled receptor kinase 2 (GRK2) phosphorylates and desensitizes ligand-activated G protein-coupled-receptors. Here, evidence is shown for a novel role of GRK2 in regulating chemokine-mediated signals. The presence of increased levels of GRK2 in human embryonic kidney (HEK) 293 cells produced a significant reduction of the extracellular signal-regulated kinase (ERK) response to CCL2. This effect is independent of its role in receptor phosphorylation because the kinase-deficient mutant GRK2K220R was able to reduce this response, and ERK activation by CCR2BIX, a phosphorylation-defective receptor mutant, was also inhibited by GRK2. Constructs containing the Galpha(q)-binding RGS-like RH domain of GRK2 or its Gbetagamma-binding domain could not reproduce the inhibition, thus revealing that GRK2 acts downstream of G proteins. Interestingly, chemokine-driven mitogen-activated protein kinase kinase (MEK) stimulation is not affected in cells overexpressing GRK2 or GRK2K220R or in splenocytes from heterozygous GRK2 mice, where reduced kinase levels correlate with enhanced ERK activation by chemokines. We find GRK2 and MEK in the same multimolecular complex, thus suggesting a mechanism for GRK2 regulation of ERK activity that involves a direct or coordinate interaction with MEK. These results suggest an important role for GRK2 in the control of chemokine induction of ERK activation at the level of the MEK-ERK interface.

Chronic beta-adrenergic receptor stimulation enhances the expression of G-Protein coupled receptor kinases, GRK2 and GRK5, in both the heart and peripheral lymphocytes

BACKGROUND

Enhanced expression of G protein-coupled receptor kinase (GRK) has been reported in failing hearts and in the present study the stability of enhanced GRK mRNA expression, and the correlation between the expression level of GRK mRNA in peripheral lymphocytes and in the heart were both evaluated.

METHODS AND RESULTS

Isoproterenol was injected into rats for 2 weeks, and then GRK5 mRNA was assessed by quantitative reverse transcriptase-palymerase chain reaction. An enhanced expression of cardiac GRK5 mRNA was observed even after 4 weeks of recovery. The isoproterenol-induced increased expression of GRK2 and GRK5 mRNA was equally observed in the heart and lymphocytes, and there was a close correlation between the heart and lymphocytes in the level of expression of each GRK mRNA.

CONCLUSIONS

The GRK mRNA level is maintained at a high level for a long period without continuous beta-adrenergic receptor stimulation. The level in circulating lymphocytes could be used as a surrogate marker to estimate the level of cardiac GRK expression and, presumably, the beta-adrenergic receptor function of cardiomyocytes.

G protein-coupled receptor kinase 2 in multiple sclerosis and experimental autoimmune encephalomyelitis

Many modulators of inflammation, including chemokines, neuropeptides, and neurotransmitters signal via G protein-coupled receptors (GPCR). GPCR kinases (GRK) can phosphorylate agonist-activated GPCR thereby promoting receptor desensitization. Here we describe that in leukocytes from patients with active relapsing-remitting multiple sclerosis (MS) or with secondary progressive MS, GRK2 levels are significantly reduced. Unexpectedly, cells from patients during remission express even lower levels of GRK2. The level of GRK2 in leukocytes of patients after stroke, a neurological disorder with paralysis but without an autoimmune component, was similar to GRK2 levels in cells from healthy individuals. In addition, we demonstrate that the course of recombinant myelin oligodendrocyte glycoprotein (1-125)-induced experimental autoimmune encephalomyelitis (EAE), an animal model for MS, is markedly different in GRK2(+/-) mice that express 50% of the GRK2 protein in comparison with wild-type mice. Onset of EAE was significantly advanced by 5 days in GRK2(+/-) mice. The earlier onset of EAE was associated with increased early infiltration of the CNS by T cells and macrophages. Although disease scores in the first phase of EAE were similar in both groups, GRK2(+/-) animals did not develop relapses, whereas wild-type animals did. The absence of relapses in GRK2(+/-) mice was associated with a marked reduction in inflammatory infiltrates in the CNS. Recombinant myelin oligodendrocyte glycoprotein-induced T cell proliferation and cytokine production were normal in GRK2(+/-) animals. We conclude that down-regulation of GRK2 expression may have important consequences for the onset and progression of MS.

Pathophysiological roles of G-protein-coupled receptor kinases

G-protein-coupled receptor kinases (GRKs) interact with the agonist-activated form of G-protein-coupled receptors (GPCRs) to effect receptor phosphorylation and to initiate profound impairment of receptor signalling, or desensitization. GPCRs form the largest family of cell surface receptors known and defects in GRK function have the potential consequence to affect GPCR-stimulated biological responses in many pathological situations. This review focuses on the physiological role of GRKs revealed by genetically modified animals but also develops the involvement of GRKs in human diseases as, Oguchi disease, heart failure, hypertension or rhumatoid arthritis. Furthermore, the regulation of GRK levels in opiate addiction, cancers, psychiatric diseases, cystic fibrosis and cardiac diseases is discussed. Both transgenic mice and human pathologies have demonstrated the importance of GRKs in the signalling pathways of rhodopsin, beta-adrenergic and dopamine-1 receptors. The modulation of GRK activity in animal models of cardiac diseases can be effective to restore cardiac function in heart failure and opens a novel therapeutic strategy in diseases with GPCR dysregulation.

The importance of timing of adrenergic drug delivery in relation to the induction and onset of adjuvant-induced arthritis

Stressful events often precede onset and exacerbate established rheumatic diseases. There are numerous reports of abnormal autonomic function in rheumatoid arthritis (RA) patients. Targeting the sympathetic nervous system (SNS) with adrenergic receptor (AR) drugs in RA patients and animal models of the disease have revealed mixed results, with treatments inhibiting and exacerbating disease pathology. We tested the hypothesis that variability in disease outcome following adrenergic drug treatment is due to different roles played by the SNS at different disease stages. The contribution of beta2- and alpha-AR subtypes to disease pathology was studied at different disease stages in adjuvant-induced arthritis (AA), an animal model of RA. Lewis rats were given twice-daily intraperitoneal (i.p.) injections of an alpha-AR antagonist (phentolamine: 500 microg/kg) or a beta2-AR agonist (terbutaline: 1200 microg/day), initiated at adjuvant challenge or disease onset, and continued through severe disease. Both adrenergic therapies, when initiated at adjuvant challenge exacerbated disease pathology. In contrast, SH1293, an adrenergic drug that targets both alpha- and beta-AR (300 microg/day; twice-daily), initiated at adjuvant challenge did not exacerbate disease severity. Additionally, the same treatment regimen of phentolamine, terbutaline or SH1293 initiated at disease onset attenuated joint-inflammation and dramatically reduced bone destruction in the arthritic hind limbs. These data support the SNS playing different roles in disease pathology preclinically and after disease onset. Given current drug therapies are not effective in preventing bone destruction, these data support using adrenergic drugs as bone sparing treatments in RA.

Post-receptorial mechanisms underlie functional disregulation of beta2-adrenergic receptors in lymphocytes from Multiple Sclerosis patients

Increased density of beta2-adrenergic receptors has been demonstrated on peripheral blood mononuclear cells (PBMCs) from Multiple Sclerosis (MS) patients. In this study we found that isoproterenol reduces T-cell proliferation and IFNgamma secretion in PBMCs cultures from healthy controls and IFNbeta-treated but not untreated MS patients. Reduced expression levels of G protein coupled receptor kinase (GRK)2/3 (p < 0.05) and increased isoproterenol-induced cAMP accumulation (p < 0.0001) were found in PBMCs from all MS patients. Dibutyryl cAMP reduced the proliferation of PBMCs from all subgroups but in a slighter manner in untreated MS patients. We conclude that signalling through beta2-adrenergic receptors is chronically up-regulated but functionally uncoupled to immunoregulatory functions of lymphocytes from MS patients. Disregulation downstream the cAMP-associated signalling may underlie such a phenomenon.

Beta 2-adrenergic receptor regulation of human neutrophil function is sexually dimorphic

While the mechanisms underlying the marked sexual dimorphism in inflammatory diseases are not well understood, the sexually dimorphic sympathoadrenal axis profoundly affects the inflammatory response. We tested whether adrenergic receptor-mediated activation of human neutrophil function is sexually dimorphic, since neutrophils provide the first line of defense in the inflammatory response. There was a marked sexual dimorphism in beta(2)-adrenergic receptor binding, using the specific beta(2)-adrenergic receptor ligand, [(3)H]-dihydroalprenolol, with almost three times more binding sites on neutrophils from females (20,878 +/- 2470) compared to males (7331 +/- 3179). There was also a marked sexual dimorphism in the effects of isoprenaline, a beta-adrenergic receptor agonist, which increased nondirected locomotion (chemokinesis) in neutrophils obtained from females, while having no effect on neutrophils from males. Isoprenaline stimulated the release of a chemotactic factor from neutrophils obtained from females, but not from males. This chemotactic factor acts on the G protein-coupled CXC chemokine receptor 2 (CXCR2) chemokine receptor, since an anti-CXCR2 antibody and the selective nonpeptide CXCR2 antagonist SB225002, inhibited chemotaxis produced by this factor. While interleukin- (IL-) 8 is a principal CXCR2 ligand, isoprenaline did not produce an increase in IL-8 release from neutrophils. IL-8-induced chemotaxis was inhibited in a sexually dimorphic manner by isoprenaline, which also stimulated release of a mediator from neutrophils that induced chemotaxis, that was inhibited by anti-CXCR2 antibodies. These findings indicate an important role for adrenergic receptors in the modulation of neutrophil trafficking, which could contribute to sex-differences in the inflammatory response.

Hypoxia/ischemia modulates G protein-coupled receptor kinase 2 and beta-arrestin-1 levels in the neonatal rat brain

BACKGROUND AND PURPOSE

Neurotransmitters, neuropeptides, chemokines, and many other molecules signal through G protein-coupled receptors (GPCRs). GPCR kinases (GRKs) and beta-arrestins play a crucial role in regulating the responsiveness of multiple GPCRs. Reduced expression of GRK and beta-arrestins leads to supersensitization of GPCRs and will thereby increase the response to neuropeptides and neurotransmitters. We analyzed GRK and beta-arrestin expression after cerebral hypoxia/ischemia (HI).

MATERIALS AND METHODS

Twelve-day-old rat pups were exposed to 90 minutes of hypoxia (fraction of inspired oxygen [FiO2] 0.08) after ligation of the right carotid artery, a procedure that induces unilateral damage in the right hemisphere. At 6, 12, 24, and 48 hours after HI, the left (hypoxic) and right (hypoxic/ischemic) hemispheres were analyzed for GRK and beta-arrestin protein and mRNA expression by Western blotting and real-time polymerase chain reaction, respectively. In addition, we analyzed GRK2 expression in the hippocampus by immunohistochemistry.

RESULTS

HI downregulated GRK2 protein expression in both hemispheres at 24 to 48 hours after HI, and the effect was more pronounced in the ipsilateral hemisphere. HI induced no global change in GRK6 protein expression. However, GRK2 was markedly decreased in the hippocampal region of the ipsilateral hemisphere that will be severely damaged after HI. No changes in global mRNA levels for GRK2 were detected. In contrast, HI increased beta-arrestin-1 protein expression as well as mRNA levels at 6 to 12 hours after HI.

CONCLUSIONS

Neonatal HI-induced brain damage is associated with specific changes in the GPCR desensitization machinery. We hypothesize that these changes result in supersensitization of multiple GPCRs and might therefore contribute to HI-induced brain damage.

In vitro adrenergic modulation of cellular immune functions in experimental autoimmune encephalomyelitis

OBJECTIVE

To analyze the effects in vitro of alpha- and beta-adrenoceptor agonists on splenocyte proliferation and on proinflammatory cytokine production in splenocytes and peritoneal macrophages (MF) in different stages of EAE.

METHODS

Splenocytes and peritoneal macrophages were harvested in the acute phase of EAE and in remission, and from controls. The beta-agonist terbutaline, the alpha(1)-agonist methoxamine, and the alpha(2)-agonist UK-14304 were added with ConA or lipopolysaccharide (LPS). TNF-alpha and IFN-gamma contents in supernatant and splenocyte proliferation were determined.

RESULTS

Terbutaline and UK-14304 significantly suppressed TNF-alpha production by MF. However, EAE acute phase rats were resistant to the suppressive effect of UK-14304. Terbutaline significantly suppressed IFN-gamma and TNF-alpha production by splenocytes. EAE acute phase and remission animals showed reduced terbutaline-induced inhibition of IFN-gamma production.

CONCLUSIONS

Disturbed sympathetic-immune communication in EAE is characterized by alterations in adrenergic sensitivity via both alpha- and beta-adrenergic pathways.

Reduced GRK2 level in T cells potentiates chemotaxis and signaling in response to CCL4

Chemokine receptors belong to the family of G-protein-coupled receptors (GPCR). Phosphorylation of GPCR by GPCR kinases (GRKs) is considered to play an important role in desensitization of these receptors. We have recently shown in patients with rheumatoid arthritis that the level of GRK2 in lymphocytes is reduced by approximately 50%. However, the physiological relevance of reduced GRK2 levels in lymphocytes is not known. Here, we investigated whether reduced GRK2 expression changes the chemotactic response of T cells to the chemokines CCL3, CCL4, and CCL5. Activated T cells from GRK2+/- mice, which have a 50% reduction in GRK2 protein levels, showed a significant 40% increase in chemotaxis toward the CCR5 ligand CCL4. In addition, chemotaxis toward the CCR1 and CCR5 ligands CCL3 and CCL5 was also increased. Binding of CCL4 to activated T cells from GRK2+/- and wild-type (WT) mice was similar, but agonist-induced CCR5 phosphorylation was attenuated in GRK2+/- cells. Moreover, the calcium response and phosphorylation of protein kinase B and extracellular-regulated kinase in response to CCL4 were significantly increased in GRK2+/- T cells, showing that signaling is increased when the level of GRK2 is reduced. GRK2+/- and WT cells do become refractory to restimulation with CCL4. In conclusion, a 50% decrease in T cell GRK2 expression results in increased responsiveness to CCL3, CCL4, and CCL5, suggesting that the 50% reduction in lymphocyte GRK2 level as observed during inflammation can have functional consequences for the response of these cells to chemokines.

Non-visual GRKs: are we seeing the whole picture?

G-protein-coupled receptor kinases (GRKs) comprise a family of seven mammalian serine/threonine protein kinases that phosphorylate and regulate agonist-occupied or constitutively active G-protein-coupled receptors (GPCRs). Studies of the details and consequences of these mechanisms have focused heavily on the original beta-adrenoceptor kinase (beta-ARK) family (GRK2 and GRK3) and, in particular, on phosphorylation-dependent recruitment of adaptor proteins such as the beta-arrestins. However, recent work has indicated roles for the other, non-visual GRKs (GRK4, GRK5 and GRK6) and has revealed potential phosphorylation-independent regulation of GPCRs by GRK2 and GRK3. In this article, we review this newer information and attempt to put it into context with GRKs as physiological regulators that could be appropriate targets for future pharmacological intervention.

Increased Acute Inflammation, Leukotriene B4-Induced Chemotaxis, and Signaling in Mice Deficient for G Protein-Coupled Receptor Kinase 6

Directed migration of polymorphonuclear neutrophils (PMN) is required for adequate host defense against invading organisms and leukotriene B(4) (LTB(4)) is one of the most potent PMN chemoattractants. LTB(4) exerts its action via binding to BLT1, a G protein-coupled receptor. G protein-coupled receptors are phosphorylated by G protein-coupled receptor kinases (GRK) in an agonist-dependent manner, resulting in receptor desensitization. Recently, it has been shown that the human BLT1 is a substrate for GRK6. To investigate the physiological importance of GRK6 for inflammation and LTB(4) signaling in PMN, we used GRK6-deficient mice. The acute inflammatory response (ear swelling and influx of PMN into the ear) after topical application of arachidonic acid was significantly increased in GRK6(-/-) mice. In vitro, GRK6(-/-) PMN showed increased chemokinetic and chemotactic responses to LTB(4). GRK6(-/-) PMN respond to LTB(4) with a prolonged increase in intracellular calcium and prolonged actin polymerization, suggesting impaired LTB(4) receptor desensitization in the absence of GRK6. However, pre-exposure to LTB(4) renders both GRK6(-/-) as well as wild-type PMN refractory to restimulation with LTB(4), indicating that the presence of GRK6 is not required for this process to occur. In conclusion, GRK6 deficiency leads to prolonged BLT1 signaling and increased neutrophil migration.

Neural immune pathways and their connection to inflammatory diseases

Inflammation and inflammatory responses are modulated by a bidirectional communication between the neuroendocrine and immune system. Many lines of research have established the numerous routes by which the immune system and the central nervous system (CNS) communicate. The CNS signals the immune system through hormonal pathways, including the hypothalamic-pituitary-adrenal axis and the hormones of the neuroendocrine stress response, and through neuronal pathways, including the autonomic nervous system. The hypothalamic-pituitary-gonadal axis and sex hormones also have an important immunoregulatory role. The immune system signals the CNS through immune mediators and cytokines that can cross the blood-brain barrier, or signal indirectly through the vagus nerve or second messengers. Neuroendocrine regulation of immune function is essential for survival during stress or infection and to modulate immune responses in inflammatory disease. This review discusses neuroimmune interactions and evidence for the role of such neural immune regulation of inflammation, rather than a discussion of the individual inflammatory mediators, in rheumatoid arthritis.

Regulators of G protein signalling: potential targets for treatment of allergic inflammatory diseases such as asthma

Asthma, a disease that affects nearly 15% of the world's population, is characterised by lung inflammation and reversible airway obstruction, which leads to wheezing and dyspnoea. Asthma is a prototype for allergic processes initiated by tissue inflammatory leukocytes, such as mast cells, whose secreted mediators recruit lymphocytes and eosinophils to the lung parenchyma. Signals transmitted through G-protein-coupled receptors (GPCRs) contribute to both the development and perpetuation of allergic processes, and pharmacological agents that block or stimulate GPCR action have been a mainstay of allergic disease therapy. Despite the widespread use of GPCR-targeted agents, little is understood about intracellular regulation of G protein pathways in immune cells. Regulators of G protein signalling (RGS proteins) enhance G protein deactivation and may contribute to the specificity and precision characteristic of GPCR signalling pathways. This review discusses the emerging functions of RGS proteins in immune processes and inflammatory states such as asthma, and their potential value as therapeutic targets for the treatment of allergic disease.

Phosphodiesterase 4 inhibitors reduce human dendritic cell inflammatory cytokine production and Th1-polarizing capacity

Inhibitors of cAMP-specific phosphodiesterase (PDE) 4 have been shown to inhibit inflammatory mediator release and T cell proliferation, and are considered candidate therapies for T(h)1-mediated diseases. However, little is known about how PDE4 inhibitors influence dendritic cells (DC), the cells responsible for the priming of naive T(h) cells. Therefore, we investigated the PDE profile of monocyte-derived DC, and whether PDE4 inhibitors modulate DC cytokine production and T cell-polarizing capacity. We mainly found cAMP-specific PDE4 enzymatic activity in both immature and mature DC. In contrast to monocytes that mainly express PDE4B, we found that PDE4A is the predominant PDE4 subtype present in DC. Immature DC showed reduced ability to produce IL-12p70 and tumor necrosis factor (TNF)-alpha upon lipopolysaccharide or CD40 ligand (CD40L) stimulation in the presence of PDE4 inhibitors, whereas cytokine production upon CD40L stimulation of fully mature DC in the presence of PDE4 inhibitors was not affected. Exposure to PDE4 inhibitors for 2 days during DC maturation did not influence T cell-stimulatory capacity or acquisition of a mature phenotype, but increased the expression of the chemokine receptor CXCR4. Furthermore, DC matured in the presence of PDE4 inhibitors showed reduced capacity to produce IL-12p70 and TNF-alpha upon subsequent CD40L stimulation. Using these PDE4 inhibitor-matured DC to stimulate naive T cells resulted in a reduction of IFN-gamma-producing (T(h)1) cells. These findings indicate that PDE4 inhibitors can affect T cell responses by acting at the DC level and may increase our understanding of the therapeutic implication of PDE4 inhibitors for T(h)1-mediated disorders.

Disease-drug interaction: Reduced response to propranolol despite increased concentration in the rat with inflammation

Inflammatory conditions reduce clearance, hence increase plasma concentration of drugs such as propranolol that are efficiently cleared by the liver. The therapeutic consequences of this increased plasma drug concentration is mainly unknown. However, for sotalol, another beta-adrenergic antagonist, inflammation causes reduced potency. Sotalol, however, is renally cleared; hence, its clearance is unaffected by inflammation. We examined if the inflammation-induced increased plasma propranolol concentration compensates for the reduced responsiveness. A modified lead I ECG was used to record PR interval and heart rate (HR). ECG was monitored following oral administration of 3, 5, 10, 15, 20, 25, and 30 mg/kg propranolol to both control and adjuvant arthritis (AA) rats. To confirm altered pharmacokinetics, single 25 mg/kg doses of propranolol were administered to both AA and control rats, with an inserted cannula in their right jugular vein for serial blood sampling. As expected, AA caused a significant reduction in the propranolol oral clearance and subsequently substantial increases in plasma total and unbound drug concentration. Interestingly, however, despite the elevated propranolol concentrations, the effect on HR remained unchanged and the prolongation of PR interval was significantly reduced in AA compared with control rats. The reduced sensitivity to propranolol in AA rats is suggestive of altered beta-adrenergic receptors function.

Regulated expression of alpha-1 adrenergic receptors in the immune system

The catecholamines norepinephrine and epinephrine are used by the sympathetic nervous system to communicate with other organ systems, including the immune system. Adrenergic receptors on target cells bind these catecholamines and modulate the activity of the target cell. The beta 2-adrenergic receptor is the most abundantly expressed and best studied adrenergic receptor in the immune system. Here, I summarize data from our own laboratory and from others on the expression and possible function of alpha 1-adrenergic receptors in the immune system. alpha 1-Adrenergic receptor expression in the immune system can be regulated by glucocorticoids, by beta 2-adrenergic agonists, and by cytokines. In addition, the possible pathophysiological implications of the expression of alpha 1-adrenergic receptors on immune cells from arthritis patients are discussed.

The beta 2-adrenergic agonist salbutamol potentiates oral induction of tolerance, suppressing adjuvant arthritis and antigen-specific immunity

Therapeutic protocols for treating autoimmune diseases by feeding autoantigens during the disease process have not been very successful to date. In vitro it has been shown that beta-adrenergic agonists inhibit pro-inflammatory cytokine production and up-regulate anti-inflammatory cytokine production. We hypothesized that the protective effect of oral administration of Ag would be enhanced by oral coadministration of the beta(2)-adrenergic agonist salbutamol. Here we demonstrate that oral administration of salbutamol in combination with the Ag mycobacterial 65-kDa heat shock protein increased the efficacy of disease-suppressive tolerance induction in rat adjuvant arthritis. To study the mechanism of salbutamol in more detail, we also tested oral administration of salbutamol in an OVA tolerance model in BALB/c mice. Oral coadministration of OVA/salbutamol after immunization with OVA efficiently suppressed both cellular and humoral responses to OVA. Coadministration of salbutamol was associated with an immediate increase in IL-10, TGF-beta, and IL-1R antagonist in the intestine. The tolerizing effect of salbutamol/OVA was maintained for at least 12 wk. At this time point IFN-gamma production in Ag-stimulated splenocytes was increased in the OVA/salbutamol-treated animals. In conclusion, salbutamol can be of great clinical benefit for the treatment of autoimmune diseases by promoting oral tolerance induction.

Norepinephrine, the beta-adrenergic receptor, and immunity

Over the past 20 years, a significant effort has been made to define a role for the neuroendocrine system in the regulation of immunity. It was expected that these experimental findings would help to establish a strategy for the development of clinical interventions to either suppress or augment immunological function for disease prevention. However, the translation of these basic experimental findings into clinical interventions has been difficult. Possible explanations for this difficulty are that the findings from human and animal studies do not agree and/or that the results obtained within one species are rarely verified in the other. Our goal in writing this review is to address this issue by summarizing the published findings from human studies and comparing them to published findings from animal studies. Although far from being exhaustive, this review summarizes and discusses at least the past 10 years of findings in which a change in immunity and a change in catecholamine levels and/or stimulation of the beta(2)-adrenergic receptor has been documented.

Altered expression of autonomic neurotransmitter receptors and proliferative responses in lymphocytes from a chronic mild stress model of depression: effects of fluoxetine

We studied beta-adrenergic and muscarinic cholinergic receptor (MR) expression and proliferative response in lymphocytes from animals under chronic mild stress (CMS) model of depression (CMS animals). Animals were subjected to CMS (periods of food or water deprivation, changes in lighting conditions, tilted cage, etc.) for 12 weeks. CMS lymphocytes showed an altered mitogen-induced proliferation. CMS-B and -T lymphocytes showed an increment on beta-adrenoceptor number and on intracellular responses to a beta-agonist. CMS-T cells showed higher MR expression and lower cGMP responses than normal lymphocytes. MR were not detectable in normal B cells while CMS-B cells showed both MR expression and cGMP response. Beta and muscarinic stimulation influenced lymphocyte proliferative responses, in accordance with cAMP and cGMP responses. After 12 weeks of the CMS procedure, animals were treated with fluoxetine while the CMS procedure continued. Fluoxetine treatment reverted the alterations induced by CMS. These findings suggest a possible mechanism for the immune alterations found in depressive disorders and for the effect of fluoxetine treatment on immune response.

Oxidative stress decreases G protein-coupled receptor kinase 2 in lymphocytes via a calpain-dependent mechanism

G protein-coupled receptor kinase (GRK) 2 plays a crucial role in regulating the extent of desensitization and resensitization of G protein-coupled receptors (GPCRs). We have shown that the expression level of GRK2 in lymphocytes decreases during inflammatory diseases such as arthritis. Reactive oxygen species play an important role in a variety of inflammatory conditions, including arthritis. We demonstrate herein that oxidative stress, induced by exposure of lymphocytes to H(2)O(2), results in a 50% reduction in GRK2 protein levels and GRK activity with no changes in mRNA expression. Treatment of lymphocytes with the tyrosine kinase inhibitor genistein partially reverses the effect of H(2)O(2) on GRK2 levels, although we did not detect direct tyrosine phosphorylation of GRK2. Inhibition of the nonproteasomal protease calpain by calpeptin can prevent the H(2)O(2)-induced GRK2 decrease. In vitro experiments confirm that GRK2 is partially digested by m-calpain in a calcium-dependent way. Functionally, H(2)O(2)-induced decrease in GRK2 levels is associated with an ~70% decrease in agonist-induced beta(2)-adrenergic receptor sequestration. We describe oxidative stress as a novel mechanism for regulation of the intracellular level of GRK2 during inflammatory processes. Moreover, our data demonstrate that oxidative stress may change the functioning of GPCRs via calpain-dependent regulation of GRK2 levels.

Interferon beta-1a counteracts effects of activation on the expression of G-protein-coupled receptor kinases 2 and 3, beta-arrestin-1, and regulators of G-protein signalling 2 and 16 in human mononuclear leukocytes

Activation regulates the responsiveness of G-protein-coupled receptors (GPCRs) on T cells, and modifications in the activity of GPCRs characterize lymphocytes from some immune disorders such as multiple sclerosis (MS) and rheumatoid arthritis (RA). Some lines of evidence suggest that such an effect is connected with the altered expression of some GPCRs regulatory proteins. Herein we demonstrate that phitoemagglutinin (PHA)-induced activation leads to differential expression of G-protein-coupled receptor kinase (GRK) 2, GRK3, beta-arrestin-1, regulators of G-protein signalling (RGS) 2, and RGS16 and decreases responsiveness of mononuclear leukocytes (MNL) to the beta-adrenergic agonist isoproterenol. Interferon beta-1a (IFN beta-1a), which is known to ameliorate the course of MS, counteracts the activation-induced effects on the expression of these GPCR regulatory proteins in MNL. Furthermore, IFN beta-1a quenches the effects of PHA on the isoproterenol-induced accumulation of cyclic AMP (cAMP). We suggest that regulation of GPCRs responsiveness may be a relevant property of IFN beta-1a in MS.

Stress hormones, proinflammatory and antiinflammatory cytokines, and autoimmunity

Recent evidence indicates that glucocorticoids and catecholamines, the major stress hormones, inhibit the production of proinflammatory cytokines, such as interleukin (IL)-12, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma, whereas they stimulate the production of antiinflammatory cytokines, such as IL-10, IL-4, and transforming growth factor (TGF)-beta. Thus, systemically, an excessive immune response, through activation of the stress system, stimulates an important negative feedback mechanism, which protects the organism from an "overshoot" of proinflammatory cytokines and other products of activated macrophages with tissue-damaging potential. Conversely, in certain local responses and under certain conditions, stress hormones actually may boost regional immune responses, through induction of TNF-alpha, IL-1, and IL-8, and by inhibiting TGF-beta production. Therefore, conditions that are associated with significant changes in stress system activity, such as acute or chronic stress, cessation of chronic stress, severe exercise, and pregnancy and the postpartum period, through modulation of the systemic or local pro/antiinflammatory cytokine balance, may suppress or potentiate autoimmune diseases activity and/or progression.

Immunopathogenesis of rheumatic diseases in the context of neuroendocrine interactions

Growing evidence supports the hypothesis that alterations of the stress response and interactions between the neuroendocrine and immune systems contribute to the pathogenesis of rheumatic diseases such as rheumatoid arthritis (RA). In particular, the hypothalamus-pituitary-adrenal (HPA) axis and the autonomic nervous system (ANS) are of special interest. Polymorphisms of the corticotropin-releasing hormone (CRH)-regulating region have been described recently. These polymorphisms are differentially distributed in RA patients and healthy subjects of various ethnic origin, thus supporting the hypothesis that they represent a new genetic marker for RA susceptibility. The decreased expression of beta(2)-adrenergic receptors (beta(2)-R) on lymphatic cells in rheumatic diseases like RA, together with an impaired influence of catecholamines on immune function in these patients, further underlines the concept of a dysfunction of the ANS in rheumatic diseases. Results from work in this field will provide more insight into the pathogenesis of RA and help to establish novel therapies for this chronic rheumatic disease.

Defective lymphocyte chemotaxis in beta-arrestin2- and GRK6-deficient mice

Lymphocyte chemotaxis is a complex process by which cells move within tissues and across barriers such as vascular endothelium and is usually stimulated by chemokines such as stromal cell-derived factor-1 (CXCL12) acting via G protein-coupled receptors. Because members of this receptor family are regulated ("desensitized") by G protein-coupled receptor kinase (GRK)-mediated receptor phosphorylation and beta-arrestin binding, we examined signaling and chemotactic responses in splenocytes derived from knockout mice deficient in various beta-arrestins and GRKs, with the expectation that these responses might be enhanced. Knockouts of beta-arrestin2, GRK5, and GRK6 were examined because all three proteins are expressed at high levels in purified mouse CD3+ T and B220+ B splenocytes. CXCL12 stimulation of membrane GTPase activity was unaffected in splenocytes derived from GRK5-deficient mice but was increased in splenocytes from the beta-arrestin2- and GRK6-deficient animals. Surprisingly, however, both T and B cells from beta-arrestin2-deficient animals and T cells from GRK6-deficient animals were strikingly impaired in their ability to respond to CXCL12 both in transwell migration assays and in transendothelial migration assays. Chemotactic responses of lymphocytes from GRK5-deficient mice were unaffected. Thus, these results indicate that beta-arrestin2 and GRK6 actually play positive regulatory roles in mediating the chemotactic responses of T and B lymphocytes to CXCL12.

Extracellular signal-regulated kinases control expression of G protein-coupled receptor kinase 2 (GRK2)

G protein-coupled receptor kinase 2 (GRK2) phosphorylates G protein-coupled receptors resulting in uncoupling from G proteins. Receptors modulate GRK2 expression, however the mechanistic basis for this effect is largely unknown. Here we report a novel mechanism by which receptors use the extracellular signal-regulated kinase (ERK) cascade to regulate GRK2 cellular levels. ERK activation by receptor stimulation elevated endogenous GRK2 while antagonist treatment decreased cellular GRK2. Activating ERK by overexpressing constitutive active MEK-1 or Ras elevated GRK2 protein levels while blocking ERK using PD98059 or dominant negative Ras abolished this effect. These data suggest ERK is a critical regulator of GRK2 levels.

Heterotrimeric G protein signaling: role in asthma and allergic inflammation

Asthma and rhinitis are pathophysiologic conditions associated with a prototypical allergic response to inhaled allergens consisting of both neuromechanical and inflammatory components. Heptahelical receptors that bind guanosine triphosphate-binding proteins (G proteins), referred to as G protein-coupled receptors (GPCRs), have been intimately linked with asthma and allergic inflammation for many years. G protein signaling mediates responses throughout the immune, nervous, and muscular systems that might contribute to the pathogenesis of allergic processes and asthma. For example, GPCR agonists or antagonists are used as therapies for asthma either by promoting airway smooth muscle relaxation (beta2 adrenergic receptor agonists) or by inhibiting inflammation in the nasal mucosa and airways (cysteinyl leukotriene receptor antagonists). The focus of this review is to explore how downstream signaling cascades elicited by GPCR activation contribute to the allergic phenotype and the mechanism by which pharmaceuticals alter signaling to generate a therapeutic effect. We also discuss physiologic modulators of G protein signaling, such as regulator of G protein signaling proteins and G protein receptor kinases, inasmuch as they represent potential new therapeutic targets in the treatment of atopy and other inflammatory conditions.

Somatic mutations in thyroid nodular disease

Thyroid nodules can be found in up to 50% of inhabitants of iodine-deficient areas and are classified as hot or cold thyroid nodules according to their scintigraphic characteristics. Studies of hot thyroid nodules with comparable mutation detection methods and screening at least exon 10 of the TSH receptor reported frequencies for somatic TSH-receptor mutations ranging from 20 to 82% in patients with similar iodine supply. We have recently screened 75 hot thyroid nodules for somatic TSH-receptor mutations with the more sensitive DGGE method and found somatic TSH-receptor mutations in 57% and Gsalpha mutations in 3%. As 50% of the mutation-negative nodules from female patients are of monoclonal origin when tested for X-chromosome inactivation somatic mutations in other genes are likely to cause the development of hot thyroid nodules. Scintigraphically nonsuppressible areas have been identified in up to 40% of euthyroid goiters in iodine-deficient areas. We recently identified somatic TSH-receptor mutations in microscopic autonomous areas with increased 125T uptake in euthyroid goiters studied by autoradiography 20 years ago. These constitutively activating somatic TSH-receptor mutations in minute autoradiographically hot areas of euthyroid goiters are very likely starting foci which most likely lead to toxic thyroid nodules in iodine-deficient goiters. Therefore iodine deficiency does not only lead to euthyroid goiters but also to thyroid autonomy. The latter is also suggested by epidemiologic studies. Similar mechanisms induced by iodine deficiency and the subsequent hyperplasia, mutagenesis, and selection of cell clones could also lead to cold thyroid nodules by somatic mutations that only initiate growth but not hyperfunction of the affected thyroid epithelial cell. Somatic ras mutations have frequently been detected in histologically characterized thyroid adenomas or adenomatous nodules. However, they seem to be rare in cold thyroid nodules. Since the majority of these latter nodules and 60% of the cold thyroid nodules are monoclonal other somatic mutations are likely in these nodules.

Increased expression of G protein-coupled receptor kinases in cystic fibrosis lung

A reduction in airway beta-adrenoceptor density has been reported in cystic fibrosis lung but the mechanism underlying this defect remains unclear. In this study, we have investigated whether the decrease in beta2-adrenoceptor associates with altered G protein-coupled receptor kinase (GRK) levels. We assessed GRK activity by rhodopsin phosphorylation, and beta2-adrenoceptor and GRK at the mRNA and protein levels by Northern and Western blotting in peripheral lung samples from normal donors and patients with cystic fibrosis. GRK activity was significantly increased in peripheral cystic fibrosis lung with parallel increases in GRK2/5 mRNAs and protein expression. Functionally, isoproterenol-stimulated adenylyl cyclase activity was also diminished by 65% in cystic fibrosis lung homogenates. These data suggest that the increase in GRK activity may be one of the mechanisms underlying alterations in the coupling between beta2-adrenoceptor and adenylyl cyclase via G-protein and may thus contribute to the downregulation of beta2-adrenoceptor in cystic fibrosis lung.

Signal transduction in rheumatoid arthritis

Extracellular signals are transduced intracellularly by multiple pathways, resulting in alterations in the transcription and translation of specific proteins. The end result of some of these signalling pathways is the production of proteins, including cytokines and matrix metalloproteinases, that are implicated in the pathogenesis of rheumatoid arthritis. This chapter includes a discussion of these signal transduction pathways, including tumour necrosis factor receptor signalling, interleukin-1, -4, and -6 receptor signalling, stress- and mitogen-activated protein kinase pathways, CD14 and Toll-like receptor signalling, and T cell signal transduction. The known effects of currently available rheumatoid arthritis (RA) therapeutics on these signalling pathways are also reviewed. In addition, potential future targets for therapeutic intervention in RA are discussed.

Mens sana in corpore sano--and vice versa. The role of the autonomic nervous system in the immune-neuroendocrine dialogue

Adrenergic and cholinergic transmitters of the autonomic nervous system have important roles in the mutual interrelationships between the brain and the immune system. Besides expressing functional adrenergic and cholinergic receptors, lymphocytes and other immune cells were found to synthesize and release catecholamines and acetylcholine pointing to a possible role of these mediators in the intrinsic regulation of the immune system. In this review we will summarize concepts of Psychoneuroimmunology on the basis of data as obtained in vitro and in experimental studies in animal models, and discuss their relevance to human clinical medicine.

Beta-arrestin- and c-Src-dependent degradation of G-protein-coupled receptor kinase 2

G-protein-coupled receptor kinase 2 (GRK2) plays a key role in the regulation of G-protein-coupled receptors (GPCRs). GRK2 expression is altered in several pathological conditions, but the molecular mechanisms that modulate GRK2 cellular levels are largely unknown. We recently have described that GRK2 is degraded rapidly by the proteasome pathway. This process is enhanced by GPCR stimulation and is severely impaired in a GRK2 mutant that lacks kinase activity (GRK2-K220R). In this report, we find that beta-arrestin function and Src-mediated phosphorylation of GRK2 are critically involved in GRK2 proteolysis. Overexpression of beta-arrestin triggers GRK2-K220R degradation based on its ability to recruit c-Src, since this effect is not observed with beta-arrestin mutants that display an impaired c-Src interaction. The presence of an inactive c-Src mutant or of tyrosine kinase inhibitors strongly inhibits co-transfected or endogenous GRK2 turnover, respectively, and a GRK2 mutant with impaired phosphorylation by c-Src shows a markedly retarded degradation. This pathway for the modulation of GRK2 protein stability puts forward a new feedback mechanism for regulating GRK2 levels and GPCR signaling.

In vivo immunomodulation by peripheral adrenergic and cholinergic agonists/antagonists in rat and mouse models

Our work is devoted to defining relationships between the immune system and the adrenergic and cholinergic systems in vivo. In the rat model, we have shown that the cells of different immune compartments express the genes of a defined set of adrenergic/cholinergic receptors, and it was shown that lymphocytes are a site of non-neuronal production of norepinephrine and acetylcholine. Furthermore, using implantable slow-release tablets containing adrenergic or cholinergic agonists/antagonists, distinct and partly opposite effects were observed on peripheral immune functions. Concerning sympathetic immunoregulation, our data--in contrast to those of other studies--suggest that an enhanced adrenergic tonus leads to immunosuppression primarily via alpha 2-receptor-mediated mechanisms. Beta-blockade strongly enhances this effect, most likely by inhibition of pineal melatonin synthesis. In recent experiments on the kinetics it was found that the continuous alpha-adrenergic treatment entails a strong suppression of cellular responsiveness during the first few hours, which is increasingly followed by a general loss of lymphocytes in blood and lymphoid organs most likely due to enhanced apoptosis. More recently, we have extended our studies to the mouse model. First data obtained with RNAse protection assays suggest a biphasic effect on the gene expression of several cytokines in spleen cells due to adrenergic in vivo treatment.

Involvement of the hypothalamic--pituitary--adrenal/gonadal axis and the peripheral nervous system in rheumatoid arthritis: viewpoint based on a systemic pathogenetic role

From the compendium presented above, the following statements become evident: 1) Inappropriately low secretion of cortisol in relation to inflammation is a typical feature of the inflammatory disease in patients with RA. 2) The secretion of adrenal androgens is significantly reduced, which is a problem in postmenopausal women and elderly men due to a lack of downstream sex hormones. 3) Serum levels of testosterone are markedly reduced in RA. 4) Sympathetic nerve fibers are markedly reduced in the synovial tissue of patients with RA, whereas proinflammatory sensory fibers (substance P) are present. 5) Substance P serves to continuously sense painful stimuli in the periphery, and the nociceptive input from the inflamed joint shows a large amplification in the spinal cord. This leads to continuous pain with stabilization of the afferent sensory input and continuous release of proinflammatory substance P into the lumen of the joint. From these facts it is obvious that alterations of the systemic antiinflammatory feedback systems contribute significantly to the pathogenesis of RA. Disease therapy directed at these alterations must provide a mechanism to replace the adrenal glands (glucocorticoids), the gonadal glands (androgens), and the sympathetic nervous system (adenosine increase by low-dose MTX, sulfasalazine, and salicylates) in order to integrate their immunosuppressive effects at the local site of synovial inflammation. Although local processes of the adaptive immune system are important in pathogenesis in the acute phase of RA, these mechanisms may be less important during the chronic phase of the disease in the absence of a specific trigger. We believe that a defect of systemic antiinflammatory feedback systems is an important factor in the perpetuation of RA. This review reinforces the belief that combined therapeutic approaches on a neuroendocrine immune basis are of crucial importance in a pathogenetically oriented therapy of RA.

Adjuvant arthritis induces down-regulation of G protein-coupled receptor kinases in the immune system

G protein-coupled receptors (GPCR) play a crucial role in the regulation of the immune response by, e.g., chemokines, PGs, and beta(2)-adrenergic agonists. The responsiveness of these GPCRs is turned off by the family of G protein-coupled receptor kinases (GRK1-6). These kinases act by phosphorylating the GPCR in an agonist-dependent manner, resulting in homologous desensitization of the receptor. Although GRKs are widely expressed throughout the body, leukocytes express relatively high levels of GRKs, in particular GRK2, -3, and -6. We investigated whether in vivo the inflammatory disease adjuvant arthritis (AA) induces changes in GRK expression and function in the immune system. In addition, we analyzed whether the systemic effects of AA also involve changes in GRKs in nonimmune organs. At the peak of the inflammatory process, we observed a profound down-regulation of GRK2, -3, and -6 in splenocytes and mesenteric lymph node cells from AA rats. Interestingly, no changes in GRK were observed in thymocytes and in nonimmune organs such as heart and pituitary. During the remission phase of AA, GRK levels in spleen and mesenteric lymph nodes are returning to baseline levels. The decrease in GRK2 at the peak of AA is restricted to CD45RA(+) B cells and CD4(+) T cells, and was not observed in CD8(+) T cells. In conclusion, we demonstrate in this study, for the first time, that an inflammatory process in vivo induces a tissue-specific down-regulation of GRKs in the immune system.

Interactions of autonomic nervous, neuroendocrine, and immune systems in rheumatoid arthritis

In general, it is assumed that the two pathways (i.e., HPA axis and sympathetic nervous system) probably act cooperatively to maintain homeostasis. The previously mentioned studies clearly point to a disturbance in the interaction between the ANS, the HPA axis, and the immune system in chronic rheumatic diseases (Fig. 2). Even early on in the course of RA, these changes can be observed. Along with the results obtained in animal models, an important role of neuroendocrine interactions in the pathogenesis of RA is proposed. Further studies are required to establish the exact contribution of the ANS in the initiation and perpetuation of RA. To date, it is quite obvious that neuropeptides play a part in the orchestration of the various molecules (e.g., cytokines) exerting modulatory effects on immune cells. One can speculate that therapeutic implications are likely to result from investigations on the ANS-immune interactions. Based on early observations that blocking catecholamine actions ameliorate symptoms of RA, it is quite promising to follow this avenue in investigating ANS-immune interactions of various time points of the disease. Conversely, further studies are required to determine the contribution of the HPA axis to the onset of RA. Results from ongoing studies are eagerly awaited so as to establish new therapeutic options. In the future,it may be possible to interfere with the inflammatory process in RA by an exactly timed neuroendocrine intervention right at or even before the onset of disease. Therapy with steroids in RA might be better planned based on the genetically determined reactivity of an individual's HPA axis. In this respect, a recent report by Masi et al is of special interest. Based on the current literature on the disturbances in the neuroendocrine, immune, and microvascular systems found in early RA, the authors hypothesize that an imbalance in the interactive homeostasis of these systems develops during a long preclinical phase and eventually leads to the outbreak of the disease in genetically predisposed individuals. This interesting hypothesis includes the perspective that individuals prone to develop RA may be identified in a preclinical phase and treated prophylactically. In any event, results from all these studies are promising in two ways: to gain more insight in the pathogenic process of RA and to establish novel therapies to help the patients bear their burden of a chronic rheumatic disease.

The influence of the hormonal system on pediatric rheumatic diseases

The role of NEI interactions in children with chronic inflammatory rheumatic disorders has not been systematically studied to the same extent as in adults. The data that are currently available suggest that NEI mechanisms are involved in the pathophysiology of some of the diseases. These include JRA, JSLE, and JAS. Prolactin has been most extensively investigated, showing interesting parallels with findings in adult rheumatologic diseases. Limited data on cortisol suggest a deficiency of production in JRA, a situation similar to that in adult RA. These findings suggest that there is a proinflammatory hormonal bias in children with JRA and JSLE. The data in children with chronic autoimmune inflammatory disorders seem to be identical to those seen in adults with RA and SLE, but a clear delineation of the role of the neuroendocrine-immune system in disease pathophysiology is still required. The neuroendocrine aspects of pediatric rheumatologic disease observed to date suggest a number of avenues for further research in the field of neuroendocrine immunology, which may open up novel therapeutic options.

Stress induces increases in IL-6 production by leucocytes of patients with the chronic inflammatory disease juvenile rheumatoid arthritis: a putative role for alpha(1)-adrenergic receptors

Juvenile rheumatoid arthritis (JRA) is characterized by chronic inflammation of the joints. In the present study we demonstrate that exposure of JRA patients to a noradrenergic stressor (cold pressor test) results in enhanced LPS-induced IL-6 production by peripheral blood cells of these patients. Healthy, age-matched controls had the same rise in norepinephrine, but do not respond with changes in IL-6 production after exposure to the cold pressor test. Moreover, PBMC of patients with JRA express mRNA encoding alpha(1)-adrenergic receptors (AR), predominantly of the alpha(1d)-AR subtype. In contrast, we could not detect mRNA encoding for alpha(1)-AR in PBMC of healthy controls. The results of this study suggest that expression of alpha(1)-AR mRNA in PBMC during chronic inflammation is associated with altered responses of the immune system to stress.

Biology of heterotrimeric G-protein signaling

The G proteins are components of a complex membrane signaling system designed to modulate extracellular signals as they are transmitted into the cell. The principal components are the receptor, the G proteins including the alpha, beta, gamma subunits and the effector. Associated with these molecules are several molecular processes by which the signal is transmitted, and regulated including desensitization. Molecules such as arrestin, the RGS (regulators of the G-protein signaling) as well as downstream kinases associated with cyclic AMP are key to regulating the G protein signal. Membrane lipids are key for both anchoring this signal system to the plasma membrane but also in defining the signaling process. Through understanding the biology of the signal system, a number of diseases have been linked to dysfunction of the G protein system. It is clear that this important membrane signal system will become the target for more intense investigation and pharmacologic manipulation to treat critical illness.

Therapeutic potential of phosphodiesterase-4 and -3 inhibitors in Th1-mediated autoimmune diseases

Phosphodiesterase-4 (PDE4) inhibitors have the potential to modulate immune responses from the Th1 toward the Th2 phenotype and are considered candidate therapies for Th1-mediated autoimmune disorders. However, depending on the model and cell types employed, studies of atopic individuals have come to the opposite conclusion, i.e., that PDE inhibitors may be beneficial in asthma. Using in vitro immunopharmacologic techniques we analyzed the effects of PDE4 and PDE3 inhibitors on human immune cells to address these discrepancies and broaden our understanding of their mechanism of action. Our results indicate that PDE inhibitors have complex inhibitory effects within in vivo achievable concentration ranges on Th1-mediated immunity, whereas Th2-mediated responses are mostly unaffected or enhanced. The Th2 skewing of the developing immune response is explained by the effects of PDE inhibitors on several factors contributing to T cell priming: the cytokine milieu; the type of costimulatory signal, i.e., up-regulation of CD86 and down-regulation of CD80; and the Ag avidity. The combination of PDE4 and PDE3 inhibitors expresses synergistic effects and may broaden the therapeutic window. Finally, we observed a differential sensitivity to PDE inhibition in autoreactive vs foreign Ag-specific T cells and cells derived from multiple sclerosis patients vs those derived from healthy donors. This suggests that PDE inhibition weakens the strength of the T cell stimulus and corrects the underlying disease-associated cytokine skew in T cell-mediated autoimmune disorders. These new findings broaden the understanding of the immunomodulatory actions of PDE inhibitors and underscore their promising drug profile for the treatment of autoimmune disorders.

The importance of being receptive

Neuroendocrine system and immune system can communicate via the use of soluble mediators like hormones, neurotransmitters and cytokines. The level of mediators secreted by either of these systems creates the milieu in which immune and neuroendocrine responses take place. For adequate communication between the systems, receptors for hormones, neurotransmitters and cytokines are required. This review describes the role of regulated expression and function of receptors for hormones and neurotransmitters within the immune system in neuroendocrine-immune communication.

Tachykinin receptor modulators: novel therapeutics for rheumatoid arthritis

The activation of a cellular immune response in a genetically susceptible individual is widely recognised as a main step in triggering rheumatoid arthritis (RA). The tachykinins, substance P (SP) and neurokinin A (NKA), can play a major role in different immune diseases. In patients with inflammatory joint disease, elevated levels of SP have been demonstrated in the synovial fluid of affected joints. It is well known that SP and, to a lesser extent, NKA are deeply involved in the processing of nociceptive signals and exert many pro-inflammatory actions, which may be elicited by an increased neuronal neurokinin release in arthritis; the mechanism behind this increase remains to be fully elucidated. Different observations suggest that one approach to the treatment of RA might be to inhibit the local effects of neurokinins in the affected joints. This review will summarise the more relevant aspects of this topic.