cAMP is not involved in interleukin-1-induced interleukin-6 release from human astrocytoma cells

The P2X7 receptor links mechanical strain to cytokine IL-6 up-regulation and release in neurons and astrocytes

Mechanical strain in neural tissues can lead to the up-regulation and release of multiple cytokines including interleukin 6 (IL-6). In the retina, the mechanosensitive release of ATP can autostimulate P2X7 receptors on both retinal ganglion cell neurons and optic nerve head astrocytes. Here, we asked whether the purinergic signaling contributed to the IL-6 response to increased intraocular pressure (IOP) in vivo, and stretch or swelling in vitro. Rat and mouse eyes were exposed to non-ischemic elevations in IOP to 50-60 mmHg for 4 h. A PCR array was used to screen cytokine changes, with quantitative (q)PCR used to confirm mRNA elevations and immunoblots used for protein levels. P2X7 antagonist Brilliant Blue G (BBG) and agonist (4-benzoyl-benzoyl)-ATP (BzATP) were injected intravitreally. ELISA was used to quantify IL-6 release from optic nerve head astrocytes or retinal ganglion cells. Receptor identity was confirmed pharmacologically and in P2X7^-/- mice, acute elevation of IOP altered retinal expression of multiple cytokine genes. Elevation of IL-6 was greatest, with expression of IL1rn, IL24, Tnf, Csf1, and Lif also increased more than twofold, while expression of Tnfsf11, Gdf9, and Tnfsf4 were reduced. qPCR confirmed the rise in IL-6 and extracellular ATP marker ENTPD1, but not pro-apoptotic genes. Intravitreal injection of P2X7 receptor antagonist BBG prevented the pressure-dependent rise in IL-6 mRNA and protein in the rat retina, while injection of P2X7 receptor agonist BzATP was sufficient to elevate IL-6 expression. IOP elevation increased IL-6 in wild-type but not P2X7R knockout mice. Application of mechanical strain to isolated optic nerve head astrocytes increased IL-6 levels. This response was mimicked by agonist BzATP, but blocked by antagonists BBG and A839977. Stretch or BzATP led to IL-6 release from both astrocytes and isolated retinal ganglion cells. The mechanosensitive up-regulation and release of cytokine IL-6 from the retina involves the P2X7 receptor, with both astrocytes and neurons contributing to the response.

Interleukin-6, a major cytokine in the central nervous system

Interleukin-6 (IL-6) is a cytokine originally identified almost 30 years ago as a B-cell differentiation factor, capable of inducing the maturation of B cells into antibody-producing cells. As with many other cytokines, it was soon realized that IL-6 was not a factor only involved in the immune response, but with many critical roles in major physiological systems including the nervous system. IL-6 is now known to participate in neurogenesis (influencing both neurons and glial cells), and in the response of mature neurons and glial cells in normal conditions and following a wide arrange of injury models. In many respects, IL-6 behaves in a neurotrophin-like fashion, and seemingly makes understandable why the cytokine family that it belongs to is known as neuropoietins. Its expression is affected in several of the main brain diseases, and animal models strongly suggest that IL-6 could have a role in the observed neuropathology and that therefore it is a clear target of strategic therapies.

IL-6 expression induced by adenosine A2b receptor stimulation in U373 MG cells depends on p38 mitogen activated kinase and protein kinase C

Adenosine binds to a class of G-protein coupled receptors, which are further distinguished as A(1), A(2a), A(2b) and A(3) adenosine receptors. As we have shown earlier, the stable adenosine analogue NECA (N6-(R)-phenylisopropyladenosine) stimulates IL-6 expression in the human astrocytoma cell line U373 MG via the A(2b) receptor. The mechanism by which NECA promotes astrocytic IL-6 expression has not been identified. By using various inhibitors of signal transduction, we found that p38 mitogen-activated protein kinases (MAPK) activation (inhibitor SB202190), but not extracellular signal-regulated kinase (ERK) (PD98059) and c-jun N-terminal kinase (JNK)(SP600125), is essential in the NECA-induced signalling cascade that leads to the increase in IL-6 synthesis in U373 MG cells. Results obtained with protein kinase C (PKC) inhibitors that have different substrate specificities, indicated that the PKC delta and epsilon isoforms are also involved in adenosine receptor A(2b) dependent upregulation of IL-6 expression. This is supported by the fact that NECA induced the activation of PKC delta and epsilon in U373 MG cells.

Suppression of beta-adrenergic responsiveness of L-type Ca2+ current by IL-1beta in rat ventricular myocytes

The possible mechanism by which interleukin-1beta (IL-1beta) affects beta-adrenergic responsiveness of L-type Ca2+ current (ICa,L) was examined in adult rat ventricular myocytes by use of whole cell patch-clamp techniques. In the presence of isoproterenol (Iso), exposure for 3 min to IL-1beta suppressed the Iso-activated ICa,L. In the presence of IL-1beta, the response of ICa,L to Iso was decreased, and the EC50 for Iso stimulation was increased. However, IL-1beta had no effect on [3H]CGP-12177 binding, displacement of [3H]CGP-12177 binding by Iso, or on basal and Iso-enhanced cAMP content. When ICa,L was activated by extracellular application of forskolin or 8-(4-chlorophenylthio)-cAMP, a membrane-permeable cAMP analog, or by intracellular dialysis with cAMP, IL-1beta had little effect on ICa,L. In contrast, in the presence of cAMP, IL-1beta still suppressed the Iso-enhanced ICa,L. These results show that the IL-1beta-induced decrease in beta-adrenergic responsiveness of ICa,L does not result from inhibition of beta-adrenoceptor binding, adenylyl cyclase activity, or cAMP-mediated pathways, suggesting a cAMP-independent mechanism.

Identification and functional importance of IL-1 receptors on rat parietal cells

We studied the expression of interleukin-1 (IL-1) receptors and the effect of IL-1beta on the function of highly enriched (>97%) rat parietal cells. RT-PCR of parietal cell poly(A)+ RNA with primers specific for the rat IL-1 receptor revealed a single 547-kb PCR product highly homologous to the published sequence of the IL-1 receptor. Northern blot analysis of poly(A)+ RNA of rat parietal cells and brain revealed a single RNA species of 5.7 kb. Cytochemistry of parietal cell IL-1 receptor was performed with biotinylated recombinant human IL-1beta, visualized by avidin-coupled fluorescein. Corresponding to the high degree of parietal cell enrichment, 95% of the cells stained positive. Basal H+ production ([14C]aminopyrine accumulation) was not changed by IL-1beta (0.25-100 pg/ml) nor was the response to histamine or carbachol when added simultaneously with the cytokine. However, when parietal cells were preincubated with IL-1beta (0.5-5 pg/ml) for 10 min before the addition of histamine or carbachol, the response to these secretagogues was reduced by 35 and 67%, respectively. Inhibition by IL-1beta was fully reversed by the human recombinant IL-1 receptor antagonist. Preincubation of parietal cells with IL-1beta failed to alter histamine-stimulated cAMP production but markedly inhibited carbachol-induced formation of D-myo-inositol 1,4, 5-trisphosphate. In fura 2-loaded, purified parietal cells, 10 min preincubation with IL-1beta dramatically reduced the initial transient peak elevation of intracellular Ca2+ concentration in response to carbachol. We conclude that rat parietal cells express IL-1 receptors mediating inhibition of H+ production. The antisecretory effect of IL-1beta may contribute to hypoacidity secondary to acute Helicobacter pylori infection or during chronic colonization by H. pylori preferring the fundic mucosa.

Interleukin-6 (IL-6)--a molecule with both beneficial and destructive potentials

Interleukin-6 (IL-6), a member of the neuropoietic cytokine family, initially was described in terms of its activities in the immune system and during inflammation. Accumulating evidence supports an essential role of IL-6 in the development, differentiation, regeneration and degeneration of neurons in the peripheral and central nervous system. Major sites of IL-6 synthesis are neurons and glial cells. Interleukin-6 functions are mediated by a specific receptor system composed of a binding site and a signal transducer. This receptor system can be modulated by a complex of IL-6 and soluble IL-6 receptor acting as agonist. The IL-6 can exert completely opposite actions on neurons, triggering either neuronal survival after injury or causing neuronal degeneration and cell death in disorders such as Alzheimer's disease. Development of selective IL-6 agonists and antagonists, as well as the usage of soluble IL-6 receptors, offers new possibilities for the treatment of neurodegenerative disorders. Furthermore, optimized genetic mouse models, including transgenic and knockout animals, should help to define the physiological and pathophysiological role of IL-6 in the nervous system.

Interleukin-1 signal transduction

Interleukin-1 (IL-1) is primarily an inflammatory cytokine, although it is capable of mediating a wide variety of effects on many different cell types. Nearly every known signal transduction pathway has been reported to be activated in response to IL-1. However, the significance of many of these signaling events is unclear, due to the use of different and sometimes unique cell lines in studying IL-1-initiated signal transduction. Complicating matters further is the lack of association in many studies between identified IL-1-induced signals and subsequent biological responses. In this article, we review what is known about IL-1 receptor signaling and, whenever possible, correlate signaling events to biological responses.