Possible Regulation of P-Glycoprotein Function by Adrenergic Agonists II: Study with Isolated Rat Jejunal Sheets and Caco-2 Cell monolayers

To clarify the regulation of drug absorption by the enteric nervous system, we investigated how adrenergic agonists (adrenaline (ADR), clonidine (CLO), dobutamine (DOB)) and dibutyryl cAMP (DBcAMP) affected P-glycoprotein (P-gp) function by utilizing isolated rat jejunal sheets and Caco-2 cell monolayers. ADR and CLO significantly decreased the secretory transport (Papptotal) of rhodamine-123 and tended to decrease the transport via P-gp (PappP-gp) and passive transport (Papppassive). In contrast, DBcAMP significantly increased and DOB tended to increase Papptotal and both tended to increase PappP-gpand Papppassive. Changes in P-gp expression on brush border membrane by adrenergic agonists and DBcAMP were significantly correlated with PappP-gp, while P-gp expression was not changed in whole cell homogenates, suggesting that the trafficking of P-gp would be responsible for its functional changes. Papppassive was inversely correlated with transmucosal or transepithelial electrical resistance, indicating that adrenergic agonists affected the paracellular permeability. Adrenergic agonists also changed cAMP levels, which were significantly correlated with PappP-gp. Furthermore, protein kinase A (PKA) or PKC inhibitor significantly decreased PappP-gp in Caco-2 cell monolayers, suggesting that they would partly contribute to the changes in P-gp activity. In conclusion, adrenergic agonists regulated P-gp function and paracellular permeability, which would be caused via adrenoceptor stimulation.

Role of the cAMP-PKA-NF-κB pathway in Mucin1 over-expression in A549 cells during Respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is the most common pathogen associated with acute lower respiratory tract infections in infants and young children worldwide. RSV commonly presents as bronchiolitis in young children; however, it can sometimes progress to pneumonia, respiratory failure, apnoea and even death. Although mucin1 (MUC1), a type of transmembrane glycoprotein present on airway epithelial surfaces, plays a crucial anti-inflammatory role in airway infections; however, its roles in RSV-associated acute lower respiratory tract infections have rarely been explored. In this study, we first revealed very high MUC1 protein levels in the exacerbation phase in sputum samples from children with RSV bronchiolitis. Because MUC1 is the downstream target of tumour necrosis factor-alpha (TNF-α) in RSV-infected A549 cells, we observed the inhibition of NF-κB activity, main downstream signalling of TNF-α and remarkably reduced levels of MUC1 in RSV-infected and TNF-α treated A549 cells. Furthermore, the cyclic adenosine monophosphate (cAMP) analogue (dbcAMP) downregulated the protein levels of p-IκBα and MUC1 in TNF-α-treated A549 cells. By contrast, a protein kinase A inhibitor (KT5720) up-regulated the levels of those proteins. dbcAMP and KT5720 had the same effects on MUC1 protein levels in RSV-infected A549 cells. In conclusion, we found that the cAMP-PKA-NF-κB pathway may play a role in the regulation of MUC-1 over-expression during RSV infection.

Dietary dibutyryl cAMP supplementation regulates the fat deposition in adipose tissues of finishing pigs via cAMP/PKA pathway

This study investigated potential mechanism of dibutyryl-cAMP (db-cAMP) on porcine fat deposition. (1) Exp.1, 72 finishing pigs were allotted to 3 treatments (0, 10 or 20 mg/kg dbcAMP) with 6 replicates. dbcAMP increased the hormone sensitive lipase (HSL) activity and expression of β-adrenergic receptor (β-AR) and growth hormone receptor (GHR), but decreased expression of peroxisome proliferator-activated receptor gamma 2 (PPAR-γ2) and adipocyte fatty acid binding protein (A-FABP) in back fat. dbcAMP upregulated expression of β-AR, GHR, PPAR-γ2 and A-FABP, but decreased insulin receptor (INSR) expression in abdominal fat. Dietary dbcAMP increased HSL activity and expression of G protein-coupled receptor (GPCR), cAMP-response element-binding protein (CREB) and insulin-like growth factor-1 (IGF-1), but decreased fatty acid synthase (FAS) and lipoprotein lipase (LPL) activities, and expression of INSR, cAMP-response element-binding protein (C/EBP-α) and A-FABP in perirenal fat. (2) Exp. 2, dbcAMP suppressed the proliferation and differentiation of porcine preadipocytes in a time- and dose-dependent manner, which might be associated with increased activities of cAMP and protein kinase A (PKA), and expression of GPCR, β-AR, GHR and CREB via inhibiting C/EBP-α and PPAR-γ2 expression. Collectively, dbcAMP treatment may reduce fat deposition by regulating gene expression related to adipocyte differentiation and fat metabolism partially via cAMP-PKA pathway.

Signaling in cAMP-stimulated ecdysteroidogenesis in prothoracic glands of the silkworm, Bombyx mori

In the present study, we investigated downstream pathways of cyclic adenosine monophosphate (cAMP) signaling (which is related to prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis) in Bombyx mori prothoracic glands (PGs). Results showed that treatment with either dibutyryl cAMP (dbcAMP) or 1-methyl-3-isobutylxanthine (MIX) inhibited phosphorylation of adenosine 5'-monophosphate-activated protein kinase (AMPK) and activated phosphorylation of the translational repressor, 4E-binding protein (4E-BP), a marker of target of rapamycin (TOR) signaling. A chemical activator of AMPK (5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside, AICAR) increased dbcAMP-inhibited AMPK phosphorylation and blocked dbcAMP-stimulated phosphorylation of 4E-BP, indicating that inhibition of AMPK phosphorylation lies upstream of dbcAMP-stimulated TOR signaling. Treatment of PGs with dbcAMP and MIX also stimulated phosphorylation of a 37-kDa protein, as recognized by a protein kinase C (PKC) substrate antibody, indicating that cAMP activates PKC signaling. Treatment with either LY294002 or AICAR did not affect dbcAMP-stimulated phosphorylation of the PKC-dependent 37-kDa protein, indicating that cAMP-stimulated PKC signaling is not related to phosphoinositide 3-kinase (PI3K) or AMPK. In addition, dbcAMP-stimulated ecdysteroidogenesis in PGs was partially inhibited by pretreatment with either LY294002, AICAR, or calphostin C. From these results, we concluded that AMPK/TOR/4E-BP and PKC pathways are involved in ecdysteroidogenesis of PGs stimulated by cAMP signaling in B. mori.

Synchronization of In Vitro Maturation in Porcine Oocytes

When removed from the follicles, during the 44 h process of in vitro maturation (IVM) fully grown porcine oocytes resume meiosis spontaneously from the late diplotene stage of the first meiotic prophase and proceed to the metaphase-II (MII) stage at which they remain arrested until fertilization. However, the spontaneous resumption may start at various times causing heterogeneity in the nuclear stage and also in cytoplasmic characteristics within a population. Those oocytes that reach the MII stage earlier than others undergo an aging process which is detrimental for further embryo development. The synchronization of nuclear progression of porcine oocytes can be achieved by a transient inhibition of meiotic resumption during the first 20-22 h of IVM by the elevation of intracellular levels of cyclic adenosine monophosphate (cAMP) using the cellular membrane-permeable analog of cAMP, dibutyryl cyclic AMP. A simple and efficient protocol for such treatment is described below.

The Hippo pathway mediates inhibition of vascular smooth muscle cell proliferation by cAMP

AIMS

Inhibition of vascular smooth muscle cell (VSMC) proliferation by intracellular cAMP prevents excessive neointima formation and hence angioplasty restenosis and vein-graft failure. These protective effects are mediated via actin-cytoskeleton remodelling and subsequent regulation of gene expression by mechanisms that are incompletely understood. Here we investigated the role of components of the growth-regulatory Hippo pathway, specifically the transcription factor TEAD and its co-factors YAP and TAZ in VSMC.

METHODS AND RESULTS

Elevation of cAMP using forskolin, dibutyryl-cAMP or the physiological agonists, Cicaprost or adenosine, significantly increased phosphorylation and nuclear export YAP and TAZ and inhibited TEAD-luciferase report gene activity. Similar effects were obtained by inhibiting RhoA activity with C3-transferase, its downstream kinase, ROCK, with Y27632, or actin-polymerisation with Latrunculin-B. Conversely, expression of constitutively-active RhoA reversed the inhibitory effects of forskolin on TEAD-luciferase. Forskolin significantly inhibited the mRNA expression of the pro-mitogenic genes, CCN1, CTGF, c-MYC and TGFB2 and this was reversed by expression of constitutively-active YAP or TAZ phospho-mutants. Inhibition of YAP and TAZ function with RNAi or Verteporfin significantly reduced VSMC proliferation. Furthermore, the anti-mitogenic effects of forskolin were reversed by overexpression of constitutively-active YAP or TAZ.

CONCLUSION

Taken together, these data demonstrate that cAMP-induced actin-cytoskeleton remodelling inhibits YAP/TAZ-TEAD dependent expression of pro-mitogenic genes in VSMC. This mechanism contributes novel insight into the anti-mitogenic effects of cAMP in VSMC and suggests a new target for intervention.

Acute glucagon induces postprandial peripheral insulin resistance

Glucagon levels are often moderately elevated in diabetes. It is known that glucagon leads to a decrease in hepatic glutathione (GSH) synthesis that in turn is associated with decreased postprandial insulin sensitivity. Given that cAMP pathway controls GSH levels we tested whether insulin sensitivity decreases after intraportal (ipv) administration of a cAMP analog (DBcAMP), and investigated whether glucagon promotes insulin resistance through decreasing hepatic GSH levels.Insulin sensitivity was determined in fed male Sprague-Dawley rats using a modified euglycemic hyperinsulinemic clamp in the postprandial state upon ipv administration of DBcAMP as well as glucagon infusion. Glucagon effects on insulin sensitivity was assessed in the presence or absence of postprandial insulin sensitivity inhibition by administration of L-NMMA. Hepatic GSH and NO content and plasma levels of NO were measured after acute ipv glucagon infusion. Insulin sensitivity was assessed in the fed state and after ipv glucagon infusion in the presence of GSH-E. We founf that DBcAMP and glucagon produce a decrease of insulin sensitivity, in a dose-dependent manner. Glucagon-induced decrease of postprandial insulin sensitivity correlated with decreased hepatic GSH content and was restored by administration of GSH-E. Furthermore, inhibition of postprandial decrease of insulin sensitivity L-NMMA was not overcome by glucagon, but glucagon did not affect hepatic and plasma levels of NO. These results show that glucagon decreases postprandial insulin sensitivity through reducing hepatic GSH levels, an effect that is mimicked by increasing cAMP hepatic levels and requires physiological NO levels. These observations support the hypothesis that glucagon acts via adenylate cyclase to decrease hepatic GSH levels and induce insulin resistance. We suggest that the glucagon-cAMP-GSH axis is a potential therapeutic target to address insulin resistance in pathological conditions.

NCI-H295R, a human adrenal cortex-derived cell line, expresses purinergic receptors linked to Ca²⁺-mobilization/influx and cortisol secretion

Purinergic receptor expression and involvement in steroidogenesis were examined in NCI-H295R (H295R), a human adrenal cortex cell line which expresses all the key enzymes necessary for steroidogenesis. mRNA/protein for multiple P1 (A_2A and A_2B), P2X (P2X₅ and P2X₇), and P2Y (P2Y₁, P2Y₂, P2Y₆, P2Y₁₂, P2Y₁₃, and P2Y₁₄) purinergic receptors were detected in H295R. 2MeS-ATP (10–1000 µM), a P2Y₁ agonist, induced glucocorticoid (GC) secretion in a dose-dependent manner, while other extracellular purine/pyrimidine agonists (1–1000 µM) had no distinct effect on GC secretion. Extracellular purines, even non-steroidogenic ones, induced Ca²⁺-mobilization in the cells, independently of the extracellular Ca²⁺ concentration. Increases in intracellular Ca²⁺ concentration induced by extracellular purine agonists were transient, except when induced by ATP or 2MeS-ATP. Angiotensin II (AngII: 100 nM) and dibutyryl-cyclic AMP (db-cAMP: 500 µM) induced both GC secretion and Ca²⁺-mobilization in the presence of extracellular Ca²⁺ (1.2 mM). GC secretion by AngII was reduced by nifedipine (10–100 µM); whereas the Ca²⁺ channel blocker did not inhibit GC secretion by 2MeS-ATP. Thapsigargin followed by extracellular Ca²⁺ exposure induced Ca²⁺-influx in H295R, and the cells expressed mRNA/protein of the component molecules for store-operated calcium entry (SOCE): transient receptor C (TRPC) channels, calcium release-activated calcium channel protein 1 (Orai-1), and the stromal interaction molecule 1 (STIM1). In P2Y₁-knockdown, 2MeS-ATP-induced GC secretion was significantly inhibited. These results suggest that H295R expresses a functional P2Y₁ purinergic receptor for intracellular Ca²⁺-mobilization, and that P2Y₁ is linked to SOCE-activation, leading to Ca²⁺-influx which might be necessary for glucocorticoid secretion.

Progesterone increases manganese superoxide dismutase expression via a cAMP-dependent signaling mediated by noncanonical Wnt5a pathway in human endometrial stromal cells

CONTEXT

Manganese superoxide dismutase (Mn-SOD), an antioxidant enzyme in the mitochondria, protects cells by scavenging superoxide radicals in human endometrial stromal cells (ESCs). Mn-SOD increases in ESCs during decidualization induced by progesterone.

OBJECTIVE

The present study investigated the molecular mechanism for Mn-SOD expression induced by progesterone in human ESCs.

METHODS

ESCs were incubated with medroxyprogesterone acetate (MPA; 10(-6) m) or dibutyryl-cAMP (0.5 mm) for 17 d. To determine whether a cAMP-dependent signaling pathway is involved in the MPA-induced Mn-SOD expression, ESCs were treated with H89, an inhibitor of cAMP-dependent protein kinase A. A chromatin immunoprecipitation assay was performed to examine the binding of cAMP-binding protein to the cAMP-response element on the Mn-SOD gene promoter. To examine the involvement of Wnt5a signaling, anti-Wnt5a antibodies were used to neutralize the Wnt5a activities.

RESULTS

Mn-SOD and Wnt5a mRNA levels and intracellular cAMP concentrations were significantly increased by MPA. These increases were accompanied by an increase in the mRNA expression of IGF-binding protein-1, a marker of decidualization. The increase in Mn-SOD mRNA levels by MPA or dibutyryl-cAMP was completely inhibited by H89. The chromatin immunoprecipitation assay revealed that MPA induced cAMP-binding protein binding with cAMP-response element on the Mn-SOD gene promoter. The increase in intracellular cAMP concentrations by MPA was completely inhibited by treatment with anti-Wnt5a antibodies. MPA treatment had no effects on β-catenin expression.

CONCLUSIONS

Progesterone increased Mn-SOD expression via a cAMP-dependent pathway in ESCs during decidualization. cAMP-dependent signaling stimulated by progesterone is mediated by noncanonical Wnt5a pathways that signal independently of β-catenin.

Regulation of gap junction coupling in bovine ciliary epithelium

Aqueous humor is formed by fluid transfer from the ciliary stroma sequentially across the pigmented ciliary epithelial (PE) cells, gap junctions, and nonpigmented ciliary epithelial (NPE) cells. Which connexins (Cx) contribute to PE-NPE gap junctional formation appears species specific. We tested whether small interfering RNA (siRNA) against Cx43 (siCx43) affects bovine PE-NPE communication and whether cAMP affects communication. Native bovine ciliary epithelial cells were studied by dual-cell patch clamping, Lucifer Yellow (LY) transfer, quantitative polymerase chain reaction with reverse transcription (qRT-PCR), and Western immunoblot. qRT-PCR revealed at least 100-fold greater expression for Cx43 than Cx40. siCx43 knocked down target mRNA expression by 55 +/- 7% after 24 h, compared with nontargeting control siRNA (NTC1) transfection. After 48 h, siCx43 reduced Cx43 protein expression and LY transfer. The ratio of fluorescence intensity (R(f)) in recipient to donor cell was 0.47 +/- 0.09 (n = 11) 10 min after whole cell patch formation in couplets transfected with NTC1. siCx43 decreased R(f) by approximately 60% to 0.20 +/- 0.07 (n = 13, P < 0.02). Dibutyryl-cAMP (500 microM) also reduced LY dye transfer by approximately 60%, reducing R(f) from 0.41 +/- 0.05 (n = 15) to 0.17 +/- 0.05 (n = 20) after 10 min. Junctional currents were lowered by approximately 50% (n = 6) after 10-min perfusion with 500 microM dibutyryl-cAMP (n = 6); thereafter, heptanol abolished the currents (n = 5). Preincubation with the PKA inhibitor H-89 (2 microM) prevented cAMP-triggered current reduction (n = 6). We conclude that 1) Cx43, but not Cx40, is a major functional component of bovine PE-NPE gap junctions; and 2) under certain conditions, cAMP may act through PKA to inhibit bovine PE-NPE gap junctional communication.

Involvement of cAMP/Epac/PI3K-dependent pathway in the antiproteolytic effect of epinephrine on rat skeletal muscle

Very little is known about the signaling pathways by which catecholamines exert anabolic effects on muscle protein metabolism, stimulating protein synthesis and suppressing proteolysis. The present work tested the hypothesis that epinephrine-induced inhibition of muscle proteolysis is mediated through the cAMP/Epac/PI3K-dependent pathway with the involvement of AKT and Foxo. The incubation of extensor digitorum longus (EDL) muscles from rats with epinephrine and/or insulin increased the phosphorylation of AKT and its downstream target Foxo3a, a well-known effect that prevents Foxo translocation to the nucleus and the activation of proteolysis. Similar effects on AKT/Foxo signaling were observed in muscles incubated with DBcAMP (cAMP analog). The stimulatory effect of epinephrine on AKT phosphorylation was completely blocked by wortmannin (selective PI3K inhibitor), suggesting that the epinephrine-induced activation of AKT is mediated through PI3K. As for epinephrine and DBcAMP, the incubation of muscles with 8CPT-2Me-cAMP (selective Epac agonist) reduced rates of proteolysis and increased phosphorylation levels of AKT and Foxo3a. The specific PKA agonist (N6BZ-cAMP) inhibited proteolysis and abolished the epinephrine-induced AKT and Foxo3a phosphorylation. On the other hand, inhibition of PKA by H89 further increased the phosphorylation levels of AKT and Foxo3a induced by epinephrine, DBcAMP or 8CPT-2Me-cAMP. These findings suggest that the antiproteolytic effect of the epinephrine on isolated skeletal muscle may occur through a cAMP/Epac/PI3K-dependent pathway, which leads to the phosphorylation of AKT and Foxo3a. The parallel activation of PKA-dependent pathway also inhibits proteolysis and seems to limit the stimulatory effect of cAMP on AKT/Foxo3a signaling.

Reactive oxygen-induced reactive oxygen formation during human sperm capacitation

Physiological processes are often activated by reactive oxygen species (ROS), such as the superoxide anion (O(2)(*)(-)) and nitric oxide (NO*) produced by cells. We studied the interactions between NO* and O(2)(*)(-), and their generators (NO* synthase, NOS, and a still elusive oxidase), in human spermatozoa during capacitation (transformations needed for acquisition of fertility). Albumin, fetal cord serum ultrafiltrate, and L-arginine triggered capacitation and ROS generation (NO* and O(2)(*)(-)) and superoxide dismutase (SOD) and NOS inhibitors prevented all these effects. Surprisingly, capacitation due to exogenous NO* (or O(2)(*)(-)) was also blocked by SOD (or NOS inhibitors). Probes used were proven specific and innocuous on spermatozoa. Whereas O(2)(*)(-) was needed only for 30 min, the continuous NO* generation was essential for hours. Capacitation caused a time-dependent increase in protein tyrosine nitration that was prevented by SOD and NOS inhibitors, suggesting that O(2)(*)(-) and NO*. also act via the formation of ONOO(-). Spermatozoa treated with NO* (or O(2)(*)(-)) initiated a dose-dependent O(2)(*)(-) (or NO*) production, providing, for the first time in cells, a strong evidence for a two-sided ROS-induced ROS generation. Data presented show a close interaction between NO* and O(2)(*)(-) and their generators during sperm capacitation.

Role of 1alpha,25(OH)2 vitamin D3 on alpha-[1-(14)C]MeAIB accumulation in immature rat testis

1,25D3 is critical for the maintenance of normal reproduction since reduced fertility is observed in male rats on a vitamin D-deficient diet. Vitamin D-deficient male rats have incomplete spermatogenesis and degenerative testicular changes. In the present study we have examined the ionic involvement and intracellular messengers of the stimulatory effect of 1,25D3 on amino acid accumulation in immature rat testis. 1,25D3 stimulates amino acid accumulation from 10(-12) to 10(-6) M by increasing the slope to reach a maximum value at 10(-10) M, as compared to the control group. No effect was observed at a lower dose (10(-13) M). Time-course showed an increase on amino acid accumulation after 15, 30, and 60 min of incubation with 1,25D3 (10(-10) M). 1,25D3 stimulated amino acid accumulation in 11-day-old rat testis but not in testis that were 20 days old. Cycloheximide totally blocked the 1,25D3 action on amino acid accumulation. Furthermore, a localized elevation of cAMP increased the stimulatory effect of 1,25D3 and the blockage of PKA nullified the action of the hormone. In addition, 1,25D3 action on amino acid accumulation was also mediated by ionic pathways, since verapamil and apamine diminished the hormone effect. The stimulatory effect of 1,25D3 on amino acid accumulation is age-dependent and specific to this steroidal hormone since testosterone was not able to change amino acid accumulation in both ages studied. This study provides evidence for a dual effect for 1,25D3, pointing to a genomic effect that can be triggered by PKA, as well as to a rapid response involving Ca2+/K+ channels on the plasma membrane.

Cyclic AMP enhances Smad-mediated BMP signaling through PKA-CREB pathway

We present experimental results indicating involvement of cyclic AMP (cAMP)-mediated signaling in bone morphogenetic protein (BMP)-induced osteoblastic gene expression at the transcriptional level by luciferase activity assay in C2C12 cells using the promoter sequence of the Id1 gene, an early-response gene to BMPs, which contains both a BMP-responsive element (BRE) and a cAMP-response element (CRE). In cells transfected with luciferase gene driven by wild-type Id1 promoter, treatment with BMP-4 increased luciferase expression, which was further enhanced by the addition of dibutyryl cAMP (dbcAMP). This dbcAMP-enhanced luciferase expression was significantly suppressed when the CRE site in the Id1 promoter was replaced by mutated CRE or endogenous CRE-binding protein (CREB) was knocked down by transfection of CREB RNAi. Pretreatment of cells with protein kinase A (PKA) inhibitor, H89, also dramatically reduced dbcAMP-enhanced luciferase expression. Immunoprecipitation assay showed phosphorylated-Smad1/5/8, phosphorylated-CREB, and CREB-binding protein (CBP) formed the transcriptional complex. These data indicate that cAMP-PKA/CREB/CRE signaling potentially enhances BMP-induced transcription through the BRE in the promoter of the BMP-responsive gene through a PKA-mediated pathway.

The cyclic GMP-protein kinase G pathway regulates cytoskeleton dynamics and motility in astrocytes

We have previously demonstrated that inflammatory compounds that increase nitric oxide (NO) synthase expression have a biphasic effect on the level of the NO messenger cGMP in astrocytes. In this work, we demonstrate that NO-dependent cGMP formation is involved in the morphological change induced by lipopolysaccharide (LPS) in cultured rat cerebellar astroglia. In agreement with this, dibutyryl-cGMP, a permeable cGMP analogue, and atrial natriuretic peptide, a ligand for particulate guanylyl cyclase, are both able to induce process elongation and branching in astrocytes resulting from a rapid, reversible and concentration-dependent redistribution of glial fibrillary acidic protein (GFAP) and actin filaments without significant change in protein levels. These effects are also observed in astrocytes co-cultured with neurons. The cytoskeleton rearrangement induced by cGMP is prevented by the specific protein kinase G inhibitor Rp-8Br-PET-cGMPS and involves downstream inhibition of RhoA GTPase since is not observed in cells transfected with constitutively active RhoA. Furthermore, dibutyryl-cGMP prevents RhoA-membrane association, a step necessary for its interaction with effectors. Stimulation of the cGMP-protein kinase G pathway also leads to increased astrocyte migration in an in vitro scratch-wound assay resulting in accelerated wound closure, as seen in reactive gliosis following brain injury. These results indicate that cGMP-mediated pathways may regulate physio-pathologically relevant responses in astroglial cells.

Peripheral antinociceptive effect of pertussis toxin: activation of the arginine/NO/cGMP/PKG/ ATP-sensitive K channel pathway

The aim of the present study was to determine the effect of pertussis toxin (PTX) on inflammatory hypernociception measured by the rat paw pressure test and to elucidate the mechanism involved in this effect. In this test, prostaglandin E(2) (PGE(2)) administered subcutaneously induces hypernociception via a mechanism associated with neuronal cAMP increase. Local intraplantar pre-treatment (30 min before), and post-treatment (5 min after) with PTX (600 ng/paw1, in 100 microL) reduced hypernociception induced by prostaglandin E(2) (100 ng/paw, in 100 microL, intraplantar). Furthermore, local intraplantar pre-treatment (30 min before) with PTX (600 ng/paw, in 100 microL) reduced hypernociception induced by DbcAMP, a stable analogue of cAMP (100 microg/paw, in 100 microL, intraplantar), which indicates that PTX may have an effect other than just G(i)/G(0) inhibition. PTX-induced analgesia was blocked by selective inhibitors of nitric oxide synthase (L-NMMA), guanylyl cyclase (ODQ), protein kinase G (KT5823) and ATP-sensitive K(+) channel (Kir6) blockers (glybenclamide and tolbutamide). In addition, PTX was shown to induce nitric oxide (NO) production in cultured neurons of the dorsal root ganglia. In conclusion, this study shows a peripheral antinociceptive effect of pertussis toxin, resulting from the activation of the arginine/NO/cGMP/PKG/ATP-sensitive K(+) channel pathway.

Inhibitory effect of NPY on isoprenaline-induced osteoclastogenesis in mouse bone marrow cells

The effect of neuropeptide Y (NPY), a co-transmitter with noradrenaline in peripheral sympathetic nerve fibers, on the osteoclastogenesis in mouse bone marrow cell cultures treated with isoprenaline, a beta-adrenergic receptor (beta-AR) agonist, was examined. The mouse bone marrow cells constitutively expressed mRNAs for the NPY-Y1 receptor and beta2-AR. NPY inhibited the formation of osteoclast-like cells induced by isoprenaline but not that by 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3) or soluble receptor activator of nuclear factor-kappaB ligand (RANKL); and it suppressed the production of RANKL and cyclic AMP (cAMP) increased by isoprenaline but not those increased by 1alpha,25(OH)2D3. NPY also inhibited osteoclastogenesis induced by forskolin, an activator of adenylate cyclase; however, it did not inhibit that induced by exogenously supplied dibutyryl cAMP, a cell-permeable cAMP analog that activates cAMP-dependent protein kinase. These results demonstrate that NPY inhibited the isoprenaline-induced osteoclastogenesis by blocking the agonist-elicited increases in the production of cAMP and RANKL in mouse bone marrow cells, suggesting an interaction between NPY and beta-AR agonist in bone resorption.

Differentiated astrocytes acquire sensitivity to hydrogen sulfide that is diminished by the transformation into reactive astrocytes

Hydrogen sulfide (H2S) enhances the induction of hippocampal long-term potentiation (LTP) and induces calcium waves in astrocytes. Based on these observations, H2S has been proposed to be a synaptic modulator in the brain. Here we show that differentiated astrocytes acquire sensitivity to H2S that is diminished by their transformation into reactive astrocytes. Although sodium hydrosulfide hydrate (NaHS), a donor of H2S, did not increase the intracellular concentration of Ca2+ in progenitors, exposure of progenitors to leukemia inhibitory factor (LIF), which induces differentiation into glial fibrillary acidic protein (GFAP)-positive astrocytes, greatly increased the sensitivity to NaHS. In contrast, epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), dibutyryl cyclic AMP (db cAMP) and interleukin-1beta (IL-1beta) induced the conversion to reactive astrocytes with diminished sensitivity to NaHS. This suppressive effect of EGF on the sensitivity to NaHS was inhibited by cycloheximide, indicating that de novo protein synthesis was required for the suppression of H2S sensitivity.

Cyclic AMP and cyclic GMP suppress TNFalpha-induced hepatocyte apoptosis by inhibiting FADD up-regulation via a protein kinase A-dependent pathway

Cyclic AMP (cAMP) and cyclic GMP (cGMP) suppress apoptosis in many cell types, including hepatocytes. We have previously shown that membrane-permeable cAMP and cGMP analogs attenuate tumor necrosis factor alpha plus actinomycin D (TNFalpha/ActD)-induced apoptosis in hepatocytes at a step upstream of caspase activation and cytochrome c release. Recently we have also shown that FADD levels increase 10 folds in response to TNFalpha/ActD. Therefore we hypothesized that cAMP and cGMP would inhibit FADD upregulation. We show here that cyclic nucleotide analogs dibutyryl cAMP (db-cAMP) and 8-bromo-cGMP (Br-cGMP) inhibit cell death and the cleavages of multiple caspases including caspase-10, -9, -8, -3, and -2, as well as suppress FADD protein up-regulation in TNFalpha/ActD-induced apoptosis. The inhibitory effects of cAMP were seen at lower concentrations than cGMP. Both cAMP and cGMP prevented FADD overexpression and cell death in hepatocytes transfected with the FADD gene. A protein kinase A (PKA) inhibitor, KT 5720, reversed the inhibition of FADD protein levels induced by cAMP or cGMP. In conclusion, our findings indicate that cAMP and cGMP prevent TNFalpha/ActD-induced apoptosis in hepatocytes and that this occurs in association with a near complete inhibition of the upregulation of FADD via a PKA-dependent mechanism.

Activation of cyclic AMP pathway prevents CD34(+) cell apoptosis

OBJECTIVE

Although cAMP is involved in a number of physiologic functions, its role in hematopoietic cell fate decision remains poorly understood. We have recently demonstrated that in CD34(+)-derived megakaryocytes, cAMP-related agents prevent apoptosis. In this study we addressed the question of whether cAMP also regulates survival of their precursors, CD34(+) cells.

METHODS

Apoptosis was evaluated by fluorescence microscopy, and detection of hypodiploid or annexin V(+) cells by flow cytometry. Mitochondrial membrane potential and bcl-xL or caspase-3 expression were assessed by flow cytometry. Colony-forming units were studied by clonogenic assays in methylcellulose.

RESULTS

We found that two different cAMP analogs such as Dibutiril-cAMP and sp-5,6-DCl-BIMPS (BIMPS) promoted survival of human umbilical cord-derived CD34(+) cells by suppressing apoptosis induced by either nitric oxide (NO) or serum deprivation. Involvement of PKA and PI3K pathway was demonstrated by the ability of their specific inhibitors Rp-cAMP and Wortmannin or LY294002 respectively to reverse the antiapoptotic effect of BIMPS. Treatment of CD34(+) cell with BIMPS not only restrained the bcl-xL downregulation but also suppressed the loss of mitochondrial membrane potential and caspase-3 activation induced by serum starvation. While thrombopoietin (TPO), granulocyte colony-stimulating factor (G-CSF) or stem cell factor (SCF) were not able to increase cAMP levels, the antiapoptotic activity exerted by these growth factors was blocked by inhibition of the adenylate cyclase and synergized by BIMPS. Cyclic AMP analogs suppressed the decreased colony formation in cells exposed to NO or serum deprivation.

CONCLUSION

Altogether, our results strongly suggest that cAMP appears to be not only a key pathway controlling CD34(+) survival, but also a mediator of the TPO-, G-CSF- and SCF-mediated cytoprotection.

Activation dependent expression of MMPs in peripheral blood mononuclear cells involves protein kinase A

Monocyte/Macrophages are integral cellular components of inflammation. Matrix metalloproteinases (MMPs) produced by these cells play a crucial role in every aspect of inflammation. Results of the investigations on activation dependent upregulation of MMPs in human peripheral blood mononuclear cells in culture using different lectins as an in vitro model system to mimic inflammatory monocytes are presented. Under normal physiological conditions the monocytes produced only very low amount of MMPs in an indomethacin insensitive PG/cAMP independent manner. Zymographic analysis and ELISA showed that treatment of monocyte with lectins like concanavalin A (ConA), wheat germ agglutinin (WGA) and Artocarpus lakoocha agglutinin (ALA) caused upregulation of MMPs and the maximum effect was produced by ALA. ALA significantly upregulated MMP-9 in a concentration and time dependent manner. Immunoblot analysis and RT-PCR confirmed ALA mediated upregulation of MMP-9 production. Inhibition of ALA effect by indomethacin and reversal of the indomethacin effect by Bt(2)cAMP indicated involvement of cAMP dependent signaling pathway. Further support for the prostaglandin mediated effect was obtained by the upregulation of cyclooxygenase by ALA. H-89, an inhibitor of protein kinase A (PKA), inhibited the expression of MMP-9 indicating that ALA mediated upregulation of MMP-9 is mediated through PKA pathway. Increase in MMP production and increase in cyclooxygenase activity and inhibition of the effect of ALA on MMP production by indomethacin suggested that the ALA activated monocytes in culture can be used as an in vitro model system to study the intracellular signaling process involved in the mediation of inflammatory response.

Docosahexaenoic acid-containing phosphatidylethanolamine enhances HL-60 cell differentiation by regulation of c-jun and c-myc expression

18:1/docosahexaenoic acid (DHA)-containing phosphatidylethanolamine (PE) enhanced cell differentiation and growth inhibition of HL-60 induced by dibutyryl cAMP (dbcAMP) in a dose-dependent manner. The combined treatment of 200 microM dbcAMP and 50 microM 18:1/DHA-PE increased the NBT reducing activity, which is as an indicator of cell differentiation, to more than 75% from 40% of cells treated with 200 microM dbcAMP alone. In HL-60 cells treated with 50 microM 18:1/DHA-PE and 200 microM dbcAMP for 24 h, the expression level of c-jun mRNA and c-Jun protein were remarkably elevated compared to cells treated with dbcAMP alone. In contrast, there was no difference in the expression levels of c-fos mRNA and c-Fos protein between the combination of 18:1/DHA-PE + dbcAMP or dbcAMP alone. On the other hand, the combine treatment of 18:1/DHA-PE and dbcAMP markedly reduced the expression level of c-myc oncogene during 48 h incubation. The decreases of c-myc mRNA by 18:1/DHA-PE and/or dbcAMP was correlated with growth inhibition effect. Thus, 18:1/DHA-PE might enhance dbcAMP-induced HL-60 cell differentiation and growth inhibition by regulation of c-jun and c-myc mRNA and their products.

Calcium-induced acrosomal exocytosis requires cAMP acting through a protein kinase A-independent, Epac-mediated pathway

Epac, a guanine nucleotide exchange factor for the small GTPase Rap, binds to and is activated by the second messenger cAMP. In sperm, there are a number of signaling pathways required to achieve egg-fertilizing ability that depend upon an intracellular rise of cAMP. Most of these processes were thought to be mediated by cAMP-dependent protein kinases. Here we report a new dependence for the cAMP-induced acrosome reaction involving Epac. The acrosome reaction is a specialized type of regulated exocytosis leading to a massive fusion between the outer acrosomal and the plasma membranes of sperm cells. Ca2+ is the archetypical trigger of regulated exocytosis, and we show here that its effects on acrosomal release are fully mediated by cAMP. Ca2+ failed to trigger acrosomal exocytosis when intracellular cAMP was depleted by an exogenously added phosphodiesterase or when Epac was sequestered by specific blocking antibodies. The nondiscriminating dibutyryl-cAMP and the Epac-selective 8-(p-chlorophenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate analogues triggered the acrosome reaction in the effective absence of extracellular Ca2+. This indicates that cAMP, via Epac activation, has the ability to drive the whole cascade of events necessary to bring exocytosis to completion, including tethering and docking of the acrosome to the plasma membrane, priming of the fusion machinery, mobilization of intravesicular Ca2+, and ultimately, bilayer mixing and fusion. cAMP-elicited exocytosis was sensitive to anti-alpha-SNAP, anti-NSF, and anti-Rab3A antibodies, to intra-acrosomal Ca2+ chelators, and to botulinum toxins but was resistant to cAMP-dependent protein kinase blockers. These experiments thus identify Epac in human sperm and evince its indispensable role downstream of Ca2+ in exocytosis.

Influence of pentoxifylline on natural cytotoxicity and expression of granzymes and PI-9, a specific granzyme B inhibitor

Pentoxifylline (PTX) is an unspecific inhibitor of phosphodiesterase activity that increases intracellular concentration of cyclic nucleotides, mainly cAMP. Since PTX improves microcirculatory blood flow, it is commonly and often chronically used in peripheral vascular diseases. On the other hand PTX also displays a variety of immunomodulatory activities. PTX inhibits natural cytotoxicity and it has previously been suggested that it could partially act also through its influence on perforin/granzyme-dependent pathways. However, the underlying mechanisms are obscure and it remains unknown whether PTX inhibits natural cytotoxicity influencing only leukocytes or also acting on target cells. In this study, we show that PTX inhibits expression of granzyme A in human leukocytes probably due to suppression of phosphodiesterase activity. Contrary, PTX does not affect expression of granzyme B and H. On the other hand we hypothesized that PTX could inhibit natural cytotoxicity not only affecting leukocytes but also due to generation of resistance to leukocyte-mediated cytotoxicity in target cells e.g. through overexpression of PI-9, a specific granzyme B inhibitor. We found that at the mRNA level, PTX stimulates expression of PI-9 in K562 cells. However, we did not observe such an influence at the protein level, in either K562 cells or in human leukocytes. It may suggest that other PTX-triggered molecular events may interfere with PI-9 overexpression in these cells at the further, post-transcriptional levels. According to these results, PTX did not affect resistance of target cells to natural cytotoxicity. Altogether, PTX inhibits natural cytotoxicity affecting mainly effector but not target cells and in case of the effector cells, besides previously reported mechanisms, it can also inhibit granzyme A expression.

Targeting prostaglandin E2 receptors as an alternative strategy to block cyclooxygenase-2-dependent extracellular matrix-induced matrix metalloproteinase-9 expression by macrophages

COX-2-dependent prostaglandin (PG) E2 synthesis regulates macrophage MMP expression, which is thought to destabilize atherosclerotic plaques. However, the administration of selective COX-2 inhibitors paradoxically increases the frequency of adverse cardiovascular events potentially through the loss of anti-inflammatory prostanoids and/or disturbance in the balance of pro- and anti-thrombotic prostanoids. To avoid these collateral effects of COX-2 inhibition, a strategy to identify and block specific prostanoid-receptor interactions may be required. We previously reported that macrophage engagement of vascular extracellular matrix (ECM) triggers proteinase expression through a MAPKerk1/2-dependent increase in COX-2 expression and PGE2 synthesis. Here we demonstrate that elicited macrophages express the PGE2 receptors EP1-4. When plated on ECM, their expression of EP2 and EP4, receptors linked to PGE2-induced activation of adenylyl cyclase, is strongly stimulated. Forskolin and dibutryl cyclic-AMP stimulate macrophage matrix metalloproteinase (MMP)-9 expression in a dose-dependent manner. However, an EP2 agonist (butaprost) has no effect on MMP-9 expression, and macrophages from EP2 null mice exhibited enhanced COX-2 and MMP-9 expression when plated on ECM. In contrast, the EP4 agonist (PGE1-OH) stimulated macrophage MMP-9 expression, which was inhibited by the EP4 antagonist ONO-AE3-208. When compared with COX-2 silencing by small interfering RNA or inhibition by celecoxib, the EP4 antagonist was as effective in inhibiting ECM-induced proteinase expression. In addition, ECM-induced MMP-9 expression was blocked in macrophages in which EP4 was silenced by small interfering RNA. Thus, COX-2-dependent ECM-induced proteinase expression is effectively blocked by selective inhibition of EP4, a member of the PGE2 family of receptors.