Lipopolysaccharide attenuates mRNA levels of several adenylyl cyclase isoforms in vivo

Role of Myeloid Cell-Specific Adenylyl Cyclase Type 7 in Lipopolysaccharide- and Alcohol-Induced Immune Responses

Clinical and experimental evidence indicates that alcohol use causes various abnormalities in the immune system and compromises immune functions. However, the mechanistic understanding of ethanol's effects on the immune system remains limited. Cyclic AMP (cAMP) regulates multiple processes, including immune responses. Earlier research indicated that type 7 adenylyl cyclase (AC7) regulates the immune system and is highly responsive to ethanol. Therefore, we hypothesized that AC7 is a central player in regulating the effects of alcohol on innate immune responses. To test this hypothesis, we utilized a myeloid lineage-specific AC7 KO mouse model and compared the effects of acute and chronic ethanol treatment on their innate immune responses induced by systemic lipopolysaccharide (LPS) challenge. Our results demonstrate that AC7 KO mice had significantly lower survival rates under LPS challenge. Chronic ethanol consumption rescued AC7 KO mice from LPS-induced death. AC7 KO and ethanol, acute and chronic, affected several measurements of cytokine mRNA expressions, including IL-1β, TNFα, IL-6, and IL-10 in the lung and liver. In a few cases, statistical analysis indicated that these two factors interacted, suggesting that AC7 played some role in ethanol's effect on cytokine expression. Thus, this study demonstrated AC7's role in ethanol's effect on the innate immune response.

Adcy9 Gene Inactivation Improves Cardiac Function After Myocardial Infarction in Mice

BACKGROUND

Polymorphisms in the adenylate cyclase 9 (ADCY9) gene influence the benefits of the cholesteryl ester transfer protein (CETP) modulator dalcetrapib on cardiovascular events after acute coronary syndrome. We hypothesized that Adcy9 inactivation could improve cardiac function and remodelling following myocardial infarction (MI) in absence of CETP activity.

METHODS

Wild-type (WT) and Adcy9-inactivated (Adcy9Gt/Gt) male mice, transgenic or not for human CETP (tgCETP+/-), were subjected to MI by permanent left anterior descending coronary artery ligation and studied for 4 weeks. Left ventricular (LV) function was assessed by echocardiography at baseline, 1, and 4 weeks after MI. At sacrifice, blood, spleen and bone marrow cells were collected for flow cytometry analysis, and hearts were harvested for histologic analyses.

RESULTS

All mice developed LV hypertrophy, dilation, and systolic dysfunction, but Adcy9Gt/Gt mice exhibited reduced pathologic LV remodelling and better LV function compared with WT mice. There were no differences between tgCETP+/- and Adcy9Gt/Gt tgCETP+/- mice, which both exhibited intermediate responses. Histologic analyses showed smaller cardiomyocyte size, reduced infarct size, and preserved myocardial capillary density in the infarct border zone in Adcy9Gt/Gt vs WT mice. Count of bone marrow T cells and B cells were significantly increased in Adcy9Gt/Gt mice compared with the other genotypes.

CONCLUSIONS

Adcy9 inactivation reduced infarct size, pathologic remodelling, and cardiac dysfunction. These changes were accompanied by preserved myocardial capillary density and increased adaptive immune response. Most of the benefits of Adcy9 inactivation were only observed in the absence of CETP.

Isoforskolin, an adenylyl cyclase activator, attenuates cigarette smoke-induced COPD in rats

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is characterized by limited airflow due to pulmonary and alveolar abnormalities from exposure to cigarette smoke (CS). Current therapeutic drugs are limited and the development of novel treatments to prevent disease progression is challenging. Isoforskolin (ISOF) from the plant Coleus forskohlii is an effective activator of adenylyl cyclase (AC) isoforms. Previously we found ISOF could attenuate acute lung injury in animal models, while the effect of ISOF on COPD has not been elucidated.

PURPOSE

In this study, we aimed to evaluate the efficacy of ISOF on COPD and reveal its potential mechanisms.

METHODS

A rat model of COPD was established by long-term exposure to CS, then the rats were orally administered with ISOF (0.5, 1 and 2 mg/kg). The pulmonary function, lung morphology, inflammatory cells and cytokines in serum or bronchoalveolar lavage fluid (BALF) were evaluated. Transcriptomics, proteomics and network pharmacology analysis were utilized to identify potential mechanisms of ISOF. Droplet digital PCR was used to detect the mRNA expression of AC1-10 in donor lung tissues. AC activation was determined in recombinant human embryonic kidney 293 (HEK293) cells stably expressing human AC isoforms. In addition, ISOF caused trachea relaxation ex vivo were assessed in isolated trachea rings from guinea pigs.

RESULTS

ISOF significantly ameliorated pathological damage of lung tissue and improved pulmonary function in COPD rats. ISOF treatment decreased the number of inflammatory cells in peripheral blood, and also the levels of pro-inflammatory cytokines in serum and BALF. Consistent with omics-based analyses, ISOF markedly downregulated the mTOR level in lung tissue. Flow cytometry analysis revealed that ISOF treatment reduced the ratio of Th17/Treg cells in peripheral blood. Furthermore, the expression levels of AC1 and AC2 are relatively higher than other AC isoforms in normal lung tissues, and ISOF could potently activate AC1 and AC2 in vitro and significantly relax isolated guinea pig trachea.

CONCLUSION

Collectively, our studies suggest that ISOF exerts its anti-COPD effect by improving lung function, anti-inflammation and trachea relaxation, which may be related to AC activation, mTOR signaling and Th17/Treg balance.

Rare and intractable fibrodysplasia ossificans progressiva shows different PBMC phenotype possibly modulated by ascorbic acid and propranolol treatment

Fibrodysplasia Ossificans Progressiva (FOP) is a rare congenital intractable disease associated with a mutation in ACVR1 gene, characterized by skeleton malformations. Ascorbic acid (AA) and propranolol (PP) in combination is reported to minimize flare-ups in patients. FOP leukocyte phenotype may possibly be modulated by AA and PP treatment. In this study, expression of 22 potential target genes was analyzed by RT-PCR in peripheral blood mononuclear cells culture (PBMC) from FOP patients and controls to determine effectiveness of the combination therapy. PBMC were treated with AA, PP and AA+PP combination. Basal expression of 12 of the 22 genes in FOP PBMC was statistically different from controls. ACVR1, ADCY2, ADCY9 and COL3 were downregulated while COL1 was upregulated. ADRB1, ADRB2, RUNX2, TNF-α and ACTB, were all overexpressed in FOP PBMC. In control, AA upregulated COL1, SVCT1, ACTB, AGTR2 and downregulated ADCY2. In FOP cells, AA upregulated ACVR1, BMP4, COL1, COL3, TNF-α, ADCY2, ADCY9, AGTR2 and MAS, while downregulated ADBR2, RUNX2, ADCY1, SVCT1 and ACTB. PP increased ADBR1 and decreased RUNX2, TNF-α, AGTR1, ACTB and CHRNA7 genes in treated control PBMC compared to untreated. PP upregulated ADBR1, ADBR2 and MAS, and downregulated TNF-α and ACTB in treated FOP PBMC versus untreated. AA+PP augmented ADRB1 and ADRB2 expressions in control PBMC. In FOP PBMC, AA+PP augmented ACVR1, COL1, COL3, ADBR1, AGTR2 and MAS expression and downregulated ADBR2, RUNX2, ACTB and MRGD. These data show distinct gene expression modulation in leukocytes from FOP patients when treated with AA and or PP.

Adenylyl cyclase 1 as a major isoform to generate cAMP signaling for apoA-1-mediated cholesterol efflux pathway

HDL apoA-1-mediated cholesterol efflux pathway requires multiple cellular proteins and signal transduction processes, including adenylyl cyclase (AC)/cAMP signaling. Due to the existence of multiple transmembrane AC isoforms, it was not known how many AC isoforms are expressed and which ones are essential for cholesterol efflux in macrophage foam cells. These questions were investigated in THP-1 macrophages in this study. Quantitative RT-PCR detected mRNAs for all nine transmembrane AC isoforms, but only the mRNA and protein of the AC1 isoform were consistently upregulated by cholesterol loading and apoA-1. AC1 shRNA interference decreased AC1 mRNA and protein levels, resulting in reduction of apoA-1-mediated cAMP production and cholesterol efflux, while the intracellular cholesterol levels remained high. Confocal microscopy showed that apoA-1 promoted translocation of cholesterol and formation of cholesterol-apoA-1 complexes (protrusions) on the cholesterol-loaded macrophage surface. AC1 shRNA-interfered macrophages showed no translocation of cholesterol to the cell surface. AC1 shRNA interference also disrupted cellular localization of the intracellular cholesterol indicator protein adipophillin, and the expression as well as surface translocation of ABCA1. Together, our results show that AC1 is a major isoform for apoA-1-activated cAMP signaling to promote cholesterol transport and exocytosis to the surface of THP-1 macrophage foam cells.

Abnormal Mitochondrial cAMP/PKA Signaling Is Involved in Sepsis-Induced Mitochondrial and Myocardial Dysfunction

Adrenergic receptors couple to Gs-proteins leading to transmembrane adenylyl cyclase activation and cytosolic cyclic adenosine monophosphate (cAMP) production. Cyclic AMP is also produced in the mitochondrial matrix, where it regulates respiration through protein kinase A (PKA)-dependent phosphorylation of respiratory chain complexes. We hypothesized that a blunted mitochondrial cAMP-PKA pathway would participate in sepsis-induced heart dysfunction. Adult male mice were subjected to intra-abdominal sepsis. Mitochondrial respiration of cardiac fibers and myocardial contractile performance were evaluated in response to 8Br-cAMP, PKA inhibition (H89), soluble adenylyl cyclase inhibition (KH7), and phosphodiesterase inhibition (IBMX; BAY60-7550). Adenosine diphosphate (ADP)-stimulated respiratory rates of cardiac fibers were reduced in septic mice. Compared with controls, stimulatory effects of 8Br-cAMP on respiration rates were enhanced in septic fibers, whereas inhibitory effects of H89 were reduced. Ser-58 phosphorylation of cytochrome c oxidase subunit IV-1 was reduced in septic hearts. In vitro, incubation of septic cardiac fibers with BAY60-7550 increased respiratory control ratio and improved cardiac MVO₂ efficiency in isolated septic heart. In vivo, BAY60-7550 pre-treatment of septic mice have limited impact on myocardial function. Mitochondrial cAMP-PKA signaling is impaired in the septic myocardium. PDE2 phosphodiesterase inhibition by BAY60-7550 improves mitochondrial respiration and cardiac MVO₂ efficiency in septic mice.

Lipopolysaccharide-induced pulmonary endothelial barrier disruption and lung edema: critical role for bicarbonate stimulation of AC10

Bacteria-induced sepsis is a common cause of pulmonary endothelial barrier dysfunction and can progress toward acute respiratory distress syndrome. Elevations in intracellular cAMP tightly regulate pulmonary endothelial barrier integrity; however, cAMP signals are highly compartmentalized: whether cAMP is barrier-protective or -disruptive depends on the compartment (plasma membrane or cytosol, respectively) in which the signal is generated. The mammalian soluble adenylyl cyclase isoform 10 (AC10) is uniquely stimulated by bicarbonate and is expressed in pulmonary microvascular endothelial cells (PMVECs). Elevated extracellular bicarbonate increases cAMP in PMVECs to disrupt the endothelial barrier and increase the filtration coefficient (Kf) in the isolated lung. We tested the hypothesis that sepsis-induced endothelial barrier disruption and increased permeability are dependent on extracellular bicarbonate and activation of AC10. Our findings reveal that LPS-induced endothelial barrier disruption is dependent on extracellular bicarbonate: LPS-induced barrier failure and increased permeability are exacerbated in elevated bicarbonate compared with low extracellular bicarbonate. The AC10 inhibitor KH7 attenuated the bicarbonate-dependent LPS-induced barrier disruption. In the isolated lung, LPS failed to increase Kf in the presence of minimal perfusate bicarbonate. An increase in perfusate bicarbonate to the physiological range (24 mM) revealed the LPS-induced increase in Kf, which was attenuated by KH7. Furthermore, in PMVECs treated with LPS for 6 h, there was a dose-dependent increase in AC10 expression. Thus these findings reveal that LPS-induced pulmonary endothelial barrier failure requires bicarbonate activation of AC10.

Higher TNFα responses in young males compared to females are associated with attenuation of monocyte adenylyl cyclase expression

Tumor necrosis factor α (TNFα) expression is strongly attenuated by the intracellular signaling mediator cyclic adenosine monophosphate (cAMP), which is synthesized by adenylyl cyclase (AC) enzymes. We have compared AC regulation and TNFα production in male and female monocytes, and characterized the role of monocyte AC isoforms in TNFα regulation. Males and females, age groups 20-30 years and 50-70 years donated blood for this study. In lipopolysaccharide-stimulated blood from young male donors, we observed significantly higher TNFα responses (6h, p=0.03) compared to females of the same age, a difference not observed in the older donors. Rapid down-regulation of the monocyte AC isoforms AC4, AC7 and AC9 were observed in young males. AC-directed siRNA experiments in the human monocyte cell line THP-1 demonstrated that AC7 and AC9 knock-down significantly induced TNFα release (p=0.01 for both isoforms). These data indicate that the stronger TNFα-responses in young males may be partly associated with male-specific down-regulation of adenylyl cyclases.

Cholecystokinin inhibits inducible nitric oxide synthase expression by lipopolysaccharide-stimulated peritoneal macrophages

Cholecystokinin (CCK) was first described as a gastrointestinal hormone. However, apart from its gastrointestinal effects, studies have described that CCK also plays immunoregulatory roles. Taking in account the involvement of inducible nitric oxide synthase- (iNOS-) derived NO in the sepsis context, the present study was undertaken to investigate the role of CCK on iNOS expression in LPS-activated peritoneal macrophages. Our results revealed that CCK reduces NO production and attenuates the iNOS mRNA expression and protein formation. Furthermore, CCK inhibited the nuclear factor- (NF-) κB pathway reducing IκBα degradation and minor p65-dependent translocation to the nucleus. Moreover, CCK restored the intracellular cAMP content activating the protein kinase A (PKA) pathway, which resulted in a negative modulatory role on iNOS expression. In peritoneal macrophages, the CCK-1R expression, but not CCK-2R, was predominant and upregulated by LPS. The pharmacological studies confirmed that CCK-1R subtype is the major receptor responsible for the biological effects of CCK. These data suggest an anti-inflammatory role for the peptide CCK in modulating iNOS-derived NO synthesis, possibly controlling the macrophage activation through NF-κB, cAMP-PKA, and CCK-1R pathways. Based on these findings, CCK could be used as an adjuvant agent to modulate the inflammatory response and prevent systemic complications commonly found during sepsis.

cAMP with other signaling cues converges on Rac1 to stabilize the endothelial barrier- a signaling pathway compromised in inflammation

cAMP is one of the most potent signaling molecules to stabilize the endothelial barrier, both under resting conditions as well as under challenge of barrier-destabilizing mediators. The two main signaling axes downstream of cAMP are activation of protein kinase A (PKA) as well as engagement of exchange protein directly activated by cAMP (Epac) and its effector GTPase Rap1. Interestingly, both pathways activate GTP exchange factors for Rac1, such as Tiam1 and Vav2 and stabilize the endothelial barrier via Rac1-mediated enforcement of adherens junctions and strengthening of the cortical actin cytoskeleton. On the level of Rac1, cAMP signaling converges with other barrier-enhancing signaling cues induced by sphingosine-1-phosphate (S1P) and angiopoietin-1 (Ang1) rendering Rac1 as an important signaling hub. Moreover, activation of Rap1 and inhibition of RhoA also contribute to barrier stabilization, emphasizing that regulation of small GTPases is a central mechanism in this context. The relevance of cAMP/Rac1-mediated barrier protection under pathophysiologic conditions can be concluded from data showing that inflammatory mediators causing multi-organ failure in systemic inflammation or sepsis interfere with this signaling axis on the level of cAMP or Rac1. This is in line with the well-known efficacy of cAMP to abrogate the barrier breakdown in response to most barrier-compromising stimuli. New is the notion that the tight endothelial barrier under resting conditions is maintained by (1) continuous cAMP formation induced by hormones such as epinephrine or (2) by activation of Rac1 downstream of S1P that is secreted by erythrocytes and activated platelets.

Alcoholic Hepatitis: Steroids vs. Pentoxifylline

Alcoholic hepatitis (AH) remains a major cause of liver-related morbidity and mortality in the United States and is actually increasing in certain areas of Europe. Thus, there is a pressing need for new therapies/approaches. Major barriers for reducing morbidity, mortality, and costs of care include: lack of translational animal and human studies of new therapies for AH; limited trials of combination therapies in AH targeted at specific disease mechanisms (e.g., gut permeability, cytokines, oxidative stress); limited studies on non-invasive, non-mortality end points; few studies on mechanisms of steroid non-responsiveness; and inadequate prognostic indicators, to name only a few. In spite of these gaps, we have made major advances in understanding mechanisms for AH and appropriate therapies for AH. This article reviews mechanisms and rationale for use of steroids and pentoxifylline in AH and future directions in therapy.

Multiple facets of cAMP signalling and physiological impact: cAMP compartmentalization in the lung

Therapies involving elevation of the endogenous suppressor cyclic AMP (cAMP) are currently used in the treatment of several chronic inflammatory disorders, including chronic obstructive pulmonary disease (COPD). Characteristics of COPD are airway obstruction, airway inflammation and airway remodelling, processes encompassed by increased airway smooth muscle mass, epithelial changes, goblet cell and submucosal gland hyperplasia. In addition to inflammatory cells, airway smooth muscle cells and (myo)fibroblasts, epithelial cells underpin a variety of key responses in the airways such as inflammatory cytokine release, airway remodelling, mucus hypersecretion and airway barrier function. Cigarette smoke, being next to environmental pollution the main cause of COPD, is believed to cause epithelial hyperpermeability by disrupting the barrier function. Here we will focus on the most recent progress on compartmentalized signalling by cAMP. In addition to G protein-coupled receptors, adenylyl cyclases, cAMP-specific phospho-diesterases (PDEs) maintain compartmentalized cAMP signalling. Intriguingly, spatially discrete cAMP-sensing signalling complexes seem also to involve distinct members of the A-kinase anchoring (AKAP) superfamily and IQ motif containing GTPase activating protein (IQGAPs). In this review, we will highlight the interaction between cAMP and the epithelial barrier to retain proper lung function and to alleviate COPD symptoms and focus on the possible molecular mechanisms involved in this process. Future studies should include the development of cAMP-sensing multiprotein complex specific disruptors and/or stabilizers to orchestrate cellular functions. Compartmentalized cAMP signalling regulates important cellular processes in the lung and may serve as a therapeutic target.

Use of inotropes and vasopressor agents in critically ill patients

Inotropes and vasopressors are biologically and clinically important compounds that originate from different pharmacological groups and act at some of the most fundamental receptor and signal transduction systems in the body. More than 20 such agents are in common clinical use, yet few reviews of their pharmacology exist outside of physiology and pharmacology textbooks. Despite widespread use in critically ill patients, understanding of the clinical effects of these drugs in pathological states is poor. The purpose of this article is to describe the pharmacology and clinical applications of inotropic and vasopressor agents in critically ill patients.

Melanocortin 4 receptor activation induces brain-derived neurotrophic factor expression in rat astrocytes through cyclic AMP-protein kinase A pathway

Melanocortin 4 receptors (MC4R) are mainly expressed in the brain. We previously showed that the anti-inflammatory action of α-melanocyte-stimulating hormone (α-MSH) in rat hypothalamus and in cultured astrocytes involved MC4R activation. However, MC4R mechanisms of action remain undetermined. Since brain-derived neurotrophic factor (BDNF) may be mediating MC4R hypothalamic anorexigenic actions, we determined melanocortin effects on BDNF expression in rat cultured astrocytes and certain mechanisms involved in MC4R signaling. α-MSH and its analogue NDP-MSH, induced production of cAMP in astrocytes. This effect was completely blocked by the MC4R antagonist, HS024. We found that NDP-MSH increased BDNF mRNA and protein levels in astrocytes. The effect of NDP-MSH on BDNF expression was abolished by the adenylate cyclase inhibitor SQ22536, and decreased by the PKA inhibitor Rp-cAMP. Since melanocortins are immunomodulators, we investigated their actions with bacterial lipopolysaccharide (LPS) and interferon-γ (IFN-γ) stimulus. Although both α-MSH and LPS+IFN-γ increased cAMP responding element binding protein (CREB) activation, LPS+IFN-γ did not modify BDNF expression. On the other hand, α-MSH did not modify basal or LPS+IFN-γ-induced nuclear factor-κB activation. Our results show for the first time that MC4R activation in astrocytes induces BDNF expression through cAMP-PKA-CREB pathway without involving NF-κB.

Prostaglandin E2 and T cells: friends or foes?

Our understanding of the key players involved in the differential regulation of T-cell responses during inflammation, infection and auto-immunity is fundamental for designing efficient therapeutic strategies against immune diseases. With respect to this, the inhibitory role of the lipid mediator prostaglandin E₂ (PGE₂) in T-cell immunity has been documented since the 1970s. Studies that ensued investigating the underlying mechanisms substantiated the suppressive function of micromolar concentrations of PGE₂ in T-cell activation, proliferation, differentiation and migration. However, the past decade has seen a revolution in this perspective, since nanomolar concentrations of PGE₂ have been shown to potentiate Th1 and Th17 responses and aid in T-cell proliferation. The understanding of concentration-specific effects of PGE₂ in other cell types, the development of mice deficient in each subtype of the PGE₂ receptors (EP receptors) and the delineation of signalling pathways mediated by the EP receptors have enhanced our understanding of PGE₂ as an immune-stimulator. PGE₂ regulates a multitude of functions in T-cell activation and differentiation and these effects vary depending on the micro-environment of the cell, maturation and activation state of the cell, type of EP receptor involved, local concentration of PGE₂ and whether it is a homeostatic or inflammatory scenario. In this review, we compartmentalize the various aspects of this complex relationship of PGE₂ with T lymphocytes. Given the importance of this molecule in T-cell activation, we also address the possibility of using EP receptor antagonism as a potential therapeutic approach for some immune disorders.

Neuroanatomical distribution and neurochemical characterization of cells expressing adenylyl cyclase isoforms in mouse and rat brain

Transmembrane adenylyl cyclases (Adcy) are involved in the regulation of multiple brain processes such as synaptic plasticity, learning and memory. They synthesize intracellular cyclic adenosine monophosphate (cAMP) following activation by G-protein coupled receptors. We examined the neuroanatomical distribution of the nine Adcy isoforms in rat and mouse brain by in situ hybridization, as well as their location in glutamatergic, GABAergic and cholinergic neurons in several mouse brain areas by double in situ hybridization. The Adcys are widely distributed throughout the brain in both rat and mouse, being especially abundant in cortex, hippocampus, thalamic nuclei, the olfactory system and the granular layer of the cerebellum. Double-labeling experiments showed that Adcy isoforms are differently expressed in glutamatergic, GABAergic and cholinergic neuronal cell populations. We report the neuroanatomical distribution of the nine known Adcy isoforms in rat and mouse brain and their cellular localization.

Cyclic AMP-guanine exchange factor activation inhibits JNK-dependent lipopolysaccharide-induced apoptosis in rat hepatocytes

Lipopolysaccharide (LPS) is known to damage hepatocytes by cytokines released from activated Kupffer cells, but the ancillary role of LPS as a direct hepatotoxin is less well characterized. The aim of this study was to determine the direct effect of LPS on hepatocyte viability and the underlying signaling mechanism. Rat hepatocyte cultures treated overnight with LPS (500 ng/mL) induced apoptosis as monitored morphologically (Hoechst 33258) and biochemically (cleavage of caspase 3 and 9 and the appearance of cytochrome C in the cytoplasm). LPS-induced apoptosis was additive to that induced by glycochenodeoxycholate or Fas ligand, was associated with activation of c-Jun N-terminal kinase B (JNK) and p38 mitogen-activated protein kinases (MAPK), and inhibition of protein kinase (AKT). Inhibition of JNK by SP600125, but not of p38 MAPK by SB203580 attenuated LPS-induced apoptosis, indicating JNK dependency. CPT-2-Me-cAMP, an activator of cAMP-GEF, decreased apoptosis due to LPS alone or in combination with glycochenodeoxycholate or Fas ligand. CPT-2-Me-cAMP also prevented LPS-induced activation of JNK and inhibition of AKT Taken together, these results suggest that LPS can induce hepatocyte apoptosis directly in vitro in a JNK-dependent manner and activation of cAMP-GEF protects against the LPS-induced apoptosis most likely by reversing the effect of LPS on JNK and AKT

Characterization of mouse heart adenylyl cyclase

Chronic heart failure is one of the most frequent causes of death in humans. Knockout of type 5 adenylyl cyclase (AC) in mice causes longevity and protection from cardiomyopathy, and an AC5 inhibitor reduces beta-adrenoceptor-stimulated Ca(2+) inward currents in isolated mouse cardiomyocytes. These data indicate that selective AC5 inhibitors may be beneficial in chronic heart failure. Therefore, we characterized AC in mouse heart membranes. Real-time polymerase chain reaction and immunoblot analysis suggested that AC5 is an important heart AC isoform. Enzyme kinetics of heart AC and recombinant AC5 in the presence of Mg(2+) were similar. Moreover, the inhibitory profile of eight 2'(3')-O-(N-methylanthraniloyl) (MANT)-nucleoside 5'-([gamma-thio])triphosphates on mouse heart in the presence of Mg(2+) was almost identical to that of AC5. MANT-ITP was the most potent inhibitor of heart AC and recombinant AC5, with K(i) values in the 15 to 25 nM range in the presence of Mg(2+) and in the 1 to 5 nM range in the presence of Mn(2+). However, in the presence of Mn(2+), we also noted differences between mouse heart AC and AC5 with respect to enzyme kinetics and forskolin analog effects. In conclusion, with regard to expression and kinetics and inhibition by MANT-nucleotides in the presence of Mg(2+), AC5 is an important AC isoform in heart, with MANT-ITP being an excellent starting point for the design of AC5-selective inhibitors. Unfortunately, a limitation of our study is the fact that immunologically and biochemically, AC5 and AC6 are quite similar, although they have different roles in heart. Moreover, lack of antibody specificity and Mn(2+) masking AC5 effects were problems.

Lipopolysaccharide-induced endothelial barrier breakdown is cyclic adenosine monophosphate dependent in vivo and in vitro

OBJECTIVES

To determine whether cyclic adenosine monophosphate (cAMP) is critically involved in lipopolysaccharide (LPS)-induced breakdown of endothelial barrier functions in vivo and in vitro.

DESIGN

Experimental laboratory research.

SETTING

Research laboratory.

SUBJECTS

Wistar rats and cultured human microvascular endothelial cells.

INTERVENTION

Permeability measurements in single postcapillary venules in vivo and permeability measurements and cell biology techniques in vitro.

MEASUREMENTS AND RESULTS

We demonstrate that within 120 minutes LPS increased endothelial permeability in rat mesenteric postcapillary venules in vivo and caused a barrier breakdown in human dermal microvascular endothelial cells in vitro. This was associated with the formation of large intercellular gaps and fragmentation of vascular endothelial cadherin immunostaining. Furthermore, claudin 5 immunostaining at cell borders was drastically reduced after LPS treatment. Interestingly, activity of the small GTPase Rho A, which has previously been suggested to mediate the LPS-induced endothelial barrier breakdown, was not increased after 2 hours. However, activity of Rac 1, which is known to be important for maintenance of endothelial barrier functions, was significantly reduced to 64 +/- 8% after 2 hours. All LPS-induced changes of endothelial cells were blocked by a forskolin-mediated or rolipram-mediated increase of cAMP. Consistently, enzyme-linked immunosorbent assay-based measurements demonstrated that LPS significantly decreased intracellular cAMP.

CONCLUSION

In summary, our data demonstrate that LPS disrupts endothelial barrier properties by decreasing intracellular cAMP. This mechanism may involve inactivation of Rac 1 rather than activation of Rho A.

Hepatic sinusoidal cells in health and disease: update from the 14th International Symposium

This review aims to give an update of the field of the hepatic sinusoid, supported by references to presentations given at the 14th International Symposium on Cells of the Hepatic Sinusoid (ISCHS2008), which was held in Tromsø, Norway, August 31-September 4, 2008. The subtitle of the symposium, 'Integrating basic and clinical hepatology', signified the inclusion of both basal and applied clinical results of importance in the field of liver sinusoidal physiology and pathophysiology. Of nearly 50 oral presentations, nine were invited tutorial lectures. The authors of the review have avoided writing a 'flat summary' of the presentations given at ISCHS2008, and instead focused on important novel information. The tutorial presentations have served as a particularly important basis in the preparation of this update. In this review, we have also included references to recent literature that may not have been covered by the ISCHS2008 programme. The sections of this review reflect the scientific programme of the symposium (http://www.ub.uit.no/munin/bitstream/10037/1654/1/book.pdf): 1. Liver sinusoidal endothelial cells. 2. Kupffer cells. 3. Hepatic stellate cells. 4. Immunology. 5. Tumor/metastasis. Symposium abstracts are referred to by a number preceded by the letter A.

EBV infection renders B cells resistant to growth inhibition via adenylyl cyclase

Cyclic AMP (cAMP) is an important physiological growth inhibitor of lymphoid cells, and the cAMP/protein kinase A (PKA) pathway is disrupted in several immunological disorders and cancers. Epstein Barr virus (EBV) infection of B lymphocytes is responsible for the development of lymphoproliferative disease as well as certain B-lymphoid malignancies. Here we hypothesized that EBV infection might render B lymphocytes resistant to cAMP/PKA-mediated growth inhibition. To test this, we assessed the growth-inhibitory response of cAMP-elevating compounds such as forskolin and isoproterenol, as well as the PKA activator 8-CPT-cAMP in normal B lymphocytes, EBV-infected B cells and in the EBV-negative B lymphoid cell line Reh. We could demonstrate that EBV infection indeed abolished cAMP-mediated growth inhibition of B cells. The defect was pinpointed to defective adenylyl cyclase (AC) activation by forskolin and isoproterenol, resulting in reduced formation of cAMP and lack of PKA activation and CREB phosphorylation. In contrast, 8-CPT-cAMP which directly activates PKA was able to inhibit EBV-infected B cell growth. The physiological implications of these results were underlined by the observation that the ability of forskolin to inhibit camptothecin-induced apoptosis was abolished in EBV-infected B cells. We conclude that EBV infection of B cells abrogates the activation of AC and thereby cAMP formation, and that this dysfunction renders the cells resistant to growth inhibition via the cAMP/PKA pathway.