ß-adrenergic stimulation increases macrophage CD14 expression and E. coli phagocytosis through PKA signaling mechanisms

Adrenergic Signaling Regulation Of Macrophage Function: Do We Understand It Yet?

Macrophages are immune cells that are widespread throughout the body and critical for maintaining tissue homeostasis. Their remarkable plasticity allows them to acquire different phenotypes, becoming able either to fight infection (M1-like, classically activated macrophages) or to promote tissue remodeling and repair (M2-like, alternatively activated macrophages). These phenotypes are induced by different cues present in the microenvironment. Among the factors that might regulate macrophage activation are mediators produced by different branches of the nervous system. The regulation exerted by the sympathetic nervous system (SNS) on macrophages (and the immune system in general) is becoming a subject of increasing interest, indeed a great number of articles have been published lately. Catecholamines (noradrenaline and adrenaline) activate α and β adrenergic receptors expressed by macrophages and shape the effector functions of these cells in contexts as diverse as the small intestine, the lung, or the adipose tissue. Activation of different subsets of receptors seems to produce antagonistic effects, with α adrenergic receptors generally associated with pro-inflammatory functions and β adrenergic receptors (particularly β2) related to the resolution of inflammation and tissue remodeling. However, exceptions to this paradigm have been reported, and the factors contributing to these apparently contradictory observations are still far from being completely understood. Additionally, macrophages per se seem to be sources of catecholamines, which is also a subject of some debate. In this review, we discuss how activation of adrenergic receptors modulates macrophage effector functions and its implications for inflammatory responses and tissue homeostasis.

β-Adrenoceptor regulation of metabolism in U937 derived macrophages

Macrophages have important roles in the immune system including clearing pathogens and wound healing. Metabolic phenotypes in macrophages have been associated with functional phenotypes, where pro-inflammatory macrophages have an increased rate of glycolysis and anti-inflammatory macrophages primarily use oxidative phosphorylation. β-adrenoceptor (βAR) signalling in macrophages has been implicated in disease states such as cancer, atherosclerosis and rheumatoid arthritis. The impact of βAR signalling on macrophage metabolism has not been defined. Using metabolomics and proteomics, we describe the impact of βAR signalling on macrophages treated with isoprenaline. We found that βAR signalling alters proteins involved in cytoskeletal rearrangement and redox homeostasis of the cell. We showed that βAR signalling in macrophages shifts glucose metabolism from glycolysis towards the tricarboxylic acid cycle and pentose phosphate pathways. We also show that βAR signalling perturbs purine metabolism by accumulating adenylate and guanylate pools. Taken together, these results indicate that βAR signalling shifts metabolism to support redox processes and upregulates proteins involved in cytoskeletal changes, which may contribute to βAR effects on macrophage function.

Combination of metformin with sodium selenite induces a functional phenotypic switch of human GM-CSF monocyte-derived macrophages

OBJECTIVES

We evaluated the effects of metformin (Met, 1,1‑dimethylbiguanide hydrochloride) combined or not with sodium selenite (Ss, Na₂SeO₃) on the functional activities of LPS-activated GM-CSF monocyte-derived macrophages (GM-MDM).

MATERIALS AND METHODS

Human GM-MDMs from three healthy donors were treated with Met or Ss alone, or with the combination of Met and Ss, and assayed for various biological activities and cytokines expression.

RESULTS

Met alone and Ss alone had significantly different effects on phagocytosis and killing capacities and IL-β production, but had similar effects on the downregulation of inducible nitric oxide synthase (iNOS) activity, relative nicotinamide adenine dinucleotide reduced (NADH) dehydrogenase (Complex I), intracellular free calcium ions (_ifCa²⁺), and on the upregulation of arginase activity. Additionally, iNOS activity-to-arginase activity ratio was downregulated in Met or Ss treated-GM-MDMs, and, conversely, upregulated in GM-MDMs treated with Met + Ss in combination, indicating that arginase activity dominates that of iNOS when the two treatments are associated. Moreover, combination of Met with Ss significantly upregulated hydrogen peroxide (H₂O₂) production and phagocytic capacity, but significantly downregulated the production of IL-1β, iNOS activity and killing capacity. On the contrary, we show that Met alone induced significant downregulation of phagocytic capacity and slight upregulation of killing capacity. Nevertheless, Ss seems to accentuate the effect of Met on the downregulation of NO production, as well as to reverse its effect on both phagocytic and killing capacities. On the other hand, all treatments induced a sharp decrease in relative levels of NADH dehydrogenase, and a marked decrease in the levels of _ifCa²⁺. Finally, we found that GM-MDMs treated with Met or Ss, or Met combined with Ss exhibited different functional activation phenotypes, as indicated by the surface expression of co-stimulatory and cell activation and presentation molecules CD14, CD80, CD86 and HLA-DR.

CONCLUSIONS

Our results demonstrated that Met/Ss combination can play an important role in the modulation of functional activities of human LPS-activated GM-MDMs. Additionally, the overall effects of Met and the induction of "M2" GM-MDMs-associated arginase could be influenced by its combination with Ss.

Stress hormone signaling through β-adrenergic receptors regulates macrophage mechanotype and function

Critical functions of immune cells require them to rapidly change their shape and generate forces in response to cues from their surrounding environment. However, little is known about how soluble factors that may be present in the microenvironment modulate key aspects of cellular mechanobiology-such as immune cell deformability and force generation-to impact functions such as phagocytosis and migration. Here we show that signaling by soluble stress hormones through β-adrenoceptors (β-AR) reduces the deformability of macrophages; this is dependent on changes in the organization of the actin cytoskeleton and is associated with functional changes in phagocytosis and migration. Pharmacologic interventions reveal that the impact of β-AR signaling on macrophage deformability is dependent on actin-related proteins 2/3, indicating that stress hormone signaling through β-AR shifts actin organization to favor branched structures rather than linear unbranched actin filaments. These findings show that through remodeling of the actin cytoskeleton, β-AR-mediated stress hormone signaling modulates macrophage mechanotype to impact functions that play a critical role in immune response.-Kim, T.-H., Ly, C., Christodoulides, A., Nowell, C. J., Gunning, P. W., Sloan, E. K., Rowat, A. C. Stress hormone signaling through β-adrenergic receptors regulates macrophage mechanotype and function.

G2A Protects Mice against Sepsis by Modulating Kupffer Cell Activation: Cooperativity with Adenosine Receptor 2b

G2A is a GPCR abundantly expressed in immune cells. G2A^-/- mice showed higher lethality, higher plasma cytokines, and an impaired bacterial clearance in response to a murine model of sepsis (cecal ligation and puncture), which were blocked by GdCl₃, an inhibitor of Kupffer cells. Anti-IL-10 Ab reversed the impaired bacterial clearance in G2A^-/- mice. Indomethacin effectively blocked both the increased i.p. IL-10 levels and the impaired bacterial clearance, indicating that disturbed PG system is the proximal cause of these phenomena. Stimulation with LPS/C5a induced an increase in Escherichia coli phagocytosis and intracellular cAMP levels in G2A^+/+ peritoneal macrophages but not G2A^-/- cells, which showed more PGE₂/nitrite release and intracellular reactive oxygen species levels. Heterologous coexpression of G2A and adenosine receptor type 2b (A2bAR) induced a synergistic increase in cAMP signaling in a ligand-independent manner, with the evidence of physical interaction of G2A with A2bAR. BAY 60-6583, a specific agonist for A2bAR, increased intracellular cAMP levels in Kupffer cells from G2A^+/+ but not from G2A^-/- mice. Both G2A and A2bAR were required for antiseptic action of lysophosphatidylcholine. These results show inappropriate activation of G2A^-/- Kupffer cells to septic insults due to an impaired cAMP signaling possibly by lack of interaction with A2bAR.

Recombinant expression of Epinephelus lanceolatus serum amyloid A (ElSAA) and analysis of its macrophage modulatory activities

Serum amyloid A (SAA) is an acute-phase protein that plays a crucial role in the inflammatory response. In this study, we identified an SAA homolog from Epinephelus lanceolatus (ElSAA). Molecular characterization revealed that ElSAA contains a fibronectin-like motif that is typical of SAAs. Recombinant ElSAA protein (rElSAA) was produced in E. coli BL21 (DE3) cells and purified as a soluble protein. To analyze its biological activity, mouse Raw264.7 macrophage cells were treated with various concentrations of rElSAA. Expression of several inflammation-related cytokines, including tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, IL-6, and IL-10, was induced by rElSAA. This protein also triggered macrophage differentiation, as evidenced by increases in cell size and complexity. To determine whether rElSAA regulates macrophage polarization, we assessed gene expression of M1 and M2 markers. The results demonstrated that rElSAA induced the expression of both M1 and M2 markers, suggesting that it promotes the differentiation of macrophages into a mixed M1/M2 phenotype. To evaluate whether rElSAA enhances phagocytosis via an opsonization-dependent mechanism, GFP-labeled E. coli cells were pretreated with rElSAA, followed by incubation with Raw264.7 cells. Flow cytometry was used to monitor the phagocytic uptake of GFP-labeled E. coli by macrophages. Surprisingly, incubating E. coli with rElSAA did not enhance bacterial uptake by macrophages. However, preincubating Raw264.7 cells with various concentrations of rElSAA, followed by infection with E. coli (multiplicity of infection = 20 or 40), resulted in a clear enhancement of macrophage phagocytic capacity. In conclusion, we have identified SAA from E. lanceolatus and have demonstrated that rElSAA promotes inflammatory cytokine production and macrophage differentiation. In addition, rElSAA enhances phagocytosis of bacteria by macrophages via an opsonization-independent mechanism.

The common, autoimmunity-predisposing 620Arg > Trp variant of PTPN22 modulates macrophage function and morphology

The C1858T single nucleotide polymorphism (SNP) in PTPN22 (protein tyrosine phosphatase nonreceptor 22) leads to the 620 Arg to Trp polymorphism in its encoded human protein LYP. This allelic variant is associated with multiple autoimmune diseases, including type 1 diabetes (T1D), Crohn's disease, rheumatoid arthritis and systemic lupus erythematosus. However, the underlying mechanisms are poorly understood. To study how this polymorphism influences the immune system, we generated a mouse strain with a knock-in of the Trp allele, imitating the human disease-associated variant. We did not find significant difference between the polymorphic and the wild type mice on the proportion of total CD4 T cell, CD8 T cell, NK cell, memory T lymphocyte, macrophage, dendritic cells in both peripheral lymph nodes and spleen. However, macrophages from Trp/Trp mice showed altered morphology and enhanced function, including higher expression of MHCII and B7 molecules and increased phagocytic ability, which further leads to a higher T-cell activation by specific antigen. Our model shows no alteration in immune cell profile by the Trp allele, but brings up macrophages as an important player to consider in explaining the PTPN22 Trp allele effect on autoimmune disease risk.

Therapeutic potential and limitations of cholinergic anti-inflammatory pathway in sepsis

Sepsis is one of the main causes of mortality in hospitalized patients. Despite the recent technical advances and the development of novel generation of antibiotics, severe sepsis remains a major clinical and scientific challenge in modern medicine. Unsuccessful efforts have been dedicated to the search of therapeutic options to treat the deleterious inflammatory components of sepsis. Recent findings on neuronal networks controlling immunity raised expectations for novel therapeutic strategies to promote the regulation of sterile inflammation, such as autoimmune diseases. Interesting studies have dissected the anatomical constituents of the so-called "cholinergic anti-inflammatory pathway", suggesting that electrical vagus nerve stimulation and pharmacological activation of beta-2 adrenergic and alpha-7 nicotinic receptors could be alternative strategies for improving inflammatory conditions. However, the literature on infectious diseases, such as sepsis, is still controversial and, therefore, the real therapeutic potential of this neuroimmune pathway is not well defined. In this review, we will discuss the beneficial and detrimental effects of neural manipulation in sepsis, which depend on the multiple variables of the immune system and the nature of the infection. These observations suggest future critical studies to validate the clinical implications of vagal parasympathetic signaling in sepsis treatment.

Neuroendocrine regulation of inflammation

The interaction between the sympathetic nervous system and the immune system has been documented over the last several decades. In this review, the neuroanatomical, cellular, and molecular evidence for neuroimmune regulation in the maintenance of immune homeostasis will be discussed, as well as the potential impact of neuroimmune dysregulation in health and disease.

Isoproterenol‑mediated heme oxygenase‑1 induction inhibits high mobility group box 1 protein release and protects against rat myocardial ischemia/reperfusion injury in vivo

Isoproterenol (ISO) has been reported to inhibit high mobility group box 1 (HMGB1) protein release via heme oxygenase-1 (HO-1) induction in lipopolysaccharide (LPS)-activated RAW 264.7 cells and increase the survival rate of cecal ligation and puncture (CLP)-induced septic mice. Therefore, it was examined whether ISO-mediated HO-1 induction inhibits HMGB1 release in cardiac myocytes and attenuates myocardial ischemia/reperfusion (I/R) injury in rats. Anesthetized male rats were pretreated with ISO [intraperitoneal (i.p.) injection of 10 mg/kg] prior to ischemia in the absence and/or presence of zinc protoporphyrin IX (ZnPPIX, i.p., 10 mg/kg), which is an inhibitor of HO-1, and then subjected to ischemia for 30 min followed by reperfusion for 24 h. The myocardial I/R injury and oxidative stress were assessed. In addition, the HO-1 protein and HMGB1 expression were measured by western blot analysis. ISO significantly attenuated the myocardial I/R injury, reduced oxidative stress, and induced HO-1 and reduced HMGB1 release. However, all these effects caused by ISO were significantly reversed in the presence of ZnPPIX. These results suggested that ISO has a pivotal role in the protective effects on myocardial I/R injury. This protection mechanism is possibly due to the inhibition of HMGB1 release via the induction of HO-1.

Norepinephrine inhibits macrophage migration by decreasing CCR2 expression

Increased incidences of infectious and septic complications during post-burn courses represent the main contributor to burn injury mortality. Sustained increases in catecholamine levels, especially norepinephrine (NE), contribute to immune disturbances in severely burned patients. The precise mechanisms underlying NE-mediated immunoregulation are not fully understood. Here we hypothesize that persistently elevated NE levels are associated with immunodysfunctions. We examined the effects of NE on the phenotype and functions of bone marrow-derived macrophages (BMMs). Whole mouse bone marrow cells were treated in vitro with 40 ng/mL of M-CSF and with 1 x 10^-6 M or 1 x 10^-8 M of NE or without NE for 7 days; cells were collected and stained with antibodies for CD11b, F4/80, MHC II and the inflammatory CC chemokine receptor 2 (CCR2). We found 1 x 10^-6 M of NE inhibited MHC II and CCR2 expression on CD11b⁺/F4/80⁺ BMM cells. It also inhibited BMM proliferation by inhibiting CSF-1R expression. On the contrary, 1 x 10^-8 M of NE slightly increased both MHC II and CCR2 expression on CD11b⁺/F4/80⁺ BMM cells but inhibited CD11b⁺/F4/80⁺ BMM proliferation. MCP-1 based migration assay showed that the migration of 1 x 10^-6 M of NE-treated BMM toward MCP-1 was significantly decreased compared to BMM without NE treatment. Both 1 x 10^-8 M and 1 x 10^-6 M of NE enhanced TNF-α production and phagocytosis of FITC-Dextran. Intracellular staining of transcriptional factor MafB showed that 1 x 10^-6 M of NE treatment enhanced its expression, whereas 1 x 10^-8 M of NE decreased expression. Stimulation with LPS in the last 24-hours of BMM culture further decreased CCR2 and MHC II expression of these BMM, suggesting the synergistic effect of LPS and NE on macrophage. Our results demonstrate that NE regulates macrophage differentiation, proliferation and function, and may play a critical role in the dysfunctional immune response post-burn.

β2-Adrenoreceptor agonist inhibits antigen cross-presentation by dendritic cells

Despite widespread usage of β-adrenergic receptor (AR) agonists and antagonists in current clinical practice, our understanding of their interactions with the immune system is surprisingly sparse. Among the AR expressed by dendritic cells (DC), β2-AR can modify in vitro cytokine release upon stimulation. Because DC play a pivotal role in CD8(+) T cell immune responses, we examined the effects of β2-AR stimulation on MHC class I exogenous peptide presentation and cross-presentation capacities. We demonstrate that β2-AR agonist-exposed mature DC display a reduced ability to cross-present protein Ags while retaining their exogenous peptide presentation capability. This effect is mediated through the nonclassical inhibitory G (Gαi/0) protein. Moreover, inhibition of cross-presentation is neither due to reduced costimulatory molecule expression nor Ag uptake, but rather to impaired phagosomal Ag degradation. We observed a crosstalk between the TLR4 and β2-AR transduction pathways at the NF-κB level. In vivo, β2-AR agonist treatment of mice inhibits Ag protein cross-presentation to CD8(+) T cells but preserves their exogenous MHC class I peptide presentation capability. These findings may explain some side effects on the immune system associated with stress or β-agonist treatment and pave the way for the development of new immunomodulatory strategies.

CD14 deficiency impacts glucose homeostasis in mice through altered adrenal tone

The toll-like receptors comprise one of the most conserved components of the innate immune system, signaling the presence of molecules of microbial origin. It has been proposed that signaling through TLR4, which requires CD14 to recognize bacterial lipopolysaccharide (LPS), may generate low-grade inflammation and thereby affect insulin sensitivity and glucose metabolism. To examine the long-term influence of partial innate immune signaling disruption on glucose homeostasis, we analyzed knockout mice deficient in CD14 backcrossed into the diabetes-prone C57BL6 background at 6 or 12 months of age. CD14-ko mice, fed either normal or high-fat diets, displayed significant glucose intolerance compared to wild type controls. They also displayed elevated norepinephrine urinary excretion and increased adrenal medullary volume, as well as an enhanced norepinephrine secretory response to insulin-induced hypoglycemia. These results point out a previously unappreciated crosstalk between innate immune- and sympathoadrenal- systems, which exerts a major long-term effect on glucose homeostasis.

The impact of acute-stressor exposure on splenic innate immunity: a gene expression analysis

Exposure to intense, acute-stressors modulates immune function. We have previously reported, for example, that exposure to a single session of inescapable tailshock suppresses acquired and potentiates innate immune responses mediated by the spleen. The mechanisms for these changes remain unknown, however, they likely involve stress-induced modulation of cytokines. Cytokines operate in coordinated networks that include other immunoregulatory factors. Broad-scoped analyses are required to gain an understanding of the net-impact of stress on these immunoregulatory factors and the immune system. The goal of this study, therefore, is to examine the impact of acute-stressor exposure on network-wide changes in splenic immunoregulatory factor expression. One hundred and sixty-one genes linked to innate immune responses were quantified in the spleen following exposure to tailshock using an RT-PCR based gene array. Expression changes in 17 of the measured genes were confirmed using individual RT-PCR reactions. Further assessment of the expression changes using Exploratory Gene Association Networks (EGAN) identified important ontologies, processes and pathways that are indicative of a broader impact of stress on the immune system. Interestingly, EGAN identified several linkages between immunoregulatory factors that may be important in explaining previous results concerning the functional consequences of stress on splenic immunity. Additional processes, some of which are novel to this study, were also uncovered that may be important in directing future studies examining the impact of stress on the immune system. In this way, these analyses provide a better understanding of how acute stressor exposure modulates splenic immunity and may function as predictive tool for future related studies.

β₁-adrenergic receptor-mediated HO-1 induction, via PI3K and p38 MAPK, by isoproterenol in RAW 264.7 cells leads to inhibition of HMGB1 release in LPS-activated RAW 264.7 cells and increases in survival rate of CLP-induced septic mice

High mobility group box (HMGB)-1 plays an important role in sepsis-associated death in experimental studies. Heme oxygenase-1 (HO-1) inducers were reported to reduce HMGB1 release in experimental sepsis. Previously, we reported on the importance of the β₁-adrenergic receptor and protein kinase A pathway in the regulation of HO-1 expression by isoproterenol (ISO) in RAW 264.7 cells. We investigated whether ISO reduces HMGB1 release in LPS-activated RAW 264.7 cells and improves survival rate in septic mice due to HO-1 induction. ISO concentration-dependently increased HO-1 via Nrf-2 translocation and inhibited release of HMGB1 through the β₁-adrenergic receptor (β₁-AR) in LPS-activated RAW 264.7 cells. This conclusion was supported by the finding that dobutamine but not salbutamol increased HO-1 expression in both RAW 264.7 cells. ISO failed to inhibit HMGB1 release when HO-1 expression was suppressed by ZnPPIX, an HO-1 inhibitor in RAW 264.7 cells. ISO significantly inhibited phosphorylation of IκB-α and NF-κB-driven luciferase activity in LPS-activated RAW 264.7 cells. In addition, LY294002, a PI3K inhibitor, and SB203580, a p38 MAPK inhibitor, significantly inhibited not only HO-1 induction but also HMGB1 release by ISO. Importantly, ISO increased HO-1 protein expression in heart and lung tissues, reduced HMGB1 in plasma and increased survival rate in CLP-treated septic mice, which was significantly reversed by co-treatment with ZnPPIX. Taken together, we conclude that inhibition of HMGB1 release during sepsis via β₁-AR-mediated HO-1 induction is a novel mechanism for the beneficial effects of ISO in the treatment of sepsis.