Genetic variation in in-vitro cytokine-induced production of nitric oxide by murine peritoneal macrophages

Response to Oxidative Burst-Induced Hypoxia Is Associated With Macrophage Inflammatory Profiles as Revealed by Cellular Genome-Wide Association

Background

In mammalian species, hypoxia is a prominent feature of inflammation. The role of hypoxia in regulating macrophage responses via alteration in metabolic pathways is well established. Recently, oxidative burst-induced hypoxia has been shown in murine macrophages after phagocytosis. Despite the available detailed information on the regulation of macrophage function at transcriptomic and epigenomic levels, the association of genetic polymorphism and macrophage function has been less explored. Previously, we have shown that host genetics controls approximately 80% of the variation in an oxidative burst as measured by nitric oxide (NO^-). Further studies revealed two clusters of transcription factors (hypoxia-related and inflammatory-related) are under the genetic control that shapes macrophages’ pro-inflammatory characteristics.

Material and Methods

In the current study, the association between 43,066 autosomal Single Nucleic Polymorphism (SNPs) and the ability of MDMs in production of NO^- in response to E. coli was evaluated in 58 Holstein cows. The positional candidate genes near significant SNPs were selected to perform functional analysis. In addition, the interaction between the positional candidate genes and differentially expressed genes from our previous study was investigated.

Results

Sixty SNPs on 22 chromosomes of the bovine genome were found to be significantly associated with NO^- production of macrophages. The functional genomic analysis showed a significant interaction between positional candidate genes and mitochondria-related differentially expressed genes from the previous study. Further examination showed 7 SNPs located in the vicinity of genes with roles in response to hypoxia, shaping approximately 73% of the observed individual variation in NO^- production by MDM. Regarding the normoxic condition of macrophage culture in this study, it was hypothesized that oxidative burst is responsible for causing hypoxia at the cellular level.

Conclusion

The results suggest that the genetic polymorphism via regulation of response to hypoxia is a candidate step that perhaps shapes macrophage functional characteristics in the pathway of phagocytosis leading to oxidative burst, hypoxia, cellular response to hypoxia and finally the pro-inflammatory responses. Since all cells in one individual carry the same alleles, the effect of genetic predisposition of sensitivity to hypoxia will likely be notable on the clinical outcome to a broad range of host-pathogen interactions.

Transcriptomic Profiles of Monocyte-Derived Macrophages in Response to Escherichia coli is Associated with the Host Genetics

Reactive Nitrogen Species (RNS) are a group of bactericidal molecules produced by macrophages in response to pathogens in a process called oxidative burst. Nitric oxide (NO^-) is a member of RNS produced from arginine by inducible Nitric Oxide Synthase (iNOS) enzyme. The activity of iNOS and production of NO^- by macrophages following stimulation is one of the indicators of macrophage polarization towards M1/proinflammatory. Production of NO^- by bovine monocyte-derived macrophage (MDM) and mouse peritoneal macrophages has been shown to be strongly associated with host genetic with the heritability of 0.776 in bovine MDM and 0.8 in mouse peritoneal macrophages. However, the mechanism of genetic regulation of macrophage response has remained less explored. In the current study, the transcriptome of bovine MDMs was compared between two extreme phenotypes that had been classified as high and low responder based on NO^- production. The results showed that 179 and 392 genes were differentially expressed (DE) between high and low responder groups at 3 and 18 hours after exposure to Escherichia coli, respectively. A set of 11 Transcription Factors (TFs) (STAT1, IRF7, SPI1, STAT4, IRF1, HIF1A, FOXO3, REL, NFAT5, HIC1, and IRF4) at 3 hours and a set of 13 TFs (STAT1, IRF1, HIF1A, STAT4, ATF4, TP63, EGR1, CDKN2A, RBL1, E2F1, PRDM1, GATA3, and IRF4) at 18 hours after exposure to E. coli were identified to be differentially regulated between the high and low responder phenotypes. These TFs were found to be divided into two clusters of inflammatory- and hypoxia-related TFs. Functional analysis revealed that some key canonical pathways such as phagocytosis, chemotaxis, antigen presentation, and cell-to-cell signalling are enriched among the over-expressed genes by high responder phenotype. Based on the results of this study, it was inferred that the functional characteristics of bovine MDMs are associated with NO-based classification. Since NO^- production is strongly associated with host genetics, this study for the first time shows the distinct proinflammatory profiles of macrophages are controlled by the natural genetic polymorphism in an outbred population. In addition, the results suggest that genetics can be considered as a new dimension in the current model of macrophage polarization which is currently described by the combination of stimulants, only.

The effect of host genetics on in vitro performance of bovine monocyte-derived macrophages

The dynamic interaction between the host and pathogens, along with environmental factors, influences the regulation of mammalian immune responses. Therefore, comprehensive in vivo immune-phenotyping during an active response to a pathogen can be complex and prone to confounding effects. Evaluating critical fundamental aspects of the immune system at a cellular level is an alternative approach to reduce this complexity. Therefore, the objective of the current study was to examine an in vitro model for functional phenotyping of bovine monocyte-derived macrophages (MDM), cells which play a crucial role at all phases of inflammation, as well influence downstream immune responses. As indicators of MDM function, phagocytosis and nitric oxide (NO^-) production were tested in MDM of 16 cows in response to 2 common bacterial pathogens of dairy cows, Escherichia coli and Staphylococcus aureus. Notable functional variations were observed among the individuals (coefficient of variation: 33% for phagocytosis and 70% in the production of NO^-). The rank correlation analysis revealed a significant, positive, and strong correlation (rho = 0.92) between NO^- production in response to E. coli and S. aureus, and a positive but moderate correlation (rho = 0.58) between phagocytosis of E. coli and S. aureus. To gain further insight into this trait, another 58 cows were evaluated solely for NO^- response against E. coli. The pedigree of the tested animals was added to the statistical model and the heritability was estimated to be 0.776. Overall, the finding of this study showed a strong effect of host genetics on the in vitro activities of MDM and the possibility of ranking Holstein cows based on the in vitro functional variation of MDM.

A defective TLR4 signaling for IFN-β expression is responsible for the innately lower ability of BALB/c macrophages to produce NO in response to LPS as compared to C57BL/6

C57BL/6 mice macrophages innately produce higher levels of NO than BALB/c cells when stimulated with LPS. Here, we investigated the molecular events that account for this intrinsic differential production of NO. We found that the lower production of NO in BALB/c is not due to a subtraction of L-arginine by arginase, and correlates with a lower iNOS accumulation, which is independent of its degradation rate. Instead, the lower accumulation of iNOS is due to the lower levels of iNOS mRNA, previously shown to be also independent of its stability, suggesting that iNOS transcription is less efficient in BALB/c than in C57BL/6 macrophages. Activation of NFκB is more efficient in BALB/c, thus not correlating with iNOS expression. Conversely, activation of STAT-1 does correlate with iNOS expression, being more prominent in C57BL/6 than in BALB/c macrophages. IFN-β and IL-10 are more highly expressed in C57BL/6 than in BALB/c macrophages, and the opposite is true for TNF-α. Whereas IL-10 and TNF-α do not seem to participate in their differential production of NO, IFN-β has a determinant role since 1) anti-IFN-β neutralizing antibodies abolish STAT-1 activation reducing NO production in C57BL/6 macrophages to levels as low as in BALB/c cells and 2) exogenous rIFN-β confers to LPS-stimulated BALB/c macrophages the ability to phosphorylate STAT-1 and to produce NO as efficiently as C57BL/6 cells. We demonstrate, for the first time, that BALB/c macrophages are innately lower NO producers than C57BL/6 cells because they are defective in the TLR-4-induced IFN-β-mediated STAT-1 activation pathway.

Reactive oxygen species and nitric oxide in cutaneous leishmaniasis

Cutaneous leishmaniasis affects millions of people around the world. Several species of Leishmania infect mouse strains, and murine models closely reproduce the cutaneous lesions caused by the parasite in humans. Mouse models have enabled studies on the pathogenesis and effector mechanisms of host resistance to infection. Here, we review the role of nitric oxide (NO), reactive oxygen species (ROS), and peroxynitrite (ONOO⁻) in the control of parasites by macrophages, which are both the host cells and the effector cells. We also discuss the role of neutrophil-derived oxygen and nitrogen reactive species during infection with Leishmania. We emphasize the role of these cells in the outcome of leishmaniasis early after infection, before the adaptive T_h-cell immune response.

Differential sensitivity of C57BL/6 (M-1) and BALB/c (M-2) macrophages to the stimuli of IFN-gamma/LPS for the production of NO: correlation with iNOS mRNA and protein expression

C57BL/6 and BALB/c mice are prototype hosts for the study of resistance and susceptibility to several infectious diseases. In many cases, resistance of C57BL/6 is due to the microbicidal effect of nitric oxide (NO) produced by macrophages in response to interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha), mainly secreted by Th1 cells and macrophages, respectively. BALB/c, usually unable to give rise to Th1 lymphocytes, does not control certain infections. However, we and others have previously observed that regardless of the adaptive immune response, C57BL/6 (M-1) macrophages are far more sensitive to the stimulus of IFN-gamma-plus lipopolysaccharide (LPS) for the production of NO than are BALB/c (M-2) cells, a feature that might also account for resistance. Here, we report that the differential production of NO by M-1 and M-2 macrophages correlates with the accumulation of inducible nitric oxide synthase (iNOS) mRNA and protein, which shows that expression of iNOS is differentially regulated in M-1 and M-2 cells. The higher accumulation of iNOS mRNA in M-1 cells is independent of its stability, and, thus, it is possible that transcription of the iNOS gene in these cells may be more efficient than in M-2 cells. A remarkable finding is that the level of iNOS protein is much higher in M-1 macrophages than in M-2 cells, as compared with the mRNA levels, which makes us speculate that differential translational or posttranslational controls of iNOS gene are operative.

Immunomodulatory effects ofBacillus firmus on mouse peritoneal cellsin Vitro

The effect of nonpathogenic G+ bacterium B. firmus (BF) on stimulation of mouse peritoneal cells in vitro was evaluated by testing nitric-oxide-synthesis induction and cytokine formation. The reactivity was compared of peritoneal cells from two inbred mouse strains, C57B1/6 and BALB/c, which differ in their immunological reactivity. Peritoneal macrophages from C57B1/6 produced more nitric oxide after a 1-d cultivation with inactivated BF than those of BALB/c mice. In both strains, production can be further increased by adding exogenous IFN-gamma to the culture. There were no significant differences between peritoneal cells of these two mouse strains in cytokine production after optimal in vitro stimulation with BF. BF effectively activated peritoneal cells for the production of TNF-alpha, IL-1beta and IL-10, delipidated bacterium (DBF) being more efficient than BF in induction of IL-10 and TNF-alpha. On the other hand, BF had only small effect on IFN-gamma production and no detectable effect on IL-12 production. Macrophage activation by BF/DBF can represent one of the mechanisms responsible for previously described immunomodulatory activity of BF.

Microglial-macrophage synthesis of tumor necrosis factor after focal cerebral ischemia in mice is strain dependent

Commonly used inbred mouse strains display substantial differences in sensitivity to focal cerebral ischemia. Such differences can often be ascribed to differences in vascular anatomy. The authors investigated whether a contributing factor could be strain-related differences in cellular synthesis of the pleiotropic and potential neurotoxic cytokine tumor necrosis factor (TNF) in the border zone of and within the focal cerebral infarct. In all mouse strains investigated they found that TNF was synthesized by infarct and periinfarct infiltrating Mac-1 immunopositive microglia-macrophages. BALB/c mice, which developed the largest infarcts, contained significantly fewer TNF-producing microglia-macrophages compared with SJL and C57BL/6 mice at both 12 and 24 hours after permanent occlusion of the distal part of the middle cerebral artery. SJL mice developed larger infarcts than C57BL/6 mice, whereas the number of TNF-producing microglia-macrophages per infarct volume unit was comparable. Western blotting data confirmed the increased TNF levels in SJL mice compared with BALB/c and C57BL/6 mice. Furthermore, mice with 12-hour postischemic survival consistently contained two-to threefold more TNF-producing microglia-macrophages than mice with 24-hour survival. The data show that the magnitude of the cellular TNF response to cerebral ischemia is strain dependent, while the time-profile and the cellular sources of TNF are similar irrespective of genetic background. Furthermore, the lack of correlation between infarct size and cellular TNF response suggests that the functionally important TNF is produced in the very early phase (minutes to a few hours) after induction of ischemia, just as it raises the possibility that different mouse strains display different sensitivities to TNF.

Macrophage activation by antiviral acyclic nucleoside phosphonates in dependence on priming immune stimuli

Acyclic nucleoside phosphonates (ANPs) are potent broad-spectrum antivirals, also effective against immunodeficiency viruses and hepatitis viruses. Effects of several ANPs on in vitro cytokine gene expression and nitric oxide (NO) production by murine peritoneal macrophages were investigated. Included in the study were 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA; Adefovir), 9-(R)-[2-(phosphonomethoxy)propyl]adenine [(R)-PMPA; Tenofovir], 9-(S)-[2-(phosphonomethoxy)propyl]adenine; (S)-PMPA), 9-[2-(phosphonomethoxy)ethyl]-2,6-diaminopurine (PMEDAP), 9-(R)-[2-(phosphonomethoxy)propyl]-2,6-diaminopurine (PMPDAP), and 9-[2-(phosphonomethoxy)ethyl]guanine (PMEG). Some of them, i.e. (R)-PMPA, (S)-PMPA, and PMEG, stimulate secretion of TNF-alpha and IL-10 in a concentration-dependent manner, and enhance the IFN-gamma-induced secretion of TNF-alpha. Although unable to activate production of nitric oxide (NO) on their own, these compounds substantially augment NO formation induced by IFN-gamma. Analysis of the expression of inducible NO synthase mRNA indicates that the NO-enhancing effect of ANPs is mediated posttranscriptionally. In contrast to IFN-gamma, production of NO triggered by lipopolysaccharide (LPS) alone, or synergistically by LPS+IFN-gamma, remains unaltered by ANPs. The immunomodulatory effects have been differentially expressed in distinct genotypes of inbred strains of mice, including the low NO-responders Balb/c and high NO-responders C3H/HeN. Although less effectively, PMEG and (R)-PMPA also increase production of TNF-alpha and NO by the IFN-gamma- but not LPS-co-stimulated macrophages from C3H/HeJ mice, which are otherwise hypo-responsive to major immune stimuli provided by IFN-gamma and LPS. It can be concluded that the expression of immunomodulatory properties of ANPs depends on the immune state of cells and its activation by distinct priming signals.