Nitric oxide causes macrophage migration via the HIF-1-stimulated small GTPases Cdc42 and Rac1

Vav1-dependent Rac1 activation mediates hypoxia-induced gemcitabine resistance in pancreatic ductal adenocarcinoma cells through upregulation of HIF-1α expression

Hypoxia has been shown to induce gemcitabine (GEM) resistance in pancreatic ductal adenocarcinoma (PDAC) cells, however, the underlying mechanisms remain to be clarified. In the present study, we investigated whether activation of Vav1/Rac1/HIF-1α axis is responsible for hypoxia-induced GEM resistance in PDAC cells. Our results showed that Rac1 activation contributed to hypoxia-induced GEM resistance in PANC-1 cells. Hypoxia treatment led to an increased expression level of Vav1, which was responsible for Rac1 activation and GEM resistance in PDAC cells. Furthermore, Rac1 mediated hypoxia-induced GEM resistance by upregulating HIF-1α in PDAC cells. Taken together, these findings suggest that hypoxia induces GEM resistance in PDAC cells by activating the Vav1/Rac1/HIF-1α signaling pathway.

Intelectin enhances the phagocytosis of macrophages via CDC42-WASF2-ARPC2 signaling axis in Megalobrama amblycephala

Intelectin has been identified in various vertebrates and plays an important role in the host immune system. In our previous studies, recombinant Megalobrama amblycephala intelectin (rMaINTL) protein with excellent bacterial binding and agglutination activities enhances the phagocytic and killing activities of macrophages in M. amblycephala; however, the underlying regulatory mechanisms remain unclear. The present study showed that treatment with Aeromonas hydrophila and LPS induced the expression of rMaINTL in macrophages, and its level and distribution in macrophages or kidney tissue markedly increased after incubation or injection with rMaINTL. The cellular structure of macrophages was significantly affected after incubation with rMaINTL, resulting in an increased surface area and pseudopodia extension, which might contribute to enhancing the phagocytic ability of macrophages. Then, digital gene expression profiling analysis of the kidneys from rMaINTL-treated juvenile M. amblycephala identified some phagocytosis-related signaling factors that were enriched in pathways involved in the regulation of the actin cytoskeleton. In addition, qRT-PCR and western blotting verified that rMaINTL upregulated the expression of CDC42, WASF2, and ARPC2 in vitro and in vivo; however, the expression of these proteins was inhibited by a CDC42 inhibitor in macrophages. Moreover, CDC42 mediated the promotion of rMaINTL on actin polymerization by increasing the F-actin/G-actin ratio, which led to the extension of pseudopodia and remodeling of the macrophage cytoskeleton. Furthermore, the enhancement of macrophage phagocytosis by rMaINTL was blocked by the CDC42 inhibitor. These results suggested that rMaINTL induced the expression of CDC42 as well as the downstream signaling molecules WASF2 and ARPC2, thereby facilitating actin polymerization to promote cytoskeletal remodeling and phagocytosis. Overall, MaINTL enhanced the phagocytosis activity of macrophages in M. amblycephala via activation of the CDC42-WASF2-ARPC2 signaling axis.

Blood CDC42 overexpression is associated with an increased risk of acute exacerbation, inflammation and disease severity in patients with chronic obstructive pulmonary disease

It has been previously reported that cell division control 42 (CDC42) protein can regulate macrophage recruitment, T cell-associated inflammation and lung injury. However, its role in chronic obstructive pulmonary disease (COPD) remain poorly understood. Therefore, the present study aimed to investigate the possible association among CDC42 expression, the risk of acute exacerbation and disease features in patients with COPD. Peripheral blood mononuclear cells (PBMCs) and serum samples were collected from 60 patients with acute exacerbation COPD (AE-COPD), 60 patients with stable COPD (S-COPD) and 60 healthy control (HCs) individuals. The mRNA expression levels of CDC42 in PBMCs were then measured using reverse transcription-quantitative PCR. The serum levels of TNF-α, IL-1β, IL-6 and IL-17 were measured using ELISA. The results showed that the expression of CDC42 was dysregulated among patients with AE-COPD and S-COPD compared with that in HCs. Specifically, the expression level of CDC42 was the highest in patients with AE-COPD, followed by those with S-COPD and the lowest in HCs (P<0.001). Furthermore, receiver operating characteristic curve analysis demonstrated that CDC42 expression was associated with an increased risk of acute exacerbation in COPD with an area under curve of 0.690 (95% confidence interval=0.595-0.785). CDC42 was found to be positively associated with Global Initiative for Chronic Obstructive Lung Disease staging in patients with AE-COPD (P<0.01) and S-COPD (P<0.05). Additionally, CDC42 expression associated positively with the serum levels of TNF-α, IL-1β, IL-6 and IL-17 in patients with AE-COPD (all P<0.05). However, this association was weaker in patients with S-COPD and became negligible in HCs. In conclusion, data from the present study suggest that CDC42 is associated with an increased risk of acute exacerbation, inflammation and disease severity in patients with COPD, implicating its application as a potential biomarker for COPD.

PBMC CDC42 reveals the disease activity and treatment efficacy of TNF inhibitor in patients with ankylosing spondylitis

OBJECTIVE

Cell division cycle 42 (CDC42) regulates the polarization of M2 macrophage and maintains the T cell homeostasis, to participate in multiple autoimmune diseases, while its clinical involvement in ankylosing spondylitis (AS) remains unclear. Hence, the current study aimed to investigate the correlation of CDC42 with clinical characteristics and treatment outcome in AS patients receiving tumor necrosis factor (TNF) inhibitor therapy.

METHODS

Peripheral blood mononuclear cell (PBMC) CDC42 expression was detected at baseline, week (W) 4, W8, and W12 after TNF inhibitor treatment in 91 AS patients and in 50 HCs after enrollment. Furthermore, serum TNF-α, interferon-γ (IFN-γ), interleukin-10 (IL-10), and interleukin-17A (IL-17A) from AS patients were detected at baseline.

RESULTS

Blood CDC42 was lower in AS patients compared with HCs (p < 0.001). Additionally, blood CDC42 was negatively linked with CRP (r = -0.349, p = 0.001), BASDAI score (r = -0.243, p = 0.020), and ASDAS_CRP score (r = -0.238, p = 0.023) in AS patients; however, blood CDC42 was not correlated with other clinical characteristics. Besides, CDC42 was negatively correlated with TNF-α (r = -0.237, p = 0.024) and IL-17A (r = -0.339, p = 0.001) but not with IFN-γ (p = 0.083) or IL-10 (p = 0.280). Moreover, blood CDC42 was elevated after TNF inhibitor treatment (p < 0.001). Meanwhile, blood CDC42 was not varied at baseline and W4 between response patients and non-response patients, while it was higher at W8 (p = 0.019) and W12 (p = 0.002) in response patients than in non-response patients after treatment.

CONCLUSION

Blood CDC42 deficiency links with elevated pro-inflammatory cytokines, disease activity and unsatisfying response to TNF inhibitor in AS patients.

Arginine deprivation: a potential therapeutic for cancer cell metastasis? A review

Arginine is a semi essential amino acid that is used in protein biosynthesis. It can be obtained from daily food intake or synthesized in the body through the urea cycle using l-citrulline as a substrate. Arginine has a versatile role in the body because it helps in cell division, wound healing, ammonia disposal, immune system, and hormone biosynthesis. It is noteworthy that l-arginine is the precursor for the biosynthesis of nitric oxide (NO) and polyamines. In the case of cancer cells, arginine de novo synthesis is not enough to compensate for their high nutritional needs, forcing them to rely on extracellular supply of arginine. In this review, we will go through the importance of arginine deprivation as a novel targeting therapy by discussing the different arginine deprivation agents and their mechanism of action. We will also focus on the factors that affect cell migration and on the influence of arginine on metastases through polyamine and NO.

Carbon Nanomaterials Stimulate HMGB1 Release From Macrophages and Induce Cell Migration and Invasion

Carbon nanomaterials (CNMs) are widely used in industrial and medical sectors. The increasing exposure of CNMs necessitates the studies of their potential environmental and health effects. High-mobility group box-1 (HMGB1) is a nuclear DNA-binding protein, but when released from cells, may cause sustained inflammatory response and promote cell migration and invasion. In this work, we found that 7-day exposure of 2.5 mg/kg/day CNMs, including C60, single-walled carbon nanotubes, and graphene oxides significantly elevated the level of HMGB1 in blood and lung lavage fluids in C57BL/6 mice. Subsequently, cellular effects and underlying mechanism were explored by using Raw264.7. The results showed that noncytotoxic CNMs enhanced HMGB1 intracellular translocation and release via activating P2X7 receptor. Released HMGB1 further activated receptor for advanced glycation endproducts (RAGE) and downstream signaling pathway by upregulating RAGE and Rac1 expression. Simultaneously, CNMs prepared the cells for migration and invasion by modulating MMP2 and TIMP2 gene expression as well as cytoskeleton reorganization. Intriguingly, released HMGB1 from macrophages promoted the migration of nearby lung cancer cell, which can be efficiently inhibited by neutralizing antibodies against HMGB1 and RAGE. Taken together, our work demonstrated that CNMs stimulated HMGB1 release and cell migration/invasion through P2X7R-HMGB1-RAGE pathway. The revealed mechanisms might facilitate a better understanding on the inflammatory property and subsequent cell functional alteration of CNMs.

TLR2 Promotes Monocyte/Macrophage Recruitment Into the Liver and Microabscess Formation to Limit the Spread of Listeria Monocytogenes

TLR2 signaling plays a critical protective role against acute Listeria monocytogenes (Lm) infection by up-regulating inflammatory cytokines and promoting macrophage antimicrobial capabilities. However, the underlying mechanism by which TLR2 regulates hepatic macrophage-mediated anti-Lm immune responses remains poorly understood. In this study, we found that both the absolute number and proportion of monocyte/macrophage (Mo/MΦ) in the liver and spleen of Tlr2 ^-/- mice were significantly lower compared to wild type mice. Changes in TLR2 signaling in both hepatocytes and Mo/MΦs were associated with the infiltration of Mo/MΦs in response to Lm-infection. Analyses by proteome profiler array and ELISA revealed that hepatocytes recruited Mo/MΦs via TLR2-dependent secretion of CCL2 and CXCL1, which was confirmed by receptor blocking and exogenous chemokine administration. Importantly, we found that TLR2 contributed to macrophage mobility in the liver through a TLR2/NO/F-actin pathway, facilitating the formation of macrophage-associated hepatic microabscesses. Moreover, TLR2 activation induced the expression of several PRRs on hepatic macrophages associated with the recognition of Lm and augmented macrophage bacterial clearance activity. Our findings provide insight into the intrinsic mechanisms of TLR2-induced Mo/MΦ migration and mobility, as well as the interaction between macrophages and hepatocytes in resistance to Lm infection.

Hypoxia, Metabolism and Immune Cell Function

Hypoxia is a hallmark of inflamed, infected or damaged tissue, and the adaptation to inadequate tissue oxygenation is regulated by hypoxia-inducible factors (HIFs). HIFs are key mediators of the cellular response to hypoxia, but they are also associated with pathological stress such as inflammation, bacteriological infection or cancer. In addition, HIFs are central regulators of many innate and adaptive immunological functions, including migration, antigen presentation, production of cytokines and antimicrobial peptides, phagocytosis as well as cellular metabolic reprogramming. A characteristic feature of immune cells is their ability to infiltrate and operate in tissues with low level of nutrients and oxygen. The objective of this article is to discuss the role of HIFs in the function of innate and adaptive immune cells in hypoxia, with a focus on how hypoxia modulates immunometabolism.

Cell type-dependent HIF1 α-mediated effects of hypoxia on proliferation, migration and metastatic potential of human tumor cells

Tumor hypoxia promotes neoangiogenesis and contributes to the radio- and chemotherapy resistant and aggressive phenotype of cancer cells. However, the migratory response of tumor cells and the role of small GTPases regulating the organization of cytoskeleton under hypoxic conditions have yet to be established. Accordingly, we measured the proliferation, migration, RhoA activation, the mRNA and protein levels of hypoxia inducible factor-1alpha (HIF-1α) and three small G-proteins, Rac1, cdc42 and RhoA in a panel of five human tumor cell lines under normoxic and hypoxic conditions. Importantly, HT168-M1 human melanoma cells with high baseline migration capacity showed increased HIF-1α and small GTPases expression, RhoA activation and migration under hypoxia. These activities were blocked by anti- HIF-1α shRNA. Moreover, the in vivo metastatic potential was promoted by hypoxia mimicking CoCl₂ treatment and reduced upon inhibition of HIF-1α in a spleen to liver colonization experiment. In contrast, HT29 human colon cancer cells with low migration capacity showed limited response to in vitro hypoxia. The expression of the small G-proteins decreased both at mRNA and protein levels and the RhoA activation was reduced. Nevertheless, the number of lung or liver metastatic colonies disseminating from orthotopic HT29 grafts did not change upon CoCl₂ or chetomin treatment. Our data demonstrates that the hypoxic environment induces cell-type dependent changes in the levels and activation of small GTPases and results in varying migratory and metastasis promoting responses in different human tumor cell lines.

Macrophage NOS2 in Tumor Leukocytes

SIGNIFICANCE

Leukocytes and especially macrophages are a major cellular constituent of the tumor mass. The tumor microenvironment not only determines their activity but in turn these cells also contribute to tumor initiation and progression. Recent Advances: Proinflammatory stimulated macrophages upregulate inducible nitric oxide synthase (NOS2) and produce high steady-state NO concentrations. NO provokes tumor cell death by initiating apoptosis and/or necrosis. Mechanisms may comprise p53 accumulation, immunestimulatory activities, and an increased efficacy of chemo- and/or radiotherapy. However, the potential cytotoxic activity of macrophages often is compromised in the tumor microenvironment and instead a protumor activity of macrophages dominates. Contributing factors are signals generated by viable and dying tumor cells, attraction and activation of myeloid-derived suppressor cells, and hypoxia. Limited oxygen availability not only attenuates NOS2 activity but also causes accumulation of hypoxia-inducible factors 1 and 2 (HIF-1/HIF-2). Activation of the HIF system is tightly linked to NO formation and affects the expression of macrophage phenotype markers that in turn add to tumor progression.

CRITICAL ISSUES

To make use of the cytotoxic arsenal of activated macrophages directed against tumor cells, it will be critical to understand how, when, and where these innate immune responses are blocked and whether it will be possible to reinstall their full capacity to kill tumor cells.

FUTURE DIRECTIONS

Low-dose irradiation or proinflammatory activation of macrophages in the tumor microenvironment may open options to boost NOS2 expression and activity and to initiate immunestimulatory features of NO that may help to restrict tumor growth. Antioxid. Redox Signal. 26, 1023-1043.

Metabolic regulation of macrophages during tissue repair: insights from skeletal muscle regeneration

Macrophages are highly versatile cells that are involved both in the mounting and the resolution of inflammatory responses. Besides their properties in innate immunity to fight against pathogens, macrophages are essential for tissue repair, during which they adopt sequential inflammatory status. While the acquisition of some canonical polarized inflammatory statuses in vitro (M1/M2) is beginning to be understood at the molecular level, the regulation of macrophage skewing in vivo has been less investigated. Immunometabolism, in particular, is an emerging field, and most of the studies so far have investigated the control of macrophage polarization using in vitro set-ups. In this context, skeletal muscle regeneration is an excellent paradigm to study tissue repair, since the sequential steps of inflammatory response and tissue repair are well characterized. In this Review, after introducing macrophage populations and functions during skeletal muscle regeneration, we present the current knowledge on the metabolic regulation of macrophage inflammatory status, with particular emphasis on the comparison between in vitro and in vivo models of macrophage activation. We also discuss the metabolic regulation of macrophages in vivo during skeletal muscle regeneration.

Hif-1α regulates macrophage-endothelial interactions during blood vessel development in zebrafish

Macrophages are known to interact with endothelial cells during developmental and pathological angiogenesis but the molecular mechanisms modulating these interactions remain unclear. Here, we show a role for the Hif-1α transcription factor in this cellular communication. We generated hif-1aa;hif-1ab double mutants in zebrafish, hereafter referred to as hif-1α mutants, and find that they exhibit impaired macrophage mobilization from the aorta-gonad-mesonephros (AGM) region as well as angiogenic defects and defective vascular repair. Importantly, macrophage ablation is sufficient to recapitulate the vascular phenotypes observed in hif-1α mutants, revealing for the first time a macrophage-dependent angiogenic process during development. Further substantiating our observations of vascular repair, we find that most macrophages closely associated with ruptured blood vessels are Tnfα-positive, a key feature of classically activated macrophages. Altogether, our data provide genetic evidence that Hif-1α regulates interactions between macrophages and endothelial cells starting with the mobilization of macrophages from the AGM.

The molecular mechanism regulating macrophage interaction with endothelial cells during development is unclear. Here, the authors show that in zebrafish mutation of hypoxia-inducible factor-1α impairs macrophage mobilization from the aorta-gonad-mesonephros, causing defects in angiogenesis and vessel repair.

Impaired Healing of a Cutaneous Wound in an Inducible Nitric Oxide Synthase-Knockout Mouse

Background. We investigated the effects of loss of inducible nitric oxide synthase (iNOS) on the healing process of cutaneous excisional injury by using iNOS-null (KO) mice. Population of granulation tissue-related cell types, that is, myofibroblasts and macrophages, growth factor expression, and reepithelialization were evaluated. Methods. KO and wild type (WT) mice of C57BL/6 background were used. Under general anesthesia two round full-thickness excision wounds of 5.0 mm in diameter were produced in dorsal skin. After specific intervals of healing, macroscopic observation, histology, immunohistochemistry, and real-time reverse transcription-polymerase chain reaction (RT-PCR) were employed to evaluate the healing process. Results. The loss of iNOS retards granulation tissue formation and reepithelialization in excision wound model in mice. Detailed analyses showed that myofibroblast appearance, macrophage infiltration, and mRNA expression of transforming growth factor b and of collagen 1α2 were all suppressed by lacking iNOS. Conclusions. iNOS is required in the process of cutaneous wound healing. Lacking iNOS retards macrophage invasion and its expression of fibrogenic components that might further impair fibrogenic behaviors of fibroblasts.

Metabolic reprogramming & inflammation: Fuelling the host response to pathogens

Successful immune responses to pathogens rely on efficient host innate processes to contain and limit bacterial growth, induce inflammatory response and promote antigen presentation for the development of adaptive immunity. This energy intensive process is regulated through multiple mechanisms including receptor-mediated signaling, control of phago-lysomal fusion events and promotion of bactericidal activities. Inherent macrophage activities therefore are dynamic and are modulated by signals and changes in the environment during infection. So too does the way these cells obtain their energy to adapt to altered homeostasis. It has emerged recently that the pathways employed by immune cells to derive energy from available or preferred nutrients underline the dynamic changes associated with immune activation. In particular, key breakpoints have been identified in the metabolism of glucose and lipids which direct not just how cells derive energy in the form of ATP, but also cellular phenotype and activation status. Much of this comes about through altered flux and accumulation of intermediate metabolites. How these changes in metabolism directly impact on the key processes required for anti-microbial immunity however, is less obvious. Here, we examine the 2 key nutrient utilization pathways employed by innate cells to fuel central energy metabolism and examine how these are altered in response to activation during infection, emphasising how certain metabolic switches or 'reprogramming' impacts anti-microbial processes. By examining carbohydrate and lipid pathways and how the flux of key intermediates intersects with innate immune signaling and the induction of bactericidal activities, we hope to illustrate the importance of these metabolic switches for protective immunity and provide a potential mechanism for how altered metabolic conditions in humans such as diabetes and hyperlipidemia alter the host response to infection.

Nitric oxide promotes epidermal stem cell migration via cGMP-Rho GTPase signalling

The migration and reepithelization of epidermal stem cells (ESCs) are the most critical processes in wound healing. The gaseous messenger nitric oxide (NO) has multiple biological effects, but its actions on ESCs are poorly understood. In this study, an NO donor, S-nitroso-N-acetylpenicillamine (SNAP), was found to facilitate the in vitro migration of human ESCs (huESCs) in both live-imaging and scratch models. In addition, pull-down assays demonstrated that SNAP could activate the small GTPases RhoA and Rac1 of the Rho family, but not Cdc42. Moreover, the effects of SNAP on the migration and F-actin polymerization of ESCs could be blocked by inhibitors of cGMP, PKG, RhoA or Rac1, and by a specific siRNA of RhoA or Rac1, but not by a Cdc42 inhibitor or siRNA. Furthermore, the roles of NO in ESC migration via cGMP-Rho GTPase signalling in vivo were confirmed by tracing 5-bromo-2-deoxyuridine (BrdU)-labelled cells in a superficial, partial-thickness scald mouse model. Thus, the present study demonstrated that the NO donor SNAP could promote huESC migration in vitro. Furthermore, NO was found to induce ESC migration via cGMP-Rho GTPase RhoA and Rac1 signalling, but not Cdc42 signalling, both in vivo and in vitro.

Light-Emitting Diode Irradiation (640 nm) Regulates Keratinocyte Migration and Cytoskeletal Reorganization Via Hypoxia-Inducible Factor-1α

OBJECTIVE

The objective of this study was to determine the effect of light-emitting diode (LED) irradiation on the migration and proliferation of keratinocytes.

BACKGROUND DATA

Keratinocytes play a key role in re-epithelialization during wound healing; it is speculated that low-level LED therapy might improve keratinocyte migration and proliferation.

MATERIALS AND METHODS

Human keratinocyte cells (HKCs) were isolated from child or adult foreskins and irradiated with LED light with a wavelength of 640 nm and a dosage of 12 or 24 J/cm(2). Cell motility, migration, and proliferation were examined using live cell imaging, scratch assay, and a colorimetric cell counting assay, respectively. Hypoxia-inducible factor-1α (HIF-1α) protein levels were analyzed by using Western blotting. Filamentous actin (F-actin) was stained by phalloidin. YC-1 [3-(5-hydroxymethyl-2-furyl)-1-benzylindazole] was used as an HIF-1 inhibitor, and CoCl2 (cobalt chloride) and DMOG (dimethyloxaloyl glycine) are HIF-1α activators.

RESULTS

LED irradiation significantly promoted cell motility and migration, but did not significantly influence cell proliferation in HKCs. Furthermore, LED irradiation resulted in a reorganization of cellular F-actin and a dramatic upregulation of HIF-1α expression. Suppression of HIF-1α using the compound YC-1 prevented reorganization of the actin cytoskeleton following LED irradiation, suggesting that the effect of LED irradiation on the cytoskeleton is mediated through HIF-1α. Conversely, chemical activation of HIF-1α via DMOG or CoCl2 resulted in a reorganization of F-actin.

CONCLUSIONS

LED irradiation may increase keratinocyte migration via HIF-1α-dependent cytoskeletal reorganization.

Dendritic Cells under Hypoxia: How Oxygen Shortage Affects the Linkage between Innate and Adaptive Immunity

Dendritic cells (DCs) are considered as one of the main regulators of immune responses. They collect antigens, process them, and present typical antigenic structures to lymphocytes, thereby inducing an adaptive immune response. All these processes take place under conditions of oxygen shortage (hypoxia) which is often not considered in experimental settings. This review highlights how deeply hypoxia modulates human as well as mouse immature and mature dendritic cell functions. It tries to link in vitro results to actual in vivo studies and outlines how hypoxia-mediated shaping of dendritic cells affects the activation of (innate) immunity.

Lipopolysaccharide induces inducible nitric oxide synthase-dependent podocyte dysfunction via a hypoxia-inducible factor 1α and cell division control protein 42 and Ras-related C3 botulinum toxin substrate 1 pathway

Urine protein loss in immune complex-mediated diseases such as lupus nephritis is associated with podocyte foot process effacement (podocytopathy) but is not always dependent on glomerular immune complex deposition. Several murine and human studies have associated lupus nephritis with inducible nitric oxide synthase (iNOS) expression in what appear to be podocytes. This study was conducted to determine mechanisms of immune-complex-independent and iNOS-dependent podocyte dysfunction. Conditionally immortalized podocytes were cultured with lipopolysaccharide (LPS) and nitric oxide (NO), superoxide (SO), or peroxynitrite donors in the presence or absence of inhibitors of iNOS, reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase or monocyte chemotactic protein 1 (MCP-1), or with sepiapterin to increase coupling of iNOS homodimers. Podocyte NO, SO, and MCP-1 production and nitrotyrosine modifications were determined. The podocytopathy phenotype was determined by measuring cell motility and membrane permeability to albumin. This study determined that NO produced by iNOS is sufficient and necessary to induce podocytopathy. NO probably induces this phenotype via hypoxia-inducible factor 1α and cell division control protein 42 and Ras-related C3 botulinum toxin substrate 1 pathways. With LPS stimulation, neither SO nor peroxynitrite produced by uncoupled iNOS or NADPH oxidase nor MCP-1 was sufficient to induce the full phenotype. This study supports the notion that iNOS may induce autocrine podocyte dysfunction. Thus, targeting iNOS or the pathways of its induction may have therapeutic benefit.

Nitric oxide enhances keratinocyte cell migration by regulating Rho GTPase via cGMP-PKG signalling

Objective

Nitric oxide (NO) has been shown to improve wound healing, but the mechanism underlying this function is not well defined. Here, we explored the effect of NO on the migration of a human keratinocyte cell line (HaCaT) and its possible mechanism.

Methods

The effects of NO on HaCaT cells in the presence of different concentrations of the NO donor sodium nitroprusside (SNP) were evaluated in a cell migration assay. Subsequently, the cytoskeleton reorganization of cultured HaCaT cells stained with rhodamine-phalloidin was observed with a confocal laser scanning microscope. The mRNA expression and active proteins of CDC42, Rac1 and RhoA in the cultured cells were determined via RT-PCR and pull-down assays, respectively. Furthermore, the roles of various inhibitors or agonists specific to cGMP, PKG and CDC42, Rac1, RhoA in the effects of NO on HaCaT cell migration, F-actin stress fibre formation, and Rho GTPase expression were observed.

Results

It was also found HaCaT cell migration was increased by SNP in a dose-dependent manner, and the other two NO donors either spermine NONOate or SNAP had almost the same effects on HaCat cell migrations. The formation of F-actin stress fibres in SNP-treated HaCaT cells was increased. The mRNA expression and the active proteins of CDC42, Rac1 and RhoA were found to be upregulated after SNP treatment. Similar effects were observed after the cells were treated with a cGMP or PKG agonist. Additionally, the SNP-mediated upregulation of the mRNA expression and the active proteins of CDC42, Rac1 and RhoA were inhibited by the addition of an inhibitor of cGMP or PKG. Moreover, the SNP-mediated promoting effects of migration and cytoskeleton reorganization were inhibited by treatment with inhibitors of cGMP, PKG, CDC42, Rac1 and RhoA respectively.

Conclusion

Our data indicated that the stimulatory effects of NO on cell migration of HaCaT cells are mediated by the cGMP signalling pathway via the upregulation of Rho-GTPase expression, which might promote cytoskeleton reorganization.

Hypoxia-Inducible Factor (HIF) as a Pharmacological Target for Prevention and Treatment of Infectious Diseases

In the present era of ever-increasing antibiotic resistance and increasingly complex and immunosuppressed patient populations, physicians and scientists are seeking novel approaches to battle difficult infectious disease conditions. Development of a serious infection implies a failure of innate immune capabilities in the patient, and one may consider whether pharmacological strategies exist to correct and enhance innate immune cell function. Hypoxia-inducible factor-1 (HIF-1), the central regulator of the cellular response to hypoxic stress, has recently been recognized to control the activation state and key microbicidal functions of immune cells. HIF-1 boosting drugs are in clinical development for anemia and other indications, and could be repositioned as infectious disease therapeutics. With equal attention to opportunities and complexities, we review our current understanding of HIF-1 regulation of microbial host-pathogen interactions with an eye toward future drug development.

Induction of inducible nitric oxide synthase (iNOS) expression by oxLDL inhibits macrophage derived foam cell migration

OBJECTIVE

Deletion of inducible nitric oxide synthase (iNOS) in apolipoprotein E knockout mice was shown to mitigate the extent of arteriosclerosis. Oxidized low density lipoprotein (oxLDL) inhibits macrophage migration and traps foam cells, possibly through a mechanism involving oxidative stress. Here, we addressed whether a reduction of iNOS-mediated oxidative stress remobilizes macrophage-derived foam cells and may reverse plaque formation.

METHODS

Migration of RAW264.7 cells and bone marrow cells was quantified using a modified Boyden chamber. iNOS expression, phalloidin staining, focal adhesion kinase phosphorylation, lipid peroxides, nitric oxide (NO) and reactive oxygen species (ROS) production were assessed.

RESULTS

oxLDL treatment significantly reduced cell migration compared to unstimulated cells (p < 0.05). This migratory arrest was reversed by co-incubation with a pharmacologic iNOS inhibitor 1400 W (p < 0.05) and iNOS-siRNA (p > 0.05). Furthermore, apoE/iNOS double knockout macrophages do not show migratory arrest in response to oxLDL uptake, compared to apoE knockout controls (p > 0.05). We documented significantly increased iNOS expression following oxLDL treatment and downregulation using 1400 W and small inhibitory RNA (siRNA). iNOS inhibition was associated with a reduction in NO and peroxynitrite (ONOO-)- and increased superoxide generation. Trolox treatment of RAW264.7 cells restored migration indicating that peroxynitrite mediated lipid peroxide formation is involved in the signaling pathway mediating cell arrest..

CONCLUSIONS

Here, we provide pharmacologic and genetic evidence that oxLDL induced iNOS expression inhibits macrophage-derived foam cell migration. Therefore, reduction of peroxynitrite and possibly lipid hydroperoxide levels in plaques represents a valuable therapeutic approach to reverse migratory arrest of macrophage-derived foam cells and to impair plaque formation.

Phagocyte-myocyte interactions and consequences during hypoxic wound healing

Myocardial infarction (MI), secondary to atherosclerotic plaque rupture and occlusive thrombi, triggers acute margination of inflammatory neutrophils and monocyte phagocyte subsets to the damaged heart, the latter of which may give rise briefly to differentiated macrophage-like or dendritic-like cells. Within the injured myocardium, a primary function of these phagocytic cells is to remove damaged extracellular matrix, necrotic and apoptotic cardiac cells, as well as immune cells that turn over. Recognition of dying cellular targets by phagocytes triggers intracellular signaling, particularly in macrophages, wherein cytokines and lipid mediators are generated to promote inflammation resolution, fibrotic scarring, angiogenesis, and compensatory organ remodeling. These actions cooperate in an effort to preserve myocardial contractility and prevent heart failure. Immune cell function is modulated by local tissue factors that include secreted protease activity, oxidative stress during clinical reperfusion, and hypoxia. Importantly, experimental evidence suggests that monocyte function and phagocytosis efficiency is compromised in the setting of MI risk factors, including hyperlipidemia and ageing, however underlying mechanisms remain unclear. Herein we review seminal phagocyte and cardiac molecular factors that lead to, and culminate in, the recognition and removal of dying injured myocardium, the effects of hypoxia, and their relationship to cardiac infarct size and heart healing.

Hypoxia-regulated target genes implicated in tumor metastasis

Hypoxia is an important microenvironmental factor that induces cancer metastasis. Hypoxia/hypoxia-inducible factor-1α (HIF-1α) regulates many important steps of the metastatic processes, especially epithelial-mesenchymal transition (EMT) that is one of the crucial mechanisms to cause early stage of tumor metastasis. To have a better understanding of the mechanism of hypoxia-regulated metastasis, various hypoxia/HIF-1α-regulated target genes are categorized into different classes including transcription factors, histone modifiers, enzymes, receptors, kinases, small GTPases, transporters, adhesion molecules, surface molecules, membrane proteins, and microRNAs. Different roles of these target genes are described with regards to their relationship to hypoxia-induced metastasis. We hope that this review will provide a framework for further exploration of hypoxia/HIF-1α-regulated target genes and a comprehensive view of the metastatic picture induced by hypoxia.

Irradiation promotes an m2 macrophage phenotype in tumor hypoxia

Macrophages display different phenotypes with distinct functions and can rapidly respond to environmental changes. Previous studies on TRAMP-C1 tumor model have shown that irradiation has a strong impact on tumor microenvironments. The major changes include the decrease of microvascular density, the increase of avascular hypoxia, and the aggregation of tumor-associated macrophages in avascular hypoxic regions. Similar changes were observed no matter the irradiation was given to tissue bed before tumor implantation (pre-IR tumors), or to established tumors (IR tumors). Recent results on three murine tumors, TRAMP-C1 prostate adenocarcinoma, ALTS1C1 astrocytoma, and GL261 glioma, further demonstrate that different phenotypes of inflammatory cells are spatially distributed into different microenvironments in both IR and pre-IR tumors. Regions with avascular hypoxia and central necrosis have CD11b^high/Gr-1+ neutrophils in the center of the necrotic area. Next to them are CD11b^low/F4/80+ macrophages that sit at the junctions between central necrotic and surrounding hypoxic regions. The majority of cells in the hypoxic regions are CD11b^low/CD68+ macrophages. These inflammatory cell populations express different levels of Arg I. This distribution pattern, except for neutrophils, is not observed in tumors receiving chemotherapy or an anti-angiogenesis agent which also lead to avascular hypoxia. This unique distribution pattern of inflammatory cells in IR tumor sites is interfered with by targeting the expression of a chemokine protein, SDF-1α, by tumor cells, and this also increases radiation-induced tumor growth delay. This indicates that irradiated-hypoxia tissues have distinct tumor microenvironments that favor the development of M2 macrophages and that is affected by the levels of tumor-secreted SDF-1α.

Hypoxia inducible factor-1 as a target for neurodegenerative diseases

Hypoxia inducible factor-1 (HIF-1) is a transcriptional factor responsible for cellular and tissue adaption to low oxygen tension. HIF-1, a heterodimer consisting of a constitutively expressed β subunit and an oxygen-regulated α subunit, regulates a series of genes that participate in angiogenesis, iron metabolism, glucose metabolism, and cell proliferation/survival. The activity of HIF-1 is controlled by post-translational modifications on different amino acid residues of its subunits, mainly the alpha subunit. Besides in ischemic stroke (see review [1]), emerging evidence has revealed that HIF-1 activity and expression of its down-stream genes, such as vascular endothelial growth factor and erythropoietin, are altered in a range of neurodegenerative diseases. At the same time, experimental and clinical evidence has demonstrated that regulating HIF-1 might ameliorate the cellular and tissue damage in the neurodegenerative diseases. These new findings suggest HIF-1 as a potential medicinal target for the neurodegenerative diseases. This review focuses on HIF-1α protein modifications and HIF-1's potential neuroprotective roles in Alzheimer's (AD), Parkinson's (PD), Huntington's diseases (HD), and amyotrophic lateral sclerosis (ALS).

Endothelial cell HIF-1α and HIF-2α differentially regulate metastatic success

The hypoxia inducible transcription factors (HIFs) control many mediators of vascular response, including both angiogenic factors and small molecules such as nitric oxide (NO). In studying how endothelial HIF response itself affects metastasis, we found that loss of HIF-1α in endothelial cells reduces NO synthesis, retards tumor cell migration through endothelial layers, and restricts tumor cell metastasis, and that loss of HIF-2α has in each case the opposite effect. This results from differential regulation of NO homeostasis that in turn regulates vascular endothelial growth factor expression in an NO-dependent feedback loop. These opposing roles for the two HIF factors indicate that both they and endothelial cells regulate metastasis as malignancy progresses.

Cardiac triglyceride accumulation following acute lipid excess occurs through activation of a FoxO1-iNOS-CD36 pathway

Obesity due to nutrient excess leads to chronic pathologies including type 2 diabetes and cardiovascular disease. Related to nutrient excess, FoxO1 has a role in regulating fatty acid uptake and oxidation and triglyceride (TG) storage by mechanisms that are largely unresolved. We examined the mechanism behind palmitate (PA)-induced TG accumulation in cardiomyocytes. To mimic lipid excess, rat ventricular myocytes were incubated with albumin-bound PA (1 mM) or rats were administered Intralipid (20%). PA-treated cardiomyocytes showed a substantial increase in TG accumulation, accompanied by amplification of nuclear migration of phospho-p38 and FoxO1, iNOS induction, and translocation of CD36 to the plasma membrane. PA also increased Cdc42 protein and its tyrosine nitration, thereby rearranging the cytoskeleton and facilitating CD36 translocation. These effects were duplicated by TNF-α and reversed by the iNOS inhibitor 1400 W. PA increased the nuclear interaction between FoxO1 and NF-κB, reduced the nuclear presence of PGC-1α, and downregulated expression of oxidative phosphorylation proteins. In vivo a robust increase in cardiac TGs after Intralipid administration was also associated with augmentation of nuclear FoxO1 and iNOS expression. Impeding this FoxO1-iNOS-CD36 pathway could decrease cardiac lipid accumulation and oxidative/nitrosative stress and help ameliorate the cardiovascular complications associated with obesity and diabetes.

Hypoxia inducible factor-dependent regulation of angiogenesis by nitro-fatty acids

OBJECTIVE

Nitro-fatty acids (NO(2)-FAs) are emerging as a new class of cell signaling mediators. Because NO(2)-FAs are found in the vascular compartment and their impact on vascularization remains unknown, we aimed to investigate the role of NO(2)-FAs in angiogenesis.

METHODS AND RESULTS

The effects of nitrolinoleic acid and nitrooleic acid were evaluated on migration of endothelial cell (EC) in vitro, EC sprouting ex vivo, and angiogenesis in the chorioallantoic membrane assay in vivo. At 10 μmol/L, both NO(2)-FAs induced EC migration and the formation of sprouts and promoted angiogenesis in vivo in an NO-dependent manner. In addition, NO(2)-FAs increased intracellular NO concentration, upregulated protein expression of the hypoxia inducible factor-1α (HIF-1α) transcription factor by an NO-mediated mechanism, and induced expression of HIF-1α target genes, such as vascular endothelial growth factor, glucose transporter-1, and adrenomedullin. Compared with typical NO donors such as spermine-NONOate and deta-NONOate, NO(2)-FAs were slightly less potent inducers of EC migration and HIF-1α expression. Short hairpin RNA-mediated knockdown of HIF-1α attenuated the induction of vascular endothelial growth factor mRNA expression and EC migration stimulated by NO(2)-FAs.

CONCLUSION

Our data disclose a novel physiological role for NO(2)-FAs, indicating that these compounds induce angiogenesis in an NO-dependent mechanism via activation of HIF-1α.

Interactions between nitric oxide and hypoxia-inducible factor signaling pathways in inflammatory disease

Induction and activation of nitric oxide (NO) synthases (NOS) and excessive production of NO are common features of almost all diseases associated with infection and acute or chronic inflammation, although the contribution of NO to the pathophysiology of these diseases is highly multifactorial and often still a matter of controversy. Because of its direct impact on tissue oxygenation and cellular oxygen (O(2)) consumption and re-distribution, the ability of NO to regulate various aspects of hypoxia-induced signaling has received widespread attention. Conditions of tissue hypoxia and the activation of hypoxia-inducible factors (HIF) have been implicated in hypoxia or in cancer biology, but are also being increasingly recognized as important features of acute and chronic inflammation. Thus, the activation of HIF transcription factors has been increasingly implicated in inflammatory diseases, and recent studies have indicated its critical importance in regulating phagocyte function, inflammatory mediator production, and regulation of epithelial integrity and repair processes. Finally, HIF also appears to contribute to important features of tissue fibrosis and epithelial-to-mesenchymal transition, processes that are associated with tissue remodeling in various non-malignant chronic inflammatory disorders. In this review, we briefly summarize the current state of knowledge with respect to the general mechanisms involved in HIF regulation and the impact of NO on HIF activation. Secondly, we will summarize the major recent findings demonstrating a role for HIF signaling in infection, inflammation, and tissue repair and remodeling, and will address the involvement of NO. The growing interest in hypoxia-induced signaling and its relation with NO biology is expected to lead to further insights into the complex roles of NO in acute or chronic inflammatory diseases and may point to the importance of HIF signaling as key feature of NO-mediated events during these disorders.

S-alkylating labeling strategy for site-specific identification of the s-nitrosoproteome

S-nitrosylation, a post-translational modification of cysteine residues induced by nitric oxide, mediates many physiological functions. Due to the labile nature of S-nitrosylation, detection by mass spectrometry (MS) is challenging. Here, we developed an S-alkylating labeling strategy using the irreversible biotinylation on S-nitrosocysteines for site-specific identification of the S-nitrosoproteome by LC-MS/MS. Using COS-7 cells without endogenous nitric oxide synthase, we demonstrated that the S-alkylating labeling strategy substantially improved the blocking efficiency of free cysteines, minimized the false-positive identification caused by disulfide interchange, and increased the digestion efficiency for improved peptide identification using MS analyses. Using this strategy, we identified total 586 unique S-nitrosylation sites corresponding to 384 proteins in S-nitroso-N-acetylpenicillamine (SNAP)/l-cysteine-treated mouse MS-1 endothelial cells, including 234 previously unreported S-nitrosylated proteins. When the topologies of 84 identified transmembrane proteins were further analyzed, their S-nitrosylation sites were found to mostly face the cytoplasmic side, implying that S-nitrosylation occurs in the cytoplasm. In addition to the previously known acid/basic motifs, the ten deduced consensus motifs suggested that combination of local hydrophobicity and acid/base motifs in the tertiary structure contribute to the specificity of S-nitrosylation. Moreover, the S-nitrosylated cysteines showed preference on beta-strand, having lower relative surface accessibility at the S-nitrosocysteines.

Knockout of HIF-1α in tumor-associated macrophages enhances M2 polarization and attenuates their pro-angiogenic responses

Tumor-associated macrophages (TAMs) constitute major infiltrates of solid tumors and express a marker profile that characterizes alternatively activated macrophages (MФs). TAMs accumulate in hypoxic tumor regions, express high amounts of hypoxia-inducible factor-1 (HIF-1) and contribute to tumor angiogenesis and invasiveness. However, the precise role of HIF-1 on MФ infiltration and phenotype alterations remains poorly defined. Therefore, we cocultured wild type (wt) versus HIF-1α(-/-) MФs with tumor spheroids. Both, wt and HIF-1α(-/-) MФs, infiltrated hypoxic regions of tumor spheroids at equal rates and got alternatively activated. Interestingly, significantly higher amounts of HIF-1α(-/-) MФs expressed the TAM markers CD206 and stabilin-1 compared with wt phagocytes. Stimulation of infiltrated TAMs with lipopolysaccharide (LPS)/interferon-γ revealed a reduced expression of the pro-inflammatory markers interleukin (IL)-6, tumor necrosis factor-α and inducible nitric oxide synthase in HIF-1α(-/-) MФs. Furthermore, HIF-1α(-/-) MФs were less cytotoxic toward tumor cells. Although infiltration of MФs increased the invasive potential of tumor spheroids independently of HIF-1, the ability to stimulate differentiation of stem cells toward CD31-positive cells was triggered by wt but not by HIF-1α(-/-) MФs. Our data suggest that HIF-1α-deficient MФs develop a more prominent TAM marker profile accompanied by reduced cytotoxicity, whereas HIF-1 seems indispensable for the angiogenesis-promoting properties of TAMs.