Hypoxia-inducible factor-1α regulation of myeloid cells

HIF-1α is required to differentiate the neonatal Macrophage protein secretome from adults

The immune response to stress diverges with age, with neonatal macrophages implicated in tissue regeneration versus tissue scarring and maladaptive inflammation in adults. Integral to the macrophage stress response is the recognition of hypoxia and pathogen-associated molecular patterns (PAMPs), which are often coupled. The age-specific, cell-intrinsic nature of this stress response remains vague. To uncover age-defined divergences in macrophage crosstalk potential after exposure to hypoxia and PAMPs, we interrogated the secreted proteomes of neonatal versus adult macrophages via non-biased mass spectrometry. Through this approach, we newly identified age-specific signatures in the secretomes of neonatal versus adult macrophages in response to hypoxia and the prototypical PAMP, lipopolysaccharide (LPS). Neonatal macrophages secreted proteins most consistent with an anti-inflammatory, regenerative phenotype protective against apoptosis and oxidative stress, dependent on hypoxia inducible transcription factor-1α (HIF-1α). In contrast, adult macrophages secreted proteins consistent with a pro-inflammatory, glycolytic phenotypic signature consistent with pathogen killing. Taken together, these data uncover fundamental age and HIF-1α dependent macrophage responses that may be targeted to calibrate the innate immune response during stress and inflammation.

Hypoxic Functional Regulation Pathways in the GI Tract: Focus on the HIF-1α and Microbiota's Crosstalk

Hypoxia is an essential gastrointestinal (GI) tract phenomenon that influences both physiologic and pathologic states. Hypoxia-inducible factors (HIFs), the primary drivers of cell adaptation to low-oxygen environments, have been identified as critical regulators of gut homeostasis: directly, through the induction of different proteins linked to intestinal barrier stabilization (ie, adherent proteins, tight junctions, mucins, integrins, intestinal trefoil factor, and adenosine); and indirectly, through the regulation of several immune cell types and the modulation of autophagy and inflammatory processes. Furthermore, hypoxia and HIF-related sensing pathways influence the delicate relationship existing between bacteria and mammalian host cells. In turn, gut commensals establish and maintain the physiologic hypoxia of the GI tract and HIF-α expression. Based on this premise, the goals of this review are to (1) highlight hypoxic molecular pathways in the GI tract, both in physiologic and pathophysiologic settings, such as inflammatory bowel disease; and (2) discuss a potential strategy for ameliorating gut-related disorders, by targeting HIF signaling, which can alleviate inflammatory processes, restore autophagy correct mechanisms, and benefit the host-microbiota equilibrium.

Multiple roles for hypoxia inducible factor 1-alpha in airway epithelial cells during mucormycosis

During pulmonary mucormycosis, inhaled sporangiospores adhere to, germinate, and invade airway epithelial cells to establish infection. We provide evidence that HIF1α plays dual roles in airway epithelial cells during Mucorales infection. We observed an increase in HIF1α protein accumulation and increased expression of many known HIF1α-responsive genes during in vitro infection, indicating that HIF1α signaling is activated by Mucorales infection. Inhibition of HIF1α signaling led to a substantial decrease in the ability of R. delemar to invade cultured airway epithelial cells. Transcriptome analysis revealed that R. delemar infection induces the expression of many pro-inflammatory genes whose expression was significantly reduced by HIF1α inhibition. Importantly, pharmacological inhibition of HIF1α increased survival in a mouse model of pulmonary mucormycosis without reducing fungal burden. These results suggest that HIF1α plays two opposing roles during mucormycosis: one that facilitates the ability of Mucorales to invade the host cells and one that facilitates the ability of the host to mount an innate immune response.

Transcriptomic profiling of peripheral blood cells in HPV-associated carcinoma patients receiving combined valproic acid and avelumab

Human papillomavirus (HPV)-associated cancer continues to evade the immune system by promoting a suppressive tumor microenvironment. Therefore, immunotherapy appears to be a promising approach for targeting HPV-associated tumors. We hypothesized that valproic acid (VA) as an epigenetic agent combined with avelumab may enhance the antitumor immunity in HPV-associated solid tumors. We performed bulk RNA-sequencing (RNA-Seq) on total peripheral blood mononuclear cells (PBMCs) of seven nonresponders (NRs) and four responders (Rs). A total of 39 samples (e.g., pretreatment, post-VA, postavelumab, and endpoint) were analyzed. Also, we quantified plasma analytes and performed flow cytometry. We observed a differential pattern in immune response following treatment with VA and/or avelumab in NRs vs. Rs. A significant upregulation of transcripts associated with NETosis [the formation of neutrophil extracellular traps (NETs)] and neutrophil degranulation pathways was linked to the presence of a myeloid-derived suppressor cell signature in NRs. We noted the elevation of IL-8/IL-18 cytokines and a distinct transcriptome signature at the baseline and endpoint in NRs. By using the receiver operator characteristics, we identified a cutoff value for the plasma IL-8/IL-18 to discriminate NRs from Rs. We found differential therapeutic effects for VA and avelumab in NRs vs. Rs. Thus, our results imply that measuring the plasma IL-8/IL-18 and bulk RNA-Seq of PBMCs may serve as valuable biomarkers to predict immunotherapy outcomes.

HIF-1α is Required to Differentiate the Neonatal Macrophage Secretome from Adults

The immune response to stress diverges with age, with neonatal macrophages implicated in tissue regeneration versus tissue scarring and maladaptive inflammation in adults. Integral to the macrophage stress response is the recognition of hypoxia and pathogen-associated molecular patterns (PAMPs), which are often coupled. The age-specific, cell-intrinsic nature of this stress response remains vague. To uncover age-defined divergences in macrophage crosstalk potential after exposure to hypoxia and PAMPs, we interrogated the secreted proteomes of neonatal versus adult macrophages via non-biased mass spectrometry. Through this approach, we newly identified age-specific signatures in the secretomes of neonatal versus adult macrophages in response to hypoxia and the prototypical PAMP, lipopolysaccharide (LPS). Neonatal macrophages polarized to an anti-inflammatory, regenerative phenotype protective against apoptosis and oxidative stress, dependent on hypoxia inducible transcription factor-1α ( HIF-1α). In contrast, adult macrophages adopted a pro-inflammatory, glycolytic phenotypic signature consistent with pathogen killing. Taken together, these data uncover fundamental age and HIF-1α dependent macrophage programs that may be targeted to calibrate the innate immune response during stress and inflammation.

2-Deoxy-D-glucose ameliorates inflammation and fibrosis in a silicosis mouse model by inhibiting hypoxia-inducible factor-1α in alveolar macrophages

Inhaling silica causes the occupational illness silicosis, which mostly results in the gradual fibrosis of lung tissue. Previous research has demonstrated that hypoxia-inducible factor-1α (HIF-1α) and glycolysis-related genes are up-regulated in silicosis. The role of 2-deoxy-D-glucose (2-DG) as an inhibitor of glycolysis in silicosis mouse models and its molecular mechanisms remain unclear. Therefore, we used 2-DG to observe its effect on pulmonary inflammation and fibrosis in a silicosis mouse model. Furthermore, in vitro cell experiments were conducted to explore the specific mechanisms of HIF-1α. Our study found that 2-DG down-regulated HIF-1α levels in alveolar macrophages induced by silica exposure and reduced the interleukin-1β (IL-1β) level in pulmonary inflammation. Additionally, 2-DG reduced silica-induced pulmonary fibrosis. From these findings, we hypothesize that 2-DG reduced glucose transporter 1 (GLUT1) expression by inhibiting glycolysis, which inhibits the expression of HIF-1α and ultimately reduces transcription of the inflammatory cytokine, IL-1β, thus alleviating lung damage. Therefore, we elucidated the important regulatory role of HIF-1α in an experimental silicosis model and the potential defense mechanisms of 2-DG. These results provide a possible effective strategy for 2-DG in the treatment of silicosis.

Method to Regulate Monocyte Function by Silencing HIF-1α mRNA in a Model of Retinal Neovascularization

Circulating monocytes migrate into the retina in response to inflammation and neovascularization. Furthermore, under inflammatory conditions such as diabetes, healthy monocytes become activated in the circulation. However, the contribution of activated monocytes to neovascularization is largely unknown. HIF-1α has been shown to contribute to the pathogenesis of neovascularization. We describe here the synthesis of a hybrid nanomaterial for targeted delivery and gene silencing in activated monocytes that are associated with pathological neovascularization. To test the gene silencing ability of AS-shRNA-lipids in vitro, we used the probe to inhibit HIF-1α mRNA induced in mouse monocytes by exposing them to hypoxia. In addition, we tested AS-shRNA-lipids for inhibition of neovascularization in vivo using the mouse model of oxygen-induced retinopathy (OIR). Significant reduction of neovascularization was achieved in mouse OIR by targeting activated monocytes using intraperitoneal injections of AS-shRNA-lipids. Expression of HIF-1α and CD14 mRNA were both inhibited in circulating cells, suggesting normalization of the activated monocytes in P17 OIR animals treated with AS-shRNA-lipids. We hypothesized that inhibition of HIF-1α mRNA in activated monocytes may have a direct impact on VEGF expression in the retinal tissues in vivo. We observed that VEGF mRNA expression was inhibited in P17 retinal tissues after systemic treatment with HIF-1α-targeted AS-shRNA-lipids. These findings may provide a framework for a strategy to inhibit retinal neovascularization by targeting circulating activated monocytes.

Comparison of hyperoxia or normoxia resolution of intermittent hypoxia and intermittent hyperoxia episodes on liver histopathology, IGF-1, IGFBP-3, and GHBP in neonatal rats

OBJECTIVE

Extremely low gestational age neonates requiring oxygen therapy for chronic lung disease experience repeated fluctuations in arterial oxygen saturation, or intermittent hypoxia (IH), during the first few weeks of life. These events are associated with a high risk for reduced growth, hypertension, and insulin resistance in later life. This study tested the hypothesis that IH, or intermittent hyperoxia have similar negative effects on the liver; somatic growth; and liver insulin-like growth factor (IGF)-I, IGF binding protein (BP)-3, and growth hormone binding protein (GHBP), regardless of resolution in normoxia or hyperoxia between episodes.

DESIGN

Newborn rats on the first day of life (P0) were exposed to two IH paradigms: 1) hyperoxia (50% O2) with brief hypoxia (12% O2); or 2) normoxia (21% O2) with hypoxia (12% O2); intermittent hypoxia (50% O2/21% O2); hyperoxia only (50% O2); or room air (RA, 21% O2). Pups were euthanized on P14 or placed in RA until P21. Controls remained in RA from P0-P21. Growth, liver histopathology, apoptosis, IGFI, IGFBP-3, and GHBP were assessed.

RESULTS

Pathological findings of the liver hepatocytes, including cellular swelling, steatosis, apoptosis, necrosis and focal sinusoid congestion were seen in the IH and intermittent hyperoxia groups, and were particularly severe in the 21-12% O2 group during exposure (P14) with no significant improvements during recovery/reoxygenation (P21). These effects were associated with induction of HIF1α, and reductions in liver IGFI, IGFBP-3, and GHBP.

CONCLUSIONS

Exposure to IH or intermittent hyperoxia during the first few weeks of life regardless of resolution in RA or hyperoxia is detrimental to the immature liver. These findings may suggest that interventions to prevent frequent fluctuations in oxygen saturation during early neonatal life remain a high priority.

Hypoxia inducible factor-1α is an important regulator of macrophage biology

Hypoxia-inducible factor-1 (HIF-1), a heterodimeric transcription factor composed of the α and β subunits, regulates cellular adaptive responses to hypoxia. Macrophages, which are derived from monocytes, function as antigen-presenting cells that activate various immune responses. HIF-1α regulates the immune response, viability, migration, phenotypic plasticity, and metabolism of macrophages. Specifically, macrophage-derived HIF-1α can prevent excessive pro-inflammatory responses by attenuating the transcriptional activity of nuclear factor-kappa B in vivo and in vitro. HIF-1α modulates macrophage migration by inducing the release of various chemokines and providing necessary energy. HIF-1α promotes macrophage M1 polarization by targeting glucose metabolism. Additionally, HIF-1α induces the upregulation of glycolysis-related enzymes and intermediates of the tricarboxylic acid cycle and pentose phosphate pathway. HIF-1α promotes macrophage apoptosis, necroptosis and reduces autophagy. The current review highlights the mechanisms associated with the regulation of HIF-1α stabilization in macrophages as well as the role of HIF-1α in modulating the physiological functions of macrophages.

Targeted inhibition of the GRK2/HIF-1α pathway is an effective strategy to alleviate synovial hypoxia and inflammation

G-protein coupled receptor (GPCR) kinases (GRKs) and hypoxia-inducible factor-1α (HIF-1α) play key roles in rheumatoid arthritis (RA). Several studies have demonstrated that HIF-1α expression is positively regulated by GRK2, suggesting its posttranscriptional effects on HIF-1α. In this study, we review the role of HIF-1α and GRK2 in RA pathophysiology, focusing on their proinflammatory roles in immune cells and fibroblast-like synoviocytes (FLS).We then introduce several drugs that inhibit GRK2 and HIF-1α, and briefly outline their molecular mechanisms. We conclude by presenting gaps in knowledge and our prospects for the pharmacological potential of targeting these proteins and the relevant downstream signaling pathways.Future research is warranted and paramount for untangling these novel and promising roles for GRK2 and HIF-1α in RA.

Cigarette smoke-induced airspace disease in mice develops independently of HIF-1α signaling in leukocytes

The pathogenesis of chronic obstructive pulmonary disease (COPD), a prevalent disease primarily caused by cigarette smoke exposure, is incompletely elucidated. Studies in humans and mice have suggested that hypoxia-inducible factor-1α (HIF-1α) may play a role. Reduced lung levels of HIF-1α are associated with decreased vascular density, whereas increased leukocyte HIF-1α may be responsible for increased inflammation. To elucidate the specific role of leukocyte HIF-1α in COPD, we exposed transgenic mice with conditional deletion or overexpression of HIF-1α in leukocytes to cigarette smoke for 7 mo. Outcomes included pulmonary physiology, aerated lung volumes via microcomputed tomography, lung morphometry and histology, and cardiopulmonary hemodynamics. On aggregate, cigarette smoke increased the aerated lung volume, quasi-static lung compliance, inspiratory capacity of all strains while reducing the total alveolar septal volume. Independent of smoke exposure, mice with leukocyte-specific HIF-1α overexpression had increased quasi-static compliance, inspiratory capacity, and alveolar septal volume compared with mice with leukocyte-specific HIF-1α deletion. However, the overall development of cigarette smoke-induced lung disease did not vary relative to control mice for either of the conditional strains. This suggests that the development of murine cigarette smoke-induced airspace disease occurs independently of leukocyte HIF-1α signaling.

Expression of proliferation-related genes in BM-MSC-treated ALL cells in hypoxia condition is regulated under the influence of epigenetic factors in-vitro

Mesenchymal stem cells affect ALL cell biology under hypoxic conditions. We studied survival, proliferation, expression, and promoter methylation levels of essential genes involved in expanding MOLT-4 cells co-cultured with BM-MSC under the hypoxic condition. Here, MOLT-4 cells were co-cultured with BMMSCs under hypoxic conditions. First, the apoptosis rate was evaluated by Flow cytometry. Then, MOLT-4 cells' proliferation rate was assessed using MTT assay, and the expressions and methylation rates of genes were determined by qRT-PCR and MS-qPCR, respectively. The results showed that although MOLT-4 cells proliferation and survival rates were reduced under hypoxic conditions, this reduction was not statistically significant. Also, we showed that hypoxic conditions caused upregulation of candidate genes and affected their methylation status. Besides, it was revealed that Pontin was downregulated, while KDM3A, SKP2, and AURKA had an upward trend in the presence of MOLT-4 cells plus BM-MSC. The co-culture of leukemia cells with BMMSCs under hypoxic conditions may be a potential therapeutic approach for ALL.

β-Glucan Induces Distinct and Protective Innate Immune Memory in Differentiated Macrophages

Bacterial infections are a common and deadly threat to vulnerable patients. Alternative strategies to fight infection are needed. β-Glucan, an immunomodulator derived from the fungal cell wall, provokes resistance to infection by inducing trained immunity, a phenomenon that persists for weeks to months. Given the durability of trained immunity, it is unclear which leukocyte populations sustain this effect. Macrophages have a life span that surpasses the duration of trained immunity. Thus, we sought to define the contribution of differentiated macrophages to trained immunity. Our results show that β-glucan protects mice from Pseudomonas aeruginosa infection by augmenting recruitment of innate leukocytes to the site of infection and facilitating local clearance of bacteria, an effect that persists for more than 7 d. Adoptive transfer of macrophages, trained using β-glucan, into naive mice conferred a comparable level of protection. Trained mouse bone marrow-derived macrophages assumed an antimicrobial phenotype characterized by enhanced phagocytosis and reactive oxygen species production in parallel with sustained enhancements in glycolytic and oxidative metabolism, increased mitochondrial mass, and membrane potential. β-Glucan induced broad transcriptomic changes in macrophages consistent with early activation of the inflammatory response, followed by sustained alterations in transcripts associated with metabolism, cellular differentiation, and antimicrobial function. Trained macrophages constitutively secreted CCL chemokines and robustly produced proinflammatory cytokines and chemokines in response to LPS challenge. Induction of the trained phenotype was independent of the classic β-glucan receptors Dectin-1 and TLR-2. These findings provide evidence that β-glucan induces enhanced protection from infection by driving trained immunity in macrophages.

Oxygen-sensing mechanisms in development and tissue repair

Under normoxia, hypoxia inducible factor (HIF) α subunits are hydroxylated by PHDs (prolyl hydroxylase domain proteins) and subsequently undergo polyubiquitylation and degradation. Normal embryogenesis occurs under hypoxia, which suppresses PHD activities and allows HIFα to stabilize and regulate development. In this Primer, we explain molecular mechanisms of the oxygen-sensing pathway, summarize HIF-regulated downstream events, discuss loss-of-function phenotypes primarily in mouse development, and highlight clinical relevance to angiogenesis and tissue repair.

Baicalein resensitizes tamoxifen-resistant breast cancer cells by reducing aerobic glycolysis and reversing mitochondrial dysfunction via inhibition of hypoxia-inducible factor-1α

Drug resistance is a major hurdle for the effectiveness of tamoxifen (TAM) to provide clinical benefit. Therefore, it is essential to identify a sensitizer that could be used to improve TAM efficacy in treating TAM-resistant breast cancer. Here, we investigated the ability of baicalein to reverse TAM resistance. We found that baicalein increased the efficacy of TAM in inhibiting proliferation and inducing apoptosis of TAM-resistant cells. It also enhanced the TAM-induced growth reduction of resistant cells from NOD/SCID mouse mammary fat pads, without causing obvious systemic toxicity. Analyses using the CellMiner tool and the Kaplan-Meier plotter database showed that HIF-1α expression was inversely correlated with TAM therapeutic response in NCI-60 cancer cells and breast cancer patients. HIF-1α expression was increased in TAM-resistant cells due to an increase in mRNA levels and reduced ubiquitin-mediated degradation. Baicalein reduced HIF-1α expression by promoting its interaction with PHD2 and pVHL, thus facilitating ubiquitin ligase-mediated proteasomal degradation and thereby suppressing the nuclear translocation, binding to the hypoxia-response element, and transcriptional activity of HIF-1α. As a result, baicalein downregulated aerobic glycolysis by restricting glucose uptake, lactate production, ATP generation, lactate/pyruvate ratio and expression of HIF-1α-targeted glycolytic genes, thereby enhancing the antiproliferative efficacy of TAM. Furthermore, baicalein interfered with HIF-1α inhibition of mitochondrial biosynthesis, which increased mitochondrial DNA content and mitochondrial numbers, restored the generation of reactive oxygen species in mitochondria, and thus enhanced the TAM-induced mitochondrial apoptotic pathway. The HIF-1α stabilizer dimethyloxallyl glycine prevented the baicalein-induced downregulation of glycolysis and mitochondrial biosynthesis and reduced the effects of baicalein on reversing TAM resistance. Our results indicate that baicalein is a promising candidate to help overcome TAM resistance by sensitizing resistant cells to TAM-induced growth inhibition and apoptosis. The mechanism underlying the effects of baicalein consists of inhibition of HIF-1α-mediated aerobic glycolysis and mitochondrial dysfunction.

Age-related differences in hypoxia-associated genes and cytokine profile in male Wistar rats

Hypoxia tolerance of the organism depends on many factors, including age. High newborn organisms tolerance and high level of oxidative stress throughout aging were demonstrated by many studies. However, there is lack of investigations reflecting the expression of key hypoxia-inducible factor HIF in different age organisms in correlation to levels of pro-inflammatory and anti-inflammatory cytokines. Liver is a sensitive to hypoxia organ, and is an important organ in providing an acute reaction to infections – it synthesizes acute inflammation phase proteins, in particular, C-reactive protein. The aim of study was to determine relationship between age-related tolerance to hypoxia and HIF-1 and PHD2 (prolyl hydroxylase domain protein) expression levels in the liver and the production of cytokines in the spleen in newborn, prepubertal and adult Wistar rats. Newborn rats are characterized by high mRNA Hif-1α expression level in the liver, accompanied by a low content of HIF-1 protein and high level of PHD2. The growth in HIF-1α protein level throughout age is accompanied by the growth of pro-inflammatory cytokines level. Prepubertal animals are the least hypoxia resistant and their HIF-1α mRNA expression level was higher than in adult animals. The PHD2 activity in prepubertal animals was significantly reduced in comparison to newborn rats, and the HIF-1α protein level did not change. Further studies require the identification of additional mechanisms, determining the regulation of the HIF-1α level in prepubertal animals.

Neutrophil metabolism in the cancer context

Neutrophils are critical innate immune cells for the host anti-bacterial defense. Throughout their lifecycle, neutrophils are exposed to different microenvironments and modulate their metabolism to survive and sustain their functions. Although tumor cell metabolism has been intensively investigated, how neutrophil metabolism is affected in cancer remains largely to be discovered. Neutrophils are described as mainly glycolytic cells. However, distinct tumor-associated neutrophil (TAN) states may co-exist in tumors and adapt their metabolism to exert different or even opposing activities ranging from tumor cell killing to tumor support. In this review, we gather evidence about the metabolic mechanisms that underly TANs' pro- or anti-tumoral functions in cancer. We first discuss how tumor-secreted factors and the heterogenous tumor microenvironment can have a strong impact on TAN metabolism. We then describe alternative metabolic pathways used by TANs to exert their functions in cancer, from basic glycolysis to more recently-recognized but less understood metabolic shifts toward mitochondrial oxidative metabolism, lipid and amino acid metabolism and even autophagy. Last, we discuss promising strategies targeting neutrophil metabolism to combat cancer.

HIF in the heart: development, metabolism, ischemia, and atherosclerosis

The heart forms early in development and delivers oxygenated blood to the rest of the embryo. After birth, the heart requires kilograms of ATP each day to support contractility for the circulation. Cardiac metabolism is omnivorous, utilizing multiple substrates and metabolic pathways to produce this energy. Cardiac development, metabolic tuning, and the response to ischemia are all regulated in part by the hypoxia-inducible factors (HIFs), central components of essential signaling pathways that respond to hypoxia. Here we review the actions of HIF1, HIF2, and HIF3 in the heart, from their roles in development and metabolism to their activity in regeneration and preconditioning strategies. We also discuss recent work on the role of HIFs in atherosclerosis, the precipitating cause of myocardial ischemia and the leading cause of death in the developed world.

Metabolic reprogramming of immune cells: Shaping the tumor microenvironment in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a typical inflammation‐induced cancer and displays a complex interaction between the tumor microenvironment and tumor development. Immune cells in the HCC microenvironment play both pro‐ and anti‐tumoral roles in HCC progression. An increasing number of findings indicate that metabolic reprogramming is essential for immune cell differentiation and function. In this review, we discuss the metabolic changes of different immune cells and correlate these findings to HCC progression.

The role of HIF-1α in BCG-stimulated macrophages polarization and their tumoricidal effects in vitro

BCG is widely used for cancer treatment, where macrophages play an important role. However, the mechanism of BCG affecting macrophages remains poorly understood. In this study, we used BCG to stimulate myeloid-derived macrophages lacking HIF-1α, the levels of TNF-α, IL-1β, CD86 of macrophages and their effects on the growth of tumor cells MCA207 and B16-F10 were detected. We found that the absence of HIF-1α prevents BCG-stimulated macrophages from polarizing towards the M (BCG) and attenuating its killing effect on tumor cells. In addition, we demonstrated that the tumors of mice lacking HIF-1α in macrophages were significantly increased by the experiment of mice transplantation. Our study provides relevant evidence for exploring the mechanism of the BCG vaccine in the prevention and treatment of related diseases.

Hypoxia-inducible factor-1 drives divergent immunomodulatory functions in the pathogenesis of autoimmune diseases

Hypoxia-inducible factor-1 (HIF-1) is a heterodimeric (HIF-1α/ HIF-1β) transcription factor in which the oxygen-sensitive HIF-1α subunit regulates gene transcription to mediate adaptive tissue responses to hypoxia. HIF-1 is a key mediator in both regulatory and pathogenic immune responses, because ongoing inflammation in localized tissues causes increased oxygen consumption and consequent hypoxia within the inflammatory lesions. In autoimmune diseases, HIF-1 plays complex and divergent roles within localized inflammatory lesions by orchestrating a critical immune interplay sponsoring the pathogenesis of the disease. In this review, we have summarized the role of HIF-1 in lymphoid and myeloid immunomodulation in autoimmune diseases. HIF-1 drives inflammation by controlling the Th17/T_reg /Tr1 balance through the tipping of the differentiation of CD4⁺ T cells in favour of pro-inflammatory Th17 cells while suppressing the development of anti-inflammatory T_reg /Tr1 cells. On the other hand, HIF-1 plays a protective role by facilitating the expression of anti-inflammatory cytokine IL-10 in and expansion of CD1d^hi CD5⁺ B cells, known as regulatory B cells or B10 cells. Apart from lymphoid cells, HIF-1 also controls the activation of macrophages, neutrophils and dendritic cells, thus eventually further influences the activation and development of effector/regulatory T cells by facilitating the creation of a pro/anti-inflammatory microenvironment within the autoinflammatory lesions. Based on the critical immunomodulatory roles that HIF-1 plays, this master transcription factor seems to be a potent druggable target for the treatment of autoimmune diseases.

Transcription Factors Interplay Orchestrates the Immune-Metabolic Response of Leishmania Infected Macrophages

Leishmaniasis is a group of heterogenous diseases considered as an important public health problem in several countries. This neglected disease is caused by over 20 parasite species of the protozoa belonging to the Leishmania genus and is spread by the bite of a female phlebotomine sandfly. Depending on the parasite specie and the immune status of the patient, leishmaniasis can present a wide spectrum of clinical manifestations. As an obligate intracellular parasite, Leishmania colonize phagocytic cells, mainly the macrophages that orchestrate the host immune response and determine the fate of the infection. Once inside macrophages, Leishmania triggers different signaling pathways that regulate the immune and metabolic response of the host cells. Various transcription factors regulate such immune-metabolic responses and the associated leishmanicidal and inflammatory reaction against the invading parasite. In this review, we will highlight the most important transcription factors involved in these responses, their interactions and their impact on the establishment and the progression of the immune response along with their effect on the physiopathology of the disease.

Short-Chain Fatty Acids Promote Intracellular Bactericidal Activity in Head Kidney Macrophages From Turbot (Scophthalmus maximus L.) via Hypoxia Inducible Factor-1α

Short-chain fatty acids (SCFAs) are mainly produced by microbiota through the fermentation of carbohydrates in the intestine. Acetate, propionate, and butyrate are the most abundant SCFA metabolites and have been shown to be important in the maintenance of host health. In this study, head kidney macrophages (HKMs) were isolated and cultured from turbots. We found that the antibacterial activity of HKMs was increased after these cells were incubated with sodium butyrate, sodium propionate or sodium acetate. Interestingly, our results showed that all three SCFAs enhanced the expression of hypoxia inducible factor-1 α (HIF-1α) in HKMs, and further study confirmed that butyrate augmented the oxygen consumption of these cells. Moreover, HIF-1α inhibition diminished the butyrate-promoted intracellular bacterial killing activity of macrophages, and SCFAs also raised the gene expression and activity of lysozymes in HKMs via HIF-1α signaling. In addition, our results suggested that butyrate induced HIF-1α expression and the bactericidal activity of HKMs through histone deacetylase inhibition, while G protein-coupled receptors did not contribute to this effect. Finally, we demonstrated that butyrate induced a similar response in the murine macrophage cell line RAW264.7. In conclusion, our results demonstrated that SCFAs promoted HIF-1α expression via histone deacetylase inhibition, leading to the enhanced production of antibacterial effectors and increased bacterial killing of macrophages.

Hypoperfusion is a potential inducer of immunosuppressive network in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease which causes a non-reversible cognitive impairment and dementia. The primary cause of late-onset AD remains unknown although its pathology was discovered over a century ago. Recently, the vascular hypothesis of AD has received backing from evidence emerging from neuroimaging studies which have revealed the presence of a significant hypoperfusion in the brain regions vulnerable to AD pathology. In fact, hypoxia can explain many of the pathological changes evident in AD pathology, e.g. the deposition of β-amyloid plaques and chronic low-grade inflammation. Hypoxia-inducible factor-1α (HIF-1α) stimulates inflammatory responses and modulates both innate and adaptive immunity. It is known that hypoxia-induced inflammation evokes compensatory anti-inflammatory response involving tissue-resident microglia/macrophages and infiltrated immune cells. Hypoxia/HIF-1α induce immunosuppression by (i) increasing the expression of immunosuppressive genes, (ii) stimulating adenosinergic signaling, (iii) enhancing aerobic glycolysis, i.e. lactate production, and (iv) augmenting the secretion of immunosuppressive exosomes. Interestingly, it seems that these common mechanisms are also involved in the pathogenesis of AD. In AD pathology, an enhanced immunosuppression appears, e.g. as a shift in microglia/macrophage phenotypes towards the anti-inflammatory M2 phenotype and an increase in the numbers of regulatory T cells (Treg). The augmented anti-inflammatory capacity promotes the resolution of acute inflammation but persistent inflammation has crucial effects not only on immune cells but also harmful responses to the homeostasis of AD brain. I will examine in detail the mechanisms of the hypoperfusion/hypoxia-induced immunosuppressive state in general and especially, in its association with AD pathogenesis. These immunological observations support the vascular hypothesis of AD pathology.

Mechanisms controlling bacterial infection in myeloid cells under hypoxic conditions

Various factors of the tissue microenvironment such as the oxygen concentration influence the host-pathogen interaction. During the past decade, hypoxia-driven signaling via hypoxia-inducible factors (HIF) has emerged as an important factor that affects both the pathogen and the host. In this chapter, we will review the current knowledge of this complex interplay, with a particular emphasis given to the impact of hypoxia and HIF on the inflammatory and antimicrobial activity of myeloid cells, the bacterial responses to hypoxia and the containment of bacterial infections under oxygen-limited conditions. We will also summarize how low oxygen concentrations influence the metabolism of neutrophils, macrophages and dendritic cells. Finally, we will discuss the consequences of hypoxia and HIFα activation for the invading pathogen, with a focus on Pseudomonas aeruginosa, Mycobacterium tuberculosis, Coxiella burnetii, Salmonella enterica and Staphylococcus aureus. This includes a description of the mechanisms and microbial factors, which the pathogens use to sense and react to hypoxic conditions.

Current perspectives on the immunopathogenesis of sarcoidosis

Sarcoidosis is an inflammatory systemic disease that commonly affects the lungs or lymph nodes but can manifest in other organs. Herein, we review the latest evidence establishing how innate and adaptive immune responses contribute to the pathogenesis and clinical course of sarcoidosis. We discuss the possible role of microbial organisms as etiologic agents in sarcoidosis and the evidence supporting sarcoidosis as an autoimmune disease. We also discuss how animal and in vitro human models have advanced our understanding of the immunopathogenesis of sarcoidosis. Finally, we discuss therapeutics for sarcoidosis and the effects on the immune system.

The Metabolic Basis of Immune Dysfunction Following Sepsis and Trauma

Critically ill, severely injured and high-risk surgical patients are vulnerable to secondary infections during hospitalization and after hospital discharge. Studies show that the mitochondrial function and oxidative metabolism of monocytes and macrophages are impaired during sepsis. Alternatively, treatment with microbe-derived ligands, such as monophosphoryl lipid A (MPLA), peptidoglycan, or β-glucan, that interact with toll-like receptors and other pattern recognition receptors on leukocytes induces a state of innate immune memory that confers broad-spectrum resistance to infection with common hospital-acquired pathogens. Priming of macrophages with MPLA, CPG oligodeoxynucleotides (CpG ODN), or β-glucan induces a macrophage metabolic phenotype characterized by mitochondrial biogenesis and increased oxidative metabolism in parallel with increased glycolysis, cell size and granularity, augmented phagocytosis, heightened respiratory burst functions, and more effective killing of microbes. The mitochondrion is a bioenergetic organelle that not only contributes to energy supply, biosynthesis, and cellular redox functions but serves as a platform for regulating innate immunological functions such as production of reactive oxygen species (ROS) and regulatory intermediates. This review will define current knowledge of leukocyte metabolic dysfunction during and after sepsis and trauma. We will further discuss therapeutic strategies that target leukocyte mitochondrial function and might have value in preventing or reversing sepsis- and trauma-induced immune dysfunction.

Hypoxia is a key mechanism for regulating inflammation in ulcerative colitis

Intestinal bowel diseases (IBD), including ulcerative colitis (UC), is the group of difficult to diagnose widespread among the population diseases. Pathogenesis of the disease is associated with a complex interaction of the genetic factors, the environment, the microbiome and the unpredicted reaction of the immune system, and the existing treatment methods are not effective enough. It is known, that hypoxia plays a key role in both system and local inflammatory reactions, mainly due to microcirculatory disorders and disseminated intravascular coagulation. Therefore a lot of studies have demonstrated that severity of any inflammatory diseases, including Crohn's disease (CD) and UC depends on hypoxia resistance. In this review we discussed microcirculation of blood and physiological hypoxia in the intestine, the role of hypoxia-inducible factors in the development of IBD and UC, as well as their influence on the severity of the inflammatory process. Authors described the protective effect of various PHD inhibitors and its benefits and disadvantages, so as new approaches of searching of very specific low molecular weight substanses as drugs for the control of IBD and UC.

Hypoxia-inducible factors in metabolic reprogramming during sepsis

Sepsis is a highly heterogeneous syndrome that is caused by an imbalanced host response to infection. Despite huge investments, sepsis remains a contemporary threat with significant burden on health systems. Vascular dysfunction and elevated oxygen consumption by highly metabolically active immune cells result in tissue hypoxia during inflammation. The transcription factor hypoxia-inducible factor-1a (HIF1α), and its family members, plays an important role in cellular metabolism and adaptation to cellular stress caused by hypoxia. In this review, we discuss the role of HIF in sepsis. We show possible mechanisms by which the inflammatory response activated during sepsis affects the HIF pathway. The activated HIF pathway in turn changes the metabolism of both innate and adaptive immune cells. As HIF expression in leukocytes of septic patients can be directly linked with mortality, we discuss multiple ways of interfering with the HIF signaling pathway.