Hypoxia and HIF-1 activation in bacterial infections

Mycobacterium marinum as a model for understanding principles of mycobacterial pathogenesis

Mycobacterium marinum is a fish pathogen that has become a powerful and well-established model that has accelerated our understanding of the mechanisms of mycobacterial disease. M. marinum is a versatile surrogate for understanding the closely related human pathogen M. tuberculosis, which causes tuberculosis in humans. M. marinum has defined key mechanisms of pathogenesis, both shared with M. tuberculosis and unique to this species. In this review, we discuss the discovery of M. marinum as an occasional human pathogen, the shared aspects of pathogenesis with M. tuberculosis, and how M. marinum has been exploited as a model to define the molecular mechanisms of mycobacterial pathogenesis across several phases of infection.

STING contributes to the inflammation and proliferation of Staphylococcus aureus via mitochondrial reactive oxygen species-hypoxic inducible factor 1α axis in epithelial cells

Staphylococcus aureus infection poses a serious threat to the dairy industry and public health safety. The stimulator of interferon gene (STING) signaling pathway has been well established as effective in defending against viral infections. However, the role of STING is controversial during bacterial infections. Herein, we provide an insight into the role of STING during S. aureus infection. Our data revealed that the STING signaling pathway was activated in S. aureus-infected cells. In vitro investigations demonstrated that inhibiting STING reduced inflammation, hypoxia-inducible factor-1 alpha (HIF1α) expression, and mitochondrial reactive oxygen species (mROS) production. Interestingly, blocking HIF1α eliminated the escalation of inflammation associated with STING. Additionally, suppressing mROS production significantly reduced HIF1α expression and inflammation levels, while elevating mROS had the opposite effect. These results indicate that STING promoted inflammation through the mROS-HIF1α pathway. Given that glycolysis is driven by HIF1α, we investigated the role of glycolysis during infection. As expected, STING-elevated inflammation was linked with HIF1α-driven glycolysis. In terms of pathogenesis, STING contributed to S. aureus proliferation within cells and mouse mammary glands. Collectively, our findings demonstrate that STING facilitates infection via the mROS-HIF1α-glycolysis axis, highlighting its potential as a promising anti-inflammatory target.

HIF-1α-Induced GPR171 Expression Mediates CCL2 Secretion by Mast Cells to Promote Gastric Inflammation During Helicobacter pylori Infection

BACKGROUND

Helicobacter pylori (H. pylori) infection is one of the most important risk factors for chronic gastritis, gastric ulcers, and gastric cancer. Mast cells act as a crucial regulator in bacterial infection. The mechanisms underlying mast cell activation and their role in H. pylori infection remain poorly understood.

MATERIALS AND METHODS

In gastric mucosal tissue, the number of mast cells, G-protein-coupled receptor 171 (GPR171) and CCL2 expression were detected by immunohistochemistry (IHC) or immunofluorescence between H. pylori-negative and H. pylori-positive patients. Mast cells were co-cultured with H. pylori, and transcriptome sequencing, RT-qPCR, and Western blotting (WB) were performed to identify receptors involved in mast cell activation. WB, chromatin immunoprecipitation (ChIP), and dual-luciferase reporter assays were conducted to investigate the molecular mechanism by which HIF-1α regulates GPR171 expression. Lentiviral knockdown, ELISA, WB, and IHC were used to evaluate the role of GPR171 during H. pylori infection. An in vivo mouse model of H. pylori infection was employed to assess the effects of GPR171 blockade on CCL2 expression and gastric mucosal inflammation.

RESULTS

In the study, we found that mast cell numbers were greatly increased and correlated with the severity of inflammation in H. pylori-infected patients. We found a new receptor, GPR171, was upregulated and involved in mast cell activation upon H. pylori infection. Furthermore, H. pylori infection induced the expression of GPR171 by promoting the activation of hypoxia-inducible factor 1 alpha (HIF-1α), which directly bound to hypoxia response elements in the GPR171 promoter and regulated its transcriptional activity. Blockade or loss of GPR171 in mast cells partially inhibited CCL2 secretion via the ERK1/2 signaling pathway. In the human gastric mucosa, CCL2 derived from mast cells was associated with gastric inflammation during H. pylori infection. In vivo murine studies indicated that H. pylori infection significantly upregulated CCL2 expression, while GPR171 inhibition partially reduced CCL2 levels and alleviated gastric mucosal inflammation.

CONCLUSIONS

We provide a novel mechanism that H. pylori activates mast cells to promote gastric inflammation.

Stimuli-Responsive Nanomedicines for the Treatment of Non-cancer Related Inflammatory Diseases

Nanomedicines offer a means to overcome the limitations associated with traditional drug dosage formulations by affording drug protection, enhanced drug bioavailability, and targeted drug delivery to affected sites. Inflamed tissues possess unique microenvironmental characteristics (including excessive reactive oxygen species, low pH levels, and hypoxia) that stimuli-responsive nanoparticles can employ as triggers to support on-demand delivery, enhanced accumulation, controlled release, and activation of anti-inflammatory drugs. Stimuli-responsive nanomedicines respond to physicochemical and pathological factors associated with diseased tissues to improve the specificity of drug delivery, overcome multidrug resistance, ensure accurate diagnosis and precision therapy, and control drug release to improve efficacy and safety. Current stimuli-responsive nanoparticles react to intracellular/microenvironmental stimuli such as pH, redox, hypoxia, or specific enzymes and exogenous stimuli such as temperature, magnetic fields, light, and ultrasound via bioresponsive moieties. This review summarizes the general strategies employed to produce stimuli-responsive nanoparticles tailored for inflammatory diseases and all recent advances, reports their applications in drug delivery, and illustrates the progress made toward clinical translation.

Oxygen-supplying nanotherapeutics for bacterial septic arthritis via hypoxia-relief-enhanced antimicrobial and anti-inflammatory phototherapy

Bacterial septic arthritis, an inflammatory disease caused by bacterial infections, is often accompanied by the emergence of multidrug-resistant bacteria, making therapeutic treatment a formidable challenge. With the emergence of antibiotic resistance, research on antimicrobial photodynamic therapy (aPDT) has regained attention. However, insufficient singlet oxygen production due to the hypoxia in the infection microenvironment is recognized as a key limiting the efficacy of aPDT. Hence, in this study, we designed a bacteria-targeted liposomal nanoplatform (MCPL) to alleviate hypoxia in the infectious microenvironment and enhance aPDT for bacterial septic arthritis. The nanoplatform was developed by integrating the phototherapeutic agent CyI and small-sized Pt NPs into thermosensitive liposomes, with modification of maltohexose on the liposome surface. In vitro and in vivo studies showed that MCPL could specifically target bacterial cell membranes and be thermally activated to catalytically convert endogenous hydrogen peroxide (H2O2) in the septic joint, supplementing local O2 reservoirs. This, in turn, supplies additional substrate pools for photodynamic conversion into reactive oxygen species (ROS) with bacterial toxicity. Furthermore, the antibacterial mechanism revealed that MCPL can regulate the HIF-1α and NF-κB signaling pathways in immune cells, acting as an effective modulator of antioxidant and anti-inflammatory pathways in both macrophages and neutrophils. This study demonstrates that MCPL could not induce bacterial multidrug resistance and provide as an innovative approach for treating bacterial septic arthritis.

Transcriptomic Study of Testicular Hypoxia Adaptation in Tibetan Sheep

The Tibetan sheep is a typical hypoxia-tolerant mammal, which lives on the plateau, at an altitude of between 2500 and 5000 m above sea level; the study of its hypoxic adaptation mechanism provides a reference for exploring the hypoxic adaptation mechanism of other animals. To grope for the genetic mechanism of adaptation to the hypoxic environment at the transcriptional level in Tibetan sheep testicular tissue, and to identify candidate genes and key pathways related to sheep adaptation, histological observation of testicular tissues from two sheep breeds was carried out using haematoxylin-eosin (HE) conventional staining. A total of 103 differentially expressed genes (DEGs) were authenticated in high altitude Tibetan sheep (ZYH) and low altitude Tibetan sheep (ZYM) by RNA sequencing technology (RNA-Seq), which included 50 up-regulated genes and 53 down-regulated genes. Functional analyses revealed several terms and pathways that were closely related to testis adaptation to the plateau. Several genes (including GGT5, AGTR2, EDN1, LPAR3, CYP2C19, IGFBP3, APOC3 and PKC1) were remarkably enriched in several pathways and terms, which may impact the Plateau adaptability of sheep by adjusting its reproductive activity and sexual maturation, and protecting Sertoli cells, various spermatocytes, and spermatogenesis processes. The results make a reasonable case for a better understanding of the molecular mechanisms of adaptation to altitude in sheep.

HMGB1 lactylation drives neutrophil extracellular trap formation in lactate-induced acute kidney injury

Rationale

Acute kidney injury (AKI) is a clinical syndrome associated with a multitude of conditions. Although renal replacement therapy (RRT) remains the cornerstone of treatment for advanced AKI, its implementation can potentially pose risks and may not be readily accessible across all healthcare settings and regions. Elevated lactate levels are implicated in sepsis-induced AKI; however, it remains unclear whether increased lactate directly induces AKI or elucidates the underlying mechanisms.

Methods

For human, the measurement of lactate in arterial blood gas is performed using the direct determination of L-lactate through an electrode oxidation method by a blood gas analyzer. For mice, enzyme-linked immunosorbent assay (ELISA) kits were employed to quantify the concentrations of lactate and AKI biomarkers in blood and cell supernatant. The mouse model of AKI was performed with a single intraperitoneal (i.p.) administration of lactate (30 mg/kg) and low-dose LPS (2 mg/kg) for 24 h. Proteomic analysis was conducted to identify lactylated proteins in kidney tissues. Techniques such as, immunoprecipitation, western blotting and immunofluorescence were used to evaluate the levels of HMGB1 lactylation, neutrophil extracellular traps (NETs)and to assess related molecular signaling pathways.

Main results

Our findings indicate that lactate serves as an independent predictor of AKI in patients with acute decompensated heart failure (ADHF). We observed that co-administration of lactate with low-dose lipopolysaccharide (LPS) resulted in lactate overproduction, which subsequently elevated serum levels of creatinine (Cre) and blood urea nitrogen (BUN). Furthermore, the combined application of lactate and low-dose LPS was shown to provoke HMGB1 lactylation within renal tissues. Notably, pretreatment with HMGB1 small interfering RNA (siRNA) effectively diminished lactate-mediated HMGB1 lactylation and alleviated the severity of AKI. Additionally, lactate accumulation was found to enhance the expression levels of NETs in the bloodstream, with circulating NETs levels positively correlating with HMGB1 lactylation. Importantly, pre-administration of HMGB1 inhibitors (glycyrrhizin) or lactate dehydrogenase A (LDH-A) inhibitors (oxamate) reversed the upregulation of NETs induced by lactate and low-dose LPS in both the blood and polymorphonuclear neutrophils (PMNs) cell supernatant, thereby ameliorating AKI associated with lactate accumulation.

Conclusions

These findings illuminate the role of lactate-mediated HMGB1 lactylation in inducing AKI in mice through the activation of the HMGB1-NETs signaling pathway.

Intestinal E. coli-produced yersiniabactin promotes profibrotic macrophages in Crohn's disease

Inflammatory bowel disease (IBD)-associated fibrosis causes significant morbidity. Mechanisms are poorly understood but implicate the microbiota, especially adherent-invasive Escherichia coli (AIEC). We previously demonstrated that AIEC producing the metallophore yersiniabactin (Ybt) promotes intestinal fibrosis in an IBD mouse model. Since macrophages interpret microbial signals and influence inflammation/tissue remodeling, we hypothesized that Ybt metal sequestration disrupts this process. Here, we show that macrophages are abundant in human IBD-fibrosis tissue and mouse fibrotic lesions, where they co-localize with AIEC. Ybt induces profibrotic gene expression in macrophages via stabilization and nuclear translocation of hypoxia-inducible factor 1-alpha (HIF-1α), a metal-dependent immune regulator. Importantly, Ybt-producing AIEC deplete macrophage intracellular zinc and stabilize HIF-1α through inhibition of zinc-dependent HIF-1α hydroxylation. HIF-1α+ macrophages localize to sites of disease activity in human IBD-fibrosis strictures and mouse fibrotic lesions, highlighting their physiological relevance. Our findings reveal microbiota-mediated metal sequestration as a profibrotic trigger targeting macrophages in the inflamed intestine.

TGFβ1 Restores Energy Homeostasis of Human Trophoblast Cells Under Hyperglycemia In Vitro by Inducing PPARγ Expression, AMPK Activation, and HIF1α Degradation

Elevated glucose levels at the fetal-maternal interface are associated with placental trophoblast dysfunction and increased incidence of pregnancy complications. Trophoblast cells predominantly utilize glucose as an energy source, metabolizing it through glycolysis in the cytoplasm and oxidative respiration in the mitochondria to produce ATP. The TGFβ1/SMAD2 signaling pathway and the transcription factors PPARγ, HIF1α, and AMPK are key regulators of cell metabolism and are known to play critical roles in extravillous trophoblast cell differentiation and function. While HIF1α promotes glycolysis over mitochondrial respiration, PPARγ and AMPK encourage the opposite. However, the interplay between TGFβ1 and these energy-sensing regulators in trophoblast cell glucose metabolism remains unclear. This study aimed to investigate whether and how TGFβ1 regulates energy metabolism in trophoblast cells exposed to normal and high glucose conditions. The trophoblast JEG-3 cells were incubated in normal (5 mM) and high (25 mM) glucose conditions for 24 h in the absence and the presence of TGFβ1. The protein expression levels of phosphor (p)-SMAD2, GLUT1/3, HIF1α, PPARγ, p-AMPK, and specific OXPHOS protein subunits were determined by western blotting, and ATP and lactate production by bioluminescent assay kits. JEG-3 cells exposed to 25 mM glucose decreased ATP production but did not affect lactate production. These changes led to a reduction in the expression levels of GLUT1/3, mitochondrial respiratory chain proteins, and PPARγ, coinciding with an increase in HIF1α expression. Conversely, TGFβ1 treatment at 25 mM glucose reduced HIF1α expression while enhancing the expression levels of GLUT1/3, PPARγ, p-AMPK, and mitochondrial respiratory chain proteins, thereby rejuvenating ATP production. Our findings reveal that high glucose conditions disrupt cellular glucose metabolism in trophoblast cells by perturbing mitochondrial oxidative respiration and decreasing ATP production. Treatment with TGFβ1 appears to counteract this trend, probably by enhancing both glycolytic and mitochondrial metabolism, suggesting a potential regulatory role of TGFβ1 in placental trophoblast cell glucose metabolism.

The miR-26a/SIRT6/HIF-1α axis regulates glycolysis and inflammatory responses in host macrophages during Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis. Here, a macrophage infection model was used to unravel the role of the histone deacetylase sirtuin 6 (SIRT6) in Mtb-triggered regulation of the innate immune response. Mtb infection downregulated microRNA-26a and upregulated its target SIRT6. SIRT6 suppressed glycolysis and expression of HIF-1α-dependent glycolytic genes during infection. In addition, SIRT6 regulated the levels of intracellular succinate which controls stabilization of HIF-1α, as well as the release of interleukin (IL)-1β. Furthermore, SIRT6 inhibited inducible nitric oxide synthase (iNOS) and proinflammatory IL-6 but augmented anti-inflammatory arginase expression. The miR-26a/SIRT6/HIF-1α axis therefore regulates glycolysis and macrophage immune responses during Mtb infection. Our findings link SIRT6 to rewiring of macrophage signaling pathways facilitating dampening of the antibacterial immune response.

Exposure to normobaric hypoxia shapes the acute inflammatory response in human whole blood cells in vivo

Cells of the immune defence, especially leukocytes, often have to perform their function in tissue areas that are characterized by oxygen deficiency, so-called hypoxia. Physiological hypoxia significantly affects leukocyte function and controls the innate and adaptive immune response mainly through transcriptional gene regulation via the hypoxia-inducible factors (HIFs). Multiple pathogens including components of bacteria, such as lipopolysaccharides (LPS) trigger the activation of leukocytes. HIF pathway activation enables immune cells to adapt to both hypoxic environments in physiological and inflammatory settings and modulates immune cell responses through metabolism changes and crosstalk with other immune-relevant signalling pathways. To study the mutual influence of both processes in vivo, we used a human endotoxemia model, challenging participants with an intravenous LPS injection post or prior to a 4-h stay in a hypoxic chamber with normobaric hypoxia of 10.5% oxygen. We analysed changes in gene expression in whole blood cells and determined inflammatory markers to unveil the crosstalk between both processes. Our investigations showed differentially altered gene expression patterns of HIF and target genes upon in vivo treatment with LPS and hypoxia. Further, we found evidence for effects of hypoxic priming upon inflammation in combination with immunomodulatory effects in whole blood cells in vivo. Our work elucidates the complex interplay of hypoxic and inflammatory HIF regulation in human immune cells and offers new perspectives for further clinical research.

Hypoxia-inducible factor-driven glycolytic adaptations in host-microbe interactions

Mammalian cells utilize glucose as a primary carbon source to produce energy for most cellular functions. However, the bioenergetic homeostasis of cells can be perturbed by environmental alterations, such as changes in oxygen levels which can be associated with bacterial infection. Reduction in oxygen availability leads to a state of hypoxia, inducing numerous cellular responses that aim to combat this stress. Importantly, hypoxia strongly augments cellular glycolysis in most cell types to compensate for the loss of aerobic respiration. Understanding how this host cell metabolic adaptation to hypoxia impacts the course of bacterial infection will identify new anti-microbial targets. This review will highlight developments in our understanding of glycolytic substrate channeling and spatiotemporal enzymatic organization in response to hypoxia, shedding light on the integral role of the hypoxia-inducible factor (HIF) during host-pathogen interactions. Furthermore, the ability of intracellular and extracellular bacteria (pathogens and commensals alike) to modulate host cellular glucose metabolism will be discussed.

Less is more! Low amount of Fusobacterium nucleatum supports macrophage-mediated trophoblast functions in vitro

F. nucleatum, involved in carcinogenesis of colon carcinomas, has been described as part of the commensal flora of the female upper reproductive tract. Although its contribution to destructive inflammatory processes is well described, its role as commensal uterine bacteria has not been thoroughly investigated. Since carcinogenesis shares similar mechanisms with early pregnancy development (including proliferation, invasion, blood supply and the induction of tolerance), these mechanisms induced by F. nucleatum could play a role in early pregnancy. Additionally, implantation and placentation require a well-balanced immune activation, which might be suitably managed by the presence of a limited amount of bacteria or bacterial residues. We assessed the effect of inactivated F. nucleatum on macrophage-trophoblast interactions. Monocytic cells (THP-1) were polarized into M1, M2a or M2c macrophages by IFN-γ, IL-4 or TGF-β, respectively, and subsequently treated with inactivated fusobacteria (bacteria:macrophage ratio of 0.1 and 1). Direct effects on macrophages were assessed by viability assay, flow cytometry (antigen presentation molecules and cytokines), qPCR (cytokine expression), in-cell Western (HIF and P-NF-κB) and ELISA (VEGF secretion). The function of first trimester extravillous trophoblast cells (HTR-8/SVneo) in response to macrophage-conditioned medium was microscopically assessed by migration (scratch assay), invasion (sprouting assay) and tube formation. Underlying molecular changes were investigated by ELISA (VEGF secretion) and qPCR (matrix-degrading factors and regulators). Inflammation-primed macrophages (M1) as well as high bacterial amounts increased pro-inflammatory NF-κB expression and inflammatory responses. Subsequently, trophoblast functions were impaired. In contrast, low bacterial stimulation caused an increased HIF activation and subsequent VEGF-A secretion in M2c macrophages. Accordingly, there was an increase of trophoblast tube formation. Our results suggest that a low-mass endometrial/decidual microbiome can be tolerated and while it supports implantation and further pregnancy processes.

eQTLs identify regulatory networks and drivers of variation in the individual response to sepsis

Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection, for which disease heterogeneity is a major obstacle to developing targeted treatments. We have previously identified gene-expression-based patient subgroups (sepsis response signatures [SRS]) informative for outcome and underlying pathophysiology. Here, we aimed to investigate the role of genetic variation in determining the host transcriptomic response and to delineate regulatory networks underlying SRS. Using genotyping and RNA-sequencing data on 638 adult sepsis patients, we report 16,049 independent expression (eQTLs) and 32 co-expression module (modQTLs) quantitative trait loci in this disease context. We identified significant interactions between SRS and genotype for 1,578 SNP-gene pairs and combined transcription factor (TF) binding site information (SNP2TFBS) and predicted regulon activity (DoRothEA) to identify candidate upstream regulators. Overall, these approaches identified putative mechanistic links between host genetic variation, cell subtypes, and the individual transcriptomic response to infection.

Nanozymes for the Therapeutic Treatment of Diabetic Foot Ulcers

Diabetic foot ulcers (DFU) are chronic, refractory wounds caused by diabetic neuropathy, vascular disease, and bacterial infection, and have become one of the most serious and persistent complications of diabetes mellitus because of their high incidence and difficulty in healing. Its malignancy results from a complex microenvironment that includes a series of unfriendly physiological states secondary to hyperglycemia, such as recurrent infections, excessive oxidative stress, persistent inflammation, and ischemia and hypoxia. However, current common clinical treatments, such as antibiotic therapy, insulin therapy, surgical debridement, and conventional wound dressings all have drawbacks, and suboptimal outcomes exacerbate the financial and physical burdens of diabetic patients. Therefore, development of new, effective and affordable treatments for DFU represents a top priority to improve the quality of life of diabetic patients. In recent years, nanozymes-based diabetic wound therapy systems have been attracting extensive interest by integrating the unique advantages of nanomaterials and natural enzymes. Compared with natural enzymes, nanozymes possess more stable catalytic activity, lower production cost and greater maneuverability. Remarkably, many nanozymes possess multienzyme activities that can cascade multiple enzyme-catalyzed reactions simultaneously throughout the recovery process of DFU. Additionally, their favorable photothermal-acoustic properties can be exploited for further enhancement of the therapeutic effects. In this review we first describe the characteristic pathological microenvironment of DFU, then discuss the therapeutic mechanisms and applications of nanozymes in DFU healing, and finally, highlight the challenges and perspectives of nanozyme development for DFU treatment.

Unraveling the role of HIF-1α in sepsis: from pathophysiology to potential therapeutics-a narrative review

Sepsis is characterized by organ dysfunction resulting from a dysregulated inflammatory response triggered by infection, involving multifactorial and intricate molecular mechanisms. Hypoxia-inducible factor-1α (HIF-1α), a notable transcription factor, assumes a pivotal role in the onset and progression of sepsis. This review aims to furnish a comprehensive overview of HIF-1α's mechanism of action in sepsis, scrutinizing its involvement in inflammatory regulation, hypoxia adaptation, immune response, and organ dysfunction. The review encompasses an analysis of the structural features, regulatory activation, and downstream signaling pathways of HIF-1α, alongside its mechanism of action in the pathophysiological processes of sepsis. Furthermore, it will delve into the roles of HIF-1α in modulating the inflammatory response, including its association with inflammatory mediators, immune cell activation, and vasodilation. Additionally, attention will be directed toward the regulatory function of HIF-1α in hypoxic environments and its linkage with intracellular signaling, oxidative stress, and mitochondrial damage. Finally, the potential therapeutic value of HIF-1α as a targeted therapy and its significance in the clinical management of sepsis will be discussed, aiming to serve as a significant reference for an in-depth understanding of sepsis pathogenesis and potential therapeutic targets, as well as to establish a theoretical foundation for clinical applications.

Association of Serum Soluble Transferrin Receptor Concentration With Markers of Inflammation: Analysis of 1001 Patients From a Tertiary Rheumatology Center

OBJECTIVE

Soluble transferrin receptor (sTfR) is considered to be a useful biomarker for the diagnosis of iron deficiency, especially in the setting of inflammation, as it is thought to not be affected by inflammation. We analyzed the relationship between sTfR levels and inflammatory markers in patients with known or suspected inflammatory rheumatic disease (IRD).

METHODS

Blood samples of 1001 patients with known or suspected IRD referred to a tertiary rheumatology center were analyzed. Study participants were classified as patients with active IRD and patients with inactive IRD or without IRD. Correlation analyses were used to explore the relationship between sTfR levels and inflammatory markers (ie, C-reactive protein [CRP], erythrocyte sedimentation rate [ESR]). We applied multiple linear regression analysis to evaluate the predictive value of CRP levels for sTfR concentrations after adjustment for potential confounding factors.

RESULTS

There were positive correlations between inflammatory markers (CRP, ESR) and serum sTfR levels (ρ 0.44, ρ 0.43, respectively; P < 0.001), exceeding the strength of correlation between inflammatory markers and the acute phase reactant ferritin (ρ 0.30, ρ 0.23, respectively; P < 0.001). Patients with active IRD demonstrated higher serum sTfR levels compared to patients with inactive or without IRD (mean 3.99 [SD 1.69] mg/L vs 3.31 [SD 1.57] mg/L; P < 0.001). After adjustment for potential confounding factors, CRP levels are predictive for serum sTfR concentrations (P < 0.001).

CONCLUSION

The study provides evidence against the concept that sTfR is a biomarker not affected by inflammation.

PFKFB3-Meditated Glycolysis via the Reactive Oxygen Species-Hypoxic Inducible Factor 1α Axis Contributes to Inflammation and Proliferation of Staphylococcus aureus in Epithelial Cells

Mastitis caused by antibiotic-resistant strains of Staphylococcus aureus is a significant concern in the livestock industry due to the economic losses it incurs. Regulating immunometabolism has emerged as a promising approach for preventing bacterial inflammation. To investigate the possibility of alleviating inflammation caused by S aureus infection by regulating host glycolysis, we subjected the murine mammary epithelial cell line (EpH4-Ev) to S aureus challenge. Our study revealed that S aureus can colonize EpH4-Ev cells and promote inflammation through hypoxic inducible factor 1α (HIF1α)-driven glycolysis. Notably, the activation of HIF1α was found to be dependent on the production of reactive oxygen species (ROS). By inhibiting PFKFB3, a key regulator in the host glycolytic pathway, we successfully modulated HIF1α-triggered metabolic reprogramming by reducing ROS production in S aureus-induced mastitis. Our findings suggest that there is a high potential for the development of novel anti-inflammatory therapies that safely inhibit the glycolytic rate-limiting enzyme PFKFB3.

Downregulation of Hypoxia Inducible Factor-1α in Primary Human Natural Killer Cells Using Small Interfering RNA Delivery with ExPERT ATx by MaxCyte

Natural killer (NK) cells are innate cytokine-producing and cytolytic effector lymphocytes. Their function is responsive to environmental factors, e.g., hypoxia, a frequent feature of inflamed tissues. Such responses require that the NK cells up-regulate HIF-1α (hypoxia inducible factor-1α), the major mediator of cellular responses to hypoxia that affects cell survival as well as immune responses. Thus, a major approach to the study of NK cell effector function under hypoxic conditions involves the ability to regulate HIF-1α levels in primary human NK cells. One difficulty with this approach, however, is that NK cells are difficult-to-transfect cells and common transfection methods, including electroporation or lipofection, suffer from variable transfection efficiency and cell viability. Moreover, the detection of HIF-1α is technically challenging because of the rapid degradation of the protein under normoxic conditions. Here, using the commercially available ExPERT ATx by MaxCyte, we report a workflow for the reliable delivery of small interfering RNA (siRNA) for targeting HIF-1α expression in primary human NK cells. We further provide a protocol for the detection of HIF-1α by immunoblot analysis demonstrating its efficient downregulation by siRNA. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Isolation of natural killer cells from human peripheral blood mononuclear cells Basic Protocol 2: Delivery of non-coding small interfering RNA and HIF-1α targeting siRNA into natural killer cells using ExPERT ATx Basic Protocol 3: Assessing the downregulation of HIF-1α protein using immunoblot analysis Support Protocol 1: Exemplary assessment of transfection efficiency using fluorescently labeled non-targeting siRNA Support Protocol 2: Exemplary assessment of NK cell viability 20 hr post-transfection Support Protocol 3: Exemplary assessment of HIF-1α knockdown using immunoblot analysis.

Role of HIF in fish inflammation

The hypoxia-inducing factor (HIF) is a central transcription factor in cellular oxygen sensing and regulation. It is common that the inflammation always appears in many diseases, like infectious diseases in fishes, and the inflammation is often accompanied by hypoxia, as a hallmark of inflammation. Besides coordinating cellular responses to low oxygen, HIF-mediated hypoxia signaling pathway is also crucial for immune responses such as the regulations of innate immune cell phenotype and function, as well as metabolic reprogramming under the inflammation. However, the understanding of the molecular mechanisms by which HIFs regulate the inflammatory response in fish is still very limited. Here, we review the characteristics of HIF as well as its roles in innate immune cells and the infections caused by bacteria and viruses. The regulatory effects of HIF on the metabolic reprogramming of innate immune cells are also discussed and the future research directions are outlooked. This paper will serve as a reference for elucidating the molecular mechanism of HIF regulating inflammation and identifying treatment strategies to target HIF for fish disease.

Pathogenesis of non-infection related inflammatory root resorption in permanent teeth: A narrative review

BACKGROUND

The mechanism of action of root resorption in a permanent tooth can be classified as infection-related (e.g., microbial infection) or non-infection-related (e.g., sterile damage). Infection induced root resorption occurs due to bacterial invasion. Non-infection-related root resorption stimulates the immune system through a different mechanism.

OBJECTIVES

The aim of this narrative review is to describe the pathophysiologic process of non-infection-related inflammatory processes involved in root resorption of permanent teeth.

METHODS

A literature search on root resorption was conducted using Scopus (PubMed and Medline) and Google Scholar databases to highlight the pathophysiology of bone and root resorption in non-infection-related situations. The search included key words covering the relevant category. It included in vitro and in vivo studies, systematic reviews, case series, reviews, and textbooks in English. Conference proceedings, lectures and letters to the editor were excluded.

RESULTS

Three types of root resorption are related to the non-infection mechanism of action, which includes surface resorption due to either trauma or excessive orthodontic forces, external replacement resorption and external cervical resorption. The triggers are usually damage associated molecular patterns and hypoxia conditions. During this phase macrophages and clastic cells act to eliminate the damaged tissue and bone, eventually enabling root resorption and bone repair as part of wound healing.

DISCUSSION

The resorption of the root occurs during the inflammatory phase of wound healing. In this phase, damaged tissues are recognized by macrophages and neutrophiles that secrete interlaukines such as TNF-α, IL-1, IL-6, IL-8. Together with the hypoxia condition that accelarates the secretion of growth factors, the repair of the damaged perioduntiom, including damaged bone, is initiated. If the precementum and cementoblast are injured, root resorption can occur.

CONCLUSIONS

Wound healing exhibits different patterns of action that involves immune stimulation in a bio-physiological activity, that occurs in the proper sequence, with overlapping phases. Two pathologic conditions, DAMPs and hypoxia, can activate the immune cells including clastic cells, eliminating damaged tissue and bone. Under certain conditions, root resorption occurs as a side effect.

Unraveling the protective mechanisms of Chuanfangyihao against acute lung injury: Insights from experimental validation

Chuanfangyihao (CFYH) is an effective treatment for acute lung injury (ALI) in clinical practice; however, its underlying mechanism of action remains unclear. Therefore, the aim of the present study was to elucidate the pharmacological mechanism of action of CFYH in ALI through experimental validation. First, a rat model of ALI was established using lipopolysaccharide (LPS). Next, the pathological changes in the lungs of the rats and the pathological damage were scored. The wet/dry weight ratios were measured, and ROS content was detected using flow cytometry. ELISA was used to examine IL-6, TNF-α, IL-1β, IL-18, and LDH levels. Immunohistochemistry was used to detect Beclin-1 and NLRP3 expression. Western blotting was performed to analyze the expression of HMGB1, RAGE, TLR4, NF-κB p65, AMPK, p-AMPK, mTOR, p-mTOR, Beclin-1, LC3-II/I, p62, Bcl-2, Bax, Caspase-3, Caspase-1, and GSDMD-NT. The mRNA levels of HMGB1, RAGE, AMPK, mTOR, and HIF-1α were determined using reverse transcription quantitative PCR. CFYH alleviated pulmonary edema and decreased the expression of IL-6, TNF-α, TLR4, NF-κB p65, HMGB1/RAGE, ROS, and HIF-1α. In addition, pretreatment with CFYH reversed ALI-induced programmed cell death. In conclusion, CFYH alleviates LPS-induced ALI, and these findings provide a preliminary clarification of the predominant mechanism of action of CFYH in ALI.

Morphological and Molecular Biological Features of the Systemic Inflammatory Response in Old Wistar Rats with High and Low Resistance to Hypoxia

Morphological and molecular biological features of LPS-induced systemic inflammatory response were assessed in old male Wistar rats with high (HR) and low (LR) resistance to hypoxia. The systemic inflammatory response was modeled by intraperitoneal injection of E. coli O26:B6 LPS; the animals were sacrificed after 6 h. In histological sections, the number of neutrophils in the interalveolar septa and the area of necrosis in the liver were determined. The expression levels of Hif1a, Hif2a, Nfkb, Vegf, Il1b, Il6, Il10, and Tgfb mRNA in the liver and serum concentrations of HIF-1α and IL-1β were determined. In 4-6 h after LPS injection, 3 (43%) of 7 HR rats died, whereas no deaths were observed among LR rats. At 6 h after LPS injection, the number of neutrophils in the interalveolar septa of the lungs in LR rats was significantly higher than in HR rats, while the area of necrosis in the liver did not differ. At the same time, the mRNA expression levels of the proinflammatory cytokine genes Il1b and Il6 increased in the liver of both HR and LR rats, whereas the expression of Il10 increased only in HR rats. The expression of the Hif1a gene in the liver was higher in LR rats, but the content of HIF-1α protein in blood serum was higher in HR animals. These data should be taken into account when developing new approaches to the therapy of systemic inflammatory response in infectious and inflammatory diseases in the elderly.

Metformin Reduces Bone Resorption in Apical Periodontitis Through Regulation of Osteoblast and Osteoclast Differentiation

INTRODUCTION

We have previously demonstrated that auxiliary metformin therapy promotes healing of apical periodontitis. Here we aimed to investigate the effects of metformin on osteoblast differentiation and osteoclast formation in cultured cells and rat apical periodontitis.

METHODS

Murine pre-osteoblasts MC3T3-E1 and macrophages RAW264.7 were cultured under hypoxia (2% oxygen) or normoxia (21% oxygen) and stimulated with receptor activator of nuclear factor-κB ligand (RANKL) when indicated. Metformin was added to the cultures to evaluate its anti-hypoxic effects. Expressions of osteoblast differentiation regulator runt-related transcription factor 2 (RUNX2), RANKL, and osteoclast marker tartrate-resistant acid phosphatase (TRAP) were assessed by Western blot. Apical periodontitis was induced in mandibular first molars of 10 Sprague-Dawley rats. Root canal therapy with or without metformin supplement was performed. Periapical bone resorption was measured by micro-computed tomography. Immunohistochemistry was used to examine RUNX2, RANKL, and TRAP expressions.

RESULTS

Hypoxia suppressed RUNX2 expression and enhanced RANKL synthesis in pre-osteoblasts. TRAP production increased in macrophages after hypoxia and/or RANKL stimulation. Metformin reversed hypoxia-induced RUNX2 suppression and RANKL synthesis in pre-osteoblasts. Metformin also inhibited hypoxia and RANKL-enhanced TRAP synthesis in macrophages. Intracanal metformin diminished bone loss in rat apical periodontitis. Comparing with vehicle control, cells lining bone surfaces in metformin-treated lesions had significantly stronger expression of RUNX2 and decreased synthesis of RANKL and TRAP.

CONCLUSIONS

Alleviation of bone resorption by intracanal metformin was associated with enhanced osteoblast differentiation and diminished osteoclast formation in rat apical periodontitis. Our results endorsed the role of metformin as an effective medicament for inflammatory bone diseases.

Research progress of nanoparticle targeting delivery systems in bacterial infections

Bacterial infection is a huge threat to the health of human beings and animals. The abuse of antibiotics have led to the occurrence of bacterial multidrug resistance, which have become a difficult problem in the treatment of clinical infections. Given the outstanding advantages of nanodrug delivery systems in cancer treatment, many scholars have begun to pay attention to their application in bacterial infections. However, due to the similarity of the microenvironment between bacterial infection lesions and cancer sites, the targeting and accuracy of traditional microenvironment-responsive nanocarriers are questionable. Therefore, finding new specific targets has become a new development direction of nanocarriers in bacterial prevention and treatment. This article reviews the infectious microenvironment induced by bacteria and a series of virulence factors of common pathogenic bacteria and their physiological functions, which may be used as potential targets to improve the targeting accuracy of nanocarriers in lesions.

Mitochondria in hypoxic pulmonary hypertension, roles and the potential targets

Mitochondria are the centrol hub for cellular energy metabolisms. They regulate fuel metabolism by oxygen levels, participate in physiological signaling pathways, and act as oxygen sensors. Once oxygen deprived, the fuel utilizations can be switched from mitochondrial oxidative phosphorylation to glycolysis for ATP production. Notably, mitochondria can also adapt to hypoxia by making various functional and phenotypes changes to meet the demanding of oxygen levels. Hypoxic pulmonary hypertension is a life-threatening disease, but its exact pathgenesis mechanism is still unclear and there is no effective treatment available until now. Ample of evidence indicated that mitochondria play key factor in the development of hypoxic pulmonary hypertension. By hypoxia-inducible factors, multiple cells sense and transmit hypoxia signals, which then control the expression of various metabolic genes. This activation of hypoxia-inducible factors considered associations with crosstalk between hypoxia and altered mitochondrial metabolism, which plays an important role in the development of hypoxic pulmonary hypertension. Here, we review the molecular mechanisms of how hypoxia affects mitochondrial function, including mitochondrial biosynthesis, reactive oxygen homeostasis, and mitochondrial dynamics, to explore the potential of improving mitochondrial function as a strategy for treating hypoxic pulmonary hypertension.

Proteomic analysis to identification of hypoxia related markers in spinal tuberculosis: a study based on weighted gene co-expression network analysis and machine learning

OBJECTIVE

This article aims at exploring the role of hypoxia-related genes and immune cells in spinal tuberculosis and tuberculosis involving other organs.

METHODS

In this study, label-free quantitative proteomics analysis was performed on the intervertebral discs (fibrous cartilaginous tissues) obtained from five spinal tuberculosis (TB) patients. Key proteins associated with hypoxia were identified using molecular complex detection (MCODE), weighted gene co-expression network analysis(WGCNA), least absolute shrinkage and selection operator (LASSO), and support vector machine recursive feature Elimination (SVM-REF) methods, and their diagnostic and predictive values were assessed. Immune cell correlation analysis was then performed using the Single Sample Gene Set Enrichment Analysis (ssGSEA) method. In addition, a pharmaco-transcriptomic analysis was also performed to identify targets for treatment.

RESULTS

The three genes, namely proteasome 20 S subunit beta 9 (PSMB9), signal transducer and activator of transcription 1 (STAT1), and transporter 1 (TAP1), were identified in the present study. The expression of these genes was found to be particularly high in patients with spinal TB and other extrapulmonary TB, as well as in TB and multidrug-resistant TB (p-value < 0.05). They revealed high diagnostic and predictive values and were closely related to the expression of multiple immune cells (p-value < 0.05). It was inferred that the expression of PSMB9, STAT 1, and TAP1 could be regulated by different medicinal chemicals.

CONCLUSION

PSMB9, STAT1, and TAP1, might play a key role in the pathogenesis of TB, including spinal TB, and the protein product of the genes can be served as diagnostic markers and potential therapeutic target for TB.

Ultrastructural Evidence of Mitochondrial Dysfunction in Osteomyelitis Patients

Osteomyelitis is a difficult-to-treat disease with high chronification rates. First studies suggest increases in mitochondrial fission and mitochondrial dysfunction as possible contributors to the accumulation of intracellular reactive oxygen species and thereby to the cell death of infected bone cells. The aim of the present study is to analyze the ultrastructural impact of bacterial infection on osteocytic and osteoblastic mitochondria. Human infected bone tissue samples were visualized via light microscopy and transmission electron microscopy. Osteoblasts, osteocytes and their mitochondria were analyzed histomorphometrically and compared with the control group of noninfectious human bone tissue samples. The results depicted swollen hydropic mitochondria including depleted cristae and a decrease in matrix density in the infected samples. Furthermore, perinuclear clustering of mitochondria could also be observed regularly. Additionally, increases in relative mitochondrial area and number were found as a correlate for increased mitochondrial fission. In conclusion, mitochondrial morphology is altered during osteomyelitis in a comparable way to mitochondria from hypoxic tissues. This gives new perspectives on the treatment strategies since the manipulation of mitochondrial dynamics may improve bone cell survival as a potential new target for the therapy of osteomyelitis.

Morphofunctional Changes in the Thymus in Prepubertal Male Wistar Rats in LPS-Induced Systemic Inflammatory Response in Relation to Hypoxia Tolerance

The dynamics of morphofunctional changes in the thymus during the LPS-induced systemic inflammatory response was assessed in prepubertal male Wistar rats in relationship with the resistance to hypoxia. The systemic inflammatory response was modeled by intraperitoneal administration of E. coli O26:B6 LPS. In histological sections of the thymus, the relative number of thymic bodies and proliferative activity of cells were evaluated. The relative number of CD3⁺CD4⁺, CD3⁺CD8⁺, and CD4⁺CD8⁺ cells in the thymus was determined by flow cytometry. The content of HIF-1α and endotoxin was determined in the blood serum. The expression level of Nfkb mRNA was assessed in the liver. The most pronounced changes in the indicators of the functional state of the thymus were detected 3 and 6 h after LPS administration following the increase in the content of HIF-1α and endotoxin in blood serum and Nfkb mRNA expression in the liver. In the thymus, a decrease in the number of thymic bodies consisting of 3-5 epithelial cells and an increase in the number of bodies consisting of 5 or more cells was observed. In 24 h after LPS administration, the relative number of CD3⁺CD4⁺ and CD3⁺CD8⁺ cells in the thymus decreased. At the same time, the number of Ki-67⁺ cells in the subcapsular zone of the thymus increased 6 and 24 h after LPS administration. These data should be taken into account in the development of approaches to the treatment of infectious and inflammatory diseases in prepubertal children.

Evaluating Bacterial Pathogenesis Using a Model of Human Airway Organoids Infected with Pseudomonas aeruginosa Biofilms

Pseudomonas aeruginosa is one of the leading invasive agents of human pulmonary infection, especially in patients with compromised immunity. Prior studies have used various in vitro models to establish P. aeruginosa infection and to analyze transcriptomic profiles of either the host or pathogen, and yet how much those works are relevant to the genuine human airway still raises doubts. In this study, we cultured and differentiated human airway organoids (HAOs) that recapitulate, to a large extent, the histological and physiological features of the native human mucociliary epithelium. HAOs were then employed as a host model to monitor P. aeruginosa biofilm development. Through dual-species transcriptome sequencing (RNA-seq) analyses, we found that quorum sensing (QS) and several associated protein secretion systems were significantly upregulated in HAO-associated bacteria. Cocultures of HAOs and QS-defective mutants further validated the role of QS in the maintenance of a robust biofilm and disruption of host tissue. Simultaneously, the expression magnitude of multiple inflammation-associated signaling pathways was higher in the QS mutant-infected HAOs, suggesting that QS promotes immune evasion at the transcriptional level. Altogether, modeling infection of HAOs by P. aeruginosa captured several crucial facets in host responses and bacterial pathogenesis, with QS being the most dominant virulence pathway showing profound effects on both bacterial biofilm and host immune responses. Our results revealed that HAOs are an optimal model for studying the interaction between the airway epithelium and bacterial pathogens. IMPORTANCE Human airway organoids (HAOs) are an organotypic model of human airway mucociliary epithelium. The HAOs can closely resemble their origin organ in terms of epithelium architecture and physiological function. Accumulating studies have revealed the great values of the HAO cultures in host-pathogen interaction research. In this study, HAOs were used as a host model to grow Pseudomonas aeruginosa biofilm, which is one of the most common pathogens found in pulmonary infection cases. Dual transcriptome sequencing (RNA-seq) analyses showed that the cocultures have changed the gene expression pattern of both sides significantly and simultaneously. Bacterial quorum sensing (QS), the most upregulated pathway, contributed greatly to biofilm formation, disruption of barrier function, and subversion of host immune responses. Our study therefore provides a global insight into the transcriptomic responses of both P. aeruginosa and human airway epithelium.

Loss of Vhl alters trabecular bone loss during S. aureus osteomyelitis in a cell-specific manner

Osteomyelitis, or bone infection, is a major complication of accidental trauma or surgical procedures involving the musculoskeletal system. Staphylococcus aureus is the most frequently isolated pathogen in osteomyelitis and triggers significant bone loss. Hypoxia-inducible factor (HIF) signaling has been implicated in antibacterial immune responses as well as bone development and repair. In this study, the impact of bone cell HIF signaling on antibacterial responses and pathologic changes in bone architecture was explored using genetic models with knockout of either Hif1a or a negative regulator of HIF-1α, Vhl. Deletion of Hif1a in osteoblast-lineage cells via Osx-Cre (Hif1aΔOB ) had no impact on bacterial clearance or pathologic changes in bone architecture in a model of post-traumatic osteomyelitis. Knockout of Vhl in osteoblast-lineage cells via Osx-Cre (VhlΔOB ) caused expected increases in trabecular bone volume per total volume (BV/TV) at baseline and, intriguingly, did not exhibit an infection-mediated decline in trabecular BV/TV, unlike control mice. Despite this phenotype, bacterial burdens were not affected by loss of Vhl. In vitro studies demonstrated that transcriptional regulation of the osteoclastogenic cytokine receptor activator of NF-κB ligand (RANKL) and its inhibitor osteoprotegerin (OPG) is altered in osteoblast-lineage cells with knockout of Vhl. After observing no impact on bacterial clearance with osteoblast-lineage conditional knockouts, a LysM-Cre model was used to generate Hif1aΔMyeloid and VhlΔMyeloid mouse models to explore the impact of myeloid cell HIF signaling. In both Hif1aΔMyeloid and VhlΔMyeloid models, bacterial clearance was not impacted. Moreover, minimal impacts on bone architecture were observed. Thus, skeletal HIF signaling was not found to impact bacterial clearance in our mouse model of post-traumatic osteomyelitis, but Vhl deletion in the osteoblast lineage was found to limit infection-mediated trabecular bone loss, possibly via altered regulation of RANKL-OPG gene transcription.

Gold Nanoclusters-Based NIR-II Photosensitizers with Catalase-like Activity for Boosted Photodynamic Therapy

Photodynamic therapy (PDT) under fluorescence imaging as a selective and non-invasive treatment approach has been widely applied for the therapy of cancer and bacterial infections. However, its treatment efficiency is hampered by high background fluorescence in the first near-infrared window (NIR-I, 700–900 nm) and oxygen-dependent photosensitizing activity of traditional photosensitizers. In this work, we employ gold nanoclusters (BSA@Au) with the second near-infrared (NIR-II, 1000–1700 nm) fluorescence and catalase-like activity as alternative photosensitizers to realize highly efficient PDT. The bright NIR-II fluorescence of BSA@Au enables the visualization of PDT for tumor with a high signal-to-background ratio (SBR = 7.3) in 4T1 tumor-bearing mouse models. Furthermore, the catalase-like activity of BSA@Au endows its oxygen self-supplied capability, contributing to a five-fold increase in the survival period of tumor-bearing mice receiving boosted PDT treatment compared to that of the control group. Moreover, we further demonstrate that BSA@Au-based PDT strategy can be applied to treat bacterial infections. Our studies show the great potential of NIR-II BSA@Au as a novel photosensitizer for boosted PDT against cancer and bacterial infections.

Hypoxia and Alpha-Synuclein: Inextricable Link Underlying the Pathologic Progression of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease, with typical motor symptoms as the main clinical manifestations. At present, there are about 10 million patients with PD in the world, and its comorbidities and complications are numerous and incurable. Therefore, it is particularly important to explore the pathogenesis of PD and find possible therapeutic targets. Because the etiology of PD is complex, involving genes, environment, and aging, finding common factors is the key to identifying intervention targets. Hypoxia is ubiquitous in the natural environment and disease states, and it is considered to be closely related to the etiology of PD. Despite research showing that hypoxia increases the expression and aggregation of alpha-synuclein (α-syn), the most important pathogenic protein, there is still a lack of systematic studies on the role of hypoxia in α-syn pathology and PD pathogenesis. Considering that hypoxia is inextricably linked with various causes of PD, hypoxia may be a co-participant in many aspects of the PD pathologic process. In this review, we describe the risk factors for PD, and we discuss the possible role of hypoxia in inducing PD pathology by these risk factors. Furthermore, we attribute the pathological changes caused by PD etiology to oxygen uptake disorder and oxygen utilization disorder, thus emphasizing the possibility of hypoxia as a critical link in initiating or promoting α-syn pathology and PD pathogenesis. Our study provides novel insight for exploring the pathogenesis and therapeutic targets of PD.

Hypoxia signaling in human health and diseases: implications and prospects for therapeutics

Molecular oxygen (O₂) is essential for most biological reactions in mammalian cells. When the intracellular oxygen content decreases, it is called hypoxia. The process of hypoxia is linked to several biological processes, including pathogenic microbe infection, metabolic adaptation, cancer, acute and chronic diseases, and other stress responses. The mechanism underlying cells respond to oxygen changes to mediate subsequent signal response is the central question during hypoxia. Hypoxia-inducible factors (HIFs) sense hypoxia to regulate the expressions of a series of downstream genes expression, which participate in multiple processes including cell metabolism, cell growth/death, cell proliferation, glycolysis, immune response, microbe infection, tumorigenesis, and metastasis. Importantly, hypoxia signaling also interacts with other cellular pathways, such as phosphoinositide 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) signaling, nuclear factor kappa-B (NF-κB) pathway, extracellular signal-regulated kinases (ERK) signaling, and endoplasmic reticulum (ER) stress. This paper systematically reviews the mechanisms of hypoxia signaling activation, the control of HIF signaling, and the function of HIF signaling in human health and diseases. In addition, the therapeutic targets involved in HIF signaling to balance health and diseases are summarized and highlighted, which would provide novel strategies for the design and development of therapeutic drugs.

Coxiella burnetii Affects HIF1α Accumulation and HIF1α Target Gene Expression

HIF1α is an important transcription factor regulating not only cellular responses to hypoxia, but also anti-infective defense responses. We recently showed that HIF1α hampers replication of the obligate intracellular pathogen Coxiella burnetii which causes the zoonotic disease Q fever. Prior to development of chronic Q fever, it is assumed that the bacteria enter a persistent state. As HIF1α and/or hypoxia might be involved in the induction of C. burnetii persistence, we analyzed the role of HIF1α and hypoxia in the interaction of macrophages with C. burnetii to understand how the bacteria manipulate HIF1α stability and activity. We demonstrate that a C. burnetii-infection initially induces HIF1α stabilization, which decreases then over the course of an infection. This reduction depends on bacterial viability and a functional type IV secretion system (T4SS). While neither the responsible T4SS effector protein(s) nor the molecular mechanism leading to this partial HIF1α destabilization have been identified, our results demonstrate that C. burnetii influences the expression of HIF1α target genes in multiple ways. Therefore, a C. burnetii infection promotes HIF1α-mediated upregulation of several metabolic target genes; affects apoptosis-regulators towards a more pro-apoptotic signature; and under hypoxic conditions, shifts the ratio of the inflammatory genes analyzed towards a pro-inflammatory profile. Taken together, C. burnetii modulates HIF1α in a still elusive manner and alters the expression of multiple HIF1α target genes.

Structural Analysis of Mitochondrial Dynamics-From Cardiomyocytes to Osteoblasts: A Critical Review

Mitochondria play a crucial role in cell physiology and pathophysiology. In this context, mitochondrial dynamics and, subsequently, mitochondrial ultrastructure have increasingly become hot topics in modern research, with a focus on mitochondrial fission and fusion. Thus, the dynamics of mitochondria in several diseases have been intensively investigated, especially with a view to developing new promising treatment options. However, the majority of recent studies are performed in highly energy-dependent tissues, such as cardiac, hepatic, and neuronal tissues. In contrast, publications on mitochondrial dynamics from the orthopedic or trauma fields are quite rare, even if there are common cellular mechanisms in cardiovascular and bone tissue, especially regarding bone infection. The present report summarizes the spectrum of mitochondrial alterations in the cardiovascular system and compares it to the state of knowledge in the musculoskeletal system. The present paper summarizes recent knowledge regarding mitochondrial dynamics and gives a short, but not exhaustive, overview of its regulation via fission and fusion. Furthermore, the article highlights hypoxia and its accompanying increased mitochondrial fission as a possible link between cardiac ischemia and inflammatory diseases of the bone, such as osteomyelitis. This opens new innovative perspectives not only for the understanding of cellular pathomechanisms in osteomyelitis but also for potential new treatment options.

Vascular Changes and Hypoxia in Periodontal Disease as a Link to Systemic Complications

The hypoxic microenvironment caused by oral pathogens is the most important cause of the disruption of dynamic hemostasis between the oral microbiome and the immune system. Periodontal infection exacerbates the inflammatory response with increased hypoxia and causes vascular changes. The chronicity of inflammation becomes systemic as a link between oral and systemic diseases. The vascular network plays a central role in controlling infection and regulating the immune response. In this review, we focus on the local and systemic vascular network change mechanisms of periodontal inflammation and the pathological processes of inflammatory diseases. Understanding how the vascular network influences the pathology of periodontal diseases and the systemic complication associated with this pathology is essential for the discovery of both local and systemic proactive control mechanisms.

Heat shock protein 70 attenuates hypoxia‑induced apoptosis of pulmonary microvascular endothelial cells isolated from neonatal rats

Pulmonary microvascular endothelial cell (PMVEC) apoptosis is the initial stage of adult pulmonary hypertension (PH), which involves high pulmonary arterial pressure and pulmonary vascular remodeling. However, the mechanism regulating PMVEC apoptosis and its involvement in the early stages of neonatal hypoxic PH (HPH) pathogenesis are currently unclear. The present study aimed to investigate the effects of heat shock protein 70 (HSP70) on hypoxia‑induced apoptosis in PMVECs. PMVECs isolated from neonatal Sprague‑Dawley rats were transfected with lentivirus with or without HSP70, or treated with the synthetic HSP70 inhibitor N‑formyl‑3,4‑methylenedioxy‑benzylidene-g-butyrolactam under hypoxic conditions (5% O2) for 24, 48 or 72 h. PMVEC apoptosis was evaluated by performing flow cytometry and mitochondrial membrane potential (MMP) assays. The expression levels of HSP70, hypoxia‑inducible factor‑1α (HIF‑1α) and apoptosis‑associated proteins were determined by conducting reverse transcription‑quantitative PCR and western blotting. Following 24, 48 or 72 h of hypoxia, the apoptotic rates of PMVECs were significantly elevated compared with cells under normoxic conditions. The MMP was significantly reduced, whereas the mRNA and protein expression levels of HIF‑1α, cytochrome c (cyt C), caspase‑3 and HSP70 were enhanced by hypoxia compared with those under normoxic conditions. Additionally, the mRNA and protein expression levels of B‑cell lymphoma 2 (Bcl‑2) were significantly downregulated in the hypoxia group compared with those in the normoxia group. In hypoxic PMVECs, HSP70 overexpression decreased the apoptotic rate and the expression levels of cyt C, downregulated the expression levels of caspase‑3 and HIF‑1α, and increased the MMP and the expression levels of Bcl‑2. HSP70 inhibition resulted in the opposite outcomes compared with those of HSP70 overexpression. Therefore, the results of the present study suggested that HSP70 may inhibit mitochondrial pathway‑mediated apoptosis in isolated neonatal rat PMVECs in early‑stage hypoxia, which may be associated with HSP70‑mediated HIF‑1α downregulation. Overall, HSP70 may be protective against neonatal HPH through the HSP70/HIF‑1α pathway.

Glycolytic Metabolism Is Critical for the Innate Antibacterial Defense in Acute Streptococcus pneumoniae Otitis Media

Objective

Streptococcus pneumoniae (S.pn) is a common respiratory pathogen and a frequent cause of acute otitis media (AOM) in children. However, little is known about the immunometabolism during AOM. This study was to assess the presence of glucose metabolic reprogramming during AOM and its underlying mechanism affecting inflammatory response and middle ear injury.

Methods

The levels of glycolytic metabolism were evaluated by measuring the expression of glycolysis-related genes and the production of metabolites. HE stain, immunofluorescence, immunohistochemistry, enzyme-linked immunosorbent assay (ELISA) and Western blot were performed to measure the effect of glucose metabolic reprogramming on inflammatory response, pneumococcal clearance, hypoxia-inducible factor 1 alpha (HIF-1α) expression and cytokine secretion during AOM, respectively.

Results

The analysis of microarray revealed an increase of the expression of glycolysis-related genes during S.pn-induced AOM, which was verified by real-time PCR. Increased glycolysis promoted the production of IL-1β and TNF-α and facilitated the clearance of S.pn by enhancing phagocytosis and killing capability of neutrophils, but also aggravated the middle ear injury. Furthermore, these pathogenic effects could be reversed after glycolytic inhibitor 2DG treatment. Additionally, HIF-1α was observed to involve in glycolytic metabolism during AOM.

Conclusion

S.pn infection induced increased glycolysis conversion during AOM, which promoted inflammatory responses and bacterial clearance, but also aggravated tissue damage.

MicroRNA-18b-5p Downregulation Favors Mycobacterium tuberculosis Clearance in Macrophages via HIF-1α by Promoting an Inflammatory Response

The modulation of the interaction between macrophages and Mycobacterium tuberculosis (M.tb) through microRNA during M.tb infection is increasingly capturing the attention of researchers. However, the potential role of microRNA-18b-5p (miR-18b) is not elucidated yet. In this study, miR-18b was found to be downregulated in M.tb-infected macrophage cell lines (THP-1 and RAW264.7) in time- and dose-dependent manners. Furthermore, when the miR-18b mimic and inhibitor and small interfering RNA hypoxia-inducible factor 1α (si-HIF-1α) were transfected into the macrophages separately or in combination, it was found that miR-18b targeted hypoxia-inducible factor 1α (HIF-1α). During M.tb infection, the decrease in the expression of miR-18b facilitated HIF-1α expression, which led to the increased production of pro-inflammatory cytokines, such as IL-6, resulting in decreased bacterial survival in the host cells. Moreover, the phosphorylation of p38 MAPK and NF-κB p65 was activated by the miR-18b inhibitor. Our findings expand the current understanding of the M.tb-cell interaction mechanism and provide a potential target to control M.tb infection.

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.

Gefitinib Results in Robust Host-Directed Immunity Against Salmonella Infection Through Proteo-Metabolomic Reprogramming

The global rise of antibiotic-resistant strains of Salmonella has necessitated the development of alternative therapeutic strategies. Recent studies have shown that targeting host factors may provide an alternative approach for the treatment of intracellular pathogens. Host-directed therapy (HDT) modulates host cellular factors that are essential to support the replication of the intracellular pathogens. In the current study, we identified Gefitinib as a potential host directed therapeutic drug against Salmonella. Further, using the proteome analysis of Salmonella-infected macrophages, we identified EGFR, a host factor, promoting intracellular survival of Salmonella via mTOR-HIF-1α axis. Blocking of EGFR, mTOR or HIF-1α inhibits the intracellular survival of Salmonella within the macrophages and in mice. Global proteo-metabolomics profiling indicated the upregulation of host factors predominantly associated with ATP turn over, glycolysis, urea cycle, which ultimately promote the activation of EGFR-HIF1α signaling upon infection. Importantly, inhibition of EGFR and HIF1α restored both proteomics and metabolomics changes caused by Salmonella infection. Taken together, this study identifies Gefitinib as a host directed drug that holds potential translational values against Salmonella infection and might be useful for the treatment of other intracellular infections.

Influence of Hypoxia on the Epithelial-Pathogen Interactions in the Lung: Implications for Respiratory Disease

Under normal physiological conditions, the lung remains an oxygen rich environment. However, prominent regions of hypoxia are a common feature of infected and inflamed tissues and many chronic inflammatory respiratory diseases are associated with mucosal and systemic hypoxia. The airway epithelium represents a key interface with the external environment and is the first line of defense against potentially harmful agents including respiratory pathogens. The protective arsenal of the airway epithelium is provided in the form of physical barriers, and the production of an array of antimicrobial host defense molecules, proinflammatory cytokines and chemokines, in response to activation by receptors. Dysregulation of the airway epithelial innate immune response is associated with a compromised immunity and chronic inflammation of the lung. An increasing body of evidence indicates a distinct role for hypoxia in the dysfunction of the airway epithelium and in the responses of both innate immunity and of respiratory pathogens. Here we review the current evidence around the role of tissue hypoxia in modulating the host-pathogen interaction at the airway epithelium. Furthermore, we highlight the work needed to delineate the role of tissue hypoxia in the pathophysiology of chronic inflammatory lung diseases such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease in addition to novel respiratory diseases such as COVID-19. Elucidating the molecular mechanisms underlying the epithelial-pathogen interactions in the setting of hypoxia will enable better understanding of persistent infections and complex disease processes in chronic inflammatory lung diseases and may aid the identification of novel therapeutic targets and strategies.

A Comparative Transcriptome Analysis of Human and Porcine Choroid Plexus Cells in Response to Streptococcus suis Serotype 2 Infection Points to a Role of Hypoxia

Streptococcus suis (S. suis) is an important opportunistic pathogen, which can cause septicemia and meningitis in pigs and humans. Previous in vivo observations in S. suis-infected pigs revealed lesions at the choroid plexus (CP). In vitro experiments with primary porcine CP epithelial cells (PCPEC) and human CP epithelial papilloma (HIBCPP) cells demonstrated that S. suis can invade and traverse the CP epithelium, and that the CP contributes to the inflammatory response via cytokine expression. Here, next generation sequencing (RNA-seq) was used to compare global transcriptome profiles of PCPEC and HIBCPP cells challenged with S. suis serotype (ST) 2 infected in vitro, and of pigs infected in vivo. Identified differentially expressed genes (DEGs) were, amongst others, involved in inflammatory responses and hypoxia. The RNA-seq data were validated via quantitative PCR of selected DEGs. Employing Gene Set Enrichment Analysis (GSEA), 18, 28, and 21 enriched hallmark gene sets (GSs) were identified for infected HIBCPP cells, PCPEC, and in the CP of pigs suffering from S. suis ST2 meningitis, respectively, of which eight GSs overlapped between the three different sample sets. The majority of these GSs are involved in cellular signaling and pathways, immune response, and development, including inflammatory response and hypoxia. In contrast, suppressed GSs observed during in vitro and in vivo S. suis ST2 infections included those, which were involved in cellular proliferation and metabolic processes. This study suggests that similar cellular processes occur in infected human and porcine CP epithelial cells, especially in terms of inflammatory response.

Mechanism and Basis of Traditional Chinese Medicine Against Obesity: Prevention and Treatment Strategies

In the last few decades, the incidences of obesity and related metabolic disorders worldwide have increased dramatically. Major pathophysiology of obesity is termed "lipotoxicity" in modern western medicine (MWM) or "dampness-heat" in traditional Chinese medicine (TCM). "Dampness-heat" is a very common and critically important syndrome to guild clinical treatment in TCM. However, the pathogenesis of obesity in TCM is not fully clarified, especially by MWM theories compared to TCM. In this review, the mechanism underlying the action of TCM in the treatment of obesity and related metabolic disorders was thoroughly discussed, and prevention and treatment strategies were proposed accordingly. Hypoxia and inflammation caused by lipotoxicity exist in obesity and are key pathophysiological characteristics of "dampness-heat" syndrome in TCM. "Dampness-heat" is prevalent in chronic low-grade systemic inflammation, prone to insulin resistance (IR), and causes variant metabolic disorders. In particular, the MWM theories of hypoxia and inflammation were applied to explain the "dampness-heat" syndrome of TCM, and we summarized and proposed the pathological path of obesity: lipotoxicity, hypoxia or chronic low-grade inflammation, IR, and metabolic disorders. This provides significant enrichment to the scientific connotation of TCM theories and promotes the modernization of TCM.

Hypoxia/HIF Modulates Immune Responses

Oxygen availability varies throughout the human body in health and disease. Under physiological conditions, oxygen availability drops from the lungs over the blood stream towards the different tissues into the cells and the mitochondrial cavities leading to physiological low oxygen conditions or physiological hypoxia in all organs including primary lymphoid organs. Moreover, immune cells travel throughout the body searching for damaged cells and foreign antigens facing a variety of oxygen levels. Consequently, physiological hypoxia impacts immune cell function finally controlling innate and adaptive immune response mainly by transcriptional regulation via hypoxia-inducible factors (HIFs). Under pathophysiological conditions such as found in inflammation, injury, infection, ischemia and cancer, severe hypoxia can alter immune cells leading to dysfunctional immune response finally leading to tissue damage, cancer progression and autoimmunity. Here we summarize the effects of physiological and pathophysiological hypoxia on innate and adaptive immune activity, we provide an overview on the control of immune response by cellular hypoxia-induced pathways with focus on the role of HIFs and discuss the opportunity to target hypoxia-sensitive pathways for the treatment of cancer and autoimmunity.

Hypoxia-inducible factor-1α involved in macrophage regulation in ayu (Plecoglossus altivelis) under hypoxia

Hypoxia-inducible factor-1α (HIF-1α) plays a critical role in immune and inflammatory responses and is important in controlling a variety of processes in monocytes and macrophages. However, the role of HIF-1α in the teleost immune system remains less known. In this study, we cloned the cDNA sequence of HIF-1α from the ayu (Plecoglossus altivelis, PaHIF-1α). Sequence and phylogenetic tree analysis showed that PaHIF-1α clustered within the fish HIF-1α tree and was closely related to that of Northern pike (Esox lucius). PaHIF-1α was expressed in all tested tissues and expression increased in liver, head kidney, and body kidney upon Vibrio anguillarum infection. PaHIF-1α was found to regulate the expression of cytokines in ayu monocytes/macrophages (MO/MФ). PaHIF-1α mediated hypoxia-induced enhancement of MO/MФ phagocytic and bactericidal activities to enhance host defenses. Compared with the control, intermittent hypoxia further increased the expression of PaHIF-1α mRNA, improved the survival rate, and reduced the bacterial load of V. anguillarum-infected ayu. Therefore, PaHIF-1α may play a predominant role in the modulation of ayu MO/MФ function.

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.

Differences in Tolerance to Hypoxia: Physiological, Biochemical, and Molecular-Biological Characteristics

Hypoxia plays an important role in the development of many infectious, inflammatory, and tumor diseases. The predisposition to such disorders is mostly provided by differences in basic tolerance to oxygen deficiency, which we discuss in this review. Except the direct exposure of different-severity hypoxia in decompression chambers or in highland conditions, there are no alternative methods for determining organism tolerance. Due to the variability of the detection methods, differences in many parameters between tolerant and susceptible organisms are still not well-characterized, but some of them can serve as biomarkers of susceptibility to hypoxia. At the moment, several potential biomarkers in conditions after hypoxic exposure have been identified both in experimental animals and humans. The main potential biomarkers are Hypoxia-Inducible Factor (HIF)-1, Heat-Shock Protein 70 (HSP70), and NO. Due to the different mechanisms of various high-altitude diseases, biomarkers may not be highly specific and universal. Therefore, it is extremely important to conduct research on hypoxia susceptibility biomarkers. Moreover, it is important to develop a method for the evaluation of organisms' basic hypoxia tolerance without the necessity of any oxygen deficiency exposure. This can contribute to new personalized medicine approaches' development for diagnostics and the treatment of inflammatory and tumor diseases, taking into account hypoxia tolerance differences.