Prolyl Hydroxylase Domain-2 Protein Regulates Lipopolysaccharide-Induced Vascular Inflammation

Therapeutic targeting of hypoxia inducible factor in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by bilateral chest infiltration and acute hypoxic respiratory failure. ARDS carries significant morbidity and mortality despite advancements in medical management, calling for the development of novel therapeutic targets. Hypoxia-inducible factor (HIF) is a heterodimeric protein involved in various essential pathways, including metabolic reprogramming, immune modulation, angiogenesis and cell cycle regulation. HIF is routinely degraded in homeostasis conditions via the prolyl hydroxylase domain/von Hippel-Lindau protein pathway. However, HIF is stabilized in ARDS via various mechanisms (oxygen-dependent and independent) as an endogenous protective pathway and plays multifaceted roles in different cell populations. This review focuses on the functional role of HIF and its target genes during ARDS, as well as how HIF has evolved as a therapeutic target in current medical management.

PHD1-3 oxygen sensors in vivo-lessons learned from gene deletions

Oxygen sensors enable cells to adapt to limited oxygen availability (hypoxia), affecting various cellular and tissue responses. Prolyl-4-hydroxylase domain 1-3 (PHD1-3; also called Egln1-3, HIF-P4H 1-3, HIF-PH 1-3) proteins belong to the Fe2+- and 2-oxoglutarate-dependent dioxygenase superfamily and utilise molecular oxygen (O2) alongside 2-oxoglutarate as co-substrate to hydroxylate two proline residues of α subunits of the dimeric hypoxia inducible factor (HIF) transcription factor. PHD1-3-mediated hydroxylation of HIF-α leads to its degradation and inactivation. Recently, various PHD inhibitors (PHI) have entered the clinics for treatment of renal anaemia. Pre-clinical analyses indicate that PHI treatment may also be beneficial in numerous other hypoxia-associated diseases. Nonetheless, the underlying molecular mechanisms of the observed protective effects of PHIs are only partly understood, currently hindering their translation into the clinics. Moreover, the PHI-mediated increase of Epo levels is not beneficial in all hypoxia-associated diseases and PHD-selective inhibition may be advantageous. Here, we summarise the current knowledge about the relevance and function of each of the three PHD isoforms in vivo, based on the deletion or RNA interference-mediated knockdown of each single corresponding gene in rodents. This information is crucial for our understanding of the physiological relevance and function of the PHDs as well as for elucidating their individual impact on hypoxia-associated diseases. Furthermore, this knowledge highlights which diseases may best be targeted by PHD isoform-selective inhibitors in case such pharmacologic substances become available.

A Novel ARNT-Dependent HIF-2α Signaling as a Protective Mechanism for Cardiac Microvascular Barrier Integrity and Heart Function Post-Myocardial Infarction

Myocardial infarction (MI) significantly compromises the integrity of the cardiac microvascular endothelial barrier, leading to enhanced leakage and inflammation that contribute to the progression of heart failure. While HIF2α is highly expressed in cardiac endothelial cells (ECs) under hypoxic conditions, its role in regulating microvascular endothelial barrier function during MI is not well understood. In this study, we utilized mice with a cardiac-specific deletion of HIF2α, generated through an inducible Cre (Cdh5Cre-ERT2) recombinase system. These mice exhibited no apparent phenotype under normal conditions. However, following left anterior descending (LAD) artery ligation-induced MI, they showed increased mortality associated with enhanced cardiac vascular leakage, inflammation, worsened cardiac function, and exacerbated heart remodeling. These outcomes suggest a protective role for endothelial HIF2α in response to cardiac ischemia. Parallel investigations in human cardiac microvascular endothelial cells (CMVECs) revealed that loss of ecHif2α led to diminished endothelial barrier function, characterized by reduced tight-junction protein levels and increased cell death, along with elevated expression of IL6 and other inflammatory markers. These effects were substantially reversed by overexpressing ARNT, a critical dimerization partner for HIF2α during hypoxia. Additionally, ARNT deletion also led to increased CMVEC permeability. Interestingly, ARNT, rather than HIF2α itself, directly binds to the IL6 promoter to suppress IL6 expression. Our findings demonstrate the critical role of endothelial HIF2α in response to MI and identify the HIF2α/ARNT axis as a transcriptional repressor, offering novel insights for developing therapeutic strategies against heart failure following MI.

Astragaloside IV restrains pyroptosis and fibrotic development of pulmonary artery smooth muscle cells to ameliorate pulmonary artery hypertension through the PHD2/HIF1α signaling pathway

BACKGROUND

Astragaloside (AS)-IV, extracted from traditional Chinese medicine Astragalus mongholicus, has been widely used in the anti-inflammatory treatment for cardiovascular disease. However, the mechanism by which AS-IV affects pulmonary artery hypertension (PAH) development remains largely unknown.

METHODS

Monocrotaline (MCT)-induced PAH model rats were administered with AS-IV, and hematoxylin-eosin staining and Masson staining were performed to evaluate the histological change in pulmonary tissues of rats. Pulmonary artery smooth muscle cells (PASMCs) were treated by hypoxia and AS-IV. Pyroptosis and fibrosis were assessed by immunofluorescence, western blot and enzyme-linked immunosorbent assay.

RESULTS

AS-IV treatment alleviated pulmonary artery structural remodeling and pulmonary hypertension progression induced by MCT in rats. AS-IV suppressed the expression of pyroptosis-related markers, the release of pro-inflammatory cytokine interleukin (IL)-1β and IL-18 and fibrosis development in pulmonary tissues of PAH rats and in hypoxic PAMSCs. Interestingly, the expression of prolyl-4-hydroxylase 2 (PHD2) was restored by AS-IV administration in PAH model in vivo and in vitro, while hypoxia inducible factor 1α (HIF1α) was restrained by AS-IV. Mechanistically, silencing PHD2 reversed the inhibitory effect of AS-IV on pyroptosis, fibrosis trend and pyroptotic necrosis in hypoxia-cultured PASMCs, while the HIF1α inhibitor could prevent these PAH-like phenomena.

CONCLUSION

Collectively, AS-IV elevates PHD2 expression to alleviate pyroptosis and fibrosis development during PAH through downregulating HIF1α. These findings may provide a better understanding of AS-IV preventing PAH, and the PHD2/HIF1α axis may be a potential anti-pyroptosis target during PAH.

Matrine Attenuates Lung Injury by Modulating Macrophage Polarization and Suppressing Apoptosis

INTRODUCTION

Persistent lung inflammation is a characteristic of sepsis-induced lung injury. Matrine, the active ingredient from Sophora flavescens, has exhibited anti-inflammatory activities. This study investigated the effects of prophylactic administration of matrine on macrophage polarization, apoptosis, and tissue injury in a cecal ligation and puncture (CLP)-induced murine lung injury model.

METHODS

Mice were randomly allocated into four groups: Sham, CLP, Sham + Matrine, and CLP + Matrine. Lung tissues were collected at 24 h post-CLP. Histopathology and immunofluorescence analysis were performed to evaluate lung injury and macrophage infiltration in the lung, respectively. Caspase-3 activities, TUNEL staining, and anti-apoptotic proteins were examined to assess apoptosis. To determine the mechanism of action of matrine, protein levels of Sirtuin 1 (SIRT1), nuclear factor κB (NF-κB), p53 and the messenger RNA levels of p53-mediated proapoptotic genes were examined to elucidate the associated signaling pathways.

RESULTS

Histopathological evaluation showed that matrine prophylaxis attenuated sepsis-induced lung injury. Matrine prophylaxis attenuated sepsis-induced infiltration of the total population of macrophages in the lung. Matrine inhibited M1 macrophage infiltration, but increased M2 macrophage infiltration, thus resulting in a decrease in the proportion of M1 to M2 macrophages in septic lung. Sepsis-induced lung injury was associated with apoptotic cell death as evidenced by increases in caspase-3 activity, TUNEL-positive cells, and decreases in antiapoptotic proteins, all of which were reversed by matrine prophylaxis. Matrine restored sepsis-induced downregulation of SIRT1 and deacetylation of NF-κB p65 subunit and p53, thus inactivating NF-κB pathway and suppressing p53-induced proapoptotic pathway in septic lung.

CONCLUSIONS

In summary, this study demonstrated that matrine exhibited pro-M2 macrophage polarization and antiapoptotic effects in sepsis-induced lung injury, which might be, at least partly, due to the modulation of SIRT1/NF-κB and SIRT1/p53 pathways.

Tissue Engineering as a Promising Treatment for Glottic Insufficiency: A Review on Biomolecules and Cell-Laden Hydrogel

Glottic insufficiency is widespread in the elderly population and occurs as a result of secondary damage or systemic disease. Tissue engineering is a viable treatment for glottic insufficiency since it aims to restore damaged nerve tissue and revitalize aging muscle. After injection into the biological system, injectable biomaterial delivers cost- and time-effectiveness while acting as a protective shield for cells and biomolecules. This article focuses on injectable biomaterials that transport cells and biomolecules in regenerated tissue, particularly adipose, muscle, and nerve tissue. We propose Wharton's Jelly mesenchymal stem cells (WJMSCs), induced pluripotent stem cells (IP-SCs), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), insulin growth factor-1 (IGF-1) and extracellular vesicle (EV) as potential cells and macromolecules to be included into biomaterials, with some particular testing to support them as a promising translational medicine for vocal fold regeneration.

Personalized medicine using omics approaches in acute respiratory distress syndrome to identify biological phenotypes

In the last decade, research on acute respiratory distress syndrome (ARDS) has made considerable progress. However, ARDS remains a leading cause of mortality in the intensive care unit. ARDS presents distinct subphenotypes with different clinical and biological features. The pathophysiologic mechanisms of ARDS may contribute to the biological variability and partially explain why some pharmacologic therapies for ARDS have failed to improve patient outcomes. Therefore, identifying ARDS variability and heterogeneity might be a key strategy for finding effective treatments. Research involving studies on biomarkers and genomic, metabolomic, and proteomic technologies is increasing. These new approaches, which are dedicated to the identification and quantitative analysis of components from biological matrixes, may help differentiate between different types of damage and predict clinical outcome and risk. Omics technologies offer a new opportunity for the development of diagnostic tools and personalized therapy in ARDS. This narrative review assesses recent evidence regarding genomics, proteomics, and metabolomics in ARDS research.

Cre toxicity in mouse models of cardiovascular physiology and disease

The Cre-LoxP system provides a widely used method for studying gene requirements in the mouse as the main mammalian genetic model organism. To define the molecular and cellular mechanisms that underlie cardiovascular development, function and disease, various mouse strains have been engineered that allow Cre-LoxP-mediated gene targeting within specific cell types of the cardiovascular system. Despite the usefulness of this system, evidence is accumulating that Cre activity can have toxic effects in cells, independently of its ability to recombine pairs of engineered LoxP sites in target genes. Here, we have gathered published evidence for Cre toxicity in cells and tissues relevant to cardiovascular biology and provide an overview of mechanisms proposed to underlie Cre toxicity. Based on this knowledge, we propose that each study utilising the Cre-LoxP system to investigate gene function in the cardiovascular system should incorporate appropriate controls to account for Cre toxicity.

Novel biomarkers for acute respiratory distress syndrome: genetics, epigenetics and transcriptomics

Acute respiratory distress syndrome (ARDS) can be induced by multiple clinical factors, including sepsis, acute pancreatitis, trauma, intestinal ischemia/reperfusion and burns. However, these factors alone may poorly explain the risk and outcomes of ARDS. Emerging evidence suggests that genomic-based or transcriptomic-based biomarkers may hold the promise to establish predictive or prognostic stratification methods for ARDS, and also to help in developing novel therapeutic targets for ARDS. Notably, genetic/epigenetic variations correlated with susceptibility and prognosis of ARDS and circulating microRNAs have emerged as potential biomarkers for diagnosis or prognosis of ARDS. Although limited by sample size, ethnicity and phenotypic heterogeneity, ongoing genetic/transcriptomic research contributes to the characterization of novel biomarkers and ultimately helps to develop innovative therapeutics for ARDS patients.

Hypoxia-Inducible Factor Signaling in Inflammatory Lung Injury and Repair

Inflammatory lung injury is characterized by lung endothelial cell (LEC) death, alveolar epithelial cell (AEC) death, LEC-LEC junction weakening, and leukocyte infiltration, which together disrupt nutrient and oxygen transport. Subsequently, lung vascular repair is characterized by LEC and AEC regeneration and LEC-LEC junction re-annealing, which restores nutrient and oxygen delivery to the injured tissue. Pulmonary hypoxia is a characteristic feature of several inflammatory lung conditions, including acute lung injury (ALI), acute respiratory distress syndrome (ARDS), and severe coronavirus disease 2019 (COVID-19). The vascular response to hypoxia is controlled primarily by the hypoxia-inducible transcription factors (HIFs) 1 and 2. These transcription factors control the expression of a wide variety of target genes, which in turn mediate key pathophysiological processes including cell survival, differentiation, migration, and proliferation. HIF signaling in pulmonary cell types such as LECs and AECs, as well as infiltrating leukocytes, tightly regulates inflammatory lung injury and repair, in a manner that is dependent upon HIF isoform, cell type, and injury stimulus. The aim of this review is to describe the HIF-dependent regulation of inflammatory lung injury and vascular repair. The review will also discuss potential areas for future study and highlight putative targets for inflammatory lung conditions such as ALI/ARDS and severe COVID-19. In the development of HIF-targeted therapies to reduce inflammatory lung injury and/or enhance pulmonary vascular repair, it will be vital to consider HIF isoform- and cell-specificity, off-target side-effects, and the timing and delivery strategy of the therapeutic intervention.

Reproducibility of developmental neuroplasticity in in vitro brain tissue models

The current prevalence of neurodevelopmental, neurodegenerative diseases, stroke and brain injury stimulates studies aimed to identify new molecular targets, to select the drug candidates, to complete the whole set of preclinical and clinical trials, and to implement new drugs into routine neurological practice. Establishment of protocols based on microfluidics, blood-brain barrier- or neurovascular unit-on-chip, and microphysiological systems allowed improving the barrier characteristics and analyzing the regulation of local microcirculation, angiogenesis, and neurogenesis. Reconstruction of key mechanisms of brain development and even some aspects of experience-driven brain plasticity would be helpful in the establishment of brain in vitro models with the highest degree of reliability. Activity, metabolic status and expression pattern of cells within the models can be effectively assessed with the protocols of system biology, cell imaging, and functional cell analysis. The next generation of in vitro models should demonstrate high scalability, 3D or 4D complexity, possibility to be combined with other tissues or cell types within the microphysiological systems, compatibility with bio-inks or extracellular matrix-like materials, achievement of adequate vascularization, patient-specific characteristics, and opportunity to provide high-content screening. In this review, we will focus on currently available and prospective brain tissue in vitro models suitable for experimental and preclinical studies with the special focus on models enabling 4D reconstruction of brain tissue for the assessment of brain development, brain plasticity, and drug kinetics.

Hypoxia response and acute lung and kidney injury: possible implications for therapy of COVID-19

Coronavirus disease 2019 (COVID-19) is a pandemic of unprecedented severity affecting millions of people around the world and causing several hundred thousands of deaths. The presentation of the disease ranges from asymptomatic manifestations through to acute respiratory distress syndrome with the necessity of mechanical ventilation. Cytokine storm and maladaptive responses to the viral spread in the body could be responsible for the severity of disease. Many patients develop acute kidney injury (AKI) during the course of their disease, especially in more severe cases. Many factors could cause kidney damage during infection from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. It is still unclear whether direct viral damage or the overexpression of cytokines and inflammatory factors are preeminent. According to autoptic studies, in most of the cases, AKI is due proximal tubular damage. However, cases of collapsing focal segmental glomerulosclerosis were reported as well in the absence of signs of direct viral infection of the kidney. Considering that severe hypoxia is a hallmark of severe SARS-CoV-2 infection, the involvement of the hypoxia-inducible factor (HIF) system is very likely, possibly influencing the inflammatory response and outcome in both the lungs and kidneys. Several bodies of evidence have shown a possible role of the HIF pathway during AKI in various kidney disease models. Similar observations were made in the setting of acute lung injury. In both organs, HIF activation by means of inhibition of the prolyl-hydroxylases domain (PHD) could be protective. Considering these promising experimental data, we hypothesize that PHD inhibitors could be considered as a possible new therapy against severe SARS-CoV-2 infection.

Macrophage HIF-1α mediates obesity-related adipose tissue dysfunction via interleukin-1 receptor-associated kinase M

Hypoxia leading to stabilization of hypoxia-inducible factor 1α (HIF-1α) serves as an early upstream initiator for adipose tissue (AT) dysfunction. Monocyte-derived macrophage infiltration in AT contributes to inflammation, fibrosis and obesity-related metabolic dysfunction. It was previously reported that myeloid cell-specific deletion of Hif-1α protected against high-fat diet (HFD)-induced AT dysfunction. Prolyl hydroxylases (PHDs) are key regulators of HIF-1α. We examined the effects of myeloid cell-specific upregulation and stabilization of Hif-1α via deletion of prolyl-hydroxylase 2 (Phd2) and whether interleukin-1 receptor associated kinase-M (Irak-M), a known downstream target of Hif-1α, contributes to Hif-1α-induced AT dysfunction. Our data show that with HFD, Hif-1α and Irak-M expressions were increased in the AT macrophages of Phd2^flox/flox/LysMcre mice compared with LysMcre mice. With HFD, Phd2^flox/flox/LysMcre mice exhibited increased AT inflammation, fibrosis, and systemic insulin resistance compared with control mice. Furthermore, Phd2^flox/flox/LysMcre mice bone marrow-derived macrophages exposed to hypoxia in vitro also had increased expressions of both Hif-1α and Irak-M. In wild-type mice, HFD induced upregulation of both HIF-1a and Irak-M in adipose tissue. Despite equivalent expression of Hif-1α compared with wild-type mice, globally-deficient Irak-M mice fed a HFD exhibited less macrophage infiltration, decreased inflammation and fibrosis and improved glucose tolerance. Global Irak-M deficiency was associated with an alternatively-activated macrophage phenotype in the AT after HFD. Together, these data show for the first time that an Irak-M-dependent mechanism likely mediates obesity-related AT dysfunction in conjunction with Hif-1α upregulation.

Inhibition of Endothelial PHD2 Suppresses Post-Ischemic Kidney Inflammation through Hypoxia-Inducible Factor-1

BACKGROUND

Prolyl-4-hydroxylase domain-containing proteins 1-3 (PHD1 to PHD3) regulate the activity of the hypoxia-inducible factors (HIFs) HIF-1 and HIF-2, transcription factors that are key regulators of hypoxic vascular responses. We previously reported that deficiency of endothelial HIF-2 exacerbated renal ischemia-reperfusion injury, whereas inactivation of endothelial PHD2, the main oxygen sensor, provided renoprotection. Nevertheless, the molecular mechanisms by which endothelial PHD2 dictates AKI outcomes remain undefined.

METHODS

To investigate the function of the endothelial PHD2/HIF axis in ischemic AKI, we examined the effects of endothelial-specific ablation of PHD2 in a mouse model of renal ischemia-reperfusion injury. We also interrogated the contribution of each HIF isoform by concurrent endothelial deletion of both PHD2 and HIF-1 or both PHD2 and HIF-2.

RESULTS

Endothelial deletion of Phd2 preserved kidney function and limited transition to CKD. Mechanistically, we found that endothelial Phd2 ablation protected against renal ischemia-reperfusion injury by suppressing the expression of proinflammatory genes and recruitment of inflammatory cells in a manner that was dependent on HIF-1 but not HIF-2. Persistence of renoprotective responses after acute inducible endothelial-specific loss of Phd2 in adult mice ruled out a requirement for PHD2 signaling in hematopoietic cells. Although Phd2 inhibition was not sufficient to induce detectable HIF activity in the kidney endothelium, in vitro experiments implicated a humoral factor in the anti-inflammatory effects generated by endothelial PHD2/HIF-1 signaling.

CONCLUSIONS

Our findings suggest that activation of endothelial HIF-1 signaling through PHD2 inhibition may offer a novel therapeutic approach against ischemic AKI.

PHD2 exerts anti-cancer and anti-inflammatory effects in colon cancer xenografts mice via attenuating NF-κB activity

Recent studies suggested that prolyl hydroxylase 2 (PHD2) functions as an important regulator in vascular inflammation and Streptococcus pneumonia infection. However, whether PHD2 contributed to tumor progression prompted by intratumoral inflammation remains elusive. In this study, the effects of PHD2 in colon cancer were evaluated, and the underlying molecular mechanisms were investigated. The results showed that overexpressing PHD2 exerted proliferative and migratory inhibition in colon cancer cells. The expression of cell cycle and epithelial-mesenchymal transition (EMT)-associated proteins were changed: CyclinD1, CDK4, N-cadherin, and Vimentin were down-regulated, while E-cadherin was up-regulated in PHD2-overexpressing colon cancer cells. Moreover, in colon cancer xenograft mice, PHD2 overexpression suppressed tumor growth accompanied by decreased Ki67 expression. Importantly, we further demonstrated that overexpressing PHD2 attenuated inflammation in colon cancer xenograft mice through weakening accumulation of myeloid-derived suppressor cells (MDSCs) and M2-like tumor-associated macrophages (TAMs), as well as secretions of pro-inflammatory cytokines including G-CSF, TNF-α, IL-6, IL-8, IL-1β, and IL-4. Mechanistically, PHD2 overexpression obviously suppressed NF-κB activity through decreasing phosphorylated IκB-α while increasing cytoplasmic NF-κB p65 levels in colon cancer. Our findings support the anti-cancer and anti-inflammatory roles of PHD2 and offer a preclinical proof of tumor progression regulated by cancer cells and inflammation.