Pharmacological HIF-1 stabilization promotes intestinal epithelial healing through regulation of α-integrin expression and function

Crosstalk between hypoxia-inducible factor-1α and short-chain fatty acids in inflammatory bowel disease: key clues toward unraveling the mystery

The human intestinal tract constitutes a complex ecosystem, made up of countless gut microbiota, metabolites, and immune cells, with hypoxia being a fundamental environmental characteristic of this ecology. Under normal physiological conditions, a delicate balance exists among these complex "residents", with disruptions potentially leading to inflammatory bowel disease (IBD). The core pathology of IBD features a disrupted intestinal epithelial barrier, alongside evident immune and microecological disturbances. Central to these interconnected networks is hypoxia-inducible factor-1α (HIF-1α), which is a key regulator in gut cells for adapting to hypoxic conditions and maintaining gut homeostasis. Short-chain fatty acids (SCFAs), as pivotal gut metabolites, serve as vital mediators between the host and microbiota, and significantly influence intestinal ecosystem. Recent years have seen a surge in research on the roles and therapeutic potential of HIF-1α and SCFAs in IBD independently, yet reviews on HIF-1α-mediated SCFAs regulation of IBD under hypoxic conditions are scarce. This article summarizes evidence of the interplay and regulatory relationship between SCFAs and HIF-1α in IBD, pivotal for elucidating the disease's pathogenesis and offering promising therapeutic strategies.

Hypoxia-Induced Signaling in Gut and Liver Pathobiology

Oxygen (O2) is essential for cellular metabolism and biochemical reactions. When the demand for O2 exceeds the supply, hypoxia occurs. Hypoxia-inducible factors (HIFs) are essential to activate adaptive and survival responses following hypoxic stress. In the gut (intestines) and liver, the presence of oxygen gradients or physiologic hypoxia is necessary to maintain normal homeostasis. While physiologic hypoxia is beneficial and aids in normal functions, pathological hypoxia is harmful as it exacerbates inflammatory responses and tissue dysfunction and is a hallmark of many cancers. In this review, we discuss the role of gut and liver hypoxia-induced signaling, primarily focusing on HIFs, in the physiology and pathobiology of gut and liver diseases. Additionally, we examine the function of HIFs in various cell types during gut and liver diseases, beyond intestinal epithelial and hepatocyte HIFs. This review highlights the importance of understanding hypoxia-induced signaling in the pathogenesis of gut and liver diseases and emphasizes the potential of HIFs as therapeutic targets.

Integrated bioinformatics and network pharmacology identifying the mechanisms and molecular targets of Guipi Decoction for treatment of comorbidity with depression and gastrointestinal disorders

BACKGROUND

Guipi decoction (GPD) not only improves gastrointestinal (GI) function, but also depressive mood. The bioinformatics study aimed to reveal potential crosstalk genes and related pathways between depression and GI disorders. A network pharmacology approach was used to explore the molecular mechanisms and potential targets of GPD for the simultaneous treatment of depression comorbid GI disorders.

METHODS

Differentially expressed genes (DEGs) of major depressive disorder (MDD) were identified based on GSE98793 and GSE19738, and GI disorders-related genes were screened from the GeneCards database. Overlapping genes between MDD and GI disorders were obtained to identify potential crosstalk genes. Protein-protein interaction (PPI) network was constructed to screen for hub genes, signature genes were identified by LASSO regression analysis, and single sample gene set enrichment analysis (ssGSEA) was performed to analyze immune cell infiltration. In addition, based on the Traditional Chinese Medicine Systems Pharmacology (TCMSP) database, we screened the active ingredients and targets of GPD and identified the intersection targets of GPD with MDD and GI disorder-related genes, respectively. A "component-target" network was constructed using Cytoscape, the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed.

RESULTS

The MDD-corrected dataset contained 2619 DEGs, and a total of 109 crosstalk genes were obtained. 14 hub genes were screened, namely SOX2, CRP, ACE, LEP, SHH, CDH2, CD34, TNF, EGF, BDNF, FN1, IL10, PPARG, and KIT. These genes were identified by LASSO regression analysis for 3 signature genes, including TNF, EGF, and IL10. Gamma.delta.T.cell was significantly positively correlated with all three signature genes, while Central.memory.CD4.T.cell and Central.memory.CD8.T.cell were significantly negatively correlated with EGF and TNF. GPD contained 134 active ingredients and 248 targets, with 41 and 87 relevant targets for the treatment of depression and GI disorders, respectively. EGF, PPARG, IL10 and CRP overlap with the hub genes of the disease.

CONCLUSION

We found that GPD may regulate inflammatory and oxidative stress responses through EGF, PPARG, IL10 and CRP targets, and then be involved in the treatment of both depression and GI disorders.

Genome-wide characterization of integrin (ITG) gene family and their expression profiling in half-smooth tongue sole (Cynoglossus semilaevis) upon Vibrio anguillarum infection

Integrins (ITGs) are transmembrane heterodimer receptors with ITGα subunit and ITGβ subunit, participating in various physiological processes, including immunity. At present, systematic research on ITGs in teleost is scarce, especially in half-smooth tongue sole (Cynoglossus semilaevis). In this study, a set of 28 ITG genes in half-smooth tongue sole have been identified and characterized. The phylogenetic analysis showed that ITGα and ITGβ subunits were respectively classified into five and two clusters, consistent with previous studies. The selection pressure analysis indicated that most of ITG genes were under purifying selection, except for ITGα11b and ITGαL with positive selection. The expression profiles of eight selected ITG genes, including ITGα1, ITGα5, ITGα8, ITGα11, ITGβ1, ITGβ2, ITGβ3, and ITGβ8, were analyzed in healthy tissues and after infection with Vibrio anguillarum, revealed their implications in immune response. The study provided a comprehensive characterization and expression analysis of ITG genes in half-smooth tongue sole, setting a solid foundation for further functional studies and promising potential in disease control.

Integrin β1 is a key determinant of the expression of angiotensin-converting enzyme 2 (ACE2) in the kidney epithelial cells

The expression of the angiotensin-converting enzyme 2 (ACE2) is altered in multiple chronic kidney diseases like hypertension and renal fibrosis, where the signaling from the basal membrane proteins is critical for the development and progression of the various pathologies. Integrins are heterodimeric cell surface receptors that have important roles in the progression of these chronic kidney diseases by altering various cell signaling pathways in response to changes in the basement membrane proteins. It is unclear whether integrin or integrin-mediated signaling affects the ACE2 expression in the kidney. The current study tests the hypothesis that integrin β1 regulates the expression of ACE2 in kidney epithelial cells. The role of integrin β1 in ACE2 expression in renal epithelial cells was investigated by shRNA-mediated knockdown and pharmacological inhibition. In vivo studies were carried out using epithelial cell-specific deletion of integrin β1 in the kidneys. Deletion of integrin β1 from the mouse renal epithelial cells reduced the expression of ACE2 in the kidney. Furthermore, the downregulation of integrin β1 using shRNA decreased ACE2 expression in human renal epithelial cells. ACE2 expression levels were also decreased in renal epithelial cells and cancer cells when treated with an integrin α2β1 antagonist, BTT 3033. SARS-CoV-2 viral entry to human renal epithelial cells and cancer cells was also inhibited by BTT 3033. This study demonstrates that integrin β1 positively regulates the expression of ACE2, which is required for the entry of SARS-CoV-2 into kidney cells.

Personalized redox medicine in inflammatory bowel diseases: an emerging role for HIF-1α and NRF2 as therapeutic targets

Inflammatory bowel diseases (IBD), encompassing Crohn's disease (CD) and ulcerative colitis (UC), are intimately associated with inflammation and overproduction of reactive oxygen species (ROS). Temporal and inter-individual variabilities in disease activity and response to therapy pose significant challenges to diagnosis and patient care. Discovery and validation of truly integrative biomarkers would benefit from embracing redox metabolomics approaches with prioritization of central regulatory hubs. We here make a case for applying a personalized redox medicine approach that aims to selectively inhibit pathological overproduction and/or altered expression of specific enzymatic sources of ROS without compromising physiological function. To this end, improved 'clinical-omics integration' may help to better understand which particular redox signaling pathways are disrupted in what patient. Pharmacological interventions capable of activating endogenous antioxidant defense systems may represent viable therapeutic options to restore local/systemic redox status, with HIF-1α and NRF2 holding particular promise in this context. Achieving the implementation of clinically meaningful mechanism-based biomarkers requires development of easy-to-use, robust and cost-effective tools for secure diagnosis and monitoring of treatment efficacy. Ultimately, matching redox-directed pharmacological interventions to individual patient phenotypes using predictive biomarkers may offer new opportunities to break the therapeutic ceiling in IBD.

Hypoxia inducible factor prolyl hydroxylases in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic disease that is characterized by intestinal inflammation. Epithelial damage and loss of intestinal barrier function are believed to be the hallmark pathologies of the disease. In IBD, the resident and infiltrating immune cells consume much oxygen, rendering the inflamed intestinal mucosa hypoxic. In hypoxia, the hypoxia-inducible factor (HIF) is induced to cope with the lack of oxygen and protect intestinal barrier. Protein stability of HIF is tightly controlled by prolyl hydroxylases (PHDs). Stabilization of HIF through inhibition of PHDs is appearing as a new strategy of IBD treatment. Studies have shown that PHD-targeting is beneficial to the treatment of IBD. In this Review, we summarize the current understanding of the role of HIF and PHDs in IBD and discuss the therapeutic potential of targeting PHD-HIF pathway for IBD treatment.

Hyperbaric Oxygen Therapy and Tissue Regeneration: A Literature Survey

By addressing the mechanisms involved in transcription, signaling, stress reaction, apoptosis and cell-death, cellular structure and cell-to-cell contacts, adhesion, migration as well as inflammation; HBO upregulates processes involved in repair while mechanisms perpetuating tissue damage are downregulated. Many experimental and clinical studies, respectively, cover wound healing, regeneration of neural tissue, of bone and cartilage, muscle, and cardiac tissue as well as intestinal barrier function. Following acute injury or in chronic healing problems HBO modulates proteins or molecules involved in inflammation, apoptosis, cell growth, neuro- and angiogenesis, scaffolding, perfusion, vascularization, and stem-cell mobilization, initiating repair by a variety of mechanisms, some of them based on the modulation of micro-RNAs. HBO affects the oxidative stress response via nuclear factor erythroid 2-related factor 2 (Nrf2) or c-Jun N-terminal peptide and downregulates inflammation by the modulation of high-mobility group protein B1 (HMGB-1), toll-like receptor 4 and 2 (TLR-4, TLR-2), nuclear factor kappa-B (NFκB), hypoxia-inducible factor (HIF-1α) and nitric oxide (NO•). HBO enhances stem-cell homeostasis via Wnt glycoproteins and mammalian target of rapamycin (mTOR) and improves cell repair, growth, and differentiation via the two latter but also by modulation of extracellular-signal regulated kinases (ERK) and the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT) pathway. The HBO-induced downregulation of matrix metalloproteinases-2 and 9 (MMP-2/-9), rho-associated protein kinase (ROCK) and integrins improve healing by tissue remodeling. Interestingly, the action of HBO on single effector proteins or molecules may involve both up- or downregulation, respectively, depending on their initial level. This probably mirrors a generally stabilizing potential of HBO that tends to restore the physiological balance rather than enhancing or counteracting single mechanisms.

Editorial of the Special Issue "Dietary Fiber and Inflammatory Bowel Disease"

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is a chronic disease of the gastrointestinal (GI) tract; its burden has significantly increased in recent decades, with 6.8 million cases of IBD reported in 2017 according to the Global Burden of Disease study [...].

Neutrophil-Epithelial Crosstalk During Intestinal Inflammation

Neutrophils are the most abundant leukocyte population in the human circulatory system and are rapidly recruited to sites of inflammation. Neutrophils play a multifaceted role in intestinal inflammation, as they contribute to the elimination of invading pathogens. Recently, their role in epithelial restitution has been widely recognized; however, they are also associated with bystander tissue damage. The intestinal epithelium provides a physical barrier to prevent direct contact of luminal contents with subepithelial tissues, which is extremely important for the maintenance of intestinal homeostasis. Numerous studies have demonstrated that transepithelial migration of neutrophils is closely related to disease symptoms and disruption of crypt architecture in inflammatory bowel disease and experimental colitis. There has been growing interest in how neutrophils interact with the epithelium under inflammatory conditions. Most studies focus on the effects of neutrophils on intestinal epithelial cells; however, the effects of intestinal epithelial cells on neutrophils during intestinal inflammation need to be well-established. Based on these data, we have summarized recent articles on the role of neutrophil-epithelial interactions in intestinal inflammation, particularly highlighting the epithelium-derived molecular regulators that mediate neutrophil recruitment, transepithelial migration, and detachment from the epithelium, as well as the functional consequences of their crosstalk. A better understanding of these molecular events may help develop novel therapeutic targets for mitigating the deleterious effects of neutrophils in inflammatory bowel disease.

Homocysteine-targeting compounds as a new treatment strategy for diabetic wounds via inhibition of the histone methyltransferase SET7/9

In hypoxia and hyperglycemia, SET7/9 plays an important role in controlling HIF-1α methylation and regulating the transcription of HIF-1α target genes, which are responsible for angiogenesis and wound healing. Here, we report the Ir(III) complex Set7_1a bearing acetonitrile (ACN) ligands as a SET7/9 methyltransferase inhibitor and HIF-1α stabilizer. Interestingly, Set7_1a could engage SET7/9 and strongly inhibit SET7/9 activity, especially after preincubation with homocysteine (Hcy), which is elevated in diabetes. We hypothesize that Set7_1a exchanges ACN subunits for Hcy to disrupt the interaction between SET7/9 and SAM/SAH, which are structurally related to Hcy. Inhibition of SET7/9 methyltransferase activity by Set7_1a led to reduced HIF-1α methylation at the lysine 32 residue, causing increased HIF-1α level and recruitment of HIF-1α target genes that promote angiogenesis, such as VEGF, GLUT1, and EPO, in hypoxia and hyperglycemia. Significantly, Set7_1a improved wound healing in a type 2 diabetic mouse model by activating HIF-1α signaling and downstream proangiogenic factors. To our knowledge, this is the first Hcy-targeting iridium compound shown to be a SET7/9 antagonist that can accelerate diabetic wound healing. More importantly, this study opens a therapeutic avenue for the treatment of diabetic wounds by the inhibition of SET7/9 lysine methyltransferase activity.

Animal trials have demonstrated the potential of a new drug strategy to heal the wounds associated with diabetes, especially in the feet,which often lead to chronic damage, sometimes treatable only by amputation. Leung CH and Lin L at the University of Macau, China, and Ma DL at the Hong Kong Baptist University tested the new therapy on a mouse model of type 2 diabetes. The treatment uses a homocysteine-targeting metal complex that inhibits a key enzyme SET7/9 involved in the processes that cause diabetic wounds. The treatment activated a molecular signalling cascade involved in generating the new blood vessels needed for wounds to heal. It could help address the urgent need for better treatments for this serious problem.

Eosinophils, Hypoxia-Inducible Factors, and Barrier Dysfunction in Functional Dyspepsia

Functional dyspepsia (FD) is a highly prevalent disorder of gut-brain interaction (DGBI), previously known as a functional gastrointestinal disorder. Characterized by early satiety, postprandial fullness, and/or epigastric pain or burning, diagnosis depends on positive symptomatology and exclusion of obvious structural diseases. A subtle inflammatory phenotype has been identified in FD patients, involving an increase in duodenal mucosal eosinophils, and imbalances in the duodenal gut microbiota. A dysregulated epithelial barrier has also been well described in FD and is thought to be a contributing factor to the low-grade duodenal inflammation observed, however the mechanisms underpinning this are poorly understood. One possible explanation is that alterations in the microbiota and increased immune cells can result in the activation of cellular stress response pathways to perpetuate epithelial barrier dysregulation. One such cellular response pathway involves the stabilization of hypoxia-inducible factors (HIF). HIF, a transcriptional protein involved in the cellular recognition and adaptation to hypoxia, has been identified as a critical component of various pathologies, from cancer to inflammatory bowel disease (IBD). While the contribution of HIF to subtle inflammation, such as that seen in FD, is unknown, HIF has been shown to have roles in regulating the inflammatory response, particularly the recruitment of eosinophils, as well as maintaining epithelial barrier structure and function. As such, we aim to review our present understanding of the involvement of eosinophils, barrier dysfunction, and the changes to the gut microbiota including the potential pathways and mechanisms of HIF in FD. A combination of PubMed searches using the Mesh terms functional dyspepsia, functional gastrointestinal disorders, disorders of gut-brain interaction, duodenal eosinophilia, barrier dysfunction, gut microbiota, gut dysbiosis, low-grade duodenal inflammation, hypoxia-inducible factors (or HIF), and/or intestinal inflammation were undertaken in the writing of this narrative review to ensure relevant literature was included. Given the findings from various sources of literature, we propose a novel hypothesis involving a potential role for HIF in the pathophysiological mechanisms underlying FD.

Gill and Liver Transcript Expression Changes Associated With Gill Damage in Atlantic Salmon (Salmo salar)

Gill damage represents a significant challenge in the teleost fish aquaculture industry globally, due to the gill’s involvement in several vital functions and direct contact with the surrounding environment. To examine the local and systemic effects accompanying gill damage (which is likely to negatively affect gill function) of Atlantic salmon, we performed a field sampling to collect gill and liver tissue after several environmental insults (e.g., harmful algal blooms). Before sampling, gills were visually inspected and gill damage was scored; gill scores were assigned from pristine [gill score 0 (GS0)] to severely damaged gills (GS3). Using a 44K salmonid microarray platform, we aimed to compare the transcriptomes of pristine and moderately damaged (i.e., GS2) gill tissue. Rank Products analysis (5% percentage of false-positives) identified 254 and 34 upregulated and downregulated probes, respectively, in GS2 compared with GS0. Differentially expressed probes represented genes associated with functions including gill remodeling, wound healing, and stress and immune responses. We performed gill and liver qPCR for all four gill damage scores using microarray-identified and other damage-associated biomarker genes. Transcripts related to wound healing (e.g., neb and klhl41b) were significantly upregulated in GS2 compared with GS0 in the gills. Also, transcripts associated with immune and stress-relevant pathways were dysregulated (e.g., downregulation of snaclec 1-like and upregulation of igkv3) in GS2 compared with GS0 gills. The livers of salmon with moderate gill damage (i.e., GS2) showed significant upregulation of transcripts related to wound healing (i.e., chtop), apoptosis (e.g., bnip3l), blood coagulation (e.g., f2 and serpind1b), transcription regulation (i.e., pparg), and stress-responses (e.g., cyp3a27) compared with livers of GS0 fish. We performed principal component analysis (PCA) using transcript levels for gill and liver separately. The gill PCA showed that PC1 significantly separated GS2 from all other gill scores. The genes contributing most to this separation were pgam2, des, neb, tnnt2, and myom1. The liver PCA showed that PC1 significantly separated GS2 from GS0; levels of hsp70, cyp3a27, pparg, chtop, and serpind1b were the highest contributors to this separation. Also, hepatic acute phase biomarkers (e.g., serpind1b and f2) were positively correlated to each other and to gill damage. Gill damage-responsive biomarker genes and associated qPCR assays arising from this study will be valuable in future research aimed at developing therapeutic diets to improve farmed salmon welfare.

Defects in NLRP6, autophagy and goblet cell homeostasis are associated with reduced duodenal CRH receptor 2 expression in patients with functional dyspepsia

Functional dyspepsia (FD) affects up to 15% of the population and is characterised by recurring upper gastrointestinal (GI) symptoms occurring in the absence of clinically identifiable pathology. Psychological stress is a key factor associated with the onset of FD and locally acting hypothalamic-pituitary-adrenal (HPA) axis hormones have been implicated in GI motility and barrier dysfunction. Recent pre-clinical work has identified mechanistic pathways linking corticotropin-releasing hormone (CRH) with the innate epithelial immune protein NLRP6, an inflammasome that has been shown to regulate GI mucus secretion. We recruited twelve FD patients and twelve healthy individuals to examine whether dysregulation of hypothalamic-pituitary adrenal (HPA) axis hormones and altered NLRP6 pathways were evident in the duodenal mucosa. Protein expression was assessed by immunoblot and immunohistochemistry in D2 duodenal biopsies. Plasma HPA axis hormones were assayed by ELISA and enteroid and colorectal cancer cell line cultures were used to verify function. FD patients exhibited reduced duodenal CRH-receptor 2, compared to non-GI disease controls, indicating a dysregulation of duodenal HPA signalling. The loss of CRH-receptor 2 correlated with reduced NLRP6 expression and autophagy function, processes critical for maintaining goblet cell homeostasis. In accordance, duodenal goblet cell numbers and mucin exocytosis was reduced in FD patients compared to controls. In vitro studies demonstrated that CRH could reduce NLRP6 in duodenal spheroids and promote mucus secretion in the HT29-MTX-E12 cell line. In conclusion, FD patients exhibit defects in the NLRP6-autophagy axis with decreased goblet cell function that may drive symptoms of disease. These features correlated with loss of CRH receptor 2 and may be driven by dysregulation of HPA signalling in the duodenum of FD patients.

HIF-Dependent NFATC1 Activation Upregulates ITGA5 and PLAUR in Intestinal Epithelium in Inflammatory Bowel Disease

Intestinal epithelial cells exist in physiological hypoxia, leading to hypoxia-inducible factor (HIF) activation and supporting barrier function and cell metabolism of the intestinal epithelium. In contrast, pathological hypoxia is a common feature of some chronic disorders, including inflammatory bowel disease (IBD). This work was aimed at studying HIF-associated changes in the intestinal epithelium in IBD. In the first step, a list of genes responding to chemical activation of hypoxia was obtained in an in vitro intestinal cell model with RNA sequencing. Cobalt (II) chloride and oxyquinoline treatment of both undifferentiated and differentiated Caco-2 cells activate the HIF-signaling pathway according to gene set enrichment analysis. The core gene set responding to chemical hypoxia stimulation in the intestinal model included 115 upregulated and 69 downregulated genes. Of this set, protein product was detected for 32 genes, and fold changes in proteome and RNA sequencing significantly correlate. Analysis of publicly available RNA sequencing set of the intestinal epithelial cells of patients with IBD confirmed HIF-1 signaling pathway activation in sigmoid colon of patients with ulcerative colitis and terminal ileum of patients with Crohn's disease. Of the core gene set from the gut hypoxia model, expression activation of ITGA5 and PLAUR genes encoding integrin α5 and urokinase-type plasminogen activator receptor (uPAR) was detected in IBD specimens. The interaction of these molecules can activate cell migration and regenerative processes in the epithelium. Transcription factor analysis with the previously developed miRGTF tool revealed the possible role of HIF1A and NFATC1 in the regulation of ITGA5 and PLAUR gene expression. Detected genes can serve as markers of IBD progression and intestinal hypoxia.

The role of hypoxia-inducible factor 1-alpha in inflammatory bowel disease

Inflammatory bowel disease (IBD) develops as a result of a combination of genetic predisposition, dysbiosis of the gut microbiota, and environmental influences, which is mainly represented by ulcerative colitis (UC) and Crohn's disease (CD). IBDs can result in inflammatory hypoxia by causing intestinal inflammation and vascular damage. The hypoxia-inducible factor 1-alpha (HIF-1α), as a transcription factor, can regulate the cellular adaptation to low oxygen levels and support the development and function of the gut barrier. HIF-αplays its functions through translocating into the nucleus, dimerizing with HIF-1β, and binding to hypoxia-responsive elements of HIF-1 target genes. So far, most studies have addressed the function of HIF-1α in murine models of IBD. In this review, we aim to outline the major roles of HIF-1α in the IBD.

Epithelial wound healing in inflammatory bowel diseases: the next therapeutic frontier

Patients with one of the many chronic inflammatory disorders broadly classified as inflammatory bowel disease (IBD) now have a diverse set of immunomodulatory therapies at their disposal. Despite these recent medical advances, complete sustained remission of disease remains elusive for most patients. The full healing of the damaged intestinal mucosa is the primary goal of all therapies. Achieving this requires not just a reduction of the aberrant immunological response, but also wound healing of the epithelium. No currently approved therapy directly targets the epithelium. Epithelial repair is compromised in IBD and normally facilitates re-establishment of the homeostatic barrier between the host and the microbiome. In this review, we summarize the evidence that epithelial wound healing represents an important yet underdeveloped therapeutic modality for IBD. We highlight 3 general approaches that are promising for developing a new class of epithelium-targeted therapies: epithelial stem cells, cytokines, and microbiome engineering. We also provide a frank discussion of some of the challenges that must be overcome for epithelial repair to be therapeutically leveraged. A concerted approach by the field to develop new therapies targeting epithelial wound healing will offer patients a game-changing, complementary class of medications and could dramatically improve outcomes.

Hypoxia and HIF-1 as key regulators of gut microbiota and host interactions

Oxygen (O₂) availability is a key factor regulating microbiota composition and the homeostatic function of cells in the intestinal mucosa of vertebrates. Microbiota-derived metabolites increase O₂ consumption by intestinal epithelial cells (IECs), reducing its availability in the gut and leading to hypoxia. This physiological hypoxia activates cellular hypoxic sensors that adapt the metabolism and function of IECs and mucosa-resident cells, such as type-3 innate lymphoid cells (ILC3s). In this review, we discuss recent evidence suggesting that the intricate and multidirectional interactions among the microbiota, hypoxia/hypoxic sensors, and mammalian host cells (IECs and ILC3s) determine how the intestinal barrier and host-microbiota-pathogens connections are molded. Understanding these interactions might provide new treatment possibilities for dysbiosis, as well as certain inflammatory and infectious diseases.