Epithelial Barrier Regulation by Hypoxia-Inducible Factor

Effect of hypoxia on the mucus system and intragastric microecology in the gastrointestinal tract

Digestive diseases have a high incidence worldwide, with various geographic, age, and gender factors influencing the occurrence and development of the diseases. The main etiologic factors involve genetics, environment, lifestyle, and dietary habits. In a low-oxygen environment, however, the body's tissue cells activate hypoxia-inducible factor (HIF), which produces different inflammatory mediators. Hypoxia impacts health at the molecular level by modulating cellular stress responses, metabolic pathways, and immune functions. It also alters gene expression and cellular behavior, thereby affecting gastrointestinal function. Under normal physiological conditions, the gastrointestinal mucus system serves as a crucial protective barrier, defending against mechanical injury, pathogenic invasion, and exposure to harmful chemicals. The integrity and functionality of this barrier are dependent on the synthesis and regulation of mucins and mucus, which are influenced by multiple factors. Additionally, the composition and diversity of the gastric microbiota are shaped by factors such as Helicobacter pylori infection, diet, and lifestyle. A balanced gastric microbiota supports gastrointestinal health and fortifies the mucus barrier. However, hypoxia can disrupt this equilibrium, leading to inflammation, alterations in the mucus layer, and destabilization of the gastric microbiota. Understanding the interplay between hypoxia, the mucus system, and the gastric microbiota is essential for identifying novel therapeutic strategies. Future research should elucidate the mechanisms through which hypoxia influences these systems and develop interventions to mitigate its adverse effects on gastrointestinal health. We examined the impact of hypoxia on the gastrointestinal mucus system and gastric microbiota, highlighting its implications for human health and potential therapeutic approaches.

Sympathetic-Mediated Intestinal Cell Death Contributes to Gut Barrier Impairment After Stroke

Tissue injury induced by stroke is traditionally thought to be localised to the brain. However, there is an accumulating body of evidence to demonstrate that stroke promotes pathophysiological consequences in peripheral tissues including the gastrointestinal system. In this study, we investigated the mechanisms underlying gut permeability after stroke. We utilised the clinically relevant experimental model of stroke called permanent intraluminal middle cerebral artery occlusion (pMCAO) to examine the effect of cerebral ischaemia on the gut. We detected stroke-induced gut permeability at 5 h after pMCAO. At this timepoint, we observed significantly elevated intestinal epithelial cell death in post-stroke mice compared to their sham-operated counterparts. At 24 h after stroke onset when the gut barrier integrity is restored, our findings indicated that post-stroke intestinal epithelium had higher expression of genes associated with fructose metabolism, and hyperplasia of intestinal crypts and goblet cells, conceivably as a host compensatory mechanism to adapt to the impaired gut barrier. Furthermore, we discovered that stroke-induced gut permeability was mediated by the activation of the sympathetic nervous system as pharmacological denervation decreased the stroke-induced intestinal epithelial cell death, goblet cell and crypt hyperplasia, and gut permeability to baseline levels. Our study identifies a previously unknown mechanism in the brain-gut axis by which stroke triggers intestinal cell death and gut permeability.

Real-world of Limosilactobacillus reuteri in mitigation of acute experimental colitis

Probiotics have been proposed as a potential strategy for managing ulcerative colitis (UC). However, the underlying mechanisms mediating microbiota-host crosstalk remain largely elusive. Here, we report that Limosilactobacillus reuteri (L. reuteri), as a probiotic, secretes cytoplasmic membrane vesicles (CMVs) that communicate with host cells, alter host physiology, and alleviate dextran sulfate sodium (DSS)-induced colitis. First, L. reuteri-CMVs selectively promoted the proliferation of the beneficial bacterium Akkermansia muciniphila (AKK) by upregulating the expression of glycosidases (beta-N-acetylhexosaminidase and alpha-N-acetylglucosaminidase) involved in glycan degradation and metabolic pathways and restored the disrupted gut microbiota balance. Second, L. reuteri-CMVs were taken up by intestinal epithelial cells (IECs), elevated the expression of ZO-1, E-cadherin (Cdh1), and Occludin (Ocln), decreased intestinal permeability, and exerted protective effects on epithelial tight junction functionality. RNA sequencing analysis demonstrated that L. reuteri-CMVs repaired intestinal barrier by activating the HIF-1 signaling pathway and upregulating HMOX1 expression. Third, L. reuteri-CMVs increased the population of double positive (DP) CD4+CD8+ T cells in the intestinal epithelial layer, suppressing gut inflammation and maintaining gut mucosal homeostasis. Finally, L. reuteri-CMVs exhibited satisfactory stability and safety in the gastrointestinal tract and specifically targeted the desired sites in colitis mice. Collectively, these findings shed light on how L. reuteri interact with the host in colitis, and provide new insights into potential strategies for alleviating colitis.

Influence of Hypoxia on the Airway Epithelium

The necessity of oxygen for metabolic processes means that hypoxia can lead to serious cell and tissue damage. On the other hand, in some situations, hypoxia occurs under physiological conditions and serves as an important regulation factor. The airway epithelium is specific in that it gains oxygen not only from the blood supply but also directly from the luminal air. Many respiratory diseases are associated with airway obstruction or excessive mucus production thus leading to luminal hypoxia. The main goal of this review is to point out how the airway epithelium reacts to hypoxic conditions. Cells detect low oxygen levels using molecular mechanisms involving hypoxia-inducible factors (HIFs). In addition, the cells of the airway epithelium appear to overexpress HIFs in hypoxic conditions. HIFs then regulate many aspects of epithelial cell functions. The effects of hypoxia include secretory cell stimulation and hyperplasia, epithelial barrier changes, and ciliogenesis impairment. All the changes can impair mucociliary clearance, exacerbate infection, and promote inflammation leading to damage of airway epithelium and subsequent airway wall remodeling. The modulation of hypoxia regulatory mechanisms may be one of the strategies for the treatment of obstructive respiratory diseases or diseases with mucus hyperproduction. Keywords: Secretory cells, Motile cilia, Epithelial barrier, Oxygenation, Obstructive respiratory diseases.

Bacteria and fungi of the lung: allies or enemies?

Moving from the earlier periods in which the lungs were believed to represent sterile environments, our knowledge on the lung microbiota has dramatically increased, from the first descriptions of the microbial communities inhabiting the healthy lungs and the definition of the ecological rules that regulate its composition, to the identification of the changes that occur in pathological conditions. Despite the limitations of lung as a microbiome reservoir due to the low microbial biomass and abundance, defining its microbial composition and function in the upper and lower airways may help understanding the impact on local homeostasis and its disruption in lung diseases. In particular, the understanding of the metabolic and immune significance of microbes, their presence or lack thereof, in health and disease states could be valuable in development of novel druggable targets in disease treatments. Next-generation sequencing has identified intricate inter-microbe association networks that comprise true mutualistic or antagonistic direct or indirect relationships in the respiratory tract. In this review, the tripartite interaction of bacteria, fungi and the mammalian host is addressed to provide an integrated view of the microbial-host cross-talk in lung health and diseases from an immune and metabolic perspective.

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

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

An investigation into the HIF-dependent intestinal barrier protective mechanism of Qingchang Wenzhong decoction in ulcerative colitis management

ETHNOPHARMACOLOGICAL RELEVANCE

Ulcerative colitis (UC) is a chronic, non-specific inflammatory disease affecting the colon and rectum with an etiology that remains elusive. Traditional Chinese medicine (TCM) has been widely used on long-term UC treatment to better maintain the efficacy than traditional aminosalicylic acid or glucocorticosteroids and to ease financial burden of patients. Qingchang Wenzhong Decoction (QCWZD) is a modern TCM decoction with established clinical efficacy but the mechanism of its protection on intestinal barrier function remains unclear.

AIM OF THE STUDY

Current findings highlight that the activation of the hypoxia inducible factor (HIF) pathway can facilitate the repair of intestinal epithelium barrier. This study is to investigate the protective effects of QCWZD and its HIF-targeted ingredients on hypoxia-dependent intestinal barrier.

METHODS

The mice model of UC was induced by dextran sulfate sodium (DSS). Disease activity index (DAI) and histopathology scores and colon length were used to measure the severity of colitis. The DAO activity in serum and protein expression of tight junction (TJ) proteins were detected to explore the function of intestinal barrier. The protein levels of HIF-1α and its downstream gene heme oxygenase-1 (HO-1) were measured as well. HIF-targeted active ingredients in QCWZD were selected by network pharmacology and molecular docking. Protective effects of six constituents on HIF-related anti-oxidative and barrier protective pathway were evaluated by lipopolysaccharide (LPS)-induced HT29 and RAW264.7 cells, through the measurement of the production of ROS and mRNA level of pro-inflammatory cytokines. HIF-1α knockdown was carried out to explore the correlation of protection effects with HIF-related pathway of the active ingredients.

RESULTS

QCWZD effectively alleviated colitis induced by DSS and demonstrated a protective effect on intestinal barrier function by upregulating HIF-related pathways. Six specific ingredients in QCWZD, targeting HIF, successfully reduced the production of cellular ROS and proinflammatory cytokines in LPS-induced cells. It is noteworthy that the barrier protection provided by these molecules is intricately linked with the HIF-related pathway.

CONCLUSIONS

This study elucidates the HIF-related molecular mechanism of QCWZD in protecting the function of the epithelial barrier. Six compounds targeting the activation of the HIF-dependent pathway were demonstrated to unveil a novel therapeutic approach for managing UC.

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.

Mimicry of microbially-derived butyrate reveals templates for potent intestinal epithelial HIF stabilizers

Microbiota-derived short-chain fatty acids, including butyrate (BA), have multiple beneficial health effects. In the colon, BA concentrations range from 10 to 20 mM and up to 95% is utilized as energy by the mucosa. BA plays a key role in epithelial-barrier regulation and anti-inflammation, and regulates cell growth and differentiation, at least in part, due to its direct influence on stabilization of the transcription factor hypoxia-inducible factor (HIF). It remains unclear whether BA is the optimal metabolite for such a response. In this study, we explored metabolite mimicry as an attractive strategy for the biological response to HIF. We discovered that 4-mercapto butyrate (MBA) stabilizes HIF more potently and has a longer biological half-life than BA in intestinal epithelial cells (IECs). We validated the MBA-mediated HIF transcriptional activity through the induction of classic HIF gene targets in IECs and enhanced epithelial barrier formation in vitro. In-vivo studies with MBA revealed systemic HIF stabilization in mice, which was more potent than its parent BA metabolite. Mechanistically, we found that MBA enhances oxygen consumption and that the sulfhydryl group is essential for HIF stabilization, but exclusively as a four-carbon SCFA. These findings reveal a combined biochemical mechanism for HIF stabilization and provide a foundation for the discovery of potent metabolite-like scaffolds.

Role of HIF1α and HIF2α in Cre Recombinase-Induced Retinal Pigment Epithelium Pathology and Its Secondary Effect on Choroidal Neovascularization

CreTrp1 mice are widely used for conditional retinal pigment epithelium (RPE) gene function studies. Like other Cre/LoxP models, phenotypes in CreTrp1 mice can be affected by Cre-mediated cellular toxicity, leading to RPE dysfunction, altered morphology and atrophy, activation of innate immunity, and consequent impairment of photoreceptor function. These effects are common among the age-related alterations of RPE that feature in early/intermediate forms of age-related macular degeneration. This article characterizes Cre-mediated pathology in the CreTrp1 line to elucidate the impact of RPE degeneration on both developmental and pathologic choroidal neovascularization. Nonredundant roles of the two major components of the hypoxia-inducible factor (HIF) family of transcription regulators, HIF1α and HIF2α, were identified. Genetic ablation of Hif1a protected against Cre-induced degeneration of RPE and choroid, whereas ablation of Hif2a exacerbated this degeneration. Furthermore, HIF1α deficiency protected CreTrp1 mice against laser-induced choroidal neovascularization, whereas HIF2α deficiency exacerbated the phenotype. Cre-mediated degeneration of the RPE in CreTrp1 mice offers an opportunity to investigate the impact of hypoxia signaling in the context of RPE degeneration. These findings indicate that HIF1α promotes Cre recombinase-mediated RPE degeneration and laser-induced choroidal neovascularization, whereas HIF2α is protective.

Melatonin attenuates chronic intermittent hypoxia-induced intestinal barrier dysfunction in mice

BACKGROUND AND PURPOSE

Chronic intermittent hypoxia (CIH) triggers subclinical intestinal barrier disruption prior to systemic low-grade inflammation. Increasing evidence suggests therapeutic effects of melatonin on systemic inflammation and gut microbiota remodelling. However, whether and how melatonin alleviates CIH-induced intestinal barrier dysfunction remains unclear.

EXPERIMENTAL APPROACH

C57BL/6 J mice and Caco-2 cell line were treated. We evaluated gut barrier function spectrophotometrically using fluorescein isothiocyanate (FITC)-labelled dextran. Immunohistochemical and immunofluorescent staining were used to detect morphological changes in the mechanical barrier. Western blotting (WB) and quantitative real-time polymerase chain reaction (qRT-PCR) revealed the expression of tight junctions, signal transducer and activator of transcription 3 (STAT3) levels. 16 S rRNA analysis of the colonic contents microflora. Flow cytometry was used to detect cytokines and Th17 cells with and without melatonin supplementation.

KEY RESULTS

We found that CIH could induce colonic mucosal injury, including reduction in the number of goblet cells and decrease the expression of intestinal tight junction proteins. CIH could decrease the abundance of the beneficial genera Clostridium, Akkermansia, and Bacteroides, while increasing the abundance of the pathogenic genera Desulfovibrio and Bifidobacterium. Finally, CIH facilitated Th17 differentiation via the phosphorylation of signal transducer and activator of transcription 3 (STAT3) in vitro and elevated the circulating pro-inflammatory cytokine in vivo. Melatonin supplementation ameliorated CIH-induced intestinal mucosal injury, gut microbiota dysbiosis, enteric Th17 polarization, and systemic low-grade inflammation reactions mentioned-above.

CONCLUSION AND IMPLICATIONS

Melatonin attenuated CIH-induced intestinal barrier dysfunction by regulating gut flora dysbiosis, mucosal epithelium integrity, and Th17 polarization via STAT3 signalling.

Regulatory Functions of Hypoxia in Host-Parasite Interactions: A Focus on Enteric, Tissue, and Blood Protozoa

Body tissues are subjected to various oxygenic gradients and fluctuations and hence can become transiently hypoxic. Hypoxia-inducible factor (HIF) is the master transcriptional regulator of the cellular hypoxic response and is capable of modulating cellular metabolism, immune responses, epithelial barrier integrity, and local microbiota. Recent reports have characterized the hypoxic response to various infections. However, little is known about the role of HIF activation in the context of protozoan parasitic infections. Growing evidence suggests that tissue and blood protozoa can activate HIF and subsequent HIF target genes in the host, helping or hindering their pathogenicity. In the gut, enteric protozoa are adapted to steep longitudinal and radial oxygen gradients to complete their life cycle, yet the role of HIF during these protozoan infections remains unclear. This review focuses on the hypoxic response to protozoa and its role in the pathophysiology of parasitic infections. We also discuss how hypoxia modulates host immune responses in the context of protozoan infections.

Roxadustat protect mice from DSS-induced colitis in vivo by up-regulation of TLR4

BACKGROUND

The incidence of inflammatory bowel disease (IBD) is growing in the population. At present, the etiology of inflammatory bowel disease remains unclear, and there is no effective and low-toxic therapeutic drug. The role of the PHD-HIF pathway in relieving DSS-induced colitis is gradually being explored.

METHODS

Wild-type C57BL/6 mice were used as a model of DSS-induced colitis to explore the important role of Roxadustat in alleviating DSS-induced colitis. High-throughput RNA-Seq and qRT-PCR methods were used to screen and verify the key differential genes in the colon of mice between normal saline (NS) and Roxadustat groups.

RESULTS

Roxadustat could alleviate DSS-induced colitis. Compared with the mice in the NS group, TLR4 were significantly up-regulated in the Roxadustat group. TLR4 KO mice were used to verify the role of TLR4 in the alleviation of DSS-induced colitis by Roxadustat.

CONCLUSION

Roxadustat has a repairing effect on DSS-induced colitis, and may alleviate DSS-induced colitis by targeting the TLR4 pathway and promote intestinal stem cell proliferation.

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.

Biogenic Selenium Nanoparticles Synthesized by Lactobacillus casei ATCC 393 Alleviate Acute Hypobaric Hypoxia-Induced Intestinal Barrier Dysfunction in C57BL/6 Mice

Exposure to hypobaric hypoxia at high altitude will cause different tissue and organ damage over a long period of time. Studies have shown that hypobaric hypoxia can cause severe primary intestinal barrier dysfunction, and then cause multiple organ dysfunction. Our previous research showed that selenium nanoparticles (SeNPs) synthesized by Lactobacillus casei ATCC 393 (L. casei ATCC 393) can effectively alleviate intestinal barrier dysfunction caused by oxidative stress and inflammation in mice. This study was conducted to investigate the protective effect of biological SeNPs synthesized by L. casei ATCC 393 on intestinal barrier function in acute hypobaric hypoxic stress mice. The results showed that compared with the hypobaric hypoxic, the SeNPs synthesized by L. casei ATCC 393 by oral administration could effectively alleviate the shortening of intestinal villi, which decreased the level of diamine oxidase (DAO) and myeloperoxidase (MPO), and the expression level of tight junction protein in ileum was increased. In addition, SeNPs significantly increased the activities of superoxide dismutase (SOD), cyclooxygenase (COX-1) and glutathione peroxidase (GPx), and decreased the level of malondialdehyde (MDA), and inhibit the increase of hypoxia related factor. SeNPs effectively regulate the intestinal microecology disorder caused by hypobaric hypoxia stress, and maintain the intestinal microecology balance. In addition, oral administration of SeNPs had better protective effect on intestinal barrier function of mice under hypobaric hypoxia stress. These results suggested that SeNPs synthesized by L. casei ATCC 393 can effectively alleviate the damage of intestinal barrier function under acute hypobaric hypoxic stress, which may be closely related to the antioxidant activity of SeNPs.

Hypoxia-inducible factor as a bridge between healthy barrier function, wound healing, and fibrosis

The healthy mammalian intestine is lined by a single layer of epithelial cells. These cells provide a selectively permeable barrier to luminal contents and normally do so in an efficient and effective manner. Barrier function in the healthy mucosa is provided via several mechanisms including epithelial junctional complexes, mucus production, as well as mucosal-derived antimicrobial proteins. As tissue metabolism is central to the maintenance of homeostasis in the mucosa, intestinal [Formula: see text] levels are uniquely low due to counter-current blood flow and the presence of the microbiota, resulting in the stabilization of the transcription factor hypoxia-inducible factor (HIF). Ongoing studies have revealed that HIF molds normal intestinal metabolism and is central to the coordination of barrier regulation during both homeostasis and active disease. During acute inflammation, HIF is central to controlling the rapid restitution of the epithelium consistent with normal wound healing responses. In contrast, HIF may also contribute to the fibrostenotic response associated with chronic, nonresolving inflammation. As such, HIF may function as a double-edged sword in the overall course of the inflammatory response. Here, we review recent literature on the contribution of HIF to mucosal barrier function, wound healing, and fibrosis.

Oxygen-dependent regulation of permeability in low resistance intestinal epithelial cells infected with Giardia lamblia

Intestinal epithelial cells (IECs) reside in a highly anaerobic environment that is subject to daily fluctuations in partial oxygen pressure (pO₂), depending on intestinal tissue perfusion. This condition, known as physiological hypoxia, has a major impact on the maintenance of gut homeostasis, such as effects on the integrity and function of the intestinal epithelial barrier. Giardia lamblia is a microaerophilic protozoan parasite that infects and colonizes the small intestine of its host, causing watery diarrhea. The disease, known as giardiasis, is associated with enhanced intestinal permeability and disruption or reorganization of tight junction (TJ) proteins between IECs. Given the central role of oxygen in gut homeostasis, in this study, we aimed to evaluate whether pO₂ affects intestinal permeability (flux of ions and macromolecules) and TJ protein expression in human IECs during G. lamblia infection. Using human cell lines HuTu-80 and Caco-2 as models of "loose" (low resistance) and "tight" (high resistance) intestines, respectively, we elucidated that low pO₂ drives intestinal barrier dysfunction in IECs infected with trophozoites through dephosphorylation of protein kinase C (PKC α/β II). Additionally, we demonstrated that IECs infected with trophozoites in the presence of a pharmacological PKC activator (phorbol 12-myristate 13-acetate) partially restored the barrier function, which was correlated with increased protein expression levels of zonula occludens (ZO)-2 and occludin. Collectively, these results support the emerging theory that molecular oxygen impacts gut homeostasis during Giardia infection via direct host signaling pathways. These findings further our knowledge regarding Giardia-host interactions and the pathophysiological mechanisms of human giardiasis.

Enhanced oxidative phosphorylation of IgG plasma cells can contribute to hypoxia in the mucosa of active ulcerative colitis

Mucosal hypoxia is detected in the mucosa of ulcerative colitis (UC), however the mechanism and the cause of hypoxia is not fully understood, while a dense infiltration of plasma cells is observed in the inflamed mucosa of UC. When differentiating from a B cell to a plasma cell, the energy metabolism dramatically shifts from glycolysis to oxidative phosphorylation, which results in a large amount of oxygen consumption of the plasma cell. We hypothesized that the plasma cell infiltration into the inflamed mucosa contributes to the mucosal hypoxia in UC in part. We examined the association between mucosal hypoxia and plasma cell infiltration in UC. More IgG plasma cells (but not IgA plasma cells) were distributed, and the nuclear and cell sizes were enlarged in hypoxic mucosa compared to normoxic mucosa in UC. Oxidative phosphorylation signature genes of these IgG plasma cells were markedly upregulated compared to those of other lymphoid cells infiltrating the lamina propria of inflamed mucosa of UC. Enlarged IgG plasma cells, which increase in number in the inflamed mucosa of UC, can be related to the hypoxic state of the inflamed mucosa of UC.

Counteracting Health Risks by Modulating Homeostatic Signaling

Homeostasis was initially conceptualized by Bernard and Cannon around a century ago as a steady state of physiological parameters that vary within a certain range, such as blood pH, body temperature, and heart rate^1,2. The underlying mechanisms that maintain homeostasis are explained by negative feedbacks that are executed by the neuronal, endocrine, and immune systems. At the cellular level, homeostasis, such as that of redox and energy steady state, also exists and is regulated by various cell signaling pathways. The induction of homeostatic mechanism is critical for human to adapt to various disruptive insults (stressors); while on the other hand, adaptation occurs at the expense of other physiological processes and thus runs the risk of collateral damages, particularly under conditions of chronic stress. Conceivably, anti-stress protection can be achieved by stressor-mimicking medicinals that elicit adaptive responses prior to an insult and thereby serve as health risk countermeasures; and in situations where maladaptation may occur, downregulating medicinals could be used to suppress the responses and prevent subsequent pathogenesis. Both strategies are preemptive interventions particularly suited for individuals who carry certain lifestyle, environmental, or genetic risk factors. In this article, we will define and characterize a new modality of prophylactic intervention that forestalls diseases via modulating homeostatic signaling. Moreover, we will provide evidence from the literature that support this concept and distinguish it from other homeostasis-related interventions such as adaptogen, hormesis, and xenohormesis.

Microenvironmental Metabolites in the Intestine: Messengers between Health and Disease

The intestinal mucosa is a highly absorptive organ and simultaneously constitutes the physical barrier between the host and a complex outer ecosystem. Intestinal epithelial cells (IECs) represent a special node that receives signals from the host and the environment and translates them into corresponding responses. Specific molecular communication systems such as metabolites are known to transmit information across the intestinal boundary. The gut microbiota or food-derived metabolites are extrinsic factors that influence the homeostasis of the intestinal epithelium, while mitochondrial and host-derived cellular metabolites determine the identity, fitness, and regenerative capacity of IECs. Little is known, however, about the role of intrinsic and extrinsic metabolites of IECs in the initiation and progression of pathological processes such as inflammatory bowel disease and colorectal cancer as well as about their impact on intestinal immunity. In this review, we will highlight the most recent contributions on the modulatory effects of intestinal metabolites in gut pathophysiology, with a particular focus on metabolites in promoting intestinal inflammation or colorectal tumorigenesis. In addition, we will provide a perspective on the role of newly identified oncometabolites from the commensal and opportunistic microbiota in shaping response and resistance to antitumor therapy.

Imitating Hypoxia and Tumor Microenvironment with Immune Evasion by Employing Three Dimensional in vitro Cellular Models: Impressive Tool in Drug Discovery

The heterogeneous tumor microenvironment is exceptionally perplexing and not wholly comprehended. Different multifaceted alignments lead to the generation of oxygen destitute situations within the tumor niche that modulate numerous intrinsic tumor microenvironments. Disentangling these communications is vital for scheming practical therapeutic approaches that can successfully decrease tumor allied chemotherapy resistance by utilizing the innate capability of the immune system. Several research groups have concerned with a protruding role for oxygen metabolism along with hypoxia in the immunity of healthy tissue. Hypoxia in addition to hypoxia-inducible factors (HIFs) in the tumor microenvironment plays an important part in tumor progression and endurance. Although numerous hypoxia-focused therapies have shown promising outcomes both in vitro and in vivo these outcomes have not effectively translated into clinical preliminaries. Distinctive cell culture techniques have utilized as an in vitro model for tumor niche along with tumor microenvironment and proficient in more precisely recreating tumor genomic profiles as well as envisaging therapeutic response. To study the dynamics of tumor immune evasion, three-dimensional (3D) cell cultures are more physiologically important to the hypoxic tumor microenvironment. Recent research has revealed new information and insights into our fundamental understanding of immune systems, as well as novel results that have been established as potential therapeutic targets. There are a lot of patented 3D cell culture techniques which will be highlighted in this review. At present notable 3D cell culture procedures in the hypoxic tumor microenvironment, discourse open doors to accommodate both drug repurposing, advancement, and divulgence of new medications and will deliberate the 3D cell culture methods into standard prescription disclosure especially in the field of cancer biology which will be discussing here.

Betulinic acid hydroxamate prevents colonic inflammation and fibrosis in murine models of inflammatory bowel disease

Intestinal fibrosis is a common complication of inflammatory bowel disease (IBD) and is defined as an excessive accumulation of scar tissue in the intestinal wall. Intestinal fibrosis occurs in both forms of IBD: ulcerative colitis and Crohn's disease. Small-molecule inhibitors targeting hypoxia-inducing factor (HIF) prolyl-hydroxylases are promising for the development of novel antifibrotic therapies in IBD. Herein, we evaluated the therapeutic efficacy of hydroxamate of betulinic acid (BHA), a hypoxia mimetic derivative of betulinic acid, against IBD in vitro and in vivo. We showed that BAH (5-20 μM) dose-dependently enhanced collagen gel contraction and activated the HIF pathway in NIH-3T3 fibroblasts; BAH treatment also prevented the loss of trans-epithelial electrical resistance induced by proinflammatory cytokines in Caco-2 cells. In two different murine models (TNBS- and DSS-induced IBD) that cause colon fibrosis, oral administration of BAH (20, 50 mg/kg·d, for 17 days) prevented colon inflammation and fibrosis, as detected using immunohistochemistry and qPCR assays. BAH-treated animals showed a significant reduction of fibrotic markers (Tnc, Col1a2, Col3a1, Timp-1, α-SMA) and inflammatory markers (F4/80⁺, CD3⁺, Il-1β, Ccl3) in colon tissue, as well as an improvement in epithelial barrier integrity and wound healing. BHA displayed promising oral bioavailability, no significant activity against a panel of 68 potential pharmacological targets and was devoid of genotoxicity and cardiotoxicity. Taken together, our results provide evidence that oral administration of BAH can alleviate colon inflammation and colitis-associated fibrosis, identifying the enhancement of colon barrier integrity as a possible mechanism of action, and providing a solid rationale for additional clinical studies.

Creatine Supplementation for Patients with Inflammatory Bowel Diseases: A Scientific Rationale for a Clinical Trial

Based on theoretical considerations, experimental data with cells in vitro, animal studies in vivo, as well as a single case pilot study with one colitis patient, a consolidated hypothesis can be put forward, stating that “oral supplementation with creatine monohydrate (Cr), a pleiotropic cellular energy precursor, is likely to be effective in inducing a favorable response and/or remission in patients with inflammatory bowel diseases (IBD), like ulcerative colitis and/or Crohn’s disease”. A current pilot clinical trial that incorporates the use of oral Cr at a dose of 2 × 7 g per day, over an initial period of 2 months in conjunction with ongoing therapies (NCT02463305) will be informative for the proposed larger, more long-term Cr supplementation study of 2 × 3–5 g of Cr per day for a time of 3–6 months. This strategy should be insightful to the potential for Cr in reducing or alleviating the symptoms of IBD. Supplementation with chemically pure Cr, a natural nutritional supplement, is well tolerated not only by healthy subjects, but also by patients with diverse neuromuscular diseases. If the outcome of such a clinical pilot study with Cr as monotherapy or in conjunction with metformin were positive, oral Cr supplementation could then be used in the future as potentially useful adjuvant therapeutic intervention for patients with IBD, preferably together with standard medication used for treating patients with chronic ulcerative colitis and/or Crohn’s disease.

Inhibition of HIF-prolyl hydroxylases improves healing of intestinal anastomoses

Anastomotic leakage (AL) accounts for a major part of in-house mortality in patients undergoing colorectal surgery. Local ischemia and abdominal sepsis are common risk factors contributing to AL and are characterized by upregulation of the hypoxia-inducible factor (HIF) pathway. The HIF pathway is critically regulated by HIF-prolyl hydroxylases (PHDs). Here, we investigated the significance of PHDs and the effects of pharmacologic PHD inhibition (PHI) during anastomotic healing. Ischemic or septic colonic anastomoses were created in mice by ligation of mesenteric vessels or lipopolysaccharide-induced abdominal sepsis, respectively. Genetic PHD deficiency (Phd1-/-, Phd2+/-, and Phd3-/-) or PHI were applied to manipulate PHD activity. Pharmacologic PHI and genetic PHD2 haplodeficiency (Phd2+/-) significantly improved healing of ischemic or septic colonic anastomoses, as indicated by increased bursting pressure and reduced AL rates. Only Phd2+/- (but not PHI or Phd1-/-) protected from sepsis-related mortality. Mechanistically, PHI and Phd2+/- induced immunomodulatory (M2) polarization of macrophages, resulting in increased collagen content and attenuated inflammation-driven immune cell recruitment. We conclude that PHI improves healing of colonic anastomoses in ischemic or septic conditions by Phd2+/--mediated M2 polarization of macrophages, conferring a favorable microenvironment for anastomotic healing. Patients with critically perfused colorectal anastomosis or abdominal sepsis could benefit from pharmacologic PHI.

Quercetin: a savior of alveolar barrier integrity under hypoxic microenvironment

High altitude pulmonary edema (HAPE) is generally characterized by the loss of alveolar epithelial barrier integrity. The current study was undertaken to assess the noninvasive approaches of HAPE diagnosis and to evaluate the prophylactic potential of quercetin in preventing alveolar junction impairments. Male SD rats fed with quercetin 1 h prior to hypoxia (7,620 m, for 6 h) were selected. PET/CT imaging was performed to visualize the lung uptake of ¹⁸F-FDG in animals under hypoxia. Further, oxidant status, catalase activity, hematological & blood gas parameters were evaluated. Moreover, tight junction (TJ) proteins (ZO-1, JAM-C, Claudin-4, and occludin) expression analysis was accomplished using immune-blotting. The structural differences in lung epithelia were noted by TEM imaging. Quercetin prophylaxis has significantly reduced the FDG uptake in rat lungs under hypoxia. It has also dramatically alleviated the protein oxidation followed by an elevation in catalase activity in the lungs under hypoxia. The TJ protein expression in the lungs has also been restored to normal upon quercetin pre-treatment. Concomitantly, the quercetin preconditioning has elicited the stable blood gas and hematological parameters under hypoxia. The observations from TEM imaging have also implicated the normal lung epithelial structures in the quercetin pretreated animals under hypoxia. Quercetin prophylaxis has significantly restored alveolar epithelium integrity by abating oxidative stress in the lungs under hypoxia.Abbreviations: CT- Computed Tomography¹⁸F-FDG- Fluorodeoxyglucose (¹⁸FHAPE- High Altitude Pulmonary EdemaHb- HemoglobinHCT- HematocritHCO₃^- BicarbonateJAM- Junctional Adhesion MoleculeKBq- Killo BecquerelPaO₂- Partial pressure of arterial oxygenPaCO₂- Partial pressure of arterial carbon di-oxidePET- Positron Emission TomographyRBC- Red Blood CorpusclesSD- Sprague DawleyTJ- Tight JunctionsTEM- Transmission Electron MicroscopyWBC- White Blood CorpusclesZO- Zona Occludin.

Functional foods from the tropics to relieve chronic normobaric hypoxia

Functional foods with antioxidant and anti-inflammatory properties are regarded as a complementary therapy to improve chronic diseases such as obesity and inflammatory bowel disease (IBD). Obesity is a chronic low-grade inflammatory state leading to organ damage with increased risk of common diseases including cardiovascular and metabolic disease, non-alcoholic fatty liver disease, osteoarthritis and some cancers. IBD is a chronic intestinal inflammation categorised as Crohn's disease and ulcerative colitis depending on the location of inflammation. These inflammatory states are characterised by normobaric hypoxia in adipose and intestinal tissues, respectively. Tropical foods especially from Australia and South America are discussed in this review to show their potential in attenuation of these chronic diseases. The phytochemicals from these foods have antioxidant and anti-inflammatory activities to reduce chronic normobaric hypoxia in the tissues. These health benefits of the tropical foods are relevant not only for health economy but also in providing a global solution by improving the sustainability of their cultivation and assisting the local economies.

Relationship between intestinal microbiota, diet and biological systems: an integrated view

The health-disease process can be influenced by the intestinal microbiota. As this plays a fundamental role in protecting the organism, the importance of studying the composition and diversity of this community becomes increasingly evident. Changes in the composition of the intestinal bacterial community may result in dysbiosis, and this process may contribute to triggering various diseases in all biological systems. This imbalance of intestinal microbiota homeostasis may alter commensal bacteria and the host metabolism, as well as immune function. Dysbiosis also causes an increase in intestinal permeability due to exposure to molecular patterns associated with the pathogen and lipopolysaccharides, leading to a chronic inflammatory process that can result in diseases for all biological systems. In this context, dietary intervention through the use of probiotics, prebiotics and antioxidant foods can be considered a contribution to the modulation of intestinal microbiota. Probiotics have been used to provide up to 10 billion colony forming units, and probiotic foods, Kefir and fermented natural yogurt are also used. Prebiotics, in turn, are found in supplemental formulations of processed foods and in functional foods that are also sources of phenolic compounds, such as flavonoids, antioxidant and anti-inflammatory substances, polyunsaturated fatty acids, vitamins, and minerals. In this review, we will discuss the relationship between an imbalance in the intestinal microbiota with the development of diseases, besides indicating the need for future studies that can establish bacterial parameters for the gastrointestinal tract by modulating the intestinal microbiota, associated with the adoption of healthy habits during all life cycles.

The HIF target ATG9A is essential for epithelial barrier function and tight junction biogenesis

Intestinal epithelial cells (IECs) exist in a metabolic state of low oxygen tension termed "physiologic hypoxia." An important factor in maintaining intestinal homeostasis is the transcription factor hypoxia-inducible factor (HIF), which is stabilized under hypoxic conditions and mediates IEC homeostatic responses to low oxygen tension. To identify HIF transcriptional targets in IEC, chromatin immunoprecipitation (ChIP) was performed in Caco-2 IECs using HIF-1α- or HIF-2α-specific antibodies. ChIP-enriched DNA was hybridized to a custom promoter microarray (termed ChIP-chip). This unbiased approach identified autophagy as a major HIF-1-targeted pathway in IEC. Binding of HIF-1 to the ATG9A promoter, the only transmembrane component within the autophagy pathway, was particularly enriched by exposure of IEC to hypoxia. Validation of this ChIP-chip revealed prominent induction of ATG9A, and luciferase promoter assays identified a functional hypoxia response element upstream of the TSS. Hypoxia-mediated induction of ATG9A was lost in cells lacking HIF-1. Strikingly, we found that lentiviral-mediated knockdown (KD) of ATG9A in IECs prevents epithelial barrier formation by >95% and results in significant mislocalization of multiple tight junction (TJ) proteins. Extensions of these findings showed that ATG9A KD cells have intrinsic abnormalities in the actin cytoskeleton, including mislocalization of the TJ binding protein vasodilator-stimulated phosphoprotein. These results implicate ATG9A as essential for multiple steps of epithelial TJ biogenesis and actin cytoskeletal regulation. Our findings have novel applicability for disorders that involve a compromised epithelial barrier and suggest that targeting ATG9A may be a rational strategy for future therapeutic intervention.

Ruffles and spikes: Control of tight junction morphology and permeability by claudins

Epithelial barrier function is regulated by a family of transmembrane proteins known as claudins. Functional tight junctions are formed when claudins interact with other transmembrane proteins, cytosolic scaffold proteins and the actin cytoskeleton. The predominant scaffold protein, zonula occludens-1 (ZO-1), directly binds to most claudin C-terminal domains, crosslinking them to the actin cytoskeleton. When imaged by immunofluorescence microscopy, tight junctions most frequently are linear structures that form between tricellular junctions. However, tight junctions also adapt non-linear architectures exhibiting either a ruffled or spiked morphology, which both are responses to changes in claudin engagement of actin filaments. Other terms for ruffled tight junctions include wavy, tortuous, undulating, serpentine or zig-zag junctions. Ruffling is under the control of hypoxia induced factor (HIF) and integrin-mediated signaling, as well as direct mechanical stimulation. Tight junction ruffling is specifically enhanced by claudin-2, antagonized by claudin-1 and requires claudin binding to ZO-1. Tight junction spikes are sites of active vesicle budding and fusion that appear as perpendicular projections oriented towards the nucleus. Spikes share molecular features with focal adherens junctions and tubulobulbar complexes found in Sertoli cells. Lung epithelial cells under stress form spikes due to an increase in claudin-5 expression that directly disrupts claudin-18/ZO-1 interactions. Together this suggests that claudins are not simply passive cargoes controlled by scaffold proteins. We propose a model where claudins specifically influence tight junction scaffold proteins to control interactions with the cytoskeleton as a mechanism that regulates tight junction assembly and function.

Hypoxia and Innate Immunity: Keeping Up with the HIFsters

Recent years have witnessed an emergence of interest in understanding metabolic changes associated with immune responses, termed immunometabolism. As oxygen is central to all aerobic metabolism, hypoxia is now recognized to contribute fundamentally to inflammatory and immune responses. Studies from a number of groups have implicated a prominent role for oxygen metabolism and hypoxia in innate immunity of healthy tissue (physiologic hypoxia) and during active inflammation (inflammatory hypoxia). This inflammatory hypoxia emanates from a combination of recruited inflammatory cells (e.g., neutrophils, eosinophils, and monocytes), high rates of oxidative metabolism, and the activation of multiple oxygen-consuming enzymes during inflammation. These localized shifts toward hypoxia have identified a prominent role for the transcription factor hypoxia-inducible factor (HIF) in the regulation of innate immunity. Such studies have provided new and enlightening insight into our basic understanding of immune mechanisms, and extensions of these findings have identified potential therapeutic targets. In this review, we summarize recent literature around the topic of innate immunity and mucosal hypoxia with a focus on transcriptional responses mediated by HIF.

Metabolism at the centre of the host-microbe relationship

Maintaining homoeostatic host–microbe interactions is vital for host immune function. The gut microbiota shapes the host immune system and the immune system reciprocally shapes and modifies the gut microbiota. However, our understanding of how these microbes are tolerated and how individual, or communities of, gut microbes influence host function is limited. This review will focus on metabolites as key mediators of this complex host–microbe relationship. It will look at the central role of epithelial metabolism in shaping the gut microbiota, how microbial metabolites influence the epithelium and the mucosal and peripheral immune system, and how the immune system shapes microbial composition and metabolism. Finally, this review will look at how metabolites are involved in cross‐talk between different members of the microbiota and their role during infections.