Human intelectin-1 (ITLN1) genetic variation and intestinal expression

Omentin-General Overview of Its Role in Obesity, Metabolic Syndrome and Other Diseases; Problem of Current Research State

Background: Omentin (omentin-1, intelectin-1, ITLN-1) is an adipokine considered to be a novel substance. Many chronic, inflammatory, or civilization diseases are linked to obesity, in which omentin plays a significant role. Methods: MEDLINE and SCOPUS databases were searched using the keywords "omentin" or "intelectin-1". Then the most recent articles providing new perspectives on the matter and the most important studies, which revealed crucial insight, were selected to summarize the current knowledge on the role of omentin in a literature review. Results and Conclusions: The valid role of this adipokine is evident in the course of metabolic syndrome. In most cases, elevated omentin expression is correlated with the better course of diseases, including: type 2 diabetes mellitus, polycystic ovary syndrome, rheumatoid arthritis, metabolic dysfunction-associated steatotic liver disease, Crohn's disease, ulcerative colitis, atherosclerosis, or ischemic stroke, for some of which it can be a better marker than the currently used ones. However, results of omentin studies are not completely one-sided. It was proven to participate in the development of asthma and atopic dermatitis and to have different concentration dynamics in various types of tumors. All of omentin's effects and properties make it an attractive subject of research, considering still unexplored inflammation mechanisms, in which it may play an important role. Omentin was proven to prevent osteoarthritis, hepatocirrhosis, and atherosclerosis in mouse models. All of the above places omentin among potential therapeutic products, and not only as a biomarker. However, the main problems with the omentin's research state are the lack of standardization, which causes many contradictions and disagreements in this field.

The human gut Bacteroides eggerthii expresses a new galactofuranose-containing lipooligosaccharide with weak immunostimulatory properties

Lipopolysaccharides (LPS) decorating the cell surface of Gram-negative bacteria exhibit nuanced functionalities linked to their precise structural composition. However, despite their critical role in health and disease, information on the structure and function of LPS from members of the human gut microbiota is still limited. Here, we deciphered the complete structure of the LPS isolated from the human gut bacterium Bacteroides eggerthii 1_2_48FAA. We showed that B. eggerthii 1_2_48FAA produces an R-type LPS (or lipooligosaccharide, LOS) composed of a heterogeneous mixture of tetra- and penta-acylated lipid A species with different degree of phosphorylation, and a compact galactofuranose-containing core oligosaccharide. Using in vitro human cell lines, we showed that B. eggerthii 1_2_48FAA LOS acts as a weak activator of TLR4-mediated signaling. Moreover, we observed that expression of maturation markers CD40, CD80 and CD86 on monocytes-derived dendritic cells upon B. eggerthii 1_2_48FAA LOS exposure was significantly lower compared to pro-inflammatory Escherichia coli LPS. Taken together, these data provide new structural and biological insights into LPS from gut bacteria, underscoring the importance of structural features in modulating host immunity.

Insights Into Glycobiology and the Protein-Glycan Interactome Using Glycan Microarray Technologies

Glycans linked to proteins and lipids and also occurring in free forms have many functions, and these are partly elicited through specific interactions with glycan-binding proteins (GBPs). These include lectins, adhesins, toxins, hemagglutinins, growth factors, and enzymes, but antibodies can also bind glycans. While humans and other animals generate a vast repertoire of GBPs and different glycans in their glycomes, other organisms, including phage, microbes, protozoans, fungi, and plants also express glycans and GBPs, and these can also interact with their host glycans. This can be termed the protein-glycan interactome, and in nature is likely to be vast, but is so far very poorly described. Understanding the breadth of the protein-glycan interactome is also a key to unlocking our understanding of infectious diseases involving glycans, and immunology associated with antibodies binding to glycans. A key technological advance in this area has been the development of glycan microarrays. This is a display technology in which minute quantities of glycans are attached to the surfaces of slides or beads. This allows the arrayed glycans to be interrogated by GBPs and antibodies in a relatively high throughput approach, in which a protein may bind to one or more distinct glycans. Such binding can lead to novel insights and hypotheses regarding both the function of the GBP, the specificity of an antibody and the function of the glycan within the context of the protein-glycan interactome. This article focuses on the types of glycan microarray technologies currently available to study animal glycobiology and examples of breakthroughs aided by these technologies.

Soluble Human Lectins at the Host-Microbe Interface

Human lectins are integral to maintaining microbial homeostasis on the skin, in the blood, and at mucosal barriers. These proteins can recognize microbial glycans and inform the host about its microbial status. In accordance with their roles, their production can vary with tissue type. They also can have unique structural and biochemical properties, and they can influence microbial colonization at sites proximal and distal to their tissue of origin. In line with their classification as innate immune proteins, soluble lectins have long been studied in the context of acute infectious disease, but only recently have we begun to appreciate their roles in maintaining commensal microbial communities (i.e., the human microbiota). This review provides an overview of soluble lectins that operate at host-microbe interfaces, their glycan recognition properties, and their roles in physiological and pathological mechanisms.

Innovative insights: ITLN1 modulates renal injury in response to radiation

Radiation-induced kidney injury is a common side effect of radiotherapy, as the pelvic region is in close proximity to the kidneys, posing a risk of inducing radiation-induced kidney injury when treating any pelvic malignancies with radiotherapy. This type of injury typically manifests as chronic kidney disease a few months after radiotherapy, with the potential to progress to end-stage renal disease. Radiation-induced damage involves various components of the kidney, including glomeruli, tubules, interstitium, and extracellular matrix. Therefore, investigating its molecular mechanisms is crucial. In this study, we extensively searched literature databases, selecting recent transcriptomic studies related to acute kidney injury (AKI) published in the past decade. We downloaded the raw RNA sequencing datasets GSE30718 and GSE66494 related to AKI from the GEO database and identified that intestinal-type lectin ITLN1 plays a significant role in regulating radiation-induced kidney injury in rats. Differential gene analysis was performed using chip data from the GEO database, and further bioinformatics analysis identified 13 genes that may be involved in regulating kidney injury, with ITLN1 being the most relevant to kidney damage, thus selected as the target gene for this study. Subsequently, a rat model of radiation-induced kidney injury was established for experimental validation, assessing kidney tissue morphology and injury extent through staining observation and immunohistochemical staining. The protective effect of ITLN1 on kidney function was evaluated by measuring changes in rat body weight and blood pressure, serum kidney injury markers, and kidney structure. The experimental results indicate that overexpression of ITLN1 can improve kidney function in rats with radiation-induced kidney injury by activating the Akt/GSK-3β/Nrf2 signaling pathway, suppressing oxidative stress, cell apoptosis, inflammation, cellular senescence, and fibrosis. This study highlights the significant role of ITLN1 in regulating kidney injury, providing a novel target for future treatments of radiation-induced kidney injury.

A common polymorphism in the Intelectin-1 gene influences mucus plugging in severe asthma

By incompletely understood mechanisms, type 2 (T2) inflammation present in the airways of severe asthmatics drives the formation of pathologic mucus which leads to airway mucus plugging. Here we investigate the molecular role and clinical significance of intelectin-1 (ITLN-1) in the development of pathologic airway mucus in asthma. Through analyses of human airway epithelial cells we find that ITLN1 gene expression is highly induced by interleukin-13 (IL-13) in a subset of metaplastic MUC5AC+ mucus secretory cells, and that ITLN-1 protein is a secreted component of IL-13-induced mucus. Additionally, we find ITLN-1 protein binds the C-terminus of the MUC5AC mucin and that its deletion in airway epithelial cells partially reverses IL-13-induced mucostasis. Through analysis of nasal airway epithelial brushings, we find that ITLN1 is highly expressed in T2-high asthmatics, when compared to T2-low children. Furthermore, we demonstrate that both ITLN-1 gene expression and protein levels are significantly reduced by a common genetic variant that is associated with protection from the formation of mucus plugs in T2-high asthma. This work identifies an important biomarker and targetable pathways for the treatment of mucus obstruction in asthma.

Transcriptomic Profiling and Cellular Composition of Creeping Fat in Crohn's disease

BACKGROUND AND AIMS

Creeping fat [CF] is a poorly understood feature of Crohn's disease [CD], characterized by the wrapping of mesenteric adipose tissue [MAT] around the inflamed intestine. The aim of this study was to investigate the transcriptional profile and compositional features of CF.

METHODS

We collected 59 MAT samples: 23 paired samples from patients with CD (CF [CD-CF] and MAT around the uninflamed intestine [CD-MAT]) and 13 MAT samples from non-CD patients [Con-MAT]. Differentially expressed gene [DEG], functional pathway, cell deconvolution, and gene co-expression network analyses were performed.

RESULTS

By comparing three different MAT samples, we identified a total of 529 DEGs [|log2FoldChange| > 1.5; false discovery rate < 0.05]. Of these, 323 genes showed an incremental pattern from Con-MAT to CD-MAT, and to CD-CF, while 105 genes displayed a decremental pattern. Genes with an incremental pattern were related to immune cell responses, including B- and T-cell activation, while genes with a decremental pattern were involved in cell trafficking and migration. Cell deconvolution analysis revealed significant changes in cellular composition between the CD-CF and Con-MAT groups, with increased proportions of B-cells/plasma cells [p = 1.16 × 10-4], T-cells [p = 3.66 × 10-3], and mononuclear phagocytes [p = 3.53 × 10-2] in the CD-CF group. In contrast, only the B-cell/plasma cell component showed a significant increase [p = 1.62 × 10-2] in the CD-MAT group compared to Con-MAT.

CONCLUSION

The distinct transcriptional profiles and altered cellular components of each MAT found in our study provide insight into the mechanisms behind CF and highlight its possible role in the pathogenesis of CD.

Application of enzyme-linked immunosorbent assay to detect antimicrobial peptides in human intestinal lumen

Intestinal transplantation is the definitive treatment for intestinal failure. However, tissue rejection and graft-versus-host disease are relatively common complications, necessitating aggressive immunosuppression that can itself pose further complications. Tracking intraluminal markers in ileal effluent from standard ileostomies may present a noninvasive and sensitive way to detect developing pathology within the intestinal graft. This would be an improvement compared to current assessments, which are limited by poor sensitivity and specificity, contributing to under or over-immunosuppression, respectively, and by the need for invasive biopsies. Herein, we report an approach to reproducibly analyze ileal fluid obtained through stoma sampling for antimicrobial peptide/protein concentrations, reasoning that these molecules may provide an assessment of intestinal homeostasis and levels of intestinal inflammation over time. Concentrations of lysozyme (LYZ), myeloperoxidase (MPO), calprotectin (S100A8/A9) and β-defensin 2 (DEFB2) were assessed using adaptations of commercially available enzyme-linked immunosorbent assays (ELISAs). The concentration of α-defensin 5 (DEFA5) was assessed using a newly developed sandwich ELISA. Our data support that with proper preparation of ileal effluent specimens, precise and replicable determination of antimicrobial peptide/protein concentrations can be achieved for each of these target molecules via ELISA. This approach may prove to be reliable as a clinically useful assessment of intestinal homeostasis over time for patients with ileostomies.

Microbial experience through housing in a farmyard-type environment alters intestinal barrier properties in mouse colons

To close the gap between ultra-hygienic research mouse models and the much more environmentally exposed conditions of humans, we have established a system where laboratory mice are raised under a full set of environmental factors present in a naturalistic, farmyard-type habitat-a process we have called feralization. In previous studies we have shown that feralized (Fer) mice were protected against colorectal cancer when compared to conventionally reared laboratory mice (Lab). However, the protective mechanisms remain to be elucidated. Disruption of the protective intestinal barrier is an acknowledged player in colorectal carcinogenesis, and in the current study we assessed colonic mucosal barrier properties in healthy, feralized C57BL/6JRj male mice. While we found no effect of feralization on mucus layer properties, higher expression of genes encoding the mucus components Fcgbp and Clca1 still suggested mucus enforcement due to feralization. Genes encoding other proteins known to be involved in bacterial defense (Itln1, Ang1, Retnlb) and inflammatory mechanisms (Zbp1, Gsdmc2) were also higher expressed in feralized mice, further suggesting that the Fer mice have an altered intestinal mucosal barrier. These findings demonstrate that microbial experience conferred by housing in a farmyard-type environment alters the intestinal barrier properties in mice possibly leading to a more robust protection against disease. Future studies to unravel regulatory roles of feralization on intestinal barrier should aim to conduct proteomic analyses and in vivo performance of the feralized mice intestinal barrier.

Diagnostic and Prognostic Value of Serum Omentin-1 in Sepsis: A Prospective Study in Critically Ill Patients

Background and Objectives: Omentin-1, also known as intelectin-1, is a novel adipokine with anti-inflammatory activities implicated in inflammatory diseases and sepsis. We aimed to explore serum omentin-1 and its kinetics in critically ill patients early in sepsis and its association with severity and prognosis. Materials and Methods: Serum omentin-1 was determined in 102 critically ill patients with sepsis during the first 48 h from sepsis onset and 1 week later, and in 102 age- and gender-matched healthy controls. The outcome of sepsis at 28 days after enrollment was recorded. Results: Serum omentin-1 at enrollment was significantly higher in patients compared to controls (763.3 ± 249.3 vs. 451.7 ± 122.3 μg/L, p < 0.001) and it further increased 1 week after (950.6 ± 215.5 vs. 763.3 ± 249.3 μg/L, p < 0.001). Patients with septic shock (n = 42) had higher omentin-1 compared to those with sepsis (n = 60) at enrollment (877.9 ± 241.2 vs. 683.1 ± 223.7 μg/L, p < 0.001) and 1 week after (1020.4 ± 224.7 vs. 901.7 ± 196.3 μg/L, p = 0.007). Furthermore, nonsurvivors (n = 30) had higher omentin-1 at sepsis onset (952.1 ± 248.2 vs. 684.6 ± 204.7 μg/L, p < 0.001) and 1 week after (1051.8 ± 242 vs. 908.4 ± 189.8 μg/L, p < 0.01). Patients with sepsis and survivors presented higher kinetics than those with septic shock and nonsurvivors (Δ(omentin-1)% 39.8 ± 35.9% vs. 20.2 ± 23.3%, p = 0.01, and 39.4 ± 34.3% vs. 13.3 ± 18.1%, p < 0.001, respectively). Higher omentin-1 at sepsis onset and 1 week after was an independent predictor of 28-day mortality (HR 2.26, 95% C.I. 1.21-4.19, p = 0.01 and HR: 2.15, 95% C.I. 1.43-3.22, p < 0.001, respectively). Finally, omentin-1 was significantly correlated with the severity scores, the white blood cells, coagulation biomarkers, and CRP, but not procalcitonin and other inflammatory biomarkers. Conclusions: Serum omentin-1 is increased in sepsis, while higher levels and lower kinetics during the first week of sepsis are associated with the severity and 28-day mortality of sepsis. Omentin-1 may be a promising biomarker of sepsis. However, more studies are needed to explore its role in sepsis.

Intelectin-1 binds and alters the localization of the mucus barrier-modifying bacterium Akkermansia muciniphila

Intelectin-1 (ITLN1) is a lectin secreted by intestinal epithelial cells (IECs) and upregulated in human ulcerative colitis (UC). We investigated how ITLN1 production is regulated in IECs and the biological effects of ITLN1 at the host-microbiota interface using mouse models. Our data show that ITLN1 upregulation in IECs from UC patients is a consequence of activating the unfolded protein response. Analysis of microbes coated by ITLN1 in vivo revealed a restricted subset of microorganisms, including the mucolytic bacterium Akkermansia muciniphila. Mice overexpressing intestinal ITLN1 exhibited decreased inner colonic mucus layer thickness and closer apposition of A. muciniphila to the epithelial cell surface, similar to alterations reported in UC. The changes in the inner mucus layer were microbiota and A. muciniphila dependent and associated with enhanced sensitivity to chemically induced and T cell-mediated colitis. We conclude that by determining the localization of a select group of bacteria to the mucus layer, ITLN1 modifies this critical barrier. Together, these findings may explain the impact of ITLN1 dysregulation on UC pathogenesis.

Lectin recruits pathogenic bugs

Colitis is an irritable bowel disorder affecting about 7 million patients worldwide, but the causes are diverse and not fully understood. In this issue, Matute et al. (2022. J. Exp. Med.https://doi.org/10.1084/jem.20211938) found that a stress-induced lectin, intelectin-1, recruits pathogenic bacteria to the gut and exacerbates colitis.

Treatment of peanut allergy and colitis in mice via the intestinal release of butyrate from polymeric micelles

The microbiome modulates host immunity and aids the maintenance of tolerance in the gut, where microbial and food-derived antigens are abundant. Yet modern dietary factors and the excessive use of antibiotics have contributed to the rising incidence of food allergies, inflammatory bowel disease and other non-communicable chronic diseases associated with the depletion of beneficial taxa, including butyrate-producing Clostridia. Here we show that intragastrically delivered neutral and negatively charged polymeric micelles releasing butyrate in different regions of the intestinal tract restore barrier-protective responses in mouse models of colitis and of peanut allergy. Treatment with the butyrate-releasing micelles increased the abundance of butyrate-producing taxa in Clostridium cluster XIVa, protected mice from an anaphylactic reaction to a peanut challenge and reduced disease severity in a T-cell-transfer model of colitis. By restoring microbial and mucosal homoeostasis, butyrate-releasing micelles may function as an antigen-agnostic approach for the treatment of allergic and inflammatory diseases.

The role of goblet cells and mucus in intestinal homeostasis

The intestinal tract faces numerous challenges that require several layers of defence. The tight epithelium forms a physical barrier that is further protected by a mucus layer, which provides various site-specific protective functions. Mucus is produced by goblet cells, and as a result of single-cell RNA sequencing identifying novel goblet cell subpopulations, our understanding of their various contributions to intestinal homeostasis has improved. Goblet cells not only produce mucus but also are intimately linked to the immune system. Mucus and goblet cell development is tightly regulated during early life and synchronized with microbial colonization. Dysregulation of the developing mucus systems and goblet cells has been associated with infectious and inflammatory conditions and predisposition to chronic disease later in life. Dysfunctional mucus and altered goblet cell profiles are associated with inflammatory conditions in which some mucus system impairments precede inflammation, indicating a role in pathogenesis. In this Review, we present an overview of the current understanding of the role of goblet cells and the mucus layer in maintaining intestinal health during steady-state and how alterations to these systems contribute to inflammatory and infectious disease.

Characterization of an intelectin-1 (Itln1) knockout mouse model

Intelectins are carbohydrate-binding proteins implicated in innate immunity and highly conserved across chordate evolution, including both ascidians and humans. Human intelectin-1 (ITLN1) is highly abundant within the intestinal mucosa and binds microbial but not host glycans. Genome-wide association studies identified SNPs in ITLN1 that are linked to susceptibility for Crohn's disease. Moreover, ITLN1 has been implicated in the pathophysiology of obesity and associated metabolic disease. To gain insight on biological activities of human ITLN1 in vivo, we developed a C57BL/6 mouse model genetically targeting the gene encoding the functional mouse ortholog. In wild-type C57BL/6 mice, both mRNA and protein analysis showed high expression of Itln1 in the small intestine, but manifold lower levels in colon and other extraintestinal tissues. Whereas intestinal expression of human ITLN1 localizes to goblet cells, our data confirm that mouse Itln1 is expressed in Paneth cells. Compared to wild-type littermate controls, mice homozygous for the Itln1 hypomorphic trapping allele had reduced expression levels of Itln1 expression (~10,000-fold). The knockout mice exhibited increased susceptibility in an acute model of experimentally induced colitis with 2% w/v dextran sulfate sodium (DSS). In a model of chronic colitis using a lower dose of DSS (1.5% w/v), which enabled a detailed view of disease activity across a protracted period, no differences were observed in body weight, fecal texture, hemoccult scores, food/water intake, or colon length at necropsy, but there was a statistically significant genotype over time effect for the combined fecal scores of disease activity. In model of diet-induced obesity, using two western-style diets, which varied in amounts of sugar (as sucrose) and saturated fat (as lard), mice with Itln1 expression ablated showed no increased susceptibility, in terms of weight gain, food intake, plasma markers of obesity compared to wildtype littermates. While the mouse genetic knockout model for Itln1 holds promise for elucidating physiological function(s) for mammalian intelectins, results reported here suggest that Itln1, a Paneth cell product in C57BL/6 mice, likely plays a minor role in the pathophysiology of chemically induced colitis or diet-induced obesity.

Human intelectin-2 (ITLN2) is selectively expressed by secretory Paneth cells

Intelectins (intestinal lectins) are highly conserved across chordate evolution and have been implicated in various human diseases, including Crohn's disease (CD). The human genome encodes two intelectin genes, intelectin-1 (ITLN1) and intelectin-2 (ITLN2). Other than its high sequence similarity with ITLN1, little is known about ITLN2. To address this void in knowledge, we report that ITLN2 exhibits discrete, yet notable differences from ITLN1 in primary structure, including a unique amino terminus, as well as changes in amino acid residues associated with the glycan-binding activity of ITLN1. We identified that ITLN2 is a highly abundant Paneth cell-specific product, which localizes to secretory granules, and is expressed as a multimeric protein in the small intestine. In surgical specimens of ileal CD, ITLN2 mRNA levels were reduced approximately five-fold compared to control specimens. The ileal expression of ITLN2 was unaffected by previously reported disease-associated variants in ITLN2 and CD-associated variants in neighboring ITLN1 as well as NOD2 and ATG16L1. ITLN2 mRNA expression was undetectable in control colon tissue; however, in both ulcerative colitis (UC) and colonic CD, metaplastic Paneth cells were found to express ITLN2. Together, the data reported establish the groundwork for understanding ITLN2 function(s) in the intestine, including its possible role in CD.

Extensive variation in the intelectin gene family in laboratory and wild mouse strains

Intelectins are a family of multimeric secreted proteins that bind microbe-specific glycans. Both genetic and functional studies have suggested that intelectins have an important role in innate immunity and are involved in the etiology of various human diseases, including inflammatory bowel disease. Experiments investigating the role of intelectins in human disease using mouse models are limited by the fact that there is not a clear one-to-one relationship between intelectin genes in humans and mice, and that the number of intelectin genes varies between different mouse strains. In this study we show by gene sequence and gene expression analysis that human intelectin-1 (ITLN1) has multiple orthologues in mice, including a functional homologue Itln1; however, human intelectin-2 has no such orthologue or homologue. We confirm that all sub-strains of the C57 mouse strain have a large deletion resulting in retention of only one intelectin gene, Itln1. The majority of laboratory strains have a full complement of six intelectin genes, except CAST, SPRET, SKIVE, MOLF and PANCEVO strains, which are derived from different mouse species/subspecies and encode different complements of intelectin genes. In wild mice, intelectin deletions are polymorphic in Mus musculus castaneus and Mus musculus domesticus. Further sequence analysis shows that Itln3 and Itln5 are polymorphic pseudogenes due to premature truncating mutations, and that mouse Itln1 has undergone recent adaptive evolution. Taken together, our study shows extensive diversity in intelectin genes in both laboratory and wild-mice, suggesting a pattern of birth-and-death evolution. In addition, our data provide a foundation for further experimental investigation of the role of intelectins in disease.