Galectin-2 at the enterocyte brush border of the small intestine

Prominosomes - a particular class of extracellular vesicles containing prominin-1/CD133?

Extracellular membrane vesicles (EVs) offer promising values in various medical fields, e.g., as biomarkers in liquid biopsies or as native (or bioengineered) biological nanocarriers in tissue engineering, regenerative medicine and cancer therapy. Based on their cellular origin EVs can vary considerably in composition and diameter. Cell biological studies on mammalian prominin-1, a cholesterol-binding membrane glycoprotein, have helped to reveal new donor membranes as sources of EVs. For instance, small EVs can originate from microvilli and primary cilia, while large EVs might be produced by transient structures such as retracting cellular extremities of cancer cells during the mitotic rounding process, and the midbody at the end of cytokinesis. Here, we will highlight the various subcellular origins of prominin-1+ EVs, also called prominosomes, and the potential mechanism(s) regulating their formation. We will further discuss the molecular and cellular characteristics of prominin-1, notably those that have a direct effect on the release of prominin-1+ EVs, a process that might be directly implicated in donor cell reprogramming of stem and cancer stem cells. Prominin-1+ EVs also mediate intercellular communication during embryonic development and adult homeostasis in healthy individuals, while disseminating biological information during diseases.

Integrated omics profiling reveals systemic dysregulation and potential biomarkers in the blood of patients with neuromyelitis optica spectrum disorders

BACKGROUND

Neuromyelitis optica spectrum disorders (NMOSD) are autoimmune conditions that affect the central nervous system. The contribution of peripheral abnormalities to the disease's pathogenesis is not well understood.

METHODS

To investigate this, we employed a multi-omics approach analyzing blood samples from 52 NMOSD patients and 46 healthy controls (HC). This included mass cytometry, cytokine arrays, and targeted metabolomics. We then analyzed the peripheral changes of NMOSD, and features related to NMOSD's disease severity. Furthermore, an integrative analysis was conducted to identify the distinguishing characteristics of NMOSD from HC. Additionally, we unveiled the variations in peripheral features among different clinical subgroups within NMOSD. An independent cohort of 40 individuals with NMOSD was utilized to assess the serum levels of fibroblast activation protein alpha (FAP).

RESULTS

Our analysis revealed a distinct peripheral immune and metabolic signature in NMOSD patients. This signature is characterized by an increase in monocytes and a decrease in regulatory T cells, dendritic cells, natural killer cells, and various T cell subsets. Additionally, we found elevated levels of inflammatory cytokines and reduced levels of tissue-repair cytokines. Metabolic changes were also evident, with higher levels of bile acids, lactates, triglycerides, and lower levels of dehydroepiandrosterone sulfate, homoarginine, octadecadienoic acid (FA[18:2]), and sphingolipids. We identified distinctive biomarkers differentiating NMOSD from HC and found blood factors correlating with disease severity. Among these, fibroblast activation protein alpha (FAP) was a notable marker of disease progression.

CONCLUSIONS

Our comprehensive blood profile analysis offers new insights into NMOSD pathophysiology, revealing significant peripheral immune and metabolic alterations. This work lays the groundwork for future biomarker identification and mechanistic studies in NMOSD, highlighting the potential of FAP as a marker of disease progression.

Omentin expression in the ovarian follicles of Large White and Meishan sows during the oestrous cycle and in vitro effect of gonadotropins and steroids on its level: Role of ERK1/2 and PI3K signaling pathways

Omentin (ITLN1) is a novel adipokine mainly expressed in the white adipose tissue. It plays a crucial role in the metabolic homeostasis and insulin sensitivity. Our last study documented that ITLN1 levels in the adipose tissue and plasma are lower in fat Meishan (MS) compared to normal weight Large White (LW) pigs. The aim of this study was to investigate transcript and protein concentrations of ITLN1 as well as its immunolocalisation in the ovarian follicles and examine the molecular mechanism involved in the regulation of its expression in response to gonadotropins (FSH, LH) and steroids (P4, T, E2). Ovarian follicles were collected from LW and MS sows on days 2-3, 10-12, and 14-16 of the oestrous. We found the elevated ITLN1 expression in the ovarian follicles and the increase of concentrations in follicular fluid (FF) of LW pigs vs MS pigs; in both breeds of pigs, the levels of ITLN1 increased with the oestrous progression. We noted ITLN1 signals in oocyte, granulosa and theca cells. Gonadotropins and steroids increased ITLN1 levels in the ovarian follicle cells of LW pigs, while in MS pigs, we observed only the stimulatory effect of LH and T. Both extracellular signal-regulated kinase (ERK1/2) and phosphatidylinositol 3'-kinase (PI3K) were involved in the regulation of ITLN1. Our study demonstrated the levels and regulation of ITLN1 in the porcine ovarian follicles through ERK1/2 and PI3K signaling pathways.

Placental galectins: a subfamily of galectins lose the ability to bind β-galactosides with new structural features†

Galectins are a phylogenetically conserved family of soluble β-galactoside binding proteins. There are 16 different of galectins, each with a specific function determined by its distinct distribution and spatial structure. Galectin-13, galectin-14, and galectin-16 are distinct from other galectin members in that they are primarily found in placental tissue. These galectins, also referred to as placental galectins, play critical roles in regulating pregnancy-associated processes, such as placenta formation and maternal immune tolerance to the embedded embryo. The unique structural characteristics and the inability to bind lactose of placental galectins have recently received significant attention. This review primarily examines the novel structural features of placental galectins, which distinguish them from the classic galectins. Furthermore, it explores the correlation between these structural features and the loss of β-galactoside binding ability. In addition, the newly discovered functions of placental galectins in recent years are also summarized in our review. A detailed understanding of the roles of placental galectins may contribute to the discovery of new mechanisms causing numerous pregnancy diseases and enable the development of new diagnostic and therapeutic strategies for the treatment of these diseases, ultimately benefiting the health of mothers and offspring.

Galectin-2 in Health and Diseases

Galectin-2 is a prototype member of the galactoside-binding galectin family. It is predominately expressed in the gastrointestinal tract but is also detected in several other tissues such as the placenta and in the cardiovascular system. Galectin-2 expression and secretion by epithelial cells has been reported to contribute to the strength of the mucus layer, protect the integrity of epithelia. A number of studies have also suggested the involvement of galectin-2 in tissue inflammation, immune response and cell apoptosis. Alteration of galectin-2 expression occurs in inflammatory bowel disease, coronary artery diseases, rheumatoid arthritis, cancer, and pregnancy disorders and has been shown to be involved in disease pathogenesis. This review discusses our current understanding of the role and actions of galectin-2 in regulation of these pathophysiological conditions.

Morbid Obesity in Women Is Associated with an Altered Intestinal Expression of Genes Related to Cancer Risk and Immune, Defensive, and Antimicrobial Response

Background: Little is known about the relation between morbid obesity and duodenal transcriptomic changes. We aimed to identify intestinal genes that may be associated with the development of obesity regardless of the degree of insulin resistance (IR) of patients. Material and Methods: Duodenal samples were assessed by microarray in three groups of women: non-obese women and women with morbid obesity with low and high IR. Results: We identified differentially expressed genes (DEGs) associated with morbid obesity, regardless of IR degree, related to digestion and lipid metabolism, defense response and inflammatory processes, maintenance of the gastrointestinal epithelium, wound healing and homeostasis, and the development of gastrointestinal cancer. However, other DEGs depended on the IR degree. We mainly found an upregulation of genes involved in the response to external organisms, hypoxia, and wound healing functions in women with morbid obesity and low IR. Conclusions: Regardless of the degree of IR, morbid obesity is associated with an altered expression of genes related to intestinal defenses, antimicrobial and immune responses, and gastrointestinal cancer. Our data also suggest a deficient duodenal immune and antimicrobial response in women with high IR.

Cherry Valley Duck Galectin-2 Plays an Essential Role in Avian Pathogenic Escherichia coli Infection-Induced Innate Immune Response

Galectins play important roles in the host's innate immunity as pattern recognition receptors. In this study, the coding sequences of galectin-2 were identified from Cherry Valley ducks. Tissue distribution of duck galectin-2 (duGal-2) in healthy ducks and ducks infected with avian pathogenic Escherichia coli (APEC) was studied, respectively. The results showed that duGal-2 expression was higher in the gut, kidney, and liver tissue, and weakly expressed in the lung and brain, in healthy ducks; however, the expression level of duGal-2 was detected as being up-regulated after infection with APEC. In addition, knockdown or overexpression of duGal-2 in DEFs was achieved by small interference RNA (siRNA) transfection and plasmid transduction, respectively. The knockdown of duGal-2 led to a decrease in the expression of some inflammatory cytokines such as IL-1β, IL-6, and IL-8, while the expression levels of anti-inflammatory factor IL-10 were up-regulated. At the same time, the bacterial load of APEC was increased after knockdown of duGal-2 in vitro. However, the opposite results were obtained in the duGal-2 overexpression group. Taken together, duGal-2 plays an important role in the host against APEC infection.

The Galectin Family as Molecular Targets: Hopes for Defeating Pancreatic Cancer

Galectins are a family of proteins that bind β-galactose residues through a highly conserved carbohydrate recognition domain. They regulate several important biological functions, including cell proliferation, adhesion, migration, and invasion, and play critical roles during embryonic development and cell differentiation. In adults, different galectin members are expressed depending on the tissue type and can be altered during pathological processes. Numerous reports have shown the involvement of galectins in diseases, mostly inflammation and cancer. Here, we review the state-of-the-art of the role that different galectin family members play in pancreatic cancer. This tumor is predicted to become the second leading cause of cancer-related deaths in the next decade as there is still no effective treatment nor accurate diagnosis for it. We also discuss the possible translation of recent results about galectin expression and functions in pancreatic cancer into clinical interventions (i.e., diagnosis, prediction of prognosis and/or therapy) for this fatal disease.

Galectins in the Pathogenesis of Cerebrovascular Accidents: An Overview

Due to limitations of neuroimaging, such as the isodense appearance of blood to neuronal tissue in subacute hemorrhagic stroke, a body of studies have been performed to evaluate candidate biomarkers which may aid in accurate determination of cerebrovascular accident type. Beyond aiding in the delineation of stroke cause, biomarkers could also confer useful prognostic information to help clinicians plan use of resources. One of the candidate biomarkers studied for detection of cerebrovascular accident (CVA) includes a class of proteins called galectins. Galectins bind β-galactoside through a highly conserved carbohydrate recognition domain, endowing an ability to interact with carbohydrate moieties on glycoproteins, some of which are relevant to CVA response. Furthermore, galectins-1, -2, -3, -9, and -12 are expressed in tissues relevant to CVA, and some exhibit characteristics (eg, extracellular secretion) that could render feasible their detection in serum. Galectins-1 and -3 appear to have the largest amounts of preclinical evidence, consistently demonstrating increased activity and expression levels during CVA. However, a lack of standardization of biochemical assays across cohort studies limits further translation of these basic science studies. This review aims to increase awareness of the biochemical roles of galectins in CVA, while also highlighting challenges and remaining questions preventing the translation of basic science observations into a clinically useful test.

Structural mechanisms for the S-nitrosylation-derived protection of mouse galectin-2 from oxidation-induced inactivation revealed by NMR

Galectin-2 (Gal-2) is a lectin thought to play protective roles in the gastrointestinal tract. Oxidation of mouse Gal-2 (mGal-2) by hydrogen peroxide (H₂ O₂ ) results in the loss of sugar-binding activity, whereas S-nitrosylation of mGal-2, which does not change its sugar-binding profile, has been shown to protect the protein from H₂ O₂ -induced inactivation. One of the two cysteine residues, C57, has been identified as being responsible for controlling H₂ O₂ -induced inactivation; however, the underlying molecular mechanism has not been elucidated. We performed structural analyses of mGal-2 using nuclear magnetic resonance (NMR) and found that residues near C57 experienced significant chemical shift changes following S-nitrosylation, and that S-nitrosylation slowed the H₂ O₂ -induced aggregation of mGal-2. We also revealed that S-nitrosylation improves the thermal stability of mGal-2 and that the solvent accessibility and/or local dynamics of residues near C57 and the local dynamics of the core-forming residues in mGal-2 are reduced by S-nitrosylation. Structural models of Gal-2 indicated that C57 is located in a hydrophobic pocket that can be plugged by S-nitrosylation, which was supported by the NMR experiments. Based on these results, we propose two structural mechanisms by which S-nitrosylation protects mGal-2 from H₂ O₂ -induced aggregation without changing its sugar-binding profile: (a) stabilization of the hydrophobic pocket around C57 that prevents oxidation-induced destabilization of the pocket, and (b) prevention of oxidation of C57 during the transiently unfolded state of the protein, in which the residue is exposed to H₂ O₂ .

DATABASE

Nuclear magnetic resonance assignments for non-S-nitrosylated mGal-2 and S-nitrosylated mGal-2 have been deposited in the BioMagResBank (http://www.bmrb.wisc.edu/) under ID code 27237 for non-S-nitrosylated mGal-2 and ID code 27238 for S-nitrosylated mGal-2.

A proto-type galectin-2 from rock bream (Oplegnathus fasciatus): Molecular, genomic, and expression analysis, and recognition of microbial pathogens by recombinant protein

A β-galactoside binding lectin, designated as galectin-2, was identified and characterized from rock bream Oplegnathus fasciatus (OfGal-2). The cDNA of OfGal-2 comprised of 692 bp with a coding sequence of 396 bp, encoding a putative polypeptide of 131 amino acids. Gene structure analysis of OfGal-2 revealed a four exon-three intron organization. A single carbohydrate-binding domain containing all seven important residues for carbohydrate binding was located in the third exon, which formed a carbohydrate-binding pocket. Homology screening and sequence analysis demonstrated that OfGal-2 is an evolutionarily conserved proto-type galectin. OfGal-2 transcripts were detected in several healthy fish tissues, with the highest level observed in the intestine, followed by the liver. The expression of OfGal-2 was elevated upon the injection of various mitogenic stimulants and pathogens in a time-dependent manner. Upregulated expression in the liver after tissue injury suggested its role as a damage-associated molecular pattern. Recombinant OfGal-2 protein had hemagglutinating potential and possessed affinity towards lactose and galactose. Moreover, the recombinant protein agglutinated and bound potential pathogenic bacteria and a ciliate. The results of this study indicate that the galectin-2 from rock bream has a potential role in immunity, particularly in the recognition of invading pathogens.

Human galectin-2 interacts with carbohydrates and peptides non-classically: new insight from X-ray crystallography and hemagglutination

Galectin-2 (Gal-2) plays a role in cancer, myocardial infarction, immune response, and gastrointestinal tract diseases. The only reported crystal structure of Gal-2 shows that it is a dimer in which the monomer subunits have almost identical structures, each binding with one molecule of lactose. In this study, we crystallized Gal-2 under new conditions that produced three crystal structures. In each Gal-2 dimer structure, lactose was shown to be bound to only one of the carbohydrate recognition domain subunits. In solution studies, the thermal shift assay demonstrated that inequivalent monomer subunits in the Gal-2 dimer become equivalent upon ligand binding. In addition, galectin-mediated erythrocyte agglutination assays using lactose and larger complex polysaccharides as inhibitors showed the structural differences between Gal-1 and Gal-2. Overall, our results reveal some novel aspects to the structural differentiation in Gal-2 and expand the potential for different types of molecular interactions that may be specific to this lectin.

Galectin-3 regulates desmoglein-2 and intestinal epithelial intercellular adhesion

The desmosomal cadherins, desmogleins, and desmocollins mediate strong intercellular adhesion. Human intestinal epithelial cells express the desmoglein-2 isoform. A proteomic screen for Dsg2-associated proteins in intestinal epithelial cells identified a lectin referred to as galectin-3 (Gal3). Gal3 bound to N-linked β-galactosides in Dsg2 extracellular domain and co-sedimented with caveolin-1 in lipid rafts. Down-regulation of Gal3 protein or incubation with lactose, a galactose-containing disaccharide that competitively inhibits galectin binding to Dsg2, decreased intercellular adhesion in intestinal epithelial cells. In the absence of functional Gal3, Dsg2 protein was internalized from the plasma membrane and degraded in the proteasome. These results report a novel role of Gal3 in stabilizing a desmosomal cadherin and intercellular adhesion in intestinal epithelial cells.

Fine-tuning of prototype chicken galectins: structure of CG-2 and structure-activity correlations

The comparatively small number of members of the family of adhesion/growth-regulatory galectins in chicken predestines this system as an attractive model to study the divergence of these lectins after gene duplication. Expression profiling of the three homodimeric (prototype) chicken galectins (CG-1A, CG-1B and CG-2) has raised evidence of distinct functionalities, explaining the interest in a detailed crystallographic analysis of CG-2. As revealed here, marked differences are found in the ligand-binding site and in the contact pattern within the homodimer interface, underlying a characteristic orientation of the two subunits. Notably, a distinctive trimer of dimers that is unique in all galectin crystal structures reported to date forms the core unit of the crystallographic assembly. Combination with spectroscopic and thermodynamic measurements, and comparisons with CG-1A and CG-1B, identify differential changes in the circular-dichroism spectra in the presence of lactose, reflecting the far-reaching impact of the ligand on hydrodynamic behaviour, and inter-galectin differences in both the entropy and the enthalpy of binding. This structural information is a salient step to complete the analysis of the full set of galectins from this model organism.

Dietary cholesterol induces trafficking of intestinal Niemann-Pick Type C1 Like 1 from the brush border to endosomes

The transmembrane protein Niemann-Pick C1 Like 1 (NPC1L1) belongs to the Niemann-Pick C1 (NPC1) family of cholesterol transporters and is mainly expressed in the liver and the small intestine. NPC1L1 is believed to be the main transporter responsible for the absorption of dietary cholesterol. Like NPC1, NPC1L1 contains a sterol sensing domain, suggesting that it might be sensitive to dietary cholesterol. To test this hypothesis, mucosal explants were cultured in the presence or absence of cholesterol. In the absence of cholesterol NPC1L1 was localized mainly in the brush border of the enterocyte, colocalizing with the brush border enzyme aminopeptidase N (APN), and only a minor part was present in intracellular compartments. In contrast, following culture in the presence of cholesterol a major part of NPC1L1 was found in intracellular compartments positive for the early endosomal marker early endosome antigen 1, whereas only a minor fraction was left in the brush border. Neither APN, lactase, nor sucrase-isomaltase was endocytosed in parallel, demonstrating that this is a selective cholesterol-induced endocytosis of NPC1L1. Conceivably either the induced internalization could be due to NPC1L1 acting as an endocytic cholesterol receptor or it could be a mechanism to reduce the cholesterol uptake. The fluorescent cholesterol analog NBD-cholesterol readily labeled the cytoplasm also under conditions nonpermissible for endocytosis, arguing against a receptor-mediated uptake. We therefore propose that cholesterol is absorbed by NPC1L1 acting as a membrane transporter and that NPC1L1 is internalized to an endosomal compartment to reduce the absorption of cholesterol.

Domains of increased thickness in microvillar membranes of the small intestinal enterocyte

The apical surface of the enterocyte is sculpted into a dense array of cylindrical microvillar protrusions by supporting actin filaments. Membrane microdomains (rafts) enriched in cholesterol and glycosphingolipids comprise roughly 50% of the microvillar membrane and play a vital role in orchestrating absorptive/digestive action of dietary nutrients at this important cellular interface. Increased membrane thickness is believed to be a morphological characteristic of rafts. Thus, we investigated whether the high contents of lipid rafts in the microvillar membrane is reflected in local variations in membrane thickness. We measured membrane thickness directly from electron micrographs of sections of fixed mucosal tissue. Indeed, mapping of the microvillar membrane revealed a biphasic distribution of membrane thickness. As a point of reference the thickness distribution of the basolateral membrane was clearly monophasic. The encountered domains of increased thickness (DITs) occupied 48% of the microvillar membrane and from the data we estimated the area of a single DIT to have a lower limit of 600 nm(2). In other experiments we mapped the organization of biochemically defined lipid rafts by immunogold labeling of alkaline phosphatase, a well documented raft marker. Strikingly, the alkaline phosphatase localized to distinct regions of the membrane in a pattern similar to the observed distribution of DITs. Although we were unable to measure membrane thickness directly on the immunogold labeled specimens, and thereby establish an unequivocal connection between DITs and rafts, we conclude that the brush border membrane of the enterocyte contains microdomains distinguishable both by membrane morphology and protein composition.