The potential role of Osteopontin in the maintenance of commensal bacteria homeostasis in the intestine

Bovine milk osteopontin improved intestinal health of pregnant rats fed a high-fat diet through improving bile acid metabolism

The main purpose of the current study was to investigate the ameliorative effects of bovine milk osteopontin (bmOPN) on the gut dysfunction of pregnant rats fed a high-fat diet (HFD). Bovine milk osteopontin was supplemented at a dose of 6 mg/kg body weight. Bovine milk osteopontin supplementation during pregnancy reduced colonic inflammation of HFD dams, and it also increased the colonic expression of ZO-1 and claudin-4 of HFD dams. Bovine milk osteopontin significantly enriched the relative abundance of Bacteroidetes, whereas it decreased Proteobacteria, Helicobacteraceae, and Desulfovibrionaceae in feces of HFD dams. The levels of isobutyric acid and pentanoic acid in the HFD + bmOPN group were higher than that of the HFD group. Functional predication analysis of microbial genomes revealed that bmOPN supplementation to HFD pregnancies changed 4 Kyoto Encyclopedia of Genes and Genomes pathways including bile acid biosynthesis. Further, bmOPN enriched hepatic taurochenodeoxycholic acid and tauroursodeoxycholic acid plus taurohyodeoxycholic acid in the gut of HFD maternal rats. Our findings suggested that bmOPN improved the gut health of HFD pregnant rats partially through modulating bile acid biosynthesis.

Gut microbiota and neonatal acute kidney injury biomarkers

One of the most frequent issues in newborns is acute kidney injury (AKI), which can lengthen their hospital stay or potentially raise their chance of dying. The gut-kidney axis establishes a bidirectional interplay between gut microbiota and kidney illness, particularly AKI, and demonstrates the importance of gut microbiota to host health. Since the ability to predict neonatal AKI using blood creatinine and urine output as evaluation parameters is somewhat constrained, a number of interesting biomarkers have been developed. There are few in-depth studies on the relationships between these neonatal AKI indicators and gut microbiota. In order to gain fresh insights into the gut-kidney axis of neonatal AKI, this review is based on the gut-kidney axis and describes relationships between gut microbiota and neonatal AKI biomarkers.

A New Perspective on Metabolic Syndrome with Osteopontin: A Comprehensive Review

Metabolic syndrome (MetS) imposes a substantial burden on the healthcare systems and economies of countries and is a major public health concern worldwide. MetS is mainly caused by an imbalance between calorie intake and energy expenditure; however, it is recognized that additional variables, such as chronic inflammation, may have the same predictive potential as insulin resistance or MetS components in the genesis of type 2 diabetes and cardiovascular events. More importantly, the early diagnosis or treatment of MetS may significantly reduce the burden on the health systems of the disease with any prevention or biomarker and should not be underestimated. Osteopontin (OPN), also called secreted phosphoprotein 1, is a soluble protein found mostly in body fluids. Studies suggest that serum OPN levels may be an early and new biomarker to predict metabolic and cardiovascular complications significantly associated with some diseases. This review aims to provide specific insight into the new biomarker OPN in MetS. With this purpose, it is examined the link between the MetS cornerstones and OPN. In addition, the interaction between the microbiota and MetS is predicted to be bidirectional, and the microbiota may act as a bridge in this interaction process. Increased OPN levels may have unfavourable consequences for cardiovascular diseases, diabetes, and obesity, all of which are components of MetS. Further studies are required to evaluate the use of OPN levels as a clinical biomarker risk of MetS.

Role of Enterocyte Enpp2 and Autotaxin in Regulating Lipopolysaccharide Levels, Systemic Inflammation and Atherosclerosis

Conversion of lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA) by autotaxin, a secreted phospholipase D, is a major pathway for producing LPA. We previously reported that feeding Ldlr^-/- mice standard mouse chow supplemented with unsaturated LPA or LPC qualitatively mimicked the dyslipidemia and atherosclerosis induced by feeding a Western diet (WD). Here we report that adding unsaturated LPA to standard mouse chow also increased the content of reactive oxygen species (ROS) and oxidized phospholipids (OxPL) in jejunum mucus. To determine the role of intestinal autotaxin, enterocyte specific Ldlr^-/-/Enpp2 knockout (iKO) mice were generated. In control mice, the WD increased enterocyte Enpp2 expression and raised autotaxin levels. Ex vivo, addition of OxPL to jejunum from Ldlr^-/- mice on a chow diet induced expression of Enpp2. In control mice, the WD raised OxPL levels in jejunum mucus, and decreased gene expression in enterocytes for a number of peptides and proteins that affect antimicrobial activity. On the WD, the control mice developed elevated levels of LPS in jejunum mucus and plasma, with increased dyslipidemia and increased atherosclerosis. All of these changes were reduced in the iKO mice. We conclude that the WD increases the formation of intestinal OxPL, which i) induce enterocyte Enpp2 and autotaxin resulting in higher enterocyte LPA levels; that ii) contribute to the formation of ROS that help to maintain the high OxPL levels; iii) decrease intestinal antimicrobial activity; and iv) raise plasma LPS levels that promote systemic inflammation and enhance atherosclerosis.

Intestinal Osteopontin Protects From Alcohol-induced Liver Injury by Preserving the Gut Microbiome and the Intestinal Barrier Function

BACKGROUND & AIMS

The gut-liver axis plays a key role in the pathogenesis of alcohol-associated liver disease (ALD). We demonstrated that Opn^-/- develop worse ALD than wild-type (WT) mice; however, the role of intestinal osteopontin (OPN) in ALD remains unknown. We hypothesized that overexpression of OPN in intestinal epithelial cells (IECs) could ameliorate ALD by preserving the gut microbiome and the intestinal barrier function.

METHODS

Opn^{KI IEC}, Opn^ΔIEC, and WT mice were fed control or ethanol Lieber-DeCarli diet for 6 weeks.

RESULTS

Opn^{KI IEC} but not Opn^ΔIEC mice showed improved intestinal barrier function and protection from ALD. There were less pathogenic and more beneficial bacteria in ethanol-fed Opn^{KI IEC} than in WT mice. Fecal microbiome transplant (FMT) from Opn^{KI IEC} to WT mice protected from ALD. FMT from ethanol-fed WT to Opn^{KI IEC} mice failed to induce ALD. Antimicrobial peptides, Il33, pSTAT3, aryl hydrocarbon receptor (Ahr), and tight-junction protein expression were higher in IECs from jejunum of ethanol-fed Opn^{KI IEC} than of WT mice. Ethanol-fed Opn^{KI IEC} showed more tryptophan metabolites and short-chain fatty acids in portal serum than WT mice. FMT from Opn^{KI IEC} to WT mice enhanced IECs Ahr and tight-junction protein expression. Oral administration of milk OPN replicated the protective effect of Opn^{KI IEC} mice in ALD.

CONCLUSION

Overexpression of OPN in IECs or administration of milk OPN maintain the intestinal microbiome by intestinal antimicrobial peptides. The increase in tryptophan metabolites and short-chain fatty acids signaling through the Ahr in IECs, preserve the intestinal barrier function and protect from ALD.

Oxidized phospholipids cause changes in jejunum mucus that induce dysbiosis and systemic inflammation

We previously reported that adding a concentrate of transgenic tomatoes expressing the apoA-I mimetic peptide 6F (Tg6F) to a Western diet (WD) ameliorated systemic inflammation. To determine the mechanism(s) responsible for these observations, Ldlr^−/− mice were fed chow, a WD, or WD plus Tg6F. We found that a WD altered the taxonomic composition of bacteria in jejunum mucus. For example, Akkermansia muciniphila virtually disappeared, while overall bacteria numbers and lipopolysaccharide (LPS) levels increased. In addition, gut permeability increased, as did the content of reactive oxygen species and oxidized phospholipids in jejunum mucus in WD-fed mice. Moreover, gene expression in the jejunum decreased for multiple peptides and proteins that are secreted into the mucous layer of the jejunum that act to limit bacteria numbers and their interaction with enterocytes including regenerating islet-derived proteins, defensins, mucin 2, surfactant A, and apoA-I. Following WD, gene expression also decreased for Il36γ, Il23, and Il22, cytokines critical for antimicrobial activity. WD decreased expression of both Atoh1 and Gfi1, genes required for the formation of goblet and Paneth cells, and immunohistochemistry revealed decreased numbers of goblet and Paneth cells. Adding Tg6F ameliorated these WD-mediated changes. Adding oxidized phospholipids ex vivo to the jejunum from mice fed a chow diet reproduced the changes in gene expression in vivo that occurred when the mice were fed WD and were prevented with addition of 6F peptide. We conclude that Tg6F ameliorates the WD-mediated increase in oxidized phospholipids that cause changes in jejunum mucus, which induce dysbiosis and systemic inflammation.

Osteopontin Takes Center Stage in Chronic Liver Disease

Osteopontin (OPN) was first identified in 1986. The prefix osteo- means bone; however, OPN is expressed in other tissues, including liver. The suffix -pontin means bridge and denotes the role of OPN as a link protein within the extracellular matrix. While OPN has well-established physiological roles, multiple "omics" analyses suggest that it is also involved in chronic liver disease. In this review, we provide a summary of the OPN gene and protein structure and regulation. We outline the current knowledge on how OPN is involved in hepatic steatosis in the context of alcoholic liver disease and non-alcoholic fatty liver disease. We describe the mechanisms whereby OPN participates in inflammation and liver fibrosis and discuss current research on its role in hepatocellular carcinoma and cholangiopathies. To conclude, we highlight important points to consider when doing research on OPN and provide direction for making progress on how OPN contributes to chronic liver disease.

Dietary osteopontin-enriched algal protein as nutritional support in weaned pigs infected with F18-fimbriated enterotoxigenic Escherichia coli

This study investigated the effects of dietary osteopontin (OPN)-enriched algal protein on growth, immune status, and fecal fermentation profiles of weaned pigs challenged with a live infection of F18-fimbriated enterotoxigenic E. coli (ETEC). At 21 d of age, 54 pigs (5.95 ± 0.28 kg BW; blocked by BW) were allotted to 1 of 3 experimental groups combining dietary and health statuses. A control diet, containing 1% wild-type algal protein, was fed to both sham-inoculated (NC) and ETEC-inoculated (PC) pigs, while the test diet contained 1% OPN-enriched algal protein as fed only to ETEC-inoculated pigs (OA). All pigs received their assigned dietary treatment starting at study initiation to permit a 10-d acclimation period prior to inoculation. Growth performance, fecal dry matter, as well as hematological, histopathological, immune, and microbiota outcomes were analyzed by ANOVA, where treatment and time were considered as fixed effects and pig as a random effect; significance was accepted at P < 0.05. Overall, ETEC-inoculated pigs (PC and OA) exhibited decreased (P < 0.05) ADG and G:F, as well as increased (P < 0.05) peripheral blood helper T-cells and total leukocyte counts, compared with NC pigs during the postinoculation period. The OA treatment also elicited the highest (P < 0.05) concentrations of circulating tumor necrosis factor-α and volatile fatty acid concentrations in luminal contents at various postinoculation time-points, compared with other treatments. A principal coordinate analysis based on Unifrac weighted distances indicated that NC and OA groups had similar overall bacterial community structures, while PC pigs exhibited greater diversity, but infection status had no impact on α-diversity. Osteopontin-specific effects on microbial community structure included enrichment within Streptococcus and Blautia genera and decreased abundance of 12 other genera as compared with PC pigs. Overall, ETEC-infected pigs receiving 1% OPN-enriched algal protein exhibited changes immunity, inflammatory status, and colonic microbial community structure that may benefit weanling pigs experiencing F18 ETEC infection.

Exercise training modulates the gut microbiota profile and impairs inflammatory signaling pathways in obese children

Childhood obesity has reached epidemic levels and is a serious health concern associated with metabolic syndrome, nonalcoholic fatty liver disease, and gut microbiota alterations. Physical exercise is known to counteract obesity progression and modulate the gut microbiota composition. This study aims to determine the effect of a 12-week strength and endurance combined training program on gut microbiota and inflammation in obese pediatric patients. Thirty-nine obese children were assigned randomly to the control or training group. Anthropometric and biochemical parameters, muscular strength, and inflammatory signaling pathways in mononuclear cells were evaluated. Bacterial composition and functionality were determined by massive sequencing and metabolomic analysis. Exercise reduced plasma glucose levels and increased dynamic strength in the upper and lower extremities compared with the obese control group. Metagenomic analysis revealed a bacterial composition associated with obesity, showing changes at the phylum, class, and genus levels. Exercise counteracted this profile, significantly reducing the Proteobacteria phylum and Gammaproteobacteria class. Moreover, physical activity tended to increase some genera, such as Blautia, Dialister, and Roseburia, leading to a microbiota profile similar to that of healthy children. Metabolomic analysis revealed changes in short-chain fatty acids, branched-chain amino acids, and several sugars in response to exercise, in correlation with a specific microbiota profile. Finally, the training protocol significantly inhibited the activation of the obesity-associated NLRP3 signaling pathway. Our data suggest the existence of an obesity-related deleterious microbiota profile that is positively modified by physical activity intervention. Exercise training could be considered an efficient nonpharmacological therapy, reducing inflammatory signaling pathways induced by obesity in children via microbiota modulation.

Physical fitness regimens could stimulate shifts in gut microbiome composition and metabolism that counteract health risks associated with childhood obesity. This condition can increase the risk of metabolic and cardiovascular disease later in life. Several studies have indicated that disturbances in the microbial populations in the digestive tract may contribute to these diseases. Researchers led by Sonia Sánchez-Campos of the Institute of Biomedicine, León,Spain, recently assessed the impact of exercise and endurance training on microbiome composition in obese children. They determined that these regimens can produce measurable shifts in the gut microbe population, yielding bacterial communities that are more similar to those seen in non-obese children. These shifts were accompanied by alterations in metabolic activity that may help mitigate inflammatory signaling and other processes that fuel obesity-related disease.

Osteopontin and iCD8α Cells Promote Intestinal Intraepithelial Lymphocyte Homeostasis

Intestinal intraepithelial lymphocytes (IEL) comprise a diverse population of cells residing in the epithelium at the interface between the intestinal lumen and the sterile environment of the lamina propria. Because of this anatomical location, IEL are considered critical components of intestinal immune responses. Indeed, IEL are involved in many different immunological processes, ranging from pathogen control to tissue stability. However, despite their critical importance in mucosal immune responses, very little is known about the homeostasis of different IEL subpopulations. The phosphoprotein osteopontin is important for critical physiological processes, including cellular immune responses, such as survival of Th17 cells and homeostasis of NK cells among others. Because of its impact in the immune system, we investigated the role of osteopontin in the homeostasis of IEL. In this study, we report that mice deficient in the expression of osteopontin exhibit reduced numbers of the IEL subpopulations TCRγδ⁺, TCRβ⁺CD4⁺, TCRβ⁺CD4⁺CD8α⁺, and TCRβ⁺CD8αα⁺ cells in comparison with wild-type mice. For some IEL subpopulations, the decrease in cell numbers could be attributed to apoptosis and reduced cell division. Moreover, we show in vitro that exogenous osteopontin stimulates the survival of murine IEL subpopulations and unfractionated IEL derived from human intestines, an effect mediated by CD44, a known osteopontin receptor. We also show that iCD8α IEL but not TCRγδ⁺ IEL, TCRβ⁺ IEL, or intestinal epithelial cells, can promote survival of different IEL populations via osteopontin, indicating an important role for iCD8α cells in the homeostasis of IEL.

Innate CD8αα+ cells promote ILC1-like intraepithelial lymphocyte homeostasis and intestinal inflammation

Innate CD8αα+ cells, also referred to as iCD8α cells, are TCR-negative intraepithelial lymphocytes (IEL) possessing cytokine and chemokine profiles and functions related to innate immune cells. iCD8α cells constitute an important source of osteopontin in the intestinal epithelium. Osteopontin is a pleiotropic cytokine with diverse roles in bone and tissue remodeling, but also has relevant functions in the homeostasis of immune cells. In this report, we present evidence for the role of iCD8α cells in the homeostasis of TCR-negative NKp46+NK1.1+ IEL (ILC1-like). We also show that the effect of iCD8α cells on ILC1-like IEL is enhanced in vitro by osteopontin. We show that in the absence of iCD8α cells, the number of NKp46+NK1.1+ IEL is significantly reduced. These ILC1-like cells are involved in intestinal pathogenesis in the anti-CD40 mouse model of intestinal inflammation. Reduced iCD8α cell numbers results in a milder form of intestinal inflammation in this disease model, whereas treatment with osteopontin increases disease severity. Collectively, our results suggest that iCD8α cells promote survival of NKp46+NK1.1+ IEL, which significantly impacts the development of intestinal inflammation.

Gut and immune effects of bioactive milk factors in preterm pigs exposed to prenatal inflammation

Prenatal inflammation may predispose to preterm birth and postnatal inflammatory disorders such as necrotizing enterocolitis (NEC). Bioactive milk ingredients may help to support gut maturation in such neonates, but mother's milk is often insufficient after preterm birth. We hypothesized that supplementation with bioactive ingredients from bovine milk [osteopontin (OPN), caseinoglycomacropeptide (CGMP), colostrum (COL)] supports gut, immunity, and NEC resistance in neonates born preterm after gram-negative infection before birth. Using preterm pigs as a model for preterm infants, fetal pigs were given intraamniotic injections of lipopolysaccharide (LPS; 1 mg/fetus) and delivered 3 days later (90% gestation). For 5 days, groups of LPS-exposed pigs were fed formula (FOR), bovine colostrum (COL), or formula enriched with OPN or CGMP. LPS induced intraamniotic inflammation and postnatal systemic inflammation but limited effects on postnatal gut parameters and NEC. Relative to FOR, COL feeding to LPS-exposed pigs showed less diarrhea, NEC severity, reduced gut IL-1β and IL-8 levels, greater gut goblet cell density and digestive enzyme activities, and blood helper T-cell fraction. CGMP improved neonatal arousal and gut lactase activities and reduced LPS-induced IL-8 secretion in intestinal epithelial cells (IECs) in vitro. Finally, OPN tended to reduce diarrhea and stimulated IEC proliferation in vitro. No effects on villus morphology, circulating cytokines, or colonic microbiota were observed among groups. In conclusion, bioactive milk ingredients exerted only modest effects on gut and systemic immune parameters in preterm pigs exposed to prenatal inflammation. Short-term, prenatal exposure to inflammation may render the gut less sensitive to immune-modulatory milk effects. NEW & NOTEWORTHY Prenatal inflammation is a risk factor for preterm birth and postnatal complications including infections. However, from clinical studies, it is difficult to separate the effects of only prenatal inflammation from preterm birth. Using cesarean-delivered preterm pigs with prenatal inflammation, we documented some beneficial gut effects of bioactive milk diets relative to formula, but prenatal inflammation appeared to decrease the sensitivity of enteral feeding. Special treatments and diets may be required for this neonatal population.

Surface-immobilized plant-derived osteopontin as an effective platform to promote osteoblast adhesion and differentiation

In this report, recombinant human osteopontin synthesized in tobacco plants (p-rhOPN) is introduced as a potential bioactive molecule that can promote osteoblast adhesion and differentiation. A glass substrate (SiO₂/Si-OH) grafted with poly(acrylic acid) (SiO₂/Si-PAA) was prepared by surface-initiated reversible addition-fragmentation chain transfer polymerization and used as a carboxyl-rich platform for the chemical conjugation of p-rhOPN. The PAA grafting and subsequent p-rhOPN immobilization were confirmed by water contact angle, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy analyses. Indirect ELISA quantification revealed that the p-rhOPN immobilization efficiency was above 95% and the surface coverage was a function of the p-rhOPN concentration. MC-3T3-E1 cells cultured on the SiO₂/Si-PAA substrate immobilized with various concentrations (0.6-30 ng/mL) of p-rhOPN (SiO₂/Si-p-rhOPN) exhibited superior cell spreading compared to those cultured on SiO₂/Si-OH or gelatin-modified glass substrate (SiO₂/Si-gelatin). Polymerase chain reaction analysis indicated that the SiO₂/Si-p-rhOPN substrates with high level of immobilized p-rhOPN promoted MC-3T3-E1 cell differentiation, as demonstrated by the higher transcript expression levels of the osteogenic differentiation regulatory gene, Runt-related transcription factor 2, compared to cells cultured on SiO₂/Si-OH or SiO₂/Si-gelatin. Given that p-rhOPN can be more economically produced than the commercially available OPN derived from human or mammalian sources, then, together with its well-preserved biological function in spite of being chemically conjugated to the substrates, it is likely that p-rhOPN could be more broadly applied for the development of materials for bone tissue engineering with a promising medical and commercial value.

Microbiota - an amplifier of autoimmunity

Many studies describe dysbiosis as a change in the microbiota that accompanies autoimmune illnesses, but little is known about whether these changes are a cause or consequence of an altered immune state. The immune system actively shapes the composition of the microbiota, with divergent outcomes in healthy or autoimmune-prone individuals. The gut microbiota in turn acts as an acquired endocrine organ, influencing the physiology of the host via release of nutrients and chemical messengers. Dysbiosis arising from abnormal immune function can initiate or amplify autoimmunity through multiple mechanisms. We examine how the bidirectional relationship between resident microbes and the immune system contributes to autoimmune diseases.