Identification of major milk fat globule membrane proteins from pony mare milk highlights the molecular diversity of lactadherin across species

Comparative proteomic analysis of the changes in mare milk associated with different lactation stages and management systems

Mare milk has traditionally been attributed a number of health promoting properties. However, knowledge on its composition and functionality remains scarce, with particularly limited studies on mare milk proteomics. This study deeply characterized mare milk proteome accounting for both caseins and proteins in the whey fraction, also addressing the impact of lactation stage and different management systems. Milk samples from Basque Mountain Horse breed mares belonging to three different farms and three lactation stages were analysed after in-gel and in-solution digestion using nLC-MS/MS. Among the 469 proteins identified, the content of alpha-1 antitrypsin was significantly higher in pasture-based compared to other systems. Moreover, lactation stage significantly affected the content of beta-lactoglobulin II, immunoglobulin-like domain-containing protein, interferon alpha-inducible protein 27, lactotransferrin, polypeptide N-acetylgalactosaminyltransferase, and transforming acidic coiled-coil containing protein 2. This study contributes to the deep characterization of mare milk proteome and provides new insights into the effect of different production factors.

Identification and comparison of milk fat globule membrane and whey proteins from Selle Français, Welsh pony, and Tieling Draft horse mare's milk

Horse's milk, with a high nutritional value and few allergenic proteins, could substitute cow's milk for infant consumption. Herein, a label-free, proteomic method was used to identify and compare milk fat globule membrane (MFGM) and whey proteins from three different horse breeds: Selle Français (SF), Welsh pony (WP), and Tieling Draft Horse (TDH). In MFGMs, 16 (SF), 66 (WP), and 45 (TDH) unique proteins were identified, which are involved in the endocytosis, ribosome, and staphylococcus aureus infection pathways, respectively. In whey, 31 (SF), 75 (WP), and 23 (TDH) unique proteins were identified, which are involved in the autophagy-animal, phenylalanine metabolism, and Vasopressin-regulated water reabsorption pathways, respectively. SF contained the lowest concentration of β-lactoglobulin, which can cause allergic reactions in humans. Our findings describe the nutritional differences and functional diversities of MFGM and whey proteins in different horse breeds, which could support developing formula more suitable for human infants.

Plasma metabolome of healthy and Rhodococcus equi-infected foals over time

BACKGROUND

Foals that develop pulmonary ultrasonographic lesions on Rhodococcus equi (R. equi) endemic farms are treated with antibiotics because those at risk of developing clinical pneumonia (~20%) cannot be recognised early. Candidate biomarkers identified using metabolomics may aid targeted treatment strategies against R. equi.

OBJECTIVES

(1) To describe how foal ageing affects their plasma metabolome (birth to 8 weeks) and (2) to establish the effects that experimental infection with Rhodococcus equi (R. equi) has on foal metabolome.

STUDY DESIGN

Experimental study.

METHODS

Nine healthy newborn foals were experimentally infected with R. equi as described in a previous study. Foals were treated with oral antibiotics if they developed clinical pneumonia (n = 4, clinical group) or remained untreated if they showed no signs of disease (n = 5, subclinical group). A group of unchallenged foals (n = 4) was also included in the study. By the end of the study period (8 weeks), all foals were free of disease. This status was confirmed with transtracheal wash fluid evaluation and culture as well as thoracic ultrasonography. Plasma metabolomics was determined by GC-MS weekly for the study duration (8 weeks).

RESULTS

Foals' plasma metabolome was altered by ageing (birth to 8 weeks) and experimental infection with R. equi as demonstrated using multivariate statistical analysis. The intensities of 25 and 28 metabolites were altered by ageing and infection (p < 0.05) respectively. Furthermore, 20 metabolites changed by more than 2-fold between clinical and subclinical groups.

MAIN LIMITATIONS

The number of foals is limited. Foals were experimentally infected with R. equi.

CONCLUSIONS

Ageing and R. equi infection induced changes in the plasma metabolome of foals. These results provide an initial description of foal's plasma metabolome and serve as background for future identification of R. equi pneumonia biomarkers.

The xanthine oxidase and its associated activities in the ovine milk and liver: distinctive in impact of in vivo molybdenum

Xanthine oxidase is molybdenum and iron-containing flavoprotein, catalyzing the final oxidation stage of purines and oxidative transformation of pterins and some aliphatic and aromatic aldehydes. Despite the importance of this enzyme, the distribution of xanthine oxidase in traditional household animal’s milk and tissues is unknown. Formerly, we have found most of the xanthine oxidase molecules in animal milk are inactive because of a lack of molybdenum. Ovine milk was processed by inserting in vivo molybdenum (tungsten) into drinking water. We gave opposite dates in the presence of tungsten too. Heating the milk of animals at 80 °C for 5 minutes in the presence of molybdenum and cysteine led to a sharp increase of xanthine oxidase and its associated – nitrate reductase and nitrite reductase activities. The change of xanthine oxidase and its associated activities were examined by spectrophotometry after treatment. It was established that metal ions added in drinking water for animals have an impact on enzyme activities. The activity is formed in the ovine liver even in the absence of exogenous molybdenum in drinking water. The associated activities of liver enzymes in the presence of molybdenum in drinking water had slightly increased. Tungsten-containing water led to the loss of all activities of liver xanthine oxidase. It is proposed that the liver contains a special protein involving in the incorporation of molybdenum (or tungsten) into xanthine oxidase molecule, however, the milk or mammary gland compounds lack this protein.

A High-Throughput Comparative Proteomics of Milk Fat Globule Membrane Reveals Breed and Lactation Stages Specific Variation in Protein Abundance and Functional Differences Between Milk of Saanen Dairy Goat and Holstein Bovine

Large variations in the bioactivities and composition of milk fat globule membrane (MFGM) proteins were observed between Saanen dairy goat and Holstein bovine at various lactation periods. In the present study, 331, 250, 182, and 248 MFGM proteins were characterized in colostrum and mature milk for the two species by Q-Orbitrap HRMS-based proteomics techniques. KEGG pathway analyses displayed that differentially expressed proteins in colostrum involved in galactose metabolism and an adipogenesis pathway, and the differentially expressed proteins in mature milk associated with lipid metabolism and a PPAR signaling pathway. These results indicated that the types and functions of MFGM proteins in goat and bovine milk were different, and goat milk had a better function of fatty acid metabolism and glucose homeostasis, which can enhance our understanding of MFGM proteins in these two species across different lactation periods, and they provide significant information for the study of lipid metabolism and glycometabolism of goat milk.

Whole Goat Milk as a Source of Fat and Milk Fat Globule Membrane in Infant Formula

Cow milk is the most common dairy milk and has been extensively researched for its functional, technological and nutritional properties for a wide range of products. One such product category is infant formula, which is the most suitable alternative to feed infants, when breastfeeding is not possible. Most infant formulas are based on cow milk protein ingredients. For several reasons, consumers now seek alternatives such as goat milk, which has increasingly been used to manufacture infant, follow-on and young child formulas over the last 30 years. While similar in many aspects, compositional and functional differences exist between cow and goat milk. This offers the opportunity to explore different formulations or manufacturing options for formulas based on goat milk. The use of whole goat milk as the only source of proteins in formulas allows levels of milk fat, short and medium chain fatty acids, sn-2 palmitic acid, and milk fat globule membrane (MFGM) to be maximised. These features improve the composition and microstructure of whole goat milk-based infant formula, providing similarities to the complex human milk fat globules, and have been shown to benefit digestion, and cognitive and immune development. Recent research indicates a role for milk fat and MFGM on digestive health, the gut–brain axis and the gut–skin axis. This review highlights the lipid composition of whole goat milk-based infant formula and its potential for infant nutrition to support healthy digestion, brain development and immunity. Further work is warranted on the role of these components in allergy development and the advantages of goat milk fat and MFGM for infant nutrition and health.

In vitro Fermentation of Digested Milk Fat Globule Membrane From Ruminant Milk Modulates Piglet Ileal and Caecal Microbiota

Lipids in milk are secreted as a triacylglycerol core surrounded by a trilayer membrane, the milk fat globule membrane (MFGM). This membrane, known to have important roles in infant brain and intestinal development, is composed of proteins, glycoproteins, and complex lipids. We hypothesized that some of the beneficial properties of MFGM are due to its effects on the gastrointestinal microbiota. This study aimed to determine the effect of a commercial phospholipid concentrate (PC) and enriched bovine, caprine, and ovine MFGM fractions on ileal and hindgut microbiota in vitro. Digestion of PC and MFGMs was conducted using an in vitro model based on infant gastric and small intestine conditions. The recovered material was then in vitro fermented with ileal and caecal inocula prepared from five piglets fed a commercial formula for 20 days before ileal and caecal digesta were collected. After each fermentation, samples were collected to determine organic acid production and microbiota composition using 16S rRNA sequencing. All substrates, except PC (5%), were primarily fermented by the ileal microbiota (8–14%) (P < 0.05). PC and caprine MFGM reduced ileal microbiota alpha diversity compared to ileal inoculum. Caprine MFGM increased and PC reduced the ileal ratio of firmicutes:proteobacteria (P < 0.05), respectively, compared to the ileal inoculum. Bovine and ovine MFGMs increased ileal production of acetic, butyric, and caproic acids compared to other substrates and reduced the proportions of ileal proteobacteria (P < 0.0001). There was a limited fermentation of bovine (3%), caprine (2%), and ovine (2%) MFGMs by the caecal microbiota compared to PC (14%). In general, PC and all MFGMs had a reduced effect on caecal microbiota at a phylum level although MFG source-specific effects were observed at the genus level. These indicate that the main effects of the MFGM in the intestinal microbial population appears to occur in the ileum.

Comparative Analysis of Milk Fat Globular Membrane (MFGM) Proteome between Saudi Arabia Camelus dromedary Safra and Wadha Breeds

Camel milk is traditionally known to have medicinal properties and many potential health benefits. Natural milk contains many soluble proteins and nanoparticles, such as a milk fat globule membrane (MFGM), a three-layered membrane covering of milk fat globule mainly composed of proteins and lipids, which plays an important role in human health. MFGM proteins account for 1%-4% of total milk proteins, and their nutritive value and distribution depends on the different breeds. The differential composition of these membrane proteins among different camel breeds has not been explored. The current study, therefore, aimed to quantitatively analyze and compare the MFGM proteome between the milk produced by the two most common Saudi camel breeds, Camelus dromedarius: Safra and Wadha. Two-dimensional difference in gel electrophoresis (2D-DIGE) and mass spectrometry analysis revealed a total of 44 MFGM proteins that were identified with a significant difference in abundance (p ≤ 0.05; fold change ≥ 1.5) between the two breeds. Thirty-one proteins were up-regulated and 13 proteins were down-regulated in the Safra breed compared to the Wadha breed. The proteins identified with an increased abundance included α-lactalbumin, lactadherin, and annexin a8, whereas the down-regulated proteins included butyrophilin subfamily 1 member a1, lactotransferrin, and vinculin. The differentially abundant proteins were analyzed by the UNIPROT system and gene ontology (GO) to reveal their associations with known biological functions and pathways. Enzyme-linked immunosorbent assay (ELISA) confirmed the 2D-DIGE findings of butyrophilin (BTN) and α-lactalbumin (α-LA) levels obtained from Safra and Wadha breeds.

Evaluation of Dietary Bovine Milk Fat Globule Membrane Supplementation on Growth, Serum Cholesterol and Lipoproteins, and Neurodevelopment in the Young Pig

Introduction: Milk fat globule membrane (MFGM) is a protein- and phospholipid-rich membrane that surrounds the lipid droplet in milk. We have previously reported that a diet composed of a combination of prebiotics, bovine MFGM (bMFGM), and lactoferrin (bLf) supported brain development in young pigs. Due to the growing interest of its potential benefits in neurodevelopment, the present study focused on the effects of dietary bMFGM alone using the pig as a translational model. Methods: Male pigs were provided ad libitum access to milk replacer with added whey protein-lipid concentrate (source of bMFGM) at 0 (CONT), 2.5 (MFGM-2.5), or 5 (MFGM-5.0) g/L from postnatal day (PND) 2 to 31. Blood was collected from pigs at PND 15 and 31, and pigs underwent behavioral testing using the novel object recognition task starting at PND 25. At PND 31, magnetic resonance imaging was conducted and animals were subsequently euthanized for tissue collection. Results: No group differences in body weight gain or milk intake were observed. At PND 31, few group differences were detected in absolute and relative brain volumes, brain water diffusivity outcomes, or behavioral parameters using the novel object recognition task. Serum lipoprotein was higher in pigs receiving diets with added dietary bMFGM compared with the CONT group. Serum cholesterol and high-density lipoprotein significantly higher (all P < 0.05) in the MFGM-2.5 compared with the CONT group. However, cholesterol concentrations within the brain prefrontal cortex and hippocampus did not differ among dietary groups. Conclusion: In this pig model, dietary supplementation with bMFGM was well-tolerated and supported growth and dietary intake similar to the control formula. Added dietary bMFGM was associated with increased serum lipoprotein, but no group differences in early brain cholesterol concentrations, macrostructure, microstructure, or recognition memory pigs at 31 days of age. Further examination of longitudinal brain development and myelination in the pig, particularly at later ages/maturation, is warranted.

N-glycosylation proteomic characterization and cross-species comparison of milk fat globule membrane proteins from mammals

Glycosylation of proteins has been implicated in various biological functions and has received much attention; however, glycoprotein components and inter-species complexity have not yet been elucidated fully in milk proteins. N-linked glycosylation sites and glycoproteins in milk fat globule membrane (MFGM) fractions were investigated by combining N-glycosylated peptides enrichment and high-accuracy Q Exactive identification, to map the N-glycoproteome profiles in Holstein and Jersey cows, buffaloes, yaks, goats, camels, horses, and humans. A total of 399 N-glycoproteins with 677 glycosylation sites were identified in the MFGM fractions of the studied mammals. Most glycosylation sites in humans were classified as known and those in the other studied mammals as unknown, according to Swiss-Prot annotations. Functionally, most of the identified glycoproteins were associated with the 'response to stimulus' GO category. N-glycosylated protein components of MFGM fractions from Holstein and Jersey cows, buffaloes, yaks, and goats were more similar to each other compared with those of camels, horses and human. The findings increased the number of known N-glycosylation sites in the milk from dairy animal species, revealed the complexity of the MFGM glycoproteome, and provided useful information to further explore the mechanism of MFGM glycoproteins biosynthesis among the studied mammals.

Identification of Equine Lactadherin-derived Peptides That Inhibit Rotavirus Infection via Integrin Receptor Competition

Human rotavirus is the leading cause of severe gastroenteritis in infants and children under the age of 5 years in both developed and developing countries. Human lactadherin, a milk fat globule membrane glycoprotein, inhibits human rotavirus infection in vitro, whereas bovine lactadherin is not active. Moreover, it protects breastfed infants against symptomatic rotavirus infections. To explore the potential antiviral activity of lactadherin sourced by equines, we undertook a proteomic analysis of milk fat globule membrane proteins from donkey milk and elucidated its amino acid sequence. Alignment of the human, bovine, and donkey lactadherin sequences revealed the presence of an Asp-Gly-Glu (DGE) α2β1 integrin-binding motif in the N-terminal domain of donkey sequence only. Because integrin α2β1 plays a critical role during early steps of rotavirus host cell adhesion, we tested a minilibrary of donkey lactadherin-derived peptides containing DGE sequence for anti-rotavirus activity. A 20-amino acid peptide containing both DGE and RGD motifs (named pDGE-RGD) showed the greatest activity, and its mechanism of antiviral action was characterized; pDGE-RGD binds to integrin α2β1 by means of the DGE motif and inhibits rotavirus attachment to the cell surface. These findings suggest the potential anti-rotavirus activity of equine lactadherin and support the feasibility of developing an anti-rotavirus peptide that acts by hindering virus-receptor binding.

Proteomic characterization and comparison of mammalian milk fat globule proteomes by iTRAQ analysis

Milk fat globule membrane (MFGM) proteins are known to be involved in many biological functions; however, their components and inter-species complexity have not yet been completely elucidated. We investigated the protein composition of the MFGM-enriched fraction from Holstein, Jersey, yak, buffalo, goat, camel, horse, and human. Extracted proteins from the MFGM-enriched fractions were identified and quantified by an iTRAQ proteomic approach. We identified 520 protein species categorized as biological processes, cellular components and molecular function according to their annotation. Cellular process, localization, transport, signal transduction, and response to stimulus were the most common biological processes; binding and catalytic activities were the most prevalent molecular functions. Pathway analysis revealed several pathways, including glycolysis/gluconeogenesis, peroxisome proliferator-activated receptor signaling, and fatty acid biosynthesis. Quantified MFGM-enriched proteins were subjected to discriminative proteomic profiling by principal component analysis and a hierarchical clustering method, and then organized into four major clusters: (1) Holstein, Jersey, and yak milk; (2) buffalo and goat milk; (3) Holstein, Jersey, buffalo, yak, and goat milk; and (4) camel, horse, and human milk. These novel quantitative data provide insight into the protein composition of the MFGM and their potential physiological functions, and highlight the significant differences in the MFGM fractions among mammalian species.

BIOLOGICAL SIGNIFICANCE

Milk fat globule membrane (MFGM) proteins have exhibited a relatively larger diversity than other milk fractions, and implicated health beneficial effects. Proteomic analysis of MFGM protein was mainly focused on human, bovine and goat in previous studies. Recently, there is an increasing demand for natural milk from minor dairy animals. Differences in protein components were not yet elucidated that required the integration of this information across multiple species. Thus, iTRAQ analysis of the proteins in MFGM fractions from Holstein, Jersey, yak, buffalo, goat, camel, horse, and human was performed in this study. A total of 520 proteins were identified and quantified in the MFGM fractions. The results were contributed to a comprehensive overview and discriminative profiling of the MFGM proteome across species.

Validation of RNA isolated from milk fat globules to profile mammary epithelial cell expression during lactation and transcriptional response to a bacterial infection

Mastitis, an inflammation of the mammary gland, is the most costly infectious disease of dairy ruminants worldwide. Although it receives considerable attention, the early steps of the host response remain poorly defined. Here, we report a noninvasive method using milk fat globules (MFG) as a source of mammary RNA to follow the dynamics of the global transcriptional response of mammary epithelial cells (MEC) during the course of a bacterial infection. We first assessed that RNA isolated from MFG were representative of MEC RNA; we then evaluated whether MFG RNA could be used to monitor the MEC response to infection. Sufficiently high yields of good-quality RNA (RNA integrity numbers ranging between 6.7 and 8.7) were obtained from goat MFG for subsequent analyses. Contamination of MFG by macrophages and neutrophils, which can be trapped during creaming, was assessed and when using quantitative real-time PCR for cell-type specific markers, was shown to be weak enough (<8%) to affect MFG gene expression profiling. Using microarrays, we showed that RNA extracted from MFG and from mammary alveolar parenchyma shared approximately 90% of the highlighted probes corresponding in particular to genes encoding milk proteins (CSN, BLG, LALBA) and enzymes involved in milk fat synthesis and secretion (FASN, XDH, ADRP, SCD, and DGAT1). In addition, a gene involved in the acute-phase reaction, coding for the serum amyloid A3 (SAA3) protein, was found within the first 50 most highly expressed genes in a noninfectious context in both mammary alveolar parenchyma and MFG, strongly suggesting that SAA3 is expressed in MEC. We took advantage of this noninvasive RNA sampling to follow the early proinflammatory response of MEC during the course of a bacterial infection and showed that the levels of mRNA encoding SAA3 sharply increased at 24h postinfection. Taken together, our results demonstrate that MFG represent a unique source of MEC RNA to noninvasively sample sufficient amounts of high-quality RNA to assess the dynamics of MEC gene expression in vivo, especially during the first steps of infection, thereby paving the way for the discovery of early biomarkers for the control of intramammary infections. Furthermore, this noninvasive technique could be used to provide mammary transcriptomic data on a large scale, thus filling the gap between genomic and phenotypic data.