Human milk is uniquely optimized for the needs of the developing infant. Its composition is complex and dynamic, driven primarily by maternal genetics, and to a lesser extent by diet and environment. One important component that is gaining attention is the milk fat globule (MFG). The MFG is composed of a triglyceride-rich core surrounded by a tri-layer membrane, also known as the milk fat globule membrane (MFGM) that originates from mammary gland epithelia. The MFGM is enriched with glycerophospholipids, sphingolipids, cholesterol, and proteins, some of which are glycosylated, and are known to exert numerous biological roles. Mounting evidence suggests that the structure of the MFG and bioactive components of the MFGM may benefit the infant by aiding in the structural and functional maturation of the gut through the provision of essential nutrients and/or regulating various cellular events during infant growth and immune education. Further, antimicrobial peptides and surface carbohydrate moieties surrounding the MFG might have a pivotal role in shaping gut microbial populations, which in turn may promote protection against immune and inflammatory diseases early in life. This review seeks to: (1) understand the components of the MFG, as well as maternal factors including genetic and lifestyle factors that influence its characteristics; (2) examine the potential role of this milk component on the intestinal immune system; and (3) delineate the mechanistic roles of the MFG in infant intestinal maturation and establishment of the microbiota in the alimentary canal.

Human milk delivers an array of bioactive components that safeguard infant growth and development and maintain healthy gut microbiota. Milk fat globule membrane (MFGM) is a biologically functional fraction of milk increasingly linked to beneficial outcomes in infants through protection from pathogens, modulation of the immune system and improved neurodevelopment. In the present study, we characterized the fecal microbiome and metabolome of infants fed a bovine MFGM supplemented experimental formula (EF) and compared to infants fed standard formula (SF) and a breast-fed reference group. The impact of MFGM on the fecal microbiome was moderate; however, the fecal metabolome of EF-fed infants showed a significant reduction of several metabolites including lactate, succinate, amino acids and their derivatives from that of infants fed SF. Introduction of weaning food with either human milk or infant formula reduces the distinct characteristics of breast-fed- or formula-fed- like infant fecal microbiome and metabolome profiles. Our findings support the hypothesis that higher levels of protein in infant formula and the lack of human milk oligosaccharides promote a shift toward amino acid fermentation in the gut. MFGM may play a role in shaping gut microbial activity and function.

Formula-fed (FF) infants exhibit a different metabolic profile than breast-fed (BF) infants. Two potential mechanisms are the higher protein level in formula compared with breast milk and the removal of the milk fat and associated milk fat globule membranes (MFGM) during production of infant formula. To determine whether MFGM may impact metabolism, formula-fed infants were randomly assigned to receive either an MFGM isolate-supplemented experimental formula (EF) or a standard formula (SF) from 2 until 6 months and compared with a BF reference group. Infants consuming EF had higher levels of fatty acid oxidation products compared to infants consuming SF. Although the protein level in the study formula was approximately 12 g/L (lower than most commercial formulas), a metabolic difference between FF and BF remained such that FF infants had higher levels of amino acid catabolism by-products and a low efficiency of amino acid clearance (preference for protein metabolism). BF infants had higher levels of fatty acid oxidation products (preference for fat metabolism). These unique, energy substrate-driven metabolic outcomes did not persist after diet was shifted to weaning foods and appeared to be disrupted by complementary feeding. Our results suggest that MFGM may have a role in directing infant metabolism.

Vitamin D is a hormone that regulates gene transcription. Prenatal vitamin D has been linked to immune and vascular function in the placenta, a key organ of pregnancy. Transcriptome-wide RNA sequencing can provide a more complete representation of the placental effects of vitamin D. We investigated the association between prenatal vitamin D concentrations and placental gene expression in a large, prospective pregnancy cohort. Participants were recruited from Shelby County, TN, United States, in the Conditions Affecting Neurocognitive Development and Learning in Early childhood (CANDLE) study. Vitamin D (plasma total 25-hydroxyvitatmin D, [25(OH)D]) was measured at midpregnancy (16-28 wk) and delivery. RNA was sequenced from placental samples collected at birth. We identified differentially expressed genes (DEGs) using adjusted linear regression models. We also conducted weighted gene coexpression network analysis. The median 25(OH)D of participants was 21.8 ng/mL at midpregnancy (N = 774; IQR: 15.4-26.5 ng/mL) and 23.6 ng/mL at delivery (n = 753; IQR: 16.8-29.1 ng/mL). Placental expression of 17 DEGs was associated with 25(OH)D at midpregnancy, but only 1 DEG was associated with 25(OH)D at delivery. DEGs were related to energy metabolism, cytoskeletal function, and transcriptional regulation. We identified 2 weighted gene coexpression network analysis gene modules whose expression was associated with 25(OH)D at midpregnancy and 1 module associated with 25(OH)D at delivery. These modules were enriched for genes related to mitochondrial and cytoskeletal function and were regulated by transcription factors including ARNT2 and FOSL2. We also identified 12 modules associated with 25(OH)D in females and 1 module in males. 25(OH)D during midpregnancy, but not at delivery, is associated with placental gene expression at birth. Future research is needed to investigate a potential role of vitamin D in modulating placental mitochondrial metabolism, intracellular transport, and transcriptional regulation during pregnancy.

Prenatal exposure to phthalates, pervasive endocrine-disrupting chemicals, has been linked to child health outcomes, including prematurity and low birthweight. Placental transcriptomics data can reveal mechanisms by which environmental toxicants alter placental and fetal growth. This study aims to investigate the placental transcriptome as a mediator between prenatal maternal urinary phthalate metabolites and placental efficiency. We identified significant associations between maternal urinary concentrations of phthalate metabolites and the placental transcriptome (132 genes and 27 gene modules). Placental efficiency was modeled as the ratio of birthweight to placental weight (BW:PW) and as birthweight adjusted for placental weight (BW_adj) and was also significantly associated with the placental transcriptome (460 genes and 11 gene modules). 4 genes and 9 gene modules exhibited significant mediation of the relationship between maternal urinary concentrations of phthalate metabolites and placental efficiency measures. These genes were involved in syncytialization, metabolism, DNA damage and cellular senescence, and steroid biosynthesis-processes essential to fetal growth and development because of the placenta's role in nutrient supply, hormone production, and detoxification. These findings suggest a key mediating role of the placental transcriptome in toxicological mechanisms by which phthalates may disrupt fetal growth.