Abstract
Simple SummaryAs the irreplaceable nutrient source for young mammals, milk has a number of biological functions. Milk derived extracellular vesicles are a recently discovered component of milk and have potential regulatory effects on intestinal health and immunity. In this study, in vivo and in vitro experiments were performed to examine the effects of porcine milk small extracellular vesicles (PM-sEVs) on intestinal immunity. As a result, PM-sEVs promoted intestinal secretory immunoglobulin A (SIgA) levels, and increased the expression levels of the polymeric immunoglobulin receptor (pIgR) both in mice and piglet. We identified circ-XPO4 in PM-sEVs as a crucial circRNA, which promotes the expression of pIgR via the suppression of miR-221-5p in the intestinal cell. In conclusion, our research provides a new understanding of the nutritional physiology of porcine milk in intestinal immunity.Secretory immunoglobulin A (SIgA) plays an important role in gut acquired immunity and mucosal homeostasis. Breast milk is the irreplaceable nutritional source for mammals after birth. Current studies have shown the potential functional role of milk-derived small extracellular vesicles (sEVs) and their RNAs cargo in intestinal health and immune regulation. However, there is a lack of studies to demonstrate how milk-derived sEVs affect intestinal immunity in recipient. In this study, through in vivo experiments, we found that porcine milk small extracellular vesicles (PM-sEVs) promoted intestinal SIgA levels, and increased the expression levels of polymeric immunoglobulin receptor (pIgR) both in mice and piglet. We examined the mechanism of how PM-sEVs increased the expression level of pIgR in vitro by using a porcine small intestine epithelial cell line (IPEC-J2). Through bioinformatics analysis, dual-luciferase reporter assays, and overexpression or knockdown of the corresponding non-coding RNAs, we identified circ-XPO4 in PM-sEVs as a crucial circRNA, which leads to the expression of pIgR via the suppression of miR-221-5p in intestinal cells. Importantly, we also observed that oral administration of PM-sEVs increased the level of circ-XPO4 and decreased the level of miR-221-5p in small intestine of piglets, indicating that circRNAs in milk-derived sEVs act as sponge for miRNAs in recipients. This study, for the first time, reveals that PM-sEVs have a capacity to stimulate intestinal SIgA production by delivering circRNAs to receptors and sponging the recipient’s original miRNAs, and also provides valuable data for insight into the role and mechanism of animal milk sEVs in intestinal immunity.
Highlights
The gut is the core organ to absorb nutrients, and provides a robust mucosal immune barrier and protection for the body [1]
The exosomal positive markers TSG101, CD63, and Alix were highly expressed on PM-small extracellular vesicles (sEVs) rather than porcine milk somatic cell (PM-SC), while Calnexin only expressed on PM-SC (Figure 1C)
The results revealed that polymeric immunoglobulin receptor (pIgR) mRNA and protein expression levels of IPEC-J2 cells were increased in the group treated with 100 μg/mL porcine milk small extracellular vesicles (PM-sEVs) (p < 0.05, Figure 2F–H), compared with the control group
Summary
The gut is the core organ to absorb nutrients, and provides a robust mucosal immune barrier and protection for the body [1]. Exosomes (a type of sEVs) can transport ncRNAs, including microRNAs (miRNAs) [9], long noncoding RNAs (lncRNAs) [10], and circular RNAs (circRNAs) [11], from donor to recipient cells, and perform corresponding biological functions. Studies have shown that milk sEVs promote the growth of IECs [15] and reduce intestinal injury induced by oxidative stress [16,17] and necrotizing enterocolitis [18]. Our recent work has shown that PM-sEVs contain lncRNAs and circRNAs, and many circRNAs were predicted to be involved in regulating intestinal barrier and mucosal immunity by targeting corresponding miRNAs [27]. Recent studies have shown that sEVs circRNAs regulate gene expression in recipient cells by acting as miRNA sponges [11,28]. We further identified circ-XPO4 in PM-sEVs as a crucial circRNA that promotes the expression of pIgR in the piglet intestine
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