Lipopolysaccharide promotes apoptosis and oxidative injury of porcine small intestinal epithelial cells by down-regulating the expression of glutamine transporter ASCT2

Lay Summary Glutamine (Gln) is the main energy source for animal eukaryotic cells including intestinal epithelial cells (IECs), which is absorbed mainly mediated by Alanine-Serine-Cysteine transporter 2 (ASCT2). Previous studies have shown that lipopolysaccharide (LPS) stimulation can lead to oxidative damage, increased apoptosis, decreased glutamine absorption, and down-regulated ASCT2 mRNA and protein expression, suggesting that ASCT2 expression is involved in intestinal injury. However, the relationship between ASCT2 expression and cell apoptosis during cell injury has not been discussed in detail. The present study showed that ASCT2 expression was negatively correlated with apoptosis, and positively correlated with the anti-oxidant capacity of porcine small intestinal epithelial cells (IPEC-J2). According to the results of this study, it can be preliminarily concluded that LPS promotes the apoptosis and oxidative injury of IPEC-J2 cells by down-regulating the expression of ASCT2. The present study aimed to investigate the effects of lipopolysaccharide (LPS) stimulation on oxidative damage, apoptosis, and glutamine (Gln) transporter Alanine-Serine-Cysteine transporter 2 (ASCT2) expression in porcine small intestinal epithelial cells (IPEC-J2), and preliminarily elucidated the relationship between ASCT2 expression level and oxidative damage and apoptosis of IPEC-J2 cells. IPEC-J2 cells were treated without (control group, CON, N = 6) or with 1 & mu;g/mL LPS (LPS group, LPS, N = 6). Cell viability, lactate dehydrogenase (LDH) content, malonaldehyde (MDA), anti-oxidant enzymes (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GSH-Px], and total anti-oxidant capacity [T-AOC]), apoptosis of IPEC-J2 cells, the expression of Caspase3, the expression of ASCT2 mRNA and ASCT2 protein was detected. The results showed that LPS stimulation of IPEC-J2 cells significantly reduced the cell viability, and anti-oxidant enzymes activity (SOD, CAT, and GSH-Px), and significantly increased LDH and MDA release. Flow cytometry results showed that LPS stimulation significantly increased the late apoptosis rate and the total apoptosis rate of IPEC-J2 cells. The immunofluorescence results showed that the fluorescence intensity of LPS stimulated IPEC-J2 cells was significantly enhanced. LPS stimulation significantly decreased the mRNA and protein expression of ASCT2 in IPEC-J2 cells. The correlation analysis showed that ASCT2 expression was negatively correlated with apoptosis, and positively correlated with the anti-oxidant capacity of IPEC-J2 cells. According to the results of this study, it can be preliminarily concluded that LPS promotes the apoptosis and oxidative injury of IPEC-J2 cells by down-regulating the expression of ASCT2. Due to long-term exposure to a complex environment composed of various food components, antigens, symbiotic micro-organisms and pathogens, intestinal epithelial cells are often subjected to various stresses, which may lead to intestinal oxidative damage and promote cell apoptosis. Therefore, maintaining the dynamic balance of intestinal redox state and apoptosis is of great significance for intestinal health. The results of this study can provide a new idea for the nutritional regulation of intestinal repair, that is, by upregulating intestinal ASCT2 expression to alleviate oxidative damage and reduce cell apoptosis, and thus maintain intestinal homeostasis.