Sufficient fatty acid (FA) uptake from jejunal lumen is closely associated with pediatric growth. Enterotoxigenic Escherichia coli (ETEC), which poses a big threat to young mammals’ health, is also targeted on the jejunum, however, the effects on FA uptake is not understood yet. To explore the impacts of ETEC on the FA uptake ability of jejunum epithelial enterocytes during early life, we orally gavaged weaning piglets with ETEC K88 and found intestinal inflammation combined with compromised uptake of LCFA (C16:0, C18:0, C20:3, C20:4) except for C14:0 whose chain length is similar to medium chain fatty acid (MCFA). Furthermore, we observed reduced protein expression of TJs, fatty acid transport protein 4 (FATP4), peroxisome proliferator-activated receptor γ (PPARγ), phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), and upregulated expression of p-PPARγ. In the in vitro study, we challenged polarized porcine intestine jejunum cell line IPEC-J2 with ETEC K88 and discovered similar results on intestinal barrier and expression of associated genes combined with morphological changes. Based on the constructed cellular model, we then determined lower uptake of BODIPY-labeled C16:0 without any difference in the uptake of BODIPY-labeled C12:0. The content of intracellular triglyceride which was mainly synthesized by LCFA concomitantly lowered down. Using gene knock down and overexpression, FATP4 was confirmed to be responsible for LCFA uptake. Moreover, ERK1/2 inhibitor U0126 and PPARγ antagonist T0070907 revealed ETEC could initiate cascaded phosphorylation of ERK1/2 and PPARγ resulting in hindered expression of FATP4. These results indicate ETEC challenge will cause dysfunction in FATP4-dependent LCFA uptake by phosphorylation of ERK1/2 and PPARγ. Furthermore, intestinal uptake of MCFA is in a FATP4-independent manner which is not easily disturbed by ETEC.
Diarrhea, such as steatorrhea, could result from fat absorption disorders, which could be caused by many factors, including Escherichia coli infection. However, it is not clear how E. coli affects fatty acid absorption in animals. Lipopolysaccharide (LPS), as one of the main pathogenic components of E. coli, is the main cause of the virulence of E. coli. Therefore, we used LPS to explore the underlying mechanism of E. coli that causes the inhibition of fatty acid absorption in the intestine. In this study, we found that LPS caused apoptosis of intestinal epithelial cells in mice. Further, caspase-3 activation caused the inhibition of fatty acid absorption in the intestinal porcine enterocyte cell line (IPEC-J2). However, direct treatment of LPS did not induce any significant change in fatty acid absorption in IPEC-J2. We then prepared conditioned medium of LPS-treated porcine macrophage cell line (3D4/2) for incubating IPEC-J2, as LPS initiates inflammation by activating immune cells. The conditioned medium decreased fatty acid absorption and caspase-3 activation in IPEC-J2. While inhibiting the activation of caspase-3 in IPEC-J2, conditioned medium no longer caused serious deficiency of fatty acid absorption. As IL-1β, IL-6, and TNF-α in conditioned medium increase significantly, IPEC-J2 was treated with IL-1β, IL-6, and TNF-α, respectively. Only TNF-α induced caspase-3 activation in IPEC-J2. Reducing the secretion of TNF-α in 3D4/2, there was no obvious activation of caspase-3 in IPEC-J2, and fatty acid absorption recovered effectively. Based on the above results, we hold the opinion that LPS does not suppress fatty acid absorption directly in the intestine, but may work on macrophages that secrete cytokines, such as TNF-α, inducing caspase-3 activation and finally leading to the inhibition of fatty acid absorption in intestine.
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