Cationic and neutral amino acid transporter transcript abundances are differentially expressed in the equine intestinal tract.

This study investigates the expression differences of four amino acid (AA) transporter genes in various parts of the equine (horse) intestinal tract. The results suggest that the large intestine may play a significant role in absorbing both cationic and neutral amino acids through specific transporters.

Research Methodology

• The researchers aimed to test the hypothesis that genes responsible for amino acid transport were not just present in the large intestine, but also shared similar expressions throughout the intestinal tract.
• Specifically, the study focussed on the mRNA abundance of candidate AA transporter genes – SLC7A9, SLC7A1, SLC7A8, and SLC43A1. These genes encode for b(0,+)-type amino acid transporter (b(0,+)AT), cationic AA transporter-1 (CAT-1), L-type AA transporter-2 (LAT-2), and L-type AA transporter-3 (LAT-3), respectively.
• Mucosa from the small (jejunum and ileum) and large intestine (cecum, left ventral colon, and left dorsal colon) of horses were collected, flash frozen in liquid nitrogen, and stored at -80 degrees C.
• The mRNA was then isolated from these tissue samples and cDNA was manufactured.
• A relative quantitative reverse transcription-PCR was conducted, using glyceraldehyde-3-phosphate dehydrogenase as the reference or ‘housekeeping’ gene.

Research Findings

• It was found that compared to the jejunum, both cationic and neutral AA transporter SLC7A9 mRNA abundance was similar in the ileum, cecum, and large intestinal segments.
• Cationic AA transporter SLC7A1 mRNA abundance was similar in the ileum but decreased in the cecum, left ventral colon and left dorsal colon.
• Neutral AA transporter SLC7A8 mRNA abundance decreased from the cranial (head end) to caudal (tail end) portions of the intestinal tract.
• Another neutral AA transporter, SLC43A1, showed similar mRNA abundance in the ileum and left dorsal colon, but increased in the cecum and left ventral colon compared to the jejunum.
• Neutral AA transporter SLC7A8 and SLC43A1 were found to be differentially expressed, with decreased abundance of SLC7A8 and an increased abundance of SLC43A1 in the large intestine.

Implications of the Study

• The research indicates that the large intestine might significantly contribute to both cationic and neutral amino acid uptake and absorption, primarily through the LAT-3 and b(0,+)AT transporters.
• As most studies tend to focus more on the small intestine’s role in nutrient absorption, this study helps broaden knowledge about the large intestine’s function, especially regarding amino acid absorption in horses.