Water salinity and postprandial effects on transcription of peptide and amino acid transporters in the kidney of Mozambique tilapia (Oreochromis mossambicus)

Abstract

Preservation of amino acids is highly important, as these are vital nutrients that support many physiological and biochemical processes. During fish osmoregulation, the kidney reabsorbs amino acids and short peptides that are filtered from the blood into the nephron. However, little is known about reabsorption systems in teleost kidney. To identify transporters involved in this process, we examined by PCR the expression of eight genes, coding to peptide and amino acid transporters, as well as of two ion transport systems, in the kidney of the euryhaline Mozambique tilapia (Oreochromis mossambicus). We found that three amino acid transporters (slc1a5, ASCT2; slc7a9, b0,+AT; slc6a19, B0AT) and one peptide transporter (slc15a2, PepT2) were expressed in the kidney, as were the two ion transporters VHA and NHE3 (coded by atp6v1a and slc9a3, respectively). Next, to investigate transcriptional interactions of these transporters with osmoregulation and nutritional status, we compared by qPCR expression levels in fish acclimated to either fresh or saltwater and at three time points after feeding (6, 24, 72 h). Significant effect of salinity was detected on the expression of ASCT2 and VHA, whereas time after feeding affected PepT2 and VHA transcripts. Interactions between salinity and feeding significantly affected NHE3 transcription. PepT2 expression was an order of magnitude higher than free amino acid transporters, indicating the importance of peptide reabsorption in the kidney of Mozambique tilapia. Immunofluorescence staining of PepT2 showed an apical staining while, b0,+AT antibody stained the basolateral membrane of the nephrons epithelial cells. The two transporters expression were found in separates segment of the nephrons. These results reveal specific transporters involved in kidney reabsorption of amino acids and short peptides and their response to the fish osmotic and nutritional status.