Energy and nitrogenous waste from glutamate/glutamine catabolism facilitates acute osmotic adjustment in non-neuroectodermal branchial cells

• Published in: Scientific reports Vol. 10; no. 1; p. 9460
• Main Authors: Huang, Pei-Chen, Liu, Tzu-Yen, Hu, Marian Y., Casties, Isabel, Tseng, Yung-Che
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11-06-2020; Nature Publishing Group
• Subjects: 38/39; 631/443/319/1557; 631/601/1737; 82/51; Acclimation; Acclimatization - physiology; Amino acid sequence; Animals; Carbamoyl phosphate; Deamination; Energy resources; Epithelial Cells - metabolism; Epithelium; Gills; Gills - metabolism; Glutamate-ammonia ligase; Glutamate-Ammonia Ligase - metabolism; Glutamic Acid - metabolism; Glutaminase; Glutamine; Glutamine - metabolism; Homeostasis; Humanities and Social Sciences; Hybridization; Immunocytochemistry; Ion Pumps - metabolism; multidisciplinary; Na+/K+-exchanging ATPase; Nitrogen - metabolism; Ornithine; Oryzias - metabolism; Oryzias latipes; Osmosis - physiology; Salinity; Science; Science (multidisciplinary); Sodium-Potassium-Exchanging ATPase - metabolism; Urea; Urea - metabolism
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-020-65913-1

Maintenance of homeostasis is one of the most important physiological responses for animals upon osmotic perturbations. Ionocytes of branchial epithelia are the major cell types responsible for active ion transport, which is mediated by energy-consuming ion pumps (e.g., Na
+
-K
+
-ATPase, NKA) and secondary active transporters. Consequently, in addition to osmolyte adjustments, sufficient and immediate energy replenishment is essenttableial for acclimation to osmotic changes. In this study, we propose that glutamate/glutamine catabolism and trans-epithelial transport of nitrogenous waste may aid euryhaline teleosts Japanese medaka (
Oryzias latipes
) during acclimation to osmotic changes. Glutamate family amino acid contents in gills were increased by hyperosmotic challenge along an acclimation period of 72 hours. This change in amino acids was accompanied by a stimulation of putative glutamate/glutamine transporters (Eaats, Sat) and synthesis enzymes (Gls, Glul) that participate in regulating glutamate/glutamine cycling in branchial epithelia during acclimation to hyperosmotic conditions.
In situ
hybridization of glutaminase and glutamine synthetase in combination with immunocytochemistry demonstrate a partial colocalization of
olgls1a
and
olgls2
but not
olglul
with Na
+
/K
+
-ATPase-rich ionocytes. Also for the glutamate and glutamine transporters colocalization with ionocytes was found for
oleaat1
,
oleaat3
, and
olslc38a4
, but not
oleaat2
. Morpholino knock-down of Sat decreased Na
+
flux from the larval epithelium, demonstrating the importance of glutamate/glutamine transport in osmotic regulation. In addition to its role as an energy substrate, glutamate deamination produces NH
4
+
, which may contribute to osmolyte production; genes encoding components of the urea production cycle, including carbamoyl phosphate synthetase (CPS) and ornithine transcarbamylase (OTC), were upregulated under hyperosmotic challenges. Based on these findings the present work demonstrates that the glutamate/glutamine cycle and subsequent transepithelial transport of nitrogenous waste in branchial epithelia represents an essential component for the maintenance of ionic homeostasis under a hyperosmotic challenge.