Hydrolysis Activity of Pyloric Cecal Enterocytes of Brown Trout (Salmo trutta) toward Monoacylglycerol and Lysophosphatidylcholine

Abstract

Some lipid digestion pathways in fish deviate from those in mammals, and many differences may also be species dependent. This report describes a pathway for monoacylglycerol (MAG) and lysophospholipid absorption by intestinal enterocytes in brown trout that may be of significance in salmonids. When culturing primary cells in a medium containing 1- and 2-MAG, we observed a massive hydrolysis of unesterified fatty acids. The hydrolysis activity was retained in the medium even after the removal of the cells. To further characterize these activities, both extracellular and isolated membrane proteins were tested for lipase activity toward triacylglycerol (TAG), diacylglycerol (DAG), MAG, phosphatidylcholine (PtdCho), and lysoPtdCho. In both cases, the main hydrolyzing activity was toward MAG followed by lysoPtdCho with very little activity toward DAG, TAG, or PtdCho. The extracellular and membrane proteins were partially purified by fast protein liquid chromatography and identified by proteomics (liquid chromatography-tandem mass spectrometry) focusing on lipase/hydrolase enzymes. In the membrane protein fraction, the data suggested that MAG was produced as an intermediate in the hydrolysis of lysoPtdCho by either lysophospholipase C or lysophospholipase D activity. Both abhydrolase-domain-containing protein 6 and abhydrolase-domain-containing protein 12 were identified in the membrane protein and they could be responsible for the hydrolysis of MAG. In the culture medium, low-peptide matches were found for ABHD6 and phospholipases and further studies are needed. In summary, trout enterocytes are capable of hydrolyzing MAG and lysoPtdCho. The enzymes are both extracellular and membrane bound. The pathways may be of significance during lipid absorption in fish lacking a 1,3 specific pancreatic lipase.

Response mechanism of ♀ Epinephelus fuscoguttatus × ♂ Epinephelus lanceolatus under low-temperature and waterless stresses using TMT proteomic analysis

“…FABP (fatty acid-binding protein) (Lei et al 2020 ) that participates in the transfer process of fatty acids was upregulated due to strengthened synthesis of fatty acids under low temperature, while the proteins CPT-1 (carnitine O-palmitoyltransferase 1) (Coccia et al 2014 ) and ACAC (acetyl-coa acyltransferase) (Ayisi et al 2018 ) related with the oxidative decomposition of fatty acids were downregulated in groups B and C. This finding suggests that the energy supply for the oxidation of very-long-chain fatty acids was suppressed. In groups B and C, PLB-1 (phospholipase B-like 1) (Li et al 2018 ) that participated in the synthesis of phospholipid got upregulated, indicating relieved decomposition of cytomembrane phospholipid. As such, the as-synthesized fatty acids may participate in phospholipid synthesis to resist the potential change of cytomembrane mobility under low-temperature dormant and waterless preservation status.…”