title: Regulation of leucine catabolism by metabolic fuels in mammary epithelial cells.
abstract: Lactation is associated with elevated catabolism of branched-chain amino acids (BCAA) in mammary glands to produce glutamate, glutamine, alanine, aspartate, and asparagine. This study determined effects of metabolic fuels on the catabolism of leucine (a representative BCAA) in bovine mammary epithelial cells. Cells were incubated at 37 °C for 2 h in Krebs buffer containing 0.5 mM L-leucine and either L-[1-(14)C]leucine or L-[U-(14)C]leucine. The medium also contained 0-5 mM D-glucose, 0-2 mM L-glutamine, 0-4 mM DL-β-hydroxybutyrate, or 0-2 mM oleic acid. Rates of leucine decarboxylation were 60 % lower, but rates of α-ketoisocaproate production were 34 % higher, in the presence of 2 mM glucose than in its absence. All variables of leucine catabolism did not differ between 2 and 5 mM glucose or between 0 and 4 mM DL-β-hydroxybutyrate. Compared with 0-0.25 mM glutamine, 0.5 and 2 mM L-glutamine reduced leucine transport, transamination, and decarboxylation. In contrast, increasing the concentration of oleic acid from 0 to 2 mM dose-dependently stimulated leucine transamination, decarboxylation, and oxidation of carbons 2-6. Oleic acid also enhanced the abundance of cytosolic BCAA transaminase, while reducing the phosphorylated level (inactive state) of the E1α subunit of the mitochondrial branched-chain α-ketoacid dehydrogenase complex. Thus, hypoglycemia or ketosis in early lactation does not likely affect BCAA metabolism in mammary epithelial cells. Increasing circulating levels of BCAA and oleic acid may have great potential to increase the syntheses of glutamate, glutamine, aspartate, alanine, and asparagine by lactating mammary glands, thereby leading to enhanced production of milk for suckling neonates.
authors.affiliation: College of Animal Science, South China Agricultural University, Guangzhou 510642, People's Republic of China. sgleijian@163.com
authors.forename: Jian
authors.initials: J
authors.lastname: Lei
authors.forename: Dingyuan
authors.initials: D
authors.lastname: Feng
authors.forename: Yongliang
authors.initials: Y
authors.lastname: Zhang
authors.forename: Sudath
authors.initials: S
authors.lastname: Dahanayaka
authors.forename: Xilong
authors.initials: X
authors.lastname: Li
authors.forename: Kang
authors.initials: K
authors.lastname: Yao
authors.forename: Junjun
authors.initials: J
authors.lastname: Wang
authors.forename: Zhenlong
authors.initials: Z
authors.lastname: Wu
authors.forename: Zhaolai
authors.initials: Z
authors.lastname: Dai
authors.forename: Guoyao
authors.initials: G
authors.lastname: Wu
mesh_terms: D020155:3-Hydroxybutyric Acid / Q000378:metabolism* / Q000494:pharmacology; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002250:Carbon Radioisotopes; D002417:Cattle; D002478:Cells, Cultured; D003470:Culture Media / Q000737:chemistry; D003653:Decarboxylation / Q000187:drug effects; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D005973:Glutamine / Q000378:metabolism* / Q000494:pharmacology; D007651:Keto Acids / Q000378:metabolism; D007930:Leucine / Q000378:metabolism* / Q000494:pharmacology; D008321:Mammary Glands, Animal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019301:Oleic Acid / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D000637:Transaminases / Q000235:genetics / Q000378:metabolism
chemical_list: D002250:Carbon Radioisotopes; D003470:Culture Media; D007651:Keto Acids; D005973:Glutamine; D019301:Oleic Acid; C013082:alpha-ketoisocaproic acid; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000637:Transaminases; C019798:branched-chain-amino-acid transaminase; D007930:Leucine; D005947:Glucose; D020155:3-Hydroxybutyric Acid