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Abstract
To define the developmental expression of microsomal triglyceride transfer protein (MTP) large subunit mRNA and protein, samples of small intestine and liver were collected from 40-day gestation fetal, 2-day-old newborn, 3-week-old suckling, and 2-month-old weanling swine. In fetal animals, MTP mRNA expression was high in intestine and liver. Postnatally, jejunal expression paralleled the intake of a high-fat breast milk diet and declined after weaning. Ileal expression was comparable with that of jejunum in 2-day-old animals, but declined to low levels afterward. Hepatic expression declined postnatally and remained low. MTP protein expression generally paralleled mRNA expression, except in fetal intestine in which no 97 kDa protein was detected. In 2-day-old piglets, a high-triacylglycerol diet increased jejunal and ileal MTP mRNA levels, as compared to a low-triacylglycerol diet. To test the roles of glucocorticoids and fatty acids in MTP regulation, a newborn swine enterocyte cell line (IPEC-1) was used. Except at day 2 of differentiation, dexamethasone did not influence MTP expression. Fatty acids either up-regulated or down-regulated MTP expression, depending on the specific fatty acid and duration of exposure. Although programmed genetic cues regulate MTP expression during development, clearly the amount and fatty acid composition of dietary lipid also play regulatory roles.
Highlights
To define the developmental expression of microsomal triglyceride transfer protein (MTP) large subunit mRNA and protein, samples of small intestine and liver were collected from 40-day gestation fetal, 2-day-old newborn, 3-week-old suckling, and 2-month-old weanling swine
There is a paucity of information on the developmental expression of MTP, with a published study of MTP large subunit expression in the fetal mouse using in situ hybridization [5], another in primary cultures of suckling rat hepatocytes [6], and one study in early-gestation human fetal small intestine [7]
We examined the influence of various fatty acids on MTP large subunit expression in IPEC-1 cells
Summary
To define the developmental expression of microsomal triglyceride transfer protein (MTP) large subunit mRNA and protein, samples of small intestine and liver were collected from 40-day gestation fetal, 2-day-old newborn, 3-week-old suckling, and 2-month-old weanling swine. In vivo regulation of MTP expression in liver and small intestine has been studied to a limited extent in adult animal models (hamsters and rats) [2, 4]. There is a paucity of information on the developmental expression of MTP, with a published study of MTP large subunit expression in the fetal mouse using in situ hybridization [5], another in primary cultures of suckling rat hepatocytes [6], and one study in early-gestation human fetal small intestine [7] Such regulation may have important implications for lipid absorption and metabolism in the neonate [8], because the neonatal mammal is dependent on breast milk with approximately half of total calories derived from lipids.
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