Intestinal apolipoprotein A-IV gene expression in the piglet

Fetal, newborn, and suckling piglets were used to study the intestinal expression of the apoA-IV gene in the immature mammal. Swine apoA-IV (42 kD) was isolated from fat-fed piglet lipoprotein-deficient plasma by adsorption to Intralipid(R) followed by preparative sodium dodecyl sulfate polyacrylamide gel elcetrophoresis (SDS-PAGE) and electroelution. Rabbit antiswine apoA-IV antibodies were raised, and apoA-IV was immunoprecipitated from small intestinal homogenates after in vivo radiolabeling with [³H]leucine. ApoA-IV synthesis was expressed as a percentage of total protein synthesis from trichloroacetic acid-precipitable counts. Fetal (40 day gestation) whole small intestine synthesis was 2.1%. Postnatally, 2-day-old new-born piglets given high triglyceride and low triglyceride duodenal infusions, as well as bile diversion, were studied. Synthesis rates in jejunal mucosa in all groups were comparable to the fetal whole intestinal value except in the jejunum of the high-triglyceride group, where synthesis was increased sevenfold. In 1- to 2-week-old fasting, cream-fed, and bile-diverted piglets synthesis was again unchanged except in the fat-fed jejunum, where synthesis doubled. Ileal synthesis rates in newborn and suckling animals were lower than jejunal rates and did not increase with lipid absorption or decrease with bile diversion. Northern blot hybridization of intestinal RNA samples from the newborn groups with an authetic cross-hybridizing human apoA-IV cDNA probe revealed a 1.8 kb signal which was strongest in the high-triglyceride jejunal samples. Slot blot hybridization showed eightfold increased apoA-IV mRNA levels in high-triglyceride jejunal samples as compared to low-triglyceride and bile-diverted jejunum with no differences in beta actin mRNA abundance. Fetal, newborn,and suckling piglet small intestine synthesizes a protein similar to human and rat apoA-IV. Jejunal synthesis of apoA-IV is up-regulated in newborn and suckling animals by dietary lipid absorption. In newborn animals this regulation appears to occur at the pre-translational level. Biliary lipid absorption does not play a regulatory role in intestinal apoA-IV synthesis in the immature swine.