Transport of maternal cholesterol to the fetus is affected by maternal plasma cholesterol concentrations in the Golden Syrian hamster

Abstract

The fetus has a high requirement for cholesterol and synthesizes cholesterol at elevated rates. Recent studies suggest that fetal cholesterol also can be obtained from exogenous sources. The purpose of the current study was to examine the transport of maternal cholesterol to the fetus and determine the mechanism responsible for any cholesterol-driven changes in transport. Studies were completed in pregnant hamsters with normal and elevated plasma cholesterol concentrations. Cholesterol feeding resulted in a 3.1-fold increase in the amount of LDL-cholesterol taken up by the fetus and a 2.4-fold increase in the amount of HDL-cholesterol taken up. LDL-cholesterol was transported to the fetus primarily by the placenta, and HDL-cholesterol was transported by the yolk sac and placenta. Several proteins associated with sterol transport and efflux, including those induced by activated liver X receptor, were expressed in hamster and human placentas: NPC1, NPC1L1, ABCA2, SCP-x, and ABCG1, but not ABCG8. NPC1L1 was the only protein increased in hypercholesterolemic placentas. Thus, increasing maternal lipoprotein-cholesterol concentrations can enhance transport of maternal cholesterol to the fetus, leading to 1) increased movement of cholesterol down a concentration gradient in the placenta, 2) increased lipoprotein secretion from the yolk sac (shown previously), and possi- Cholesterol is essential for normal fetal development. Possibly the most noted role of cholesterol is as a structural component of membranes. Sterols are also the precursor for bile acids, steroid hormones, and oxysterols, which are all synthesized by the fetus and regulate various cellular processes. Cholesterol is also required for activation of sonic hedgehog (Shh), a protein involved in brain development, and for propagation of the Shh signal (1, 2). Cholesterol is obtained endogenously by de novo synthesis and exogenously by transfer of maternal cholesterol to the fetus. Interestingly, maternal plasma triglyceride and cholesterol concentrations increase during pregnancy in humans (3, 4), possibly an adaptation to maternal and fetal needs. However, whether these changes in maternal lipoprotein concentrations result in increased transport of maternal cholesterol to the fetus is unclear.Since the fetus does not come in direct contact with the maternal circulation, maternal cholesterol destined for the fetus must initially be taken up by the placenta and yolk sac prior to transport and delivery to the fetus. Indeed, the placenta and yolk sac take up maternal LDL-and HDLcholesterol at relatively elevated rates compared with other peripheral tissues (5). LDL is taken up by the LDL receptor (LDLR), which is expressed abundantly in the placenta but expressed at low levels, if at all, in the yolk sac (5, 6). LDL-derived sterol is transported to the lysosome/endosome pathway where the ester bond is hydrolyzed (7). The unesterified cholesterol is then transported by NiemannThese studies were supported by grants HD34089 (LAW) and GM31651 (FS) from the...

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