Gestational age-dependent gene expression profiling of ATP-binding cassette transporters in the healthy human placenta

Abstract

The ATP-binding cassette (ABC) transporters control placental transfer of several nutrients, steroids, immunological factors, chemicals, and drugs at the maternal-fetal interface. We and others have demonstrated a gestational age-dependent expression pattern of two ABC transporters, P-glycoprotein and breast cancer resistance protein throughout pregnancy. However, no reports have comprehensively elucidated the expression pattern of all 50 ABC proteins, comparing first trimester and term human placentae. We hypothesized that placental ABC transporters are expressed in a gestational-age dependent manner in normal human pregnancy. Using the TaqMan^® Human ABC Transporter Array, we assessed the mRNA expression of all 50 ABC transporters in first (first trimester, n = 8) and third trimester (term, n = 12) human placentae and validated the resulting expression of selected ABC transporters using qPCR, Western blot and immunohistochemistry. A distinct gene expression profile of 30 ABC transporters was observed comparing first trimester vs. term placentae. Using individual qPCR in selected genes, we validated the increased expression of ABCA1 (P < 0.01), ABCA6 (P < 0.001), ABCA9 (P < 0.001) and ABCC3 (P < 0.001), as well as the decreased expression of ABCB11 (P < 0.001) and ABCG4 (P < 0.01) with advancing gestation. One important lipid transporter, ABCA6, was selected to correlate protein abundance and characterize tissue localization. ABCA6 exhibited increased protein expression towards term and was predominantly localized to syncytiotrophoblast cells. In conclusion, expression patterns of placental ABC transporters change as a function of gestational age. These changes are likely fundamental to a healthy pregnancy given the critical role that these transporters play in the regulation of steroidogenesis, immunological responses, and placental barrier function and integrity.

Keywords: ABC transporters; ABCA6; gestational-age; lipid transporter; placenta.

Figure 1

Heatmap indicating the time‐dependent expression of the 30 ATP‐binding cassette (ABC) genes that exhibited developmentally regulated expression in healthy human placentae. Relative quantities (Rq) of the ABC genes obtained from the Human ABC Transporters Taqman^® Array, comparing first trimester (n = 8) and term (n = 12) human placentae. Red represents increased expression, green indicates reduced expression

Figure 2

Validation of selected ABC genes by qPCR. (A) ABCA1; (B) ABCA6; (C) ABCA9; (D) ABCB1 (E); ABCB11; (F) ABCC3; and (G) ABCG4 mRNA expression, comparing first trimester (n = 8) and term (n = 12) placentae. Statistical analyses: non‐parametric Mann‐Whitney test. Data are presented as mean ± SEM. **P < 0.01 and ***P < 0.001

Figure 3

Human placental ABCA6 protein expression and immunolocalization towards term. (A) Representative ABCA6 (180 kDa) and ERK (42 kDa) immunoblots, comparing first trimester (n = 5; open bar) and term (n = 5; solid bar) human placentae, as well as placental ABCA6 expression normalized to ERK (loading control). (B and C) Representative images of ABCA6 localization in first trimester and term placentae, respectively. (D and E) Negative controls for the respective gestational age. Statistical analyses: unpaired t‐test. Data are presented as mean ± SEM *P < 0.05, arrows indicate the syncytium, scale bar: 55 μm