Abstract
Soluble human leukocyte antigen-G (HLA-G) is a non-classical class Ib HLA molecule that is secreted from blastocysts. Soluble HLA-G modulates the immune tolerance of the mother and can be used as a prognostic factor for the clinical pregnancy rate. However, the underlying mechanism of how soluble HLA-G5 affects pregnancy remains largely unknown. We hypothesized that soluble HLA-G5 promotes successful implantation and pregnancy by modulating trophoblast invasion through receptor binding and activation of extracellular signal-regulated protein kinase (ERK) signaling pathway. Recombinant HLA-G5 protein over-expressed in E. coli BL21 was purified to near homogeneity. We studied the expression of HLA-G5 and its receptors, the leukocyte immunoglobulin-like receptor subfamily B1 (LILRB1) and killer cell immunoglobulin-like receptor 2DL4 (KIR2DL4), in primary trophoblasts and trophoblastic (JAr and JEG-3) cell lines by florescence-labeled HLA-G5. HLA-G5 was detected in the primary trophoblasts and JEG-3 cells. The LILRB1 and KIR2DL4 receptors were expressed in both primary trophoblasts and trophoblastic cell lines. HLA-G5 stimulated cell invasion (p<0.05) and increased urokinase (uPA) and matrix metalloproteinases (MMPs) transcripts and their activity (p<0.05) in trophoblastic cells. HLA-G5 activated the ERK signaling pathway and induced ERK1/2 phosphorylation in the trophoblastic cell lines. Addition of ERK inhibitors (U0126 and PD98059) nullified the stimulatory effect of HLA-G5 on trophoblastic cell invasion. Taken together, HLA-G5 induced trophoblast invasion by binding to KIR2DL4 and LILRB1, by increasing uPA and MMPs expressions and by activating the ERK signaling pathway.
Highlights
Trophoblast invasion plays an important role in embryo implantation and placentation
Synthesis of the human leucocyte antigen (HLA)-G5 recombinant protein The E. coli BL21 cells treated with isopropyl-b-D-thiogalactoside over-expressed HLA-G5 proteins that were detected in the inclusion bodies (Figure 1A)
Western blot analysis (Figure 2A) and immunostaining (Figure 2B) showed that HLA-G5 protein was expressed in JEG-3 but not in JAr or NK92mi cells
Summary
Trophoblast invasion plays an important role in embryo implantation and placentation. The invasive trophoblast interacts with maternal decidual cells enabling the formation of the spiral arteries that supply the fetus during its development [1]. The trophoblast is semi-allogeneic and should elicit a maternal immune response [2], it does not express the classical human leucocyte antigen (HLA) class Ia and II, but rather the non-classical HLA class Ib molecules that confers maternal immunotolerance to the cells during pregnancy [3,4,5,6]. HLA-G is thought to protect the trophoblast from attack by the decidual natural killer (NK) cells, macrophages and cytotoxic T cells by binding to their receptors such as the leukocyte immunoglobulin-like receptor subfamily B1 (LILRB1) and the killer cell immunoglobulin-like receptor 2DL4 (KIR2DL4) [8]. HLA-G inhibits cytotoxicity leading to apoptosis of the decidual leukocytes in pregnancy complications [5,10,11]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
