Trophoblast cells primed with vasoactive intestinal peptide enhance monocyte migration and apoptotic cell clearance through αvβ3 integrin portal formation in a model of maternal-placental interaction.
OBJECTIVE
Is apoptotic cell phagocytosis by monocytes modulated by pathways elicited by vasoactive intestinal peptide (VIP) action on trophoblast?


RESULTS
Targeting trophoblast cells with VIP induces monocyte migration, polarization to anti-inflammatory phenotypes and apoptotic trophoblast cell clearance which involves increased αvβ3 integrin expression on phagocytic cells and binding to thrombospondin 1.


BACKGROUND
Monocytes recruited to the maternal-placental interface interact with trophoblast cells and differentiate to alternatively activated macrophages involved in the silent clearance of apoptotic cells. Vasoactive intestinal peptide (VIP) is an immunomodulatory polypeptide synthesized at the human placenta that can target both trophoblast cells and monocytes/macrophages. Integrin αvβ3 and thrombospondin 1 are involved in the formation of a phagocytic portal for the immunosuppressant clearance of apoptotic cells.


METHODS
This is a laboratory-based study studying monocytes isolated from peripheral blood of healthy women (n = 33) and their interaction in vitro with first trimester trophoblast cell lines. Peripheral blood monocytes were isolated from healthy volunteers by Percoll gradient and tested in co-culture settings with first trimester trophoblast cell lines (Swan 71 and HTR8) or with trophoblast cell conditioned media obtained in the presence or absence of 10 or 100 nM VIP. The effect of VIP-conditioned media on monocyte migration was assessed through transwell systems and monocyte/macrophage phenotype was determined by flow cytometry. Phagocytosis of apoptotic cells and the mechanisms involved in phagocytic portal formation were assessed by flow cytometry, confocal microscopy, immunological blockade and RT-PCR.


RESULTS
Exposing cells to 100 nM VIP increased the migration of monocytes toward trophoblast cell conditioned media (VIP conditioned medium) (P < 0.05 versus conditioned media from cells not exposed to VIP) and contributed to the monocytes acquiring an anti-inflammatory profile with increased CD39 and IL-10 expression (P < 0.05). Phagocytosis of apoptotic trophoblast cells by monocytes and monocyte-differentiated macrophages was increased by VIP conditioned medium (P < 0.05 versus media conditioned in the absence of VIP or direct addition of 100 nM VIP). The boosting effect of VIP conditioned medium on phagocytosis involved increased expression and re-localization of αvβ3 integrin on phagocytic cells along with enhanced expression of thrombospondin 1 on trophoblast cells.


CONCLUSIONS
The conclusions are based on in vitro experiments with monocytes drawn from peripheral blood of healthy individuals and trophoblast cell lines and we were unable to ascertain that these mechanisms operate similarly in vivo. We cannot rule out a differential behavior of either trophoblast cells targeted in vivo with VIP, or primary cultures of first trimester trophoblast cells assayed in vitro.


CONCLUSIONS
The results presented provide new clues for immune and trophoblast cell pharmacological targeting in pregnancy complications of immunopathologic nature.


BACKGROUND
This work was funded by the National Agency of Sciences and Technology ANPCyT (PICT 2011-0144), National Research Council CONICET (PIP 602/2012) and University of Buenos Aires (UBACyT 20020130100040BA) to C.P.L. The authors have no conflicts of interest to disclose.
Department of Biological Chemistry, School of Sciences, University of Buenos Aires, IQUIBICEN-CONICET, Ciudad Universitaria, Pab. 2, (1428) Buenos Aires, Argentina.
Daniel
D
Paparini
Department of Biological Chemistry, School of Sciences, University of Buenos Aires, IQUIBICEN-CONICET, Ciudad Universitaria, Pab. 2, (1428) Buenos Aires, Argentina.
Esteban
E
Grasso
Department of Biological Chemistry, School of Sciences, University of Buenos Aires, IQUIBICEN-CONICET, Ciudad Universitaria, Pab. 2, (1428) Buenos Aires, Argentina.
Guillermina
G
Calo
Department of Biological Chemistry, School of Sciences, University of Buenos Aires, IQUIBICEN-CONICET, Ciudad Universitaria, Pab. 2, (1428) Buenos Aires, Argentina.
Daiana
D
Vota
Department of Biological Chemistry, School of Sciences, University of Buenos Aires, IQUIBICEN-CONICET, Ciudad Universitaria, Pab. 2, (1428) Buenos Aires, Argentina.
Vanesa
V
Hauk
Department of Biological Chemistry, School of Sciences, University of Buenos Aires, IQUIBICEN-CONICET, Ciudad Universitaria, Pab. 2, (1428) Buenos Aires, Argentina.
Rosanna
R
Ramhorst
Department of Biological Chemistry, School of Sciences, University of Buenos Aires, IQUIBICEN-CONICET, Ciudad Universitaria, Pab. 2, (1428) Buenos Aires, Argentina cpleiros@qb.fcen.uba.ar.
Claudia Pérez
CP
Leirós
D017209:Apoptosis / Q000187:drug effects; D005260:Female; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism; D010920:Placenta / Q000187:drug effects / Q000378:metabolism; D011247:Pregnancy; D014327:Trophoblasts / Q000187:drug effects / Q000378:metabolism*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D039302:Integrin alphaVbeta3; D014660:Vasoactive Intestinal Peptide
apoptotic cell phagocytosis; apoptotic trophoblast cells; maternal–placental interface; monocytes; thrombospondin 1; vasoactive intestinal polypeptide