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Expression of flotillins in the human placenta: potential implications for placental transcytosis

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Abstract

A proteomics survey of human placental syncytiotrophoblast (ST) apical plasma membranes revealed peptides corresponding to flotillin-1 (FLOT1) and flotillin-2 (FLOT2). The flotillins belong to a class of lipid microdomain-associated integral membrane proteins that have been implicated in clathrin- and caveolar-independent endocytosis. In the present study, we characterized the expression of the flotillin proteins within the human placenta. FLOT1 and FLOT2 were coexpressed in placental lysates and BeWo human trophoblast cells. Immunofluorescence microscopy of first-trimester and term placentas revealed that both proteins were more prominent in villous endothelial cells and cytotrophoblasts (CTs) than the ST. Correspondingly, forskolin-induced fusion in BeWo cells resulted in a decrease in FLOT1 and FLOT2, suggesting that flotillin protein expression is reduced following trophoblast syncytialization. The flotillin proteins co-localized with a marker of fluid-phase pinocytosis, and knockdown of FLOT1 and/or FLOT2 expression resulted in decreased endocytosis of cholera toxin B subunit. We conclude that FLOT1 and FLOT2 are abundantly coexpressed in term villous placental CTs and endothelial cells, and in comparison, expression of these proteins in the ST is reduced. These findings suggest that flotillin-dependent endocytosis is unlikely to be a major pathway in the ST, but may be important in the CT and endothelium.

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Abbreviations

CPS:

Crude placental supernatant

CT:

Cytotrophoblast

CTB-594:

Cholera toxin B subunit/Alexa Fluor-594

CTH:

Crude tissue homogenate

DAPI:

4′,6-Diamidino-2-phenylindole

DIC:

Differential interference contrast

DYSF:

Dysferlin

E-cad:

E-cadherin

FCTH:

Filtered crude tissue homogenate

FLOT1:

Flotillin-1

FLOT2:

Flotillin-2

GAPDH:

Glyceraldehyde 3-phosphate dehydrogenase

GPI:

Glycosylphosphatidylinositol

IFM:

Immunofluorescence microscopy

LY-CH:

Lucifer yellow carbohydrazide

MV:

Microvillous

PPM:

Pelleted plasma membrane

SPINT1:

Serine peptidase inhibitor, Kunitz type 1

ST:

Syncytiotrophoblast

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Acknowledgments

The authors gratefully acknowledge the staff at the Pathology Core Facility at the Ohio State University (Columbus, OH) for technical assistance with cryosectioning of placental biopsy specimens. We are likewise grateful to the Campus Microscopy and Imaging Facility at The Ohio State University. This work was performed while Dr. Janelle R. Walton was a fellow in Maternal–Fetal Medicine at The Ohio State University. Portions of this work were presented in abstract form at the Annual Meeting of the Society for Gynecologic Investigation, 24–27 March 2010, Orlando, FL. The current work was supported by a grant in aid from Perinatal Resources, Inc. (Hilliard, OH) and the Ohio State University Perinatal Research and Development Fund. Additional support was provided by grants K08 HD49628 (W.E.A.) and R01 HD058084 (J.M.R.) from the National Institutes of Health.

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Authors and Affiliations

  1. Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA

    Janelle R. Walton

  2. Division of Maternal-Fetal Medicine and Ultrasound, Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, MO, 63110, USA

    Heather A. Frey

  3. Department of Physiology and Cell Biology, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA

    Dale D. Vandre & John M. Robinson

  4. Division of Infectious Diseases and Department of Microbiology, Center for Microbial Interface Biology, The Center for Retrovirus Research, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA

    Jesse J. Kwiek

  5. Department of Molecular Medicine and Anatomy, Nippon Medical School, Tokyo, 113-8602, Japan

    Tomoko Ishikawa & Toshihiro Takizawa

  6. Department of Obstetrics and Gynecology, Laboratory of Perinatal Research, The Ohio State University Wexner Medical Center, N525 Doan Hall, 410 West 10th Avenue, Columbus, OH, 43210, USA

    William E. Ackerman IV

Authors
  1. Janelle R. Walton
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  2. Heather A. Frey
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  3. Dale D. Vandre
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  8. William E. Ackerman IV
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Correspondence to William E. Ackerman IV.

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418_2012_1040_MOESM1_ESM.eps

Fig. S1 FLOT2 localization in first-trimester placenta using immunofluorescence microscopy of ultrathin cryosections. (A, B) Ultrathin cryosections prepared from a first-trimester placental specimen were co-labeled using antibodies against FLOT2 (1608; green in A) and SPINT1 (red in B). The specimens were counterstained with DAPI (blue in C–F). (C, E) A merged image of the green FLOT2 signal, the red SPINT1 signal, and the blue DAPI nuclear staining. (D, F) The same section with the DIC image merged with the fluorescence image of DAPI-stained nuclei to show the tissue morphology and to identify the CTs. Panels E and F are annotated to show the approximate locations of the ST, CT, and EC layers. These micrographs reveal that CTs are enriched in FLOT2 while the ST has less expression of this protein. Scale bar = 20 μm. EC, endothelial cell; FBC, fetal blood cell; #, intervillous space (EPS 1098 kb)

418_2012_1040_MOESM2_ESM.eps

Fig. S2 FLOT2 localization in term placenta by immunofluorescence microscopy of ultrathin cryosections. (A,B) Ultrathin cryosections prepared from a term placental specimen were co-labeled using antibodies against FLOT2 (1608; green in A) and SPINT1 (red in B). The specimens were counterstained with DAPI (blue in C and D). (C) A merged image of the green FLOT2 signal, the red SPINT1 signal, and the blue DAPI nuclear staining superimposed on the DIC image. Arrowheads denote the location of the ST apical surface. Scale bar = 20 μm. (D) Detail of boxed area in panel C, showing FLOT2 labeling (white arrows) and SPINT1 labeling (black arrows). Scale bar = 10 μm. FBC, fetal blood cell; *, lumen of fetal blood vessel; EC, endothelial cell (EPS 756 kb)

418_2012_1040_MOESM3_ESM.eps

Fig. S3 Distribution of FLOT1 and FLOT2 in unfused and fused BeWo cells. (A, B) Mononuclear BeWo cells (A) and BeWo cells treated with forskolin for 72 h (B) were immunolabeled using antibodies against FLOT1 (HPA001393; red), E-cad (green), and DAPI (blue). The leftmost panels show low-magnification photomicrographs and the boxed areas have been represented in greater detail in the adjacent panels. In panel A, wide arrows denote areas of perinuclear FLOT1 staining in individual cells, reminiscent of Golgi labeling, and double arrows indicate FLOT1 labeling at cellular boundaries, coincident with E-cad labeling in the merged image. In panel B, wide arrows show FLOT1 localization in crescent-shaped structures surrounding nuclei in syncytial structures (note the loss of E-cad labeling in this area). (C, D) Mononuclear (C) and forskolin-treated (D) BeWo cells were immunolabeled using antibodies against FLOT2 (1608; red), E-cad (green), and DAPI (blue), and have been presented in the same manner as described in A and B. In panel C, as in A, wide arrows show areas of perinuclear FLOT2 labeling, and double arrows denote labeling at cellular borders. In panel D, wide arrows indicate dispersed FLOT2 localization in crescent-shaped structures surrounding nuclei in syncytia, while the cell with an intact perimeter of E-cad labeling (asterisk) exhibits a perinuclear FLOT2 distribution (arrowhead) that is typical of that observed in unfused cells. Scale bars = 50 μm (EPS 1412 kb)

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Walton, J.R., Frey, H.A., Vandre, D.D. et al. Expression of flotillins in the human placenta: potential implications for placental transcytosis. Histochem Cell Biol 139, 487–500 (2013). https://doi.org/10.1007/s00418-012-1040-2

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