Decreased expression of fibroblast growth factor 13 in early-onset preeclampsia is associated with the increased trophoblast permeability

Highlights

• FGF13 was downregulated in human placental tissues with early-onset PE.

• The early-onset PE placenta displayed disordered trophoblast arrangement.

• Loss of FGF13 and E-cadherin were observed in primary human PE trophoblasts.

• In FGF13-silenced trophoblasts, cellular permeability increased.

• The level of FGF13 was positively associated with the level of E-cadherin.

Abstract

Objective

Intracellular protein fibroblast growth factor 13 (FGF13) is highly expressed in human placenta, although its biological function remains unexplored. The aims of this study were to investigate the expression of FGF13 in placentae with early-onset preeclampsia (PE) and the associated mechanisms in the pathophysiology of PE.

Methods

The expression levels of FGF13 in placentae obtained from patients with early-onset PE and normal pregnancies were assessed using immunofluorescent staining, Western blot assays and quantitative PCR. We knocked down FGF13 in trophoblast cell lines BeWo and HTR8/SVneo, and analyzed cell permeability. Clinical trophoblast cell-cell junctions were identified by cytokeratin 7 (CK7) immunofluorescent staining of human placental sections. The expressions of FGF13 were manipulated in BeWo and HTR8/SVneo cell lines, and the expressions of E-cadherin were quantified by reverse transcription followed by quantitative PCR, Western blot assays and immunofluorescent staining. The expressions of FGF13 and E-cadherin were further confirmed in the isolated human primary trophoblasts.

Results

Downregulation of FGF13 along with trophoblast disarrangement were found in human placentae with early-onset PE. In trophoblast cell lines decreased FGF13 expression resulted in increased cell permeability and decreased E-cadherin expression. The FGF13 insufficiency-mediated loss of E-cadherin was further confirmed in the human villous trophoblasts isolated from PE patients.

Conclusion

FGF13 was downregulated in human placentae with early-onset PE. FGF13 played an important role in maintaining placental trophoblast permeability via the modulation of E-cadherin.

Introduction

Preeclampsia (PE) is a life-threatening disease with high morbidity and mortality among the pregnant population, characterized by hypertension, severe proteinuria and pitting edema after 20 weeks of gestation. PE can be classified as early-onset or late-onset according to the gestational time in which it develops. Early-onset PE develops before 34 weeks of gestation. Unlike the normal villous morphology in late-onset PE, early-onset PE is usually concurrent with placental pathology [1,2]. As the maternal-fetal interface, the placenta mediates exchange and immune responses between the mother and fetus. Placental barrier dysfunction has been implicated in PE patients with high risks of abnormal infiltration of leukocytes, fetomaternal hemorrhage (FMH) and placental penetration of apoptotic signaling [[3], [4], [5], [6], [7]]. The physical barrier between the fetal and maternal blood circulation is composed of trophoblasts, which regulate placental permeability and orchestrate the selective secretion and absorption.

Fibroblast growth factor 13 (FGF13), also known as fibroblast growth factor homologous factor 2, belongs to the FGF homologous factor (FHF) subfamily [8]. Unlike other secretory FGF members, FGF13 lacks the N-terminal secretion signal sequence, therefore it acts in an FGFR-independent manner [9]. Previously published studies have reported that FGF13 is principally expressed in the nervous system and functions as an indispensable regulator of neuronal development. For example, FGF13 has been shown to be implicated in the regulation of neurons polarization and migration [10], activation of neural differentiation [11], and the modulation of Na⁺ currents in neural conduction [12,13]. It also has broad functions in the heart [14,15] and smooth muscle [16]. In addition to the enrichment of FGF13 in the brain, FGF13 is also highly expressed in the female reproductive system, especially in the placenta. Antibody staining has revealed that the protein levels of FGF13 are higher in placental trophoblasts than in follicle cells of the ovary and endometrial stroma cells of the endometrium (results summarized from the Human Protein Atlas Database, http://www.proteinatlas.org/ENSG00000129682-FGF13/tissue). However, the function of FGF13 in human reproduction remains unexplored.

The aims of the current study were to elucidate the potential role of FGF13 in the pathogenesis of early-onset PE and to uncover the related molecular mechanisms. This study discovered that in the human placenta, FGF13 was expressed in villous trophoblasts and was downregulated in the PE placental tissues. Therefore, we hypothesized that the expression of FGF13 regulated early-onset PE pathogenesis. We demonstrated that FGF13 was an important regulator of trophoblast permeability in placental transport and that FGF13 mediated cell junction integrity through the regulation of E-cadherin. These findings unveiled FGF13 as a novel mediator in maintaining placental function, indicating a critical role of the enriched expression of FGF13 in the reproductive system. The significantly downregulated FGF13 levels in PE human villi discovered here suggested its potential translational and clinical implications.