Expression and Distribution of Calcium-Binding Protein S100P in Human Placenta during Pregnancy

Abstract

Background: S100P is a member of the S100 family of calcium-binding proteins, and it participates in pathophysiological events, such as tumor growth and invasion. Based on the striking similarities between trophoblast cells and tumor cells with regard to proliferative and invasive properties, we raised the question of whether and how S100P expresses in trophoblast cells during development. This study aimed to investigate the expression pattern of S100P in the human placenta during pregnancy development.

Materials and methods: In this experimental study, we collected 16 first-trimester placental tissues, 10 second-trimester placental tissues, and 12 term placentas. The mRNA expression levels of S100P were detected by reverse-transcription-polymerase chain reaction (RT-PCR) and quantitative real-time PCR, the protein expression levels were detected by western blot, and the localization of S100P was measured by immunohistochemical staining. The values obtained from PCR and western blot analysis were expressed as the mean ± SD. Levene's test was used to test equal variances, and one-way analysis of variance (ANOVA) was used to evaluate differences between groups.

Results: Protein and mRNA expression of S100P could be detected in placenta during pregnancy, with minor higher levels in first-trimester (p>0.05). Immunohistochemical staining revealed that S100P protein was strongly expressed in syncytiotrophoblasts, and moderate expression was detected in villous cytotrophoblasts and cytotrophoblast columns. The S100P protein was localized to both cytoplasm and nuclei in syncytiotrophoblasts, while it only existed in the cytoplasm of cytotrophoblasts.

Conclusion: S100P was strongly detected in human placenta during pregnancy. The specific expression and distribution of S100P in human placenta throughout gestation suggested that S100P function might vary with its location in the placenta.

Keywords: Placenta; Pregnancy; S100P; Trophoblast.

Fig 1

Expression of S100P mRNA in placenta during pregnancy obtained by RT-PCR (A), and protein expression of S100P was detected by western blot (B). Fir; First-trimester placenta, Sec; Second-trimester placenta, Term; Full-term placenta and *; P>0.05. Each bar is the mean ± SEM, n=3 separate experiments.

Fig 2

In first-trimester placenta, S100P immunopositive staining showed an intense signal in the cytoplasm and nuclei of syncytiotrophoblasts, whereas villous cytotrophoblasts (A) and cytotrophoblast columns (D) were stained at the cytoplasm. Furthermore, stromal cells were also stained by S100P antibodies (A). Trophoblasts were immunoreactive to cytokeratin-7 (B, E) and villous stroma was positive to vimentin (C, F). Figures show as ×200 magnification. CTB; Cytotrophoblasts, STB; Syncytiotrophoblasts and CC; Cytotrophoblast columns.

Fig 3

In second-trimester placenta, an intense signal was still shown in syncytiotrophoblasts and stromal cells (A, D). Anti-cytokeratin-7 antibody was positive for trophoblast cells (B, E), and anti-vimentin antibody was positive for villous stroma (C, F). A, B, C: ×200 magnification and D, E, F: ×400 magnification.

Fig 4

In placenta at term, S100P immunoreactivity was still localized at the cytoplasm and nuclei of syncytiotrophoblasts, whereas the villous stroma was stained weakly or negative for S100P (A). Trophoblasts were immunoreactive to cytokeratin-7 (B) and villous stroma was positive to vimentin (C). STB; Syncytiotrophoblasts. Figures show as ×200 magnification.