Tubal Ligation Induces Quiescence in the Epithelia of the Fallopian Tube Fimbria

Abstract

Tubal ligation keeps the fimbriated end of the fallopian tube intact while interrupting the conduit for sperm and egg between the uterus and ovary. Tubal ligation is associated with an approximately 20% decreased risk of high-grade serous ovarian cancers, which mounting evidence suggests arise from the distal fallopian tube epithelium. We postulated that biological changes at the epithelial cellular level of the distal fallopian tube may account for the surgical procedure's observed risk reduction. We compared the histology, presence of epithelial progenitors (basally located CD44-positive cells), and degree of epithelial proliferation (Ki67-positive cells) of distal fallopian tube from 10 patients with previous tubal ligation and 10 age-matched patients with uncut fallopian tubes. A significantly reduced population of proliferating epithelial progenitors (basally located CD44/Ki67 dual-positive cells) was detected in the tubal ligated specimens (P = .0002). To functionally assess the effect of tubal ligation, a murine model was utilized to compare the growth capacity of distal fallopian tube epithelial cells isolated from either ligated or sham-operated tubal epithelia. Murine fallopian tube epithelial cells isolated after tubal ligation showed a significantly reduced capacity to grow organoids in culture compared to sham-operated controls (P = .002). The findings of this study show that tubal ligation is associated with a reduced presence and decreased proliferation of progenitor cells in the distal fallopian tube epithelium. These compositional and functional changes suggest that tubal ligation induces quiescence of distal fallopian tube epithelial cells.

Keywords: fallopian epithelial progenitors; fallopian tube epithelial proliferation; tubal ligation.

Figure 1.

A lower number of progenitors was detected in the distal fallopian tube epithelium of patients who underwent tubal ligation. (A) Immunohistochemistry demonstrated the representative distribution of CD44 expression in the fimbria of intact fallopian tubes (a and c) versus ligated patient samples (b and d). A lower number of basally located CD44-positive cells was seen in both pre- (a vs b) and postmenopausal (c vs d) tubal ligation patient samples. Arrows point to individual CD44-positive basal epithelial cells. (B) The median percentage of distal fallopian tube epithelial progenitors (basally located CD44-positive epithelial cells) was reduced with tubal ligation. Dot plot summarizes and compares data points of all clinical samples, confirming a statistically significant difference at P = .0113. Horizontal bars represent the median for each cohort and the vertical bars denote interquartile range.

Figure 2.

The percentage of proliferating epithelial progenitors was diminished in the distal fallopian tube of patient samples with tubal ligation. (A) Immunohistochemistry revealed a lower expression of proliferating progenitors (basally located CD44/Ki67 dual-positive epithelial cells) in the distal fallopian tube of ligated patient samples (b and d) compared to intact fallopian tubes (a and c). Light brown staining corresponds to CD44 expression and magenta staining indicates Ki67 nuclear expression. Tubal ligation samples from both pre- (b) or postmenopausal (d) patients showed a reduction in CD44/Ki67 dual expression compared to the control cohort. (B) The median percentage of proliferating progenitors was significantly lowered in the fimbria of tubal ligated patient specimens compared to age-matched controls at P = .0002. Each dot on the chart represents the percentage of basally located CD44-positive epithelial cells that also expressed Ki67. Horizontal bars represent the median for each cohort and the vertical bars denote interquartile range.

Figure 3.

Epithelial cells residing in the fimbriated end of ligated fallopian tubes had a decreased capacity for forming in vitro organoids in a murine model. (A) Experimental schema for isolation and in vitro 3-dimensional growth of fallopian tube epithelia from both ligated and intact murine fallopian tubes. (B) Epithelia obtained from ligated murine fallopian tubes showed a significant decrease in number of cells capable of organoid formation compared to intact tubes. Cumulative results from 2 independent experiments are shown with mean ± standard deviation (SD).

Figure 4.

A model for risk reduction in epithelial ovarian tumors following tubal ligation. (A) We propose that the progenitors of the distal fallopian tube are normally cycling. This may allow for accumulation of genetic mutations that lead to serous cancer initiation, such as inactivation of tumor suppressors BRCA1, BRCA2, and p53. It has been proposed by other studies that when the fallopian tube is left intact, ascending endometrial cells are able to migrate and implant onto the ovary, which may lead to the development of endometrioid and clear cell cancers. (B) Our findings suggest that tubal ligation induces a state of quiescence in epithelia of distal fimbria by leading to a decreased population of progenitor cells with a lower proliferative index. A diminished number of proliferating progenitors may lower the frequency of cumulative genetic changes associated with serous cancer. As others have previously proposed, tubal ligation may prevent the migration of endometrial cells from initiating endometrioid and clear cell cancers on the ovary by interrupting the conduit between the uterus and ovary.