Interstitial cystitis antiproliferative factor (APF) as a cell-cycle modulator

Abstract

Background: Interstitial cystitis (IC) is a chronic bladder disorder of unknown etiology. Antiproliferative factor (APF), a peptide found in the urine of IC patients, has previously been shown to decrease incorporation of thymidine by normal bladder epithelial cells. This study was performed to determine the effect of APF on the cell cycle of bladder epithelial cells so as to better understand its antiproliferative activity.

Methods: Explant cultures from normal bladder biopsy specimens were exposed to APF or mock control. DNA cytometry was performed using an automated image analysis system. Cell cycle phase fractions were calculated from the DNA frequency distributions and compared by two-way analysis of variance (ANOVA).

Results: APF exposure produced statistically significant increases in the proportion of tetraploid and hypertetraploid cells compared to mock control preparations, suggesting a G2 and/or M phase cell cycle block and the production of polyploidy.

Conclusions: APF has a specific effect on cell cycle distributions. The presence of a peptide with this activity may contribute to the pathogenesis of interstitial cystitis through disruption of normal urothelial proliferation and repair processes.

Figure 1

Representative DNA frequency distributions DNA frequency distributions from 10 μl mock treated (top panel) and 10 μl APF treated (bottom panel) normal bladder epithelial cell cultures show an APF associated increase in the proportion of cells with tetraploid DNA value. The presence of cells with octaploid DNA values suggests the cultures contain a mixture of cycling diploid and tetraploid cells.

Figure 2

Cumulative DNA frequency distributions Cumulative DNA frequency distributions for 10 μl mock treated (red line) and 10 μl APF (blue line) treated normal bladder epithelial cells were used to calculate cell cycle sub-population fractions.