Poster 10: Histopathology and Apoptosis in Vaginal Connective Tissues of Squirrel Monkeys With/Without Pelvic Relaxation

Abstract

OBJECTIVE: Previous studies in women have suggested that pelvic organ prolapse (POP) is associated with reduced cellularity, altered collagen content, and reduced smooth muscle content in vaginal tissues. However, to our knowledge, apoptosis in individuals with POP has never been examined. The purpose of this study was to examine apoptosis, cellularity, content of collagen, elastin, and smooth muscle, and innervation pattern in the paravaginal attachment and/or anterior vaginal wall in the squirrel monkey model of POP. METHODS: The paravaginal attachment to the levator ani (pubocaudalis) muscle and anterior vaginal wall were collected during the nonbreeding season from 7 squirrel monkeys aged 4–25 yr (n=4 parous females with POP/anterior defect, n=3 nulliparous females without POP) and processed for histology and immunofluorescence. Hematoxylin and eosin, Masson trichrome, and elastin stains were used on serial tissue sections to assess cellularity, smooth muscle/collagen content, and elastin content. The frequency of nerve bundles was also examined in elastin-stained sections (elastin is present in sheaths separating nerve fascicles). The TUNEL (dUTP nick-end labeling) assay was used to measure apoptosis. RESULTS: In the paravaginal attachment, POP/parity tended to be associated with decreased cellularity and increased apoptosis of fibroblasts (total nuclei per 105 pixels = 24 ± 7 SE POP vs 36 ± 11 SE no POP; % apoptotic nuclei = 9.2 ± 4.8 SE POP vs 1.8 ± 1.8 SE no POP). One animal with POP that had an abnormally dense deposition of connective tissue over the iliocaudalis muscle and levator ani nerve had approximately 78% apoptotic nuclei in this fascia. In the anterior vaginal wall, apoptotic nuclei in the vaginal mucosa (likely fibroblasts) were observed in 3 of 4 animals with POP but in 0 of 3 animals without POP. Reduced smooth muscle content or apoptosis of smooth muscle cells was not observed in squirrel monkeys with POP. POP/parity was not associated with decreased cellularity (fibroblasts) in the vaginal mucosa, but cellularity in the vaginal mucosa was found to decrease with age (total nuclei per 105 pixels = 35 ± 3 SE young [≤12 yr, n=5] vs 20 ± 0.1 SE old [>20 yr, n=2], P=0.048, t test). Elastin content in the vaginal mucosa (shortened, thickened fibers) increased with age (P=0.048, Fisher exact test), independent of POP/parity. The presence of nerve bundles in the anterior vaginal wall was not altered upon POP/parity status or increasing age. CONCLUSIONS: Various alterations in vaginal connective tissues are associated with POP/parity and also with normal aging in the squirrel monkey. Apoptosis of connective tissue fibroblasts would explain a mechanism to account for reduced numbers of fibroblasts seen in some parous animals with POP and may be indicative of abnormal collagen production or degradation. Investigation of additional age- and parity-matched animals without POP will help differentiate the effects of POP, parity, and aging on supportive pelvic connective tissues.