The role of smooth muscle in the pathogenesis of pelvic organ prolapse—an immunohistochemical and morphometric analysis of the cervical third of the uterosacral ligament

Mechanics of Uterosacral Ligaments: Current Knowledge, Existing Gaps, and Future Directions

The uterosacral ligaments (USLs) are important anatomical structures that support the uterus and apical vagina within the pelvis. As these structures are over-stretched, become weak, and exhibit laxity, pelvic floor disorders such as pelvic organ prolapse occur. Although several surgical procedures to treat pelvic floor disorders are directed toward the USLs, there is still a lot that is unknown about their function. This manuscript presents a review of the current knowledge on the mechanical properties of the USLs. The anatomy, microstructure, and clinical significance of the USLs are first reviewed. Then, the results of published experimental studies on the in vivo and ex vivo, uniaxial and biaxial tensile tests are compiled. Based on the existing findings, research gaps are identified and future research directions are discussed. The purpose of this exhaustive review is to help new researchers navigate scientific literature on the mechanical properties of the USLs. The use of these structures remains very popular in reconstructive surgeries that restore and augment the support of pelvic organs, especially as synthetic surgical mesh implants continue to be highly controversial.

Using the novel pelvic organ prolapse histologic quantification system to identify phenotypes in uterosacral ligaments in women with pelvic organ prolapse

BACKGROUND

Pelvic organ prolapse is common, but the underlying etiologies are poorly understood, which limits our current prevention and treatment options.

OBJECTIVE

Our primary objective was to compare the uterosacral ligament histologic features in women with and without prolapse using the novel pelvic organ prolapse histologic quantification system. Our secondary aim was to determine whether composite histologic findings in uterosacral ligaments are associated with prolapse risk factors.

STUDY DESIGN

This was a prospective cohort study in which paracervical uterosacral ligament biopsies were performed at the time of hysterectomy for primary prolapse or other benign gynecologic indications and processed for histologic evaluation. The pelvic organ prolapse quantification system was used to determine the prolapse stage. In this study, 9 prominent histologic features were semiquantitatively scored using the pelvic organ prolapse histologic quantification system in a blinded fashion and compared between prolapse and control groups. Unbiased principal component analysis of these scores was independently performed to identify potential relationships between histologic measures and prolapse risk factors.

RESULTS

The histologic scores of 81 prolapse and 33 control ligaments were analyzed. Compared with the control group, women in the prolapse group were significantly older and more likely to be in the menopausal phase. There was no difference in the number of vaginal deliveries, body mass index, hormone use, or smoking status between the groups. To control for baseline differences, patients were also stratified by age over 40 years and menopausal status. Compared with the control group, the prolapse ligaments in the premenopausal group had significantly more loss of smooth muscle fibers within the fascicles (P<.001), increased inflammatory infiltrates of neutrophils within the tissue and perineural inflammatory cells (P<.01 and P=.04, respectively), and reduced neointimal hyperplasia (P=.02). Prolapse ligaments in the postmenopausal group exhibited elevated adipose content compared with that of the control group (P=.05). Amount of fibrillar collagen, total nonvascular smooth muscle, and muscle fiber vesicles of prolapse ligaments did not differ in either the premenopausal or postmenopausal group compared with that of the control group. Unbiased principal component analysis of the histologic scores separated the prolapse ligaments into 3 phenotypes: (1) increased adipose accumulation, (2) increased inflammation, and (3) abnormal vasculature, with variable overlap with controls. Posthoc analysis of these subgroups demonstrated a positive correlation between increasing number of vaginal deliveries and body mass index with increasing adipose content in the adipocyte accumulation and inflammatory phenotype and increasing neointimal hyperplasia in the vascular phenotype. However, only the relationship between vaginal delivery and adipocytes was significant in the adipose phenotype (R²=0.13; P=.04).

CONCLUSION

Histologic phenotypes exist in pelvic support ligaments that can be distinguished using the pelvic organ prolapse histologic quantification system and principle component analysis. Vaginal delivery is associated with aberrant adipose accumulation in uterosacral ligaments. Our findings support a multifactorial etiology for pelvic organ prolapse contributing to altered smooth muscle, vasculature, and connective tissue content in crucial pelvic support structures. To confirm these associations and evaluate the biomechanical properties of histologic phenotypes of prolapse, larger studies are warranted. Closing this gap in knowledge will help optimize personalized medicine and help identify targets for prevention and treatment of this complex condition.

The role of smooth muscle cells in the pathophysiology of pelvic organ prolapse

Pelvic organ prolapse (POP) is a prevalent and disabling condition. The pathophysiology of prolapse is multifactorial, and no single mechanism adequately explains all aspects of its development. The pathophysiology of POP is complex and incompletely understood. Smooth muscle (SM), an integral part of the vaginal wall and endopelvic structures that support the pelvic viscera, has also been implicated in the pathophysiology of POP. In this article, we review the role of smooth muscle cells (SMC) in the pathophysiology of POP, also addressing the anatomy of SM in pelvic floor, morphometric analysis, biomechanical properties, and potential mechanisms.

Prospective clinical assessment of the transvaginal mesh technique for treatment of pelvic organ prolapse-5-year results

OBJECTIVES

: The objective of the study was to assess the effectiveness and complication rates for the transvaginal (TVM) technique in the treatment of pelvic organ prolapse (POP).

METHODS

: Women with symptomatic POP (POP-Q stage II-IV) were invited to participate in this institutional review board-approved 5-year study at 3 US centers. All enrolled patients underwent prolapse repair surgery with GYNEMESH PS Prolene Nonabsorbable Soft Mesh using the TVM technique. Success was defined as International Continence Society (ICS) POP-Q stage I or less. The Prolapse-Specific Inventory and quality-of-life questionnaire was used as a subjective outcome measure.

RESULTS

: Eighty-five women were included. Sixty-six patients were available for follow-up at 5 years. Overall anatomic success rates were 88% (90% confidence interval [CI], 80%-93%), 69% (90% CI, 59%-78%), and 67% (95% CI, 56%-76%) at 1, 3, and 5 years, respectively. Anatomic success rates in treated compartments were 89% (90% CI, 82%-94%), 76% (90% CI, 66%-84%), and 77% (90% CI, 67%-85%) at 1, 3, and 5 years, respectively. When defined as treated side leading edge above the hymen, success rates were 89% at 5 years. Five patients required reoperation for prolapse by 5 years. Statistically significant improvements in quality-of-life and Prolapse-Specific Inventory scores were sustained over 5 years. Mesh exposure was observed in 16 of 85 patients over the 5 years. Nine required partial mesh excision. There were 3 patients with some degree of dyspareunia, reported between 3 and 5 years, whereas in 8, preexisting dyspareunia resolved. There was 1 rectovaginal fistula reported and 2 reported ureteral injuries, one of which resulted in a ureteral-vaginal fistula; all resolved after repair.

CONCLUSIONS

: Five-year results indicated that TVM provided a stable anatomic repair. Improvements in quality of life and associated improvements in specific prolapse symptoms were sustained over the 5-year period. Mesh exposure was the most common complication.

A novel role for relaxin-2 in the pathogenesis of primary varicosis

Background

Varicose veins affect up to 40% of men and up to 51% of women. The pathophysiology of primary varicosis is poorly understood. Theories ranging from incompetence of the venous valves to structural changes in the vein wall have been proposed.

Methodology/Principal Findings

We analyzed the functional state of the intramural smooth muscle cells (n = 14 pairs matched for age and gender) and the expression of relaxin-2 and its receptors RXFP1 and RXFP2 in samples of varicose and healthy great saphenous veins (GSV) (n = 21 healthy GSV; n = 46 varicose GSV). Relaxin-2 and RXFP1 contents were determined in tissue samples (n = 9 samples per group). Pharmacological analyses were performed in a perfusion chamber. Morphometric determination of the nuclear size of the smooth muscle compartment yielded no significant difference in varicose GSV in comparison with the healthy controls. Relaxin-2 and its receptors were expressed in the muscular layer, endothelial cells and in blood vessels contained in the vein wall. Immunohistochemical expression of relaxin-2, RXFP1 and RXFP2 was significantly decreased in varicose GSV. Relaxin-2 and RXFP1 measured by ELISA and Western Blot were decreased in varicose GSV (relaxin-2 ELISA healthy vs. varicose GSV: 12.49±0.66 pg/mg versus 9.12±3.39 pg/mg of total protein; p = 0.01; Student's T-test). Contractions of vein samples induced by cholinergic or adrenergic stimulation were antagonized by relaxin-2.

Conclusions/Significance

We report that relaxin-2 and its receptors RXFP1 and RXFP2 are expressed in GSV and that their expression is significantly decreased in varicose GSV. Further, we were able to demonstrate a functional pharmacological relaxin-2 system in varicose GSV. Our results suggest a novel role for relaxin-2 in the pathogenesis of primary varicosis, rendering relaxin-2 a novel possible pharmacological agent for the treatment of this widely prevailing venous disease.

Decreased expression of elastin, fibulin-5 and lysyl oxidase-like 1 in the uterosacral ligaments of postmenopausal women with pelvic organ prolapse

AIM

Pelvic organ prolapse is associated with defects in connective tissues, including elastic fibers. The purpose of this study was to investigate the expression of fibulin-5 and lysyl oxidase-like 1 (LOXL1), which play an essential role in the synthesis and assembly of elastic fibers, in the uterosacral ligaments of women with advanced pelvic organ prolapse (POP) compared with controls.

METHOD

Specimens were obtained prospectively during transvaginal or abdominal hysterectomy from 30 women with advanced pelvic organ prolapse and 30 controls matched to the POP group for age and parity among postmenopausal women with benign gynecologic diseases. The expressions of elastin, fibulin-5 and LOXL1 in uterosacral ligaments were measured by immunohistochemistry.

RESULTS

We detected a decreased, sometimes absent, expression of fibulin-5 and LOXL1 in the uterosacral ligaments of women with POP, despite a positive expression of elastin. There was a decrease in positive percentage of LOXL1 in the POP group (23.3%) compared with the controls (60%) (P = 0.004). With immunolabeling intensity classified as negative, weak, moderate or strong, there was a decrease in the expression of fibulin-5 in the POP group (P = 0.049). We also detected a significantly decreased expression of LOXL1 in the POP group (P = 0.001).

CONCLUSIONS

There was decreased expression of fibulin-5 and LOXL1 in the uterosacral ligaments of patients with pelvic organ prolapse, while the elastin expression was equivalent, which may suggest the possibility of defects in elastic fiber remodeling in the postpartum period and contribute to POP.

Accuracy of concepts in female pelvic floor anatomy: facts and myths!

The pelvic floor is characterized by a complex morphology because different functional systems join here. Since a clear understanding of the pelvic floor region is crucial for female pelvic surgery and fundamental mechanisms of urogenital dysfunction and treatment, we here describe the accurate and functional anatomy of important pelvic structures and landmarks, clarify their terminology and point out possible errors or misunderstandings as to their existence.

Neuromuscular morphometry of the uterine ligaments and vaginal wall in women with pelvic organ prolapse

AIMS

The aim of this study was to compare neuromuscular histomorphometry of the uterine ligaments and vaginal wall in women with and without pelvic organ prolapse.

METHODS

Biopsies were obtained from the round, uterosacral, and cardinal ligaments of the uterus and apical vaginal wall of women having pelvic organ prolapse repaired (stage ≥ II; prolapse group, 37) and the same location in patients with no prolapse (stage < II; control group, 47). Routine hematoxylin-eosin (H & E) staining and immunohistochemical staining for Protein Gene Product 9.5 (PGP 9.5) and smooth muscle α-actin were performed for all specimens.

RESULTS

Smooth muscle percentage of the uterosacral and cardinal ligaments were not significantly different in women with prolapse than in women without. In round ligament, mean smooth muscle percentage was lower than in women with normal support (81.63 ± 8.2 vs. 51.63 ± 16, P=0.000). Mean distance of the smooth muscle fibers from surface epithelium of the vaginal epithelium of the women with prolapse were significantly higher than the control group (1.679 ± 0.34 vs. 2.240 ± 0.33, P = 0.000). PGP 9.5 stained area percentage of uterine ligaments and vaginal wall tissue samples were significantly lower in women with prolapse.

CONCLUSIONS

Both total innervation of the anterior vaginal epithelium and uterine ligaments, and muscular percentage of the round ligament and vaginal wall were decreased in women with pelvic organ prolapse.

Anatomy and histology of the lower urinary tract

The function of the lower urinary tract is basically storage of urine in the bladder and the at-will periodic evacuation of the stored urine. Urinary incontinence is one of the most common lower urinary tract disorders in adults, but especially in the elderly female. The urethra, its sphincters, and the pelvic floor are key structures in the achievement of continence, but their basic anatomy is little known and, to some extent, still incompletely understood. Because questions with respect to continence arise from human morbidity, but are often investigated in rodent animal models, we present findings in human and rodent anatomy and histology. Differences between males and females in the role that the pelvic floor plays in the maintenance of continence are described. Furthermore, we briefly describe the embryologic origin of ureters, bladder, and urethra, because the developmental origin of structures such as the vesicoureteral junction, the bladder trigone, and the penile urethra are often invoked to explain (clinical) observations. As the human pelvic floor has acquired features in evolution that are typical for a species with bipedal movement, we also compare the pelvic floor of humans with that of rodents to better understand the rodent (or any other quadruped, for that matter) as an experimental model species. The general conclusion is that the "Bauplan" is well conserved, even though its common features are sometimes difficult to discern.

Intergender differences in histological architecture of the fascia pelvis parietalis: a cadaveric study

The fascia pelvis parietalis (FPP) or endopelvic fascia is a well-known structure, but few studies described the detailed histological architecture, including the composite fiber directions. We hypothesized a gender-specific fiber architecture corresponding to the functional demand. For the first step to examine this hypothesis, we investigated specimens from 27 adult cadavers (10 males and 17 females) and 11 midterm fetuses (five males and six females) using immunohistochemistry and aldehyde-fuchsin staining. The adult female FPP was a solid, thick monolayered structure that was reinforced by abundant elastic fibers running across the striated muscle fibers, but it contained little or no smooth muscles (SM). In contrast, the male FPP was multilayered with abundant SM. In midterm fetuses, SM originated from the inferior part of the bladder and extended inferiorly along the gender-specific courses. Thus, we found a clear intergender difference in FPP architecture. However, the functional significance remained unknown because the basic architecture was common between nulliparous and multiparous women. Rather than for meeting the likely mechanical demands of pregnancy and vaginal delivery, the intergender difference of the FPP seemed to result from differences in the amount and migration course of bladder-derived SM as well as in hormonal background.

[Connective tissue and prolapse genesis]

The pathophysiology of pelvic floor disorders still remains not well understood. Increasing age as well as vaginal multiparity are the main commonly accepted factors. The hypothesis of a defect of connective tissues of the pelvic floor with aging due to collagen deficiency and/or elastic fiber degradation is often highlighted. The issue of a potential protective role of HRT is also discussed although the recent results from the WHI would suggest a negative impact of HRT on urinary incontinence, especially when HRT is initiated in elderly women, far from the menopause. Nevertheless, environmental factors cannot explain the full pathogenesis of pelvic organ prolapse (POP) and the contribution of genetic factors to the development of pelvic floor disorders is widely recognized. Support for a genetic influence on POP derives from reports suggesting that heritability is a strong contributing factor and a familial history of POP is considered as a classical risk factor. However, the characterization of the underlying molecular mechanisms remains limited, since POP may be considered the end result of a multifactorial process leading to destruction of vaginal wall connective tissue. Experimental studies in mice with null mutations in the genes encoding different putative factors involved in elastic fibers remodeling and homeostasis are crucial in the understanding of the pathogenesis of POP. Mice with null mutation in the gene encoding lysyl oxidase-like 1 (LOXL1) or fibulin-5, demonstrate signs of elastinopathy including the development of a POP in the postpartum. Likewise, homeobox genes such as HOXA11, which are essential in the embryonic development of the urogenital tract might also be involved in the pathogenesis of POP. The better understanding of the underlying determinants of pelvic floor disorders with a special focus on genetic factors may offer new therapeutic strategies, in addition to or replacement of surgical procedures.

Changes in expression of fibulin-5 and lysyl oxidase-like 1 associated with pelvic organ prolapse

OBJECTIVES

Pelvic organ prolapse is associated with defects in connective tissue including elastic fibers. The purpose of this study was to investigate expression of fibulin-5 and lysyl oxidase-like 1, which play an essential role in synthesis and assembly of elastic fibers in the uterosacral ligament, in samples taken from women with advanced pelvic organ prolapse compared with controls.

STUDY DESIGN

Specimens were obtained prospectively during abdominal hysterectomy from 30 women with advanced pelvic organ prolapse and 30 controls matched to the study group for age and parity among postmenopausal women with benign gynecologic pathology. Expression levels of protein and mRNA of fibulin-5 and lysyl oxidase-like 1 in uterosacral ligaments were measured by Western blot analysis and real-time quantitative polymerase chain reactions. For statistical analyses, Student's t-test, chi-square test, Mann-Whitney U test, Fisher's exact test and Spearman's correlation were used.

RESULTS

Significant decrease in the expression of mRNA of fibulin-5 was found in patients with prolapse (P-value=0.042; 0.743+/-0.229 and 1.061+/-0.537). The expression of mRNA of lysyl oxidase-like 1 was increased in the patient group (P-value=0.017; 4.099+/-2.832 and 1.816+/-1.602). Similar results were shown in Western blot analysis. Differences in expression of fibulin-5 and lysyl oxidase-like 1 were noted according to stage of prolapse (P-value=0.037 and 0.009).

CONCLUSIONS

There was decreased expression of fibulin-5 and increased expression of lysyl oxidase-like 1 in uterosacral ligaments in patients with pelvic organ prolapse, which suggests the possibility of defects in elastin synthesis.

Uterosacral ligament smooth muscle cell apoptosis is increased in women with uterine prolapse

PURPOSE

The purpose of this study was to compare the smooth muscle content and apoptosis of the uterosacral ligament in women with and without uterine prolapse.

STUDY DESIGN

Uterosacral ligaments were sampled in women with (n = 9) or without (n = 9) uterine prolapse undergoing hysterectomy. Smooth muscle of the uterosacral ligament was identified by immunohistochemistry. Digital image analysis was used to determine the fractional area of smooth muscle in the histologic cross sections. Apoptosis was assessed by terminal deoxynucelotidyl-transferase-mediated dUTP nick-end-labeling method.

RESULTS

The fractional area of nonvascular smooth muscle in the uterosacral ligament of women with uterine prolapse was significantly decreased compared to women without prolapse (0.32 +/- 0.12 vs. 0.42 +/- 0.03, P = .02) and the apoptotic index was significantly higher compared to women without prolapse (0.20 +/- 0.06 vs. 0.08 +/- 0.04, P < .01).

CONCLUSION

The fraction of smooth muscle in the uterosacral ligaments is significantly decreased, and the rate of apoptosis is higher in women with uterine prolapse compared to women without prolapse.