Evaluation of new meshes, a cell-based therapy, and animal model for pelvic organ prolapse repair

Pelvic Organ Prolapse (POP) is defined as the descent of one or more of the pelvic structures and includes uterine prolapse, vaginal vault prolapse, and anterior or posterior vaginal wall prolapse. The resultant symptoms are urinary and bowel dysfunction, incontinence, and sexual dysfunction. POP is primarily caused by childbirth injury, but ageing, obesity and other factors also contribute. Common treatment of POP is surgery and includes native tissue surgical reconstruction alone or with implantation of either synthetic or biological mesh with the former having a higher success rate. However, the long-term outcome of synthetic mesh augmented surgery is unsatisfactory due to postsurgical complications. The most common problems are mesh exposure and pain possibly due to scarring, folding and/or contraction of synthetic meshes. Polypropylene (PP) was rapidly adopted for POP surgery and was not carefully reassessed to determine whether PP met the criteria for treating the damaged pelvic floor tissues. Mesenchymal Stem Cells (MSC) have been discovered in almost every adult tissue and are highly proliferative, self-renew and differentiate into mesodermal lineages in vitro. MSC also have immunomodulatory and angiogenic properties making them ideal candidates for cell-based therapies. Recently MSC have been discovered in the regenerative endometrial lining of the uterus and specific markers (W5C5/SUSD2) have been identified for their prospective isolation. These endometrial MSC (eMSC) fulfil the classical criteria of adult MSC and can be obtained under minimally invasive procedures without anaesthesia or scarring from premenopausal women. Tissue engineering is defined as a combination of cells and materials and is widely used in the field of regenerative medicine. Many cell types from the same or a different individual can be used in combination with a synthetic, biological or composite material. Of the urogenital organs, to date, researchers have only been able to reconstruct the human bladder and urethra using tissue engineering approaches. In this thesis, new meshes designed specifically for POP repair surgery were evaluated in an abdominal wall fascial defect model to evaluate the extent of host tissue response, tissue integration and subsequent mechanical properties. Polyamide (PA), Polyamide plus Gelatin (PA+G) and Polyether-etherketone (PEEK) showed temporal inflammatory responses that were different to that seen with PP meshes with enhanced neovascularisation, collagen production, and decreased inflammation. PA and PA+G could be a future treatment option for POP repair surgery. Most women who suffer from POP are postmenopausal and we therefore characterised eMSC from postmenopausal women treated with or without exogenous estrogen. Similar to premenopausal women, eMSC can be obtained by a curettage procedure following short-term estrogen treatment. Postmenopausal eMSC are similar to premenopausal eMSC in terms of cloning efficiency and phenotype but are available in lower numbers and differentiate to a lesser degree. The next step was to test the PA+G meshes and eMSC in a nude rat fascial wound model as a small preclinical proof of principle animal model. Meshes seeded with eMSC improved the tissue integration compared to meshes alone by increasing the neovascularisation, altering macrophages from an inflammatory to wound healing phenotype, decreasing the foreign body reaction, and improving the biomechanical properties in the long term, without engraftment. This thesis also provides a comprehensive analysis of sheep vaginal tissue to generate baseline data in this large animal preclinical model, including biochemical, biomechanical and histological analyses. Sheep that have not delivered lambs have similar biomechanical and biochemical properties to parous sheep whereas pregnancy significantly changes both the tissue composition and mechanical properties. We also determined regional differences in postmenopausal sheep vagina and correlated the biochemical and histological results with postmenopausal women. The ovine vagina showed differences between the upper and lower region whereas human vagina did to a lesser degree but with similar tissue composition. These results can help to understand the biochemical tissue composition and passive biomechanical properties of ovine vagina and relate this to the histo-architecture at different reproductive stages as part of the establishment of a large animal preclinical model for evaluating regenerative medicine approaches for surgical treatment of pelvic organ prolapse. The next step would be to test the above mentioned TE construct in a large animal model; however this was not feasible within the time frame of this thesis. In conclusion eMSC are a promising source of MSC independent of a women’s stage of life and could be used for TE purposes. A Tissue Engineering construct might be the future treatment for POP but has yet to be evaluated in a large animal preclinical model.Awards: Winner of the School of Clinical Sciences Head of School’s PhD Excellence in 2014