Hypothesis / aims of study
Until recently, polypropylene meshes were often used as a surgical treatment option for Pelvic Organ Prolapse (POP). However, they have been associated with serious complications such as inflammation, pain and erosion. As a result, transvaginal meshes were banned in Australia and New Zealand in 2017. At present, there is no optimal therapy for treatment of chronic POP leaving millions of women in despair. To overcome adverse events associated with transvaginal surgery using non degradable synthetic mesh for treating pelvic organ prolapse (POP), we are developing a tissue engineering construct comprising degradable nanofibrous mesh and endometrial mesenchymal stem/stromal cells (eMSC). The aim of this study was to investigate in vivo foreign body response, angiogenesis and extracellular matrix gene expression to a nano-topographically controlled mesh made of poly (L-lactic acid)-co-poly(-caprolactone) and gelatin incorporating eMSC (PLCL/G/eMSC). Our team discovered a rare population of Mesenchymal stem cells in the endometrium (eMSCs) and has identified a single marker to isolate these rare perivascular cells. In a phase IV clinical trial, our team has also showed that eMSCs can be collected with ease even from post-menopausal women and kept in an undifferentiated state for clinical use making them an ideal choice for autologous urogynecological application. We further more compared the differences between the treatment capacity of eMSCs delivered using degradable and non-degradable.
Study design, materials and methods
PLCL polymer and gelatin (1:1, 10%w/w) was electrospun to form uniform nanofibers and assessed for fibre diameter, pore size, hydrophilicity and biomechanical properties. SUSD2+ eMSC were purified from single cell suspensions obtained from endometrial biopsies from cycling women and by magnetic bead sorting and transfected with mCherry lentivirus for cell tracking. SEM was used to characterise eMSC incorporation into the nanofiber meshes in vitro and their degradation in NSG mouse skin wound repair model of vaginal repair. Macrophage response was assessed by evaluation total (F4/80+), M1 (F4/80+CCR7+) and M2 (F4/80+/CD206+) macrophages using confocal microscopy. Gene expression for foreign body response, angiogenesis and extracellular matrix genes were obtained using RNA isolation followed by quantitative PCR.
Herein, we show a significant differences in cell-cell and cell-material communication of SUSD2+ eMSCs on PLCL+G expression. Our in vivo analysis of gene expression highlights that role of eMSCs in controlling the immune reposne and tissue integration indicated by differences in gene expression of NOS2, Mrc, AngI, AngII, MMP-9, Col1a1, Col3a1. Our results highlight that eMSCs play a significant role in controlling host-graft, cellular infiltration inside the construct and over all tissue integration. eMSC seeded on PLCL/G promoted macrophage switching from M1 to M2 phenotype to a greater extent than similarly seeded PLCL mesh and both meshes implanted without eMSC. There was also an influx of endogenous F4/80- cells (possibly fibroblasts) and collagen matrix deposition into PLCL/G/eMSC implants.
Interpretation of results
Polypropylene meshes bear no resemblance to the native vaginal tissue and may be the underlying cause of its failure in the long term. Such non-biomimetic materials are perceived as a foreign object that evokes a chronic inflammatory and immune response. This prevents integration and healing at the site of implantation. In order to overcome the impediment posed by the tissue microenvironment, it is desirable to design biomaterials that mimics some mechanical and biochemical properties of the ECM of native tissues. This makes nanofabrication of surgical constructs an attractive strategy in terms of material design. In nature, cell behaviour and structural development is supported by the nanoscale arrangement of the ECM architecture comprising of structural (primarily collagen) and functional proteins (e.g. collagen, proteoglycans) that holds the cells together through a myriad of external chemical and physical stimuli at the molecular level. This study shows that degradable nanofiber meshes boosted with eMSCs have provided an anti-inflammatory environment, promote angiogenesis and matrix synthesis that is likely to promote vaginal repair and overcome current hurdles of transvaginal meshes.