(Poster 03) Myofibroblast Phenotypes: Mechanistic Insight into Prolapse Mesh Complications

Objectives: Over 10% of women who receive polypropylene mesh (PPM) implants for pelvic organ prolapse (POP) experience complications, including pain. Pain occurs in the context of a maladaptive remodeling response predisposed to fibrosis. Increased mesh burden (area of mesh fibers in contact with the vagina) is linked to myofibroblast associated fibrotic complications in non-human primate models. Myofibroblasts are considered pathologic when they persist in wounds and are known to secrete high levels of matrix (collagen) and place tension on a tissue. Both fibroblasts and macrophages can transition to myofibroblasts (FMF and MMF cells, respectively). We investigated these cell types in with samples with increased mesh burden, hypothesizing a positive correlation.

Methods: Fifteen mesh-vaginal complexes excised from women with complications were randomly selected from a human mesh biorepository. Samples were cryosectioned and labeled for alpha smooth muscle actin (αSMA), vimentin (Vim), and CD68 via immunofluorescence, imaged at 10X using a Nikon 90i microscope, and the adventitia (site of mesh implantation) was segmented using QuPath. Cells expressing αSMA+/Vim+ (FMF), CD68+ (macrophages), and αSMA+/Vim+/CD68+ (MMF) were quantified. Mesh burden was defined as the percentage of adventitia occupied by mesh fibers. Statistical analysis, comparing cell populations between lower (0-75th percentile) and high (>75th percentile) mesh burden samples, utilized Chi Square tests for trend, Mann Whitney U-tests, and Kruskal Wallis tests using GraphPad Prism.

Results: Mean patient age was 61.75 ± 8.03 years, median gravidity was 3 ± 2, median parity was 3 ± 1, and mean time post initial mesh implantation was 68 ± 40 months. All patients were postmenopausal and used vaginal estrogen. Widespread MMF cell presence was observed in the representative immunofluorescence images of all samples, regardless of mesh burden (Figure 1). There were significantly less FMF cells than macrophages (p=0.0004) and fibroblasts (p=0.0001) and less MMF cells than macrophages (p=0.0057), and fibroblasts (0.0024) amongst the lower mesh burden samples (Figure 2A). There were significantly less FMF cells than macrophages (p=0.0038) in high mesh burden samples (Figure 2B). There was no difference between lower and high mesh burden samples in terms of the total myofibroblasts (FMF+MMF cells) (Figure 2C), but there was a significantly higher percentage of myofibroblasts that are MMF in high mesh burden samples (p=0.0196) (Figure 2D). A significant positive correlation is seen between mesh burden and the number of MMF cells present in the samples (p < 0.0001).

Conclusions: We showed that MMF cells are present in mesh vaginal explants from women with complications, and that the presence of these cells increase with mesh burden. Different cellular responses are seen amongst samples with varying mesh burden. Further studies are needed to define the threshold at which mesh burden triggers the MMF transition and correlate MMF cell presence with patient symptoms.