Biosilk and ovarioids: recombinant silk as a new tool for establishing a 3D-culture system for human ovarian primary cells

Abstract Study question Can Biosilk be used as scaffold for establishing a 3D-culture system to support attachment and growth of primary cells derived from adult ovarian biopsies? Summary answer The use of recombinant spider silk-based scaffold allowed the formation of 3D-structured ovarioids from both cortex and medulla isolated from 5 different patients. What is known already Fertility in women is adversely affected by several factors, such as age, environmental pollutants and diseases requiring gonadotoxic treatments. Understanding ovarian cell composition and organization may pave the way to novel fertility preservation methods with the ultimate goal of being applied to clinics. So far, there are no clinically established methods for in vitro growth and maturation of human ovarian follicles leading to mature competent oocytes. Therefore, exploring new 3D-culture systems for in vitro reconstruction of ovarian somatic cell niche could lead to development of novel tools to support growth of patient-specific follicles. Study design, size, duration Ovarian tissue was collected from gender reassignment patients (GRP) after informed written consent at Karolinska University Hospital Huddinge from 2019 to 2022. After separation of cortex and medulla, the samples were mechanically and enzymatically dissociated into single-cell suspensions and used to evaluate 3D- and 2D-culture methods. Freshly fixed biopsies from cortex and medulla (3x3x1 mm3) were used as control for the transcriptomic analysis and RNA-FISH assay. Participants/materials, setting, methods Tissue was obtained from five patients aged 23-31 years. Dissociated primary somatic cells seeded on Biosilk-foam scaffolds were kept in culture for 2 weeks, followed by detachment, equal division of the foams and suspension culture for additional 4 weeks (BioSilk-Ovarioids, BSO). BSOs were harvested in PFA and RNAlater (n = 6/patient, respectively) for morphological and transcriptomic analysis. Protein ZO1, and cell type-specific marker genes (AMHR2, PDGFRa, CLDN5, GJA4) were evaluated via immunodetection and RNA-FISH assay, respectively. Main results and the role of chance The sizes of BSOs from both cortex and medulla ranged between 0.5-1 mm at the end of the culture, appearing highly compacted under optical microscope. HE-stained BSO sections revealed that cells were distributed throughout the foams, showing good attachment and distribution. Marker genes were selected for specific cell types [AMHR2-granulosa, PDGFRa-stroma, CLDN5-endothelial, GJA4-perivascular cells (Wagner et al. 2020)] and used to study the representation of different somatic cells in the BSOs. The RNA-FISH analysis confirmed the presence of all cell type-specific marker genes, with predominating presence of stromal cells (PDGFRa). Newly formed ZO1-specific gap junctions were detected in both cortex- and medulla-derived BSOs, appearing mainly in the outer part of the structures. Interestingly, cell layers surrounding the original Biosilk scaffold were observed, especially in medulla-BSOs. Transcriptomic profiling of the samples showed clear separation to three main clusters by principal component analysis: freshly fixed tissue, 2D-cultures, and BSO. Moreover, clustering analysis of differentially expressed genes (DEGs) showed the presence of gene clusters in fresh tissues affected by both 3D/2D-cultures. Further analyses will focus on identification of significantly affected gene ontologies and pathways, which will further guide the optimization of the BSO culture system. Limitations, reasons for caution The tissue was derived from GRPs who always receive androgen treatments prior to surgery. As hormonal treatment may affect the ovarian environment, further trials with untreated patient samples will be needed to generalize the model to fertility preservation patients. Wider implications of the findings The establishment and development of the BSO 3D-culture system may enable the construction of patient-specific clinically significant tools for in vitro folliculogenesis. This would open new avenues for fertility restoration in patients who cannot receive auto-transplants and treatment of infertility in premature ovarian insufficiency if residual follicles remain in tissue. Trial registration number Not applicable