Identification of apelin/APJ signaling dysregulation in a human iPSC-derived granulosa cell model of Turner syndrome

The interaction between germ cells and somatic cells in the ovaries plays a crucial role in establishing the follicle reserve in mammals. Turner syndrome (TS) predominantly occurs in females who have either a partial or complete loss of one of their X chromosomes. Our understanding of the role granulosa cells (GCs) play in TS disease progression and pathogenesis remains limited. Here, we elevated GC differentiation efficiency up to the level of 80% differentiated cells from iPSCs. In our attempt to replicate the differentiation process of embryonic granulosa cells, we observed that specific genes—GATA4, FOXL2, AMHR2, CYP19A1, and FSH—were downregulated in Turner syndrome-derived granulosa cells (TS-GCs). Additionally, dysregulation of the cell cycle was observed in TS-GCs. To reveal the endogenous defects in the TS-GCs, we conducted a comparison of the global transcriptome patterns between differentiated granulosa cells derived from iPSCs in both healthy and Turner syndrome groups. The apelin/APJ pathway displayed a differential between the healthy and TS groups. Supplementation of apelin ligands and activation of apelin/APJ downstream signals via Akt/PKB restored the cell cycle progression and marker gene expression. We hypothesize that during early embryonic development failures in apelin/APJ signaling in GCs in Turner syndrome patients leads to abnormalities in ovarian development and consequently to early loss of oocytes and infertility. Overall design: We developed and employed an optimized granulosa cell differentiation protocol to exam the granulosa cells' function as a 'disease in a dish'' model using iPSCs. We differentiated iPSCs reprogrammed from TS probands and unaffected individual fibroblasts into ovarian granulosa cells.The generated hiPSC lines corresponding to each original fibroblast source are listed as follows: Control group includes GRC-WT2-10 (AG02102) and GRC-WT4-4 (AG08470); Disease group includes GRC-TS1-1 (GM01176), GRC-TS1-2 (GM01176), GRC-TS2-4 (GM06563) and GRC-TS2-6 (GM06563); Normal group includes four luteinized adult granulosa cells (cumulus GC).