Low XIST expression in Sertoli cells of Klinefelter syndrome patients causes high susceptibility of these cells to an extra X chromosome

Klinefelter syndrome(KS)is the most common genetic cause of human male infertility.However,the effect of the extra X chromosome on different testicular cell types remains poorly understood.Here,we profiled testicular single-cell transcriptomes from three KS patients and normal karyotype control individuals.Among the different somatic cells,Sertoli cells showed the greatest transcriptome changes in KS patients.Further analysis showed that X-inactive-specific transcript(XIST),a key factor that inactivates one X chromosome in female mammals,was widely expressed in each testicular somatic cell type but not in Sertoli cells.The loss of XIST in Sertoli cells leads to an increased level of X chromosome genes,and further disrupts their transcription pattern and cellular function.This phenomenon was not detected in other somatic cells such as Leydig cells and vascular endothelial cells.These results proposed a new mechanism to explain why testicular atrophy in KS patients is heterogeneous with loss of seminiferous tubules but interstitial hyperplasia.Our study provides a theoretical basis for subsequent research and related treatment of KS by identifying Sertoli cell-specific X chromosome inactivation failure.