Fertility in the Klinefelter syndrome by testicular stem cell transplantation - an experimantal approach in the XXY mice

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The most common genetic cause of human male infertility is the Klinefelter syndrome (KS, 47,XXY) resulting in testicular failure, loss of germ cells and variable degrees of androgen deficiency paralleled by changes in gonadotropins. Although the KS is well known, it is not clear whether the loss of germ cells resulting in a Sertoli-cell-only (SCO) syndrome is due to a defect of the germ cell line, a disturbance of the testicular environment, or a combination of both. Many Klinefelter patients attend our Institute for infertility. Any possible therapeutic approaches to overcome this infertility requires findings from experimental work. The proposed project seeks to elucidate those prerequisites for therapeutic approaches to gain fertility in Klinefelter patients, e.g. by making use of autologous stem cells. Since at this stage such work cannot be performed in the patients themselves, the generation and use of an appropriate animal model is indespensable. Mice bearing a supernumerary X-chromosome (karyotype 41, XXY) mimicking the conditions found in patients have been generated by breeding animals with a spontaneously mutated Y-chromosome. We established a mouse colony of the strain B6Ei.Lt-Y to obtain 41 (XXY) male mice and determined the distinct karyotype of the living animals individually by fluorescence in situ hybridisation (FISH). We will show whether the testicular environment and the pituitary-gonadal axis in males bearing a supernumerary X-chromosome are able to support development of normal, diploid spermatogonial stem cells using our well-established methods of germ cell transplantation and grafting of testicular tissue. We will characterize aspects essential for male endocrinology and testicular function as in particular the Leydig cell function and maturation. Since some Klinefelter patients produce a small amount of sperm deriving from apparently normal diploid spermatogonia, the testicular environment should be able to support spermatogenesis. However, whether this would be possible in every patient or depends on the degree of mosaicism has not been clarified. Testicular sperm with a high rate of chromosomal abnormalities increase the abortion rate. Thus questions of disturbed testicular environment and an increased risk of aneuploidy have to be solved before any clinical transplantation approach can be offered. This problem will be addressed in the mouse model by examining sperm produced after germ cell transplantation and by performing ICSI followed by chromosomal analysis of embryos.