gms | German Medical Science

Objectives: Klinefelter Syndrome (KS) is the most common chromosomal aneuploidy in men. Patients suffer from a lack of testosterone, hypogonadism along with infertility, as well as other symptoms. A mouse model closely resemblinghuman KS is available, and previous studies on tibiae of 12 month old mice showed a slight decrease in bone mass that could not be rescued by testosterone replacement. This leads to the hypothesis that the supernumerary X chromosome, along with X chromosome inactivation (XCI), may play a role in the development of this condition. Some genes escape XCI, which leads to an overexpression of their products. As a possible candidate, we identified Integral membrane protein (ITM) 2a, which escapes XCI, and is related to enchondral ossification. Aim of this project is to explore whether XXY*-mice suffer from a similar systemic bone loss compared to humans during the course of aging, and whether the supernumerary X-chromosome causes differences in gene expression related to bone development.

Methods: Bone structure of lumbar vertebrae, tibiae and femora of 24 months old male wild type (WT, n=10) and 47XXY* mice (B6Ei.Lt-Y*, n=14) were analysed by µCT. Bone volume/tissue volume (BV/TV), trabecular bone volume, trabecular thickness, number and separation, and cortical thickness were determined, and statistically evaluated (Mann-Whitney-U-test, P<0,05).In addition, tissue slices of bones, heart, liver, brain, lung and kidney were prepared for immunohistochemistry (IHC) staining using anti-ITM2a-antibody.

Results and Conclusion: Analysis of lumbar vertebrae showed significantly lower BV/TV, trabecular bone volume and trabecular number and a significantly higher trabecular separation in the XXY*-karyotype group compared to the WT. Trabecular thickness was lower but not significant, with the cortical thickness being significantly higher in the XXY*-karyotype group. Tibia and Femur analysis showed similar results. The anti-ITM2a antibody staining of bones of 24 month old mice of both karyotypes showed high expression in chondrocytes inside the growth plate, different cells inside the bone marrow, and endothelial cells. Bone analysis showed a significant reduction in trabecular bone mass along with fewer and thinner trabeculae in XXY*-karyotype mice compared to wild type, especially in lumbar vertebrae. Because of the age of 24 months, femora and tibiae displayed almost no trabecular bone substance left. The results therefore need to be interpreted with caution. ITM2a protein expression could be related to different cell types inside the bone, however, we have not found a significant difference in its quantity yet. Our results support the significance of this mouse model to investigate its impact on bone in correlation with Klinefelter Syndrome. Analysis of younger animals is in process. ITM2a serves as an interesting target to study XCI in bone.