Unraveling the mechanisms behind testicular fibrosis in Klinefelter men

Margo Willems

Research output: ThesisPhD Thesis

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Abstract

This thesis studied the mechanisms behind testicular fibrosis in Klinefelter syndrome (KS) patients, leading to infertility. In Chapter 1the current knowledge of the disorder was described in a general introduction. First, the development of the male reproductive system and the testis anatomy as well as the testicular environment were described. Next, some background information was provided concerning male infertility followed by are view in which KS is outlined in all its aspects. In Chapter 2, the aim and outline of the dissertation were clarified. In the next chapters, the results regarding the research performed on KS-related testicular fibrosis were described. First, in Chapter 3, the results of the transcriptomics study were described. The transcriptome of adult testis biopsies from KS patients was compared to control samples. A first analysis, comparing fibrotic and non-fibrotic samples lead to several fibrotic genes. The most interesting genes were those which were involved in the extracellular structure organization. A second analysis, comparing fibrotic samples with a normal karyotype (46,XY) with KS samples, lead to KS-specific genes. An overlap of these two analyses, where only X-linked genes were included, lead to the discovery of three genes which are possibly involved in KS-related testicular fibrosis: MXRA5, DCX and VCX3B. Their specific roles still need to be elucidated. Chapter 4 included the preliminary results of the proteomics study. Fibrotic and non-fibrotic testis tissue was decellularized to specifically study the role of the extracellular matrix proteins in the fibrotic process. Sadly, a problem with the protein extraction occurred, resulting in the identification of proteins in only 20% of included samples. Therefore, this research needs to be repeated. In chapter 5, the role of the immune cells, more specifically mast cells and macrophages, in KS-related testicular fibrosis was described. An increase in immune cells was found in adult KS testis tissue compared to controls, but no differences were found in younger KS boys compared to age-matched controls. This led to the conclusion that mast cells and macrophages may play a role in the testicular fibrosis seen in KS patients but that they are not the origin of the fibrotic process. In addition, the secretory products were studied, but no significant differences were found. However, an increased décor in expression, which was studied because it stimulates mast cells and macrophages to secrete tryptase and TNFα, was found in KS boys, adolescents and adults. Lastly, the vasculature in KS patients of different age groups was studied and compared to controls, showing an increase in number of the smallest blood vessels in prepubertal patients compared to controls. Chapter 6included the research on a potential ex vivo model to study testicular fibrosis since an ideal KS model is still lacking. This was generated by xenografting (pre)pubertal testis tissue to the mouse testis. Unfortunately, the KS tissue degenerated around six
154weeks after transplantation. The model was validated by evaluating the effects of a mast cell blocker, ketotifen, on the severity of the testicular fibrosis. No significant differences were found between the tissue from treated and non-treated mice. Nevertheless, the histology of the ketotifen-treated tissue looked less altered than that of non-treated tissue. The general discussion was written in Chapter 7. This included a short overview of the results of the different studies, a discussion on whether the altered KS micro-environment is the cause or consequence of the germ cell loss, an overview of the limitations seen in KS studies and the future perspectives in KS research.
Based on the findings described in this thesis, we can conclude that:
-The upregulation of X-linked genes MXRA5and DCX and the downregulation of X-linked gene VCX3B may induce KS-testicular fibrosis
-Mast cells and macrophages play a role in testicular fibrosis but are not involved in the initiation of the fibrotic process -Décor in may become an early biomarker for testicular fibrosis
-The vasculature of KS patients is comparable to controls except for an increase in the smallest blood vessels in KS boys
-Xenografting could become an ex vivo model to study KS-related testicular fibrosis, but the model needs further optimization.
Original languageEnglish
QualificationDoctor in Medical Sciences
Awarding Institution
  • Vrije Universiteit Brussel
Supervisors/Advisors
  • Goossens, Ellen, Supervisor
  • Van Saen, Dorien, Supervisor
Award date8 Dec 2022
Publication statusPublished - 2022

Keywords

  • testicular fibrosis
  • Klinefelter men

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