Testicular blood supply is altered in the 41,XXY* Klinefelter syndrome mouse model

Abstract

Hypergonadotropic hypogonadism is a major feature of Klinefelter syndrome (KS), assumed to be caused by testicular hormone resistance. It was previously shown that intratesticular testosterone levels in vivo and Leydig cell function in vitro seem to be normal indicating other functional constraints. We hypothesized that impaired testicular vascularization/blood flow could be a co-factor to the observed hypergonadotropic hypogonadism. We evaluated the testicular vascular system by measuring blood vessel sizes during postnatal development and testis blood flow in adult 41,XX Y * mice. Proportional distribution and size of blood vessels were analyzed during testicular development (1, 3, 5, 7, 10, 21 dpp, 15 wpp). While ratios of the vessel/testis area were different at 15 wpp only, a lower number of smaller and mid-sized blood vessels were detected in adult KS mice. For testicular blood flow determination we applied contrast enhanced ultrasound. Floating and reperfusion time for testicular blood flow was increased in 41,XX Y * mice (floating: XY* 28.8 ± 1.69 s vs XX Y * 44.6 ± 5.6 s, p = 0.0192; reperfusion XY* 19.7 ± 2.8 s vs XX Y *: 29.9 ± 6.2 s, p = 0.0134), indicating a diminished blood supply. Our data strengthen the concept that an impaired vascularization either in conjunction or as a result of altered KS testicular architecture contributes to hormone resistance. The presence of one or more supernumerary X-chromosomes causes Klinefelter syndrome (KS, 47,XXY) in men. This chromosomal aneuploidy occurs at a high incidence of 1-2 in 1,000 male births and is the most frequent genetic cause for male infertility. Characteristic for KS is the hypergonadotropic hypogonadism characterized by highly elevated gonadotropins and low to very-low testosterone (T) levels resulting from testicular hormone resistance. Germ cell loss prevails, generally leading to azoospermia in nearly all KS patients 1-5. During the last years, co-morbidities have been associated with KS such as cardiovascular disease (shortened QTc times), increased risk for pulmonary embolism and peripheral vascular diseases 6-11. As for vascular problems, reduced diameters of brachial, common carotid and femoral as well as of the abdominal arteries have been reported. Low T levels in KS patients have numerous effects on health and are likely contributing to the majority of symptoms but can be clinically treated by T substitution positively influencing some but not all of the symptoms 4,12,13. However, and more problematic, androgen replacement interferes with the endocrine feedback by down-regulating Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). This negatively impacts the sperm retrieval success in KS patients with remaining focal spermatogenesis 14-16. Consequently, it is of crucial importance to elucidate the underlying mechanisms causing hypergonadotropic hypogonadism to potentially develop novel therapeutic options for the treatment of KS patients. Previously, disturbed Leydig cell function was thought to be causative for serum T def...

Transcriptomic differences between fibrotic and non-fibrotic testicular tissue reveal possible key players in Klinefelter syndrome-related testicular fibrosis

“…Moreover, the KEGG analysis revealed genes involved in steroidogenesis pathogenesis to be up-regulated in the KS samples, which is in accordance with research showing an increased intratesticular testosterone level in KS men (44). Although no changes in the blood vessel density were found in KS testicular biopsies compared to controls, as reported in our previous research (25), the above nding may contribute to the hypothesis that a disturbed vascularization is present within the KS testis (45,46). In KS men, as in females, one of the two X-chromosomes is silenced to compensate for the dosage of X-linked genes.…”

Testicular microvascular flow is altered in Klinefelter syndrome and predicts circulating testosterone

“…The histological finding of a low blood vessel/testis surface ratio in a mouse model of KS led to the hypothesis that T release, rather than its production, is actually impaired in KS, by means 271 of a slower and reduced testicular blood flow. These results were confirmed in a subsequent 272 study, in which a reduction in small and medium-sized blood vessels in adult 41,XX Y * mice was described, and the CEUS study of those testes demonstrated reduced perfusion parameters, favoring impaired testicular vascularization in KS (14). However, these results were inconsistent with the findings of another histological study in human KS testicular biopsies from prepubertal, peripubertal, and adult subjects (15).…”

“…The present study examined for the first time in vivo testicular vascularization in human subjects with KS by means of CEUS compared with age-matched controls. Subjects with KS were characterized by significantly slower testicular perfusion kinetics, in both the wash-in and washout phases (Figure 2), resulting in prolonged testicular MTT; the testicular Slopein was not significantly different between the two groups, possibly because of the lack of differences in the number of larger arteries (14), in which microbubbles first appear; the PI and AUC were also not different between the two groups. Strikingly, faster testicular vascularization times were associated with better endocrine testicular function, especially with serum T levels, which showed a strong relationship with vascular parameters, correlating positively with Slopein and inversely with Tin, MTT, TTP, and 287 Tout.50% as well as gonadotropins and T/LH and cfT/LH ratios.…”

“…The present study examined for the first time in vivo testicular vascularization in human subjects with KS by means of CEUS compared with age-matched controls. Subjects with KS were characterized by significantly slower testicular perfusion kinetics, in both the wash-in and washout phases (Figure 2) , resulting in prolonged testicular MTT; the testicular Slope in was not significantly different between the two groups, possibly because of the lack of differences in the number of larger arteries (14), in which microbubbles first appear; the PI and AUC were also not different between the two groups.…”

“…The same group subsequently investigated the timing of vascular alterations during testicular development in mice, and found that such alteration are progressively acquired, with a lower number of small- and mid-sized blood vessels only in adult KS mice. They further conducted a study on testicular blood flow via contrast-enhanced ultrasonography (CEUS) and demonstrated reduced perfusion parameters, in favor of impaired testicular vascularization in KS mice (14).…”