DYRK1A Overexpression in Mice Downregulates the Gonadotropic Axis and Disturbs Early Stages of Spermatogenesis

Abstract

Down syndrome (DS) is the most common chromosomal disorder. It is responsible for intellectual disability (ID) and several medical conditions. Although men with DS are thought to be infertile, some spontaneous paternities have been reported. The few studies of the mechanism of infertility in men with DS are now dated. Recent research in zebrafish has indicated that overexpression of DYRK1A (the protein primarily responsible for ID in DS) impairs gonadogenesis at the embryonic stage. To better ascertain DYRK1A's role in infertility in DS, we investigated the effect of DYRK1A overexpression in a transgenic mouse model. We found that overexpression of DYRK1A impairs fertility in transgenic male mice. Interestingly, the mechanism in mice differs slightly from that observed in zebrafish but, with disruption of the early stages of spermatogenesis, is similar to that seen in humans. Unexpectedly, we observed hypogonadotropic hypogonadism in the transgenic mice.

Keywords: DYRK1A; Down syndrome; infertility.

Figure 1

Experiments in Tg mice and WT controls. Standard histology of testis (a–d) shows no difference in number, size, and cellular compound of seminiferous tubules between Tg mice and control. Diameter (e), and thickness (f) of 100 seminiferous tubules per mouse were measured: histograms show mean and standard deviation, no significant difference was found; (g) testis weight; (h) sperm count; (i,j) protein and mRNA levels of Dyrk1A in testis and brain; (k,f,l) IHC assay for Dyrk1A in the testis of Tg mice and WT controls. The two groups of mice did not differ in the number and intensity of Dyrk1a+ cells in seminiferous tubules. In control mice, Dyrk1a was expressed by cells close to the basal membrane, corresponding to the early stages of spermatogenesis and as show in the cropped images: double arrowheads: small cells close to the basal membrane, corresponding to spermatogonia; single arrowheads: large cells not in contact with the basal membrane, corresponding to primary spermatocytes; square brackets: later stages of spermatogenesis, with a lower Dyrk1a intensity. p value : 0.033 (*), 0.002 (**), <0.001 (***).

Figure 2

The gonadotrophic axis. Light grey: WT, dark grey: Tg; (a,b,d) gonadotropic axis and steroid level in plasma and testis; (c); mRNA levels of steroidogenesis enzymes in the testis. ALD: aldosterone, ASD: androstenedione, Testo: testosterone, Pg: progesterone, DOCS: deoxycorticosterone, CS: corticosterone. p value : 0.033 (*), 0.002 (**), <0.001 (***).

Figure 3

Spermatogenesis. (a,b): protein and mRNA levels of specific proteins involved in spermatogenesis from spermatogonial stem cells (GFRa1), spermatogonia A (Plzf and kit-L), spermatogonia B (STRA8), primary spermatocytes (SYCP3), and spermatids (Prm1). (c–p) IHC assay of testis in Tg mice and WT controls for STRA8, SYCP3, androgen receptor (AR), and caspase 3 (CASP3, an apoptosis marker). STRA8 immunostaining revealed an elevated quantity of spermatogonia B in Tg mice, in terms of the number of positive cells per tubule and the number of positive tubules in the whole section. In Tg mice, SYCP3 staining revealed aberrant expression in cells with the same morphology as spermatogonia, i.e., small cells close to the basal membrane. In WT mice, the stained cells corresponded to primary spermatocytes, as expected. There was no intergroup difference in AR staining. There was no difference in cleaved caspase-3 staining between Tg and WT mice; no apoptosis was observed in either group, relative to a heat-induced positive control (arrows). p value : 0.033 (*), 0.002 (**), <0.001 (***).

Figure 4

Mechanisms of impaired fertility in Tg mice overexpressing DYRK1A. Hypogonadotropic hypogonadism (a) might be induced by central overexpression of DYRK1A in the hypothalamus and/or the pituitary; the overexpression might be responsible for lowering the production of LH and FSH gonadotrophins. In the testis, low LH levels slow down steroidogenesis and reduce testosterone levels, which in turn reduced spermatogenesis stimulation and upregulation of AMH levels in Sertoli cells. In germ cells (b), overexpression of DYRK1A in the early stages of spermatogenesis prompts spermatogonia to self-renew rather than to differentiate and enter meiosis. This process might be mediated by activation of STAT3 and GDNF, downregulation of retinoic acid (RA), and perturbation of the mitosis-to-meiosis transition by excess AMH.