| 摘要: | Androgens/androgen receptor (AR) signaling is involved primarily in the
development of male-specific phenotypes during embryogenesis, spermatogenesis,
sexual behavior, and fertility during adult life. This signaling has also been shown to
play an important role in female ovarian folliculogenesis. The recent generation and
characterization of total and cell-specific AR knockout mice from different laboratories
demonstrated the necessity of AR signaling for male phenotype development, normal
spermatogenesis and ovarian folliculogenesis.
To examine the role of AR in testicular Sertoli cells, we used a Sertoli cell-specific
AR knockout (S-AR-/y) mouse to evaluate the chronological changes of seminiferous
tubules and the molecular mechanisms of Sertoli cell androgen/AR signals on
spermatogenesis. We found that testes morphology began changing as early as postnatal
day (PD) 10.5 in male wild-type (AR+/y), but not in S-AR-/y mice. After puberty (PD 50),
the Sertoli cell nuclei of AR+/y testes migrated to the basal area of the seminiferous
epithelium; however, in S-AR-/y testes, Sertoli cell nuclei were disarranged and
dislocated. Using quantitative RT-PCR analyses, the expression of Sertoli cell gene
profiles were compared in PD 10.5 testes. In S-AR-/y testes, the expression levels of 1)
vimentin were significantly increased and laminin α5 was significantly decreased in PD
10.5, which contributed to functional defects in cytoskeleton and production of the
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basement membrane component of Sertoli cell leading to cell morphology deterioration
and thus affecting the integrity of seminiferous epithelium; 2) claudin-11, occludin, and
gelsolin were significantly decreased in PD 10.5, which contributed to defects in intact
junctional complex formation of Sertoli cell leading to impairment of the integrity of the
blood-testis barrier (BTB); 3) calcium channel, voltage-dependent, P/Q-type, α1A
subunit; tissue-type plasminogen activator; transferrin; and epidermal fatty-acid binding
protein were significantly decreased in PD 10.5, which contributed to functional defects
in production and/or secretion of specific proteases, transport proteins, and paracrine
factors of Sertoli cell, leading to impairment of its germ cells’ nursery functions. The
impact of lacking AR in Sertoli cells mainly affects Sertoli cell functions to support and
nurture germ cells, leading to spermatogenesis arrest at the diplotene primary
spermatocyte stage prior to the accomplishment of first meiotic division.
To examine the role of AR in testicular germ cells, we used a germ cell-specific AR
knockout (G-AR-/y) mouse to evaluate direct AR functions in male germ cells. We
found that G-AR-/y exhibited normal fertility function. Histology analysis of G-AR-/y
mice testes indicated that each stage of spermatogenesis is normal and the expression of
AR in Sertoli, Leydig, and peritubular cells is unaffected. Sperm count and motility in
epididymis from G-AR-/y mice are similar to that of the AR+/y mice. The fertility tests
showed there was no difference when the AR+/y and G-AR-/y male mice were mated
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with wild type female mice (AR+/+). These data provide in vivo evidence showing male
mice without AR in germ cells can still have normal spermatogenesis and fertility,
suggesting the essential roles of AR during spermatogenesis might come from indirect
cell-cell communication in a paracrine fashion. We then compared the consequences of
AR loss in the spermatogenesis and fertility of G-AR-/y mice with two other testicular
cell-specific AR-/y mice and total AR-/y (T-AR-/y) male mice. The results show clear in
vivo evidence that androgen/AR signaling in Sertoli cells plays a direct important role in
spermatogenesis and in Leydig cells plays an autocrine regulatory role to modulate
Leydig cell steroidogenic function. T-AR-/y male mice have the most severe defects
among these mice. These contrasting data with G-AR-/y mice suggest AR might have
different roles in the various cells within testis to contribute to normal spermatogenesis
and male fertility in mice.
To examine the role of AR in ovarian granulosa cells, we used female AR knockout
(AR-/-) mouse to evaluate the molecular mechanisms of granulosa cell androgen/AR
signals on folliculogenesis and oocyte development. Earlier studies showed that mice
lacking the androgen receptor (AR-/-) were noted to have reduced fertility with abnormal
ovarian function that might involve the promotion of preantral follicle growth and
prevention of follicular atresia. However, the detailed mechanism of how AR in
granulosa cells exerts its effects on oocyte quality is poorly understood. We found that
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oocyte in vitro maturation rate was significantly poorer (60%) with loosened junction
with granulosa cells in AR-/- female mice, whereas 95 % of AR+/+ oocytes had reached
to metaphase II. Interestingly, we found these mice also had an increased frequency of
morphological alterations in the mitochondria of granulosa cells with reduced ATP
generation and aberrant mitochondrial biogenesis. Mechanism dissection found loss of
AR led to a significant decrease in the expression of peroxisome proliferator-activated
receptor gamma (PPARγ) co-activator 1-β (PGC1-β) and its sequential downstream
genes, nuclear respiratory factor 1 (NRF1) and mitochondrial transcription factor A
(TFAM), in controlling mitochondrial biogenesis. These results indicate that AR may
contribute to maintain oocyte quality and fertility via controlling the signals of
PGC1-β-mediated mitochondrial biogenesis in granulosa cells. |
