Expression of sex hormone-binding globulin and corticosteroid-binding globulin mRNAs in corpus luteum of human subjects

Genetics of androgen metabolism in women with infertility and hypoandrogenism

Hypoandrogenism in women with low functional ovarian reserve (LFOR, defined as an abnormally low number of small growing follicles) adversely affects fertility. The androgen precursor dehydroepiandrosterone (DHEA) is increasingly used to supplement treatment protocols in women with LFOR undergoing in vitro fertilization. Due to differences in androgen metabolism, however, responses to DHEA supplementation vary between patients. In addition to overall declines in steroidogenic capacity with advancing age, genetic factors, which result in altered expression or enzymatic function of key steroidogenic proteins or their upstream regulators, might further exacerbate variations in the conversion of DHEA to testosterone. In this Review, we discuss in vitro studies and animal models of polymorphisms and gene mutations that affect the conversion of DHEA to testosterone and attempt to elucidate how these variations affect female hormone profiles. We also discuss treatment options that modulate levels of testosterone by targeting the expression of steroidogenic genes. Common variants in genes encoding DHEA sulphotransferase, aromatase, steroid 5α-reductase, androgen receptor, sex-hormone binding globulin, fragile X mental retardation protein and breast cancer type 1 susceptibility protein have been implicated in androgen metabolism and, therefore, can affect levels of androgens in women. Short of screening for all potential genetic variants, hormonal assessments of patients with low testosterone levels after DHEA supplementation facilitate identification of underlying genetic defects. The genetic predisposition of patients can then be used to design individualized fertility treatments.

Immunolocalization of sex hormone-binding globulin (SHBG) in human ovarian follicles and corpus luteum

Sex hormone-binding globulin (SHBG), a hepatic carrier protein for sex steroids is expressed in different steroid-sensitive tissues, including Sertoli cells of the testis. It has been suggested that this protein may be one of the local regulators of spermatogenesis. The expression of SHBG in the ovary is currently unknown. We have previously demonstrated the synthesis of SHBG in granulosa-lutein cells from patients undergoing in vitro fertilization. In this study, the presence of SHBG in human ovarian follicles and corpora lutea is investigated, using immunohistochemistry on adult and fetal ovarian tissue sections. SHBG is localized in the whole granulosa layer at all stages of folliculogenesis, whereas, only isolated theca cells are immunostained. In primordial and primary follicles, the oocyte cytoplasm shows an intense immunostaining, which disappears after the secondary stage. In the microenvironment of the mature oocytes, SHBG is present in the surrounding cumulus cells, the perivitelline space, and nearby the oolemma. In the corpus luteum, SHBG is localized in large luteal cells, whereas, small luteal cells do not show any significant staining. By analogy with the testis, these results raise the question of an involvement of SHBG in the regulation of follicular maturation as well as in luteal function.

Expression of sex hormone-binding globulin (SHBG) in human granulosa-lutein cells

Sex hormone-binding globulin (SHBG) was classically thought to be a plasma steroid-carrying protein of hepatic origin, but recently, locally produced, membrane-bound SHBG has been shown to influence cell functions in several steroid-responsive tissues. In the ovary, SHBG is known to be present in the follicular fluid, but information about a possible intracellular presence of SHBG in this organ is still very scarce. In this study the presence of SHBG was assessed by immunohistochemistry in human granulosa-lutein cells (GLC) collected by follicle puncture for in vitro fertilization. SHBG was detected in the cytoplasm of GLC before and after in vitro culture for up to 96 h. The presence of full-length SHBG messenger RNA was demonstrated in GLC by reverse transcription-polymerase chain reaction (RT-PCR) in both cultured and uncultured cells. These results demonstrate a local synthesis of SHBG in GLC and raise the question of the physiological significance of these findings in follicular physiology.

How does endometriosis affect infertility?

Prospective and retrospective clinical trials suggest a decreased oocyte and embryo quality in women with endometriosis. Based on these observations, the authors described an altered intrafollicular milieu in endometriosis, which explains the bad quality oocytes and the resulting embryos with lower capacity to implant. Whether these changes affect the oocytes or are the consequence of genomic alterations manifested by biochemical and chromosomal differences in healthy women is an unresolved issue. If the effects of endometriosis on follicular development are nongenomic in origin, modulation of the process of folliculogenesis may be sufficient to treat the disease and cure infertility associated with endometriosis. A genomic defect needs specific genetic therapy, which currently is not available.

Levels of sex hormone-binding globulin and corticosteroid-binding globulin mRNAs in corpus luteum of human subjects: correlation with serum steroid hormone levels

To understand regulation of the function of human ovarian corpus luteum by sex steroid-binding proteins, the levels of luteal intracellular sex hormone-binding globulin (SHBG) and corticosteroid-binding globulin (CBG) mRNAs and serum steroid hormones were simultaneously determined. The expression of SHBG and CBG mRNAs was detected in all samples analyzed. SHBG mRNA level was positively correlated with serum estradiol-17 beta level (p < 0.05), but not with serum progesterone level. There was a positive correlation between SHBG mRNA level and serum estradiol-17 beta/progesterone ratio (p < 0.01). On the other hand, CBG mRNA level was positively correlated with serum estradiol-17 beta and progesterone level (p < 0.01 and p < 0.01, respectively). There was no correlation between CBG mRNA level and serum estradiol-17 beta/progesterone ratio. SHBG and CBG mRNA levels were not correlated with the levels of serum testosterone, free testosterone or cortisol. These findings suggest that the synthesis of luteal SHBG and CBG is complexly regulated by estrogen and progesterone, and that SHBG and CBG interact with estrogen and progesterone, respectively, for luteal steroidal activity.