The essential roles of TGFB1 in reproduction

Transforming growth factor beta 1 (TGFB1) is implicated as a key regulator of the development and cyclic remodelling characteristic of reproductive tissues. The physiological significance of TGFB1 in reproductive biology and fertility has been extensively examined in Tgfb1 null mutant mice. Genetic deficiency in TGFB1 causes perturbed functioning of the hypothalamic-pituitary-gonadal axis, inhibiting luteinising hormone (LH) synthesis and leading to downstream effects on testosterone production in males and estrous cycle abnormalities in females. Oocyte developmental incompetence, accompanied by early embryo arrest as well as altered pubertal mammary gland morphogenesis are observed. In addition to LH and testosterone deficiency, male Tgfb1 null mice demonstrate complete inability to mate with females, associated with failure to initiate and/or sustain successful penile intromission or ejaculation. These studies demonstrate the profound significance of TGFB1 in male and female reproductive physiology, and provide a foundation for exploring the significance of this cytokine in human infertility and sexual dysfunction.

The mechanistic basis for sexual dysfunction in male transforming growth factor beta1 null mutant mice

The cytokine transforming growth factor beta1 (TGFB1) is implicated in male sexual function. Previous behavioral studies show that Tgfb1 null mutant mice mount and display limited intromission behavior with receptive females but are unable to complete successful copulation. The studies presented here explore the physiologic basis for sexual dysfunction in Tgfb1 null mutant males. Scanning electron microscopy revealed that the surface of the penis in Tgfb1 null mutant males was abnormally coated in superficial keratinized epithelial cells. There was a significant reduction in protrusion of penile spines through the superficial tissue in Tgfb1 null mutant mice; in some mice, the spines were almost completely embedded. Histologic analysis revealed reduced skin thickness in the penis of Tgfb1 null mutant males. Nerve fibers, endothelial cells, smooth muscle actin, macrophages, and neuronal and inducible nitric oxide synthase were present in similar abundance and location in Tgfb1 null mutant mice compared with wild-type controls; however, an increase in collagen I deposition was detected. Behavioral studies revealed that Tgfb1 null mutant males undergo spontaneous noncontact erections, albeit at a reduced rate compared with control mice, and engage in less frequent genital grooming activity. These studies suggest that Tgfb1 null mutation may adversely influence copulatory behavior through effects on both altered structural integrity of the penile skin and impaired tissue compliance leading to erectile dysfunction.

Exogenous transforming growth factor beta1 replacement and fertility in male Tgfb1 null mutant mice

Analysis of Tgfb1 null mutant mice has demonstrated that the cytokine transforming growth factor β1 (TGFB1) has essential non-redundant roles in fertility. The present study attempted to alleviate the infertility phenotype of Tgfb1 null mutant male mice by administration of exogenous TGFB1, either orally by colostrum feeding or subcutaneously by delivery of recombinant human latent TGFB1 (rhLTGFB1) via osmotic mini-pumps. Bovine colostrum and fresh unpasteurised bovine milk were found to be rich sources of TGFB1 and TGFB2; however, feeding Tgfb1 null mutant mice colostrum for 2 days failed to raise serum levels of TGFB1. Administration of rhLTGFB1 (~150 μg in total) over 14 days to Tgfb1 null mutant mice resulted in detectable TGFB1 in serum; however, mean levels remained 10-fold less than in Tgfb1 heterozygous mice. After 7 days and 14 days of rhLTGFB1 administration, serum testosterone, spontaneous non-contact erections and mating behaviour were assessed. Despite the increased serum TGFB1, administration of rhLTGFB1 to Tgfb1 null mutant mice failed to improve these fertility parameters. It is concluded that sustained restoration of circulating latent TGFB1 to levels approaching the normal physiological range does not rescue the infertility phenotype caused by TGFB1 deficiency. Reproductive function in male Tgfb1 null mutant mice may not respond to systemic TGFB1 supplementation due to a requirement for local sources of TGFB1 at the site of action in the reproductive tract, or perturbed development during the neonatal period or puberty such that adult reproductive function is permanently impaired.

Mammary gland development in transforming growth factor beta1 null mutant mice: systemic and epithelial effects

The cytokine-transforming growth factor beta1 (TGFB1) is implicated in development of the mammary gland through regulation of epithelial cell proliferation and differentiation during puberty and pregnancy. We compared mammary gland morphogenesis in virgin Tgfb1(+/+), Tgfb1(+/-), and Tgfb1(-/-) mice and transplanted Tgfb1(+/+) and Tgfb1(-/-) epithelium to determine the impact of TGFB1 deficiency on development. When mammary gland tissue was evaluated relative to the timing of puberty, invasion through the mammary fat pad of the ductal epithelium progressed similarly, irrespective of genotype, albeit fewer terminal end buds were observed in mammary glands from Tgfb1(-/-) mice. The terminal end buds appeared to be normal morphologically, and a comparable amount of epithelial proliferation was evident. When transplanted into wild-type recipients, however, Tgfb1(-/-) epithelium showed accelerated invasion compared with Tgfb1(+/+) epithelium. This suggests that the normal rate of ductal extension in Tgfb1(-/-) null mutant mice is the net result of impaired endocrine or paracrine support acting to limit the consequences of unrestrained epithelial growth. By adulthood, mammary glands in cycling virgin Tgfb1(-/-) mice were morphologically similar to those in Tgfb1(+/+) and Tgfb1(+/-) animals, with a normal branching pattern, and the tissue differentiated into early alveolar structures in the diestrous phase of the ovarian cycle. Transplanted mammary gland epithelium showed a similar extent of ductal branching and evidence of secretory differentiation of luminal cells in pregnancy. These results reveal two opposing actions of TGFB1 during pubertal mammary gland morphogenesis: autocrine inhibition of epithelial ductal growth, and endocrine or paracrine stimulation of epithelial ductal growth.

Cytokine knockouts in reproduction: the use of gene ablation to dissect roles of cytokines in reproductive biology

Cytokines play many diverse and important roles in reproductive biology, and dissecting the complex interactions between these proteins and the different reproductive organs is a difficult task. One approach is to use gene ablation, or 'knockout', to analyse the effect of deletion of a single cytokine on mouse reproductive function. This review summarizes the essential roles of cytokines in reproductive biology that have been revealed by gene knockout studies, including development and regulation of the hypothalamo-pituitary-gondal axis, ovarian folliculogenesis, implantation and immune system modulation during pregnancy. However, successful utilization of this approach must consider the caveats associated with gene ablation studies, e.g. embryonic lethality, systemic effects of cytokine ablation on local reproductive processes and the limited exposure to pathogens in mice housed in laboratory conditions. New sophisticated technology that temporally or spatially regulates gene ablation can overcome some of these limitations. Discoveries on the roles of cytokines in reproductive function uncovered by gene ablation studies can now be applied to improve in vitro fertilization for infertile couples and in the development of contraceptive therapies.

Transforming growth factor-beta1 null mutation causes infertility in male mice associated with testosterone deficiency and sexual dysfunction

TGFbeta1 is a multifunctional cytokine implicated in gonad and secondary sex organ development, steroidogenesis, and spermatogenesis. To determine the physiological requirement for TGFbeta1 in male reproduction, Tgfb1 null mutant mice on a Prkdc(scid) immunodeficient background were studied. TGFbeta1-deficient males did not deposit sperm or induce pseudopregnancy in females, despite an intact reproductive tract with morphologically normal penis, seminal vesicles, and testes. Serum and intratesticular testosterone and serum androstenedione were severely diminished in TGFbeta1-deficient males. Testosterone deficiency was secondary to disrupted pituitary gonadotropin secretion because serum LH and to a lesser extent serum FSH were reduced, and exogenous LH replacement with human chorionic gonadotropin (hCG) induced serum testosterone to control levels. In the majority of TGFbeta1-deficient males, spermatogenesis was normal and sperm were developmentally competent as assessed by in vitro fertilization. Analysis of sexual behavior revealed that although TGFbeta1 null males showed avid interest in females and engaged in mounting activity, intromission was infrequent and brief, and ejaculation was not attained. Administration of testosterone to adult males, even after neonatal androgenization, was ineffective in restoring sexual function; however, erectile reflexes and ejaculation could be induced by electrical stimulation. These studies demonstrate the profound effect of genetic deficiency in TGFbeta1 on male fertility, implicating this cytokine in essential roles in the hypothalamic-pituitary-gonadal axis and in testosterone-independent regulation of mating competence.

Macrophages promote collagen fibrillogenesis around terminal end buds of the developing mammary gland

Development of the ductal network in the mammary gland is dependent in part on the presence of macrophages. Here we utilize multi-photon microscopy and second harmonic generation to describe terminal end bud 3-dimensional structure and the organization of the surrounding collagen matrix. We have applied this approach to analyze the effect of macrophage deficiency on terminal end bud structure and collagen organization, using mice homozygous for a null mutation in the colony stimulating factor-1 gene (Csf1op/Csf1op). Primary terminal end buds have an oblong shape, with long collagen I fibers close to the neck of the terminal end bud and radiating upwards in the direction of growth. Around the terminal end buds, the amount of total collagen I detected by antibody staining was not affected by macrophage deficiency. However the amount of collagen I organized into long fibers, detected by second harmonic generation signal, was reduced in Csf1op/Csf1op mice. Macrophage deficiency also caused terminal end buds to be rounder and shorter. These studies reveal a role for macrophages in collagen fibrillogenesis and in organization of the structure of terminal end buds.

Null mutation in transforming growth factor beta1 disrupts ovarian function and causes oocyte incompetence and early embryo arrest

TGFbeta1 is implicated in regulation of ovarian function and the events of early pregnancy. We have investigated the effect of null mutation in the Tgfbeta1 gene on reproductive function in female mice. The reproductive capacity of TGFbeta1 null mutant females was severely impaired, leading to almost complete infertility. Onset of sexual maturity was delayed, after which ovarian function was disrupted, with extended ovarian cycles, irregular ovulation, and a 40% reduction in oocytes ovulated. Serum FSH and estrogen content were normal, but TGFbeta1 null mutant mice failed to display the characteristic proestrus surge in circulating LH. Ovarian hyperstimulation with exogenous gonadotropins elicited normal ovulation rates in TGFbeta1 null mutant mice. After mating with wild-type stud males, serum progesterone content was reduced by 75% associated with altered ovarian expression of mRNAs encoding steroidogenic enzymes 3beta-hydroxysteroid dehydrogenase-1 and P450 17 alpha-hydroxylase/C17-20-lyase. Embryos recovered from TGFbeta1 null mutant females were developmentally arrested in the morula stage and rarely progressed to blastocysts. Attempts to rescue embryos by exogenous progesterone administration and in vitro culture were unsuccessful, and in vitro fertilization and culture experiments demonstrated that impaired development is unlikely to result from lack of maternal tract TGFbeta1. We conclude that embryo arrest is due to developmental incompetence in oocytes developed in a TGFbeta1-deficient follicular environment. This study demonstrates that TGFbeta1 is a critical determinant of normal ovarian function, operating through regulation of LH activity and generation of oocytes competent for embryonic development and successful initiation of pregnancy.

Transforming growth factor beta--a mediator of immune deviation in seminal plasma

TGFbeta is a potent immune deviating agent, driving active forms of immune tolerance in peripheral tissues through effects on the induction and resolution of inflammatory responses and phenotype skewing in antigen-presenting cells and lymphocytes. The TGFbeta content of seminal plasma from human, rodent and livestock species is amongst the highest measured in biological fluids. The seminal vesicle gland is the principal source of TGFbeta in the semen of mice, where its synthesis is regulated by testosterone. At insemination, seminal TGFbeta is deposited in the female tract and is activated by acidic vaginal pH, enzymes of male or female tract origin, or through cleavage-independent processes involving conformational change after interaction with epithelial cell docking proteins. Seminal TGFbeta has been shown to be a principal stimulating agent in the post-coital inflammatory response, and is likely to be essential for induction of immune tolerance to seminal antigens. As well as preventing aberrant immunity to spermatozoa, these events are implicated in priming an appropriate female immune response to embryo implantation, since many seminal antigens are shared by the conceptus. The cascade of immunological events elicited by seminal TGFbeta may therefore explain epidemiological observations linking acute and cumulative exposure to semen with successful placental development and pregnancy outcome. Depending on whether the female tract has evolved mechanisms to discriminate seminal antigens from opportunistic pathogens, there may be a detrimental cost of seminal TGFbeta in inhibiting protective immunity to agents of sexually transmitted disease including HIV. A better understanding of the significance and role of TGFbeta in semen will facilitate development of novel therapies for immune-based infertility disorders.

Defining the actions of transforming growth factor beta in reproduction

Members of the transforming growth factor beta (TGFbeta) family are pleiotropic cytokines with key roles in tissue morphogenesis and growth. TGFbeta1, TGFbeta2 and TGFbeta3 are abundant in mammalian reproductive tissues, where development and cyclic remodelling continue in post-natal and adult life. Potential roles for TGFbeta have been identified in gonad and secondary sex organ development, spermatogenesis and ovarian function, immunoregulation of pregnancy, embryo implantation and placental development. However, better tools must now be employed to map more precisely essential functions and the regulatory networks governing their activity. Gene ablation and transgenic models are expected to provide novel insights into distinct physiological activities for each TGFbeta isoform in normal reproductive function and reproductive pathologies. It is also necessary to consider the mechanisms controlling TGFbeta activation from latent precursor forms, and receptor and binding protein expression. Smad intracellular signalling circuitry and modulation by environmental stimuli through cross-talk with other signal transduction pathways will further constrain TGFbeta action. This review examines existing evidence for TGFbeta1, TGFbeta2 and TGFbeta3 regulation of male and female reproductive biology, and highlights prospects for future research.

Differential regulation by FSH and IGF-I of extracellular matrix IGFBP-5 in bovine granulosa cells: effect of association with the oocyte

Inhibition of insulin-like growth factor (IGF)-I induced DNA synthesis in bovine oocyte-cumulus complexes (OCCs) caused by follicle-stimulating hormone (FSH) has been linked to changes in the extracellular matrix which do not occur in mural granulosa cells (MGCs). We investigated regulation by IGF-I and FSH of secreted and extracellular matrix entrapped IGF-binding proteins. OCCs and MGCs from bovine ovaries were cultured in media supplemented with IGF-I and FSH for 24 h. Culture media and extracellular matrix were analysed for IGF-binding proteins by Western ligand blot and immunoblot and found to contain principally IGFBP-3 and -5. The combined treatment of IGF-I and FSH increased the concentration of IGFBP-3 in OCC and MGC conditioned media by 4- and 6-fold, respectively. Treatment of OCCs and not MGCs with IGF-I and FSH together increased extracellular matrix IGFBP-5 by 2.5-fold. The differential regulation of extracellular matrix IGFBP-5 in OCCs compared to MGCs suggest involvement of changes in the extracellular matrix brought about by IGF-I and FSH in overall regulation of IGF-I in the ovarian follicle.