The distribution of serum albumin in the rat testis, studied by electron microscope immunocytochemistry on ultrathin frozen sections

Induction of apoptosis by 25-hydroxycholesterol in adult rat Leydig cells: Protective effect of 17β-estradiol

Testicular macrophages can convert cholesterol into 25-hydroxycholesterol which strongly stimulates Leydig cell testosterone production. We demonstrated that 25-hydroxycholesterol reduced cholesterol biosynthesis in adult rat Leydig cells. This oxysterol can also be cytotoxic. As hydroxylated cholesterol can induce apoptosis in various cells, we investigated cell death produced by 25-hydroxycholesterol. Apoptosis was characterized by TUNEL assay and by DAPI test. Addition of 25-hydroxycholesterol, during 24h, induced a dose dependent increase of apoptosis. This effect was reduced by a treatment with a caspase-3 inhibitor (Ac-DEVD-CHO). 25-Hydroxycholesterol is known to stimulate testosterone production, but an increase of intracellular or culture medium testosterone level does not modify significantly the percentage of apoptotic cells. In contrast, addition of 17beta-estradiol (2 nM) induced a decrease of apoptotic cells. These data suggested that this oxysterol can be used by rat Leydig cells in culture for sterol metabolism, but also induces apoptosis which could be inhibited by 17beta-estradiol.

Apoptotic effects of 25-hydroxycholesterol in immature rat Sertoli cells: Prevention by 17β-estradiol

The aim of the present study was to determine whether or not apoptosis occurs in Sertoli cells in presence of 25-hydroxycholesterol, an oxysterol derived from cholesterol-containing foods or endogenous oxidation. Here, we provide evidence that 25-hydroxycholesterol can induce cultured Sertoli cells of immature rat to undergo apoptosis. The cell death was identified by analysis of fragmented DNA detected using enzyme-immunoassay. After 48 h of treatment with 50 microM of 25-hydroxycholesterol, apoptosis increased by 70% in Sertoli cells. Moreover, 50 microM of 25-hydroxycholesterol inhibited the incorporation of [14C] acetate into cholesterol by 70%. Addition of mevanolate to prevent isoprenoid deficiency do not inhibit the apoptosis generated by 25-hydroxycholesterol. In contrast, this increase of DNA fragmentation was reversed by addition of caspase-3 inhibitors as Ac-DEVD-CHO or Ac-ESMD-CHO. Bcl-2 mRNA level in the Sertoli cells decreased by 60% after 24 h exposure to 25-hydroxycholesterol. In parallel, Bax mRNA level increased by 40% in the Sertoli cells incubated in presence of 50 microM of 25-hydroxycholesterol. Physiological concentrations of 17beta-estradiol (10 or 100 nM) elicited a significant protection on apoptosis generated by 25-hydroxycholesterol in Sertoli cells. Our results show that the 25-hydroxycholesterol would control the cholesterol synthesis without toxic effect in immature rat Sertoli cells, these cells being able to protect themselves by estradiol production.

The stimulatory effect of albumin on luteinizing hormone-stimulated Leydig cell steroid production depends on its fatty acid content and correlates with conformational changes

The effects of purified albumin species and albumin fragments (0.2-1% w/v) on short-term (4 h) steroid secretion by immature rat Leydig cells, in the presence of a maximally stimulating dose of luteinizing hormone (LH), were investigated. Human albumin and the peptic fragment (comprising residues 1-387) enhanced pregnenolone production in isolated rat Leydig cells, whereas chicken albumin and the tryptic fragment (comprising residues 198-585) were not active. This stimulatory effect of human albumin and the peptic fragment correlated with the potential of these proteins to undergo a pH-dependent neutral-to-base transition as measured by circular dichroism. The tryptic fragment and chicken albumin did not have the potential to undergo such a transition. The pH-dependent conformational changes of albumin and fragments thereof occurred in parallel with a change in the binding affinity for testosterone and pregnenolone. The fatty acid oleic acid and the drug suramin, only when present in a molar ligand-to-albumin ratio equal to or higher than 2, inhibited the albumin-mediated stimulation of steroid production. These data show that the stimulatory effects of albumin species on LH-induced Leydig cell pregnenolone production depend on their fatty acid content and correlate with the potential of these molecules to undergo conformational changes. It is unknown via which mechanisms albumin exerts its stimulatory effect, but the LH action through the cyclic AMP pathway seems not to be affected.

Immunolocalization of some plasmatic proteins in basement membranes during earliest rat morphogenesis with special reference to the gonadal differentiation

Rat albumin, transferrin, angiotensinogen and T kininogen were examined immunohistochemically in the epithelial basement membranes (BMs) during the earliest rat morphogenesis. As a specific marker for BMs, laminin was used. Albumin and transferrin immunostaining appeared as early as the 11th day of gestation in all epithelial BMs. In 13-day-old mesonephric-gonadal complex, just after the onset of the sexual cord differentiation, all BMs were weakly stained. One day later, a stronger immunoreactivity was distributed along the coelomic epithelium, the Wolffian duct, the mesonephric tubules, the differentiating sexual cords and the blood vessels. The epidermal BM and all epithelial BMs of differentiating organs are also immunoreactive. The accumulation of albumin and transferrin in the BMs is probably the result of a strong release of these two major liver proteins in the embryonic blood and their diffusion in extracellular spaces. At these stages, the lack of angiotensinogen and T kininogen BM labeling is consistent with their low hepatic and plasmatic concentrations. During embryogenesis, some plasma proteins are probably trapped in the epithelial BMs and not produced by local cells.

Albumin localization in the testis of adult golden hamsters by use of immunohistochemistry

There is an increasing interest in different biochemical roles of albumin (Alb) in respect to testicular function. For this reason, Alb was localized by the peroxidase-antiperoxidase technique in the testis of adult golden hamsters. A strong Alb immunoreactivity occurred in the interstitial space and on the surface of Leydig cells. A few Sertoli cells showed a strong Alb response under the appearance of so-called leakages traversing Sertoli-Sertoli cell junctions. Spermatogonia reacted strongly, while spermatids and sperms showed rather a mild, or moderate response. Spermatocytes remained unstained. When similar maturation stages of seminiferous tubules were compared, the number of reacting cells varied strikingly. Our results support the assumption that Alb or a protein with an Alb-like immunoreactivity exerts diverse functions of the testis.

Microvascular permeability to IgG in the rat testis at puberty

Immunoglobulin G (IgG) spaces and permeability surface area products (PS) were calculated separately in the testis parenchyma, capsule and interstitial tissue in four age groups of rats to see if there were regional differences in microvascular permeability in the rat testis and if there were changes in PS with age. The results demonstrated a marked increase in PS to IgG at 27 days of age in the testicular interstitial tissue, whereas PS in the capsule did not show such consistent changes. Blood volumes per gram, as indicated by the 3 min IgG spaces, were considerably greater in the testicular capsule than in the interstitial tissue, although the weight of the capsule was only about one-third of the interstitial tissue weight. Maximal IgG spaces were reached at 5 h in the testicular parenchyma, but in most groups only at 20 h in the capsule. IgG was demonstrated immunohistochemically in the testicular interstitial tissue from 33 days of age onwards.

Localization of immunoreactive testibumin in the testis and epididymis of adult rats

Testibumin is a glycoprotein previously isolated from the spent media of primary Sertoli cell-enriched cultures prepared from 20-day-old rats. Immunoassayable testibumin is found in the highest concentrations in testis, epididymis and fluids of the male reproductive tract in adult rats. In the present study, light microscopy was used to show that immunostainable testibumin in paraffin sections of rat testis was localized along the base of the seminiferous epithelium and in finger-like projections from the base of the epithelium, corresponding to the position of the Sertoli cells. The immunostaining of Sertoli cells was shown to be specific since either purified testibumin or crude Sertoli cell-enriched culture medium could compete with antibody for binding sites in tissue sections. The observations using light microscopy were confirmed when Sertoli cells were examined by electron microscopy using a pre-embedding immunostaining technique. The epithelium of the epididymis also contained immunoreactive testibumin which was localized in the caput, corpus and cauda. Immunostainable testibumin was also localized in the corpora lutea of the rat ovary and in the epithelium of the uterine endometrium. These observations are consistent with previous reports that immunoreactive testibumin is present in these organs as demonstrated by radio-immunoassays. We conclude that (i) the immunolocalization of testibumin in Sertoli cells adds to a growing list of observations suggesting that it is made in this cell type; (ii) the other sites of testibumin synthesis in the male are uncertain but the ovary and uterus are possible sites in the female; (iii) electron microscopy following pre-embedding immunostaining and epitope selection can be used as an adjunct to conventional immunocytochemistry to localize proteins in Sertoli cells.

The albumin fraction of rat testicular fluid stimulates steroid production by isolated Leydig cells

Rat testicular fluid (rTF), but not rat serum (rS) or plasma (rP) can further increase within 4 h maximally luteinizing hormone (LH)-stimulated or 22 R-hydroxycholesterol-supported pregnenolone production by immature rat Leydig cells in vitro. This effect of rTF is dose dependent (0.05-1.2% protein, w/v) with an increase up to 4-fold. The objective of the present study was to isolate and characterize the bioactive factor(s) in rTF. After sequential ammonium sulfate fractionation, gel filtration chromatography on Superose 12 and affinity chromatography on concanavalin A-Sepharose it was shown that the albumin fraction was a major biologically active fraction in rTF. The relative specific activity in these fractions was never greater than 1.3-1.4, which is in agreement with the purification factor required to obtain pure albumin from rTF. Commercially obtained albumin fractions from human, bovine and rat sera, up to 99% purity, also increased Leydig cell steroid production more than 3-fold when added in concentrations between 0.1 and 1% w/v in combination with LH or 22R-hydroxycholesterol. Other proteins such as hemoglobin and ovalbumin were not effective in stimulation of steroid production. Bovine serum albumin (bSA, fraction V) at concentrations of 0.25 and 1.0% (w/v), had no or minor effects on LH-stimulated steroid production by rat granulosa cells or adrenocorticotrophic hormone (ACTH)-stimulated steroid production by rat adrenal cells. These findings indicate that albumin itself or minor compounds copurified with albumin represent the main biologically active component in rTF for short-term stimulation of Leydig cell steroid production. Since bioactivity could not be demonstrated in serum which contains similar amounts of albumin as rTF, inhibitory compounds may be present in rat serum.

Development of the blood-testis barrier and changes in vascular permeability at puberty in rats

The effectiveness of the blood-testis barrier to water-soluble substances was assessed in rats of various ages by measuring the volumes of distribution of Cr-EDTA and albumin, and estimating the proportion of the testis made up by interstitial tissue and tubular lumen by morphometric techniques on cryostat sections of frozen tissue. The interstitial tissue volume fell from 15 days to reach adult values at about 30 days of age. A lumen was present in some animals at 15 days, and it enlarged progressively to reach adult levels at about 45 days of age. The 1-h Cr-EDTA space began to fall after 25 days, and reached adult values by 33 days; in rats aged 25 and 30 days, the Cr-EDTA space was almost twice the measured interstitial tissue volume, but even in the older rats, the Cr-EDTA space remained appreciably greater than the interstitial tissue volume. The 20-h albumin space did not begin to fall until after 33 days, and had still not reached adult values in rats aged 44 days. Thus, the functional barrier to water-soluble markers develops later and more gradually than the barrier to electron-opaque markers as used by previous authors, and its appearance correlates more closely with enlargement of the tubular lumen than with formation of the inter-Sertoli cell junctions. The rate at which the albumin space approached its final value was used to calculate the vascular permeability to albumin. This rose to a maximum between 25 days and 33 days of age, and then fell again, although adult values had still not been reached by 44 days of age.

Rat testicular testibumin is a protein responsive to follicle stimulating hormone and testosterone that shares immunodeterminants with albumin

During a search for hormonally responsive products in media from Sertoli cell enriched cultures, a major follicle stimulating hormone responsive and testosterone-responsive protein was identified and designated CMB-1. The results of the present study indicate that this protein is related immunologically to rat albumin and rat alpha-fetoprotein (AFP) and is concentrated in the testis of the adult rat. CMB-1 was therefore termed testibumin. Testibumin was purified from Sertoli cell enriched cultures to apparent homogeneity by sequential high-performance liquid chromatography on anion-exchange, chromatofocusing, gel permeation, and hydroxylapatite columns. The purified protein consists of two concanavalin A (Con A) reactive forms: one which does not interact with Con A and the other which binds to this lectin and is eluted with methyl alpha-mannoside. Testibumin is a monomer with an apparent molecular weight of 69,000 and a pI ranging between 4.5 and 4.85. The heterogeneity of this protein was further demonstrated by crossed-immunoelectrophoresis and two-dimensional gel electrophoresis. A monospecific antiserum and highly purified testibumin were used to develop a specific radioimmunoassay which permitted studies of the hormonal responsiveness of Sertoli cell enriched culture and of the content of testibumin in the reproductive tract fluids in vivo. Even though testibumin was found in serum of both sexes, it was highly concentrated in the testicular and epididymal compartments in adult rats. This protein was compared to rat serum albumin and rat AFP immunologically. With the use of immunoblots, antiserum developed against testibumin showed partial cross-reactivity with albumin and AFP when these latter proteins were denatured and were present in amounts several orders of magnitude greater than testibumin. The extent of this cross-reactivity was then examined by comparing the ability of native and S-carboxymethylated albumin to compete with 125I-testibumin for binding to a monospecific testibumin antiserum. It was shown that the unfolded derivative of albumin showed partial cross-reactivity with testibumin. We conclude that testibumin is immunologically related to albumin and AFP as these latter proteins are related to one another and that testibumin is possibly the homologue of albumin in the seminiferous tubular compartment.

Structure and dynamics of the estrogen receptor

To evaluate the structure and function of estrogen receptor (ER) in various mammalian systems, the cytosolic forms of receptor from calf uterus and from MCF-7 human breast cancer cells have been purified to virtual homogeneity by sequential selective adsorption to estradiol-Sepharose and heparin-Sepharose. In both cases, the purified steroid-receptor complex appears to exist as an activated 5S homo- or heterodimer of mol. wt 65,000 (4S) steroid-binding subunits. Purified ER has high affinity for DNA and serves as a substrate for phosphorylation by a purified rat brain kinase. Several monoclonal antibodies prepared against affinity-purified MCF-7 cytosol ER have been used to localize receptor by an indirect immunoperoxidase technique in fixed, frozen sections of human breast tumors, human uterus, rabbit uterus and in other mammalian reproductive tissues and cancers, as well as in fixed MCF-7 cell cultures and in paraffin-embedded sections of breast tumors and human endometrium. In all cases, we have observed only nuclear localization of immunoreactive receptor in tissues and whole cells, even under conditions in which virtually all of the receptor is found in a low-salt extract (cytosol) of the target cells. Treatment of cells or tissues in vivo or in vitro with estradiol alters the intensity but not the distribution of specific staining for ER. By immunoelectron microscopy, receptor was localized in the euchromatin, but not in the marginated heterochromatin or nucleoli of MCF-7 nuclei and epithelial and stromal nuclei of postmenopausal human endometrium. These observations suggest that the majority of the unoccupied receptor may actually reside in the nucleus, rather than in the cytoplasm as previously thought. Thus, hormone action may involve binding of the steroid directly to receptor loosely associated with nuclear components, followed by conversion of the steroid-receptor complex to an activated form which becomes more tightly associated with chromatin.