Regulatory molecules for coronary expressions of VEGF and its angiogenic receptor KDR in hypoestrogenic middle-aged female rats

We studied the effects of estrogen deprivation and replacement on the protein and gene expression levels molecules that can be considered to be essential for coronary angiogenesis in middle-aged female rats. The animals were subjected to sham operation, ovariectomy, or ovariectomy with estrogen replacement therapy (ERT). Following ovariectomy, protein and gene expressions of vascular endothelial growth factor (VEGF) and its angiogenic receptor (KDR) showed a marked decline in coronary vessels, as determined by immunohistochemistry and in situ hybridization. ERT resulted in restoration of the ovariectomy-induced changes to intact levels. The coronary expression level of basic fibroblast growth factor was unaffected by estrogen deprivation or treatment. The changes in VEGF and KDR expressions were strongly associated with those in endothelial nitric oxide synthase (eNOS) expression in coronary vessels. Moreover, the age- and gender-dependent accumulation of hypoxia-inducible factor-1alpha (HIF-1alpha) protein appeared to be a determinant molecule of VEGF expression in middle-aged female rats. We reached a conclusion that the VEGF-KDR system plays a key role in coronary angiogenesis in hypoestrogenic elderly women and is critically regulated by estrogen, eNOS and HIF-1alpha.     

The critical period hypothesis of estrogen effects on cognition: Insights from basic research

Background

In addition to its primary role in reproduction estrogen impacts brain areas important for cognition, including the hippocampus and prefrontal cortex. It has been hypothesized that decline in estrogen levels in women following menopause is associated with, or can exacerbate, age-related cognitive decline. However, clinical evidence to support a role for estrogen in preventing cognitive decline in women as they age is equivocal. The critical period hypothesis of estrogen effects on cognition, which proposes that estrogen administration has to be initiated within a critical time period following the loss of ovarian function in order for it to exert positive effects on the central nervous system, is offered as one explanation for inconsistencies across studies.

Scope of review

This review details results from basic research using rodent models investigating the effects of estrogen on cognition in the aging female. Emphasis is placed on work investigating effects of timing of initiation of estrogen administration on its subsequent efficacy.

Major conclusions

Results of basic research provide support for the critical period hypothesis. Furthermore, results of work in rodent models suggest mechanisms by which the response to estrogen is altered if treatment is initiated following long-term ovarian hormone deprivation.

General significance

Understanding if and under what conditions hormone administration following the loss of ovarian function positively affects the brain and behavior could have important implications with regard to female cognitive aging. Results of basic research can contribute to this understanding and provide insight into the complex mechanisms by which estrogen affects cognition.     

Estrogen administration, postexercise tissue oxidative stress and vitamin C status in male rats

Estrogen can putatively act as an antioxidant and protect tissues from exercise-induced oxidative stress. To test the in vivo efficacy of estrogen, the effects of 2 weeks of daily estrogen (40 microg x kg(-1) body weight beta-estradiol 3-benzoate) injection on indices of immediate postexercise oxidative stress and antioxidant status were determined in adult male rats, with and without 8 weeks of prior dietary vitamin E deprivation. The treadmill running protocol (60 min at 21 m x min(-1), 12% grade) induced significant oxidative stress as indicated by muscle glutathione status. Estrogen administration had little effect on postexercise tissue glutathione status, superoxide dismutase and glutathione peroxidase activity, and vitamin E levels. Estrogen administration induced significant reductions in muscle, liver, and heart vitamin C concentrations following exercise, as well as in unexercised male rats. Tissue vitamin C loss was not directly mediated through liver glycogen or glutathione status. Thus, estrogen administration generally did not appear to influence postexercise tissue indices of oxidative stress or antioxidant status and may have contributed to a decline in overall antioxidant protection by inducing losses in tissue vitamin C content.     

Growth regulation by GTP. Regulation of nucleotide pools in Neurospora by nitrogen and sulfur control systems

Purine nucleotide pools in the fungus Neurospora crassa decline in response to carbon, nitrogen, or sulfur deprivation. There is, in addition, a decline in GTP/ATP ratios on nitrogen or sulfur deprivation in wild type. The GTP/ATP decline is missing on nitrogen deprivation of the nitrogen control mutant, nit-2, and on sulfur deprivation of the sulfur control mutant, cys-3. The nit-2 mutant also shows elevated UTP pools on nitrogen deprivation when compared with similarly treated wild type. Six-hour sulfur-deprived cys-3 shows multiple aberrations in nucleotide pools when compared with similarly treated wild type. These include very low energy charge and depletion of pools of most nucleotides. ATP in sulfur-deprived cys-3 drops by about 88%. Sulfur-deprived cys-3 is also greatly impaired in comparison with wild type in its ability to resume growth when restored to nutritional sufficiency after a period of sulfur deprivation. These results clearly demonstrate that the nitrogen (nit-2) and sulfur (cys-3 regulatory systems are not limited to control of catabolism of exogenous nitrogen and sulfur sources, respectively, but rather influence, a broader range of cellular properties than has been previously thought. The pattern of GTP pool control is consistent with a positive role for GTP in growth control. Evidence in other systems supporting such a growth-regulating role for GTP is discussed.     

Chlorosis induced by nutrient deprivation in Synechococcus sp. strain PCC 7942: not all bleaching is the same.

Cell coloration changes from normal blue-green to yellow or yellow-green when the cyanobacterium Synechococcus sp. strain PCC 7942 is deprived of an essential nutrient. We found that this bleaching process (chlorosis) in cells deprived of sulfur (S) was similar to that in cells deprived of nitrogen (N), but that cells deprived of phosphorus (P) bleached differently. Cells divided once after N deprivation, twice after S deprivation, and four times after P deprivation. Chlorophyll (Chl) accumulation stopped almost immediately upon N or S deprivation but continued for several hours after P deprivation. There was no net Chl degradation during N, S, or P deprivation, although cellular Chl content decreased because cell division continued after Chl accumulation ceased. Levels of the light-harvesting phycobiliproteins declined dramatically in a rapid response to N or S deprivation, reflecting an ordered breakdown of the phycobilisomes (PBS). In contrast, P-deprived cultures continued to accumulate PBS for several hours. Whole PBS were not extensively degraded in P-deprived cells, although the PBS contents of P-deprived cells declined because of continued cell division after PBS accumulation ceased. Levels of mRNAs encoding PBS polypeptides declined by 90 to 95% in N- or S-deprived cells and by 80 to 85% in P-deprived cells. These changes in both the synthesis and stability of PBS resulted in a 90% decline in the PC/Chl ratio of N- or S-deprived cells and a 40% decline in the PC/Chl ratio of P-deprived cells. Therefore, although bleaching appears to be a general response to nutrient deprivation, it is not the same under all nutrient-limited conditions and is probably composed of independently controlled subprocesses.     

Stepwise estrogen suppression manipulating the estrostat

Estrogen suppression is an effective endocrine treatment option in pre- as well as postmenopausal breast cancer patients. The fact that it produces clinical benefits not only in these two groups of patients that differ significantly with respect to plasma estrogen levels but also among patients with very low plasma estrogen levels due to previous hypophysectomy, adrenalectomy or treatment with first/second generation aromatase inhibitors, suggests estrogen deprivation to work independent of pretreatment plasma estrogen levels. Interestingly, in vitro studies have revealed MCF-7 cells to respond to estrogen deprivation by sensitization, causing maximum estradiol stimulation at a concentration 10⁻⁵ to 10⁻⁴ the concentration needed in wild-type cells. While results from recent phase III studies comparing novel aromatase inhibitors and inactivators to conventional therapy have suggested that a more effective hormone ablation may be translated into an improved clinical efficacy, the biochemical rationale for lack of complete cross-resistance between aromatase inhibitors and inactivators or aromatase inhibitors and megestrol acetate remains to be explained. Interestingly, patients becoming resistant to estrogen deprivation may still respond to estrogens administered in pharmacological doses. Future studies are warranted to explore alterations in gene expression and signaling mechanisms in response to different therapies in tumor tissue in vivo.     

Estrogens and progesterone during gestation in Dolichotis patagona

During pregnancy, a progesterone-binding plasma protein is present and is similar in several respects to the binding protein reported in other hystricomorphs. These findings establish estradiol-17 beta as the predominant estrogen of pregnancy and that progesterone rises during pregnancy and does not decline until after parturition. Gestation length is 96 days. This study establishes similarities between the mara and its closest relative, the guinea pig.     

Effect of maternal deprivation on polyamine metabolism in preweanling rat brain and heart

Ornithine Decarboxylase (ODC) the first and probably rate-limiting step in polyamine biosynthesis, is usually elevated in tissues with high rates of growth or protein synthesis and in preweanling rat brain is altered by hormones thought to play a role in stress such as thyroxine and cortisol. Maternal deprivation stress was examined for its effect on preweanling rat brain ODC activity. Ten day old rat pups were removed from the maternal cage, then alternately returned to the mother or placed in a warm environment after the method of Hall. Pups taken from the mother for as little as 1 hour show a significant decline in their whole brian ODC activity. The effect peaked at 2–4 hours of deprivation, at which time the brain ODC activity was 60% below that of the equally handled littermate controls. Two hours of deprivation produced a similar effect throughout preweanling development. The effect occurred in all brain regions and also in heart. Return to mother reversed rapidly the deprivation-induced ODC decline, with ODC activity overshooting to 300% of control 2 hours after return, then declining to baseline by 4 hours. Putrescine, the immediate product of the ODC reaction, declined 15% one hour after deprivation, and 50% in brain and heart after 15 hours. These data demonstrate that maternal deprivation alters polyamine metabolism in preweanling rat brain and heart.     

Estrogen and memory in women: how can we reconcile the findings?

Although several randomized controlled trials (RCTS) of surgically menopausal women have provided evidence that estrogen protects aspects of memory, many cross-sectional and longitudinal studies, including those from the RCT, the Women's Health Initiative Memory Study (WHIMS), have reported inconsistent information with regard to the relationship between estrogen and aspects of cognitive function. Although numerous reasons could be offered to explain these discrepancies in research findings, recent evidence from rodent, nonhuman primate, and human studies consistently suggests that one possibility may be critical to our understanding of the estrogenic effect on memory. Results of these animal and human studies indicate that the initiation of estrogen treatment at the time of menopause, or soon after ovariectomy (OVX), provides a window of opportunity for the preservation of memory in females whereas the administration of the hormone following a considerable delay in time after OVX has little or no beneficial effect on cognition. Considering the evidence that, in several organ systems, heightened disease risks accrue to a longer duration of estrogen deprivation in women, it would seem important to determine whether this is also true for brain structure and function in order to protect the quality of life for the considerable number of women who undergo a surgical menopause before their natural menopause had occurred.     

性激素对成年小鼠脑微管蛋白合成的影响

以3H-秋水仙碱为探针,测定小鼠脑微管蛋白含量．结果表明雌性激素具有显著的促进成年鼠脑微管蛋白合成的作用．与雌性激素相比,雄性激素促进脑微管蛋白合成的作用较弱．特别值得指出的是雌性激素促进脑微管蛋白合成的作用发生在脑发育的临界期之外,而此时甲状腺激素早已丧失了促进脑微管蛋白合成的作用．因此雌性激素在维护成年脑结构和功能的完整完善方面起着重要作用,而且这种作用可能会获得新的应用．     

Depressed prolactin cell activity in long-term blind-pinealectomized female hamsters is due to loss of estrous cyclicity

Pinealectomy in the female golden Syrian hamster is not always completely effective in preventing the suppressive effects of long-term light deprivation due to blinding on pituitary prolactin (PRL) cell activity. We examined this curious phenomenon by measuring pituitary PRL mRNA levels, PRL synthesis, and radioimmunoassayable PRL, and correlating these changes with the status of estrous cyclicity. As expected, 12 weeks of light deprivation resulted in loss of estrous cyclicity and a greater than 90% decline in all indices of pituitary PRL cell activity, compared with intact cycling controls. Pinealectomy prevented only 40-50% of this decline. However, if noncycling light-deprived pinealectomized animals were excluded, pinealectomy was completely effective, i.e., cycling intact control animals were no different than cycling blind-pinealectomized. We conclude that the inability of pinealectomy to completely prevent the decline in prolactin cell activity seen after blinding is due to the loss of estrous cyclicity in some blind-pinealectomized females, with the attendant loss of the prolactin-stimulating hormone estrogen.     

Hormonal control of neuron number in sexually dimorphic spinal nuclei of the rat: IV. Masculinization of the spinal nucleus of the bulbocavernosus with testosterone metabolites

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic motor nucleus in the rat lumbar spinal cord. SNB motoneurons and their perineal target muscles are present in adult males but reduced or absent in females. This sexual dimorphism is due to the presence of androgen during development; females treated with testosterone (T) perinatally have a masculine SNB system. To assess whether masculinization of the SNB could involve the conversion of testosterone into its active metabolites, dihydrotestosterone (DHT) and estrogen, we examined the development of the SNB in females treated perinatally with estrogen alone or in combination with dihydrotestosterone. Counts of motoneurons in the developing SNB in all groups showed the typical prenatal increase followed by a differential postnatal decline; the incidence of degenerating cells reflected this decline. Motoneuron numbers and the frequency of degenerating cells in females treated with estrogen (E) alone did not differ from those of normal females, with both groups losing large numbers of motoneurons and having a high incidence of degenerating cells. In contrast, females treated with both estrogen and dihydrotestosterone did not show the female-typical decline in motoneuron number and had a low, masculine incidence of degenerating cells. By postnatal day 10, females treated with estrogen and dihydrotestosterone had a fully masculine SNB motoneuron number, suggesting that dihydrotestosterone alone or in conjunction with estrogen may be involved in the development of the sexually dimorphic SNB system.     

Expression of estrogen receptor α and β in rat astrocytes in primary culture: effects of hypoxia and glucose deprivation

Estrogen replacement therapy could play a role in the reduction of injury associated with cerebral ischemia in vivo, which could be, at least partially, a consequence of estrogen influence of glutamate buffering by astrocytes during hypoxia/ischemia. Estrogen exerts biological effects through interaction with its two receptors: estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ), which are both expressed in astrocytes. This study explored effects of hypoxia and glucose deprivation (HGD), alone or followed by 1 h recovery, on ERα and ERβ expression in primary rat astrocyte cultures following 1 h exposure to: a) 5 % CO(2) in air (control group-CG); b) 2 % O(2)/5 % CO(2) in N(2) with glucose deprivation (HGD group-HGDG); or c) the HGDG protocol followed by 1 h CG protocol (recovery group-RG). ERα mRNA expression decreased in HGDG. At the protein level, full-length ERα (67 kDa) and three ERα-immunoreactive protein bands (63, 60 and 52 kDa) were detected. A significant decrease in the 52 kDa band was seen in HGDG, while a significant decrease in expression of the full length ERα was seen in the RG. ERβ mRNA and protein expression (a 54 kDa single band) did not change. The observed decrease in ERα protein may limit estrogen-mediated signalling in astrocytes during hypoxia and recovery.     

Membrane initiated estrogen signaling in breast cancer

Recent research has focused on effects of the estrogen receptor acting at the level of the cell membrane in breast cancer. In this review we describe 17beta-estradiol (E2)-initiated membrane signaling pathways involving the activation of several kinases that contribute to the regulation of cell proliferation and prevention of apoptosis. Although classical concepts had assigned priority to the nuclear actions of estrogen receptor, recent studies document the additional importance of estrogen receptor residing in or near the plasma membrane. A small fraction of estrogen receptor is associated with the cell membrane and mediates the rapid effects of E2. Unlike classical growth factor receptors, such as insulin-like growth factor 1 receptor (IGF1R) and epidermal growth factor receptor (EGFR), estrogen receptor has no transmembrane and kinase domains and is known to initiate E2 rapid signals by forming a protein complex with many signaling molecules. The formation of the protein complex is a critical step, leading to the activation of the MAPK1/3 (also known as MAP kinase) and AKT1 (also known as Akt) pathways. A full understanding of the mechanisms underlying these relationships, with the ultimate aim of abrogating specific steps, should lead to more-targeted strategies for treatment of hormone dependent-breast cancer.     

Estrogen deprivation aggravates intracellular calcium dyshomeostasis in the heart of obese-insulin resistant rats

The incidence of cardiovascular disease and metabolic syndrome increases after the onset of menopause, giving evidence for the vital role of estrogen. Intracellular calcium [Ca²⁺]i regulation plays an important role in the maintenance of left ventricular (LV) contractile function. Although either estrogen deprivation or obesity has been shown to strongly affect the metabolic status and LV function, the effects of estrogen deprivation on the cardiometabolic status and cardiac [Ca ²⁺]i regulation in the obese-insulin resistant condition have never been investigated. Our hypothesis was that estrogen deprivation aggravates LV dysfunction through the increased impairment of [Ca ²⁺]i homeostasis in obese-insulin resistant rats. Female rats were fed on either a high-fat (HFD, 59.28% fat) or normal (ND, 19.77% fat) diet for 13 weeks. Then, rats were divided into sham (HFS and NDS) operated or ovariectomized (HFO and NDO) groups. Six weeks after surgery, metabolic status, LV function and incidence of [Ca ²⁺]i transients were determined. NDO, HFS, and HFO rats had evidence of obese-insulin resistance indicated by increased body weight with hyperinsulinemia and euglycemia. Although NDO, HFS, and HFO rats had markedly reduced %LV fractional shortening, E/A ratio and decreased [Ca ²⁺]i transient amplitude and decay rate, HFO rats had the most severe impairments. These findings indicate that estrogen deprivation had a strong impact on abnormal LV function through [Ca ²⁺]i regulation. In addition, evidence was found that in obese-insulin resistant rats, estrogen deprivation severely aggravates LV dysfunction via increased impairment of [Ca ²⁺]i homeostasis.     

The metabolic fate of [H]estradiol in relation to dietary intake of boron in ovariectomized rats

It has been reported that boron (B) deprivation reversibly lowers plasma estradiol levels in postmenopausal women. In order to establish whether this reflects disturbances in the estrogen catabolic pathway and in particular in catechol estrogen metabolism, the influence of dietary B on the catabolism of [³H]estradiol-17β has been studied in ovariectomized rats. Rats were given diets containing <0.1 or 40 mg B.kg⁻¹, ovariectomized and then infused with [³H]estradiol-17β using osmotic pumps. Analysis of urine samples for conjugated, catechol and non-catechol estrogens did not reveal any effects of B on the recovery or the metabolic fate of tritium from the infused estradiol. These results do not therefore support the proposal that B influences estrogen catabolism by interacting with catechol estrogens.     

Localization and developmental expression of the activin signal transduction proteins Smads 2, 3, and 4 in the baboon fetal ovary

We recently demonstrated that the reduction in the number of primordial follicles in ovaries of near-term baboon fetuses deprived of estrogen in utero was associated with increased expression of alpha-inhibin, but not activin betaA and betaB or the activin receptors. Therefore, we proposed that estrogen regulates fetal ovarian follicular development by controlling the intraovarian inhibin:activin ratio. As a prelude to conducting experiments to test this hypothesis, in the current study we determined whether the primate fetal ovary expressed Smads 2/3 and 4 and whether expression of these activin-signaling proteins was altered in fetal ovaries of baboons in which estrogen production was suppressed. Western blot analyses demonstrated that the 59 kDa Smad 2, 54 kDa Smad 3, and 64 kDa Smad 4 proteins were expressed in fetal ovaries of untreated baboons at both mid and late gestation and that the level of expression was not significantly altered in late gestation by in vivo treatment with CGS 20267 or CGS 20267 and estrogen. Immunocytochemistry localized Smads 2/3 and 4 to cytoplasm of oocytes and pregranulosa cells at midgestation and oocytes and granulosa cells of primordial follicles in late gestation. Smad 4 was also detected in granulosa cell nuclei in late gestation, and nuclear expression appeared to be decreased in fetal ovaries of baboons deprived of estrogen. The site of localization of Smads correlated with localization of the activin receptors IA and IIB, which we previously showed were abundantly expressed in oocytes and (pre)granulosa cells at both mid and late gestation and unaltered by estrogen deprivation. In summary, the results of the current study are the first to show that the intracellular signaling molecules required to transduce an activin signal are expressed in the baboon fetal ovary and that expression was not altered by estrogen deprivation in utero. These findings, coupled with our previous observations showing that estrogen deprivation reduced follicle numbers and upregulated/induced expression of inhibin but not activin or the activin receptors, lend further support to the hypothesis that estrogen regulates fetal ovarian folliculogenesis by controlling the intraovarian activin:inhibin ratio.