Fetal brain regional responses to cerebral hypoperfusion: modulation by estrogen

Gestational exposure to bisphenol A induces region-specific changes in brain metabolomic fingerprints in sheep

Fetal brain development depends on maternofetal thyroid function. In rodents and sheep, perinatal BPA exposure is associated with maternal and/or fetal thyroid disruption and alterations in central nervous system development as demonstrated by metabolic modulations in the encephala of mice. We hypothesized that a gestational exposure to a low dose of BPA affects maternofetal thyroid function and fetal brain development in a region-specific manner. Pregnant ewes, a relevant model for human thyroid and brain development, were exposed to BPA (5 µg/kg bw/d, sc). The thyroid status of ewes during gestation and term fetuses at delivery was monitored. Fetal brain development was assessed by metabolic fingerprints at birth in 10 areas followed by metabolic network-based analysis. BPA treatment was associated with a significant time-dependent decrease in maternal TT4 serum concentrations. For 8 fetal brain regions, statistical models allowed discriminating BPA-treated from control lambs. Metabolic network computational analysis revealed that prenatal exposure to BPA modulated several metabolic pathways, in particular excitatory and inhibitory amino-acid, cholinergic, energy and lipid homeostasis pathways. These pathways might contribute to BPA-related neurobehavioral and cognitive disorders. Discrimination was particularly clear for the dorsal hippocampus, the cerebellar vermis, the dorsal hypothalamus, the caudate nucleus and the lateral part of the frontal cortex. Compared with previous results in rodents, the use of a larger animal model allowed to examine specific brain areas, and generate evidence of the distinct region-specific effects of fetal BPA exposure on the brain metabolome. These modifications occur concomitantly to subtle maternal thyroid function alteration. The functional link between such moderate thyroid changes and fetal brain metabolomic fingerprints remains to be determined as well as the potential implication of other modes of action triggered by BPA such as estrogenic ones. Our results pave the ways for new scientific strategies aiming at linking environmental endocrine disruption and altered neurodevelopment.

Enhancement of rapamycin production by metabolic engineering in Streptomyces hygroscopicus based on genome-scale metabolic model

Rapamycin, as a macrocyclic polyketide with immunosuppressive, antifungal, and anti-tumor activity produced by Streptomyces hygroscopicus, is receiving considerable attention for its significant contribution in medical field. However, the production capacity of the wild strain is very low. Hereby, a computational guided engineering approach was proposed to improve the capability of rapamycin production. First, a genome-scale metabolic model of Streptomyces hygroscopicus ATCC 29253 was constructed based on its annotated genome and biochemical information. The model consists of 1003 reactions, 711 metabolites after manual refinement. Subsequently, several potential genetic targets that likely guaranteed an improved yield of rapamycin were identified by flux balance analysis and minimization of metabolic adjustment algorithm. Furthermore, according to the results of model prediction, target gene pfk (encoding 6-phosphofructokinase) was knocked out, and target genes dahP (encoding 3-deoxy-d-arabino-heptulosonate-7-phosphate synthase) and rapK (encoding chorismatase) were overexpressed in the parent strain ATCC 29253. The yield of rapamycin increased by 30.8% by knocking out gene pfk and increased by 36.2 and 44.8% by overexpression of rapK and dahP, respectively, compared with parent strain. Finally, the combined effect of the genetic modifications was evaluated. The titer of rapamycin reached 250.8 mg/l by knockout of pfk and co-expression of genes dahP and rapK, corresponding to a 142.3% increase relative to that of the parent strain. The relationship between model prediction and experimental results demonstrates the validity and rationality of this approach for target identification and rapamycin production improvement.

Expression of Nitric Oxide Synthase Isoforms in the Ovine Fetal Brain: Alteration by Hormonal and Hemodynamic Stimuli

OBJECTIVE

Nitric oxide (NO) is synthesized in the brain through the action of three isoforms of nitric oxide synthase (NOS). The local generation of NO in neurons, glia, and vasculature modulates neuronal activity, as well as regional cerebral blood flow. We propose that, in the fetal brain, cerebral hypoperfusion alters the expression of NOS isoforms, and that estrogen administration modulates the NOS response to hypoperfusion.

METHODS

Sixteen chronically catheterized fetal sheep of known gestational age (124 to 128 days' gestation) were subjected to a 10-minute period of brachiocephalic occlusion (BCO) or to sham BCO; half of these fetuses were subjected to subcutaneous implant, which released 17beta-estradiol (E2; 0.25 mg/d) or placebo. Brain tissue was collected for mRNA and protein extraction 1 hour after the start of the BCO or sham BCO.

RESULTS

All three isoforms of NOS were identified in fetal brain at both the mRNA and protein levels. BCO increased NOS1 (hippocampus, brainstem), NOS2 (hypothalamus), and NOS3 (hippocampus, cortex) at the protein level. Estradiol alone increased NOS1 (brainstem, cortex), NOS2 (hippocampus, hypothalamus), and NOS3 (brainstem, cerebellum) at the protein level, changes that were not mirrored at the mRNA level. The combination of BCO and estradiol produced smaller changes in NOS1 (brainstem, cortex), NOS2 (hippocampus, hypothalamus), and NOS3 (brainstem) protein levels than those produced by either stimulus alone.

CONCLUSIONS

We conclude that the fetal brain expresses all isoforms of NOS, and that NOS expression is altered by both BCO and estradiol, but that the most prevalent effect of estradiol is to reduce specific NOS responses to cerebral hypoperfusion. The present results suggest the possibility that the neuroendocrine responses to estradiol and BCO are modulated by central nervous system (CNS) NO biosynthesis.

Comparative metabolic profiling reveals the key role of amino acids metabolism in the rapamycin overproduction by Streptomyces hygroscopicus

Rapamycin is an important natural macrolide antibiotic with antifungal, immunosuppressive and anticancer activity produced by Streptomyces hygroscopicus. In this study, a mutant strain obtained by ultraviolet mutagenesis displayed higher rapamycin production capacity compared to the wild-type S. hygroscopicus ATCC 29253. To gain insights into the mechanism of rapamycin overproduction, comparative metabolic profiling between the wild-type and mutant strain was performed. A total of 86 metabolites were identified by gas chromatography–mass spectrometry. Pattern recognition methods, including principal component analysis, partial least squares and partial least squares discriminant analysis, were employed to determine the key biomarkers. The results showed that 22 potential biomarkers were closely associated with the increase of rapamycin production and the tremendous metabolic difference was observed between the two strains. Furthermore, metabolic pathway analysis revealed that amino acids metabolism played an important role in the synthesis of rapamycin, especially lysine, valine, tryptophan, isoleucine, glutamate, arginine and ornithine. The inadequate supply of amino acids, or namely “nitrogen starvation” occurred in the mutant strain. Subsequently, the exogenous addition of amino acids into the fermentation medium of the mutant strain confirmed the above conclusion, and rapamycin production of the mutant strain increased to 426.7 mg/L after adding lysine, approximately 5.8-fold of that in the wild-type strain. Finally, the results of real-time PCR and enzyme activity assays demonstrated that dihydrodipicolinate synthase involved with lysine metabolism played vital role in the biosynthesis of rapamycin. These findings will provide a theoretical basis for further improving production of rapamycin.

Proximity of term labor deepens the fall of Doppler impedance in the fetal cerebral arteries

OBJECTIVE

To determine the existence of Doppler changes in the fetal vertebral, middle cerebral and umbilical arteries prior to term labor.

METHODS

Five hundred and twenty eight Doppler examinations of the vertebral (VA), middle cerebral (MCA) and umbilical (UA) arteries resistance indices (RI) were performed between 37 and 41 weeks gestation. For each artery, values were converted into multiples of the median (MoM) and were divided into four groups according to the interval to labor and compared using Kruskal-Wallis tests. Subsequently, values were plotted in scattergrams and linear regressions and 95% confidence intervals were calculated. Finally, using multivariate analysis and model averaging, the importance and interrelationship of Doppler measurements in the explanation of the interval to labor was evaluated.

RESULTS

Univariate and multivariate analysis confirmed that, independently of gestational age, fetuses examined close to labor presented more intense Doppler changes in the cerebral arteries with a significant reduction of the VA RI and MCA RI. This reduction was larger in the MCA. No significant changes were detected in the UA.

CONCLUSION

Before the onset of term labor, the fetal cerebral flow presents an additional reduction of impedance, which is more intense in the MCA system.

Fetal hypothalamus-pituitary-adrenal responses to estradiol sulfate

Estradiol (E(2)) is an important modifier of the activity of the fetal hypothalamus-pituitary-adrenal axis. We have reported that estradiol-3-sulfate (E(2)SO(4)) circulates in fetal blood in far higher concentrations than E(2) and that the fetal brain expresses steroid sulfatase, required for local deconjugation of E(2)SO(4). We performed the present study to test the hypothesis that chronic infusion of E(2)SO(4) chronically increases ACTH and cortisol secretion and that it shortens gestation. Chronically catheterized fetal sheep were treated with E(2)SO(4) intracerebroventricular (n = 5), E(2)SO(4) iv (n = 4), or no steroid infusion (control group, n = 5). Fetuses were subjected to arterial blood sampling every other day until spontaneous birth for plasma hormone analysis. Treatment with E(2)SO(4) attenuated preparturient increases in ACTH secretion near term without affecting the ontogenetic rise in plasma cortisol. Infusion of E(2)SO(4) intracerebroventricularly significantly increased plasma E(2), plasma E(2)SO(4), and plasma progesterone and shortened gestation compared with all other groups. These results are consistent with the conclusion that E(2)SO(4): 1) interacts with the hypothalamus-pituitary-adrenal axis primarily by stimulating cortisol secretion and inhibiting ACTH and pro-ACTH secretion by negative feedback; and 2) stimulates the secretion of E(2) and E(2)SO(4). We conclude that the endocrine response to E(2)SO(4) in the fetus is not identical with the response to E(2).

Expression of organic anion transporters 1 and 3 in the ovine fetal brain during the latter half of gestation

Development and maturation of the fetal brain is critical for homeostasis in utero, responsiveness to fetal stress and, in ruminants, control of the timing of birth. In the sheep, as in the human, the placenta secretes estrogen and other signaling molecules into both the fetal and maternal blood, molecules whose entry or exit across the blood-brain barrier is likely to be facilitated by transporters. The purpose of this study was to test the hypothesis that the ovine fetal brain expresses organic anion transporters, and that the expression of these transporters varies as a function of brain region and fetal gestational age. Brains and pituitaries were collected at the time of sacrifice from fetal and newborn sheep at 80, 100, 120, 130, 145 days gestation and on the first day of postnatal life (parturition in sheep is at approximately 147 days gestation). Hypothalamus, medullary brainstem, cerebellum, and pituitary were processed for mRNA extraction and synthesis of cDNA (4-5/group). Real-time PCR analysis of OAT1 and OAT3 expression revealed significant expression of both genes in all of the tissues tested. In hypothalamus and cerebellum, there were statistically significant increases in the expression of one or both genes towards the end of gestation. In medullary brainstem and pituitary, the levels of expression were relatively unchanged as there were no statistically significant changes with developmental age. We conclude that the ovine fetal brain expresses both OAT1 and OAT3, that the pattern of expression suggests an increasing role for these transporters in the physiology of the developing fetal brain as the fetus nears the time of spontaneous parturition.

Cerebral hypoperfusion increases estrogen receptor abundance in the ovine fetal brain and pituitary

BACKGROUND/AIMS

Estrogen is an important component of fetal neuroendocrine function in late-gestation fetal sheep; however, little is known about the regulation of estrogen receptor abundance in the brain and pituitary of fetuses. The present study was performed to test the hypotheses that estrogen receptor abundance in the fetal brain and pituitary are influenced by circulating estradiol concentrations and that they are acutely regulated after cerebral hypoperfusion.

METHODS

We studied 16 time-dated fetal sheep (124-128 days gestation) that were chronically catheterized and instrumented at least 5 days before study. Four groups (n = 4 each) were studied in which fetuses received estradiol (0.25 mg/day, producing physiological increases in fetal plasma estradiol concentrations) or placebo implants, and in which fetuses received a 10-min period of brachiocephalic occlusion (BCO) or sham-BCO. One hour after BCO or sham-BCO, fetuses were euthanized and tissues rapidly removed for analysis of estrogen receptors (ER)-alpha and -beta at the mRNA and protein levels.

RESULTS

Both BCO and estradiol treatment were effective in changing ER expression, although the effects were region-specific. BCO dramatically increased ER-alpha in the pituitary and both ER-alpha and ER-beta in the brainstem, while decreasing ER-alpha expression in the hypothalamus. Estradiol treatment decreased ER-alpha expression in the hypothalamus, whereas it increased ER-alpha expression in the brainstem, cerebral cortex and hippocampus.

CONCLUSIONS

We conclude that the expression of ER-alpha and ER-beta in the brain and pituitary of fetal sheep are influenced by circulating estrogen concentrations and acutely regulated in response to cerebral hypoperfusion.