Nutrition and fetal brain maturation. I. Responses in vitro and in vivo

Proliferative growth of neonatal cerebellar cells in culture: regulation by male and by maternal serum in late gestation

Neonatal cerebellar cells were utilized as a model system to examine the effect of 20 day pregnant rat serum on proliferative growth in the CNS. Cells were prepared by mechanical dissociation and cultured as mixed cells or populations enriched in astrocytes or oligodendrocytes. Cell proliferation was estimated by measurement of DNA, protein, and/or mitochondrial reductase activity (MTT). When mixed cells were incubated with 10% male rat serum, both total DNA and protein content increased after 6 days of culture. By contrast, neither of these parameters were altered in cultures incubated with 10% pregnant serum. When cells were incubated with either male or pregnant sera, changes in MTT activity paralleled changes in protein content. Graded concentrations of pregnant serum (5-20%) added to mixed cell cultures produced consistently lower MTT values when compared with identical concentrations of male serum. In addition, MTT activity was diminished in both astrocytes and oligodendrocytes incubated with graded concentrations of pregnant sera when compared with similar concentrations of non-pregnant sera. When potential effects of these different sera on the cell cycle were examined, an increase in the number of cells in the S and G2/M phase was similar, and DNA doubling began to increase at 96 hrs in the presence of either male or 20 day pregnant sera. Thus the inhibition of cell growth by pregnant serum was not likely a result of either cytotoxicity or a delay of entry of cells into the cell cycle. To examine whether this inhibition of cell growth may reflect the effect of pregnant serum on endogenous growth factor production, we tested the production of IGF-II by cerebellar cells. production of an endogenous source of IGF-II was apparent using an RNAse protection assay and was noted using Slot Blot analysis of mRNA extracted at sequential times during cell incubation. Mixed cell cultures also secreted immunologically defined IGF-II. These observations are consistent with the previous demonstration that the fraction of pregnant serum which bound IGF-II also inhibited cell growth. The inhibitory effect of pregnant serum was diminished by preincubating aliquots of sera with graded concentrations of IGF-I prior to adding sera to tissue culture medium. Pregnant serum inhibition was also diminished by prolonging incubation times beyond 6 days. The blunting of pregnant serum inhibition may have been consequent to either a continuing production of endogenous growth factors or to the potential emergence of resistant cells due to prolonged tissue culture incubation.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin-like growth factors and binding proteins in the fetal rat: alterations during maternal starvation and effects in fetal brain cell culture

Maternal malnutrition adversely affects fetal body and brain growth during late gestation. We utilized a fetal brain cell culture model to examine whether alternations in circulating factors may contribute to reduce brain growth during maternal starvation; we then used specific immunoassay and western blotting techniques, and purified peptides to investigate the potential role that altered levels of insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) may play in impaired growth during maternal nutritional restriction. Fetal, body, liver, and brain weight were reduced after 72 hr maternal starvation, and plasma from starved fetuses were less potent than fed fetal plasma in stimulating brain cell growth. Circulating levels of IGF-I were reduced in starved compared to fed fetuses, while levels of IGF-II were similar in both groups. In contrast, [125I]-IGF-I binding assay demonstrated an increase in the availability of plasma IGFBPs following starvation. Western ligand blotting and densitometry indicated that levels of 32 Kd IGFBPs were 2-fold higher in starved compared to fed fetal plasma. Immunoblotting and immunoprecipitation with antiserum against rat IGFBP-1 confirmed that heightened levels of immunoreactive IGFBP-1 accounted for the increase in 32 Kd IGFBPs in starved plasma. Levels of 34 Kd BPs, representing IGFBP-2, were unaffected by starvation. Reconstitution experiments in cell culture showed that IGF-I promoted fetal brain cell growth, and that when they were supplemented with IGF-I, the growth promoting activity of starved fetal plasma was restored to fed levels. These changes were measured using MTT to assess mitochondrial reductase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Retardation of fetal brain cell growth during maternal starvation: circulating factors versus altered cellular response

Maternal starvation inhibits fetal brain development during late gestation in the rat. To determine whether intrinsic or extrinsic factors might be the principal contributor to altered growth, brain cells from 20 day fetuses were cultured in a 96 well plate with MEM and 10% adult rat serum. Tissue growth was monitored by spectrophotometric measurement of the mitochondrial reduction of a chromagen 3-(4,5 dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide (MTT). After 1, 4 or 6 days incubation, MTT activity in non confluent cultures was shown to be directly related to tissue mass. When fetal brain cell cultures were incubated with 1% and 10% concentrations of adult rat serum, an 11-fold increase in MTT activity paralleled a 15-fold increase in tritiated thymidine incorporation. The impact of maternal starvation on fetal brain cell growth was examined by measuring MTT activity in fetal brain cells from fed and starved mothers. When cultures were incubated for 6 days with graded concentrations of fed adult serum (1.25-10%), the MTT response was slightly but consistently lower in cells from starved when compared with cells from fed mothers. By contrast, a marked difference in MTT activity which was paralleled by a lower DNA content became apparent when fetal rat brain cells were incubated with starved adult serum. Fetal serum and adult male serum were found to support growth equally well, while incubation of fetal brain cells with maternal sera resulted in lower MTT values than with the corresponding fetal sera. When cells were incubated with fetal sera pooled from starved mothers, MTT activity was decreased by 42 to 45%.(ABSTRACT TRUNCATED AT 250 WORDS)

The impact of maternal serum on development of enolase activity in fetal rat brain cell culture

The effect of gestational age on serum-mediated changes in enolase activity was tested in a fetal rat brain cell culture. After 6 days exposure to graded concentrations (10 and 20%) of nonpregnant female rat sera, enolase activity in brain cell cultures increased from 2.83 +/- 0.03 to 3.74 +/- 0.19 mumol/min/mg protein, P less than 0.01. By contrast, similar concentrations of 20-day maternal serum progressively decreased enzyme activity from 1.52 +/- 0.14 to 1.19 +/- 0.08 mumol/min/mg protein. The inhibitory effect was apparent at 14 days gestation and became progressively greater during late gestation to reach a maximum at 20 days. Combining equal concentrations of 20-day pregnant with either nonpregnant or adult male serum neutralized the inhibitory activity. When serum from 20-day pregnant rats was partitioned by a dialysis membrane with a 50,000 MW pore size, inhibitory activity could be similarly neutralized by male or nonpregnant female serum. When 20-day maternal serum was passed successively through filters with a greater than 300,000, 100,000, and 50,000 MW exclusion, the inhibitory activity was apparent in all fractions excluded by a molecular weight of 50,000. No inhibition was apparent in fractions that were not excluded by 50,000 MW pore size. Inhibition of enolase activity was greatest in the fraction with MW greater than 300,000. Binding of IGF II could also be demonstrated in this fraction. Binding of IGF II was evident in the fraction greater than 100,000 MW but could not be demonstrated in fractions with a lower molecular weight. The presence of mRNA for IGF II in 20-day fetal rat brain cell cultures was evident when total cellular RNA was analyzed by an RNAase protection assay. It is proposed that a high-molecular-weight component of maternal serum in late gestation can bind endogenously generated IGF II. Such binding, by depleting the necessary growth factors, could inhibit in vitro growth and development of enolase activity.

Developmental pattern of poly (ADP-ribose) synthetase and NAD glycohydrolase in the brain of the fetal and neonatal rat

Poly (ADP-ribose) synthetase and NAD glycohydrolase were examined in nuclear fractions from rat brain at sequential times during late fetal and the first two weeks of neonatal life. In whole brain, both enzymes were demonstrable at all stages of development, but followed separate patterns. Activity of the synthetase which was greatest in fetal life, fell steadily with fetal maturation from 3.90 +/- 0.06 nmol/mg DNA at 16 days, to reach a nadir of 1.36 +/- 0.09 nmol/mg DNA on the 4th postnatal day. Subsequently it underwent a non sustained neonatal rise reaching a peak of 2.46 +/- 0.07 nmol/mg DNA on the 8th day. By contrast, NAD glycohydrolase activity increased steadily throughout late fetal and during the first two weeks of neonatal life, from 12.77 +/- 0.40 nmol/mg DNA on day 16 of gestation to 25.80 +/- .95 nmol/mg DNA on neonatal day 12. In neonatal cerebellum the activity of poly (ADP-ribose) synthetase was greater at 8 than at 4 days, could be stimulated with graded concentrations of sonicated DNA up to 100 micrograms, but was inhibited by higher concentrations of DNA and by all concentrations of exogenous histone. In an in vitro culture system of fetal rat brain cells, the activity of poly (ADP-ribose) synthetase increased steadily over six days. Cycloheximide 10(-3) M completely inhibited the activity of this enzyme. NAD glycohydrolase activity increased progressively in vitro, and after 6 days in cycloheximide (10(-3) M), the cultures contained significantly greater levels of enzyme activity. It is suggested that changing activities of poly (ADP-ribose) synthetase and NAD glycohydrolase could both provide potential markers for brain cell differentiation in this system.