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F Courtin

Publications and source records attributed to F Courtin.

18 recordsLinked to original sources
PubMed1994

Induction of type III-deiodinase activity in astroglial cells by retinoids.

Thyroid hormones and retinoic acid (RA) are important modulators of growth, development, and differentiation. Type III deiodinase (D-III), which catalyzes thyroid hormones degradation in the brain and in cultured astroglial cells, is induced in astroglial cells by multiple pathways, including cAMP, 12.0-tetradecanoylphorbol-13-acetate (TPA), fibroblast growth factors, and thyroid hormones themselves. In the present study, the effects of retinoids on D-III activity were examined in astroglial cells cultures in a chemically defined medium devoid of hormones and growth factors. Incubation of astroglial cells with 5 microM all-trans-RA caused up to 200-fold increase in D-III activity, which reached a plateau after 48 h. The retinoid-induced increase in D-III activity was concentration dependent (0.5 microM all-trans-RA and 9-cis-RA producing half-maximal effect). Retinol was effective at physiological concentrations (1 and 10 microM). The 48 h effects of 5 microM all-trans-RA and 10 nM thyroid hormones on D-III activity were at least additive. Addition of 2 nM acidic fibroblast growth factor or 1 mM 8-bromo-cAMP for the last 8 h of a 48 h incubation with 5 microM all-trans-RA did not alter the induction by all-trans-RA, whereas 0.1 microM TPA in the same conditions produced an additive effect with all-trans-RA. All-trans-RA (5 microM) had little or no effect on type II deiodinase, the enzyme which catalyzes the activation of thyroxine to 3,5,3'-triiodothyronine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

12-O-tetradecanoylphorbol 13-acetate and fibroblast growth factor increase the 30-kDa substrate binding subunit of type II deiodinase in astrocytes.

Type II 5'-deiodinase (D-II) catalyzes the intracellular conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the brain. The D-II activity in astroglial cell cultures is induced by several pathways including cyclic AMP (cAMP), 12-O-tetradecanoylphorbol 13-acetate (TPA), and fibroblast growth factors (FGFs). We have examined the effect of TPA and FGFs on the 30-kDa substrate binding subunit of D-II, by affinity labeling with N-bromoacetyl-[125I]T4 in astroglial cells. TPA (0.1 microM), 20 ng/ml acidic FGF (aFGF), and 1 mM 8-bromo cyclic AMP all caused an increase in the 30-kDa protein. cAMP induced the greatest increase (fivefold) followed by TPA (3.2-fold) and FGF (2.8-fold). Glucocorticoids acted synergistically with cAMP and aFGF and promoted the effect of TPA. Affinity labeling was competitively inhibited by bromoacetyl-T4 > bromoacetyl-T3 > T4 > reverse T3 > iopanoic acid > T3 > 3,5,3'-triiodothyroacetic acid. The effect of TPA (0.1 microM) was maximum at 8 h and then gradually decreased. aFGF (20 ng/ml) plus heparin (17 micrograms/ml) induced a maximal 30-kDa increase at 8 h, which stayed stable for up to 24 h. The effect of aFGF was concentration dependent. Of the other growth factors studied, only basic FGF and platelet-derived growth factor induced small increases in the 30-kDa protein. Epidermal growth factor had little effect. In vitro labeling of cAMP, TPA, and aFGF-stimulated cell sonicates resulted in an increase in the 30-kDa protein that paralleled the increase in D-II activity.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1994

Sulfation after deiodination of 3,5,3'-triiodothyronine in rat cultured astrocytes.

The metabolism of [125I]T3 by rat astrocytes in culture was analyzed by Sephadex LH-20 chromatography and HPLC. The conjugates isolated on LH-20 were not hydrolyzed by glucuronidase, indicating the absence of glucuroconjugates. 3,3'-Diiodothyronine (3,3'T2) sulfate (3,3'T2-S) was the main product that accumulated in the medium over the T3 concentration explored (10 pM to 10 nM). The identity of the peak eluted as 3,3'T2-S was ascertained by its hydrolysis with sulfatase and the generation of 3,3'T2 identified by HPLC. 3'-Monoiodothyronine sulfate was also found in cells treated with 1 microM retinoic acid, i.e. with high type III deiodinase activity. No T3 sulfate (T3-S) was found as a metabolite of T3. Astrocytes did not break down 1 nM [125I]T3-S added to the medium. Astrocytes pretreated for 3 days with 10 nM T3 showed increased production of 3,3'T2-S from 10 nM [125I]T3. Exogenous [125I]3,3'T2 (20 nM) was conjugated to 3,3'T2-S released into the medium. Pretreatment of astrocytes with 10 nM T3 did not alter the production of 3,3'T2-S from 3,3'T2. Thus, T3 is metabolized in astrocytes by direct 5-deiodination, followed by sulfation. Whereas T3 induces its own deiodination and type III deiodinase activity, T3 does not regulate the sulfation of its main metabolite, 3,3'T2. This demonstration of sulfation of iodothyronines in cells originating from the brain raises the question of the role of this TH metabolic pathway in the brain.

Animals↗
PubMed1993

Evidence for cAMP-independent thyrotropin effects on astroglial cells.

Thyroid hormones are essential for normal brain development and function. Brain astroglial cells express type II iodothyronine 5'-deiodinase which converts thyroxine into 3,5,3'-triiodothyronine. This type II deiodinase is regulated through various signalling pathways, allowing probably for the local adaptation of the level of 3,5,3'-triiodothyronine. Our results demonstrated that thyrotropin was able to induce type II deiodinase activity in astrocytes. A thyrotropin receptor was demonstrated. It was not coupled, as in thyroid, to adenylyl cyclase and phospholipase C, but it stimulated cytosolic phospholipase A2. The stimulation by thyrotropin of both thyroxine synthesis in thyroid and its local activation in astrocytes, could protect the brain from variations in the level of 3,5,3'-triiodothyronine.

Adenylyl Cyclases↗
PubMed1992

Induction of type III deiodinase activity in astroglial cells by thyroid hormones.

The type III deiodinase (D-III) activity in astroglial cells is induced by multiple pathways activated by cAMP, 12-O-tetradecanoylphorbol-13-acetate (TPA), and fibroblast growth factors (FGFs). This study examines the effects of thyroid hormones on D-III activity in astroglial cells with or without induction by these factors. Addition of 10 nM T3 to the culture medium caused a slow increase in D-III activity, which reached a plateau after 48 h. This increase was concentration dependent (maximal response at 10 nM). Doses as low as 0.3 nM caused significant increases in D-III activity. The effect of T3 was reversible. A dose of 10 nM L-T3, D-T3, T4, 3,5,3'-triiodothyroacetic, or 3'-isopropyl-3,5-diiodothyronine produced 5- to 15-fold increases in D-III activity after 48 h. In contrast, 10 nM L-thyronine, 3-monoiodothyronine, 3,3'-diiodothyronine, 3,5-diiodothyronine, and rT3 were without effect. A dose of 10 nM T3 or T4 amplified the D-III activity stimulated by 0.1 microM TPA, 20 ng/ml acidic FGF, or 1 mM 8-bromo-cAMP 3- to 8-fold. Otherwise, T3 rapidly inhibited D-II activity. This inhibition was concentration dependent, with a half-maximal effect around 10 nM. In conclusion, thyroid hormones induce D-III activity and potentiate the D-III activity induced by cAMP, TPA, and FGFs in astroglial cells. These reversible effects together with inhibition of D-II activity may contribute to protect the brain against hyperthyroidism.

Animals↗
PubMed1991

Induction of 5-deiodinase activity in astroglial cells by 12-O-tetradecanoylphorbol 13-acetate and fibroblast growth factors.

In the brain, 5'-deiodinase (5'-D) is responsible for the metabolic activation of thyroxine (T4) into 3,5,3'-triiodothyronine (T3) and 5-deiodinase (5-D) deiodinates T4 and T3 into inactive metabolites. This study examines the effects of factors known to induce astroglial 5'-D activity on the 5-D activity in cultured rat astroglial cells. The potencies of these factors were compared after 8 h of incubation, when stimulations by these factors near their maximal effects. 12-O-Tetradecanoylphorbol 13-acetate (TPA) at 10(-7) M was a potent inducer of 5-D activity, producing a 30- to 80-fold increase after 8 h. The maximal effect of TPA was observed after about 14 h. The TPA stimulation of 5-D activity was not dependent on glucocorticoids, unlike 5'-D activity. In comparison with TPA, 8-bromo-cyclic AMP (10(-3) M) was a poor inducer of 5-D activity whereas it is an excellent inducer of 5'-D activity. It produced a 2- to 20-fold increase in 5-D activity after 8 h. Natural acidic fibroblast growth factor (20 ng/ml) produced a degree of stimulation similar to that of TPA after 8 h. The maximal effect of acidic fibroblast growth factor was observed after about 16 h (until a 120-fold increase). Recombinant acidic fibroblast growth factor also induced 5-D activity. Basic fibroblast growth factor was less potent than acidic fibroblast growth factor for increasing 5-D activity (maximal increase by 40- to 50-fold after 8 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Induction of 5'-deiodinase activity in rat astroglial cells by acidic fibroblast growth factor.

Acidic fibroblast growth factor (aFGF) induced a large increase in the type II 5'-deiodinase (5'D) activity in astroglial cells. This required a time lag of about 4 h. Half-maximal stimulation was obtained with about 7 ng/ml aFGF. This factor at 20 ng/ml induced several times more 5'D activity than did 20 ng/ml basic fibroblast growth factor (bFGF) after 8 h incubation. aFGF (20 ng/ml) produced a 10-50-fold increase in 5'D activity after 24 h, whereas the effect of 20 ng/ml bFGF had disappeared after 24 h. Heparin (17 micrograms/ml) potentiated the 5'D response to natural and recombinant aFGF. Glucocorticoids amplified the aFGF-induction of 5'D activity. This is the first demonstration in astroglial cells that a growth factor can regulate the 5'D activity.

Animals↗
PubMed1990

Effects of transforming growth factor beta 1 on astroglial cells in culture.

The effects of transforming growth factor beta 1 (TGF beta 1) on DNA synthesis and functional differentiation of astroglial cells cultured in serum-free medium were investigated. TGF beta 1 diminished and delayed the peak of DNA synthesis induced by serum. TGF beta 1-treated cells were larger than control cells. This factor delayed the appearance of process-bearing cells induced by acidic fibroblast growth factor treatment and also affected the astrocyte-specific enzyme glutamine synthetase (GS), whose accumulation is under hydrocortisone (HC) control. TGF beta 1 inhibited the induction of GS activity by HC in a dose- and time-dependent manner. Moreover, pretreatment with TGF beta 1 for 4 h maintained the inhibition of GS activity for approximately 16 h after removal of this factor from culture medium. These results suggest that TGF beta 1 may be an important regulator of astrocyte growth and differentiation.

Animals↗
PubMed1989

Induction of type II 5'-deiodinase activity in cultured rat astroglial cells by 12-O-tetradecanoylphorbol-13-acetate: dependence on glucocorticoids.

The effect of an activator of protein kinase C, 12-O-tetradecanoylphorbol-13-acetate (TPA), on the 5'-deiodinase (5'D) activity was studied in rat astroglial cells cultured in chemically defined medium. TPA promoted a large increase in the type II 5'D activity, which was maximal 5-10 h after addition of TPA and then declined to the basal level at 24 h. The optimal TPA concentration was 10(-7) M. TPA and 8-Br-cAMP, an other inducer of 5'D activity were antagonist. Otherwise, TPA stimulated 5'D activity only in the presence of glucocorticoids at concentrations from 10(-8) M to 10(-4) M. Glucocorticoids alone induced a slight increase in 5'D activity. These data indicate that protein kinase C contributes to the control of 5'D activity in astroglial cells and that its action is dependent on glucocorticoids.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1988

Thyroid hormone metabolism in neuron-enriched primary cultures of fetal rat brain cells.

The metabolism of thyroxine (T4) by cultures of embryonic-rat brain cells grown in a chemically defined medium was studied. Cells in these cultures were predominantly neurons, characterized by the developmental increase of the binding of [3H]flunitrazepam to the high-affinity (0.67 nM) benzodiazepine neuronal receptors. The cultures also contained astrocytes, characterized by immunological studies using an anti-glial fibrillary acidic protein (GFAp) and by the increase in glutamine synthetase (GS). Incubation of the cells, in situ, with 125I-labelled 3,5,3'-triiodothyronine (T3) showed the presence of a single class of high-affinity nuclear receptors for T3 with a maximal binding capacity of 270-470 fmol T3/mg DNA and a Kd of 63 +/- 13 pM. Cells incubated in situ with 50 pM [125I]T4 actively metabolized the hormone. The major metabolite, 3,3',5'-triiodothyronine (rT3) (159 +/- 43 fmol/4 h/mg DNA), was almost completely released into the medium. T3 was a minor metabolite (77 +/- 3 fmol/4 h/mg DNA), 75% of which accumulated in the cells. Of this T3, 35% was bound to the nuclear receptors after 4 h of incubation. In vitro assays showed that the 5'-deiodinase activity increased during culture and the 5-deiodinase decreased slightly. Cytosine-arabinoside (ARAc) treatment of the cultures reduced the DNA content per culture dish, corresponding to a fall in the number of GFAp-positive cells (astrocytes) and to a decrease in GS. A small increase in the number of benzodiazepine sites was observed. ARAc treatment markedly reduced the T3 production (14.5 +/- 0.7 fmol/4 h/mg DNA) and did not change the rT3 production. We suggest that T4 is metabolized to T3 in astrocytes, taken up by neurons and binds to their nuclear receptors.

Animals↗
PubMed1988

Induction of type II 5'-deiodinase activity by cyclic adenosine 3', 5'-monophosphate in cultured rat astroglial cells.

Cultured astroglial cells were found to contain a type II 5'-deiodinase (5'D) activity which was increased by 10(-3) M (Bu)2cAMP but not by 2 X 10(-3) M n-butyrate. 8-Bromo-cAMP (8-Br-cAMP) (10(-3) M) also increased this enzyme activity. Cycloheximide (2 micrograms/ml) inhibited the 8-Br-cAMP effect on 5'D activity. Forskolin (10(-5) M), cholera toxin (5 micrograms/ml), 10(-5) M isoproterenol, and 3 X 10(-6) M norephinephrine also increased the 5'D activity of astroglial cells. After a 4-h incubation these agents or cAMP analogs had maximal effect, and enzyme activities were 6- to 14-fold above control value. The stimulatory effects of isoproterenol and norepinephrine were almost completely reversed after 8 h incubation. The induction of 5'D activity by isoproterenol or norepinephrine was inhibited by the beta-adrenergic antagonist alprenolol (5 X 10(-6) M). The effect of norepinephrine was not significantly affected by the alpha 1-adrenergic antagonist, prazosin (10(-5) M). Thus, 5'D activity is controlled by agents increasing cAMP in astroglial cells, and in particular by the neurotransmitter, norephinephrine, via a beta-adrenergic mechanism.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1986

Thyroid hormone metabolism by glial cells in primary culture.

The metabolism of thyroxine (T4) and triiodothyronine (T3) in cultured glial cells was studied in situ. Cultures were prepared from fetal rat brain and grown for the last 4 days in a chemically defined medium (CDM). They contained astrocytes and oligodendrocytes as shown by the enzyme markers, glutamine synthetase and 2',3'-cyclic nucleotide phosphohydrolase. These cells contained high affinity (22-33 pM), limited capacity (120-230 fmol/mg DNA) nuclear receptors for T3. Cells incubated in situ with 50 pM [125I]T4 actively metabolized the hormone. The major iodothyronine produced was T3 (220-570 fmol/4 h/mg DNA). About 70% accumulated in the cells, the remainder was released into the medium. Within the cells, T3 was partly bound to the nuclear receptors (16.5-20 fmol/mg DNA). Reverse T3 (rT3) was a minor metabolite (30-45 fmol/4 h/mg DNA); it was almost completely released into the medium. The half-life of [125I]T3 (50 pM) was found to be about 15 h. These results show that, in situ, glial cell cultures containing astrocytes and oligodendrocytes grown in CDM actively deiodinate T4 to T3 and degrade T3 rather slowly.

Animals↗
PubMed1985

Spectral characteristics and catalytic properties of thyroid peroxidase-H2O2 compounds in the iodination and coupling reactions.

Hog thyroid peroxidase (TPO) was highly purified in order to study the spectral properties and catalytic specificities of its H2O2 compounds in iodothyronine biosynthesis. Purified TPO exhibited a Soret spectrum with an absorption maximum at 410 nm and had an A410/A280 value of 0.55. Protein iodination was only catalyzed under conditions which allowed formation of the transient TPO compound I (Fe(IV)-pi o+). On addition of an equimolar amount of H2O2, TPO formed a stable compound with an absorption maximum at 417 nm. This compound efficiently catalyzed the coupling reaction, but was unable to iodinate proteins. It catalyzed the formation of 1 mol iodothyronines/mol TPO, and therefore retained two oxidizing equivalents per molecule. It is proposed that this compound constitutes a second form of compound I whose structure might be Fe(IV)-Ro, analogous to that of cytochrome c peroxidase compound I. In the presence of an excess of H2O2, it formed TPO-compound III with an absorption maximum at 420 nm. TPO-compound III catalyzed neither the iodination nor the coupling reaction.

Animals↗
PubMed1985

Transient neonatal hyperthyroidism results in hypothyroidism in the adult rat.

Adult rats who had neonatal hyperthyroidism (NH) have reduced BW and serum T4, T3, and TSH concentrations. Pituitary TSH responses to TRH administration under basal, T4-suppressed, and propylthiouracil-stimulated conditions suggest that the thyrotroph of these animals is more sensitive to the feedback effects of thyroid hormones. These studies were undertaken to examine, with the use of various thyroid hormone-responsive variables, thyroid status of adult NH rats. NH was induced by 12 daily sc injections of T4 (0.4 microgram/g BW) to neonatal male Sprague-Dawley rats. Adult NH and control rats were then studied at 120 days of age. Adult NH rats had significantly decreased mean BW (P less than 0.001), and serum T4 (P less than 0.005), T3 (P less than 0.001), and TSH (P less than 0.001) concentrations. The percent decreases were 12% for T4, 20% for T3, and 27% for TSH in adult NH rats. Mean pituitary GH concentration and hepatic alpha-glycerophosphate dehydrogenase and malic enzyme activities were significantly decreased in adult NH rats to 54% (P less than 0.005), 52% (P less than 0.025), and 39% (P less than 0.001), respectively, of control values. Mean pituitary TSH concentrations were similar in adult NH and control rats. Mean hepatic T4 5'-deiodinase activity of adult NH rats [200 +/- (SE) 23 fmol T3/min X mg protein] was significantly decreased to 56% of control levels (355 +/- 31 fmol T3/min . mg protein; P less than 0.005). Mean pituitary T4 5'-deiodinase activity of adult NH rats (32.8 +/- 3.3 fmol T3/min . mg protein) was significantly increased compared with that of control rats (21.2 +/- 1.7 fmol T3/min . mg protein; P less than 0.025). These changes are consistent with a hypothyroid state in adult NH rats. The observation of decreased serum TSH concentration and enhanced thyrotroph sensitivity to thyroid hormones in the face of increased pituitary T4 5'-deiodinase activity suggests that increased thyrotroph monodeiodination of T4 may be the central biochemical aberration responsible for the hypothyroid state in adult NH rats.

Animals↗
PubMed1985

Subcellular localization of thyroxine 5'-deiodinase activity in bovine anterior pituitary.

Bovine anterior pituitary glands were fractionated by differential centrifugation. T4 5'-monodeiodination to T3 was found predominantly in microsomal fractions (M2; 105,000 . g pellet) enriched in glucose-6-phosphatase and 5'-nucleotidase activities. T4 5'-deiodinase activity in M2 fraction was 85.2 fmol T3/min X mg protein and represented an 8.5-fold enrichment over homogenate specific activity (10.6 fmol T3/min . mg protein). Further subcellular localization of the T4 5'-deiodinase was effected by discontinuous sucrose density gradient centrifugation. Maximum T4 5'-deiodinase activity was found in fraction P5 at the interface of densities 1.18/1.20 (200 fmol T3/min . mg protein) and correlated with the profile of glucose-6-phosphatase and not with that of 5'-nucleotidase, the maximum activity of which was recovered in fraction P1 at the interface of densities 1.03/1.12. Electron microscopic examination of the fractions confirmed that P5 contained in excess of 90% rough membranes in contrast to 10% or less in P1. Characterization of T4 5'-deiodinase activity was carried out in M2 preparations. The reaction was thiol dependent, requiring the presence of 50 mM dithiothreitol or more (Km, 38 mM), with a maximum velocity of 55-150 fmol T3/min . mg protein (n = 8). Enzyme activity was substrate dependent, with a Km for T4 between 35-70 nM. 5'-Monodeiodination of T4 was abolished by heating to 70 C for 30 min and was unaffected by EDTA. Propylthiouracil and methimazole did not inhibit T3 generation. Iopanoic acid, on the other hand, was a competitive inhibitor of the 5'-monodeiodination reaction, abolishing T3 production in a dose-dependent manner with a Ki of 3 microM. These data indicate that the bovine anterior pituitary contains significant T4 5'-deiodinase activity, which shares many properties of the type II 5'-deiodinase of the rat. Bovine anterior pituitary T4 5'-deiodinase appears to be predominantly localized in the rough endoplasmic reticulum.

Animals↗
PubMed1984

Reduction of lactoperoxidase-H2O2 compounds by ferrocyanide: indirect evidence of an apoprotein site for one of the two oxidizing equivalents.

The titration by ferrocyanide and the localization of the oxidizing equivalents of lactoperoxidase "compound II" were studied as a function of pH. It was demonstrated that 1) whatever the pH, the structure of lactoperoxidase "compound II" was compatible with a Fe IV R degree state, 2) at acidic pH, ferrocyanide preferentially reduced the oxidizing equivalent localized on the heme iron to give an Fe III R degree compound, 3) at pH 4.2 only the Fe III R degree form was obtained after reduction of lactoperoxidase "compound II" with one mole of ferrocyanide and whereas at pH greater than 4.2, a mixture of both Fe III R degree and Fe IV R forms was present, 4) lowering the pH from 7.2 to 4.0 induced a transition of Fe IV R state to Fe III R degree state, but increasing the pH from 4.0 to 7.2 did not permit the formation of Fe IV R compound from Fe III R degree compound.

Apoenzymes↗