| 1. |
- Åberg, N David, 1970, et al.
(författare)
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Insulin-like growth factor-I increases astrocyte intercellular gap junctional communication and connexin43 expression in vitro.
- 2003
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Ingår i: Journal of neuroscience research. - : Wiley. - 0360-4012. ; 74:1, s. 12-22
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Tidskriftsartikel (refereegranskat)abstract
- Connexin43 (cx43) forms gap junctions in astrocytes, and these gap junctions mediate intercellular communication by providing transport of low-molecular-weight metabolites and ions. We have recently shown that systemic growth hormone increases cx43 in the brain. One possibility was that local brain insulin-like growth factor-I (IGF-I) could mediate the effect by acting directly on astrocytes. In the present study, we examined the effects of direct application of recombinant human IGF-I (rhIGF-I) on astrocytes in primary culture concerning cx43 protein expression and gap junctional communication (GJC). After 24 hr of stimulation with rhIGF-I under serum-free conditions, the GJC and cx43 protein were analyzed. Administration of 30 ng/ml rhIGF-I increased the GJC and the abundance of cx43 protein. Cell proliferation of the astrocytes was not significantly increased by rhIGF-I at this concentration. However, a higher concentration of rhIGF-I (150 ng/ml) had no effect on GJC/cx43 but increased cell proliferation. Because of the important modulatory role of IGF binding proteins (IGFBPs) on IGF-I action, we analyzed IGFBPs in conditioned media. In cultures with a low abundance of IGFBPs (especially IGFBP-2), the GJC response to 30 ng/ml rhIGF-I was 81%, compared with the average of 25%. Finally, as a control, insulin was given in equimolar concentrations. However, GJC was not affected, which suggests that rhIGF-I acted via IGF-I receptors. In summary, the data show that rhIGF-I may increase GJC/cx43, whereas a higher concentration of rhIGF-I--at which stimulation of proliferation occurred--did not affect GJC/cx43. Furthermore, IGFBP-2 appeared to modulate the action of rhIGF-I on GJC in astrocytes by a paracrine mechanism.
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| 2. |
- Åberg, Maria A I, 1972, et al.
(författare)
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IGF-I has a direct proliferative effect in adult hippocampal progenitor cells.
- 2003
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Ingår i: Molecular and cellular neurosciences. - 1044-7431. ; 24:1, s. 23-40
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to investigate the potential direct effects of insulin-like growth factor-I (IGF-I) on adult rat hippocampal stem/progenitor cells (AHPs). IGF-I-treated cultures showed a dose-dependent increase in thymidine incorporation, total number of cells, and number of cells entering the mitosis phase. Pretreatment with fibroblast growth factor-2 (FGF-2) increased the IGF-I receptor (IGF-IR) expression, and both FGF-2 and IGF-I were required for maximal proliferation. Time-lapse recordings showed that IGF-I at 100 ng/ml decreased differentiation and increased proliferation of single AHPs. Specific inhibition of mitogen-activated protein kinase kinase (MAPKK), phosphatidylinositol 3-kinase (PI3-K), or the downstream effector of the PI3-K pathway, serine/threonine p70 S6 kinase (p70(S6K)), showed that both the MAPK and the PI3-K pathways participate in IGF-I-induced proliferation but that the MAPK activation is obligatory. These results were confirmed with dominant-negative constructs for these pathways. Stimulation of differentiation was found at a low dose (1 ng/ml) of IGF-I, clonal analysis indicating an instructive component of IGF-I signaling.
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| 3. |
- Åberg, Maria A I, 1972, et al.
(författare)
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Peripheral infusion of IGF-I selectively induces neurogenesis in the adult rat hippocampus.
- 2000
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Ingår i: The Journal of neuroscience : the official journal of the Society for Neuroscience. - 1529-2401. ; 20:8, s. 2896-903
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Tidskriftsartikel (refereegranskat)abstract
- In several species, including humans, the dentate granule cell layer (GCL) of the hippocampus exhibits neurogenesis throughout adult life. The ability to regulate adult neurogenesis pharmacologically may be of therapeutic value as a mechanism for replacing lost neurons. Insulin-like growth factor-I (IGF-I) is a growth-promoting peptide hormone that has been shown to have neurotrophic properties. The relationship between IGF-I and adult hippocampal neurogenesis is to date unknown. The aim of this study was to investigate the effect of the peripheral administration of IGF-I on cellular proliferation in the dentate subgranular proliferative zone, which contains neuronal progenitor cells, and on the subsequent migration and differentiation of progenitor cells within the GCL. Using bromodeoxyuridine (BrdU) labeling, we found a significant increase of BrdU-immunoreactive progenitors in the GCL after 6 d of peripheral IGF-I administration. To determine the cell fate in progenitor progeny, we characterized the colocalization of BrdU-immunolabeled cells with cell-specific markers. In animals treated with IGF-I for 20 d, BrdU-positive cells increased significantly. Furthermore, the fraction of newly generated neurons in the GCL increased, as evaluated by the neuronal markers Calbindin D(28K), microtubule-associated protein-2, and NeuN. There was no difference in the fraction of newly generated astrocytes. Thus, our results show that peripheral infusion of IGF-I increases progenitor cell proliferation and selectively induces neurogenesis in the progeny of adult neural progenitor cells. This corresponds to a 78 +/- 17% (p < 0.001) increase in the number of new neurons in IGF-I-treated animals compared with controls.
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| 4. |
- Leonova, Julia, et al.
(författare)
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Endothelin-1 decreases glutamate uptake in primary cultured rat astrocytes.
- 2001
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Ingår i: American journal of physiology. Cell physiology. - 0363-6143. ; 281:5
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Tidskriftsartikel (refereegranskat)abstract
- Endothelin-1 (ET-1) is a potent vasoconstrictor peptide that is also known to induce a wide spectrum of biological responses in nonvascular tissue. In this study, we found that ET-1 (100 nM) inhibited the glutamate uptake in cultured astrocytes expressing the glutamate/aspartate transporter (GLAST); astrocytes did not express the glutamate transporter-1 (GLT-1). The V(max) and the K(m) of the glutamate uptake were reduced by 57% and 47%, respectively. Application of the ET(A) and ET(B) receptor antagonists BQ-123 and BQ-788 partly inhibited the ET-1-evoked decrease in the glutamate uptake, whereas the nonspecific ET receptor antagonist bosentan completely inhibited this decrease. Incubation of the cultures with pertussis toxin abolished the effect of ET-1 on the uptake. The ET-1-induced decrease in the glutamate uptake was independent of extracellular free Ca(2+) concentration, whereas the intracellular Ca(2+) antagonists thapsigargin and 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester abolished the effect of ET-1 on the glutamate uptake. Incubation with the protein kinase C (PKC) antagonist staurosporine, but not with the fatty acid-binding protein bovine serum albumin, prevented the ET-1-induced decrease in the glutamate uptake. These results suggest that ET-1 impairs the high-affinity glutamate uptake in cultured astrocytes through a G protein-coupled mechanism, involving PKC and changes in intracellular Ca(2+).
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| 5. |
- Persson, Anders I., 1973, et al.
(författare)
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Expression of delta opioid receptor mRNA and protein in the rat cerebral cortex and cerebellum is decreased by growth hormone.
- 2003
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Ingår i: Journal of neuroscience research. - : Wiley. - 0360-4012 .- 1097-4547. ; 71:4, s. 496-503
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Tidskriftsartikel (refereegranskat)abstract
- Hormones released from the pituitary have been shown to regulate the expression of different proteins in the central nervous system. We wanted to examine whether peripheral administration of bovine growth hormone (bGH) regulates the expression of delta-opioid receptor (DOR) in the cerebral cortex and cerebellum. Expression of the DOR protein was quantified using Western blot densitometry. DOR mRNA was quantified with a solution hybridization RNase protection assay. Hypophysectomized (Hx) and untreated normal female rats were included in the study. All Hx rats were hormonally treated with cortisol (400 microg/kg/day) and L-thyroxine (10 microg/kg/day) for 19 days. Hypophysectomy resulted in a threefold increase in cerebral cortex and a twofold increase in cerebellum of the DOR protein compared with normal rats. One subgroup of Hx rats received bGH (1 mg/kg body weight) as a daily subcutaneous injection for 19 days. This treatment normalized the levels of DOR protein in the cerebral cortex and cerebellum. Immunohistochemical experiments showed that GH decreased DOR expression especially in layers II-VI in cerebral cortex and in stratum moleculare in cerebellum. Quantification of DOR mRNA by solution hybridization RNase protection assay corresponded to the DOR protein measurements. We conclude that the expression of DORs in cerebral cortex and cerebellum is regulated by GH.
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| 6. |
- Åberg, N David, 1970
(författare)
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Connexin43 in astroglial gap junctions. Regulation by age, neurotransmitters, GH and IGF-I
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Connexins form gap junctions that are aqueous pores allowing low-molecular (<1000 daltons) compounds to pass from cell to cell. In astroglial cells, connexin43 (cx43) makes up gap junctions, which in turn mediate intercellular communication within the astroglial network. Growth hormone (GH) and insulin-like growth factor I (IGF-I) have been shown to affect, for example, levels of neurotransmitters in the brain, myelination and even memory and learning. As glial cells express receptors for GH and IGF-I, we hypothesized that these hormones could affect astrocytic gap junctions and cx43. The objective of this thesis was to study the expression of cx43 in the rat brain, the effects of GH and IGF-I on cx43 expression in vivo and its regulation by neurotransmitters (5-HT and glutamate), GH, and IGF-I and their effects on gap junctional coupling (GJC) in vitro. First, the postnatal and adult expression of cx43 mRNA and protein was studied in seven brain regions. The data show a brain region-specific postnatal increase in cx43 expression with a different regulation for mRNA and protein abundance. In addition, mixed neuronal-astroglial cell cultures from four of the seven brain regions were studied in terms of cx43 mRNA and protein, which was related to functional GJC studies. Furthermore, cx43 and GJC were partially related to the extent of astroglial calcium wave propagation. Glutamate and serotonin each differentially affected GJC in astroglial primary cultures from different brain regions.The effects of bGH and rhIGF-I on cx43 expression and GJC were studied in vivo and in vitro. In vivo, hypophysectomized adult female rats, with low circulating levels of GH and IGF-I, were substituted with bGH (1 mg/kg) and rhIGF-I (0.85 mg/kg) and in vitro, bGH and rhIGF-I were added to primary astroglial cell cultures derived from the cerebral cortices of newborn rats. Systemic bGH but not rhIGF-I, increased the expression of cx43 mRNA and protein in the cerebral cortex and hypothalamus of the brain. However, in vitro, rhIGF-I increased GJC and cx43 abundance. Moreover, at a high concentration of rhIGF-I, where astroglial proliferation increased, the increase in GJC and cx43 disappeared. The astroglial cells secreted IGBFPs in vitro, and a high abundance of these was associated with a low response to rhIGF-I. As GH is known to induce IGF-I synthesis in the brain, these results indicate that the effect of GH on cx43 expression in vivo, may be mediated locally by IGF-I and interactions with IGBFPs.In conclusion, the short-term response to neurotransmitters is heterogeneous with respect to brain region in vitro as is the long-term response after treatment with GH in vivo. Altogether, the results show that cx43 and astroglial gap junctions are under dynamic regulation during maturation and that cx43 and GJC can be regulated by neurotransmitters and hormones. This may be of significance under normal physiological conditions by enhancing the spatial buffering capacity of astrocytes needed to sustain extended neurotransmission, as well as after insults to the nervous system.
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| 7. |
- Åberg, N David, 1970, et al.
(författare)
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Growth hormone increases connexin-43 expression in the cerebral cortex and hypothalamus.
- 2000
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Ingår i: Endocrinology. - 0013-7227. ; 141:10, s. 3879-86
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Tidskriftsartikel (refereegranskat)abstract
- Several studies indicate that systemic GH influences various brain functions. Connexin-43 forms gap junctions that mediate intercellular communication and establish the astroglial syncytium. We investigated the effects of peripheral administration of bovine GH (bGH) and recombinant human insulin-like growth factor I (rhIGF-I) on the expression of connexin-43 in the rat brain. Hypophysectomized female Sprague Dawley rats were substituted with cortisol (400 microg/kg x day) and L-T4 (10 microg/kg x day) and treated with either bGH (1 mg/kg x day) or rhIGF-I (0.85 mg/kg x day) for 19 days. The abundance of connexin-43 messenger RNA (mRNA) and protein in the brainstem, cerebral cortex, hippocampus, and hypothalamus was quantified by means of ribonuclease protection assays and Western blots. Treatment with bGH increased the amounts of connexin-43 mRNA and protein in the cerebral cortex and hypothalamus. No changes were found in the brainstem or hippocampus. Infusion of rhIGF-I did not affect connexin-43 mRNA or protein levels in any of the brain regions studied. These results show that administration of bGH increases the abundance of cx43 in specific brain regions, suggesting that GH may influence gap junction formation and thereby intercellular communication in the brain.
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