Biomedical subjects

Klaus Unsicker

Publications and source records attributed to Klaus Unsicker.

At least 19 recordsLinked to original sources

PubMed2006

GDNF applied to the MPTP-lesioned nigrostriatal system requires TGF-beta for its neuroprotective action.

GDNF is a potent neurotrophic factor for nigrostriatal dopaminergic neurons in vitro and in animal models of Parkinson's disease (PD), but has largely failed when tested in therapeutic applications in human PD. We report here that GDNF requires transforming growth factor-beta (TGF-beta) to elicit its neurotrophic activity. Lesioning the mouse nigrostriatal system with MPTP significantly upregulates striatal TGF-beta2 mRNA levels. As expected, GDNF protects against the destructive effects of MPTP, including losses of TH-ir nigral neurons, striatal dopamine and TH-ir fibers. Application of antibodies neutralizing all three TGF-beta isoforms to the MPTP-lesioned striatum abolishes the neurotrophic effect of GDNF. We show that TGF-beta antibodies are not toxic and do not interfere with retrograde transport of iodinated GDNF, suggesting that TGF-beta antibodies do not impair internalization and retrograde trafficking of GDNF. We conclude that striatal TGF-beta may be essential for permitting exogenous GDNF to act as a neuroprotective factor.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2006

Development of adrenal chromaffin cells in Sf1 heterozygous mice.

Adrenal medullary chromaffin cells are derivatives of the neural crest and are widely believed to share a common sympathoadrenal (SA) progenitor with sympathetic neurons. For decades, the adrenal cortical environment was assumed to be essential for channelling SA progenitors towards an endocrine chromaffin cell fate. Our recent analysis of steroidogenic factor 1(Sf1) -/- mice, which lack an adrenal cortex, has challenged this view: in Sf1 -/- mice chromaffin cells migrate to the correct "adrenal" location and undergo largely normal differentiation. In contrast to Sf1 homozygous mutants, heterozygous animals have an adrenal cortex, which, however, is smaller than in wildtype littermates. We show here that the Sf1 +/- adrenal cortical anlagen attract normal numbers of chromaffin progenitor cells into their vicinity by embryonic day 13.5 (E13.5). Two days later, however, only a few scattered cells with highly immature features have immigrated into the adrenal cortex, whereas the remainder form a coherent cell assembly ectopically located at the medial surface of the gland. These cells appear more mature than the scattered intracortical chromaffin progenitors and express the adrenaline synthesizing enzyme PNMT with a delay of 1 day in comparison with wildtype littermates. Nevertheless, chromaffin progenitor cells undergo a numerical reduction of approximately 30% by E17.5. Together, our data suggest that normal adrenocortical development is critical for the correct immigration of chromaffin progenitors into the cortical anlagen, for the timing of PNMT expression and for the regulation of chromaffin cell numbers.

Adrenal Glands↗

PubMed2006

Loss of leukemia inhibitory factor receptor beta or cardiotrophin-1 causes similar deficits in preganglionic sympathetic neurons and adrenal medulla.

Leukemia inhibitory factor (LIF) receptor beta (LIFRbeta) is a receptor for a variety of neurotrophic cytokines, including LIF, ciliary neurotrophic factor (CNTF), and cardiotrophin-1 (CT-1). These cytokines play an essential role for the survival and maintenance of developing and postnatal somatic motoneurons. CNTF may also serve the maintenance of autonomic, preganglionic sympathetic neurons (PSNs) in the spinal cord, as suggested by its capacity to prevent their death after destruction of one of their major targets, the adrenal medulla. Although somatic motoneurons and PSNs share a common embryonic origin, they are distinct in several respects, including responses to lesions. We have studied PSNs in mice with targeted deletions of the LIFRbeta or CT-1 genes, respectively. We show that LIF, CNTF, and CT-1 are synthesized in embryonic adrenal gland and spinal cord and that PSNs express LIFRbeta. In embryonic day 18.5 LIFRbeta (-/-) and CT-1 (-/-) mice, PSNs were reduced by approximately 20%. PSNs projecting to the adrenal medulla were more severely affected (-55%). Although LIFRbeta (-/-) mice revealed normal numbers of adrenal chromaffin cells and axons terminating on chromaffin cells, levels of adrenaline and numbers of adrenaline-synthesizing cells were significantly reduced. We conclude that activation of LIFRbeta is required for normal development of PSNs and one of their prominent targets, the adrenal medulla. Thus, both somatic motoneurons and PSNs in the spinal cord depend on LIFRbeta signaling for their development and maintenance, although PSNs seem to be overall less affected than somatic motoneurons by LIFRbeta deprivation.

Actins↗

PubMed2006

Muscarinic control of graded persistent activity in lateral amygdala neurons.

The cholinergic system is crucially involved in several cognitive processes including attention, learning and memory. Muscarinic actions have profound effects on the intrinsic firing pattern of neurons. In principal neurons of the entorhinal cortex (EC), muscarinic receptors activate an intrinsic cation current that causes multiple self-sustained spiking activity, which represents a potential mechanism for transiently sustaining information about novel items. The amygdala appears to be important for experience-dependent learning by emotional arousal, and cholinergic muscarinic influences are essential for the amygdala-mediated modulation of memory. Here we show that principal neurons from the lateral nucleus of the amygdala (LA) can generate intrinsic graded persistent activity that is similar to EC layer V cells. This firing behavior is linked to muscarinic activation of a calcium-sensitive non-specific cation current and can be mimicked by stimulation of cholinergic afferents that originate from the nucleus basalis of Meynert (n. M). Moreover, we demonstrate that the projections from the n. M. are essential and sufficient for the control and modulation of graded firing activity in LA neurons. We found that activation of these cholinergic afferents (i) is required to maintain and to increase firing rates in a graded manner, and (ii) is sufficient for the graded increases of stable discharge rates even without an associated up-regulation of Ca2+. The induction of persistent activity was blocked by flufenamic acid or 2-APB and remained intact after Ca2+-store depletion with thapsigargin. The internal ability of LA neurons to generate graded persistent activity could be essential for amygdala-mediated memory operations.

Acetylcholine↗

PubMed2005

Regional- and age-dependent reduction in trkB receptor expression in the hippocampus is associated with altered spine morphologies.

BACKGROUND: Changes in densities and in the morphology of dendritic spines in the hippocampus are linked to hippocampal long-term potentiation (LTP), spatial learning, and depression. Decreased brain-derived neurotrophic factor (BDNF) levels seem to contribute to depression. Through its receptor trkB, BDNF is also involved in hippocampal LTP and hippocampus-dependent learning. Conditionally gene-targeted mice in which the ablation of trkB is restricted to the forebrain and occurs only during postnatal development display impaired learning and LTP. METHODS: To examine whether there is a link among impaired hippocampal synaptic plasticity, altered spines, and trkB receptors, we performed a quantitative analysis of spine densities and spine length in the hippocampal area CA1 and the dentate gyrus in conditional mutant mice (trkB(lox/lox)CaMKII-CRE mice). TrkB protein and mRNA levels were assayed using Western blot and in situ hybridization analysis. RESULTS: Fifteen-week-old mutant mice exhibit specific reductions in spine densities and a significant increase in spine length of apical and basal dendrites in area CA1. These alterations correlate with a time- and region-specific reduction in full-length trkB mRNA in the hippocampus. CONCLUSIONS: TrkB functions in structural remodeling of hippocampal dendritic spines, which in turn may affect synaptic transmission and plasticity.

Age Factors↗

PubMed2005

Distribution of TRPC1 and TRPC5 in medial temporal lobe structures of mice.

The transient receptor potential (TRP) superfamily comprises a group of non-selective cation channels that have been implicated in both receptor and store-operated channel functions. The family of the classical TRPs (TRPCs) consists of seven members (TRPC1-7). The presence of TRPC1 and TRPC5 mRNA in the brain has previously been demonstrated by real-time polymerase chain reaction. However, the distribution of these receptors within different brain areas of mice has not been investigated in detail. We have used antibodies directed against TRPC1 and TRPC5 to study the distribution and localization of these channels in murine medial temporal lobe structures. Both TRPC1 and TRPC5 channels are present in the various nuclei of the amygdala, in the hippocampus, and in the subiculum and the entorhinal cortex. We have found that TRPC1 channels are primarily expressed on cell somata and on dendrites, whereas TRPC5 channels are exclusively located on cell bodies. Moreover, TRPC1 channels are selectively expressed by neurons, whereas TRPC5 channels are mainly expressed by neurons, but also by non-neuronal cells. The expression of TRPC1 and TRPC5 channels in mammalian temporal lobe structures suggests their involvement in neuronal plasticity, learning and memory.

Animals↗

PubMed2005

Lack of an adrenal cortex in Sf1 mutant mice is compatible with the generation and differentiation of chromaffin cells.

The diversification of neural-crest-derived sympathoadrenal (SA) progenitor cells into sympathetic neurons and neuroendocrine adrenal chromaffin cells was thought to be largely understood. In-vitro studies with isolated SA progenitor cells had suggested that chromaffin cell differentiation depends crucially on glucocorticoids provided by adrenal cortical cells. However, analysis of mice lacking the glucocorticoid receptor gene had revealed that adrenal chromaffin cells develop mostly normally in these mice. Alternative cues from the adrenal cortex that may promote chromaffin cell determination and differentiation have not been identified. We therefore investigated whether the chromaffin cell phenotype can develop in the absence of an adrenal cortex, using mice deficient for the nuclear orphan receptor steroidogenic factor-1 (SF1), which lack adrenal cortical cells and gonads. We show that in Sf1-/- mice typical chromaffin cells assemble correctly in the suprarenal region adjacent to the suprarenal sympathetic ganglion. The cells display most features of chromaffin cells, including the typical large chromaffin granules. Sf1-/- chromaffin cells are numerically reduced by about 50% compared with the wild type at embryonic day (E) 13.5 and E17.5. This phenotype is not accounted for by reduced survival or cell proliferation beyond E12.5. However, already at E12.5 the 'adrenal' region in Sf1-/- mice is occupied by fewer PHOX2B+ and TH+ SA cells as well as SOX10+ neural crest cells. Our results suggest that cortical cues are not essential for determining chromaffin cell fate, but may be required for proper migration of SA progenitors to and/or colonization of the adrenal anlage.

Adrenal Cortex↗

PubMed2005

Haploinsufficiency for trkB and trkC receptors induces cell loss and accumulation of alpha-synuclein in the substantia nigra.

The neurotrophins brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) have been shown to promote survival and differentiation of midbrain dopaminergic (DAergic) neurons in vitro and in vivo. This is consistent with their expression and that of their cognate receptors, trkB and trkC, in the nigrostriatal system. Degeneration of DAergic neurons of the substantia nigra and alpha-synuclein-positive aggregates in the remaining substantia nigra (SN) neurons are hallmarks of Parkinson's disease (PD). Reduced expression of BDNF has been reported in the SN from PD patients. Moreover, mutations in the BDNF gene have been found to play a role in the development of familial PD. We show now that haploinsufficiencies of the neurotrophin receptors trkB and/or trkC cause a reduction in numbers of SN neurons in aged (21-23 month old) mice, which is accompanied by a reduced density in striatal tyrosine hydroxylase immunoreactive (TH-ir) fibers. These aged mutant mice, in contrast to wild-type littermates, display an accumulation of alpha-synuclein in the remaining TH-positive neurons of the SN. We conclude that impairment in trkB and/or trkC signaling induces a phenotype in the aged SN, which includes two hallmarks of PD, losses of TH positive neurons and axons along with massive neuronal deposits of alpha-synuclein.

Aging↗

PubMed2005

Insulin-like growth factor 1 inhibits extracellular signal-regulated kinase to promote neuronal survival via the phosphatidylinositol 3-kinase/protein kinase A/c-Raf pathway.

Extracellular signal-regulated kinase (ERK) activation has been shown to promote neuronal death in various paradigms. We demonstrated previously that the late and sustained ERK activation in cerebellar granule neurons (CGNs) cultured in low potassium predominantly promotes plasma membrane (PM) damage. Here, we examined the effects of a well established neuronal survival factor, insulin-like growth factor 1 (IGF-1), on the ERK cell death pathway. Stimulation of CGNs with IGF-1 induced an early and transient ERK activation but abrogated the appearance of late and sustained ERK. Withdrawal or readdition of IGF-1 after 4 h in low potassium failed to prevent sustained ERK activation and cell death. IGF-1 activated the protein kinase A (PKA) to mediate ERK inhibition via c-Raf phosphorylation at an inhibitory site (Ser259). Phosphatidylinositol 3-kinase (PI3K) or PKA inhibitors, but not a specific Akt inhibitor, abrogated PKA signaling. This suggests that the PI3K/PKA/c-Raf-Ser259 pathway mediates ERK inhibition by IGF-1 independent of Akt. In addition, adenoviral-mediated expression of constitutively active MEK (mitogen-activated protein kinase kinase) or Sindbis viral-mediated expression of mutant Raf Ser259Ala both attenuated IGF-1-mediated prevention of PM damage. Activation of caspase-3 promoted DNA damage. Its inhibition by IGF-1 was both PI3K and Akt dependent but PKA independent. 8-Br-cAMP, an activator of PKA, induced phosphorylation of c-Raf-Ser259 and inhibited ERK activation without affecting caspase-3. This indicates a selective role for PKA in ERK inhibition through c-Raf-Ser259 phosphorylation. Together, these data demonstrate that IGF-1 can positively and negatively regulate the ERK pathway in the same neuronal cell, and provide new insights into the PI3K/Akt/PKA signaling pathways in IGF-1-mediated neuronal survival.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2005

The role of Phox2B in chromaffin cell development.

Phox2B, a homeodomain transcription factor closely related to Phox2A, is expressed in peripheral and central noradrenergic neurons. In neural crest (NC) derivatives Phox2B is restricted to sympathetic and parasympathetic ganglia, enteric neurons, and adrenal and extraadrenal chromaffin cells. Similar to MASH-1, Phox2B has been implicated in synchronizing pan-neuronal and catecholaminergic phenotype-specific aspects of neurogenesis. The role of Phox2B for the differentiation of the neuroendocrine NC derivatives, the adrenal medullary chromaffin cells, has not been explored. We have previously reported that in MASH-1-deficient mice most chromaffin cells are arrested at the early neuroblast stage and lack catecholaminergic differentiation. We show now that in Phox2B knockout/lacZ knockin mice the maturation of presumptive chromaffin cells is arrested at an even earlier stage of development. The cells lack the catecholaminergic marker enzyme TH and fail to form a centrally located medulla. In contrast to MASH-1 (-/-) mice they do not express dHand, Phox2A, c-ret, neurofilament, neuron-specific tubulin, and NCAM and appear ultrastructurally more immature. Many of these cells die by apoptosis. Despite the complete lack of differentiation, few lacZ-positive adrenal cells can still be found at E16.5. We conclude that Phox2B regulates very early events in the differentiation of adrenal chromaffin cells distinct to steps, which essentially require MASH-1.

Adrenal Glands↗

PubMed2005

MPTP treatment impairs tyrosine hydroxylase immunopositive fibers not only in the striatum, but also in the amygdala.

Parkinson's disease (PD) is characterized by a triad of symptoms (tremor, rigidity, and bradykinesia). Aside from this, emotional deficits are known to be associated with PD. A key structure of emotional processing is the amygdala. Emotional deficits seen in PD might be due to alterations in the catecholaminergic innervation of this limbic structure. We therefore examined whether 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) applied to C57/BL6 mice (an animal model of PD) affects the density of tyrosine hydroxylase (TH) immunoreactive fibers in the amygdala as it does in the striatum. MPTP treatment caused a prominent reduction in dopamine levels (about -70%) in the striatum (determined by high-performance liquid chromatography and electrochemical detection), accompanied by massive losses of TH-positive fibers in the striatum (-48.3%). Moreover, MPTP treatment caused prominent reductions of TH-positive fiber densities in the basolateral, lateral and central nucleus of the amygdala (about -20%). These results may provide the morphological basis for behavioral studies analyzing altered emotional responses in animal models of PD.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2004

Expression of neuronal markers suggests heterogeneity of chick sympathoadrenal cells prior to invasion of the adrenal anlagen.

We have analyzed the distribution of neural crest-derived precursors and the expression of catecholaminergic and neuronal markers in developing adrenal tissue of chick embryos. Undifferentiated neural crest cells are found in presumptive adrenal regions from embryonic day 3 (E3) onward. An increasing proportion of cells expressing tyrosine hydroxylase (TH) mRNA indicates catecholaminergic differentiation of precursors not only in primary sympathetic ganglia, but also in presumptive adrenal regions. Whereas precursors and differentiating cells show mesenchymal distribution until E5, discrete adrenal anlagen form during E6. Even during E5, catecholaminergic cells with low or undetectable neurofilament M (NF-M) mRNA expression prevail in positions at which adrenal anlagen become distinct during E6. The predominance of TH-positive and NF-M-negative cells is maintained throughout embryogenesis in adrenal tissue. RNA encoding SCG10, a pan-neuronal marker like NF-M, is strongly expressed throughout adrenal anlagen during E6 but is found at reduced levels in chromaffin cells compared with neuronal cells at E15. Two additional neuronal markers, synaptotagmin 1 and neurexin 1, are expressed at low to undetectable levels in developing chromaffin cells throughout embryogenesis. The developmental regulation of neuronal markers shows at least three different patterns among the four mRNAs analyzed. Importantly, there is no generalized downregulation of neuronal markers in developing adrenal anlagen. Thus, our observations question the classical concept of chromaffin differentiation from a common sympathoadrenal progenitor expressing neuronal properties and suggest alternative models with changing instructive signals or separate progenitor populations for sympathetic neuronal and chromaffin endocrine cells.

Adrenal Glands↗

PubMed2004

Involvement of growth differentiation factor-15/macrophage inhibitory cytokine-1 (GDF-15/MIC-1) in oxLDL-induced apoptosis of human macrophages in vitro and in arteriosclerotic lesions.

Growth differentiation factor-15/macrophage inhibitory cytokine-1 (GDF-15/MIC-1) is a new member of the transforming growth factor beta (TGF-beta) superfamily, which has most recently been found in activated macrophages (MPhi). We have now investigated GDF-15/MIC-1 in human MPhi after exposure to oxidized low-density lipoproteins (oxLDL) related mediators in vitro and in arteriosclerotic carotid arteries. Using RT-PCR and Western blotting a pronounced induction of GDF-15/MIC-1 expression by oxLDL, C6-ceramide, tumor necrosis factor (TNFalpha) and hydrogen peroxide (H2O2) was found in cultured human MPhi. In 11 human arteriosclerotic carotid arteries, immunohistochemical analyses supported by computer-assisted morphometry and regression analyses demonstrated a significant colocalization of GDF-15/MIC-1 immunoreactivity (IR) with oxLDL IR and manganese superoxide dismutase (MnSOD) IR in CD68 immunoreactive (ir) MPhi, which were also expressing AIF-IR (apoptosis-inducing factor), caspase-3-IR (CPP32), PARP-IR, c-Jun/AP-1-IR and p53-IR. Our data suggest that GDF-15/MIC-1 is inducible in human MPhi by oxLDL and its mediators in vitro and is supposed to contribute to oxidative stress dependent consequences in arteriosclerotic plaques, e.g. modulating apoptosis and inflammatory processes in activated MPhi.

Antigens, CD↗

PubMed2004

TrkB regulates neocortex formation through the Shc/PLCgamma-mediated control of neuronal migration.

The generation of complex neuronal structures, such as the neocortex, requires accurate positioning of neurons and glia within the structure, followed by differentiation, formation of neuronal connections, and myelination. To understand the importance of TrkB signaling during these events, we have used conditional and knockin mutagenesis of the TrkB neurotrophin receptor, and we now show that this tyrosine kinase receptor, through docking sites for the Shc/FRS2 adaptors and phospholipase Cgamma (PLCgamma), coordinates these events in the cerebral cortex by (1) controlling cortical stratification through the timing of neuronal migration during cortex formation, and (2) regulating both neuronal and oligodendrocyte differentiation. These results provide genetic evidence that TrkB regulates important functions throughout the formation of the cerebral cortex via recruitment of the Shc/FRS2 adaptors and PLCgamma.

Adaptor Proteins, Signal Transducing↗

PubMed2004

ERK activation promotes neuronal degeneration predominantly through plasma membrane damage and independently of caspase-3.

Our recent studies have shown that extracellular-regulated protein kinase (ERK) promotes cell death in cerebellar granule neurons (CGN) cultured in low potassium. Here we report that the "death" phenotypes of CGN after potassium withdrawal are heterogeneous, allowing the distinction between plasma membrane (PM)-, DNA-, and PM/DNA-damaged populations. These damaged neurons display nuclear condensation that precedes PM or DNA damage. Inhibition of ERK activation either by U0126 or by dominant-negative mitogen-activated protein kinase/ERK kinase (MEK) overexpression results in a dramatic reduction of PM damaged neurons and nuclear condensation. In contrast, overexpression of constitutively active MEK potentiates PM damage and nuclear condensation. ERK-promoted cellular damage is independent of caspase-3. Persistent active ERK translocates to the nucleus, whereas caspase-3 remains in the cytoplasm. Antioxidants that reduced ERK activation and PM damage showed no effect on caspase-3 activation or DNA damage. These data identify ERK as an important executor of neuronal damage involving a caspase-3-independent mechanism.

Active Transport, Cell Nucleus↗

PubMed2004

Enlarged infarct volume and loss of BDNF mRNA induction following brain ischemia in mice lacking FGF-2.

FGF-2, a potent multifunctional and neurotrophic growth factor, is widely expressed in the brain and upregulated in cerebral ischemia. Previous studies have shown that intraventricularly or systemically administered FGF-2 reduces the size of cerebral infarcts. Whether endogenous FGF-2 is beneficial for the outcome of cerebral ischemia has not been investigated. We have used mice with a null mutation of the fgf2 gene to explore the relevance of endogenous FGF-2 in brain ischemia. Focal cerebral ischemia was produced by occlusion of the middle cerebral artery (MCAO). We found a 75% increase in infarct volume in fgf2 knock-out mice versus wild type littermates (P < 0.05). This difference in the extent of ischemic damage was observed after 24 h, and correlated with decreased viability in fgf2 mutant mice following MCA occlusion. Increased infarct volume in fgf2 null mice was associated with a loss of induction in hippocampal BDNF and trkB mRNA expression. These findings indicate that signaling through trkB may contribute to ameliorating brain damage following ischemia and that bdnf and trkB may be target genes of FGF-2. Together, our data provide the first evidence that endogenous FGF-2 is important in coping with ischemic brain damage suggesting fgf2 as one crucial target gene for new therapeutic strategies in brain ischemia.

Animals↗

PubMed2003

Functions of fibroblast growth factor (FGF)-2 and FGF-5 in astroglial differentiation and blood-brain barrier permeability: evidence from mouse mutants.

Multiple evidence suggests that fibroblast growth factors (FGFs), most prominently FGF-2, affect astroglial proliferation, maturation, and transition to a reactive phenotype in vitro, and after exogenous administration, in vivo. Whether this reflects a physiological role of endogenous FGF is unknown. Using FGF-2 and FGF-5 single- and double mutant mice we show now a region-specific reduction of glial fibrillary acidic protein (GFAP), but not of S100 in gray matter astrocytes. FGF-2 is apparently the major regulator of GFAP, because in mice deficient for FGF-2, GFAP is distinctly reduced in cortex and striatum, whereas in FGF-5-/- animals only a reduction in the midbrain tegmentum can be observed. In FGF-2-/-/FGF-5-/- double mutant animals, GFAP-immunoreactivity is reduced in all three brain regions. Cortical astrocytes cultured from FGF-2-/-/FGF-5-/- double mutant mice revealed reduced levels of GFAP, but not S100 as compared with wild-type littermates. This phenotype could be rescued by exogenous FGF-2 but not FGF-5 (10 ng/ml). Electron microscopy revealed reduced levels of intermediate filaments in perivascular astroglial endfeet. This defect was accompanied by enhanced permeability of the blood-brain barrier (BBB), as detected by albumin extravasation. Levels of the tight junction proteins Occludin and ZO-1 were reduced in blood vessels of FGF-2-/-/FGF-5-/- double mutant mice as compared with wild-type littermates. Our data support the notion that endogenous FGF-2 and FGF-5 regulate GFAP expression in a region-specific manner. The observed defect in astroglial differentiation is accompanied by a defect in BBB function arguing for an indirect or direct role of FGFs in the regulation of BBB permeability in vivo.

Animals↗

PubMed2003

Transforming growth factor-beta(s) are essential for the development of midbrain dopaminergic neurons in vitro and in vivo.

Development of midbrain dopaminergic neurons is known to depend on inductive signals derived from the ventral midline, including Sonic hedgehog (Shh) as one of the identified molecules. Here we show that in addition to Shh, transforming growth factor (TGF)-beta is required for both induction and survival of ventrally located midbrain dopaminergic neurons. Like Shh, TGF-beta is expressed in early embryonic structures such as notochord and floor plate, as well as in the area where midbrain dopaminergic neurons are developing. Treatment of cells dissociated from the rat embryonic day (E) 12 midbrain floor with TGF-beta significantly increases the number of tyrosine hydroxylase (TH)-positive dopaminergic neurons within 24 hr. Neutralization of TGF-beta in vitro completely abolishes the induction of dopaminergic neurons. In the absence of TGF-beta, Shh cannot induce TH-positive neurons, and vice versa, neutralizing endogenous Shh abolishes the capacity of TGF-beta to induce dopaminergic neurons in vitro. Furthermore, neutralization of TGF-beta in vivo during chick E2-7 but not E4-7 resulted in a significant reduction in TH-positive neurons in the ventral midbrain floor but not in the locus coeruleus or diencephalon, which suggests that the TGF-beta is required for the induction of mesencephalic dopaminergic neurons with a critical time period at E2/E3. Furthermore, neutralization of TGF-beta between E6 and 10, a time period during maturation of mesencephalic dopaminergic neurons when no further inductive cues are required, also resulted in a significant loss of dopaminergic neurons, suggesting that TGF-beta is required for the promotion of survival of ventral midbrain dopaminergic neurons as well. Together, our results identify TGF-beta as an essential mediator for the induction and maintenance of midbrain dopaminergic neurons.

Animals↗