Bone morphogenetic proteins: neurotrophic roles for midbrain dopaminergic neurons and implications of astroglial cells

Protective effect of bone morphogenetic protein-6 on neurons from H2O2 injury

Bone morphogenetic protein-6 (BMP6) is a member of the TGF-beta superfamily. Expression of BMP6 and its receptors are increased when brain tissues of adult rats are injured, suggesting that BMP6 may have a neuroprotective function in the physiologic response to neurological damage. This research investigates the molecular mechanisms supporting a neuroprotective effect of BMP6 in neural cells traumatized by H(2)O(2). We demonstrate that presence of BMP6 either before or after H(2)O(2)-induced injury protects the cultured primary cortical cells from apoptosis. However, molecular mechanisms mediating the protective effects of either pre- or post-treatment with BMP6 are different. Cells pre-treated with BMP6 have attenuated MAPK activity induced by H(2)O(2), whereas the MAPK activity in cells post-treated with BMP6 remains unchanged. Further, pharmacological inhibitors of MAPKs, PD98059 and SB203580, block the protective effect of BMP6 in the cells pre-treated with BMP6 but not in the cells post-treated with BMP6. The protective effect of post-treatment with BMP6 appears to be mediated through regulation of p53 and Bax molecules, evidenced by decreased mRNA levels after BMP6 treatment. Taken together, these data suggest BMP6 protect cortical cells against oxidation stress induced by H(2)O(2) via two different mechanisms, where (1) pre-treatment with BMP6 acts through MAPK pathway and (2) post-treatment with BMP6 works by down-regulating p53 and Bax.

Mesencephalic dopamine neuron number and tyrosine hydroxylase content: Genetic control and candidate genes

The mesotelencephalic dopamine system shows substantial genetic variation which fundamentally affects normal and pathological behaviors related to motor function, motivation, and learning. Our earlier radioenzyme assay studies demonstrated significantly higher activity of tyrosine hydroxylase (TH), the first and rate limiting enzyme in the biosynthesis of catecholamine neurotransmitters, in the substantia nigra-ventral tegmental area of BALB/cJ mice in comparison with that of C57BL/6ByJ mice. Here, using quantitative immunoblotting and immunocytochemistry, we tested the hypothesis that mesencephalic TH protein content and number of nigral TH-positive neurons show strain-dependent differences in C57BL/6ByJ and BALB/cJ parallel to those observed in the TH activity studies. Immunoblotting experiments detected significantly higher mesencephalic TH protein content in BALB/cJ in comparison to C57BL/6ByJ (P<0.05). Immunocytochemical studies demonstrated that the number of TH-positive cells in substantia nigra was 31.3% higher in BALB/cJ than that in C57BL/6ByJ (P<0.01), while the average dopamine neuron volume was not significantly different. In a search for candidate genes that modulate TH content and the size of mesencephalic dopamine neuron populations we also studied near-isogenic mouse sublines derived from the C57BL/6ByJ and BALB/cJ progenitor strains. A whole-genome scan with 768 single nucleotide polymorphism markers indicated that two sublines, C4A6/N and C4A6/B, were genetically very similar (98.3%). We found significantly higher mesencephalic TH protein content in C4A6/B in comparison to C4A6/N (P=0.01), and a tendency for higher number of dopamine neurons in the substantia nigra in C4A6/B in comparison to C4A6/N, which, however, did not reach statistical significance. To identify the genetic source of the TH content difference we analyzed the single nucleotide polymorphism (SNP) genotype data of the whole-genome scan, and detected two small differential chromosome segments on chr. 13 and chr. 14. Microarray gene expression studies and bioinformatic analysis of the two differential regions implicated two cis-regulated genes (Spock1 and Cxcl14, chr. 13), and two growth factor genes [bone morphogenetic protein 6 (Bmp6) (chr. 13), and fibroblast growth factor 14 (Fgf14) (chr. 14)]. Taken together, the results suggest that (1) nigral dopamine neuron number and TH protein content may be genetically associated but further studies are needed to establish unequivocally this linkage, and (2) Spock1, Cxcl14, Bmp6, and Fgf14 are novel candidates for modulating the expression and maintenance of TH content in mesencephalic dopamine neurons in vivo.

How to make a mesodiencephalic dopaminergic neuron

Dopaminergic neurons located in the ventral mesodiencephalon are essential for the control of voluntary movement and the regulation of emotion, and are severely affected in neurodegenerative diseases such as Parkinson's disease. Recent advances in molecular biology and mouse genetics have helped to unravel the mechanisms involved in the development of mesodiencephalic dopaminergic (mdDA) neurons, including their specification, migration and differentiation, as well as the processes that govern axonal pathfinding and their specific patterns of connectivity and maintenance. Here, we follow the developmental path of these neurons with the goal of generating a molecular code that could be exploited in cell-replacement strategies to treat diseases such as Parkinson's disease.

Bone marrow stromal cells induce BMP2/4 production in oxygen-glucose-deprived astrocytes, which promotes an astrocytic phenotype in adult subventricular progenitor cells

Bone morphogenetic proteins (BMPs) affect cell proliferation and differentiation. Astrocytes in ischemic brain are highly responsive to bone marrow stromal cell (BMSC) treatment. We investigated the effects of BMSCs on astrocytes cultured under oxygen- and glucose-deprived conditions, which in part simulate in vivo stroke conditions, to test the hypothesis that BMSCs alter astrocytic expression of BMPs which may contribute to neurological functional recovery of stroke. Quantitative real-time RT-PCR showed that the expression of BMP2/4 mRNAs decreased within ischemic astrocytes, In contrast, BMP2/4 mRNA was significantly increased after cocultured with BMSCs. Western blotting also confirmed this increase at the protein level in the medium of ischemic astrocytes after coculture with BMSCs. As a source of neural stem and progenitor cells, cultured subventricular zone (SVZ) neurospheres exposed to medium obtained from ischemic astrocytes cocultured with BMSCs were significantly enriched in cells expressing the astrocytic marker glial fibrillary acidic protein (GFAP), but not at the expense of beta-III-tubulin-positive SVZ neuroblasts. The expression of BMP2/4 subsequently increased the phosphorylation of downstream effector Smad1 and the expression of notch signal pathway-induced protein Hes1 in cultured SVZ neurospheres. BMP antagonist Noggin blocked the elevation of phosphorylated Smad1 and the expression of Hes1 as well as reducing the percentage of astrocytic SVZ progenitor cells. Our results indicate that BMSCs increase BMP2/4 expression in ischemic astrocytes. These changes enhance subventricular progenitor cell gliogenesis by activating relevant signaling pathways. BMSC-stimulated signaling of endogenous astrocytes may alter the ischemic environment, promoting remodeling of brain and hence, improve functional recovery after stroke.

Brain-derived neurotrophic factor is required for the establishment of the proper number of dopaminergic neurons in the substantia nigra pars compacta

Brain-derived neurotrophic factor (BDNF) has been implicated in regulating neuronal survival, differentiation, and synaptic plasticity. Reduced expression of BDNF within the substantia nigra accompanies the deterioration of dopaminergic neurons in Parkinson's disease (PD) patients. Analysis of the effects of long-term BDNF absence from the CNS has been difficult because of the early postnatal lethality of BDNF-/- mice. Mice with a floxed BDNF allele were bred with Wnt1-Cre mice to generate Wnt-BDNF(KO) mice that lack BDNF from the midbrain-hindbrain (MHB). These mice are viable but exhibit hindlimb clutching and poor rotarod performance. Tyrosine hydroxylase (TH)-positive neuron numbers in the substantia nigra pars compacta (SNC) were estimated using stereological methods, revealing a persistent approximately 23% reduction of these cells at postnatal day 21 (P21) in Wnt-BDNF(KO) mice compared with controls. The diminishment of TH-expressing neurons was present at birth and continued through P120. This deficit appears selective for the dopaminergic population, because at P21, total neuron number within the SNC, defined as neuronal nuclei protein-positive cells, was not significantly reduced. Interestingly, and similar to observations in PD patients, SNC neuron subpopulations are not equally affected. Calbindin- and calretinin-expressing SNC populations show no significant difference between Wnt-BDNF(KO) mice and controls. Thus, BDNF depletion from the MHB selectively leads to reduced TH expression in a subpopulation of neurons, but it remains unclear whether these cells are lost.

Bone morphogenetic protein-6 is expressed early by activated astrocytes in lesions of rat traumatic brain injury

We have analyzed early expression of bone morphogenetic protein-6 in rat brains subjected to traumatic brain injury. Bone morphogenetic protein-6 was expressed in neurons of the hippocampus and cortex in normal adult rat brains. A pronounced expression of bone morphogenetic protein-6 in astroglia located to the lesion became obvious 48 h postinjury. Bone morphogenetic protein-6(+) glia were distributed around the lesion, thus demarcating the injured tissue from normal brain. Double labeling by immunohistochemistry revealed that the major glial sources for bone morphogenetic protein-6 were reactive astrocytes and few ED1(+) or W3/13(+) cells co-expressed bone morphogenetic protein-6. Furthermore, bone morphogenetic protein-6 expression in neurons located to hippocampus and cortex of the lesioned hemisphere was up-regulated 3 days postinjury. In conclusion, this is the first description of bone morphogenetic protein-6 expression in traumatic brains. Our data suggest that bone morphogenetic protein-6 might be involved in astrogliosis and neuron protection following traumatic brain injury.

Neuroregenerative effects of BMP7 after stroke in rats

Previous reports have indicated that the expression of bone morphogenetic protein-7 (BMP7) is enhanced after ischemic injury in brain. This upregulation may induce endogenous neurorepair in the ischemic brain. The purpose of this study was to examine neuroregenerative effects of BMP7 after ischemia-reperfusion injury. Adult Sprague-Dawley rats were anesthetized with chloral hydrate. Right middle cerebral artery (MCA) was transiently ligated with 10-O suture for 1 h. One day after MCA occlusion, vehicle or BMP7 was infused to the contralateral cerebral ventricle. To identify possible neurogenesis, bromodeoxyurindine (BrdU) was systemically injected on the fourth and fifth days after MCA occlusion. Animals treated with BMP7 showed a rapid correction of body asymmetry and neurological deficits, suggesting BMP7 facilitates recovery after stroke. Animals were sacrificed at 1 month after stroke and brains were analyzed using immunohistological techniques. BMP7 treatment enhanced immunoreactivity of BrdU in the subventricular zone, lesioned cortex, and corpus callosum. These BrdU-positive cells co-labeled with nestin and NeuN. Our behavioral and anatomical data suggest that BMP7 promotes neuroregeneration in stroke animals, possibly through the proliferation of new neuronal precursors after ischemia.

Bone marrow stromal cells upregulate expression of bone morphogenetic proteins 2 and 4, gap junction protein connexin-43 and synaptophysin after stroke in rats

Bone morphogenetic proteins play a key role in astrocytic differentiation. Astrocytes express the gap junctional protein connexin-43, which permits exchange of small molecules in brain and enhances synaptic efficacy. Bone marrow stromal cells produce soluble factors including bone morphogenetic protein 2 and bone morphogenetic protein 4 (bone morphogenetic protein 2/4) in ischemic brain. Here, we tested whether intra-carotid infusion of bone marrow stromal cells promotes synaptophysin expression and neurological functional recovery after stroke in rats. Adult male Wistar rats were subjected to 2 h of right middle cerebral artery occlusion. Rats were treated with or without bone marrow stromal cells at 24 h after middle cerebral artery occlusion via intra-arterial injection (n=8/group). A battery of functional tests was performed. Immunostaining of 5-bromo-2-deoxyuridine, Ki67, bone morphogenetic protein 2/4, connexin-43, synaptophysin, glial fibrillary acidic protein, neuronal nuclear antigen, and double staining of 5-bromo-2-deoxyuridine/glial fibrillary acidic protein, 5-bromo-2-deoxyuridine/neuronal nuclear antigen, glial fibrillary acidic protein/bone morphogenetic protein 2/4 and glial fibrillary acidic protein/connexin-43 were employed. Rats treated with bone marrow stromal cells significantly (P<0.05) improved functional recovery compared with the controls. 5-Bromo-2-deoxyuridine and Ki67 positive cells in the ipsilateral subventricular zone were significantly (P<0.05) increased in bone marrow stromal cell treatment group compared with the controls, respectively. Administration of bone marrow stromal cells significantly (P<0.05) promoted the proliferating cell astrocytic differentiation, and increased bone morphogenetic protein 2/4, connexin-43 and synaptophysin expression in the ischemic boundary zone compared with the controls, respectively. Bone morphogenetic protein 2/4 expression correlated with the expression of connexin-43 (r=0.84, P<0.05) and connexin-43 expression correlated with the expression of synaptophysin (r=0.73, P<0.05) in the ischemic boundary zone, respectively. Administration of bone marrow stromal cells via an intra-carotid route increases endogenous brain bone morphogenetic protein 2/4 and connexin-43 expression in astrocytes and promotes synaptophysin expression, which may benefit functional recovery after stroke in rats.

Differential transcription ofBarhl1homeobox gene in restricted functional domains of the central nervous system suggests a role in brain patterning

The mouse Barhl1 homeogene, member of the BarH subfamily, play a crucial role in the cerebellum development and its human ortholog BARHL1 has been proposed as a positional and functional candidate gene for the Joubert syndrome, a form of cerebellar ataxia. The Barhl1 expression has been demonstrated to be induced by the transcription factor Math1 involved in BMP responses. We isolated the mouse Barhl1 by screening of a cDNA library with the Xenopus Xvent-2, member of the BarH subfamily, which acts in the BMP4 pathway during embryonic patterning and neural plate differentiation. We studied the detailed Barhl1 expression pattern and showed its transcription in spatio-temporally and functionally restricted domains of the developing central nervous system (CNS). Using our new optical microscopy technology, we compare the transcript steady state level and cell density in the Barhl1-expressing regions. We found that Barhl1 was transcribed in superior and inferior colliculi in the dorsal mesencephalon at a relatively low transcriptional level. In the diencephalon, Barhl1 was found higher expressed first within the basal plate and later in the mammillary region. In the cerebellum, Barhl1 showed the highest transcriptional level restricted to the anterior and posterior rhombic lips giving rise to the external and internal cerebellar granular cells and to the deep nuclei. In the spinal cord, Barhl1 showed similar expression level than in the cerebellum and is delimited to a subset of dorsal interneurons. Therefore, our results indicated that Barhl1 homeodomain gene is exclusively transcribed in restricted CNS domain at differential transcription levels which suggest a highly regulated transcriptional mechanism. In addition, these regional and cellular specificities indicated that Barhl1 may be involved in the differentiation of the specific subsets of neuronal progenitors.

BARHL1 homeogene, the human ortholog of the mouse Barhl1 involved in cerebellum development, shows regional and cellular specificities in restricted domains of developing human central nervous system

The mouse homeobox gene Barhl1 plays a central role in cerebellum development and its expression is activated by the transcription factor Math1 which is involved in bone morphogenetic protein response pathways. We studied the human ortholog BARHL1 and we found that human, mouse, monkey, rat, and zebrafish orthologs were highly conserved and are members of the BarH homeogene family, containing Drosophila BarH1 and BarH2. The N-terminus of BARHL1 protein presents two FIL domains and an acidic domain rich in serine/threonine and proline, while the C-terminus contains a canonical proline-rich domain. Secondary structure analysis showed that outside the three helixes of the homeodomain, BARHL1 protein has essentially random coil structure. We isolated BARHL1 and defined its expression pattern in human embryonic and fetal central nervous system (CNS) and compared it to the mouse Barhl1 transcription. BARHL1 mRNA was found exclusively in the CNS restricted to p1-p4 prosomeres of the diencephalon, to the dorsal cells of the mesencephalon, to the dorsal dl1 sensory neurons of the spinal cord, and to the rhombic lips yielding the cerebellar anlage. Detailed analysis of BARHL1 expression in fetal cerebellar cell layers using our new optic microscopy technology showed BARHL1 expression in external and internal granular cells and also in mouse adult granular cells, in agreement to Barhl1 null mouse phenotype affecting the differentiation and migration of granular cells. These findings indicate that the regional and cellular specificities of BARHL1 transcriptional control well correspond to the mouse Barhl1 transcription and suggest a potential role of this gene in the differentiation of BARHL1-expressing neuronal progenitors involved in the pattern formation of human cerebral and cerebellar structures.

Differential effects of growth/differentiation factor 5 and glial cell line-derived neurotrophic factor on dopaminergic neurons and astroglia in cultures of embryonic rat midbrain

Parkinson's disease is characterized by the progressive degeneration of midbrain dopaminergic neurons. Several studies have examined the effects of the dopaminergic neurotrophins growth/differentiation factor 5 (GDF5) and glial cell line-derived neurotrophic factor (GDNF) on these neurons in vitro. However, there is little information regarding their effects on astroglial cells. Here, the effects of GDF5 and GDNF on dopaminergic neuronal and astroglial survival and differentiation in embryonic rat midbrain cultures were examined. Both GDF5 and GDNF enhanced the survival and differentiation of dopaminergic neurons. GDF5 significantly increased the survival of astroglial cells, whereas GDNF had no significant effect on these cells. The possible involvement of astroglia in the dopaminergic neurotrophic effect induced by GDF5 was investigated by examining the effect of GDF5 on the survival of dopaminergic neurons in glia-depleted midbrain cultures. There was no significant difference between the survival of dopaminergic neurons in glia-depleted cultures treated with GDF5 and that in mixed cell cultures treated with GDF5, suggesting that GDF5 acts directly on dopaminergic neurons in exerting its neurotrophic effect. GDF5 and GDNF have been established as potent neurotrophic factors for dopaminergic neurons. However, the effects of adding a combination of these neurotrophins to midbrain cultures have not been previously examined. The present study found that combined treatment with GDF5 and GDNF significantly increased the survival of dopaminergic neurons in cultures compared with that in cultures treated with either neurotrophin alone. This was an additive effect, indicating that these neurotrophins act on separate subpopulations of dopaminergic neurons.

Stroke and TGF-beta proteins: glial cell line-derived neurotrophic factor and bone morphogenetic protein

Recent studies have indicated that proteins in the transforming growth factor-beta superfamily alter damage induced by various neuronal injuries. Of these proteins, glial cell line-derived neurotrophic factor (GDNF) and bone morphogenetic protein-7 (BMP-7) have unique protective and regenerative effects in stroke animals. Delivery of GDNF or BMP-7 to brain tissue reduced cerebral infarction and improved motor functions in stroke animals. Pretreatment with these factors reduced caspase-3 activity and DNA fragmentation in the ischemic brain region, suggesting that antiapoptotic effects are involved. Beside the protective effects, BMP-7 given after stroke improves locomotor function. These regenerative effects of BMP-7 may involve the enhancement of dendritic growth and remodeling. In this review, we illustrate the neuroprotective and neuroregenerative properties of GDNF and BMP-7 and emphasize their therapeutic potential for stroke.

SVZa neural stem cells differentiate into distinct lineages in response to BMP4

Neural stem cells (NSCs) reside in the anterior portion of the forebrain subventricular zone (SVZa) and generate the progenitors which will differentiate into neurons, and via a tangential migratory pathway, known as the rostral migratory stream (RMS), migrate to the olfactory bulbs (OB). Bone morphogenetic proteins (BMPs) play significant roles in neural development at different stages and locations, but their roles have not been determined in the SVZa. To explore possible roles of BMPs in SVZa NSCs, BMP4 at various concentrations were tested for their capacity to induce SVZa NSCs. The expression of BMP4 was also examined in living cells using a reportor vector, in which the BMP4 promotor was conjugated with red fluorescent protein (RFP). In the meantime, the differentiation of SVZa NSCs was dynamically monitored by using reportor vectors of the Nestin enhancer and the promoters of TH and GFAP. In the OB, high expression of BMP4 was found using both promoter activity analysis and in situ hybridization. However, low BMP4 expression was found in the RMS and only moderate expression of BMP4 was displayed in the SVZa. The results also demonstrated that low concentrations (1-5 ng/ml) of BMP4 promoted the proliferation of SVZa NSCs but high concentrations (10-100 ng/ml) of BMP4 inhibited this proliferation. BMP4 enhanced neuron commitment before 4 days but inhibited it after 4 days. As the antagonist of BMP4, Noggin almost completely blocked all these BMP4 responses. Thus, our findings indicate that BMP4 promotes the exit from the cell cycle and triggers the differentiation of neuron progenitors in the OB. BMP4 also promotes the proliferation of the committed neuron progenitors in the RMS, but in the SVZa, BMP4 may facilitate the commitment of NSCs into astrocytes.

Neurotrophic effects of bone morphogenetic protein-7 in a rat model of Parkinson's disease

Previous studies have demonstrated that pretreatment with bone morphogenetic protein-7 (BMP7) reduces ischemic neuronal injury in vivo. Moreover, exogenous application of BMP7 increases both the number of tyrosine hydroxylase (+) cells and dopamine (DA) uptake in rat mesencephalic cell cultures. The purpose of this study was to investigate the in vivo effects of BMP7 on 6-hydroxydopamine (6-OHDA) induced lesioning of midbrain DA neurons. Adult Fischer 344 rats were anesthetized and injected with BMP7 or vehicle into the left substantia nigra, followed by local administration of 9 microg of 6-OHDA into the left medial forebrain bundle. The lesioned animals that received BMP7 pretreatment, as compared to vehicle/6-OHDA controls, had a significant reduction in methamphetamine-induced rotation 1 month after the surgery. BMP7-pretreatment partially preserved KCl-induced dopamine release in the lesioned striatum and significantly increased TH immunoreactivity in the lesioned nigra and striatum. In summary, our data suggest that BMP7 has neuroprotective and/or neuroreparative effects against 6-OHDA lesioning of the nigrostriatal DA pathway in an animal model of Parkinson's disease (PD).

Effects of growth/differentiation factor 5 on the survival and morphology of embryonic rat midbrain dopaminergic neurones in vitro

Growth/differentiation factor 5 (GDF5) is a member of the transforming growth factor-beta superfamily that is expressed in the developing CNS, including the ventral mesencephalon (VM). GDF5 has been shown to increase the survival of dopaminergic neurones in animal models of Parkinson's disease. This study was aimed at characterising the effects of GDF5 on dopaminergic neurones in vitro. Treatment with GDF5 induced a three-fold increase in the number of dopaminergic neurones in embryonic day 14 rat VM cultures after six days in vitro. A significant increase was also observed in the numbers of astrocytes in GDF5-treated cultures. GDF5 treatment also had significant effects on the morphology of dopaminergic neurones in these cultures; total neurite length, number of branch points and somal area were all significantly increased after six days in vitro. Analysis of neurite length and numbers of branch points at each level of the neuritic field revealed that the most pronounced effects of GDF5 were on the secondary and tertiary levels of the neuritic field. The specific type I receptor for GDF5, bone morphogenetic protein receptor (BMPR)-Ib, was found to be strongly expressed in freshly-dissected E14 VM tissue, but its expression was lost with increasing time in culture. Accordingly, treatment with GDF5 for 24 h from the time of plating induced increases in the numbers of dopaminergic neurones, while treatment with GDF5 for 24 h after six days in vitro did not. This study shows that GDF5 can promote both the survival and morphological differentiation of VM dopaminergic neurones in vitro, lending support to its potential as a candidate dopaminergic neurotrophin for use in the treatment of Parkinson's disease.

Induction and specification of midbrain dopaminergic cells: focus on SHH, FGF8, and TGF-?

Cell-fate decisions along the dorsoventral and anterior-posterior axis of the neural tube are dictated by factors from signaling and organizing centers. According to the prevailing notion, the formation of mesencephalic dopaminergic neurons is directed by diffusable signals from the notochord, floor plate, and isthmic organizer. Sonic hedgehog (Shh), secreted by the notochord and floor plate, and fibroblast growth factor (FGF) 8, secreted by the isthmus, are thought to be key molecules involved in the development of midbrain dopaminergic neurons. During the last decade, the introduction of elegant explant culture systems and the generation of transgenic and mutant mice have greatly contributed to a better understanding of the molecular signals that direct the induction and specification of midbrain dopaminergic neurons. In this context, experimental evidence has challenged the dominant roles of Shh and FGF8 in dopaminergic neuron development. Additional molecules have been identified as being required for the generation of mesencephalic dopaminergic neurons, particularly members of the transforming growth factor beta superfamily.

Factors promoting survival of mesencephalic dopaminergic neurons

Growth factors promoting survival of mesencephalic dopaminergic neurons are discussed in the context of their requirement during development and adulthood. The expression of growth factors should be detectable in the nigrostriatal system during critical periods of development, i.e., during the period of ontogenetic cell death and synaptogenesis and during neurite extension and neurotransmitter synthesis. Growth factors discussed include members of the family of glial-cell-line-derived neurotrophic factors (GDNF), neurotrophins, transforming growth factors beta, and low molecular compounds mimicking growth factor activities. To date, the available data support the notion that GDNF is a highly promising candidate, although GDNF-null mice lack a dopaminergic phenotype. There remains a possibility that endogenous dopaminotrophic factors remain to be discovered.

Beneficial effects of intraventricularly administered BMP-7 following a striatal 6-hydroxydopamine lesion

The present study was undertaken to investigate the effects of bone morphogenetic protein-7 (BMP-7), also named osteogenic protein-1 (OP-1), on the progression of a striatal 6-hydroxydopamine (6-OHDA) lesion. BMP-7, a member of the transforming growth factor-beta (TGF-beta) superfamily of proteins, has been shown to have protective effects in other animal models of neuronal damage. In this study, male Fischer 344 rats received striatal 6-OHDA lesions followed 1 week later by an intraventricular dose of BMP-7. No significant effect of BMP-7 treatment on spontaneous locomotor activity was observed, however BMP-7 significantly increased the density of tyrosine hydroxylase (TH) immunoreactivity (TH-ir) in the substantia nigra (SN) pars compacta, in the lesioned hemisphere [31.7+/-5.2 (optical density (O.D.) arbitrary units) control vs. 50.2+/-4.3 O.D. BMP-7-treated; p<0.05]. Interestingly, BMP-7 significantly increased TH-ir in the SN of the non-lesioned hemisphere (pars reticulata: 14.8+/-1.19 O.D. control vs. 36+/-2.6 O.D. BMP-7-treated, p<0.05; pars compacta: 29.0+/-4.9 O.D. control vs. 64.4+/-6.9 O.D. BMP-7-treated, p<0.001). A significant increase in DA concentration in the contralateral, non-lesioned hemisphere was also noted (113.2 ng/g control vs. 198.2 ng/g BMP-7-treated, p<0.01). In contrast to other intraventricularly administered neurotrophic factors, BMP-7 was not associated with an increase in the sensitivity to pain. These results suggest that BMP-7 is able to act as a dopaminotrophic agent without unwanted side effects and as such may be a useful pharmacological tool in the treatment of Parkinson's disease in humans.

Expression of bone morphogenetic proteins in the brain during normal aging and in 6-hydroxydopamine-lesioned animals

Bone morphogenetic proteins (BMPs), BMP receptors (BMPRs), and endogenous BMP antagonists have been found to be critically important for the development of the central nervous system (CNS) and peripheral organs in mammals. There is also increasing evidence that this system has significant activity in the adult CNS. Accordingly, we studied the regional distribution of endogenous BMP ligand proteins, receptors, and antagonists during aging and after lesion of the midbrain dopamine pathways produced by 6-hydroxydopamine (6-OHDA). We found that there were only small changes in the levels of these molecules as a function of age. Interestingly, levels of BMP 7 and noggin, a BMP antagonist, were uniquely elevated in substantia nigra. Moreover, after lesions of the midbrain dopamine system by 6-hydroxydopamine, there was a marked reduction in levels of all BMP ligands, receptors and antagonists bilaterally in both substantia nigra and hippocampus. There were also differential changes in BMP ligands, receptors, and antagonists in the cortex and striatum after such lesions. Taken together, our results indicate significant expression of BMP-related molecules in the adult and aging brain, and suggest a dynamic and differential regulation of these molecules after perturbations.

Heparin-binding epidermal growth factor-like growth factor: a component in chromaffin granules which promotes the survival of nigrostriatal dopaminergic neurones in vitro and in vivo

Chromaffin cells can restore function to the damaged nigrostriatal dopaminergic system in animal models of Parkinson's disease. It has been reported that a protein which is released from chromaffin granules can promote the survival of dopaminergic neurones in vitro and protect them against N-methylpyridinium ion toxicity. This neurotrophic effect has been found to be mediated by astroglial cells and blocked by inhibitors of the epidermal growth factor (EGF) receptor signal transduction pathway. Here we report the identification of bovine heparin-binding EGF-like growth factor (HB-EGF) in chromaffin granules and the cloning of the respective cDNA from bovine-derived adrenal gland. Protein extracts from bovine chromaffin granules were found to promote the survival of embryonic dopaminergic neurones in culture, to the same extent as recombinant human HB-EGF. Furthermore, the neurotrophic action of the chromaffin granule extract could be abolished by antiserum to recombinant human HB-EGF. We also show that intracerebral injection of recombinant human HB-EGF protected the nigrostriatal dopaminergic system in an in vivo adult rat model of Parkinson's disease. Intracerebral administration of this protein at the same time as a 6-hydroxydopamine lesion of the medial forebrain bundle was found to spare dopamine levels in the striatum and tyrosine hydroxylase-immunopositive neurones in the midbrain. This study has found that the main component in chromaffin granules responsible for their neurotrophic effect on dopaminergic neurones is HB-EGF. Furthermore, HB-EGF has significant protective effects on nigrostriatal dopaminergic neurones in vivo, making it a potential candidate for use in the treatment of Parkinson's disease.

Retrograde Gbb signaling through the Bmp type 2 receptor wishful thinking regulates systemic FMRFa expression in Drosophila

Amidated neuropeptides of the FMRFamide class regulate numerous physiological processes including synaptic efficacy at the Drosophila neuromuscular junction (NMJ). We demonstrate here that mutations in wishful thinking (wit) a gene encoding a Drosophila Bmp type 2 receptor that is required for proper neurotransmitter release at the neuromuscular junction, also eliminates expression of FMRFa in that subset of neuroendocrine cells (Tv neurons) which provide the systemic supply of FMRFa peptides. We show that Gbb, a Bmp ligand expressed in the neurohemal organ provides a retrograde signal that helps specify the peptidergic phenotype of the Tv neurons. Finally, we show that supplying FMRFa in neurosecretory cells partially rescues the wit lethal phenotype without rescuing the primary morphological or electrophysiological defects of wit mutants. We propose that Wit and Gbb globally regulate NMJ function by controlling both the growth and transmitter release properties of the synapse as well as the expression of systemic modulators of NMJ synaptic activity.

Genetic analysis of the roles of Hh, FGF8, and nodal signaling during catecholaminergic system development in the zebrafish brain

CNS catecholaminergic neurons can be distinguished by their neurotransmitters as dopaminergic or noradrenergic and form in distinct regions at characteristic embryonic stages. This raises the question of whether all catecholaminergic neurons of one transmitter type are specified by the same set of factors. Therefore, we performed genetic analyses to define signaling requirements for the specification of distinct clusters of catecholaminergic neurons in zebrafish. In mutants affecting midbrain- hindbrain boundary (MHB) organizer formation, the earliest ventral diencephalic dopaminergic neurons appear normal. However, after 2 d of development, we observed fewer cells than in wild types, which suggests that the MHB provides proliferation or survival factors rather than specifying ventral diencephalic dopaminergic clusters. In hedgehog (Hh) pathway mutants, the formation of catecholaminergic neurons is affected only in the pretectal cluster. Surprisingly, neither fibroblast growth factor 8 (FGF8) alone nor in combination with Hh signaling is required for specification of early developing dopaminergic neurons. We analyzed the formation of prosomeric territories in the forebrain of Hh and Nodal pathway mutants to determine whether the absence of specific dopaminergic clusters may be caused by early patterning defects ablating corresponding parts of the CNS. In Nodal pathway mutants, ventral diencephalic and pretectal catecholaminergic neurons fail to develop, whereas both anatomical structures form at least in part. This suggests that Nodal signaling is required for catecholaminergic neuron specification. In summary, our results do not support the previously suggested dominant roles for sonic hedgehog and Fgf8 in specification of the first catecholaminergic neurons, but instead indicate a novel role for Nodal signaling in this process.

TGF-betas and their roles in the regulation of neuron survival

Transforming growth factor-betas (TGF-betas) are a still growing superfamily of cytokines with widespread distribution and diverse biological functions. They fall into several subfamilies including the TGF-betas 1, 2, and 3, the bone morphogenetic proteins (BMPs), the growth/differentiation factors (GDFs), activins and inhibins, and the members of the glial cell line-derived neurotrophic factor family. Following a brief description of their general roles and signaling in development, maintenance of homeostasis, and disease, we shall focus on their distribution in the CNS and their involvement in regulating neuron survival and death.

Normal nigrostriatal innervation but dopamine dysfunction in mice carrying hypomorphic tyrosine hydroxylase alleles

We investigated the use of the mouse tyrosine hydroxylase (TH) gene to drive knock-in constructs in catecholaminergic neurons. Two targeting constructs representing truncated forms of either of the BMP receptors ALK-2 or BMPR-II preceded by an internal ribosome entry site (IRES) were introduced into the 3' untranslated region of TH. An frt-flanked neomycin-resistance (neo(r)) cassette was placed in the 3' end of the targeting constructs. Mice homozygous for the knock-in alleles showed various degrees of hypokinetic behavior, depending mainly on whether the neo(r) cassette was removed. In situ hybridization and immunohistochemistry showed that TH mRNA and protein were variously down-regulated in these mouse strains. Reduced levels of dopamine and noradrenalin were found in several brain areas. However, number and morphology of neurons in substantia nigra and their projections to striatum appeared normal in the neo(r)-positive TH hypomorphic mice as examined by markers for L-aromatic amino acid decarboxylase and the dopamine transporter. Elimination of the neo(r) cassette from the knock-in alleles partially restored TH and dopamine levels. The present neo(r)-positive TH hypomorphic mice show that nigrostriatal innervation develops independently of TH and should find use as a model for conditions of reduced catecholamine synthesis, as seen in, for example, L-dihydroxyphenylalanine-responsive dystonia/infantile parkinsonism.

Intravenous administration of bone morphogenetic protein-7 after ischemia improves motor function in stroke rats

BACKGROUND AND PURPOSE

We and others have previously reported that bone morphogenetic protein-7 (BMP-7), given before middle cerebral artery occlusion (MCAO), reduces ischemic injury in brain. Recent studies have indicated that receptors for BMP are upregulated after brain ischemia. It is possible that this upregulation may facilitate endogenous neurorepair in the ischemic brain. The purpose of this study was to determine the neuroregenerative effects of BMP-7 given parenterally after ischemia/reperfusion injury.

METHODS

Adult Sprague-Dawley rats were anesthetized with chloral hydrate. The middle cerebral artery was transiently occluded by a filament inserted through the right internal carotid artery. The filament was removed after 60-minute ischemia to allow reperfusion. Some animals were killed 24 hours after MCAO to examine BMP-7 mRNA expression. Other animals received a single dose of intravenous BMP-7 or vehicle at 24 hours after MCAO and were used for subsequent behavioral studies and BMP-7 immunostaining.

RESULTS

BMP-7 mRNA was upregulated 24 hours after MCAO in untreated animals. BMP-7 immunoreactivity was dose-dependently increased on the ischemic side of the hippocampus/dentate on day 6 after MCAO in animals receiving intravenous injection of BMP-7. Animals receiving BMP-7 also showed a decrease in body asymmetry from day 7 to day 14 and an increase in locomotor activity on day 14 after MCAO.

CONCLUSIONS

Our data indicate that BMP-7, given parenterally after stroke, can pass through the blood-brain barrier on the ischemic side and induce behavioral recovery in stroke animals at longer testing times.

Glia induce dendritic growth in cultured sympathetic neurons by modulating the balance between bone morphogenetic proteins (BMPs) and BMP antagonists

Dendritic growth in cultured sympathetic neurons requires specific trophic interactions. Previous studies have demonstrated that either coculture with glia or exposure to recombinant bone morphogenetic proteins (BMPs) is both necessary and sufficient to induce dendrite formation. These observations led us to test the hypothesis that BMPs mediate glial-induced dendritic growth. In situ hybridization and immunocytochemical studies indicate that the spatiotemporal expression of BMP5, -6, and -7 in rat superior cervical ganglia (SCG) is consistent with their proposed role in dendritogenesis. In vitro, both SCG glia and neurons were found to express BMP mRNA and protein when grown in the presence or absence of the other cell type. However, addition of ganglionic glia to cultured sympathetic neurons causes a marked increase in BMP proteins coincident with a significant decrease in follistatin and noggin. Functional assays indicate that glial-induced dendritic growth is significantly reduced by BMP7 antibodies and completely inhibited by exogenous noggin and follistatin. These data suggest that glia influence the rapid perinatal expansion of the dendritic arbor in sympathetic neurons by increasing BMP activity via modulation of the balance between BMPs and their antagonists.

TGF-beta1 increases tyrosine hydroxylase expression by a mechanism blocked by BMP-2 in human neuroblastoma SH-SY5Y cells

Human neuroblastoma SH-SY5Y cells were used to study the effects of transforming growth factor beta1 (TGF-beta1) and bone morphogenetic protein 2 (BMP-2) on neuronal differentiation and acquisition of a catecholaminergic phenotype. SH-SY5Y cells express the intracellular factors activated through the receptors of the TGFbeta superfamily members, Smad1 and Smad4, as in basal conditions or after differentiation with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or retinoic acid (RA). TGF-beta1 and BMP-2 induce differentiation in SH-SY5Y cells by different pathways: the effect of TGF-beta1 is potentiated by TPA and the effect of BMP-2 is blocked by RA. Cell differentiation due to TGF-beta1 treatment is accompanied by an increase in tyrosine hydroxylase (TH) expression, more pronounced in the presence of TPA or RA and counteracted by BMP-2. BMP-2 and RA both induce noncatecholaminergic cell differentiation, and together they may induce choline acetyltransferase expression in serum-cultured cells. In conclusion, our results suggest that TGF-beta1 and BMP-2 may contribute, in opposite ways, to regulation of the neuronal catecholaminergic phenotype.

Bone morphogenetic protein-6 is a neurotrophic factor for calbindin-positive striatal neurons

Bone morphogenetic proteins (BMPs) are a set of members of the transforming growth factor-beta superfamily recently described as promoting the differentiation of several neuronal populations within the basal ganglia. This study examined whether a member of this family, BMP-6, could exert neurotrophic effects on the neurons of the striatum, in which BMP-6 mRNA had been previously detected during development. Here we show that BMP-6 increases the number and differentiation of calbindin-positive neurons in vitro. Indeed, BMP-6 increased the total area, the perimeter, and the degree of arborization of this neuronal population. This trophic factor promoted dendritic growth without modifying axonal length or soma area. Furthermore, BMP-6 increased the number of glial fibrillary acidic protein-positive cells while decreasing the number of nestin-positive cells. The suppression of cell proliferation or glial development by the antimitotic fluorodeoxyuridine removed the effects on striatal neurons, suggesting the involvement of astroglial cells in the differentiation induced by BMP-6. The current results confirm the relevance of BMPs in the development of the striatum and emphasize the crucial importance of the trophic interaction between glial and neuronal cells.

Bone morphogenetic proteins BMP-6 and BMP-7 have differential effects on survival and neurite outgrowth of cerebellar granule cell neurons

The bone morphogenetic proteins (BMPs) play an inductive role in the generation of cerebellar granule cells embryonically. Therefore, we chose to look at their effects on cerebellar granule cell survival and differentiation postnatally. The cells express mRNA for both BMP-6 and BMP-7, as well as for the receptors BMPRIA and BMPRII, demonstrating that the postnatal cells have the ability to form the heterodimer receptors needed to respond to BMPs. BMP-7 promotes cell survival, with a maximal effect at 10 ng/ml, whereas tenfold more BMP-6 is needed: Both were active over the course of 8 days in culture. In addition, both BMPs were able to protect the neurons against death from induced apoptosis (exposure to serum-free, low-potassium medium) or exposure to glutamate. However, only BMP-6 could stimulate neurite outgrowth, measured with a neurofilament ELISA, an effect that was seen over the first 6 days in culture. These results, taken together with others in the literature, suggest that the BMPs have strong neurotrophic effects that are both neuron specific and BMP specific.

BMP-2 and cAMP elevation confer locus coeruleus neurons responsiveness to multiple neurotrophic factors

The locus coeruleus (LC) is a major target of several neurodegenerative disorders, including Parkinson's and Alzheimer's diseases. However, very little is known of the trophic requirements of LC neurons. In the present work, we have studied the biological activity of neurotrophic factors from different families in E15 primary cultures of LC neurons. In agreement with previous results, neurotrophin-3 (NT-3) and also glial cell line- derived neurotrophic factor (GDNF) increased the number of embryonic LC noradrenergic neurons in the presence of serum. In serum-free conditions, none of the factors tested, including NT-3, GDNF, neurturin, basic fibroblast growth factor (bFGF), or bone morphogenetic protein-2 (BMP-2), promoted the survival of tyrosine hydroxylase (TH)-immunoreactive neurons at 6 days in vitro. However, when BMP-2 was coadministered with any of these factors the number of LC TH-positive neurons increased twofold. Similar results were obtained by cotreatment of LC neurons with forskolin and NT-3, bFGF, or BMP-2. The strongest effect (a fourfold increase in the number of TH-positive cells) was induced by cotreatment with forskolin, BMP-2, and GDNF. Thus, our results show that LC neurons require multiple factors for their survival and development, and suggest that activation of LC neurons by bone morphogenetic proteins and cAMP plays a decisive role in conferring noradrenergic neuron responsiveness to several trophic factors.

Upregulation of acetylcholine synthesis by bone morphogenetic protein 9 in a murine septal cell line

Previous studies showed that bone morphogenetic protein 9 (BMP-9) induces the expression of choline acetyltransferase and the vesicular acetylcholine (ACh) transporter, and upregulates ACh synthesis in cultured primary neurons from embryonic mouse septum [I. López-Coviella, B. Berse, R. Krauss, R.S. Thies, J.K. Blusztajn, Induction and maintenance of the neuronal cholinergic phenotype in the central nervous system by BMP-9. Science 289 (2000) 313-316]. In the present studies we investigated the effects of BMP-9 on ACh synthesis in the cholinergic mouse SN56T17 septal cell line. BMP-9 increased ACh synthesis in these cells up to 2.5-fold in a time- and dose-dependent, saturable manner. The maximal effect of BMP-9 was observed after a 3-day treatment and the median effective concentration of BMP-9 was 0.5 ng/ml. These data show that SN56T17 cells are a useful model for studies of the effects of BMPs on the cholinergic phenotype.

Traumatic injury-induced BMP7 expression in the adult rat spinal cord

It has been reported that bone morphogenetic proteins (BMPs) are involved in the generation of the central nervous system during development. However, the roles of BMPs in mature spinal cord have not been clarified. We examined the expression of BMP7 mRNA before and after traumatic injury of the adult rat spinal cord. BMP7 mRNA was already detectable at a relatively low level in uninjured spinal cord, but was dramatically increased after injury. Semiquantitative RT-PCR study further confirmed upregulation of BMP7 mRNA in injured spinal cord. In situ hybridization indicated that expression of BMP7 mRNA was present only in glial cells in uninjured spinal cord. After injury, the number of BMP7-expressing glial cells was increased, BMP7 expression also became apparent in motor neurons. It has been suggested that BMPs promote survival of subventricular zone cells in adult rats. Thus, our results suggest that increase in the expression of BMP7 promotes survival of neurons and glial cells after acute traumatic injury. In contrast, there is increasing evidence that BMPs inhibit neurogenesis and alternatively promote gliogenesis of neural progenitors, which are also present in adult spinal cord, suggesting that injury-upregulated BMP7 may regulate differentiation of glial cells from neural progenitors and may induce gliosis after central nervous system injury.

Brain-derived neurotrophic factor (BDNF) mediates bone morphogenetic protein-2 (BMP-2) effects on cultured striatal neurones

Bone morphogenetic proteins are members of the transforming growth factor-beta superfamily that have multiple functions in the developing nervous system. One of them, bone morphogenetic protein-2 (BMP-2), promotes the differentiation of cultured striatal neurones, enhancing dendrite growth and calbindin-positive phenotype. Bone morphogenetic proteins have been implicated in cooperative interactions with other neurotrophic factors. Here we examined whether the effects of BMP-2 on cultured striatal neurones are mediated or enhanced by other neurotrophic factors. BMP-2 had a cooperative effect with low doses of brain-derived neurotrophic factor or neurotrophin-3 (but not with other neurotrophic factors such as glial cell line-derived neurotrophic factor, neurturin or transforming growth factor-beta 2) on the number of calbindin-positive striatal neurones. Moreover, BMP-2 induced phosphorylated Trk immunoreactivity in cultured striatal neurones, suggesting that neurotrophins are involved in BMP-2 neurotrophic effects. The addition of TrkB-IgG or antibodies against brain-derived neurotrophic factor abolished the effects of BMP-2 on the number and degree of differentiation of calbindin-positive striatal neurones. Indeed, BMP-2 treatment increased brain-derived neurotrophic factor protein levels in treated cultures media and BDNF immunocytochemistry revealed that this neurotrophin was produced by neuronal cells. Taken together, these results indicate that brain-derived neurotrophic factor mediates the effects of BMP-2 on striatal neurones.

Astrogliosis in the adult and developing CNS: is there a role for proinflammatory cytokines?

Astrogliosis, characterized by the enhanced expression of GFAP, represents a remarkably homotypic response of astrocytes to all types of injuries of the CNS, including injuries of the developing CNS. As such, astrocytes serve as microsensors of the injured microenvironment regardless of their location in the CNS. The diversity of insults that engender astrogliosis and the brain-wide nature of the astrocytic response suggest that common injury factors serve as the trigger of this cellular reaction. One prominent theme that has emerged in recent years is that proinflammatory cytokines and chemokines serve as a stimulus for induction of astrogliosis. Here we present a brief critique of this hypothesis based on a review of literature and some of our own recentfindings. Studies of astrocytes, in vitro, clearly indicate that these cell types are responsive to a variety of growth factors, including cytokines and chemokines. A somewhat different picture, however, can be seen from data obtained in vivo. It is true that trauma and diseases of the nervous system, as well as some exposures to neurotoxic chemicals, can be associated with the expression in brain of large varieties of cytokines and chemokines. That these same conditions result in astrogliosis has fostered the circumstantial link between cytokine/chemokine expression and the induction of astrogliosis. Several lines of evidence argue against this view, including (a) suppression of cytokine expression does not suppress gliosis, (b) gliosis can occur in the absence of enhanced expression of cytokines, (c) elevations in brain cytokines can occur in the absence of gliosis and (d) the patterns of cytokine expression in the adult and developing CNS are more consistent with a trophic role for these chemical messengers rather than a role in the induction of inflammation. Enhanced expression of cytokines and chemokines after brain injury appear to be signal transduction events unrelated to the induction of astrogliosis.

Induction of a dopaminergic phenotype in cultured striatal neurons by bone morphogenetic proteins

In the present study, we examined whether the bone morphogenetic proteins (BMPs), which are important in the developmental specification of transmitter type in certain classes of neurons, might also play a role in signaling the differentiation of a dopaminergic (DA) phenotype. We found that BMP-2, -4 and -6 were each capable of inducing, in a dose and time dependent manner, moderate levels of the DA enzyme tyrosine hydroxylase (TH) in cultured neurons from the mouse embryonic striatum. In contradistinction to other TH-inducing agents, BMPs initiated de novo TH expression without the required synergy of exogenous growth factors or co-activating substances and in neurons presumably aged (E16) beyond the critical period for induction. However, the appearance of TH in induced cells was short-lived (24 h) and could not be prolonged by repeated supplementation with the BMPs. Inhibitors of the mitogen-activated protein kinase (MAPK/ERK) signaling pathway, PD98059 and apigenin, did not prevent TH induction by BMP-4, as they did other TH inducing agents, indicating that the MAPK/ERK pathway does not mediate BMPs effects on TH expression. We conclude that BMP-2, -4 and -6 can be added to the expanding inventory of agents capable of inducing TH, making them potentially important in the specification of a DA phenotype in stem/precursor cells for the treatment of Parkinson's disease.

Therapeutic potential of bone morphogenetic proteins

Recently, there has been substantial progress in the area of bone morphogenetic protein (BMP) research. This review serves as an up-to-date summary of the history of BMPs, the mechanisms of BMP signalling and the role of BMPs in adipose, kidney, liver, bone and nervous system. The potential of BMPs as therapeutic agents will also be discussed.

Bone morphogenetic protein-6 reduces ischemia-induced brain damage in rats

BACKGROUND AND PURPOSE

Bone morphogenetic protein-6 (BMP6) and its receptors are expressed in adult and fetal brain. Receptors for BMP6 are upregulated in adult brain after injury, leading to the suggestion that BMP6 is involved in the physiological response to neuronal injury. The purpose of this study was to determine whether there was a neuroprotective effect of BMP6 in vivo and in vitro.

METHODS

Lactate dehydrogenase and microtubule-associated protein-2 (MAP-2) activities were used to determine the protective effect of BMP6 against H(2)O(2) in primary cortical cultures. The neuroprotective effects of BMP6 were also studied in chloral hydrate-anesthetized rats. BMP6 or vehicle was injected into right cerebral cortex before transient right middle cerebral artery (MCA) ligation. Animals were killed for triphenyl-tetrazolium chloride staining, caspase-3 immunoreactivity and enzymatic assays, and TUNEL assay. A subgroup of animals were used for locomotor behavioral assays.

RESULTS

Application of H(2)O(2) increased lactate dehydrogenase activity and decreased the density of MAP-2(+) neurons in culture. Both responses were attenuated by BMP6 pretreatment. Complementary in vivo studies showed that pretreatment with BMP6 increased motor performance and generated less cerebral infarction induced by MCA ligation/reperfusion in rats. Pretreatment with BMP6 did not alter cerebral blood flow or physiological parameters. There was decreased ischemia-induced caspase-3 immunoreactivity, caspase-3 enzymatic activity, and density of TUNEL-positive cells in ischemic cortex in BMP6-treated animals.

CONCLUSIONS

BMP6 reduces ischemia/reperfusion injury, perhaps by attenuating molecular events underlying apoptosis.

Bone morphogenetic protein-2, but not bone morphogenetic protein-7, promotes dendritic growth and calbindin phenotype in cultured rat striatal neurons

Bone morphogenetic proteins are members of the transforming growth factor-beta superfamily. They are widely expressed in the mammalian nervous system, where they exert trophic effects on several neuronal populations. We studied the neurotrophic activity of bone morphogenetic protein-2 and bone morphogenetic protein-7 (also called osteogenic protein-1) on cultured striatal cells, previously shown to express bone morphogenetic protein ligands and receptors. Our results indicate that only bone morphogenetic protein-2 promoted the differentiation of GABAergic neurons, especially of the calbindin-positive subpopulation, the subset of projecting striatal neurons that degenerates in Huntington's disease. Bone morphogenetic protein-2 increased the area, perimeter and degree of arborization of GABAergic neurons, promoting calbindin phenotype without altering proliferation or apoptosis. In contrast, neither bone morphogenetic protein-2 nor -7 affected striatal cholinergic interneurons. However, they both increased the number of glial fibrillary acidic protein-positive cells. Suppression of glial proliferation with 5-fluorodeoxyuridine did not abolish bone morphogenetic protein-2 effects on the differentiation of striatal neurons, ruling out an indirect mechanism through astrocytes. In conclusion, our results show that bone morphogenetic protein-2 promotes the differentiation of cultured GABAergic striatal neurons, suggesting that bone morphogenetic proteins are involved in the development of the striatum.

Misexpression of noggin leads to septal defects in the outflow tract of the chick heart

BMP-2 and BMP-4 are known to be involved in the early events which specify the cardiac lineage. Their later patterns of expression in the developing mouse and chick heart, in the myocardium overlying the atrioventricular canal (AV) and outflow tract (OFT) cushions, also suggest that they may play a role in valvoseptal development. In this study, we have used a recombinant retrovirus expressing noggin to inhibit the function of BMP-2/4 in the developing chick heart. This procedure resulted in abnormal development of the OFT and the ventricular septum. A spectrum of abnormalities was seen ranging from common arterial trunk to double outlet right ventricle. In hearts infected with noggin virus, where the neural crest cells have been labelled, the results show that BMP-2/4 function is required for the migration of neural crest cells into the developing OFT to form the aortopulmonary septum. Prior to septation, misexpression of noggin also leads to a decrease in the number of proliferating mesenchymal cells within the proximal cushions of the outflow tract. These results suggest that BMP-2/4 function may mediate several key events during cardiac development.

The effect of bone morphogenetic protein-7 (BMP-7) on functional recovery, local cerebral glucose utilization and blood flow after transient focal cerebral ischemia in rats

Bone morphogenetic protein-7 (BMP-7) has been shown to enhance dendritic growth and improve functional recovery after experimental stroke. In this study, we examined the effect of BMP-7 on functional recovery, local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCMRglu) following transient middle cerebral artery occlusion. Sprague--Dawley rats (n=29) were anesthetized with halothane/nitrous oxide and received 2-h middle cerebral artery occlusion (MCAo) by poly-L-lysine-coated intraluminal suture. Rectal and cranial temperatures were regulated at 37.0--37.5 degrees C. BMP-7 or vehicle (volume, 25 microl) was administered intracisternally in a blinded fashion at 24 h after MCAo. Neurological status was evaluated during occlusion (60 min) and daily for 2 days after MCAo. In matched animal groups, LCMRglu was measured autoradiographically with [(14)C]2-deoxyglucose (2-DG) and LCBF with [(14)C]iodoantipyrine 48 h after MCAo. Four animals groups were studied: LCMRglu series (BMP-7, n=7; vehicle, n=8); LCBF series (BMP-7, n=6; vehicle, n=8). Average three-dimensional image data sets were constructed for each group and were compared by pixel-based statistical methods. Rectal and cranial temperatures, mean blood pressure, plasma glucose and blood gases were similar among groups. BMP-7 significantly improved the total neurological score compared to vehicle at 48 h after MCAo (7.3+/-0.4 vs. 9.0+/-0.2, respectively; P<0.0003). Compared to vehicle-rats, BMP-7 enhanced glucose utilization in the basal ganglia ipsilateral to stroke and improved LCBF in ipsilateral subthalamus, but decreased LCBF and LCMRglu in contralateral cortical regions.

TGF-β modulates programmed cell death in the retina of the developing chick embryo

Programmed cell death (PCD) is a key phenomenon in the regulation of cell number in multicellular organisms. We have shown that reduction of endogenous transforming growth factor β (TGF-β) prevents apoptotic PCD of neurons in the developing peripheral and central nervous system, suggesting that TGF-β is an important mediator of ontogenetic neuron death. Previous studies suggested that there are other pro-apoptotic molecules, nerve growth factor (NGF) and brain-derived neurotrophic factor, that induce cell death in the nervous system. In the developing chick retina, NGF induces PCD by activation of the p75 receptor. We have studied the role of TGF-β and its putative interdependence with NGF-mediated PCD in the chick retina. We found that TGF-β is present in the developing chick retina during the period of PCD and is essentially required to regulate PCD of retinal cells. TGF-β2, TGF-β3 and the ligand-binding TGF-β receptor can be detected immunocytochemically in the central retina, a region where apoptosis is most prominent during the early period of PCD. Application of a TGF-β-neutralizing antibody to chick embryos in ovo resulted in a decrease in the number of TUNEL-positive cells and a reduction of free nucleosome levels. In terms of magnitude, reduction of PCD caused by the neutralization of endogenous TGF-β was equivalent to that seen after anti-NGF application. Neutralization of both factors did not result in a further decrease in apoptosis, indicating that NGF and TGF-β may act on the same cell population. Furthermore, neutralization of TGF-β did not affect the expression of NGF or the p75-receptor. Our results suggest that TGF-β and NGF are both required to regulate cell death in the chick retina in vivo.

Bone morphogenetic proteins (BMP6 and BMP7) enhance the protective effect of neurotrophins on cultured septal cholinergic neurons during hypoglycemia

The effects of two bone morphogenetic proteins (BMP6, BMP7), alone and in combination with neurotrophins, were tested on cultures of embryonic day 15 rat septum. A week-long exposure to BMP6 or BMP7 in the optimal concentration range of 2-5 n M increased the activity of choline acetyltransferase (ChAT) by 1.6-2-fold, in both septal and combined septal-hippocampal cultures. The increase in ChAT activity reached significance after 4 days and continued to increase over an 11-day exposure. Under control culture conditions neither BMP significantly altered the number of cholinergic neurons, and BMP effects on ChAT activity were less than linearly additive with those of nerve growth factor. The effects of BMPs and BMP + neurotrophin combinations were also assayed under two stress conditions: low-density culture and hypoglycemia. In low-density cultures BMPs and BMP + neurotrophin combinations preserved ChAT activity more effectively than neurotrophins alone. During 24 h hypoglycemic stress, BMPs alone did not preserve ChAT activity, but BMP + neurotrophin combinations preserved ChAT activity much more effectively than neurotrophins alone. These results demonstrate that BMP6 and BMP7 enhance ChAT activity under control and low-density stress conditions, and that during a hypoglycemic stress their trophic effect requires and complements that exerted by neurotrophins.

Distribution of bone morphogenetic protein and bone morphogenetic protein receptor transcripts in the rodent nervous system and up-regulation of bone morphogenetic protein receptor type II in hippocampal dentate gyrus in a rat model of global cerebral ischemia

Bone morphogenetic proteins belong to the transforming growth factor-beta superfamily and act through serine/threonine kinase type I and type II receptors such as bone morphogenetic protein receptor type I and type II. In order to further understand the roles that these factors exert in the nervous system, we have examined the expression pattern of seven bone morphogenetic proteins and bone morphogenetic protein receptor type I and II transcripts in the brain and spinal cord of rodent. Whereas bone morphogenetic protein receptor type I expression was low in rat brain, in situ hybridization studies performed with specific digoxigenin-labelled riboprobes revealed the presence of bone morphogenetic protein receptor type II-positive cells throughout the brain, with a notable localization in dopaminergic cells of the substantia nigra. Bone morphogenetic protein receptor type II transcripts were also expressed by large motoneuron-like cells located in the ventral horn of the spinal cord and by sensory neurons of dorsal root ganglia. In addition, we observed a significant up-regulation of bone morphogenetic protein receptor type II in the granule cells of the dentate gyrus 48 h after transient global cerebral ischemia in rat suggesting that modulation of this receptor intervenes during neuronal plasticity or repair that occur upon brain injury. Among the potential ligands for this receptor, bone morphogenetic protein-6 and bone morphogenetic protein-7 were expressed in meninges and the choroid plexus, while bone morphogenetic protein-4-expressing cells were spatially and temporally regulated in myelinated structures during development and in the adult suggesting its expression in oligodendrocytes. These data clearly indicate that besides their roles in bone and embryonic tissues, bone morphogenetic proteins and their receptors may have also important functions in adult neural tissues.

Growth/differentiation factor-15/macrophage inhibitory cytokine-1 is a novel trophic factor for midbrain dopaminergic neurons in vivo

Transforming growth factor-betas (TGF-betas) constitute an expanding family of multifunctional cytokines with prominent roles in development, cell proliferation, differentiation, and repair. We have cloned, expressed, and raised antibodies against a distant member of the TGF-betas, growth/differentiation factor-15 (GDF-15). GDF-15 is identical to macrophage inhibitory cytokine-1 (MIC-1). GDF-15/MIC-1 mRNA and protein are widely distributed in the developing and adult CNS and peripheral nervous systems, including choroid plexus and CSF. GDF-15/MIC-1 is a potent survival promoting and protective factor for cultured and iron-intoxicated dopaminergic (DAergic) neurons cultured from the embryonic rat midbrain floor. The trophic effect of GDF-15/MIC-1 was not accompanied by an increase in cell proliferation and astroglial maturation, suggesting that GDF-15/MIC-1 probably acts directly on neurons. GDF-15/MIC-1 also protects 6-hydroxydopamine (6-OHDA)-lesioned nigrostriatal DAergic neurons in vivo. Unilateral injections of GDF-15/MIC-1 into the medial forebrain bundle just above the substantia nigra (SN) and into the left ventricle (20 microgram each) immediately before a 6-OHDA injection (8 microgram) prevented 6-OHDA-induced rotational behavior and significantly reduced losses of DAergic neurons in the SN. This protection was evident for at least 1 month. Administration of 5 microgram of GDF-15/MIC-1 in the same paradigm also provided significant neuroprotection. GDF-15/MIC-1 also promoted the serotonergic phenotype of cultured raphe neurons but did not support survival of rat motoneurons. Thus, GDF-15/MIC-1 is a novel neurotrophic factor with prominent effects on DAergic and serotonergic neurons. GDF-15/MIC-1 may therefore have a potential for the treatment of Parkinson's disease and disorders of the serotonergic system.

Opposing effects of bone morphogenetic proteins on neuron production and survival in the olfactory receptor neuron lineage

In olfactory epithelium (OE) cultures, bone morphogenetic proteins (BMPs) can strongly inhibit neurogenesis. Here we provide evidence that BMPs also promote, and indeed are required, for OE neurogenesis. Addition of the BMP antagonist noggin inhibited neurogenesis in OE-stromal cell co-cultures. Bmp2, Bmp4 and Bmp7 were expressed by OE stroma, and low concentrations of BMP4 (below the threshold for inhibition of neurogenesis) stimulated neurogenesis; BMP7 did not exhibit a stimulatory effect at any concentration tested. Stromal cell conditioned medium also stimulated neurogenesis; part of this effect was due to the presence within it of a noggin-binding factor or factors. Studies of the pro-neurogenic effect of BMP4 indicated that it did not increase progenitor cell proliferation, but rather promoted survival of newly generated olfactory receptor neurons. These findings indicate that BMPs exert both positive and negative effects on neurogenesis, depending on ligand identity, ligand concentration and the particular cell in the lineage that is responding. In addition, they reveal the presence of a factor or factors, produced by OE stroma, that can synergize with BMP4 to stimulate OE neurogenesis.

Noggin antagonizes BMP signaling to create a niche for adult neurogenesis

Large numbers of new neurons are born continuously in the adult subventricular zone (SVZ). The molecular niche of SVZ stem cells is poorly understood. Here, we show that the bone morphogenetic protein (BMP) antagonist Noggin is expressed by ependymal cells adjacent to the SVZ. SVZ cells were found to express BMPs as well as their cognate receptors. BMPs potently inhibited neurogenesis both in vitro and in vivo. BMP signaling cell-autonomously blocked the production of neurons by SVZ precursors by directing glial differentiation. Purified mouse Noggin protein promoted neurogenesis in vitro and inhibited glial cell differentiation. Ectopic Noggin promoted neuronal differentiation of SVZ cells grafted to the striatum. We thus propose that ependymal Noggin production creates a neurogenic environment in the adjacent SVZ by blocking endogenous BMP signaling.

Induction and maintenance of the neuronal cholinergic phenotype in the central nervous system by BMP-9

Bone morphogenetic proteins (BMPs) have multiple functions in the developing nervous system. A member of this family, BMP-9, was found to be highly expressed in the embryonic mouse septum and spinal cord, indicating a possible role in regulating the cholinergic phenotype. In cultured neurons, BMP-9 directly induced the expression of the cholinergic gene locus encoding choline acetyltransferase and the vesicular acetylcholine transporter and up-regulated acetylcholine synthesis. The effect was reversed upon withdrawal of BMP-9. Intracerebroventricular injection of BMP-9 increased acetylcholine levels in vivo. Although certain other BMPs also up-regulated the cholinergic phenotype in vitro, they were less effective than BMP-9. These data indicate that BMP-9 is a differentiating factor for cholinergic central nervous system neurons.

Bone morphogenetic proteins and bone morphogenetic protein gene therapy in neurological surgery: a review

OBJECTIVE

To review the uses of bone morphogenetic proteins (BMPs) and BMP gene therapy for the treatment of neurosurgical disorders.

METHODS

Literature review.

RESULTS

BMPs are members of the transforming growth factor beta superfamily, and they play an important role in the growth and development of numerous tissues, including bone, brain, and spinal cord. Although the majority of previous studies have focused on the regulatory functions of BMPs in the normal growth and differentiation of the skeletal system, BMPs also seem to be exquisitely involved in the regulation of cellular proliferation, survival, differentiation, apoptosis, and lineage commitment in the central nervous system. When specific BMPs are delivered on biological matrices, they have the capacity to induce bone, cartilage, ligament, and tendon at both heterotopic and orthotopic sites, suggesting that they may play a major role in the future treatment of spinal and craniofacial pathology. For example, recent studies have clearly demonstrated the usefulness of BMPs and BMP gene therapy for the induction of spinal arthrodesis in several animal models. In addition, several BMPs have been shown to have a neuroprotective effect in animal models of head injury, cerebral ischemia, and Parkinson's disease and may therefore have direct clinical applications for the treatment of central nervous system disorders.

CONCLUSION

As the physiological activity of BMPs in the development and pathology of the central nervous system and spine are more fully elucidated, BMP therapeutics and gene therapy will probably have numerous applications in neurological surgery.