Overexpression of pitx3 upregulates expression of BDNF and GDNF in SH-SY5Y cells and primary ventral mesencephalic cultures

Roles of Transcription Factors in the Development and Reprogramming of the Dopaminergic Neurons

The meso-diencephalic dopaminergic (mdDA) neurons regulate various critical processes in the mammalian nervous system, including voluntary movement and a wide range of behaviors such as mood, reward, addiction, and stress. mdDA neuronal loss is linked with one of the most prominent human movement neurological disorders, Parkinson’s disease (PD). How these cells die and regenerate are two of the most hotly debated PD research topics. As for the latter, it has been long known that a series of transcription factors (TFs) involves the development of mdDA neurons, specifying cell types and controlling developmental patterns. In vitro and in vivo, TFs regulate the expression of tyrosine hydroxylase, a dopamine transporter, vesicular monoamine transporter 2, and L-aromatic amino acid decarboxylase, all of which are critical for dopamine synthesis and transport in dopaminergic neurons (DA neurons). In this review, we encapsulate the molecular mechanism of TFs underlying embryonic growth and maturation of mdDA neurons and update achievements on dopaminergic cell therapy dependent on knowledge of TFs in mdDA neuronal development. We believe that a deeper understanding of the extrinsic and intrinsic factors that influence DA neurons’ fate and development in the midbrain could lead to a better strategy for PD cell therapy.

Synergistic Effects of Combined Nurr1 Overexpression and Natural Inducers on the More Efficient Production of Dopaminergic Neuron-Like Cells From Stem Cells

The development of dopaminergic (DA) neurons is a very complex process, and a combination of extrinsic and intrinsic factors involves their differentiation. Transcription factor, Nurr1 plays an essential role in the differentiation and maintenance of midbrain DA neurons. Nurr1-based therapies may restore DA function in Parkinson's disease (PD) by replacing damaged cells with differentiated cells derived from stem cells. Providing tissue-specific microenvironments such as brain extract can effectively induce dopaminergic gene expression in stem cells. The present study aimed to investigate the combined effects of Nurr1 gene overexpression and a neonatal rat brain extract (NRBE) induction on dopaminergic differentiation of P19 stem cells. In order to neural differentiation induction, stably Nurr1-transfected cells were treated with 100 μg/ml of NRBE. The differentiation potential of the cells was then evaluated during a period of 1–3 weeks via various methods. The initial evaluation of the cells by direct observation under a light microscope and cresyl violet specific staining, confirmed neuron-like morphology in the differentiated cells. In addition, different molecular and cellular techniques, including real-time PCR, immunofluorescence, and flow cytometry, demonstrated that the treated cells expressed pan-neuronal and dopaminergic markers. In all experimental groups, neuronal phenotype with dopaminergic neuron-like cells characteristics mainly appeared in the second week of the differentiation protocol. Overall, the results of the present study revealed for the first time the synergistic effects of Nurr1 gene overexpression and possible soluble factors that existed in NRBE on the differentiation of P19 stem cells into dopaminergic neuron-like cells.

Complementation of dopaminergic signaling by Pitx3-GDNF synergy induces dopamine secretion by multipotent Ntera2 cells

Human teratocarcinoma cell line Ntera2 (NT2) expresses dopamine signals and has shown its safe profile for clinical applications. Attempts to restore complete dopaminergic (DAergic) phenotype enabling these cells to secrete dopamine have not been fully successful so far. We applied a blend of gene transfer techniques and a defined medium to convert NT2 cells to fully DAergic. The cells were primarily engineered to overexpress the Pitx3 gene product and then cultured in a growth medium supplemented with knockout serum and retinoic acid to form embroid bodies (EBs). Trypsinization of EB colonies produced single cells ready for differentiation. Neuronal/DAergic induction was promoted by applying conditioned medium taken from engineered human astrocytomas over-secreting glial cell-derived neurotrophic factor (GDNF). Immunocytochemistry, reverse-transcription and real-time polymerase chain reaction analyses confirmed significantly induced expression of molecules involved in dopamine signaling and metabolism including tyrosine hydroxylase, Nurr1, dopamine transporter, and aromatic acid decarboxylase. High-performance liquid chromatography analysis indicated release of dopamine only from a class of fully differentiated cells expressing Pitx3 and exposed to GDNF. In addition, Pitx3 and GDNF additively promoted in vitro neuroprotection against Parkinsonian toxin. One month after transplantation to the striatum of 6-OHDA-leasioned rats, differentiated NT2 cells survived and induced significant increase in striatal volume. Besides, cell implantation improved motor coordination in Parkinson's disease (PD) rat models. Our findings highlight the importance of Pitx3-GDNF interplay in dopamine signaling and indicate that our strategy might be useful for the restoration of DAergic fate of NT2 cells to make them clinically applicable toward cell replacement therapy of PD.

Dysregulation of Transcription Factors: A Key Culprit Behind Neurodegenerative Disorders

Neurodegenerative diseases (NDs) are considered heterogeneous disorders characterized by progressive pathological changes in neuronal systems. Transcription factors are protein molecules that are important in regulating the expression of genes. Although the clinical manifestations of NDs vary, the pathological processes appear similar with regard to neuroinflammation, oxidative stress, and proteostasis, to which, as numerous studies have discovered, transcription factors are closely linked. In this review, we summarized and reviewed the roles of transcription factors in NDs, and then we elucidated their functions during pathological processes, and finally we discussed their therapeutic values in NDs.

Vitamin D regulation of GDNF/Ret signaling in dopaminergic neurons

1,25(OH)₂D₃ (vitamin D) appears essential for the normal development of dopaminergic neurons. Vitamin D affects dopamine synthesis and metabolism as well as expression of glial cell line-derived neurotrophic factor (GDNF), which is crucial for the survival of dopaminergic neurons. We investigated the role of vitamin D on GDNF and its receptors protooncogene tyrosine-protein kinase receptor Ret (C-Ret) and GDNF family receptor alpha 1 (GFRα1) signaling. To this end, we used a developmental vitamin D-deficient rat model and SH-SY5Y cells transfected with vitamin D receptor (VDR). The absence of vitamin D ligand in gestation reduces C-Ret expression, but not GDNF and GFRα1, in embryo forebrains. Overexpression of VDR in SH-SY5Y in the absence of ligand (mimicking in vivo developmental vitamin D deficiency) also suppressed C-Ret mRNA levels. In the presence of vitamin D, C-Ret mRNA and protein expression were increased. The chromatin immunoprecipitation results suggested that C-Ret is directly regulated by vitamin D via VDR. GDNF was also increased by vitamin D in these cells. Our small interfering RNA studies showed that knocking down VDR leads to an increase in C-Ret in the absence of ligand. Finally, we confirmed the inverse relationship between GFRα1 and C-Ret, as knocking down C-Ret led to increases in GFRα1 expression. These data extend our knowledge of the diverse and important roles played by vitamin D in dopamine physiology.-Pertile, R. A. N., Cui, X., Hammond, L., Eyles, D. W. Vitamin D regulation of GDNF/Ret signaling in dopaminergic neurons.

Impact of Pitx3 gene knockdown on glial cell line-derived neurotrophic factor transcriptional activity in dopaminergic neurons

Pitx3 is strongly associated with the phenotype, differentiation, and survival of dopaminergic neurons. The relationship between Pitx3 and glial cell line-derived neurotrophic factor (GDNF) in dopaminergic neurons remains poorly understood. The present investigation sought to construct and screen a lentivirus expression plasmid carrying a rat Pitx3 short hairpin (sh)RNA and to assess the impact of Pitx3 gene knockdown on GDNF transcriptional activity in MES23.5 dopaminergic neurons. Three pairs of interference sequences were designed and separately ligated into GV102 expression vectors. These recombinant plasmids were transfected into MES23.5 cells and western blot assays were performed to detect Pitx3 protein expression. Finally, the most effective Pitx3 shRNA and a dual-luciferase reporter gene plasmid carrying the GDNF promoter region (GDNF-luciferase) were cotransfected into MES23.5 cells. Sequencing showed that the synthesized sequences were identical to the three Pitx3 interference sequences. Inverted fluorescence microscopy revealed that the lentivirus expression plasmids carrying Pitx3-shRNA had 40–50% transfection efficiency. Western blot assay confirmed that the corresponding Pitx3 of the third knockdown sequence had the lowest expression level. Dual-luciferase reporter gene results showed that the GDNF transcriptional activity in dopaminergic cells cotransfected with both plasmids was decreased compared with those transfected with GDNF-luciferase alone. Together, the results showed that the designed Pitx3-shRNA interference sequence decreased Pitx3 protein expression, which decreased GDNF transcriptional activity.

Transcription Factors: Potential Cell Death Markers in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disease with a long preclinical phase. The continuous loss of dopaminergic (DA) neurons is one of the pathogenic hallmarks of PD. Diagnosis largely depends on clinical observation, but motor dysfunctions do not emerge until 70%-80% of the nigrostriatal nerve terminals have been destroyed. Therefore, a biomarker that indicates the degeneration of DA neurons is urgently needed. Transcription factors are sequence-specific DNA-binding proteins that regulate RNA synthesis from a DNA template. The precise control of gene expression plays a critical role in the development, maintenance, and survival of cells, including DA neurons. Deficiency of certain transcription factors has been associated with DA neuron loss and PD. In this review, we focus on some transcription factors and discuss their structure, function, mechanisms of neuroprotection, and their potential for use as biomarkers indicating the degeneration of DA neurons.

Pitx3 deficiency produces decreased dopamine signaling and induces motor deficits in Pitx3(-/-) mice

Midbrain dopamine (DA) neurons are involved in cognition, control of motor activity, and emotion-related behaviors. Degeneration of DA neurons particularly in the substantia nigra is a hallmark of Parkinson's disease. The homeobox transcription factor, Pitx3, plays a critical role in the development, function, and maintenance of midbrain DA neurons. We found that in young adult Pitx3-null mice, Pitx3(-/-), there was decreased tyrosine hydroxylase staining, indicating a loss of DA neurons particularly in the substantia nigra. In addition, fast-scan cyclic voltammetry and microdialysis assays of DA release indicated that the lack of Pitx3 caused a significant reduction of striatal DA release. Tonic DA release was impaired more significantly than the phasic DA release induced by burst firing of DA neurons. Furthermore, behavioral tests revealed that Pitx3(-/-) mice displayed abnormal motor activities, including impaired motor coordination and decreased locomotion. In summary, these data provide further evidence that Pitx3 is specifically required for DA-related function and, if impaired, Pitx3 could contribute during the pathogenesis of Parkinson's disease.

Molecular mechanisms of dopaminergic subset specification: fundamental aspects and clinical perspectives

Dopaminergic (DA) neurons in the ventral mesodiencephalon control locomotion and emotion and are affected in psychiatric and neurodegenerative diseases, such as Parkinson's disease (PD). A clinical hallmark of PD is the specific degeneration of DA neurons located within the substantia nigra (SNc), whereas neurons in the ventral tegmental area remain unaffected. Recent advances have highlighted that the selective vulnerability of the SNc may originate in subset-specific molecular programming during DA neuron development, and significantly increased our understanding of the molecular code that drives specific SNc development. We here present an up-to-date overview of molecular mechanisms that direct DA subset specification, integrating our current knowledge about subset-specific roles of transcription factors, signaling pathways and morphogenes. We discuss strategies to further unravel subset-specific gene-regulatory networks, and the clinical promise of fundamental knowledge about subset specification of DA neurons, with regards to cell replacement therapy and cell-type-specific vulnerability in PD.

Impaired motor coordination in Pitx3 overexpression mice

Midbrain dopaminergic (DA) neurons are involved in the regulation of voluntary movement and in emotion-related behaviors and are affected in Parkinson's disease (PD). The homeodomain transcription factor Pitx3, which is uniquely expressed in midbrain DA neurons, plays a critical role in the development, function and maintenance of midbrain DA neurons. Pitx3 deficiency results in selective deficits of midbrain DA neurons in the substantia nigra pars compacta (SNc), reminiscent of the specific DA neuronal loss observed in PD. In this study, we found that selective overexpression of Pitx3 in intact midbrain DA neurons significantly affects the function of midbrain DA neurons. We observed changes in DA levels and gene expressions in mice overexpressing Pitx3. Furthermore, motor coordination and locomotion activities are significantly affected in mice overexpressing Pitx3, suggesting that the expression level of Pitx3 plays an important role in the function of midbrain DA neuron in vivo.

A unilateral negative feedback loop between miR-200 microRNAs and Sox2/E2F3 controls neural progenitor cell-cycle exit and differentiation

MicroRNAs have emerged as key posttranscriptional regulators of gene expression during vertebrate development. We show that the miR-200 family plays a crucial role for the proper generation and survival of ventral neuronal populations in the murine midbrain/hindbrain region, including midbrain dopaminergic neurons, by directly targeting the pluripotency factor Sox2 and the cell-cycle regulator E2F3 in neural stem/progenitor cells. The lack of a negative regulation of Sox2 and E2F3 by miR-200 in conditional Dicer1 mutants (En1(+/Cre); Dicer1(flox/flox) mice) and after miR-200 knockdown in vitro leads to a strongly reduced cell-cycle exit and neuronal differentiation of ventral midbrain/hindbrain (vMH) neural progenitors, whereas the opposite effect is seen after miR-200 overexpression in primary vMH cells. Expression of miR-200 is in turn directly regulated by Sox2 and E2F3, thereby establishing a unilateral negative feedback loop required for the cell-cycle exit and neuronal differentiation of neural stem/progenitor cells. Our findings suggest that the posttranscriptional regulation of Sox2 and E2F3 by miR-200 family members might be a general mechanism to control the transition from a pluripotent/multipotent stem/progenitor cell to a postmitotic and more differentiated cell.

Pitx3 is a critical mediator of GDNF-induced BDNF expression in nigrostriatal dopaminergic neurons

Pitx3 is a critical homeodomain transcription factor for the proper development and survival of mesodiencephalic dopaminergic (mdDA) neurons in mammals. Several variants of this gene have been associated with human Parkinson's disease (PD), and lack of Pitx3 in mice causes the preferential loss of substantia nigra pars compacta (SNc) mdDA neurons that are most affected in PD. It is currently unclear how Pitx3 activity promotes the survival of SNc mdDA neurons and which factors act upstream and downstream of Pitx3 in this context. Here we show that a transient expression of glial cell line-derived neurotrophic factor (GDNF) in the murine ventral midbrain (VM) induces transcription of Pitx3 via NF-κB-mediated signaling, and that Pitx3 is in turn required for activating the expression of brain-derived neurotrophic factor (BDNF) in a rostrolateral (SNc) mdDA neuron subpopulation during embryogenesis. The loss of BDNF expression correlates with the increased apoptotic cell death of this mdDA neuronal subpopulation in Pitx3(-/-) mice, whereas treatment of VM cell cultures with BDNF augments the survival of the Pitx3(-/-) mdDA neurons. Most importantly, only BDNF but not GDNF protects mdDA neurons against 6-hydroxydopamine-induced cell death in the absence of Pitx3. As the feedforward regulation of GDNF, Pitx3, and BDNF expression also persists in the adult rodent brain, our data suggest that the disruption of the regulatory interaction between these three factors contributes to the loss of mdDA neurons in Pitx3(-/-) mutant mice and perhaps also in human PD.

PITX3 polymorphism is not associated with Parkinson's disease in a Chinese population

Several studies have indicated that three PITX3 single nucleotide polymorphisms (SNPs), rs2281983, rs4919621 and rs3758549, are likely to be associated with Parkinson's disease (PD) in Caucasians. Some studies also suggested an age-of-onset effect. We recently reported that allele and genotype frequencies did not differ between late-onset PD (LOPD) patients and controls for all three SNPs. To extend the analysis to early-onset PD (EOPD) patients, and to test whether an age-of-onset effect exists in Chinese, we genotyped these SNPs in 290 Chinese EOPD patients using a ligase detection reaction (LDR). For all three SNPs, allele and genotype frequencies did not differ between total PD patients and controls, between LOPD patients and controls, between EOPD patients and controls, or between LOPD and EOPD patients. Our results suggest that these PITX3 SNPs do not contribute to the risk of developing PD in EOPD or LOPD in Chinese.

PITX3 gene polymorphism is associated with Parkinson's disease in Chinese population

Genetic variants of PITX3 gene have been reported to be associated with Parkinson's disease (PD) in several populations. We conducted a case-control study and genotyped the three SNPs of PITX3 gene: rs2281983, rs4919621 and rs3758549 in 512 mainland Chinese PD patients and 506 healthy controls. Our findings show that the PITX3 gene rs3758549 polymorphism is associated with PD (p=0.02). Moreover, the difference between late onset PD patients and healthy controls is stronger (p=0.007). There is no statistical difference in genotype or allele frequencies of rs2281983 or rs4919621 variant in PITX3 gene between sporadic PD (SPD) group and healthy control group in our study. To assess the possible role of the PITX3 gene rs3758549 polymorphism in PD, we conducted a meta-analysis on the topic. The results of meta-analysis further support that the PITX3 gene rs3758549 polymorphism is associated with PD: Z=3.09, p=0.002, OR=0.89. These findings suggest that the PITX3 gene rs3758549 polymorphism may increase the susceptibility of PD.

Smooth-muscle-specific expression of neurotrophin-3 in mouse embryonic and neonatal gastrointestinal tract

Vagal gastrointestinal (GI) afferents are essential for the regulation of eating, body weight, and digestion. However, their functional organization and the way that this develops are poorly understood. Neurotrophin-3 (NT-3) is crucial for the survival of vagal sensory neurons and is expressed in the developing GI tract, possibly contributing to their survival and to other aspects of vagal afferent development. The identification of the functions of this peripheral NT-3 thus requires a detailed understanding of the localization and timing of its expression in the developing GI tract. We have studied embryos and neonates expressing the lacZ reporter gene from the NT-3 locus and found that NT-3 is expressed predominantly in the smooth muscle of the outer GI wall of the stomach, intestines, and associated blood vessels and in the stomach lamina propria and esophageal epithelium. NT-3 expression has been detected in the mesenchyme of the GI wall by embryonic day 12.5 (E12.5) and becomes restricted to smooth muscle and lamina propria by E15.5, whereas its expression in blood vessels and esophageal epithelium is first observed at E15.5. Expression in most tissues is maintained at least until postnatal day 4. The lack of colocalization of beta-galactosidase and markers for myenteric ganglion cell types suggests that NT-3 is not expressed in these ganglia. Therefore, NT-3 expression in the GI tract is largely restricted to smooth muscle at ages when vagal axons grow into the GI tract, and when vagal mechanoreceptors form in smooth muscle, consistent with its role in these processes and in vagal sensory neuron survival.

Vesicular monoamine transporter 2 and dopamine transporter are molecular targets of Pitx3 in the ventral midbrain dopamine neurons

Midbrain dopamine (mDA) neurons play critical roles in the regulation of voluntary movement and their dysfunction is associated with Parkinson's disease. Pitx3 has been implicated in the proper development of mDA neurons in the substantia nigra pars compacta, which are selectively lost in Parkinson's disease. However, the basic mechanisms underlying its role in mDA neuron development and/or survival are poorly understood. Toward this goal, we sought to identify downstream target genes of Pitx3 by comparing gene expression profiles in mDA neurons of wild-type and Pitx3-deficient aphakia mice. This global gene expression analysis revealed many potential target genes of Pitx3; in particular, the expression of vesicular monoamine transporter 2 and dopamine transporter, responsible for dopamine storage and reuptake, respectively, is greatly reduced in mDA neurons by Pitx3 ablation. In addition, gain-of-function analyses and chromatin immunoprecipitation strongly indicate that Pitx3 may directly activate transcription of vesicular monoamine transporter 2 and dopamine transporter genes, critically contributing to neurotransmission and/or survival of mDA neurons. As the two genes have been known to be regulated by Nurr1, another key dopaminergic transcription factor, we propose that Pitx3 and Nurr1 may coordinately regulate mDA specification and survival, at least in part, through a merging and overlapping downstream pathway.

Retinal pigment epithelial cells secrete neurotrophic factors and synthesize dopamine: possible contribution to therapeutic effects of RPE cell transplantation in Parkinson's disease

BACKGROUND

New strategies for the treatment of Parkinson's disease (PD) are shifted from dopamine (DA) replacement to regeneration or restoration of the nigro-striatal system. A cell therapy using human retinal pigment epithelial (RPE) cells as substitution for degenerated dopaminergic (DAergic) neurons has been developed and showed promising prospect in clinical treatment of PD, but the exact mechanism underlying this therapy is not fully elucidated. In the present study, we investigated whether the beneficial effects of this therapy are related to the trophic properties of RPE cells and their ability to synthesize DA.

METHODS

We evaluated the protective effects of conditioned medium (CM) from cultured RPE cells on the DAergic cells against 6-hydroxydopamine (6-OHDA)- and rotenone-induced neurotoxicity and determined the levels of glial cell derived neurotrophic factor (GDNF) and brain derived neurotrophic factor (BDNF) released by RPE cells. We also measured the DA synthesis and release. Finally we transplanted microcarriers-RPE cells into 6-OHDA lesioned rats and observed the improvement in apomorphine-induced rotations (AIR).

RESULTS

We report here: (1) CM from RPE cells can secret trophic factors GDNF and BDNF, and protect DAergic neurons against the 6-OHDA- and rotenone-induced cell injury; (2) cultured RPE cells express L-dopa decarboxylase (DDC) and synthesize DA; (3) RPE cells attached to microcarriers can survive in the host striatum and improve the AIR in 6-OHDA-lesioned animal model of PD; (4) GDNF and BDNF levels are found significantly higher in the RPE cell-grafted tissues.

CONCLUSION

These findings indicate the RPE cells have the ability to secret GDNF and BDNF, and synthesize DA, which probably contribute to the therapeutic effects of RPE cell transplantation in PD.

In-vitro analysis of Pitx3 in mesodiencephalic dopaminergic neuron maturation

The transcription factor Pitx3 is expressed exclusively by mesodiencephalic dopaminergic neurons; however, ablation of Pitx3 results in selective degeneration of primarily dopaminergic neurons of the substantia nigra pars compacta, the neuronal population that is most vulnerable in Parkinson's disease. Although the exact molecular mechanisms of the action of Pitx3 are unclear, roles in both terminal maturation and/or survival of substantia nigra dopaminergic neurons have been suggested. To investigate the connection between Pitx3 and selective neurodegeneration, we generated embryonic stem cells from a Pitx3-deficient mouse (aphakia) for in-vitro differentiation to dopaminergic neurons. This 'loss of function'in-vitro system allowed us to examine characteristic features in dopaminergic neuron development and to assess the role that Pitx3 plays in the differentiation/maturation process. We found that aphakia embryonic stem cells generated 50% fewer tyrosine hydroxylase-positive/microtubule-associated protein (Map)2-positive mature neurons compared with control cultures. The expression of dopamine transport regulators and vesicle release proteins was reduced and dopamine release was unregulated in the Pitx3-deficient tyrosine hydroxylase-positive neurons generated. Treatment of aphakia embryonic stem cell cultures with retinoic acid resulted in a significant increase in mesodiencephalic tyrosine hydroxylase-positive neurons, providing further support for the role of Pitx3 in dopaminergic neuron specification through the retinoic acid pathway. Our study, using Pitx3-deficient embryonic stem cells in an in-vitro differentiation culture system, allowed us to assess the role of Pitx3 in the specification and final maturation of dopaminergic neurons.

Transcription factor PITX3 gene in Parkinson's disease

PITX3 is a transcription factor important for the differentiation and survival of midbrain dopaminergic neurons during the development. Recent reports suggest that single nucleotide polymorphisms (SNP) in the gene may be associated with Parkinson's disease (PD). To verify their findings and to determine the nature of the association in a subset of our PD patients we have analyzed two PITX3 SNPs (rs2281983 and rs4919621) in 265 PD patients and compared them with 210 age-matched healthy controls. Our data show that the substitutions of C/T in SNP1 and A/T in SNP2 are significantly higher in PD, and this finding is even more robust in young onset and familial PD as compared with age-matched healthy controls. Our findings indicate that PITX3 may play a role in the pathogenesis of PD.

A Simple Breeding Protocol for the Procurement of Accurately Staged Rat Donor Embryos for Neural Transplantation

Obtaining accurately staged rat embryos can be difficult because of the variety of breeding protocols employed and because precise staging cannot be confirmed until excision of the embryos from the dam. The detection of estrus, pairing of animals, and confirmation of pregnancies is generally left to commercial suppliers, as in-house breeding can be laborious and unpredictable. Here we describe a simple, reliable in-house breeding protocol for the generation of accurately staged embryos as assessed by measurements of average crown to rump length (CRL).

Pitx3-transfected astrocytes secrete brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor and protect dopamine neurons in mesencephalon cultures

The transcription factor Pitx3 is crucial for the development and differentiation of dopamine (DA) neurons. Our previous work has shown the Pitx3 can up-regulate the expression of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) in neuroblastoma cell line SH-SY5Y. Primary astrocytes are the major nonneuronal cells and can be easily modified genetically to deliver therapeutic molecules into the brain, so we investigated whether Pitx3 can increase the expression and secretion of BDNF and GDNF in primary astrocytes. We first transfected Pitx3 plasmid in purified rat astrocytes and collected the conditioned medium (CM) from the Pitx3-transfected cultures, and then we measured the BDNF and GDNF levels from the CM and tested the protective effect of the CM against rotenone-induced DA neuron injury in ventral mesencephalon (VM) cultures. We found that the BDNF and GDNF levels were 1.4-fold and 1.5-fold higher in the CM from Pitx3-transfected astrocytes than empty vectors-transfected controls. Incubation with the CM from Pitx3-transfected astrocytes significantly attenuated the rotenone-induced DA neuron injury, and such protection can be significantly blocked by preincubation with antibodies against either BDNF or GDNF, whereas preincubation with purified BDNF or GDNF replicated the neuroprotection against rotenone-induced injury in VM cultures. These results demonstrate that Pitx3-transfection in astrocytes can up-regulate BDNF and GDNF expression and produce protective benefit to DA neurons, which might be a potential therapeutic alternative for Parkinson's disease.

Etiopathogenesis of Parkinson disease: a new beginning?

Parkinson disease (PD) probably represents a syndrome of different disorders and origins converging into a relatively uniform neurodegenerative process. Although clinical-pathological studies have suggested that the presymptomatic phase of PD may be relatively short, perhaps less than a decade, the authors postulate that the pathogenic mechanisms may begin much earlier, possibly even in the prenatal period. Thus, some patients with PD may be born with a fewer than normal number of dopaminergic (and nondopaminergic) neurons as a result of genetic or other abnormalities sustained during the prenatal or perinatal period; as a result of normal age-related neuronal attrition, they eventually reach the critical threshold (60% or more) of neuronal loss needed for onset of PD to become clinically manifest. The authors review the emerging evidence that genetic disruption of normal development, coupled with subsequent environmental factors (the so called multiple-hit hypothesis), plays an important role in the etiopathogenesis of PD.

Driving GDNF expression: the green and the red traffic lights

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a potent survival factor for dopaminergic neurons of the nigrostriatal pathway that degenerate in Parkinson's disease (PD). In animal models of PD, GDNF delivery to the striatum or the substantia nigra protects dopaminergic neurons against subsequent toxin-induced injury and rescues previously damaged neurons, promoting recovery of the motor function. Thus, GDNF was proposed as a potential therapy to PD aimed at slowing down, halting or reversing neurodegeneration, an issue addressed in previous reviews. However, the use of GDNF as a therapeutic agent for PD is hampered by the difficulty in delivering it to the brain. Another potential strategy is to stimulate the endogenous expression of GDNF, but in order to do that we need to understand how GDNF expression is regulated. The aim of this review is to do a comprehensive analysis of the state of the art on the control of endogenous GDNF expression in the nervous system, focusing mainly on the nigrostriatal pathway. We address the control of GDNF expression during development, in the adult brain and after injury, and how damaged neurons signal glial cells to up-regulate GDNF. Pharmacological agents or natural molecules that increase GDNF expression and show neuroprotective activity in animal models of PD are reviewed. We also provide an integrated overview of the signalling pathways linking receptors for these molecules to the induction of GDNF gene, which might also become targets for neuroprotective therapies in PD.

Protective effect of the green tea component, L-theanine on environmental toxins-induced neuronal cell death

Several environmental neurotoxins and oxidative stress inducers are known to damage the nervous system and are considered major factors associated with the selective vulnerability of nigral dopaminergic neurons in Parkinson's disease (PD). Gamma-glutamylethylamide (L-theanine), a natural glutamate analog in green tea, has been shown to exert strong anti-ischemic effect. In this study, we investigated the protective effects of L-theanine on neurotoxicity induced by PD-related neurotoxicants, rotenone and dieldrin in cultured human dopaminergic cell line, SH-SY5Y. Our initial experiments revealed that L-theanine (500 microM) attenuated both rotenone- and dieldrin-induced DNA fragmentation and apoptotic death in SH-SY5Y cells. In addition, L-theanine partially prevented both rotenone- and dieldrin-induced heme oxygenase-1 (HO-1) up-regulation. Both rotenone- and dieldrin-induced down-regulation of extracellular signal-regulated kinase1/2 (ERK1/2) phosphorylation was significantly blocked by pretreatment with L-theanine. Furthermore, pretreatment with L-theanine significantly attenuated the down-regulation of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) production in SH-SY5Y cells. These results suggest that L-theanine directly provide neuroprotection against PD-related neurotoxicants and may be clinically useful for preventing PD symptoms.