Signalling mechanisms underlying development and maintenance of dopamine neurons

The effects of induced type I diabetes on developmental regulation of GDNF, NRTN, and NCAM proteins in the dentate gyrus of male rat offspring

BACKGROUND

Maternal diabetes during pregnancy can affect the neurological development of offspring. Glial cell-derived neurotrophic factor (GDNF), neurturin (NRTN), and neural cell adhesion molecules (NCAM) are three important proteins for brain development. Therefore, this study aimed to investigate the impacts of the mentioned neurotrophic factors in the hippocampal dentate gyrus (DG) of rat offspring born to diabetic mothers.

METHODS

Wistar female rats were randomly allocated into diabetic (STZ-D) [(45 mg/kg BW, STZ (Streptozotocin), i.p)], diabetic + NPH insulin (STZ-INS) [(4-6 unit/kg/day SC)], and control groups. The animals in all groups were mated by non-diabetic male rats. Two weeks after birth, male pups from each group were sacrificed and then protein contents of GDNF, NRTN, and NCAM were evaluated using immunohistochemistry.

RESULTS

The study found that the expression of GDNF and NRTN in the hippocampus of diabetic rat offspring was significantly higher compared to the diabetic+ insulin and control groups, respectively (P < 0.01, P < 0.001). Additionally, the expression of NCAM was significantly higher in the diabetic group the diabetic+ insulin and control groups (P < 0.01, P < 0.001).

CONCLUSIONS

The results of the study revealed that diabetes during pregnancy significantly impacts the distribution pattern of GDNF, NRTN, and NCAM in the hippocampus of rat neonates.

Gut Microbiome Dysbiosis as a Potential Risk Factor for Idiopathic Toe-Walking in Children: A Review

Idiopathic toe walking (ITW) occurs in about 5% of children. Orthopedic treatment of ITW is complicated by the lack of a known etiology. Only half of the conservative and surgical methods of treatment give a stable positive result of normalizing gait. Available data indicate that the disease is heterogeneous and multifactorial. Recently, some children with ITW have been found to have genetic variants of mutations that can lead to the development of toe walking. At the same time, some children show sensorimotor impairment, but these studies are very limited. Sensorimotor dysfunction could potentially arise from an imbalanced production of neurotransmitters that play a crucial role in motor control. Using the data obtained in the studies of several pathologies manifested by the association of sensory-motor dysfunction and intestinal dysbiosis, we attempt to substantiate the notion that malfunction of neurotransmitter production is caused by the imbalance of gut microbiota metabolites as a result of dysbiosis. This review delves into the exciting possibility of a connection between variations in the microbiome and ITW. The purpose of this review is to establish a strong theoretical foundation and highlight the benefits of further exploring the possible connection between alterations in the microbiome and TW for further studies of ITW etiology.

Similarities and differences between nigral and enteric dopaminergic neurons unravel distinctive involvement in Parkinson's disease

In addition to the well-known degeneration of midbrain dopaminergic neurons, enteric neurons can also be affected in neurodegenerative disorders such as Parkinson's disease (PD). Dopaminergic neurons have recently been identified in the enteric nervous system (ENS). While ENS dopaminergic neurons have been shown to degenerate in genetic mouse models of PD, analyses of their survival in enteric biopsies of PD patients have provided inconsistent results to date. In this context, this review seeks to highlight the distinctive and shared factors and properties that control the evolution of these two sets of dopaminergic neurons from neuronal precursors to aging neurons. Although their cellular sources and developmental times of origin differ, midbrain and ENS dopaminergic neurons express many transcription factors in common and their respective environments express similar neurotrophic molecules. For example, Foxa2 and Sox6 are expressed by both populations to promote the specification, differentiation, and long-term maintenance of the dopaminergic phenotype. Both populations exhibit sustained patterns of excitability that drive intrinsic vulnerability over time. In disorders such as PD, colon biopsies have revealed aggregation of alpha-synuclein in the submucosal plexus where dopaminergic neurons reside and lack blood barrier protection. Thus, these enteric neurons may be more susceptible to neurotoxic insults and aggregation of α-synuclein that spreads from gut to midbrain. Under sustained stress, inefficient autophagy leads to neurodegeneration, GI motility dysfunction, and PD symptoms. Recent findings suggest that novel neurotrophic factors such as CDNF have the potential to be used as neuroprotective agents to prevent and treat ENS symptoms of PD.

Spaceflight and brain plasticity: Spaceflight effects on regional expression of neurotransmitter systems and neurotrophic factors encoding genes

The critical problem of space exploration is the effect of long-term space travel on brain functioning. Current information concerning the effects of actual spaceflight on the brain was obtained on rats and mice flown on five missions of Soviet/Russian biosatellites, NASA Neurolab Mission STS90, and International Space Station (ISS). The review provides converging lines of evidence that: 1) long-term spaceflight affects both principle regulators of brain neuroplasticity - neurotransmitters (5-HT and DA) and neurotrophic factors (CDNF, GDNF but not BDNF); 2) 5-HT- (5-HT_2A receptor and MAO A) and especially DA-related genes (TH, MAO A, COMT, D1 receptor, CDNF and GDNF) belong to the risk neurogenes; 3) brain response to spaceflight is region-specific. Substantia nigra, striatum and hypothalamus are highly sensitive to the long-term spaceflight: in these brain areas spaceflight decreased the expression of both DA-related and neurotrophic factors genes. Since DA system is involved in the regulation of movement and cognition the data discussed in the review could explain dysfunction of locomotion and behavior of astronauts and direct further investigations to the DA system.

Differential expression of glial cell line-derived neurotrophic factor splice variants in the mouse brain

Glial cell line-derived neurotrophic factor (GDNF) plays a critical role in neuronal survival and function. GDNF has two major splice variants in the brain, α-pro-GDNF and β-pro-GDNF, and both isoforms have strong neuroprotective effects on dopamine neurons. However, the expression of the GDNF splice variants in dopaminergic neurons in the brain remains unclear. Therefore, in this study, we investigated the mRNA and protein expression of α- and β-pro-GDNF in the mouse brain by real-time quantitative polymerase chain reaction, using splice variant-specific primers, and western blot analysis. At the mRNA level, β-pro-GDNF expression was significantly greater than that of α-pro-GDNF in the mouse brain. In contrast, at the protein level, α-pro-GDNF expression was markedly greater than that of β-pro-GDNF. To clarify the mechanism underlying this inverse relationship in mRNA and protein expression levels of the GDNF splice variants, we analyzed the expression of sorting protein-related receptor with A-type repeats (SorLA) by real-time quantitative polymerase chain reaction. At the mRNA level, SorLA was positively associated with β-pro-GDNF expression, but not with α-pro-GDNF expression. This suggests that the differential expression of α- and β-pro-GDNF in the mouse brain is related to SorLA expression. As a sorting protein, SorLA could contribute to the inverse relationship among the mRNA and protein levels of the GDNF isoforms. This study was approved by the Animal Ethics Committee of Xuzhou Medical University, China on July 14, 2016.

Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF) Elevates Stimulus-Evoked Release of Dopamine in Freely-Moving Rats

Neurotrophic factors (NTFs) hold potential as disease-modifying therapies for neurodegenerative disorders like Parkinson's disease. Glial cell line-derived neurotrophic factor (GDNF), cerebral dopamine neurotrophic factor (CDNF), and mesencephalic astrocyte-derived neurotrophic factor (MANF) have shown neuroprotective and restorative effects on nigral dopaminergic neurons in various animal models of Parkinson's disease. To date, however, their effects on brain neurochemistry have not been compared using in vivo microdialysis. We measured extracellular concentration of dopamine and activity of dopamine neurochemistry-regulating enzymes in the nigrostriatal system of rat brain. NTFs were unilaterally injected into the striatum of intact Wistar rats. Brain microdialysis experiments were performed 1 and 3 weeks later in freely-moving animals. One week after the treatment, we observed enhanced stimulus-evoked release of dopamine in the striatum of MANF-treated rats, but not in rats treated with GDNF or CDNF. MANF also increased dopamine turnover. Although GDNF did not affect the extracellular level of dopamine, we found significantly elevated tyrosine hydroxylase (TH) and catechol-O-methyltransferase (COMT) activity and decreased monoamine oxidase A (MAO-A) activity in striatal tissue samples 1 week after GDNF injection. The results show that GDNF, CDNF, and MANF have divergent effects on dopaminergic neurotransmission, as well as on dopamine synthetizing and metabolizing enzymes. Although the cellular mechanisms remain to be clarified, knowing the biological effects of exogenously administrated NTFs in intact brain is an important step towards developing novel neurotrophic treatments for degenerative brain diseases.

Neurturin overexpression in dopaminergic neurons induces presynaptic and postsynaptic structural changes in rats with chronic 6-hydroxydopamine lesion

The structural effect of neurturin (NRTN) on the nigrostriatal dopaminergic system in animals remains unknown, although NRTN has been shown to be effective in Parkinson's disease animal models. Herein, we aimed to demonstrate that NRTN overexpression in dopaminergic neurons stimulates both neurite outgrowths in the nigrostriatal pathway and striatal dendritic spines in aging rats with chronic 6-hydroxydopamine (6-OHDA) lesion. At week 12 after lesion, pTracer-mNRTN-His or pGreenLantern-1 plasmids were intranigrally transfected using the NTS-polyplex nanoparticles system. We showed that the transgenic expression in dopaminergic neurons remained until the end of the study (12 weeks). Only animals expressing NRTN-His showed recovery of tyrosine hydroxylase (TH)+ cells (28 ± 2%), their neurites (32 ± 2%) and the neuron-specific cytoskeletal marker β-III-tubulin in the substantia nigra; striatal TH(+) fibers were also recovered (52 ± 3%), when compared to the healthy condition. Neurotensin receptor type 1 levels were also significantly recovered in the substantia nigra and striatum. Dopamine recovery was 70 ± 4% in the striatum and complete in the substantia nigra. The number of dendritic spines of striatal medium spiny neurons was also significantly increased, but the recovery was not complete. Drug-activated circling behavior decreased by 73 ± 2% (methamphetamine) and 89 ± 1% (apomorphine). Similar decrease was observed in the spontaneous motor behavior. Our results demonstrate that NRTN causes presynaptic and postsynaptic restoration of the nigrostriatal dopaminergic system after a 6-OHDA-induced chronic lesion. However, those improvements did not reach the healthy condition, suggesting that NRTN exerts lesser neurotrophic effects than other neurotrophic approaches.

Dicer and microRNAs protect adult dopamine neurons

MicroRNAs (miRs) are important post-transcriptional regulators of gene expression implicated in neuronal development, differentiation, aging and neurodegenerative diseases, including Parkinson’s disease (PD). Several miRs have been linked to PD-associated genes, apoptosis and stress response pathways, suggesting that deregulation of miRs may contribute to the development of the neurodegenerative phenotype. Here, we investigate the cell-autonomous role of miR processing RNAse Dicer in the functional maintenance of adult dopamine (DA) neurons. We demonstrate a reduction of Dicer in the ventral midbrain and altered miR expression profiles in laser-microdissected DA neurons of aged mice. Using a mouse line expressing tamoxifen-inducible CreERT2 recombinase under control of the DA transporter promoter, we show that a tissue-specific conditional ablation of Dicer in DA neurons of adult mice led to decreased levels of striatal DA and its metabolites without a reduction in neuronal body numbers in hemizygous mice (Dicer^HET) and to progressive loss of DA neurons with severe locomotor deficits in nullizygous mice (Dicer^CKO). Moreover, we show that pharmacological stimulation of miR biosynthesis promoted survival of cultured DA neurons and reduced their vulnerability to thapsigargin-induced endoplasmic reticulum stress. Our data demonstrate that Dicer is crucial for maintenance of adult DA neurons, whereas a stimulation of miR production can promote neuronal survival, which may have direct implications for PD treatment.

Role of glial cell line-derived neurotrophic factor in the pathogenesis and treatment of mood disorders

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a survival factor for dopaminergic neurons, but GDNF has also been shown to promote development, differentiation, and protection of other central nervous system neurons and was thought to play an important role in various neuropsychiatric disorders. Severe mood disorders, such as primarily major depressive disorder and bipolar affective disorder, attract particular attention. These psychopathologies are characterized by structural alterations accompanied by the dysregulation of neuroprotective and neurotrophic signaling mechanisms required for the maturation, growth, and survival of neurons and glia. The main objective of this review is to summarize the recent findings and evaluate the potential role of GDNF in the pathogenesis and treatment of mood disorders. Specifically, it describes (1) the implication of GDNF in the mechanism of depression and in the effect of antidepressant drugs and mood stabilizers and (2) the interrelation between GDNF and brain neurotransmitters, playing a key role in the pathogenesis of depression. This review provides converging lines of evidence that (1) brain GDNF contributes to the mechanism underlying depressive disorders and the effect of antidepressants and mood stabilizers and (2) there is a cross-talk between GDNF and neurotransmitters representing a feedback system: GDNF-neurotransmitters and neurotransmitters-GDNF.

Dopaminergic Neurons and Brain Reward Pathways: From Neurogenesis to Circuit Assembly

Midbrain dopaminergic (DA) neurons in the substantia nigra pars compacta and ventral tegmental area regulate extrapyramidal movement and important cognitive functions, including motivation, reward associations, and habit learning. Dysfunctions in DA neuron circuitry have been implicated in several neuropsychiatric disorders, including addiction and schizophrenia, whereas selective degeneration of DA neurons in substantia nigra pars compacta is a key neuropathological feature in Parkinson disease. Efforts to understand these disorders have focused on dissecting the underlying causes, as well as developing therapeutic strategies to replenish dopamine deficiency. In particular, the promise of cell replacement therapies for clinical intervention has led to extensive research in the identification of mechanisms involved in DA neuron development. It is hoped that a comprehensive understanding of these mechanisms will lead to therapeutic strategies that improve the efficiency of DA neuron production, engraftment, and function. This review provides a comprehensive discussion on how Wnt/β-catenin and sonic hedgehog-Smoothened signaling mechanisms control the specification and expansion of DA progenitors and the differentiation of DA neurons. We also discuss how mechanisms involving transforming growth factor-β and transcriptional cofactor homeodomain interacting protein kinase 2 regulate the survival and maturation of DA neurons in early postnatal life. These results not only reveal fundamental mechanisms regulating DA neuron development, but also provide important insights to their potential contributions to neuropsychiatric and neurodegenerative diseases.

Therapeutic potential of the endoplasmic reticulum located and secreted CDNF/MANF family of neurotrophic factors in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder where dopamine (DA) neurons in the substantia nigra degenerate and die. Since no cure for PD exists, there is a need for disease-modifying drugs. Glial cell line-derived neurotrophic factor (GDNF) and related neurturin (NRTN) can protect and repair DA neurons in neurotoxin animal models of PD. However, GDNF was unable to rescue DA neurons in an α-synuclein model of PD, and both factors have shown modest effects in phase two clinical trials. Neurotrophic factors (NTFs), cerebral DA NTF (CDNF) and mesencephalic astrocyte-derived NTF (MANF) form a novel family of evolutionarily conserved, endoplasmic reticulum (ER) located and secreted NTFs. CDNF and MANF have a unique structure and an unparalleled dual mode of action that differs from other known NTFs. Both protect cells from ER stress, and regulate the unfolded protein response via interacting with chaperons, and CDNF dissolves intracellular α-synuclein aggregates. By binding to putative plasma membrane receptors, they promote the survival of DA neurons similarly to conventional NTFs. In animal models of PD, CDNF protects and repairs DA neurons, regulates ER stress, and improves motor function more efficiently than other NTFs.

Transcriptome analysis reveals transmembrane targets on transplantable midbrain dopamine progenitors

An important challenge for the continued development of cell therapy for Parkinson's disease (PD) is the establishment of procedures that better standardize cell preparations for use in transplantation. Although cell sorting has been an anticipated strategy, its application has been limited by lack of knowledge regarding transmembrane proteins that can be used to target and isolate progenitors for midbrain dopamine (mDA) neurons. We used a "FACS-array" approach to identify 18 genes for transmembrane proteins with high expression in mDA progenitors and describe the utility of four of these targets (Alcam, Chl1, Gfra1, and Igsf8) for isolating mDA progenitors from rat primary ventral mesencephalon through flow cytometry. Alcam and Chl1 facilitated a significant enrichment of mDA neurons following transplantation, while targeting of Gfra1 allowed for robust separation of dopamine and serotonin neurons. Importantly, we also show that mDA progenitors isolated on the basis of transmembrane proteins are capable of extensive, functional innervation of the host striatum and correction of motor impairment in a unilateral model of PD. These results are highly relevant for current efforts to establish safe and effective stem cell-based procedures for PD, where clinical translation will almost certainly require safety and standardization measures in order to deliver well-characterized cell preparations.

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.

Therapeutic effects of fucoidan in 6-hydroxydopamine-lesioned rat model of Parkinson's disease: Role of NADPH oxidase-1

AIMS

To explore the effect of fucoidan treatment on oxidative stress-mediated dopaminergic neuronal damage and its potential mechanisms.

METHODS

The effect of fucoidan was investigated in a 6-hydroxydopamine (6-OHDA) rat model of PD, an animal model considered appropriate for preclinical studies of PD therapy. The effects of fucoidan treatment on animal behavior and the survival ratio of dopaminergic neurons were investigated. We further observed the effect of fucoidan on microglia and the NADPH oxidases-1 (Nox1), a family of enzymes generating reactive oxygen species (ROS).

RESULTS

We found that chronic fucoidan administration mitigated the motor dysfunction induced by 6-OHDA. Similarly, fucoidan reduced the loss of DA neurons in the SNc and DA fibers in the striatum in 6-OHDA-lesioned rats. Moreover, we found that fucoidan inhibited the 6-OHDA-stimulating expression of Nox1 in both tyrosine hydroxylase (TH)-positive neurons and non-TH-positive neurons, prevented Nox1-sensitive oxidative stress and cell damage in SNc neurons. Fucoidan also effectively inhibited nigral microglial activation.

CONCLUSION

These results support the beneficial effect of fucoidan in 6-OHDA-lesioned rat model of PD. Fucoidan may suppress the Nox1-triggered oxidative stress in the SNc to protect DA neurons from 6-OHDA-induced toxicity and achieve its beneficial effect.

Adolescent social isolation influences cognitive function in adult rats

Adolescence is a critical period for neurodevelopment. Evidence from animal studies suggests that isolated rearing can exert negative effects on behavioral and brain development. The present study aimed to investigate the effects of adolescent social isolation on latent inhibition and brain-derived neurotrophic factor levels in the forebrain of adult rats. Male Wistar rats were randomly divided into adolescent isolation (isolated housing, 38–51 days of age) and social groups. Latent inhibition was tested at adulthood. Brain-derived neurotrophic factor levels were measured in the medial prefrontal cortex and nucleus accumbens by an enzyme-linked immunosorbent assay. Adolescent social isolation impaired latent inhibition and increased brain-derived neurotrophic factor levels in the medial prefrontal cortex of young adult rats. These data suggest that adolescent social isolation has a profound effect on cognitive function and neurotrophin levels in adult rats and may be used as an animal model of neurodevelopmental disorders.

Availability of Pre- and Pro-regions of Transgenic GDNF Affects the Ability to Induce Axonal Sprout Growth

Plasmids containing four GFP-tagged isoforms of the human GDNF gene, with both pre- and pro-regions (pre-pro- GDNF), with the pre- (pre-GDNF) or the pro-region (pro-GDNF) alone, and without the pre- and pro-regions (mGDNF), were used to transfect HEK293 cells (human embryonic kidney cell line). The effect of the transgenic products on the growth of processes was studied in the spinal ganglia of 14-day rat embryos. Media conditioned by the transgenic cells were used to culture explants and dissociated cells of embryonic dorsal root ganglia attached to the bottom of the plate. Medium conditioned by gfp-transgenic HEK293 cells was used as the control. Spinal ganglia explants and dissociated cells cultured in a medium supplemented with recombinant GDNF (recGDNF) as well as in conditioned media containing the pre-GDNF and mGDNF products demonstrated active growth of processes immunopositive for neuronal marker beta-3-tubulin as early as on culture day 4. The ganglia and cells cultured in control medium and media conditioned by cells transgenic for pro-GDNF had no or very few processes even after 10 days of culture.

Human neural stem cells survive long term in the midbrain of dopamine-depleted monkeys after GDNF overexpression and project neurites toward an appropriate target

Transplanted multipotent human fetal neural stem cells (hfNSCs) significantly improved the function of parkinsonian monkeys in a prior study primarily by neuroprotection, with only 3%-5% of cells expressing a dopamine (DA) phenotype. In this paper, we sought to determine whether further manipulation of the neural microenvironment by overexpression of a developmentally critical molecule, glial cell-derived neurotrophic factor (GDNF), in the host striatum could enhance DA differentiation of hfNSCs injected into the substantia nigra and elicit growth of their axons to the GDNF-expressing target. hfNSCs were transplanted into the midbrain of 10 green monkeys exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine. GDNF was delivered concomitantly to the striatum via an adeno-associated virus serotype 5 vector, and the fate of grafted cells was assessed after 11 months. Donor cells remained predominantly within the midbrain at the injection site and sprouted numerous neurofilament-immunoreactive fibers that appeared to course rostrally toward the striatum in parallel with tyrosine hydroxylase-immunoreactive fibers from the host substantia nigra but did not mature into DA neurons. This work suggests that hfNSCs can generate neurons that project long fibers in the adult primate brain. However, in the absence of region-specific signals and despite GDNF overexpression, hfNSCs did not differentiate into mature DA neurons in large numbers. It is encouraging, however, that the adult primate brain appeared to retain axonal guidance cues. We believe that transplantation of stem cells, specifically instructed ex vivo to yield DA neurons, could lead to reconstruction of some portion of the nigrostriatal pathway and prove beneficial for the parkinsonian condition.

Molecular Pathogenesis and Pathophysiology of Parkinson’s Disease: New Targets for New Therapies

Parkinson’s disease (PD) is a complex chronic neurodegenerative disease of unknown etiology. A conceptual framework for all chronic diseases involves a series of channels or pathways (aging, genetic, environment, oxidative stress, mitochondrial damage, protein aggregation, etc.) and their interactions. Those channels with specificities may explain the ‘developmental’ program that through transcriptional reprogramming results in stressed dopamine neurons that eventually become dysfunctional or die, giving rise to the clinical manifestations of PD. In Chapter 2 we review the molecular mechanisms of those channels that may be implicated in the pathogenesis of PD and the pathophysiology of the disease based on the anatomo‐physiological complexity of the basal ganglia. This illustrates that understanding the molecular mechanisms of a disease may not be enough, or we have to reach an adequate system level to understand the disease process. Finally, we suggest that common therapies used for the treatment of other chronic diseases may be useful for the treatment (or help to advance the understanding) of PD, as well as new targets for new therapies that may be useful in the prevention of, or to stop the progression of, PD and other synucleinopathies.

[The role of neurotrophic factors in regeneration of the nervous system]

Neurotrophic factors regulate survival, development, and function of nervous tissue. They act via two different classes of receptors and activation of various signaling pathways in the target cells. Illumination of their physiological role in the maintenance of central nervous system homeostasis as well as regeneration of damaged tissue have ignited expectations to heal neurodegenerative diseases, including amyotrophic late-ral sclerosis and Parkinson disease. Advances in pharmaco-therapy, gene therapy, and stem cell biology have enabled development of novel therapies with application of regenerating cell transplantation. In the foreseeable future, it may lead to the establishment of safe and effective ways of treatment of these severe and currently incurable diseases.

Normal midbrain dopaminergic neuron development and function in miR-133b mutant mice

Midbrain dopaminergic (mDA) neurons control movement and emotion, and their degeneration leads to motor and cognitive defects in Parkinson's disease (PD). miR-133b is a conserved microRNA that is thought to regulate mDA neuron differentiation by targeting Pitx3, a transcription factor required for appropriate development of mDA substantia nigra neurons. Moreover, miR-133b has been found to be depleted in the midbrain of PD patients. However, the function of miR-133b in the intact midbrain has not been determined. Here we show that miR-133b null mice have normal numbers of mDA neurons during development and aging. Dopamine levels are unchanged in the striatum, while expression of dopaminergic genes, including Pitx3, is also unaffected. Finally, motor coordination and both spontaneous and psychostimulant-induced locomotion are unaltered in miR-133b null mice, suggesting that miR-133b does not play a significant role in mDA neuron development and maintenance in vivo.

MANF regulates dopaminergic neuron development in larval zebrafish

Mesencephalic astrocyte derived neurotrophic factor (MANF) is recognized as a dopaminergic neurotrophic factor, which can protect dopaminergic neurons from neurotoxic damage. However, little is known about the function of MANF during the vertebrate development. Here, we report that MANF expression is widespread during embryonic development and in adult organs analyzed by qPCR and in situ hybridization in zebrafish. Knockdown of MANF expression with antisense splice-blocking morpholino oligonucleotides resulted in no apparent abnormal phenotype. Nevertheless, the dopamine level of MANF morphants was lower than that of the wild type larvae, the expression levels of the two tyrosine hydroxylase gene transcripts were decreased and a decrease in neuron number in certain groups of th1 and th2 cells in the diencephalon region in MANF morphants was observed. These defects were rescued by injection of exogenous manf mRNA. Strikingly, manf mRNA could partly restore the decrease of th1 positive cells in Nr4a2-deficient larvae. These results suggest that MANF is involved in the regulation of the development of dopaminergic system in zebrafish.

Gene therapy for the treatment of Parkinson's disease: the nature of the biologics expands the future indications

The pharmaceutical industry's development of therapeutic medications for the treatment of Parkinson's disease (PD) endures, as a result of the continuing need for better agents, and the increased clinical demand due to the aging population. Each new drug offers advantages and disadvantages to patients when compared to other medical offerings or surgical options. Deep brain stimulation (DBS) has become a standard surgical remedy for the effective treatment of select patients with PD, for whom most drug regimens have failed or become refractory. Similar to DBS as a surgical option, gene therapy for the treatment of PD is evolving as a future option. In the four different PD gene therapy approaches that have reached clinical trials investigators have documented an excellent safety profile associated with the stereotactic delivery, viral vectors and doses utilized, and transgenes expressed. In this article, we review the clinically relevant gene therapy strategies for the treatment of PD, concentrating on the published preclinical and clinical results, and the likely mechanisms involved. Based on these presentations, we advance an analysis of how the nature of the gene therapy used may eventually expand the scope and utility for the management of PD.

Glial cell line-derived neurotrophic factor receptor-α1 expressed in striatum in trans regulates development and injury response of dopamine neurons of the substantia nigra

Many of the cellular effects of glial cell line-derived neurotrophic factor are initiated by binding to GNDF family receptor alpha-1 (GFRα1), and mediated by diverse intracellular signaling pathways, most notably through the Ret tyrosine kinase. Ret may be activated by the cell autonomous expression of GFRα1 ('in cis'), or by its non-cell autonomous presence ('in trans'), in either a soluble or immobilized state. GFRα1 is expressed in the striatum, a target of the dopaminergic projection of the substantia nigra. To determine whether post-synaptic expression of GFRα1 in striatum in trans has effects on the development or adult responses to injury of dopamine neurons, we have created transgenic mice in which GFRα1 expression is selectively increased in striatum and other forebrain targets of the dopaminergic projection. Post-synaptic GFRα1 has profound effects on the development of dopamine neurons, resulting in a 40% increase in their adult number. This morphologic effect was associated with an augmented motor response to amphetamine. In adult mice, post-synaptic GFRα1 expression did not affect neuron survival following neurotoxic lesion, but it did increase the preservation of striatal dopaminergic innervation. We conclude that post-synaptic striatal GFRα1 expression has important effects on the biology of dopamine neurons in vivo.

Role of BDNF and GDNF in drug reward and relapse: a review

Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) are neurotrophic factors that are critical for the growth, survival, and differentiation of developing neurons. These neurotrophic factors also play important roles in the survival and function of adult neurons, learning and memory, and synaptic plasticity. Since the mid-1990s, investigators have studied the role of BDNF and GDNF in the behavioral effects of abused drugs and in the neuroadaptations induced by repeated exposure to drugs in the mesocorticolimbic dopamine system. Here, we review rodent studies on the role of BDNF and GDNF in drug reward, as assessed in the drug self-administration and the conditioned place preference procedures, and in drug relapse, as assessed in extinction and reinstatement procedures. Our main conclusion is that whether BDNF or GDNF would facilitate or inhibit drug-taking behaviors depends on the drug type, the brain site, the addiction phase (initiation, maintenance, or abstinence/relapse), and the time interval between site-specific BDNF or GDNF injections and the reward- and relapse-related behavioral assessments.

Characterization of the intracellular localization, processing, and secretion of two glial cell line-derived neurotrophic factor splice isoforms

Endocrine and neuronal cells have highly developed secretion mechanisms, and the secretion can be either constitutive or regulated by physiological stimuli. In the constitutive pathway, intracellular transport vesicles undergo immediate fusion reactions after arrival at the target. In regulated secretion, vesicles accumulate near the target membrane until triggered to fuse, typically by a local rise in free Ca(2+). In the present study, we characterize the processing and secretion mechanisms of the glial cell line-derived neurotrophic factor (GDNF). Although the function of GDNF has been extensively studied, very little is known about the basic cell biology of GDNF and its precursor forms (alpha)pro-GDNF and (beta)pro-GDNF that have different pro-regions. Our results show that both (alpha)pro-GDNF and (beta)pro-GDNF are secreted. We demonstrate that KCl-induced depolarization increases the secretion of (beta)pro-GDNF and corresponding mature GDNF, but not (alpha)pro-GDNF and corresponding mature GDNF, to the cell medium in a Ca(2+)-dependent manner. In parallel with this, immunofluorescence analysis of cells show that (alpha)pro-GDNF/GDNF is localized mostly in the Golgi complex, whereas (beta)pro-GDNF/GDNF is localized primarily in secretogranin II and Rab3A-positive vesicles of the regulated secretory pathway. In addition, we find that matrix metalloproteinases and plasmin that cleave pro-BDNF and pro-NGF are not responsible for the cleavage of pro-GDNF, whereas furin endoproteinase, PACE4, and proprotein convertases PC5A, PC5B, and PC7 can cleave pro-GDNF into mature GDNF. Thus, the processing and secretion mechanisms of GDNF are different from those of BDNF and NGF.

Novel CDNF/MANF family of neurotrophic factors

Current therapeutic interventions for neurodegenerative diseases alleviate only disease symptoms, while treatments that could stop or reverse actual degenerative processes are not available. Parkinson's disease (PD) is a movement disorder with characteristic degeneration of dopaminergic neurons in the midbrain. Few neurotrophic factors (NTFs) that promote survival, maintenance, and differentiation of affected brain neurons are considered as potential therapeutic agents for the treatment of neurodegenerative diseases. Thus, it is important to search and study new NTFs that could also be used in therapy. In this review, we discuss novel evolutionary conserved family of NTFs consisting of two members in the vertebrates, cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF). Invertebrates, including Drosophila and Caenorhabditis have a single protein homologous to vertebrate CDNF/MANF. Characteristic feature of these proteins is eight structurally conserved cysteine residues, which determine the protein fold. The crystal structure analysis revealed that CDNF and MANF consist of two domains; an amino-terminal saposin-like domain that may interact with lipids or membranes, and a presumably unfolded carboxy-terminal domain that may protect cells against endoplasmic reticulum stress. CDNF and MANF protect midbrain dopaminergic neurons and restore motor function in 6-hydroxydopamine rat model of PD in vivo. In line, Drosophila MANF is needed for the maintenance of dopaminergic neurites and dopamine levels in the fly, suggesting that the function of CDNF/MANF proteins is evolutionary conserved. Future studies will reveal the receptors and mode of action of these novel factors, which are potential therapeutic proteins for the treatment of PD.

Pro-survival role for Parkinson's associated gene DJ-1 revealed in trophically impaired dopaminergic neurons

A mouse genetic study reveals a novel cell-survival role for the Parkinson's disease-associated gene DJ-1 in dopaminergic neurons that have reduced support from endogenous survival factors.

The mechanisms underlying the selective death of substantia nigra (SN) neurons in Parkinson disease (PD) remain elusive. While inactivation of DJ-1, an oxidative stress suppressor, causes PD, animal models lacking DJ-1 show no overt dopaminergic (DA) neuron degeneration in the SN. Here, we show that aging mice lacking DJ-1 and the GDNF-receptor Ret in the DA system display an accelerated loss of SN cell bodies, but not axons, compared to mice that only lack Ret signaling. The survival requirement for DJ-1 is specific for the GIRK2-positive subpopulation in the SN which projects exclusively to the striatum and is more vulnerable in PD. Using Drosophila genetics, we show that constitutively active Ret and associated Ras/ERK, but not PI3K/Akt, signaling components interact genetically with DJ-1. Double loss-of-function experiments indicate that DJ-1 interacts with ERK signaling to control eye and wing development. Our study uncovers a conserved interaction between DJ-1 and Ret-mediated signaling and a novel cell survival role for DJ-1 in the mouse. A better understanding of the molecular connections between trophic signaling, cellular stress and aging could uncover new targets for drug development in PD.

The major pathological event in Parkinson disease is the loss of dopaminergic neurons in a midbrain structure, the substantia nigra. The study of familial Parkinson disease has uncovered several disease-associated genes, including DJ-1. Subsequent studies have suggested that the DJ-1 protein is a suppressor of oxidative stress that might modify signaling pathways that regulate cell survival. However, because animal models lacking DJ-1 function do not show dopaminergic neurodegeneration, the function(s) of DJ-1 in vivo remain unclear. Using mouse genetics, we found that DJ-1 is required for survival of neurons of the substantia nigra only in aging conditions and only in neurons that are partially impaired in receiving trophic signals. Aging mice that lack DJ-1 and Ret, a receptor for a neuronal survival factor, lose more dopaminergic neurons in the substantia nigra as compared with aging mice that lack only Ret. Using the fruit fly Drosophila, we determined that DJ-1 interacts with constitutively active Ret and with its associated downstream signaling pathways. Therefore, understanding the molecular connections between trophic signaling, cellular stress and aging could facilitate the identification of new targets for drug development in Parkinson Disease.

Minocycline protects dopaminergic neurons against long-term rotenone toxicity

BACKGROUND

In Parkinson's disease, most of current therapies only provide symptomatic treatment and so far there is no drug which directly affects the disease process.

OBJECTIVES

To investigate the neuroprotective effects of minocycline against long-term rotenone toxicity in primary dopaminergic cell cultures.

METHODS

Embryonic mice of 14-days-old were used for preparation of primary dopaminergic cell cultures. On the 6th day in vitro, prepared cultures were treated both with minocycline alone (1, 5, 10 and 20 microM) and concomitantly with rotenone (5 and 20 nM) and minocycline. Cultures were incubated at 37 degrees C for six consecutive days. On Day in vitro culture medium was aspirated and used for measuring lactate dehydrogenase. Cultured cells were fixed in 4% paraformaldhyde and stained immunohistochemically against tyrosine hydroxylase.

RESULTS

Treatment of cultures with 5 and 20 nM of rotenone significantly decreased the survival of tyrosine hydroxylase immunoreactive neurons by 27 and 31% and increased the release of lactate dehydrogenase into the culture medium by 31 and 236%, respectively compared to untreated controls. Minocycline (1, 5, 10 microM) significantly protected tyrosine hydroxylase immunoreactive neurons by 17, 15 and 19% and 13, 22 and 23% against 5 and 20 nM of rotenone, respectively compared to rotenone-treated cultures. Minocycline (only at 10 microM) significantly decreased the release of lactate dehydrogenase by 79% and 133% against 5 and 20 nM of rotenone, respectively.

CONCLUSION

Minocycline has neuroprotective potential against the progressive loss of tyrosine hydroxylase immunoreactive neurons induced by long-term rotenone toxicity in primary dopaminergic cultures.