Sonic hedgehog promotes the survival of specific CNS neuron populations and protects these cells from toxic insult In vitro

The crucial role of VPS35 and SHH in Parkinson's disease: Understanding the mechanisms behind the neurodegenerative disorder

Parkinson's disease (PD) is indeed a complex neurodegenerative disorder recognized by the progressive depletion of dopaminergic neurons in the brain, particularly in the substantia nigra region, leading to motor impairments and other symptoms. But at the molecular level, the study about PD still lacks. As the number of cases worldwide continues to increase, it is critical to focus on the cellular and molecular mechanisms of the disease's presentation and neurodegeneration to develop novel therapeutic approaches. At the molecular level, the complexity is more due to the involvement of vacuolar protein sorting 35 (VPS35) and sonic hedgehog (SHH) signaling in PD (directly or indirectly), leading to one of the most prominent hallmarks of the disease, which is an accumulation of α-synuclein. This elevated pathogenesis may result from impaired autophagy due to mutation in the case of VPS35 and impairment in SHH signaling at the molecular level. The traditional understanding of PD is marked by the disruption of dopaminergic neurons and dopaminergic signaling, which exacerbates symptoms of motor function deficits. However, the changes at the molecular level that are being disregarded also impact the overall health of the dopaminergic system. Gaining insight into these two unique mechanisms is essential to determine whether they give neuroprotection or have no effect on the health of neurons. Hence, here we tried to simplify the understanding of the role of VPS35 and SHH signaling to comprehend it in one direction.

IGFBP5 Promotes Neuronal Apoptosis in a 6-OHDA-Toxicant Model of Parkinson's Disease by Inhibiting the Sonic Hedgehog Signaling Pathway

INTRODUCTION

Parkinson's disease (PD) is the most common neurodegenerative disease worldwide. Studies have shown that insulin-like growth factor-binding protein 5 (IGFBP5) may contribute to methamphetamine-induced neurotoxicity and neuronal apoptosis in PC-12 cells and rat striatum. Here, we studied the expression and role of IGFBP5 in the 6-OHDA-toxicant model of PD.

METHODS

PC-12 and SH-SY5Y cells were exposed to 50 μm 6-OHDA for 24 h. qRT-PCR, western blotting, CCK-8 assay, EdU staining, annexin V staining, and immunofluorescence were performed to study the effects of IGFBP5-specific siRNAs. The effects of IGFBP5 on a rat 6-OHDA model of PD were confirmed by performing behavioral tests, tyrosine hydroxylase (TH) immunofluorescence staining, and western blotting.

RESULTS

In the GSE7621 dataset, IGFBP5 was highly expressed in the substantia nigra tissues of PD patients compared to healthy controls. In PC-12 and SH-SY5Y cells, IGFBP5 was upregulated following 6-OHDA exposure in a dose-dependent manner. Silencing of IGFBP5 promoted PC-12 and SH-SY5Y proliferation and inhibited apoptosis under 6-OHDA stimulation. Silencing of IGFBP5 relieved 6-OHDA-induced TH-positive neuron loss. Hedgehog signaling pathway was predicted as a downstream signaling pathway of IGFBP5. Negative regulation between IGFBP5 and sonic hedgehog (SHH) signaling pathway was confirmed in vitro. The effects of IGFBP5 silencing on SH-SY5Y cells were partially reversed using cyclopamine, a direct inhibitor of the SHH signaling pathway. In addition, silencing of IGFBP5 attenuated motor deficits and neuronal damage in 6-OHDA-induced PD rats.

CONCLUSION

Elevated IGFBP5 expression may be involved in 6-OHDA-induced neurotoxicity through regulation of the SHH signaling pathway.

IFN-γ promotes radioresistant Nestin-expressing progenitor regeneration in the developing cerebellum by augmenting Shh ligand production

BACKGROUND

Patients with brain tumors, especially pediatric brain tumors such as cerebellar medulloblastoma, always suffer from the severe side effects of radiotherapy. Regeneration of neural cells in irradiation-induced cerebellar injury has been reported, but the underlying mechanism remains elusive.

METHODS

We established an irradiation-induced developing cerebellum injury model in neonatal mice. Microarray, KEGG analysis and semi in vivo slice culture were performed for mechanistic study.

RESULTS

Nestin-expressing progenitors (NEPs) but not granule neuron precursors (GNPs) were resistant to irradiation and able to regenerate after irradiation. NEPs underwent less apoptosis but similar DNA damage following irradiation compared with GNPs. Subsequently, they started to proliferate and contributed to granule neurons regeneration dependent on the sonic hedgehog (Shh) pathway. In addition, irradiation increased Shh ligand provided by Purkinje cells. And microglia accumulated in the irradiated cerebellum producing more IFN-γ, which augmented Shh ligand production to promote NEP proliferation.

CONCLUSIONS

NEP was radioresistant and regenerative. IFN-γ was increased post irradiation to upregulate Shh ligand, contributing to NEP regeneration. Our study provides insight into the mechanisms of neural cell regeneration in irradiation injury of the developing cerebellum and will help to develop new therapeutic targets for minimizing the side effects of radiotherapy for brain tumors.

The role of Smo-Shh/Gli signaling activation in the prevention of neurological and ageing disorders

Sonic hedgehog (Shh) signaling is an essential central nervous system (CNS) pathway involved during embryonic development and later life stages. Further, it regulates cell division, cellular differentiation, and neuronal integrity. During CNS development, Smo-Shh signaling is significant in the proliferation of neuronal cells such as oligodendrocytes and glial cells. The initiation of the downstream signalling cascade through the 7-transmembrane protein Smoothened (Smo) promotes neuroprotection and restoration during neurological disorders. The dysregulation of Smo-Shh is linked to the proteolytic cleavage of GLI (glioma-associated homolog) into GLI3 (repressor), which suppresses target gene expression, leading to the disruption of cell growth processes. Smo-Shh aberrant signalling is responsible for several neurological complications contributing to physiological alterations like increased oxidative stress, neuronal excitotoxicity, neuroinflammation, and apoptosis. Moreover, activating Shh receptors in the brain promotes axonal elongation and increases neurotransmitters released from presynaptic terminals, thereby exerting neurogenesis, anti-oxidation, anti-inflammatory, and autophagy responses. Smo-Shh activators have been shown in preclinical and clinical studies to help prevent various neurodegenerative and neuropsychiatric disorders. Redox signalling has been found to play a critical role in regulating the activity of the Smo-Shh pathway and influencing downstream signalling events. In the current study ROS, a signalling molecule, was also essential in modulating the SMO-SHH gli signaling pathway in neurodegeneration. As a result of this investigation, dysregulation of the pathway contributes to the pathogenesis of various neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD).Thus, Smo-Shh signalling activators could be a potential therapeutic intervention to treat neurocomplications of brain disorders.

Dopaminergic neurons are not a major Sonic hedgehog ligand source for striatal cholinergic or PV interneurons

A model was previously proposed that DA neurons provide SHH ligand to striatal interneurons, which in turn support the survival of DA neurons through the release of trophic factors such as Glial cell-derived neurotrophic factor (GDNF). However, some key clinical observations do not support this proposed model, and a recent independent study shows that striatal cholinergic neuron survival does not rely on intact DA neuron projections. To resolve this discrepancy, we generated several independent mouse lines to examine the exact role of DA neuron-derived Shh signaling in the maintenance of the basal ganglia circuit and to identify the Shh-producing cells in the adult brain. Our data suggest that the deletion of Shh in DA neurons does not affect DA neuron survival or locomotive function in cKO mice during aging, nor does it affect the long-term survival of cholinergic or FS PV + interneurons in the striatum (STR).

Bone Marrow-Derived Mesenchymal Stem Cell-Derived Exosomes Containing Gli1 Alleviate Microglial Activation and Neuronal Apoptosis In Vitro and in a Mouse Parkinson Disease Model by Direct Inhibition of Sp1 Signaling

This study investigated possible therapeutic effect mechanisms of exosomes from bone marrow-derived mesenchymal stem cells (BMSC) in neuronal and microglial cells and in a Parkinson disease (PD) model. Neuronal SH-SY5Y cells and microglial HMC3 cells were subjected to 1-methyl-4-phenylpyridinium (MPP+) or LPS, respectively. The mRNA and protein expression was assessed using qRT-PCR, Western blotting, and enzyme-linked immunosorbent assay. Cell viability and apoptosis of SH-SY5Y cells were examined using the MTT assay and flow cytometry. Chromatin immunoprecipitation assays were performed to assess the binding relationship between glioma-associated oncogene homolog 1 (Gli1) and the Sp1 transcription factor promoter. BMSC-derived exosomes promoted cell proliferation and inhibited apoptosis in MPP+-treated SH-SY5Y cells and suppressed inflammatory markers in LPS-treated HMC3 cells. Sp1 knockdown decreased SH-SY5Y cell damage and HMC3 immune activation. Gli1 carried by BMSC exosomes directly bound with Sp1 to inhibit Sp1-mediated LRRK2 activation whereas exosomes secreted by Gli1-knockdown in BMSC did not. In a PD mouse model induced with MPTP, BMSC exosomes decreased neuron loss injury and the inflammatory response by inhibiting Sp1 signaling. Thus, BMSC-derived exosomal Gli1 alleviates inflammatory damage and neuronal apoptosis by inhibiting Sp1 in vitro and in vivo. These findings provide the basis for the potential clinical use of BMSC-derived exosomes in PD.

Macroautophagy supports Sonic Hedgehog signaling by promoting Patched1 degradation

Autophagy is a highly conservative self-digestion process to maintain intracellular homeostasis and to ensure the survival of cells under stress. Activation of Sonic Hedgehog (Shh) signaling depends on the normal endocytic degradation of pathway receptor Patched1 (Ptch1). It is unclear whether autophagy participates in the receptor endocytosis and modulates Shh signaling transduction. Here we found that blocking macroautophagy attenuates Shh signaling due to the failed transport of Smoothened (Smo) into primary cilia. At the upstream of Smo, Ptch1 was poly-ubiquitinated through K63-conjugated ubiquitin chains. Macroautophagy participates Shh-induced degradation of poly-ubiquitinated Ptch1, contributing to the activation of Shh signaling.

Primary cilia safeguard cortical neurons in neonatal mouse forebrain from environmental stress-induced dendritic degeneration

The developing brain is under the risk of exposure to a multitude of environmental stressors. While perinatal exposure to excessive levels of environmental stress is responsible for a wide spectrum of neurological and psychiatric conditions, the developing brain is equipped with intrinsic cell protection, the mechanisms of which remain unknown. Here we show, using neonatal mouse as a model system, that primary cilia, hair-like protrusions from the neuronal cell body, play an essential role in protecting immature neurons from the negative impacts of exposure to environmental stress. More specifically, we found that primary cilia prevent the degeneration of dendritic arbors upon exposure to alcohol and ketamine, two major cell stressors, by activating cilia-localized insulin-like growth factor 1 receptor and downstream Akt signaling. We also found that activation of this pathway inhibits Caspase-3 activation and caspase-mediated cleavage/fragmentation of cytoskeletal proteins in stress-exposed neurons. These results indicate that primary cilia play an integral role in mitigating adverse impacts of environmental stressors such as drugs on perinatal brain development.

The role of Shh signalling pathway in central nervous system development and related diseases

Sonic hedgehog (Shh) plays important roles in developmental of vertebrate animal central nervous system (CNS), and Gli is its downstream signal molecule. Shh signalling is essential for pattern formation, cell-fate specification, axon guidance, proliferation, survival and differentiation of neurons in CNS development. The abnormal signalling pathway of Shh leads to the occurrence of many nervous system diseases. The mechanism of Shh signalling is complex and remains incompletely understood. Nevertheless, studies have revealed that Shh signalling pathway is classified into canonical and non-canonical pathways. Here we review the role of the Shh signalling pathway and its impact in CNS development and related diseases. Specifically, we discuss the role of Shh in the spinal cord and brain development, cell differentiation and proliferation in CNS and related diseases such as brain tumour, Parkinson's diseases, epilepsy, autism, depression and traumatic brain injury. We also highlight future directions of research that could help to clarify the mechanisms and consequences of Shh signalling in the process of CNS development and related diseases. SIGNIFICANCE OF THE STUDY: This review summarized the role of Shh signalling pathway in CNS development and related diseases such as brain tumour, Parkinson's diseases, epilepsy, autism, depression and traumatic brain injury. It also presented the author's opinions on the future research direction of Shh signalling pathway.

Induced pluripotent stem cell-based modeling of mutant LRRK2-associated Parkinson's disease

Recent advances in cell reprogramming have enabled assessment of disease-related cellular traits in patient-derived somatic cells, thus providing a versatile platform for disease modeling and drug development. Given the limited access to vital human brain cells, this technology is especially relevant for neurodegenerative disorders such as Parkinson's disease (PD) as a tool to decipher underlying pathomechanisms. Importantly, recent progress in genome-editing technologies has provided an ability to analyze isogenic induced pluripotent stem cell (iPSC) pairs that differ only in a single genetic change, thus allowing a thorough assessment of the molecular and cellular phenotypes that result from monogenetic risk factors. In this review, we summarize the current state of iPSC-based modeling of PD with a focus on leucine-rich repeat kinase 2 (LRRK2), one of the most prominent monogenetic risk factors for PD linked to both familial and idiopathic forms. The LRRK2 protein is a primarily cytosolic multi-domain protein contributing to regulation of several pathways including autophagy, mitochondrial function, vesicle transport, nuclear architecture and cell morphology. We summarize iPSC-based studies that contributed to improving our understanding of the function of LRRK2 and its variants in the context of PD etiopathology. These data, along with results obtained in our own studies, underscore the multifaceted role of LRRK2 in regulating cellular homeostasis on several levels, including proteostasis, mitochondrial dynamics and regulation of the cytoskeleton. Finally, we expound advantages and limitations of reprogramming technologies for disease modeling and drug development and provide an outlook on future challenges and expectations offered by this exciting technology.

Neurotrophic Factors: An Overview

The neurotrophins are a family of closely related proteins that were first identified as survival factors for sympathetic and sensory neurons and have since been shown to control a number of aspects of survival, development, and function of neurons in both the central and peripheral nervous systems. Limiting quantities of neurotrophins during development control the numbers of surviving neurons to ensure a match between neurons and the requirement for a suitable density of target innervation. Biological effects of each of the four mammalian neurotrophins are mediated through activation of one or more of the three members of the tropomyosin-related kinase (Trk) family of receptor tyrosine kinases (TrkA, TrkB, and TrkC). In addition, all neurotrophins activate the p75 neurotrophin receptor (p75^NTR), a member of the tumor necrosis factor receptor superfamily. Neurotrophin engagement of Trk receptors leads to activation of Ras, phosphatidylinositol 3-kinase, phospholipase C-γ1, and signaling pathways controlled through these proteins, including the mitogen-activated protein kinases. Neurotrophin availability is required into adulthood, where they control synaptic function and plasticity and sustain neuronal cell survival, morphology, and differentiation. This article will provide an overview of neurotrophin biology, their receptors, and signaling pathways.

Sonic hedgehog signalling mediates astrocyte crosstalk with neurons to confer neuroprotection

Sonic hedgehog (SHH) is a glycoprotein associated with development that is also expressed in the adult CNS and released after brain injury. Since the SHH receptors patched homolog‐1 and Smoothened are highly expressed on astrocytes, we hypothesized that SHH regulates astrocyte function. Primary mouse cortical astrocytes derived from embryonic Swiss mouse cortices, were treated with two chemically distinct agonists of the SHH pathway, which caused astrocytes to elongate and proliferate. These changes are accompanied by decreases in the major astrocyte glutamate transporter‐1 and the astrocyte intermediate filament protein glial fibrillary acidic protein. Multisite electrophysiological recordings revealed that the SHH agonist, smoothened agonist suppressed neuronal firing in astrocyte‐neuron co‐cultures and this was abolished by the astrocyte metabolic inhibitor ethylfluoroacetate, revealing that SHH stimulation of metabolically active astrocytes influences neuronal firing. Using three‐dimensional co‐culture, MAP2 western blotting and immunohistochemistry, we show that SHH‐stimulated astrocytes protect neurons from kainate‐induced cell death. Altogether the results show that SHH regulation of astrocyte function represents an endogenous neuroprotective mechanism.

Targeting sonic hedgehog signaling in neurological disorders

Sonic hedgehog (Shh) signaling influences neurogenesis and neural patterning during the development of central nervous system. Dysregulation of Shh signaling in brain leads to neurological disorders like autism spectrum disorder, depression, dementia, stroke, Parkinson's diseases, Huntington's disease, locomotor deficit, epilepsy, demyelinating disease, neuropathies as well as brain tumors. The synthesis, processing and transport of Shh ligand as well as the localization of its receptors and signal transduction in the central nervous system has been carefully reviewed. Further, we summarize the regulation of small molecule modulators of Shh pathway with potential in neurological disorders. In conclusion, further studies are warranted to demonstrate the potential of positive and negative regulators of the Shh pathway in neurological disorders.

Effect of the sonic hedgehog receptor smoothened on the survival and function of dopaminergic neurons

OBJECTIVE

To determine the influence of the sonic hedgehog (shh) pathway and its receptor smoothened (smo), on the survival and functionality of dopaminergic (DA) neurons.

BACKGROUND

During early development, shh induces the differentiation of DA neurons. However, it is unknown whether shh signaling is required in the maturation or maintenance of DA neurons during later development and adulthood due to the lethality of traditional shh knockout models.

METHODS

We utilized the cre-loxP system to achieve late developmental stage and cell type-specific deletion of the shh receptor, smo, in DA neurons by crossing DATcre (dopamine transporter) mice with Smo(loxP/loxP) mice. We assessed for differences between knockout (ko) and wildtype (wt) mice using combined histochemistry, gene expression analysis, and behavioral evaluation. Number and size of DA neurons in ventral midbrain and the DA neural terminal density in striatum were measured using unbiased stereological quantification. The survival of DA neurons under neurotoxin challenge was examined in the unilateral 6-hydroxydopamine (6-OHDA) Parkinson's disease animal model and the more subtle function under challenge of the dopaminergic system was examined by methamphetamine single- and repeated challenge in wt and ko mice.

RESULTS

Tyrosine hydroxylase (TH) positive neuronal counts and neuronal size in substantia nigra (SN) and ventral tegmental area (VTA) showed no difference between wt and DAT-Smo ko mice in young (5months) or aged (22months) mice. There was also no difference in the striatal DA projections between wt and ko mice in both age groups. In unilateral striatal 6-OHDA lesions modeling Parkinson's disease, using stereotaxic injection of 6-OHDA intrastriatally led to loss of dopaminergic neurons in SN and diminished TH positive projections in striatum. However, there was no differences in survival of DA neurons between wt and ko mice. DAT-Smo ko mice demonstrated hyperactivity compared to wt mice at 5months, but showed no difference in activity at 22months. When injected with a one-time bolus of methamphetamine (METH), despite the higher basal locomotion activity, DAT-Smo ko mice showed a diminished response to a single METH challenge. In METH sensitization testing, ko mice showed decreased sensitization compared to wt mice without evidence of a delayed shift in dynamics of sensitization. Gene expression analysis showed decreased gene expression of smo, Gli 1 (known target gene of smo) and BDNF (brain-derived neurotrophic factor) in the SN. Gene expression was not altered in striatum for the genes examined in this study including dopamine receptor genes, neurotropic genes such as Glial cell line-derived neurotrophic factor (GDNF), and bone morphogenetic protein 7 (BMP7).

CONCLUSION

Our study showed the smo receptor function is not required for the maturation and survival of DA neurons during late development, aging or under stress challenge. However, smo function has an influence on behavior in young adult mice and in responses of mice to a drug that modulates DA neurochemistry through regulation of gene expression in DA neurons. Since young adult DAT-smo ko mice show hyperactivity and altered response to a psychostimulant drug (METH), this may indicate the involvement of the shh pathway in the development of functional changes that manifest as alterations in DA pathway dynamics.

Neuroplasticity and Repair in Rodent Neurotoxic Models of Spinal Motoneuron Disease

Retrogradely transported toxins are widely used to set up protocols for selective lesioning of the nervous system. These methods could be collectively named "molecular neurosurgery" because they are able to destroy specific types of neurons by using targeted neurotoxins. Lectins such as ricin, volkensin, or modeccin and neuropeptide- or antibody-conjugated saporin represent the most effective toxins used for neuronal lesioning. Some of these specific neurotoxins could be used to induce selective depletion of spinal motoneurons. In this review, we extensively describe two rodent models of motoneuron degeneration induced by volkensin or cholera toxin-B saporin. In particular, we focus on the possible experimental use of these models to mimic neurodegenerative diseases, to dissect the molecular mechanisms of neuroplastic changes underlying the spontaneous functional recovery after motoneuron death, and finally to test different strategies of neural repair. The potential clinical applications of these approaches are also discussed.

Sonic Hedgehog Controls the Phenotypic Fate and Therapeutic Efficacy of Grafted Neural Precursor Cells in a Model of Nigrostriatal Neurodegeneration

The expression of soluble growth and survival promoting factors by neural precursor cells (NPCs) is suggested to be a prominent mechanism underlying the protective and regenerative effects of these cells after transplantation. Nevertheless, how and to what extent specific NPC-expressed factors contribute to therapeutic effects is not well understood. Using RNA silencing, the current study investigated the roles of two donor NPC molecules, namely glial cell-line derived neurotrophic factor (GDNF) and sonic hedgehog (SHH), in the protection of substantia nigra dopamine neurons in rats treated with 6-hydroxydopamine (6-OHDA). Analyses indicate that as opposed to the knock-down of GDNF, SHH inhibition caused a profound decline in nigrostriatal neuroprotection. Further, SHH silencing also curbed endogenous neurogenesis and the migration of host brdU+/dcx+ neural precursors into the striatum, which was present in the animals receiving control or GDNF silenced NPCs. A change in graft phenotype, mainly reflected by a reduced proportion of undifferentiated nestin+ cells, as well as a significantly greater host microglial activity, suggested an important role for these processes in the attenuation of neuroprotection and neurogenesis upon SHH silencing. Overall these studies reveal core mechanisms fundamental to grafted NPC-based therapeutic effects, and delineate the particular contributions of two graft-expressed molecules, SHH and GDNF, in mediating midbrain dopamine neuron protection, and host plasticity after NPC transplantation.

Spicing up endogenous neural stem cells: aromatic-turmerone offers new possibilities for tackling neurodegeneration

There is a growing interest in the therapeutic utility of compounds derived from Curcuma longa, an herb of the Zingiberaceae family that has been part of traditional medicine for centuries. Recent reports suggest that bioactive compounds isolated from the rhizome of these plants can address two key aspects of brain injury following stroke that must be dealt with for functional recovery to occur: the moderation of neuroinflammation, and the mobilization of endogenous stem cells resident in the nervous system. Defining their mechanism of action remains a question, but emerging evidence may point towards one shared with more classic modulators of neural stem cell proliferation and survival.

Heterozygous mutations in the FGF8, SHH and nodal/transforming growth factor beta pathways do not confer increased dopaminergic neuron vulnerability--a zebrafish study

Fibroblast growth factor 8 (FGF8), sonic hedgehog (SHH) and nodal signalling pathways play key roles in both development and survival of dopaminergic neurons. Both heterozygous mutations in autosomal recessively inherited Parkinson's disease (PD) genes such as parkin or PINK1 and exposure to exogenous toxins are thought to contribute to the pathogenesis of PD. The aim of our study was to investigate whether heterozygote mutations in fgf8, shh or oep lead to a reduced number of ascending dopaminergic neurons in zebrafish (Danio rerio) or confer increased susceptibility to the PD neurotoxin 1-methyl-4-phenyl-pyridinium (MPP⁺). At 3 days post fertilization, heterozygous mutations in fgf8, shh or oep did not affect the number of ascending dopaminergic neurons, nor did heterozygous mutations in fgf8, shh or oep result in increased susceptibility to MPP⁺. Further work is needed to determine whether haploinsufficiency in other neurodevelopmental genes might confer increased susceptibility to PD-related pathomechanisms.

Endogenous neural precursors influence grafted neural stem cells and contribute to neuroprotection in the parkinsonian rat

Neuroprotective and neurorescue effects after neural stem/precursor cell (NPC) transplantation have been reported, but the mechanisms underlying such phenomena are not well understood. Our recent findings in a rat Parkinson's disease (PD) model indicate that transplantation of NPCs before a 6-hydroxydopamine (6-OHDA) insult can result in nigrostriatal protection which is associated with endogenous NPC proliferation, migration and neurogenesis. Here, we sought to determine whether the observed endogenous NPC response (i) contributes to transplanted NPC-mediated neuroprotection; and/or (ii) affects graft phenotype and function. Host Fischer 344 rats were administered the antimitotic agent cytosine-β-d-arabinofuranoside (Ara-C) to eliminate actively proliferating endogenous neural precursors before being transplanted with NPCs and treated with 6-OHDA to induce nigrostriatal degeneration. Behavioral and histological analyses demonstrate that the neuroprotective response observed in NPC transplanted animals which had not received Ara-C was significantly attenuated in animals which did receive pre-transplant Ara-C. Also, while grafts in Ara-C-treated animals showed no decrease in cell number, they exhibited significantly reduced expression of the neural stem cell regulators nestin and sonic hedgehog. In addition, inhibition of the endogenous NPC response resulted in an exaggerated host glial reaction. Overall, the study establishes for the first time that endogenous NPCs contribute to transplanted NPC-mediated therapeutic effects by affecting both grafted and mature host cells in unique ways. Thus, both endogenous and transplanted NPCs are important in creating an environment suitable for neural protection and rescue, and harnessing their synergistic interaction may lead to the optimization of cell-based therapies for PD.

Rare coding SNP in DZIP1 gene associated with late-onset sporadic Parkinson's disease

An association between a rare, coding, non-synonymous SNP variant in the gene DZIP1 and Parkinson's disease was found, based on an analysis of the existing NGRC genome-wide association study dataset. The statistical analysis utilized the hypothesis-rich, targeted search unbiased assessment approach, rather than the hypothesis-free, genome-wide agnostic search paradigm. The association of DZIP1 with Parkinson's disease is discussed in the context of a Parkinson's disease stem-cell ageing theory.

The neurotrophin family of neurotrophic factors: an overview

The neurotrophins are a family of closely related proteins that were first identified as survival factors for sympathetic and sensory neurons and have since been shown to control a number of aspects of survival, development, and function of neurons in both the central and peripheral nervous systems. Limiting quantities of neurotrophins during development control the numbers of surviving neurons to ensure a match between neurons and the requirement for a suitable density of target innervation. Biological effects of each of the four mammalian neurotrophins are mediated through activation of one or more of the three members of the tropomyosin-related kinase (Trk) family of receptor tyrosine kinases (TrkA, TrkB, and TrkC). In addition, all neurotrophins activate the p75 neurotrophin receptor, a member of the tumor necrosis factor receptor superfamily. Neurotrophin engagement of Trk receptors leads to activation of Ras, phosphatidylinositol 3-kinase, phospholipase C-γ1, and signaling pathways controlled through these proteins, including the mitogen-activated protein kinases. Neurotrophin availability is required into adulthood, where they control synaptic function and plasticity and sustain neuronal cell survival, morphology, and differentiation. This chapter will provide an overview of neurotrophin biology, their receptors, and signaling pathways.

Sonic hedgehog is cytoprotective against oxidative challenge in a cellular model of amyotrophic lateral sclerosis

We have previously demonstrated that primary cilia on spinal motor neurons are reduced in G93A SOD1 (mSOD) mice, a mouse model of amyotrophic lateral sclerosis (ALS). Sonic hedgehog (Shh) signaling involves the primary cilium and Shh has been shown to be cytoprotective in models of other neurodegenerative diseases. Thus, the Shh signaling pathway may bear further study in ALS. Accordingly, we established that interference with the Shh pathway (with the Shh antagonist cyclopamine or with miRNA 3245p) sensitized HT22 cells, while augmentation of the Shh pathway (with Shh or the Shh agonist purmorphamine) protected cells against hydrogen peroxide (H₂O₂) challenge. We ectopically expressed mSOD, human wild-type SOD1 (wtSOD), or an empty vector in HT22 cells. Compared to empty vector, wtSOD decreased cell death and mSOD increased cell death in response to H₂O₂ challenge. Treatment with cyclopamine or miRNA 3245p sensitized all three transfections to H₂O₂ challenge. Treatment with recombinant human Shh or purmorphamine decreased cell death after H₂O₂ challenge, an effect more pronounced in mSOD cells. Compared with empty vector, overexpression of wtSOD increased Shh and Gli transcript levels and increased activity in a Gli-responsive reporter assay. Overexpression of mSOD did not change Shh transcript levels, but decreased Gli transcript levels, especially Gli3, and reduced activity in a Gli reporter assay. These results suggest that overexpression of mSOD but not wtSOD reduces signaling in the Shh pathway and renders mSOD cells more susceptible to H₂O₂ challenge, and that treatment with Shh or Shh agonists is cytoprotective to mSOD cells. Shh or Shh agonists merit further consideration as potential therapy in ALS.

Intravenous hedgehog agonist induces proliferation of neural and oligodendrocyte precursors in rodent spinal cord injury

BACKGROUND

Sonic hedgehog (Shh) is a glycoprotein molecule that upregulates the transcription factor gli-1 and plays a critical role in the proliferation of endogenous neural precursor cells when directly injected into adult rodent spinal cords after injury.

OBJECTIVE

To use small-molecule agonists of the hedgehog pathway in an attempt to replicate these findings with intravenous administration.

METHODS

Forty Sprague-Dawley rats were randomly divided into 4 groups. Saline treatment control groups were divided into a contusion injury group and a noninjury sham group; Shh agonist treatment groups were divided into an injury group and a noninjury sham group. Shh agonist Ag11.1 was administered to the treatment groups and saline to the control groups. Injections were performed on days 1 and 4 after surgery. On day 14, 1 group was sacrificed, and injured spinal cord portions were removed for explant cultures. After 7 days in culture, specimens were fixed for immunostaining neural precursor cells, and cell counts were taken.

RESULTS

Histological analysis demonstrated cystic cavitary lesions with a rim of white-matter sparing in all specimens. In animals treated with hedgehog agonist for a contusion injury, a significant increase in the number of nestin- and musashi-1-positive neural precursor cells at the rim of the cavity was noted.

CONCLUSION

There was a significant increase in the number of O4-positive oligodendrocyte precursors compared with uninjured controls and BrdU-positive cells, reproducing the findings of previous studies using direct Shh protein injection, which demonstrated spared white matter and increased recovery.

Foxa2 and Nurr1 synergistically yield A9 nigral dopamine neurons exhibiting improved differentiation, function, and cell survival

Effective dopamine (DA) neuron differentiation from neural precursor cells (NPCs) is prerequisite for precursor/stem cell-based therapy of Parkinson's disease (PD). Nurr1, an orphan nuclear receptor, has been reported as a transcription factor that can drive DA neuron differentiation from non-dopaminergic NPCs in vitro. However, Nurr1 alone neither induces full neuronal maturation nor expression of proteins found specifically in midbrain DA neurons. In addition, Nurr1 expression is inefficient in inducing DA phenotype expression in NPCs derived from certain species such as mouse and human. We show here that Foxa2, a forkhead transcription factor whose role in midbrain DA neuron development was recently revealed, synergistically cooperates with Nurr1 to induce DA phenotype acquisition, midbrain-specific gene expression, and neuronal maturation. Thus, the combinatorial expression of Nurr1 and Foxa2 in NPCs efficiently yielded fully differentiated nigral (A9)-type midbrain neurons with clearly detectable DA neuronal activities. The effects of Foxa2 in DA neuron generation were observed regardless of the brain regions or species from which NPCs were derived. Furthermore, DA neurons generated by ectopic Foxa2 expression were more resistant to toxins. Importantly, Foxa2 expression resulted in a rapid cell cycle exit and reduced cell proliferation. Consistently, transplantation of NPCs transduced with Nurr1 and Foxa2 generated grafts enriched with midbrain-type DA neurons but reduced number of proliferating cells, and significantly reversed motor deficits in a rat PD model. Our findings can be applied to ongoing attempts to develop an efficient and safe precursor/stem cell-based therapy for PD.

Sonic Hedgehog signaling in the mammalian brain

The discovery of a Sonic Hedgehog (Shh) signaling pathway in the mature vertebrate CNS has paved the way to the characterization of the functional roles of Shh signals in normal and diseased brain. Shh is proposed to participate in the establishment and maintenance of adult neurogenic niches and to regulate the proliferation of neuronal or glial precursors in several brain areas. Consistent with its role during brain development, misregulation of Shh signaling is associated with tumorigenesis while its recruitement in damaged neural tissue might be part of the regenerating process. This review focuses on the most recent data of the Hedgehog pathway in the adult brain and its relevance as a novel therapeutic approach for brain diseases including brain tumors.

Transplantation of subventricular zone neural precursors induces an endogenous precursor cell response in a rat model of Parkinson's disease

Realistically, future stem cell therapies for neurological conditions including Parkinson's disease (PD) will most probably entail combination treatment strategies, involving both the stimulation of endogenous cells and transplantation. Therefore, this study investigates these two modes of neural precursor cell (NPC) therapy in concert in order to determine their interrelationships in a rat PD model. Human placental alkaline phosphatase (hPAP)-labeled NPCs were transplanted unilaterally into host rats which were subsequently infused ipsilaterally with 6-hydroxydopamine (6-OHDA). The reaction of host NPCs to the transplantation and 6-OHDA was tracked by bromodeoxyuridine (BrdU) labeling. Two weeks after transplantation, in animals transplanted with NPCs we found evidence of elevated host subventricular zone NPC proliferation, neurogenesis, and migration to the graft site. In these animals, we also observed a significant preservation of striatal tyrosine hydroxylase (TH) expression and substantia nigra TH cell number. We have seen no evidence that neuroprotection is a product of dopamine neuron replacement by NPC-derived cells. Rather, the NPCs expressed glial cell line-derived neurotrophic factor (GDNF), sonic hedgehog (Shh), and stromal cell-derived factor 1 alpha (SDF1alpha), providing a molecular basis for the observed neuroprotection and endogenous NPC response to transplantation. In summary, our data suggests plausible synergy between exogenous and endogenous NPC actions, and that NPC implantation before the 6-OHDA insult can create a host microenvironment conducive to stimulation of endogenous NPCs and protection of mature nigral neurons.

Conditions for tumor-free and dopamine neuron-enriched grafts after transplanting human ES cell-derived neural precursor cells

We have previously demonstrated derivation of neural precursor (NP) cells of a midbrain-type from human embryonic stem (hES) cells to yield an enriched population of dopamine (DA) neurons. These hES-derived NPs can be expanded in vitro through multiple passages without altering their DA neurogenic potential. Here, we studied two aspects of these hES-NP cells that are critical issues in cell therapeutic approaches for Parkinson's disease (PD): cell survival and tumorigenic potential. Neuroepithelial rosettes, a potentially tumorigenic structure, disappeared during hES-NP cell expansion in vitro. Although a minor population of cells positive for Oct3/4, a marker specific for undifferentiated hES cells, persisted in culture during hES-NP cell expansion, they could be completely eliminated by subculturing hES-NPs under differentiation-inducing conditions. Consistently, no tumors/teratomas are formed in rats grafted with multipassaged hES-NPs. However, extensively expanded hES-NP cells easily underwent cell death during differentiation in vitro and after transplantation in vivo. Transgenic expression of Bcl-XL and sonic hedgehog (SHH) completely overcame the cell survival problems without increasing tumor formation. These findings indicate that hES-NP cell expansion in conjunction with Bcl-XL+SHH transgene expression may provide a renewable and safe source of DA neurons for transplantation in PD.

Endogenous stem cell proliferation induced by intravenous hedgehog agonist administration after contusion in the adult rat spinal cord

OBJECT

Sonic hedgehog (Shh) is a glycoprotein molecule that upregulates the transcription factor Gli1. The Shh protein plays a critical role in the proliferation of endogenous neural precursor cells when directly injected into the spinal cord after a spinal cord injury in adult rodents. Small-molecule agonists of the hedgehog (Hh) pathway were used in an attempt to reproduce these findings through intravenous administration.

METHODS

The expression of Gli1 was measured in rat spinal cord after the intravenous administration of an Hh agonist. Ten adult rats received a moderate contusion and were treated with either an Hh agonist (10 mg/kg, intravenously) or vehicle (5 rodents per group) 1 hour and 4 days after injury. The rats were killed 5 days postinjury. Tissue samples were immediately placed in fixative. Samples were immunohistochemically stained for neural precursor cells, and these cells were counted.

RESULTS

Systemic dosing with an Hh agonist significantly upregulated Gli1 expression in the spinal cord (p < 0.005). After spinal contusion, animals treated with the Hh agonist had significantly more nestin-positive neural precursor cells around the rim of the lesion cavity than in vehicle-treated controls (means +/- SDs, 46.9 +/- 12.9 vs 20.9 +/- 8.3 cells/hpf, respectively, p < 0.005). There was no significant difference in the area of white matter injury between the groups.

CONCLUSIONS

An intravenous Hh agonist at doses that upregulate spinal cord Gli1 transcription also increases the population of neural precursor cells after spinal cord injury in adult rats. These data support previous findings based on injections of Shh protein directly into the spinal cord.

GDNF therapy for Parkinson's disease

With an increase in the aging population, the incidence of Parkinson's disease (PD), a disabling neurodegenerative disorder mainly affecting motor function, will inevitably present a challenge to an already overburdened healthcare system. Current medical and surgical therapies offer symptomatic relief but do not provide a cure. Experimental studies suggest that GDNF has the ability to protect degenerating dopamine neurons in PD as well as promote regeneration of the nigrostriatal dopamine system. However, clinical trials of GDNF infusion to date remain inconclusive. This review will examine the experimental and clinical evidence of GDNF use in PD with particular focus on its potential as an effective therapy in the treatment of PD.

Purification and bioassay of hedgehog ligands for the study of cell death and survival

The Hedgehog (Hh) family of secreted ligands-composed of Sonic Hedgehog (Shh), Indian Hedgehog (Ihh), and Desert Hedgehog (Dhh)-possesses many roles during embryonic development, adult homeostasis, and cancer. The specific functions of the Hh proteins are intertwined with their requirement as survival factors in Hh-responsive cells. However, studies designed to dissect the anti-apoptotic role of Hhs have been hindered by the lack of simple approaches to purify large quantities of recombinant ligands in the average laboratory setting because of the natural modifications of these proteins with palmitic acid and cholesterol. In this chapter, we provide a comprehensive protocol for the expression of Shh, Ihh, and Dhh in Escherichia coli as fusion proteins with calmodulin-binding peptide to allow easy and rapid purification. The ligands are engineered with a new N-terminus containing two isoleucine residues to provide an essential hydrophobic interphase for achieving high biologic activity. The protocol includes a detailed description of a method for determination of the specific activity of the generated proteins by use of a cell culture-based luciferase approach.

Apoptosis in the medaka embryo in the early developmental stage

Apoptosis is an important event of the development of various organs. In this study, we used in situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) to visualize the temporal and spatial distribution of apoptosis in the developing medaka embryo, which is a useful model for developmental biology and genetics. Most of the apoptotic cells were distributed in the central nervous system and tailbud. In the brain and retina, most of the apoptosis occurred in the restricted period. In situ hybridization against caspase 3A and caspase 3B showed that these were distributed in the tailbud and the head, respectively. These results suggested that two types of caspase 3 were involved in apoptosis in different areas.

Cloning of zebrafish nkx6.2 and a comprehensive analysis of the conserved transcriptional response to Hedgehog/Gli signaling in the zebrafish neural tube

Sonic Hedgehog (Shh) signaling helps pattern the vertebrate neural tube, in part by regulating the dorsal/ventral expression of a number of homeodomain containing transcription factors. These Hh responsive genes have been divided into two classes, with Class II genes being activated by Hh signaling and Class I genes being repressed by Hh signaling. While the transcriptional response to varying Hh levels is well defined in chick and mouse, it is only partially described in zebrafish, despite the fact that zebrafish has emerged as a powerful genetic system for the study of neural patterning. To better characterize the Hh response in the zebrafish neural tube, we cloned the zebrafish Class II Hh target genes nkx2.9 and nkx6.2. We then analyzed the expression of a number of Class I and Class II Hh responsive genes in wild type, Hh mutant, and Hh over-expressing zebrafish embryos. We show that expression of Class I and Class II genes is highly conserved in the vertebrate neural tube. Further, ventral-most Class II gene expression was completely lost in all Hh pathway mutants analyzed, indicating high levels of Hh signaling are blocked in all of these mutants. In contrast, more dorsally expressed genes were variably affected in different Hh pathway mutants, indicating mid-levels of Hh signaling are differentially affected. This comprehensive expression study provides an important tool for the characterization of Hh signaling in zebrafish and provides a sensitive assay for determining the degree to which newly identified zebrafish mutants affect Hh signaling.

Acquisition of in vitro and in vivo functionality of Nurr1-induced dopamine neurons

Neural precursor cells provide an expandable source of neurons and glia for basic and translational applications. However, little progress has been made in directing naive neural precursors toward specific neuronal fates such as midbrain dopamine (DA) neurons. We have recently demonstrated that transgenic expression of the nuclear orphan receptor Nurr1 is sufficient to drive dopaminergic differentiation of forebrain embryonic rat neural precursors in vitro. However, Nurr1-induced DA neurons exhibit immature neuronal morphologies and functional properties and are unable to induce behavioral recovery in rodent models of Parkinson's disease (PD). Here, we report on the identification of key genetic factors that drive morphological and functional differentiation of Nurr1-derived DA neurons. We show that coexpression of Nurr1, Bcl-XL, and Sonic hedgehog (SHH) or Nurr1 and the proneural bHLH factor Mash1 is sufficient to drive naive rat forebrain precursors into neurons exhibiting the biochemical, electrophysiological, and functional properties of DA neuron in vitro. On transplantation into the striatum of Parkinsonian rats, precursor cells engineered with Nurr1/SHH/Bcl-XL or Nurr1/Mash1 survived in vivo and differentiated into mature DA neurons that can reverse the behavioral deficits in the grafted animals.

Hippi is essential for node cilia assembly and Sonic hedgehog signaling

Hippi functions as an adapter protein that mediates pro-apoptotic signaling from poly-glutamine-expanded huntingtin, an established cause of Huntington disease, to the extrinsic cell death pathway. To explore other functions of Hippi we generated Hippi knock-out mice. This deletion causes randomization of the embryo turning process and heart looping, which are hallmarks of defective left-right (LR) axis patterning. We report that motile monocilia normally present at the surface of the embryonic node, and proposed to initiate the break in LR symmetry, are absent on Hippi-/- embryos. Furthermore, defects in central nervous system development are observed. The Sonic hedgehog (Shh) pathway is downregulated in the neural tube in the absence of Hippi, which results in failure to establish ventral neural cell fate. Together, these findings demonstrate a dual role for Hippi in cilia assembly and Shh signaling during development, in addition to its proposed role in apoptosis signal transduction in the adult brain under pathogenically stressful conditions.

THE HEDGEHOG PATHWAY AND NEUROLOGICAL DISORDERS

The hedgehog pathway is a major regulator of embryonic development, and mutations that decrease its activity are known to be associated with severe defects in nervous system development. Recent evidence suggests hedgehog continues to function in adult tissue, normal as well as diseased, by regulating both cell proliferation and the production of growth and angiogenic factors. In the adult nervous system, this dual ability is especially important in regulating the behavior of neural stem and progenitor cells. This review summarizes information connecting hedgehog signaling and neural diseases, including neurodegenerative disorders and brain tumors, particularly medulloblastoma. We also describe the discovery and utility of small molecule agonists and antagonists of this pathway and their potential as novel types of therapeutics.

Hedgehog and spinal cord injury

The hedgehog (Hh) pathway is a highly conserved signalling cascade involved in many developmental processes, including a key role in morphogenesis of many tissues including the limb bud, lung, gut, hair follicle and the neural tube. Hh role in adult tissue is less well-established, however, it is known that the pathway becomes activated and reutilised in situations of repair and regeneration. In the nervous system, tissue repair appears impeded in that mature neurons undergo their final cell divisions early in life and central axons do not easily regenerate. The Hh pathway has been shown to be activated in response to nerve damage, leading to the hypothesis that enhancing Hh pathway activation in damaged nerve tissue, inducing the repair process, could offer a potentially new approach to treating neurodegenerative diseases and dysfunction, including spinal cord injury.

Delivery of sonic hedgehog or glial derived neurotrophic factor to dopamine-rich grafts in a rat model of Parkinson's disease using adenoviral vectors Increased yield of dopamine cells is dependent on embryonic donor age

The poor survival of dopamine grafts in Parkinson's disease is one of the main obstacles to the widespread application of this therapy. One hypothesis is that implanted neurons, once removed from the embryonic environment, lack the differentiation factors needed to develop the dopaminergic phenotype. In an effort to improve the numbers of dopamine neurons surviving in the grafts, we have investigated the potential of adenoviral vectors to deliver the differentiation factor sonic hedgehog or the glial cell line-derived neurotrophic factor GDNF to dopamine-rich grafts in a rat model of Parkinson's disease. Adenoviral vectors containing sonic hedgehog, GDNF, or the marker gene LacZ were injected into the dopamine depleted striatum of hemiparkinsonian rats. Two weeks later, ventral mesencephalic cell suspensions were prepared from embryos of donor ages E12, E13, E14 or E15 and implanted into the vector-transduced striatum. Pre-treatment with the sonic hedgehog vector produced a three-fold increase in the numbers of tyrosine hydroxylase-positive (presumed dopaminergic) cells in grafts derived from E12 donors, but had no effect on E13-E15 grafts. By contrast, pre-treatment with the GDNF vector increased yields of dopamine cells in grafts derived from E14 and E15 donors but had no effect on grafts from younger donors. The results indicate that provision of both trophic and differentiation factors can enhance the yields of dopamine neurons in ventral mesencephalic grafts, but that the two factors differ in the age and stage of embryonic development at which they have maximal effects.

Brain as a paradigm of organ growth: Hedgehog-Gli signaling in neural stem cells and brain tumors

The Hedgehog-Gli (Hh-Gli) signaling pathway is essential for numerous events during the development of many animal cell types and organs. In particular, it controls neural cell precursor proliferation in dorsal brain structures and regulates the number of neural stem cells in distinct embryonic, perinatal, and adult niches, such as the developing neocortex, the subventricular zone of the lateral ventricle of the forebrain, and the hippocampus. We have proposed that Hh-Gli signaling regulates dorsal brain growth during ontogeny and that its differential regulation underlays evolutionary change in the morphology (size and shape) of dorsal brain structures. It is also critically involved in sporadic brain tumorigenesis--as well as several other human cancer--suggesting that tumors derive from stem cells or progenitors maintaining an inappropriate active Hh-Gli pathway. Importantly, we and others have demonstrated that human sporadic tumors from the brain and other organs require sustained HH-GLI signaling for sustained growth and survival. Modulating HH-GLI signaling thus represents a novel rational avenue to treat, on one hand, brain degeneration and injury by inducing controlled HH-GLI-mediated regeneration and growth, and on the other hand, to combat cancer by blocking its abnormal activity in tumor cells.

Endogenous stem cell proliferation after central nervous system injury: alternative therapeutic options

The continuous regeneration of glial cells arising from endogenous stem cell populations in the central nervous system (CNS) occurs throughout life in mammals. In the ongoing research to apply stem cell therapy to neurological diseases, the capacity to harness the multipotential ability of endogenous stem cell populations has become apparent. Such cell populations proliferate in response to a variety of injury states in the CNS, but in the absence of a supportive microenvironment they contribute little to any significant behavioral recovery. In the authors' laboratory and elsewhere, recent research on the regenerative potential of these stem cells in disease states such as spinal cord injury has demonstrated that the cells' proliferative potential may be greatly upregulated in response to appropriate growth signals and exogenously applied trophic factors. Further understanding of the potential of such multipotent cells and the mechanisms responsible for creating a favorable microenvironment for them may lead to additional therapeutic alternatives in the setting of neurological diseases. These therapies would require no exogenous stem cell sources and thus would avoid the ethical and moral considerations regarding their use. In this review the authors provide a brief overview of the enhancement of endogenous stem cell proliferation following neurological insult.

Factors involved in the determination of the neurotransmitter phenotype of developing neurons of the CNS: Applications in cell replacement treatment for Parkinson's disease

The developmental stages involved in the conversion of stem cells to fully functional neurons of specific neurotransmitter phenotype are complex and not fully understood. Over the past decade many studies have been published that demonstrate that in vitro manipulation of the epigenetic environment of the stem cells allows experimental control of final neuronal phenotypic choice. This review presents the evidence for the involvement of a number of endogenous neurobiochemicals, which have been reported to potently influence DAergic (and other neurotransmitter) phenotype expression in vitro. They act at different stages on the pathway to neurotransmitter phenotype determination, and in different ways. Many are better known for their involvement in other aspects of development, and in other biochemical roles. Their proper place, and precise roles, in neurotransmitter phenotype determination in vivo will no doubt be determined in the future. Meanwhile, considerable medical benefits are offered from producing large, long-term, viable cryostores of self-regenerating multipotential neural precursor cells (i.e., brain stem cells), which can be used for cell replacement therapies in the treatment of degenerative brain diseases, such as Parkinson's disease.

Differential expression of sonic hedgehog immunoreactivity during lesion evolution in autoimmune encephalomyelitis

The signaling molecule Sonic hedgehog (Shh) is involved in several processes of central nervous system development. Recent reports indicate that Shh expression plays a role also in certain pathologic conditions in the adult brain, including multiple sclerosis and its animal model. However, the role of Shh signaling in immune-mediated demyelinating disease remains still uncertain. The aim of our study was to investigate the distribution pattern of Shh immunoreactivity (Shh-IR) during lesion evolution in myelin-oligodendrocyte-glycoprotein-induced experimental autoimmune encephalomyelitis (MOG-EAE), a model strongly mimicking multiple sclerosis. MOG-EAE was actively induced in DA rats. Histologic evaluation was performed with light and confocal microscopy on paraffin-embedded central nervous system sections from days 20 to 120 after active immunization. Shh-IR was present within the lesions of MOG-EAE during all stages of lesion evolution. The highest staining intensity for Shh was found in remyelinating lesions. In actively demyelinating, inactive demyelinated lesions, and in remyelinating lesions, Shh-IR was detected in macrophages, endothelium, and astrocytes. Shh-IR in axons was exclusively present in remyelinating lesions. Although the exact molecular mechanisms of the Shh-signaling pathway in experimental autoimmune encephalomyelitis are yet to be determined, our findings may imply a role of Shh signaling in facilitating remyelination.

Sonic hedgehog is produced by follicular dendritic cells and protects germinal center B cells from apoptosis

The Hedgehog (Hh) signaling pathway is involved in the development of many tissues during embryogenesis, but has also been described to function in adult self-renewing tissues. In the immune system, Sonic Hedgehog (Shh) regulates intrathymic T cell development and modulates the effector functions of peripheral CD4(+) T cells. In this study we investigate whether Shh signaling is involved in peripheral B cell differentiation in mice. Shh is produced by follicular dendritic cells, mainly in germinal centers (GCs), and GC B cells express both components of the Hh receptor, Patched and Smoothened. Blockade of the Hh signaling pathway reduces the survival, and consequently the proliferation and Ab secretion, of GC B cells. Furthermore, Shh rescues GC B cells from apoptosis induced by Fas ligation. Taken together, our data suggest that Shh is one of the survival signals provided by follicular dendritic cells to prevent apoptosis in GC B cells.

Neuronal expression of the transcription factor Gli1 using the Talpha1 alpha-tubulin promoter is neuroprotective in an experimental model of Parkinson's disease

Nigrostriatal neurons degenerate during Parkinson's disease. Experimentally, neurotoxins such as 6-hydroxydopamine (6-OHDA) in rodents, and MPTP in mice and non-human primates, are used to model the disease-induced degeneration of midbrain dopaminergic neurons. Glial-cell-derived neurotrophic factor (GDNF) is a very powerful neuroprotector of dopaminergic neurons in all species examined. However, recent reports have indicated the possibility that GDNF may, in the long term and if expressed in an unregulated manner, exert untoward effects on midbrain dopaminergic neuronal structure and function. Although GDNF remains a powerful neurotrophin, the search for alternative therapies based on alternative and complementary mechanisms of action to GDNF is warranted. Recently, recombinant adenovirus-derived vectors encoding the differentiation factor Sonic Hedgehog (Shh) and its downstream transcriptional activator (Gli1) were shown to protect dopaminergic neurons in the substantia nigra pars compacta from 6-OHDA-induced neurotoxicity in rats in vivo. A pancellular human CMV (hCMV) promoter was used to drive the expression of both Shh and Gli1. Since Gli1 is a transcription factor and therefore exerts its actions intracellularly, we decided to test whether expression of Gli1 within neurons would be effective for neuroprotection. We demonstrate that neuronal-specific expression of Gli1 using the neuron-specific Talpha1 alpha-tubulin (Talpha1) promoter was neuroprotective, and its efficiency was comparable to the pancellular strong viral hCMV promoter. These results suggest that expression of the transcription factor Gli1 solely within neurons is neuroprotective for dopaminergic neurons in vivo and, furthermore, that neuronal-specific promoters are effective within the context of adenovirus-mediated gene therapy-induced neuroprotection of dopaminergic midbrain neurons. Since cell-type specific promoters are known to be weaker than the viral hCMV promoter, our data demonstrate that neuronal-specific expression of transcription factors is an effective, specific, and sufficient targeted approach for neurological gene therapy applications, potentially minimizing side effects due to unrestricted promiscuous gene expression within target tissues.

Neuroprotective properties of cultured neural progenitor cells are associated with the production of sonic hedgehog

Numerous studies have shown that abnormal motor behavior improves when neural progenitor cells (NPCs) are transplanted into animal models of neurodegeneration. The mechanisms responsible for this improvement are not fully understood. Indirect anatomical evidence suggests that attention of abnormal motor behavior is attributed, at least in part, to the secretion of trophic factors from the transplanted NPCs. However, there is little direct evidence supporting this hypothesis. Here we show that NPCs isolated from the subventricular zone (SVZ) of neonatal mice are highly teratogenic when transplanted into the neural tube of developing chick embryos and are neuroprotective for fetal dopaminergic neurons in culture because they release sonic hedgehog (Shh). In addition, the neuroprotective properties of NPCs can be exploited to promote better long-term survival of transplanted fetal neurons in an animal model of Parkinson's disease. Thus, cultured NPCs isolated from the SVZ can secrete at least one potent mitogen (Shh) that dramatically affects the fate of neighboring cells. This trait may account for some of the improvement in motor behavior often reported in animal models of neurodegeneration after transplantation of cultured NPCs that were isolated from the SVZ.

Sonic hedgehog regulates early human thymocyte differentiation by counteracting the IL-7-induced development of CD34+ precursor cells

The Hedgehog (Hh) family of signaling molecules normally functions in the development of numerous tissues by regulating cellular differentiation and proliferation. Recent results have demonstrated that the different components of the Hh signaling pathway are expressed in the human thymus. In this study, we investigate the potential role of Sonic hedgehog (Shh) in human intrathymic T cell maturation. Results show that the expression of the two components of the Hh receptor, Patched and Smoothened, is mostly restricted to CD34+ precursor cells that are committing to the T cell lineage. Shh significantly increased the viability of CD34+ T cell precursors modulating bcl-2 and bax protein expression, and also inhibited their proliferation. The treatment of chimeric human-mouse fetal thymus organ cultures with Shh resulted in an arrested thymocyte differentiation and an accumulation of CD34+ progenitor cells. This effect was mainly attributed to the ability of Shh to counteract the IL-7-induced proliferation and differentiation of CD34+ cells. Shh down-regulated in the precursor cell population the expression of IL-7R as well as stromal-derived factor-1 chemokine receptor, CXCR4, and inhibited IL-7-dependent STAT5 phosphorylation. Therefore, Shh may function as a maintenance factor for intrathymic CD34+ precursor cells.