Recent genome-wide association studies indicate that a simple alteration of Leucine-rich repeat kinase 2 (LRRK2) gene expression may contribute to the etiology of sporadic Parkinson's disease (PD). However, the expression and regulation of LRRK2 protein in the sporadic PD brains remain to be determined. Here, we found that the expression of LRRK2 protein was enhanced in the sporadic PD patients using the frontal cortex tissue from a set of 16 PD patients and 7 control samples. In contrast, no significant difference was detected in the level of LRRK2 mRNA expression between the control and PD cases, suggesting a potential post-transcriptional modification of the LRRK2 protein expression in the sporadic PD brains. Indeed, it was identified that microRNA-205 (miR-205) suppressed the expression of LRRK2 protein through a conserved-binding site at the 3′-untranslated region (UTR) of LRRK2 gene. Interestingly, miR-205 expression was significantly downregulated in the brains of patients with sporadic PD, showing the enhanced LRRK2 protein levels. Also, in vitro studies in the cell lines and primary neuron cultures further established the role of miR-205 in modulating the expression of LRRK2 protein. In addition, introduction of miR-205 prevented the neurite outgrowth defects in the neurons expressing a PD-related LRRK2 R1441G mutant. Together, these findings suggest that downregulation of miR-205 may contribute to the potential pathogenic elevation of LRRK2 protein in the brains of patients with sporadic PD, while overexpression of miR-205 may provide an applicable therapeutic strategy to suppress the abnormal upregulation of LRRK2 protein in PD.
By mechanisms yet to be discerned, the co-expression of high levels of wild-type human superoxide dismutase 1 (hSOD1) with variants of hSOD1 encoding mutations linked familial amyotrophic lateral sclerosis (fALS) hastens the onset of motor neuron degeneration in transgenic mice. Although it is known that spinal cords of paralyzed mice accumulate detergent insoluble forms of WT hSOD1 along with mutant hSOD1, it has been difficult to determine whether there is co-deposition of the proteins in inclusion structures.
In the present study, we use cell culture models of mutant SOD1 aggregation, focusing on the A4V, G37R, and G85R variants, to examine interactions between WT-hSOD1 and misfolded mutant SOD1. In these studies, we fuse WT and mutant proteins to either yellow or red fluorescent protein so that the two proteins can be distinguished within inclusions structures.
Although the interpretation of the data is not entirely straightforward because we have strong evidence that the nature of the fused fluorophores affects the organization of the inclusions that form, our data are most consistent with the idea that normal dimeric WT-hSOD1 does not readily interact with misfolded forms of mutant hSOD1. We also demonstrate the monomerization of WT-hSOD1 by experimental mutation does induce the protein to aggregate, although such monomerization may enable interactions with misfolded mutant SOD1. Our data suggest that WT-hSOD1 is not prone to become intimately associated with misfolded mutant hSOD1 within intracellular inclusions that can be generated in cultured cells.
PICK1 (protein interacting with C-kinase 1) is a PKC (protein kinase C)-binding protein, which is essential for synaptic plasticity. The trafficking of PKCα-PICK1 complex to plasma membrane is critical for the internalization of GluR2 and induction of long-term depression. ICA69 (islet cell autoantigen 69 kDa) is identified as a major binding partner of PICK1. While heteromeric BAR domain complex is suggested to underlie the interaction between PICK1 and ICA69, the role of C-terminal domain of ICA69 (ICAC) in PICK1-ICA69 complex is unknown.
We found that ICAC interacted with PICK1 and regulated the trafficking of PICK1-PKCα complex. ICAC and ΔICAC (containing BAR domain) might function distinctly in the association of ICA69 with PICK1. While ΔICAC domain inclined to form clusters, the distribution of ICAC was diffuse. The trafficking of PICK1 to plasma membrane mediated by activated PKCα was inhibited by ICA69. This action might ascribe to ICAC, because overexpression of ICAC, but not ΔICAC, interrupted PKCα-mediated PICK1 trafficking. Notably, infusion of maltose binding protein (MBP) fusion protein, MBP-ICA69 or MBP-ICAC, in cerebellar Purkinje cells significantly inhibited the induction of long-term depression at parallel fiber- and climbing fiber-Purkinje cell synapses.
Our experiments showed that ICAC is an important domain for the ICA69-PICK1 interaction and plays essential roles in PICK1-mediated neuronal plasticity.
Mitochondria are dynamic organelles that constantly undergo fusion and fission to maintain their normal functionality. Impairment of mitochondrial dynamics is implicated in various neurodegenerative disorders. Amyotrophic lateral sclerosis (ALS) is an adult-onset neuromuscular degenerative disorder characterized by motor neuron death and muscle atrophy. ALS onset and progression clearly involve motor neuron degeneration but accumulating evidence suggests primary muscle pathology may also be involved. Here, we examined mitochondrial dynamics in live skeletal muscle of an ALS mouse model (G93A) harboring a superoxide dismutase mutation (SOD1G93A). Using confocal microscopy combined with overexpression of mitochondria-targeted photoactivatable fluorescent proteins, we discovered abnormal mitochondrial dynamics in skeletal muscle of young G93A mice before disease onset. We further demonstrated that similar abnormalities in mitochondrial dynamics were induced by overexpression of mutant SOD1G93A in skeletal muscle of normal mice, indicating the SOD1 mutation drives ALS-like muscle pathology in the absence of motor neuron degeneration. Mutant SOD1G93A forms aggregates inside muscle mitochondria and leads to fragmentation of the mitochondrial network as well as mitochondrial depolarization. Partial depolarization of mitochondrial membrane potential in normal muscle by carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) caused abnormalities in mitochondrial dynamics similar to that in the SOD1G93A model muscle. A specific mitochondrial fission inhibitor (Mdivi-1) reversed the SOD1G93A action on mitochondrial dynamics, indicating SOD1G93A likely promotes mitochondrial fission process. Our results suggest that accumulation of mutant SOD1G93A inside mitochondria, depolarization of mitochondrial membrane potential and abnormal mitochondrial dynamics are causally linked and cause intrinsic muscle pathology, which occurs early in the course of ALS and may actively promote ALS progression.
Background: Mutations in the gene encoding leucine-rich repeat kinase 2 (LRRK2) cause Parkinson disease.
Results: LRRK2 binds directly to three β-tubulin isoforms at the luminal face of microtubules and suppresses α-tubulin acetylation. Interaction is weakened by the R1441G LRRK2 GTPase domain mutant.
Conclusion: LRRK2 modulates microtubule stability.
Significance: Deregulation of microtubule-dependent processes likely contribute to neurodegeneration in Parkinson disease.
Mutations in LRRK2, encoding the multifunctional protein leucine-rich repeat kinase 2 (LRRK2), are a common cause of Parkinson disease. LRRK2 has been suggested to influence the cytoskeleton as LRRK2 mutants reduce neurite outgrowth and cause an accumulation of hyperphosphorylated Tau. This might cause alterations in the dynamic instability of microtubules suggested to contribute to the pathogenesis of Parkinson disease. Here, we describe a direct interaction between LRRK2 and β-tubulin. This interaction is conferred by the LRRK2 Roc domain and is disrupted by the familial R1441G mutation and artificial Roc domain mutations that mimic autophosphorylation. LRRK2 selectively interacts with three β-tubulin isoforms: TUBB, TUBB4, and TUBB6, one of which (TUBB4) is mutated in the movement disorder dystonia type 4 (DYT4). Binding specificity is determined by lysine 362 and alanine 364 of β-tubulin. Molecular modeling was used to map the interaction surface to the luminal face of microtubule protofibrils in close proximity to the lysine 40 acetylation site in α-tubulin. This location is predicted to be poorly accessible within mature stabilized microtubules, but exposed in dynamic microtubule populations. Consistent with this finding, endogenous LRRK2 displays a preferential localization to dynamic microtubules within growth cones, rather than adjacent axonal microtubule bundles. This interaction is functionally relevant to microtubule dynamics, as mouse embryonic fibroblasts derived from LRRK2 knock-out mice display increased microtubule acetylation. Taken together, our data shed light on the nature of the LRRK2-tubulin interaction, and indicate that alterations in microtubule stability caused by changes in LRRK2 might contribute to the pathogenesis of Parkinson disease.
Lrrk2; Microtubules; Molecular Genetics; Parkinson Disease; Tubulin; GTPase Mutation; RocCOR; Cytoskeletal Dynamics; Growth Cone; Tubulin Acetylation
In this study, we investigated whether phloroglucinol (1, 3, 5 - trihydroxybenzene) has therapeutic effects in cellular and animal model of Parkinson's disease (PD). PD is the second most common, chronic and progressive neurodegenerative disease, and is clinically characterized with motor dysfunctions such as bradykinesia, rigidity, postural instability, gait impairment, and resting tremor. In the brains of PD patients, dopaminergic neuronal loss is observed in the Substantia nigra. Although the exact mechanisms underlying PD are largely unknown, mitochondrial dysfunction and oxidative stress are thought to be critical factors that induce the onset of the disease. Here, phloroglucinol administration was shown to attenuate motor functional deficits evaluated with rota-rod and apomorphine-induced rotation tests in 6-hydroxydopamine (6-OHDA)-induced PD animal models. Moreover, phloroglucinol ameliorated the loss of synapses as assessed with protein levels and immunoreactivity against synaptophysin in the midbrain region of the 6-OHDA-lesioned rats. In addition, in SH-SY5Y cultures, the cytotoxicity of 6-OHDA was reduced by pre-treatment with phloroglucinol. The increase in the reactive oxygen species, lipid peroxidation, protein carbonyl formation and 8-hydroxyguanine caused by treatment with 6-OHDA was attenuated by phloroglucinol in SH-SY5Y cells. Furthermore, phloroglucinol treatment rescued the reduced levels of nuclear Nrf2, antioxidant enzymes, i.e., catalase and glutathione peroxidase, in 6-OHDA-treated cells. Taken together, phloroglucinol has a therapeutic potential for treatment of PD.
Association studies have identified several signals at the LRRK2 locus for Parkinson's disease (PD), Crohn's disease (CD) and leprosy. However, little is known about the molecular mechanisms mediating these effects. To further characterize this locus, we fine-mapped the risk association in 5,802 PD and 5,556 controls using a dense genotyping array (ImmunoChip). Using samples from 134 post-mortem control adult human brains (UK Human Brain Expression Consortium), where up to ten brain regions were available per individual, we studied the regional variation, splicing and regulation of LRRK2. We found convincing evidence for a common variant PD association located outside of the LRRK2 protein coding region (rs117762348, A>G, P = 2.56×10−8, case/control MAF 0.083/0.074, odds ratio 0.86 for the minor allele with 95% confidence interval [0.80–0.91]). We show that mRNA expression levels are highest in cortical regions and lowest in cerebellum. We find an exon quantitative trait locus (QTL) in brain samples that localizes to exons 32–33 and investigate the molecular basis of this eQTL using RNA-Seq data in n = 8 brain samples. The genotype underlying this eQTL is in strong linkage disequilibrium with the CD associated non-synonymous SNP rs3761863 (M2397T). We found two additional QTLs in liver and monocyte samples but none of these explained the common variant PD association at rs117762348. Our results characterize the LRRK2 locus, and highlight the importance and difficulties of fine-mapping and integration of multiple datasets to delineate pathogenic variants and thus develop an understanding of disease mechanisms.
β-amyloid (Aβ) peptide, accumulation of which is a culprit for Alzheimer’s disease (AD), is derived from the initial cleavage of amyloid precursor protein by the aspartyl protease BACE1. Identification of cellular mechanisms that regulate BACE1 production is of high relevance to the search for potential disease-modifying therapies that inhibit BACE1 to reduce Aβ accumulation and AD progression. In the present study, we show that the cholesterol oxidation product 27-hydroxycholesterol (27-OHC) increases BACE1 and Aβ levels in human neuroblastoma SH-SY5Y cells. This increase in BACE1 involves a crosstalk between the two transcription factors NF-κB and the endoplasmic reticulum stress marker, the growth arrest and DNA damage induced gene-153 (gadd153, also called CHOP). We specifically show that 27-OHC induces a substantial increase in NF-κB binding to the BACE1 promoter and subsequent increase in BACE1 transcription and Aβ production. The NF-κB inhibitor, sc514, significantly attenuated the 27-OHC-induced increase in NF-κB-mediated BACE1 expression and Aβ genesis. We further show that the 27-OHC-induced NF-κB activation and increased NF-κB-mediated BACE1 expression is contingent on the increased activation of gadd153. Silencing gadd153 expression with siRNA alleviated the 27-OHC-induced increase in NF-κB activation, NF-κB binding to the BACE1 promoter, and subsequent increase in BACE1 transcription and Aβ production. We also show that increased levels of BACE1 in the triple transgenic mouse model for AD is preceded by gadd153 and NF-κB activation. In summary, our study demonstrates that gadd153 and NF-κB work in concert to regulate BACE1 expression. Agents that inhibit gadd153 activation and subsequent interaction with NF-κB might be promising targets to reduce BACE1 and Aβ overproduction and may ultimately serve as disease-modifying treatments for AD.
Non-motor symptoms are increasingly recognized as important features of Parkinson’s disease (PD). LRRK2 mutations are common causes of familial and sporadic PD. Non-motor features have not been yet comprehensively evaluated in LRRK2 transgenic mouse models.
Using a transgenic mouse model overexpressing the R1441G mutation of the human LRRK2 gene, we have investigated the longitudinal correlation between motor and non-motor symptoms and determined if specific non-motor phenotypes precede motor symptoms.
We investigated the onset of motor and non-motor phenotypes on the LRRK2R1441G BAC transgenic mice and their littermate controls from 4 to 21 month-old using a battery of behavioral tests. The transgenic mutant mice displayed mild hypokinesia in the open field from 16 months old, with gastrointestinal dysfunctions beginning at 6 months old. Non-motor features such as depression and anxiety-like behaviors, sensorial functions (pain sensitivity and olfaction), and learning and memory abilities in the passive avoidance test were similar in the transgenic animals compared to littermate controls.
LRRK2R1441G BAC transgenic mice displayed gastrointestinal dysfunction at an early stage but did not have abnormalities in fine behaviors, olfaction, pain sensitivity, mood disorders and learning and memory compared to non-transgenic littermate controls. The observations on olfaction and gastrointestinal dysfunction in this model validate findings in human carriers. These mice did recapitulate mild Parkinsonian motor features at late stages but compensatory mechanisms modulating the progression of PD in these models should be further evaluated.
Bradykinesia is one of the major clinical symptoms of Parkinson`s disease (PD) for which treatment is sought. In most mouse models of PD, decreased locomotor activity can be reflected in an open field behavioral test. Therefore the open field test provides a useful tool to study the clinic symptoms of PD patients. Our previous work demonstrated that 100 Hz electro-acupuncture (EA) stimulation at ZUSANLI and SANYINJIAO protected the dopaminergic nigrostriatal system of C57BL/6 mice from MPTP toxicity, indicating that acupuncture might be an effective therapy for PD sufferers. In the present study, we investigated the effects of 100 Hz EA stimulation on the spontaneous locomotor activity in MPTP injured mice. Here we found that, in MPTP treated mice, the total movements significantly decreased and the movement time, velocity and distance dramatically increased, although the dopaminergic nigrostriatal system was devastated, revealed by immunohistochemistry and HPLC-ECD. After 12 sessions of 100 Hz EA stimulation, the total movements elevated and the movement time, velocity and distance decreased, in MPTP mice. 100 Hz EA increased striatal dopamine content in MPTP mice by 35.9%, but decreased its striatal dopamine turnover. We assumed that the injury of other regions in the brain, such as the A11 group in diencephalon, might be involved in the hypermotility in MPTP mice. The effects of 100 Hz EA on spontaneous locomotor activity in MPTP mice might not relate with the striatal dopamine, but with its neuroprotective and regulatory effects on motor circuits in the brain. Our study suggests that EA might be a promising treatment for neurological disorders including PD.
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease resulting in severe muscle weakness and eventual death by respiratory failure. Although little is known about its pathogenesis, mutations in fused in sarcoma/translated in liposarcoma (FUS) are causative for familial ALS. FUS is a multifunctional protein that is involved in many aspects of RNA processing. To elucidate the role of FUS in ALS, we overexpressed wild-type and two mutant forms of FUS in HEK-293T cells, as well as knocked-down FUS expression. This was followed by RNA-Seq to identify genes which displayed differential expression or altered splicing patterns. Pathway analysis revealed that overexpression of wild-type FUS regulates ribosomal genes, whereas knock-down of FUS additionally affects expression of spliceosome related genes. Furthermore, cells expressing mutant FUS displayed global transcription patterns more similar to cells overexpressing wild-type FUS than to the knock-down condition. This observation suggests that FUS mutants do not contribute to the pathogenesis of ALS through a loss-of-function. Finally, our results demonstrate that the R521G and R522G mutations display differences in their influence on transcription and splicing. Taken together, these results provide additional insights into the function of FUS and how mutations contribute to the development of ALS.
Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into dopaminergic (DAergic) neurons, which is one of the major cell types damaged in Parkinson’s disease (PD). For this reason, MSCs are considered a potential cell source for PD therapy. It has been proved that hypoxia is involved in the proliferation and differentiation of stem cells. In this study, we investigated the effect of hypoxia on MSC proliferation and DAergic neuronal differentiation. Our results demonstrate that 3% O2 treatment can enhance rat MSC proliferation by upregulation of phosphorylated p38 MAPK and subsequent nuclear translocation of hypoxia inducible factor (HIF)-1α. During neural differentiation, 3% O2 treatment increases the expression of HIF-1α, phosphorylated ERK and p38 MAPK. These changes are followed by promotion of neurosphere formation and further DAergic neuronal differentiation. Furthermore, we explored the physiological function of hypoxia-induced DAergic neurons from human fetal MSCs by transplanting them into parkinsonian rats. Grafts induced with hypoxia display more survival of DAergic neurons and greater amelioration of behavioral impairments. Altogether, these results suggest that hypoxia can promote MSC proliferation and DAergic neuronal differentiation, and benefit for intrastriatal transplantation. Therefore, this study may provide new perspectives in application of MSCs to clinical PD therapy.
α-synuclein(α-syn) plays a prominent role in the degeneration of midbrain dopaminergic (mDA) neurons in Parkinson disease (PD). However, only a few studies on α-syn have been carried out in the mDA neurons in vivo, which may be attributed to a lack of α-syn transgenic mice that develop PD-like severe degeneration of mDA neurons. To gain mechanistic insights into the α-syn-induced mDA neurodegeneration, we generated a new line of tetracycline-regulated inducible transgenic mice that overexpressed the PD-related α-syn A53T missense mutation in the mDA neurons. Here we show that the mutant mice developed profound motor disabilities and robust mDA neurodegeneration, resembling some key motor and pathological phenotypes of PD. We further systematically examined the subcellular abnormalities appeared in the mDA neurons of mutant mice, and observed a profound decrease of dopamine release, the fragmentation of Golgi apparatus, and impairments of autophagy/lysosome degradation pathways in these neurons. To further understand the specific molecular events leading to the α-syn-dependent degeneration of mDA neurons, we found that over-expression of α-syn promoted a proteasome-dependent degradation of nuclear receptor related 1 protein (Nurr1); while inhibition of Nurr1 degradation ameliorated the α-syn-induced loss of mDA neurons. Given that Nurr1 plays an essential role in maintaining the normal function and survival of mDA neurons, our studies suggest that the α-syn-mediated suppression of Nurr1 protein expression may contribute to the preferential vulnerability of mDA neurons in the pathogenesis of PD.
Mechanisms involved with degeneration of motor neurons in amyotrophic lateral sclerosis (ALS; Lou Gehrig's Disease) are poorly understood, but genetically inherited forms, comprising ∼10% of the cases, are potentially informative. Recent observations that several inherited forms of ALS involve the RNA binding proteins TDP43 and FUS raise the question as to whether RNA metabolism is generally disturbed in ALS. Here we conduct whole transcriptome profiling of motor neurons from a mouse strain, transgenic for a mutant human SOD1 (G85R SOD1-YFP), that develops symptoms of ALS and paralyzes at 5–6 months of age. Motor neuron cell bodies were laser microdissected from spinal cords at 3 months of age, a time when animals were presymptomatic but showed aggregation of the mutant protein in many lower motor neuron cell bodies and manifested extensive neuromuscular junction morphologic disturbance in their lower extremities. We observed only a small number of transcripts with altered expression levels or splicing in the G85R transgenic compared to age-matched animals of a wild-type SOD1 transgenic strain. Our results indicate that a major disturbance of polyadenylated RNA metabolism does not occur in motor neurons of mutant SOD1 mice, suggesting that the toxicity of the mutant protein lies at the level of translational or post-translational effects.
Spinal muscular atrophy (SMA) is a leading genetic cause of infant mortality, resulting primarily from the degeneration and loss of lower motor neurons. Studies using mouse models of SMA have revealed widespread heterogeneity in the susceptibility of individual motor neurons to neurodegeneration, but the underlying reasons remain unclear. Data from related motor neuron diseases, such as amyotrophic lateral sclerosis (ALS), suggest that morphological properties of motor neurons may regulate susceptibility: in ALS larger motor units innervating fast-twitch muscles degenerate first. We therefore set out to determine whether intrinsic morphological characteristics of motor neurons influenced their relative vulnerability to SMA. Motor neuron vulnerability was mapped across 10 muscle groups in SMA mice. Neither the position of the muscle in the body, nor the fibre type of the muscle innervated, influenced susceptibility. Morphological properties of vulnerable and disease-resistant motor neurons were then determined from single motor units reconstructed in Thy.1-YFP-H mice. None of the parameters we investigated in healthy young adult mice – including motor unit size, motor unit arbor length, branching patterns, motor endplate size, developmental pruning and numbers of terminal Schwann cells at neuromuscular junctions - correlated with vulnerability. We conclude that morphological characteristics of motor neurons are not a major determinant of disease-susceptibility in SMA, in stark contrast to related forms of motor neuron disease such as ALS. This suggests that subtle molecular differences between motor neurons, or extrinsic factors arising from other cell types, are more likely to determine relative susceptibility in SMA.
The brain is capable of remarkable synaptic reorganization following stress and injury, often using the same molecular machinery that governs neurodevelopment. This form of plasticity is crucial for restoring and maintaining network function. However, neurodegeneration and subsequent reorganization can also play a role in disease pathogenesis, as is seen in temporal lobe epilepsy and Alzheimer’s disease. β-Secretase-1 (BACE1) is a protease known for cleaving β-amyloid precursor protein into β-amyloid (Aβ), a major constituent in amyloid plaques. Emerging evidence suggests that BACE1 is also involved with synaptic plasticity and nerve regeneration. Here we examined whether BACE1 immunoreactivity (IR) was altered in pilocarpine-induced epileptic CD1 mice in a manner consistent with the synaptic reorganization seen during epileptogenesis. BACE1-IR increased in the CA3 mossy fiber field and dentate inner molecular layer in pilocarpine-induced epileptic mice, relative to controls (saline-treated mice and mice 24–48 h after pilocarpine-status), and paralleled aberrant expression of neuropeptide Y. Regionally increased BACE1-IR also occurred in neuropil in hippocampal area CA1 and in subregions of the amygdala and temporal cortex in epileptic mice, colocalizing with increased IR for growth associated protein 43 (GAP43) and polysialylated-neural cell adhesion molecule (PSA-NCAM), but reduced IR for microtubule-associated protein 2 (MAP2). These findings suggest that BACE1 is involved in aberrant limbic axonal sprouting in a model of temporal lobe epilepsy, warranting further investigation into the role of BACE1 in physiological vs. pathological neuronal plasticity.
Aberrant neuroplasticity; Temporal lobe epilepsy; Mossy fiber sprouting; Dystrophic neurites; Beta-secretase; Alzheimer’s disease
Rett syndrome (RTT) is a devastating neurodevelopmental disorder affecting 1 in 10,000 girls. Approximately 90% of cases are caused by spontaneous mutations in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2). Girls with RTT suffer from severe motor, respiratory, cognitive and social abnomalities attributed to early deficits in synaptic connectivity which manifest in the adult as a myriad of physiological and anatomical abnormalities including, but not limited to, dimished dendritic complexity. Supplementation with acetyl-L-carnitine (ALC), an acetyl group donor, ameliorates motor and cognitive deficits in other disease models through a variety of mechanisms including altering patterns of histone acetylation resulting in changes in gene expression, and stimulating biosynthetic pathways such as acetylcholine. We hypothesized ALC treatment during critical periods in cortical development would promote normal synaptic maturation, and continuing treatment would improve behavioral deficits in the Mecp21lox mouse model of RTT. In this study, wildtype and Mecp21lox mutant mice received daily injections of ALC from birth until death (postnatal day 47). General health, motor, respiratory, and cognitive functions were assessed at several time points during symptom progression. ALC improved weight gain, grip strength, activity levels, prevented metabolic abnormalities and modestly improved cognitive function in Mecp2 null mice early in the course of treatment, but did not significantly improve motor or cognitive functions assessed later in life. ALC treatment from birth was associated with an almost complete rescue of hippocampal dendritic morphology abnormalities with no discernable side effects in the mutant mice. Therefore, ALC appears to be a promising therapeutic approach to treating early RTT symptoms and may be useful in combination with other therapies.
α-Synuclein (αSYN) is genetically and neuropathologically linked to a spectrum of neurodegenerative diseases including Parkinson’s disease, dementia with Lewy bodies, and related disorders. Cognitive impairment is recapitulated in several αSYN transgenic mouse lines. However, the mechanisms of dysfunction in affected neurons are largely unknown. Here we measured neuronal activity induced gene products in the limbic system of αSYN transgenic mice upon fear conditioning (FC). Induction of the synaptic plasticity marker c-Fos was significantly reduced in the amygdala and hippocampus of (Thy1)-h[A30P]αSYN transgenic mice in an age-dependent manner. Similarly, the neuronal activity inducible polo-like kinase 2 (Plk2) that can phosphorylate αSYN at the pathological site serine-129 was up-regulated in both brain regions upon FC. Plk2 inductions were also significantly impaired in aged (Thy1)-h[A30P]αSYN transgenic mice, both in the amygdala and hippocampus. Plk2 inductions in the amygdala after FC were paralleled by a small but significant increase in the number of neuronal cell bodies immunopositive for serine-129 phosphorylated αSYN in young but not aged (Thy1)-h[A30P]αSYN transgenic mice. In addition, we observed in the aged hippocampus a distinct type of apparently unmodified transgenic αSYN profiles resembling synaptic accumulations of αSYN. Thus, the cognitive decline observed in aged αSYN transgenic mice might be due to impairment of neurotransmission and synaptic plasticity in the limbic system by distinct αSYN species.
The comorbidity between epilepsy and Alzheimer's disease (AD) is a topic of growing interest. Senile plaques and tauopathy are found in epileptic human temporal lobe structures, and individuals with AD have an increased incidence of spontaneous seizures. However, why and how epilepsy is associated with enhanced AD-like pathology remains unknown. We have recently shown β-secretase-1 (BACE1) elevation associated with aberrant limbic axonal sprouting in epileptic CD1 mice. Here we sought to explore whether BACE1 upregulation affected the development of Alzheimer-type neuropathology in mice expressing mutant human APP, presenilin and tau proteins, the triple transgenic model of AD (3×Tg-AD). 3×Tg-AD mice were treated with pilocarpine or saline (i.p.) at 6–8 months of age. Immunoreactivity (IR) for BACE1, β-amyloid (Aβ) and phosphorylated tau (p-tau) was subsequently examined at 9, 11 or 14 months of age. Recurrent convulsive seizures, as well as mossy fiber sprouting and neuronal death in the hippocampus and limbic cortex, were observed in all epileptic mice. Neuritic plaques composed of BACE1-labeled swollen/sprouting axons and extracellular AβIR were seen in the hippocampal formation, amygdala and piriform cortices of 9 month-old epileptic, but not control, 3×Tg-AD mice. Densities of plaque-associated BACE1 and AβIR were elevated in epileptic versus control mice at 11 and 14 months of age. p-Tau IR was increased in dentate granule cells and mossy fibers in epileptic mice relative to controls at all time points examined. Thus, pilocarpine-induced chronic epilepsy was associated with accelerated and enhanced neuritic plaque formation and altered intraneuronal p-tau expression in temporal lobe structures in 3×Tg-AD mice, with these pathologies occurring in regions showing neuronal death and axonal dystrophy.
Pathologic aggregates of superoxide dismutase 1 (SOD1) harboring mutations linked to familial amyotrophic lateral sclerosis (fALS) have been shown to contain aberrant intermolecular disulfide cross-links. In prior studies, we observed that intermolecular bonding was not necessary in the formation of detergent- insoluble SOD1 complexes by mutant SOD1, but we were unable to assess whether this type of bonding may be important for pathologic inclusion formation. In the present study, we visually assess the formation of large inclusions by fusing mutant SOD1 to yellow fluorescent protein (YFP).
Experimental constructs possessing mutations at all cysteine residues in SOD1 (sites 6, 57, 111, and 146 to F,S,Y,R or G,S,Y,R, respectively) were shown to maintain a high propensity of inclusion formation despite the inability to form disulfide cross-links. Interestingly, although aggregates form when all cysteines were mutated, double mutants of the ALS mutation C6G with an experimental mutation C111S exhibited low aggregation propensity.
Overall, this study is an extension of previous work demonstrating that cysteine residues in mutant SOD1 play a role in modulating aggregation and that intermolecular disulfide bonds are not required to produce large intracellular inclusion-like structures.
The FET family of proteins is composed of FUS/TLS, EWS/EWSR1, and TAF15 and possesses RNA- and DNA-binding capacities. The FET-proteins are involved in transcriptional regulation and RNA processing, and FET-gene deregulation is associated with development of cancer and protein granule formations in amyotrophic lateral sclerosis, frontotemporal lobar degeneration, and trinucleotide repeat expansion diseases. We here describe a comparative characterization of FET-protein localization and gene regulatory functions. We show that FUS and TAF15 locate to cellular stress granules to a larger extend than EWS. FET-proteins have no major importance for stress granule formation and cellular stress responses, indicating that FET-protein stress granule association most likely is a downstream response to cellular stress. Gene expression analyses showed that the cellular response towards FUS and TAF15 reduction is relatively similar whereas EWS reduction resulted in a more unique response. The presented data support that FUS and TAF15 are more functionally related to each other, and that the FET-proteins have distinct functions in cellular signaling pathways which could have implications for the neurological disease pathogenesis.
Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) is the best understood cause of dominantly inherited stroke and results from NOTCH3 mutations that lead to NOTCH3 protein accumulation and selective arterial smooth muscle degeneration. Previous studies show that NOTCH3 protein forms multimers. Here, we investigate protein interactions between NOTCH3 and other vascular Notch isoforms and characterize the effects of elevated NOTCH3 on smooth muscle gene regulation. We demonstrate that NOTCH3 forms heterodimers with NOTCH1, NOTCH3, and NOTCH4. R90C and C49Y mutant NOTCH3 form complexes which are more resistant to detergents than wild type NOTCH3 complexes. Using quantitative NOTCH3-luciferase clearance assays, we found significant inhibition of mutant NOTCH3 clearance. In coculture assays of NOTCH function, overexpressed wild type and mutant NOTCH3 significantly repressed NOTCH-regulated smooth muscle transcripts and potently impaired the activity of three independent smooth muscle promoters. Wildtype and R90C recombinant NOTCH3 proteins applied to cell cultures also blocked canonical Notch fuction. We conclude that CADASIL mutants of NOTCH3 complex with NOTCH1, 3, and 4, slow NOTCH3 clearance, and that overexpressed wild type and mutant NOTCH3 protein interfere with key NOTCH-mediated functions in smooth muscle cells.
The pesticide rotenone, a neurotoxin that inhibits the mitochondrial complex I, and destabilizes microtubules (MT) has been linked to Parkinson disease (PD) etiology and is often used to model this neurodegenerative disease (ND). Many of the mechanisms of action of rotenone are posited mechanisms of neurodegeneration; however, they are not fully understood. Therefore, the study of rotenone-affected functional pathways is pertinent to the understanding of NDs pathogenesis. This report describes the transcriptome analysis of a neuroblastoma (NB) cell line chronically exposed to marginally toxic and moderately toxic doses of rotenone. The results revealed a complex pleiotropic response to rotenone that impacts a variety of cellular events, including cell cycle, DNA damage response, proliferation, differentiation, senescence and cell death, which could lead to survival or neurodegeneration depending on the dose and time of exposure and cell phenotype. The response encompasses an array of physiological pathways, modulated by transcriptional and epigenetic regulatory networks, likely activated by homeostatic alterations. Pathways that incorporate the contribution of MT destabilization to rotenone toxicity are suggested to explain complex I-independent rotenone-induced alterations of metabolism and redox homeostasis. The postulated mechanisms involve the blockage of mitochondrial voltage-dependent anions channels (VDACs) by tubulin, which coupled with other rotenone-induced organelle dysfunctions may underlie many presumed neurodegeneration mechanisms associated with pathophysiological aspects of various NDs including PD, AD and their variant forms. Thus, further investigation of such pathways may help identify novel therapeutic paths for these NDs.
Depolarization-induced suppression of excitation (DSE) at parallel fiber-Purkinje cell synapse is an endocannabinoid-mediated short-term retrograde plasticity. Intracellular Ca2+ elevation is critical for the endocannabinoid production and DSE. Nevertheless, how elevated Ca2+ leads to DSE is unclear.
We utilized cytosolic phospholipase A2 alpha (cPLA2α) knock-out mice and whole-cell patch clamp in cerebellar slices to observed the action of cPLA2α/arachidonic acid signaling on DSE at parallel fiber-Purkinje cell synapse. Our data showed that DSE was significantly inhibited in cPLA2α knock-out mice, which was rescued by arachidonic acid. The degradation enzyme of 2-arachidonoylglycerol (2-AG), monoacylglycerol lipase (MAGL), blocked DSE, while another catabolism enzyme for N-arachidonoylethanolamine (AEA), fatty acid amide hydrolase (FAAH), did not affect DSE. These results suggested that 2-AG is responsible for DSE in Purkinje cells. Co-application of paxilline reversed the blockade of DSE by internal K+, indicating that large conductance Ca2+-activated potassium channel (BK) is sufficient to inhibit cPLA2α/arachidonic acid-mediated DSE. In addition, we showed that the release of 2-AG was independent of soluble NSF attachment protein receptor (SNARE), protein kinase C and protein kinase A.
Our data first showed that cPLA2α/arachidonic acid/2-AG signaling pathway mediates DSE at parallel fiber-Purkinje cell synapse.
Translation elongation factor isoform eEF1A2 is expressed in muscle and neurons. Deletion of eEF1A2 in mice gives rise to the neurodegenerative phenotype “wasted” (wst). Mice homozygous for the wasted mutation die of muscle wasting and neurodegeneration at four weeks post-natal. Although the mutation is said to be recessive, aged heterozygous mice have never been examined in detail; a number of other mouse models of motor neuron degeneration have recently been shown to have similar, albeit less severe, phenotypic abnormalities in the heterozygous state. We therefore examined the effects of ageing on a cohort of heterozygous +/wst mice and control mice, in order to establish whether a presumed 50% reduction in eEF1A2 expression was compatible with normal function. We evaluated the grip strength assay as a way of distinguishing between wasted and wild-type mice at 3–4 weeks, and then performed the same assay in older +/wst and wild-type mice. We also used rotarod performance and immunohistochemistry of spinal cord sections to evaluate the phenotype of aged heterozygous mice. Heterozygous mutant mice showed no deficit in neuromuscular function or signs of spinal cord pathology, in spite of the low levels of eEF1A2.