The rat striatum responds to nigro-striatal degeneration via the increased expression of proteins associated with growth and regeneration of neuronal circuitry

AAV9-mediated SMN gene therapy rescues cardiac desmin but not lamin A/C and elastin dysregulation in Smn2B/- spinal muscular atrophy mice

Structural, functional and molecular cardiac defects have been reported in spinal muscular atrophy (SMA) patients and mouse models. Previous quantitative proteomics analyses demonstrated widespread molecular defects in the severe Taiwanese SMA mouse model. Whether such changes are conserved across different mouse models, including less severe forms of the disease, has yet to be established. Here, using the same high-resolution proteomics approach in the less-severe Smn2B/- SMA mouse model, 277 proteins were found to be differentially abundant at a symptomatic timepoint (post-natal day (P) 18), 50 of which were similarly dysregulated in severe Taiwanese SMA mice. Bioinformatics analysis linked many of the differentially abundant proteins to cardiovascular development and function, with intermediate filaments highlighted as an enriched cellular compartment in both datasets. Lamin A/C was increased in the cardiac tissue, whereas another intermediate filament protein, desmin, was reduced. The extracellular matrix (ECM) protein, elastin, was also robustly decreased in the heart of Smn2B/- mice. AAV9-SMN1-mediated gene therapy rectified low levels of survival motor neuron protein and restored desmin levels in heart tissues of Smn2B/- mice. In contrast, AAV9-SMN1 therapy failed to correct lamin A/C or elastin levels. Intermediate filament proteins and the ECM have key roles in cardiac function and their dysregulation may explain cardiac impairment in SMA, especially since mutations in genes encoding these proteins cause other diseases with cardiac aberration. Cardiac pathology may need to be considered in the long-term care of SMA patients, as it is unclear whether currently available treatments can fully rescue peripheral pathology in SMA.

The mitochondrial protein Sideroflexin 3 (SFXN3) influences neurodegeneration pathways in vivo

Synapses are a primary pathological target in neurodegenerative diseases. Identifying therapeutic targets at the synapse could delay progression of numerous conditions. The mitochondrial protein SFXN3 is a neuronally enriched protein expressed in synaptic terminals and regulated by key synaptic proteins, including α-synuclein. We first show that SFXN3 uses the carrier import pathway to insert into the inner mitochondrial membrane. Using high-resolution proteomics on Sfxn3-KO mice synapses, we then demonstrate that SFXN3 influences proteins and pathways associated with neurodegeneration and cell death (including CSPα and Caspase-3), as well as neurological conditions (including Parkinson's disease and Alzheimer's disease). Overexpression of SFXN3 orthologues in Drosophila models of Parkinson's disease significantly reduced dopaminergic neuron loss. In contrast, the loss of SFXN3 was insufficient to trigger neurodegeneration in mice, indicating an anti- rather than pro-neurodegeneration role for SFXN3. Taken together, these results suggest a potential role for SFXN3 in the regulation of neurodegeneration pathways.

Analysis of the Neuroproteome Associated With Cell Therapy After Intranigral Grafting in a Mouse Model of Parkinson Disease

Advances in large-scale proteomics analysis have been very useful in understanding pathogenesis of diseases and elaborating therapeutic strategies. Proteomics has been employed to study Parkinson disease (PD); however, sparse studies reported proteome investigation after cell therapy approaches. In this study, we used liquid chromatography–tandem mass spectrometry and systems biology to identify differentially expressed proteins in a translational mouse model of PD after cell therapy. Proteins were extracted from five nigrostriatal-related brain regions of mice previously lesioned with 6-hydroxydopamine in the substantia nigra. Protein expression was compared in non-grafted brain to 1 and 7 days after intranigral grafting of E12.5 embryonic ventral mesencephalon (VM). We found a total of 277 deregulated proteins after transplantation, which are enriched for lipid metabolism, oxidative phosphorylation and PD, thus confirming that our animal model is similar to human PD and that the presence of grafted cells modulates the expression of these proteins. Notably, seven proteins (Acta1, Atp6v1e1, Eci3, Lypla2, Pip4k2a, Sccpdh, and Sh3gl2) were commonly down-regulated after engraftment in all studied brain regions. These proteins are known to be involved in the formation of lipids and recycling of dopamine (DA) vesicle at the synapse. Moreover, intranigral transplantation of VM cells decreased the expression of proteins related to oxidative stress, especially in the nigrostriatal pathway containing the DA grafted neurons. In the same regions, an up-regulation of several proteins including α-synuclein and tyrosine hydroxylase was observed, whereas expression of tetraspanin 7 was shut down. Overall, these results suggest that intranigral transplantation of VM tissue in an animal model of PD may induce a decrease of oxidative stress in the nigrostriatal pathway and a restoration of the machinery of neurotransmitters, particularly DA release to promote DA transmission through a decrease of D2 DA receptors endocytosis. Identification of new mechanistic elements involved in the nigrostriatal reconstruction process, using translational animal models and systems biology, is a promising approach to enhance the repair of this pathway in PD patients undergoing cell therapy.

Lamin A/C dysregulation contributes to cardiac pathology in a mouse model of severe spinal muscular atrophy

Cardiac pathology is emerging as a prominent systemic feature of spinal muscular atrophy (SMA), but little is known about the underlying molecular pathways. Using quantitative proteomics analysis, we demonstrate widespread molecular defects in heart tissue from the Taiwanese mouse model of severe SMA. We identify increased levels of lamin A/C as a robust molecular phenotype in the heart of SMA mice and show that lamin A/C dysregulation is also apparent in SMA patient fibroblast cells and other tissues from SMA mice. Lamin A/C expression was regulated in vitro by knockdown of the E1 ubiquitination factor ubiquitin-like modifier activating enzyme 1, a key downstream mediator of SMN-dependent disease pathways, converging on β-catenin signaling. Increased levels of lamin A are known to increase the rigidity of nuclei, inevitably disrupting contractile activity in cardiomyocytes. The increased lamin A/C levels in the hearts of SMA mice therefore provide a likely mechanism explaining morphological and functional cardiac defects, leading to blood pooling. Therapeutic strategies directed at lamin A/C may therefore offer a new approach to target cardiac pathology in SMA.

Altered mitochondrial bioenergetics are responsible for the delay in Wallerian degeneration observed in neonatal mice

Neurodegenerative and neuromuscular disorders can manifest throughout the lifespan of an individual, from infant to elderly individuals. Axonal and synaptic degeneration are early and critical elements of nearly all human neurodegenerative diseases and neural injury, however the molecular mechanisms which regulate this process are yet to be fully elucidated. Furthermore, how the molecular mechanisms governing degeneration are impacted by the age of the individual is poorly understood. Interestingly, in mice which are under 3 weeks of age, the degeneration of axons and synapses following hypoxic or traumatic injury is significantly slower. This process, known as Wallerian degeneration (WD), is a molecularly and morphologically distinct subtype of neurodegeneration by which axons and synapses undergo distinct fragmentation and death following a range of stimuli. In this study, we first use an ex-vivo model of axon injury to confirm the significant delay in WD in neonatal mice. We apply tandem mass-tagging quantitative proteomics to profile both nerve and muscle between P12 and P24 inclusive. Application of unbiased in silico workflows to relevant protein identifications highlights a steady elevation in oxidative phosphorylation cascades corresponding to the accelerated degeneration rate. We demonstrate that inhibition of Complex I prevents the axotomy-induced rise in reactive oxygen species and protects axons following injury. Furthermore, we reveal that pharmacological activation of oxidative phosphorylation significantly accelerates degeneration at the neuromuscular junction in neonatal mice. In summary, we reveal dramatic changes in the neuromuscular proteome during post-natal maturation of the neuromuscular system, and demonstrate that endogenous dynamics in mitochondrial bioenergetics during this time window have a functional impact upon regulating the stability of the neuromuscular system.

State transitions in the substantia nigra reticulata predict the onset of motor deficits in models of progressive dopamine depletion in mice

Parkinson's disease (PD) is a progressive neurodegenerative disorder whose cardinal motor symptoms are attributed to dysfunction of basal ganglia circuits under conditions of low dopamine. Despite well-established physiological criteria to define basal ganglia dysfunction, correlations between individual parameters and motor symptoms are often weak, challenging their predictive validity and causal contributions to behavior. One limitation is that basal ganglia pathophysiology is studied only at end-stages of depletion, leaving an impoverished understanding of when deficits emerge and how they evolve over the course of depletion. In this study, we use toxin- and neurodegeneration-induced mouse models of dopamine depletion to establish the physiological trajectory by which the substantia nigra reticulata (SNr) transitions from the healthy to the diseased state. We find that physiological progression in the SNr proceeds in discrete state transitions that are highly stereotyped across models and correlate well with the prodromal and symptomatic stages of behavior.

Characterization of Xenopus laevis guanine deaminase reveals new insights for its expression and function in the embryonic kidney

BACKGROUND

The mammalian guanine deaminase (GDA), called cypin, is important for proper neural development, by regulating dendritic arborization through modulation of microtubule (MT) dynamics. Additionally, cypin can promote MT assembly in vitro. However, it has never been tested whether cypin (or other GDA orthologs) binds to MTs or modulates MT dynamics. Here, we address these questions and characterize Xenopus laevis GDA (Gda) for the first time during embryonic development.

RESULTS

We find that exogenously expressed human cypin and Gda both display a cytosolic distribution in primary embryonic cells. Furthermore, while expression of human cypin can promote MT polymerization, Xenopus Gda has no effect. Additionally, we find that the tubulin-binding collapsin response mediator protein (CRMP) homology domain is only partially conserved between cypin and Gda. This likely explains the divergence in function, as we discovered that the cypin region containing the CRMP homology and PDZ-binding domain is necessary for regulating MT dynamics. Finally, we observed that gda is strongly expressed in the kidneys during late embryonic development, although it does not appear to be critical for kidney development.

CONCLUSIONS

Together, these results suggest that GDA has diverged in function between mammals and amphibians, and that mammalian GDA plays an indirect role in regulating MT dynamics. Developmental Dynamics 248:296-305, 2019. © 2019 Wiley Periodicals, Inc.

A Novel Short Isoform of Cytosolic PSD-95 Interactor (Cypin) Regulates Neuronal Development

The guanine deaminase cypin (cytosolic PSD-95 interactor) binds to PSD-95 (postsynaptic density protein 95) and regulates dendrite branching by promoting microtubule polymerization. Here, we identify a novel short isoform of cypin, termed cypinS, which is expressed in mouse and human, but not rat, tissues. Cypin and cypinS mRNA and protein levels peak at P7 and P14 in the mouse brain, suggesting a role for these isoforms during development. Interestingly, although cypinS lacks guanine deaminase activity, overexpression of cypinS increases dendrite branching. This increase occurs further away from soma than do increases resulting from overexpression of cypin. In contrast, overexpression of cypin, but not cypinS, decreases dendritic spine density and maturity. This suggests that changes to spines, but not to dendrites, may be dependent on guanine deaminase activity. Furthermore, overexpression of either cypin or cypinS increases miniature excitatory postsynaptic current (mEPSC) frequency, pointing to a presynaptic role for both isoforms. Interestingly, overexpression of cypinS results in a significantly greater increase in frequency than does overexpression of cypin. Thus, cypin and cypinS play distinct roles in neuronal development.

Mechanisms and Consequences of Dopamine Depletion-Induced Attenuation of the Spinophilin/Neurofilament Medium Interaction

Signaling changes that occur in the striatum following the loss of dopamine neurons in the Parkinson disease (PD) are poorly understood. While increases in the activity of kinases and decreases in the activity of phosphatases have been observed, the specific consequences of these changes are less well understood. Phosphatases, such as protein phosphatase 1 (PP1), are highly promiscuous and obtain substrate selectivity via targeting proteins. Spinophilin is the major PP1-targeting protein enriched in the postsynaptic density of striatal dendritic spines. Spinophilin association with PP1 is increased concurrent with decreases in PP1 activity in an animal model of PD. Using proteomic-based approaches, we observed dopamine depletion-induced decreases in spinophilin binding to multiple protein classes in the striatum. Specifically, there was a decrease in the association of spinophilin with neurofilament medium (NF-M) in dopamine-depleted striatum. Using a heterologous cell line, we determined that spinophilin binding to NF-M required overexpression of the catalytic subunit of protein kinase A and was decreased by cyclin-dependent protein kinase 5. Functionally, we demonstrate that spinophilin can decrease NF-M phosphorylation. Our data determine mechanisms that regulate, and putative consequences of, pathological changes in the association of spinophilin with NF-M that are observed in animal models of PD.

Sideroflexin 3 is an α-synuclein-dependent mitochondrial protein that regulates synaptic morphology

α-Synuclein plays a central role in Parkinson's disease, where it contributes to the vulnerability of synapses to degeneration. However, the downstream mechanisms through which α-synuclein controls synaptic stability and degeneration are not fully understood. Here, comparative proteomics on synapses isolated from α-synuclein^-/- mouse brain identified mitochondrial proteins as primary targets of α-synuclein, revealing 37 mitochondrial proteins not previously linked to α-synuclein or neurodegeneration pathways. Of these, sideroflexin 3 (SFXN3) was found to be a mitochondrial protein localized to the inner mitochondrial membrane. Loss of SFXN3 did not disturb mitochondrial electron transport chain function in mouse synapses, suggesting that its function in mitochondria is likely to be independent of canonical bioenergetic pathways. In contrast, experimental manipulation of SFXN3 levels disrupted synaptic morphology at the Drosophila neuromuscular junction. These results provide novel insights into α-synuclein-dependent pathways, highlighting an important influence on mitochondrial proteins at the synapse, including SFXN3. We also identify SFXN3 as a new mitochondrial protein capable of regulating synaptic morphology in vivo.

Morphological Changes in a Severe Model of Parkinson's Disease and Its Suitability to Test the Therapeutic Effects of Microencapsulated Neurotrophic Factors

The unilateral 6-hydroxydopamine (6-OHDA) lesion of medial forebrain bundle (MFB) in rats affords us to study the advanced stages of Parkinson's disease (PD). Numerous evidences suggest synergic effects when various neurotrophic factors are administered in experimental models of PD. The aim of the present work was to assess the morphological changes along the rostro-caudal axis of caudo-putamen complex and substantia nigra (SN) in the referred model in order to test the suitability of a severe model to evaluate new neurorestorative therapies. Administration of 6-OHDA into MFB in addition to a remarkable depletion of dopamine in the nigrostriatal system induced an increase of glial fibrillary acidic protein (GFAP)-positive cells in SN and an intense immunoreactivity for OX-42, vascular endothelial growth factor (VEGF), and Lycopersycum esculentum agglutinin (LEA) in striatum and SN. Tyrosine hydroxylase (TH) immunostaining revealed a significant decrease of the TH-immunopositive striatal volume in 6-OHDA group from rostral to caudal one. The loss of TH-immunoreactive (TH-ir) neurons and axodendritic network (ADN) was higher in caudal sections. Morphological recovery after the implantation of microspheres loaded with VEGF and glial cell line-derived neurotrophic factor (GDNF) in parkinsonized rats was related to the preservation of the TH-ir cell number and ADN in the caudal region of the SN. In addition, these findings support the neurorestorative role of VEGF+GDNF in the dopaminergic system and the synergistic effect between both factors. On the other hand, a topological distribution of the dopaminergic system was noticeable in the severe model, showing a selective vulnerability to 6-OHDA and recovering after treatment.

Characterization of unexplored amidohydrolase enzyme-pterin deaminase

Pterin deaminase is an amidohydrolase enzyme hydrolyzing pteridines to form lumazine derivatives and ammonia. The enzyme captured the attention of scientists as early as 1959 and had been patented for its application as an anticancer agent. It is ubiquitously present in prokaryotes and has been reported in some eukaryotes such as honey bee, silkworm and rats. The enzyme has been observed to have a spectrum of substrates with the formation of respective lumazines. The role of the substrates of the enzyme in various metabolic pathways warrants a significant role in the biological activity of both prokaryotes and eukaryotes. Even though the functions of the enzyme have been explored in prokaryotes, their niche in the eukaryotic system is not clear. There is very few information on the structural and functional properties of the enzyme. This review has been congregated to emphasize the significance of pterin deaminase and analyzes the lacunae in understanding the biological characters of the enzyme.

CART modulates the effects of levodopa in rat model of Parkinson's disease

Parkinson's disease (PD) is an age-related disorder characterized by a progressive degeneration of dopaminergic neurons of substantia nigra (SN). The neuropeptide cocaine- and amphetamine-regulated transcript (CART) is known to closely interact with the dopamine system and regulate psychomotor activity. We screened the effectiveness of CART in reversing the symptoms of PD in a rat model. PD like condition was induced by administering 6-hydroxydopamine (6-OHDA) directly in the SN of the right side. Fifteen days later, intraperitoneal (IP) treatment with apomorphine hydrochloride to these rats, resulted in contralateral rotations in the rotation test chamber suggesting induction of PD-like symptoms. This action of apomorphine was significantly attenuated by intracerebroventricular (ICV) treatment with CART and potentiated by CART antibody. IP treatment with levodopa also produced contralateral rotation in PD induced rats, and showed anti-Parkinson-like action. Prior treatment with CART via ICV route potentiated the anti-Parkinsonian effects of levodopa, while CART antibody produced opposite effects. CART treatment per se, to PD induced rats produced ipsilateral rotations, suggesting that the peptide may promote the endogenous release of dopamine from intact neurons. While CART-immunoreactivity in arcuate nucleus, paraventricular nucleus, striatum, substantia nigra, ventral tegmental area and locus coeruleus was reduced in the PD induced rats, levodopa treatment restored the expression of CART-immunoreactivity in these nuclei. These results suggest that endogenous CART might closely interact with the dopamine containing SN-striatal pathway which is known to profoundly influence the motor system. The study underscores the importance of CART as a potential therapeutic agent in the treatment of PD.

Proteomic Profiling of Cranial (Superior) Cervical Ganglia Reveals Beta-Amyloid and Ubiquitin Proteasome System Perturbations in an Equine Multiple System Neuropathy

Equine grass sickness (EGS) is an acute, predominantly fatal, multiple system neuropathy of grazing horses with reported incidence rates of ∼2%. An apparently identical disease occurs in multiple species, including but not limited to cats, dogs, and rabbits. Although the precise etiology remains unclear, ultrastructural findings have suggested that the primary lesion lies in the glycoprotein biosynthetic pathway of specific neuronal populations. The goal of this study was therefore to identify the molecular processes underpinning neurodegeneration in EGS. Here, we use a bottom-up approach beginning with the application of modern proteomic tools to the analysis of cranial (superior) cervical ganglion (CCG, a consistently affected tissue) from EGS-affected patients and appropriate control cases postmortem. In what appears to be the proteomic application of modern proteomic tools to equine neuronal tissues and/or to an inherent neurodegenerative disease of large animals (not a model of human disease), we identified 2,311 proteins in CCG extracts, with 320 proteins increased and 186 decreased by greater than 20% relative to controls. Further examination of selected proteomic candidates by quantitative fluorescent Western blotting (QFWB) and subcellular expression profiling by immunohistochemistry highlighted a previously unreported dysregulation in proteins commonly associated with protein misfolding/aggregation responses seen in a myriad of human neurodegenerative conditions, including but not limited to amyloid precursor protein (APP), microtubule associated protein (Tau), and multiple components of the ubiquitin proteasome system (UPS). Differentially expressed proteins eligible for in silico pathway analysis clustered predominantly into the following biofunctions: (1) diseases and disorders, including; neurological disease and skeletal and muscular disorders and (2) molecular and cellular functions, including cellular assembly and organization, cell-to-cell signaling and interaction (including epinephrine, dopamine, and adrenergic signaling and receptor function), and small molecule biochemistry. Interestingly, while the biofunctions identified in this study may represent pathways underpinning EGS-induced neurodegeneration, this is also the first demonstration of potential molecular conservation (including previously unreported dysregulation of the UPS and APP) spanning the degenerative cascades from an apparently unrelated condition of large animals, to small animal models with altered neuronal vulnerability, and human neurological conditions. Importantly, this study highlights the feasibility and benefits of applying modern proteomic techniques to veterinary investigations of neurodegenerative processes in diseases of large animals.

Topographical Distribution of Morphological Changes in a Partial Model of Parkinson's Disease--Effects of Nanoencapsulated Neurotrophic Factors Administration

Administration of various neurotrophic factors is a promising strategy against Parkinson's disease (PD). An intrastriatal infusion of 6-hydroxidopamine (6-OHDA) in rats is a suitable model to study PD. This work aims to describe stereological parameters regarding rostro-caudal gradient, in order to characterize the model and verify its suitability for elucidating the benefits of therapeutic strategies. Administration of 6-OHDA induced a reduction in tyrosine hidroxylase (TH) reactivity in the dorsolateral part of the striatum, being higher in the caudal section than in the rostral one. Loss of TH-positive neurons and axodendritic network was highly significant in the external third of substantia nigra (e-SN) in the 6-OHDA group versus the saline one. After the administration of nanospheres loaded with neurotrophic factors (NTF: vascular endothelial growth factor (VEGF) + glial cell line-derived neurotrophic factor (GDNF)), parkinsonized rats showed more TH-positive fibers than those of control groups; this recovery taking place chiefly in the rostral sections. Neuronal density and axodendritic network in e-SN was more significant than in the entire SN; the topographical analysis showed that the highest difference between NTF versus control group was attained in the middle section. A high number of bromodeoxyuridine (BrdU)-positive cells were found in sub- and periventricular areas in the group receiving NTF, where most of them co-expressed doublecortin. Measurements on the e-SN achieved more specific and significant results than in the entire SN. This difference in rostro-caudal gradients underpins the usefulness of a topological approach to the assessment of the lesion and therapeutic strategies. Findings confirmed the neurorestorative, neurogenic, and synergistic effects of VEGF+GDNF administration.