Cell death pathways differ in several mouse models with motoneurone disease: analysis of pure motoneurone populations at a presymptomatic age

Pegylated Insulin-Like Growth Factor 1 attenuates Hair Cell Loss and promotes Presynaptic Maintenance of Medial Olivocochlear Cholinergic Fibers in the Cochlea of the Progressive Motor Neuropathy Mouse

The progressive motor neuropathy (PMN) mouse is a model of an inherited motor neuropathy disease with progressive neurodegeneration. Axon degeneration associates with homozygous mutations of the TBCE gene encoding the tubulin chaperone E protein. TBCE is responsible for the correct dimerization of alpha and beta-tubulin. Strikingly, the PMN mouse also develops a progressive hearing loss after normal hearing onset, characterized by degeneration of the auditory nerve and outer hair cell (OHC) loss. However, the development of this neuronal and cochlear pathology is not fully understood yet. Previous studies with pegylated insulin-like growth factor 1 (peg-IGF-1) treatment in this mouse model have been shown to expand lifespan, weight, muscle strength, and motor coordination. Accordingly, peg-IGF-1 was evaluated for an otoprotective effect. We investigated the effect of peg-IGF-1 on the auditory system by treatment starting at postnatal day 15 (p15). Histological analysis revealed positive effects on OHC synapses of medial olivocochlear (MOC) neuronal fibers and a short-term attenuation of OHC loss. Peg-IGF-1 was able to conditionally restore the disorganization of OHC synapses and maintain the provision of cholinergic acetyltransferase in presynapses. To assess auditory function, frequency-specific auditory brainstem responses and distortion product otoacoustic emissions were recorded in animals on p21 and p28. However, despite the positive effect on MOC fibers and OHC, no restoration of hearing could be achieved. The present work demonstrates that the synaptic pathology of efferent MOC fibers in PMN mice represents a particular form of “efferent auditory neuropathy.” Peg-IGF-1 showed an otoprotective effect by preventing the degeneration of OHCs and efferent synapses. However, enhanced efforts are needed to optimize the treatment to obtain detectable improvements in hearing performances.

Gene Expression Profiling of Cutaneous Injured and Non-Injured Nociceptors in SNI Animal Model of Neuropathic Pain

Nociceptors are a particular subtype of dorsal root ganglion (DRG) neurons that detect noxious stimuli and elicit pain. Although recent efforts have been made to reveal the molecular profile of nociceptors in normal conditions, little is known about how this profile changes in pathological conditions. In this study we exploited laser capture microdissection to specifically collect individual injured and non-injured nociceptive DRG neurons and to define their gene profiling in rat spared nerve injury (SNI) model of neuropathic pain. We found minimal transcriptional changes in non-injured neurons at 7 days after SNI. In contrast, several novel transcripts were altered in injured nociceptors, and the global signature of these LCM-captured neurons differed markedly from that the gene expression patterns found previously using whole DRG tissue following SNI. Pathway analysis of the transcriptomic profile of the injured nociceptors revealed oxidative stress as a key biological process. We validated the increase of caspase-6 (CASP6) in small-sized DRG neurons and its functional role in SNI- and paclitaxel-induced neuropathic pain. Our results demonstrate that the identification of gene regulation in a specific population of DRG neurons (e.g., nociceptors) is an effective strategy to reveal new mechanisms and therapeutic targets for neuropathic pain from different origins.

Brain-Expressed X-linked (BEX) proteins in human cancers

The Brain-Expressed X-linked (BEX) family proteins are comprised of five human proteins including BEX1, BEX2, BEX3, BEX4 and BEX5. BEX family proteins are expressed in a wide range of tissues and are known to play a role in neuronal development. Recent studies suggest a role of BEX family proteins in cancers. BEX1 expression is lost in a subgroup of patients with acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). Expression of BEX1 controls cell surface receptor signaling and restores imatinib response in resistant cells. BEX2 is overexpressed in a group of breast cancer patients and also in gliomas. Increased BEX2 expression led to enhanced NF-κB signaling as well as cell proliferation. Although BEX2 acts as tumor promoter in a subset of breast cancer, BEX3 expression displayed an opposite role. Overexpression of BEX3 resulted in inhibition of tumor formation in breast cancer mouse xenograft models. The role of BEX4 and BEX5 in cancer has not yet been defined. Collectively this suggests that BEX family members have distinct roles in cancers. While BEX1 and BEX3 act as tumor suppressors, BEX2 seems to act as an oncogene.

Brca1 is expressed in human microglia and is dysregulated in human and animal model of ALS

Background

There is growing evidence that microglia are key players in the pathological process of amyotrophic lateral sclerosis (ALS). It is suggested that microglia have a dual role in motoneurone degeneration through the release of both neuroprotective and neurotoxic factors.

Results

To identify candidate genes that may be involved in ALS pathology we have analysed at early symptomatic age (P90), the molecular signature of microglia from the lumbar region of the spinal cord of hSOD1^G93A mice, the most widely used animal model of ALS. We first identified unique hSOD1^G93A microglia transcriptomic profile that, in addition to more classical processes such as chemotaxis and immune response, pointed toward the potential involvement of the tumour suppressor gene breast cancer susceptibility gene 1 (Brca1). Secondly, comparison with our previous data on hSOD1^G93A motoneurone gene profile substantiated the putative contribution of Brca1 in ALS. Finally, we established that Brca1 protein is specifically expressed in human spinal microglia and is up-regulated in ALS patients.

Conclusions

Overall, our data provide new insights into the pathogenic concept of a non-cell-autonomous disease and the involvement of microglia in ALS. Importantly, the identification of Brca1 as a novel microglial marker and as possible contributor in both human and animal model of ALS may represent a valid therapeutic target. Moreover, our data points toward novel research strategies such as investigating the role of oncogenic proteins in neurodegenerative diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-015-0023-x) contains supplementary material, which is available to authorized users.

Intricate effects of primary motor neuronopathy on contractile proteins and metabolic muscle enzymes as revealed by label-free mass spectrometry

While the long-term physiological adaptation of the neuromuscular system to changed functional demands is usually reflected by unilateral skeletal muscle transitions, the progressive degeneration of distinct motor neuron populations is often associated with more complex changes in the abundance and/or isoform expression pattern of contractile proteins and metabolic enzymes. In order to evaluate these intricate effects of primary motor neuronopathy on the skeletal muscle proteome, label-free MS was employed to study global alterations in the WR (wobbler) mouse model of progressive neurodegeneration. In motor neuron disease, fibre-type specification and the metabolic weighting of bioenergetic pathways appear to be strongly influenced by both a differing degree of a subtype-specific vulnerability of neuromuscular synapses and compensatory mechanisms of fibre-type shifting. Proteomic profiling confirmed this pathobiochemical complexity of disease-induced changes and showed distinct alterations in 72 protein species, including a variety of fibre-type-specific isoforms of contractile proteins, metabolic enzymes, metabolite transporters and ion-regulatory proteins, as well as changes in molecular chaperones and various structural proteins. Increases in slow myosin light chains and the troponin complex and a decrease in fast MBP (myosin-binding protein) probably reflect the initial preferential loss of the fast type of neuromuscular synapses in motor neuron disease.

The systematic biochemical analysis of muscle from the wobbler mouse model of motor neuron disease suggests that the loss of neuromuscular synapses causes complex changes in the protein profile of contractile tissues, affecting especially the contractile apparatus and energy metabolism.

Early gene expression changes in spinal cord from SOD1(G93A) Amyotrophic Lateral Sclerosis animal model

Amyotrophic Lateral Sclerosis (ALS) is an adult-onset and fast progression neurodegenerative disease that leads to the loss of motor neurons. Mechanisms of selective motor neuron loss in ALS are unknown. The early events occurring in the spinal cord that may contribute to motor neuron death are not described, neither astrocytes participation in the pre-symptomatic phases of the disease. In order to identify ALS early events, we performed a microarray analysis employing a whole mouse genome platform to evaluate the gene expression pattern of lumbar spinal cords of transgenic SOD1^G93A mice and their littermate controls at pre-symptomatic ages of 40 and 80 days. Differentially expressed genes were identified by means of the Bioconductor packages Agi4×44Preprocess and limma. FunNet web based tool was used for analysis of over-represented pathways. Furthermore, immunolabeled astrocytes from 40 and 80 days old mice were submitted to laser microdissection and RNA was extracted for evaluation of a selected gene by qPCR. Statistical analysis has pointed to 492 differentially expressed genes (155 up and 337 down regulated) in 40 days and 1105 (433 up and 672 down) in 80 days old ALS mice. KEGG analysis demonstrated the over-represented pathways tight junction, antigen processing and presentation, oxidative phosphorylation, endocytosis, chemokine signaling pathway, ubiquitin mediated proteolysis and glutamatergic synapse at both pre-symptomatic ages. Ube2i gene expression was evaluated in astrocytes from both transgenic ages, being up regulated in 40 and 80 days astrocytes enriched samples. Our data points to important early molecular events occurring in pre-symptomatic phases of ALS in mouse model. Early SUMOylation process linked to astrocytes might account to non-autonomous cell toxicity in ALS. Further studies on the signaling pathways presented here may provide new insights to better understand the events triggering motor neuron death in this devastating disorder.

Transcriptomic indices of fast and slow disease progression in two mouse models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is heterogeneous with high variability in the speed of progression even in cases with a defined genetic cause such as superoxide dismutase 1 (SOD1) mutations. We reported that SOD1(G93A) mice on distinct genetic backgrounds (C57 and 129Sv) show consistent phenotypic differences in speed of disease progression and life-span that are not explained by differences in human SOD1 transgene copy number or the burden of mutant SOD1 protein within the nervous system. We aimed to compare the gene expression profiles of motor neurons from these two SOD1(G93A) mouse strains to discover the molecular mechanisms contributing to the distinct phenotypes and to identify factors underlying fast and slow disease progression. Lumbar spinal motor neurons from the two SOD1(G93A) mouse strains were isolated by laser capture microdissection and transcriptome analysis was conducted at four stages of disease. We identified marked differences in the motor neuron transcriptome between the two mice strains at disease onset, with a dramatic reduction of gene expression in the rapidly progressive (129Sv-SOD1(G93A)) compared with the slowly progressing mutant SOD1 mice (C57-SOD1(G93A)) (1276 versus 346; Q-value ≤ 0.01). Gene ontology pathway analysis of the transcriptional profile from 129Sv-SOD1(G93A) mice showed marked downregulation of specific pathways involved in mitochondrial function, as well as predicted deficiencies in protein degradation and axonal transport mechanisms. In contrast, the transcriptional profile from C57-SOD1(G93A) mice with the more benign disease course, revealed strong gene enrichment relating to immune system processes compared with 129Sv-SOD1(G93A) mice. Motor neurons from the more benign mutant strain demonstrated striking complement activation, over-expressing genes normally involved in immune cell function. We validated through immunohistochemistry increased expression of the C3 complement subunit and major histocompatibility complex I within motor neurons. In addition, we demonstrated that motor neurons from the slowly progressing mice activate a series of genes with neuroprotective properties such as angiogenin and the nuclear factor (erythroid-derived 2)-like 2 transcriptional regulator. In contrast, the faster progressing mice show dramatically reduced expression at disease onset of cell pathways involved in neuroprotection. This study highlights a set of key gene and molecular pathway indices of fast or slow disease progression which may prove useful in identifying potential disease modifiers responsible for the heterogeneity of human amyotrophic lateral sclerosis and which may represent valid therapeutic targets for ameliorating the disease course in humans.

Neural control of phrenic motoneuron discharge

Phrenic motoneurons (PMNs) provide a synaptic relay between bulbospinal respiratory pathways and the diaphragm muscle. PMNs also receive propriospinal inputs, although the functional role of these interneuronal projections has not been established. Here we review the literature regarding PMN discharge patterns during breathing and the potential mechanisms that underlie PMN recruitment. Anatomical and neurophysiological studies indicate that PMNs form a heterogeneous pool, with respiratory-related PMN discharge and recruitment patterns likely determined by a balance between intrinsic MN properties and extrinsic synaptic inputs. We also review the limited literature regarding PMN bursting during respiratory plasticity. Differential recruitment or rate modulation of PMN subtypes may underlie phrenic motor plasticity following neural injury and/or respiratory stimulation; however, this possibility remains relatively unexplored.

Bex1 is involved in the regeneration of axons after injury

Successful axonal regeneration is a complex process determined by both axonal environment and endogenous neural capability of the regenerating axons in the central and the peripheral nervous systems. Numerous external inhibitory factors inhibit axonal regeneration after injury. In response, neurons express various regeneration-associated genes to overcome this inhibition and increase the intrinsic growth capacity. In the present study, we show that the brain-expressed X-linked (Bex1) protein was over-expressed as a result of peripheral axonal damage. Bex1 antagonized the axon outgrowth inhibitory effect of myelin-associated glycoprotein. The involvement of Bex1 in axon regeneration was further confirmed in vivo. We have demonstrated that Bex1 knock-out mice showed lower capability for regeneration after peripheral nerve injury than wild-type animals. Wild-type mice could recover from sciatic nerve injury much faster than Bex1 knock-out mice. Our findings suggest that Bex1 could be considered as regeneration-associated gene.

Loss of ALS2/Alsin exacerbates motor dysfunction in a SOD1-expressing mouse ALS model by disturbing endolysosomal trafficking

Background

ALS2/alsin is a guanine nucleotide exchange factor for the small GTPase Rab5 and involved in macropinocytosis-associated endosome fusion and trafficking, and neurite outgrowth. ALS2 deficiency accounts for a number of juvenile recessive motor neuron diseases (MNDs). Recently, it has been shown that ALS2 plays a role in neuroprotection against MND-associated pathological insults, such as toxicity induced by mutant Cu/Zn superoxide dismutase (SOD1). However, molecular mechanisms underlying the relationship between ALS2-associated cellular function and its neuroprotective role remain unclear.

Methodology/Principal Findings

To address this issue, we investigated the molecular and pathological basis for the phenotypic modification of mutant SOD1-expressing mice by ALS2 loss. Genetic ablation of Als2 in SOD1^H46R, but not SOD1^G93A, transgenic mice aggravated the mutant SOD1-associated disease symptoms such as body weight loss and motor dysfunction, leading to the earlier death. Light and electron microscopic examinations revealed the presence of degenerating and/or swollen spinal axons accumulating granular aggregates and autophagosome-like vesicles in early- and even pre-symptomatic SOD1^H46R mice. Further, enhanced accumulation of insoluble high molecular weight SOD1, poly-ubiquitinated proteins, and macroautophagy-associated proteins such as polyubiquitin-binding protein p62/SQSTM1 and a lipidated form of light chain 3 (LC3-II), emerged in ALS2-deficient SOD1^H46R mice. Intriguingly, ALS2 was colocalized with LC3 and p62, and partly with SOD1 on autophagosome/endosome hybrid compartments, and loss of ALS2 significantly lowered the lysosome-dependent clearance of LC3 and p62 in cultured cells.

Conclusions/Significance

Based on these observations, although molecular basis for the distinctive susceptibilities to ALS2 loss in different mutant SOD1-expressing ALS models is still elusive, disturbance of the endolysosomal system by ALS2 loss may exacerbate the SOD1^H46R-mediated neurotoxicity by accelerating the accumulation of immature vesicles and misfolded proteins in the spinal cord. We propose that ALS2 is implicated in endolysosomal trafficking through the fusion between endosomes and autophagosomes, thereby regulating endolysosomal protein degradation in vivo.

Weighted gene co-expression network analysis of the peripheral blood from Amyotrophic Lateral Sclerosis patients

Background

Amyotrophic Lateral Sclerosis (ALS) is a lethal disorder characterized by progressive degeneration of motor neurons in the brain and spinal cord. Diagnosis is mainly based on clinical symptoms, and there is currently no therapy to stop the disease or slow its progression. Since access to spinal cord tissue is not possible at disease onset, we investigated changes in gene expression profiles in whole blood of ALS patients.

Results

Our transcriptional study showed dramatic changes in blood of ALS patients; 2,300 probes (9.4%) showed significant differential expression in a discovery dataset consisting of 30 ALS patients and 30 healthy controls. Weighted gene co-expression network analysis (WGCNA) was used to find disease-related networks (modules) and disease related hub genes. Two large co-expression modules were found to be associated with ALS. Our findings were replicated in a second (30 patients and 30 controls) and third dataset (63 patients and 63 controls), thereby demonstrating a highly significant and consistent association of two large co-expression modules with ALS disease status. Ingenuity Pathway Analysis of the ALS related module genes implicates enrichment of functional categories related to genetic disorders, neurodegeneration of the nervous system and inflammatory disease. The ALS related modules contain a number of candidate genes possibly involved in pathogenesis of ALS.

Conclusion

This first large-scale blood gene expression study in ALS observed distinct patterns between cases and controls which may provide opportunities for biomarker development as well as new insights into the molecular mechanisms of the disease.

Ndel1 controls the dynein-mediated transport of vimentin during neurite outgrowth

Ndel1, the mammalian homologue of the Aspergillus nidulans NudE, is emergently viewed as an integrator of the cytoskeleton. By regulating the dynamics of microtubules and assembly of neuronal intermediate filaments (IFs), Ndel1 promotes neurite outgrowth, neuronal migration, and cell integrity (1-6). To further understand the roles of Ndel1 in cytoskeletal dynamics, we performed a tandem affinity purification of Ndel1-interacting proteins. We isolated a novel Ndel1 molecular complex composed of the IF vimentin, the molecular motor dynein, the lissencephaly protein Lis1, and the cis-Golgi-associated protein alphaCOP. Ndel1 promotes the interaction between Lis1, alphaCOP, and the vimentin-dynein complex. The functional result of this complex is activation of dynein-mediated transport of vimentin. A loss of Ndel1 functions by RNA interference fails to incorporate Lis1/alphaCOP in the complex, reduces the transport of vimentin, and culminates in IF accumulations and altered neuritogenesis. Our findings reveal a novel regulatory mechanism of vimentin transport during neurite extension that may have implications in diseases featuring transport/trafficking defects and impaired regeneration.

Progressive motor neuronopathy: a critical role of the tubulin chaperone TBCE in axonal tubulin routing from the Golgi apparatus

Axonal degeneration represents one of the earliest pathological features in motor neuron diseases. We here studied the underlying molecular mechanisms in progressive motor neuronopathy (pmn) mice mutated in the tubulin-specific chaperone TBCE. We demonstrate that TBCE is a peripheral membrane-associated protein that accumulates at the Golgi apparatus. In pmn mice, TBCE is destabilized and disappears from the Golgi apparatus of motor neurons, and microtubules are lost in distal axons. The axonal microtubule loss proceeds retrogradely in parallel with the axonal dying back process. These degenerative changes are inhibited in a dose-dependent manner by transgenic TBCE complementation that restores TBCE expression at the Golgi apparatus. In cultured motor neurons, the pmn mutation, interference RNA-mediated TBCE depletion, and brefeldin A-mediated Golgi disruption all compromise axonal tubulin routing. We conclude that motor axons critically depend on axonal tubulin routing from the Golgi apparatus, a process that involves TBCE and possibly other tubulin chaperones.

Retinoid receptors in chronic degeneration of the spinal cord: observations in a rat model of amyotrophic lateral sclerosis

Changes in distribution and expression of retinoid receptors may be part of a spinal cord protective response to acute injury and to chronic degeneration. In this study, we have combined RNA and protein expression analysis to characterize the expression profile of retinoid receptors in the lumbar spinal cord of the superoxide dismutase 1 G93A mutant rat model of amyotrophic lateral sclerosis, a fatal neurodegenerative disorder causing extensive motor neuron loss. We also report a nonsignificant change in RNA expression of binding proteins and metabolizing enzymes for retinol and retinoic acid in the mutant rat spinal cord at end-stage disease. Only retinoid X receptor beta (RXRbeta), and to a lesser extent retinoic acid receptor beta and alpha (RARbeta/alpha) were reliably detected in lumbar spinal cord at an early pre-symptomatic phase and throughout the disease progression. The expression of RXRbeta in lamina II neurons in the dorsal horn of transgenic and wild type (WT) animals was associated with extensive astrocyte staining in end-stage lumbar spinal cord from transgenic rats. RARbeta and RARalpha diffuse staining of large motor neurons in the pre-symptomatic transgenic and in the WT lumbar cord appear to decline in end-stage disease, when a selective and strong gamma motor neuron RARalpha staining becomes evident. As gliosis and motor neuron loss are key pathogenic features in amyotrophic lateral sclerosis, the selective expression of retinoid receptors in astrocytes and motor neurons may provide further clues to the role of retinoid signalling in neurodegeneration and suggest new treatment strategies based on retinoid-modulating agents.

Gene expression assays

The study of the profile of gene expression in a cell or tissue at a particular moment gives an insight into the plans of the cell for protein synthesis. Recent technological advances make it possible to analyze the expression of the entire genome in a single experiment. These "gene expression assays" complement or replace previous assays which measured the gene expression of only one gene, or a select group of genes. Within this chapter we outline the development of the gene expression assay and provide examples of the wide range of disciplines in which it is used. An overview of the current technologies is given, and includes an introduction to laser capture microdissection and linear amplification of RNA, both of which have extended the application of gene expression assays. Illustrative examples in the field of cancer and neuroscience highlight the scientific achievements. This technology has made in understanding the pathogenesis of diseases, including breast cancer, Huntington's disease, and schizophrenia. With recent advances including exon arrays to investigate alternative splicing, tiling arrays to investigate novel transcription start sites, and on-chip chromatin immunoprecipitation to investigate DNA-protein interactions, the future of gene expression assays is set to further our understanding of the complexities of gene expression.

Gene expression analysis of the murine model of amyotrophic lateral sclerosis: studies of the Leu126delTT mutation in SOD1

The pathogenic events that lead to amyotrophic lateral sclerosis (ALS) have not been elucidated. We previously described familial amyotrophic lateral sclerosis (FALS) caused by a Leu126delTT mutation in the Cu/Zn superoxide dismutase gene (SOD1) and have produced transgenic mice (TgM) carrying the same mutation (SOD1(L126delTT) TgM), which exhibited distinct ALS-like motor symptoms and pathological findings. In this study, we analyzed gene expression in the spinal cord of SOD1(L126delTT) TgM by cDNA microarray. Eleven genes were upregulated and two genes downregulated in pre-symptomatic TgM. In post-symptomatic TgM, 54 genes were upregulated and four genes downregulated. We performed real-time polymerase chain reaction (PCR) analysis of 10 of the 54 upregulated genes in the post-symptomatic TgM. The results of real-time PCR were consistent with those obtained by microarray for micro-crystallin (Crym), heat shock protein 1 (Hspb1/HSP27), serine proteinase inhibitor clade A member 3N (Serpina3n), complement component 1q subcomponent beta polypeptide (C1qb), cathepsin H (Ctsh) and polyadenylate binding protein-interacting protein 1 (Paip1). In immunohistochemical analysis, Hsbp1/HSP27 and Ctsh expression levels were increased in reactive astrocytes at the ventral horn of the spinal cord in post-symptomatic TgM, as were Crym, some of Ctsh and Paip1 in microglial cells. Increased expression of those genes was not observed in the control mice. These four genes may be related to the pathogenesis of FALS, especially with regard to the progression of reactive astrocytes and the inflammatory response of microglial cells.

The neuroprotective effects of the Wlds gene are correlated with proteasome expression rather than apoptosis

The Wld(s) gene (slow Wallerian degeneration) specifically delays axonal degeneration following injury and in several models of neurodegenerative diseases. It thus provides an interesting tool to study mechanisms of neurodegeneration. We previously crossed the Wld(s) mice with a mouse mutant that has a motoneuron disease (pmn for progressive motor neuronopathy) and showed that the Wld(s) gene prevented axonal loss, increased the life-span and prolonged the survival of the motoneuron cell bodies. In this study we show that spinal motoneurons of pmn/pmn mice, as opposed to axons, die by apoptosis that cannot be prevented by the Wld(s) gene. However, this same gene could partially rescue the proteasome impairment observed in motoneuron cell bodies and axons of pmn/pmn mice. We conclude that the neuroprotective effect of the Wld(s) gene is not related to an inhibition of apoptosis but could possibly be linked to a regulation in proteasome expression.