Continuous neurodegeneration and death pathway activation in neurons and glia in an experimental model of severe chronic epilepsy.

Whether seizures might determine the activation of cell death pathways and what could be the relevance of seizure-induced cell death in epilepsy are still highly debated issues. We recently developed an experimental model of acquired focal cortical dysplasia (the MAM-pilocarpine or MP rat) in which the occurrence of status epilepticus--SE--and subsequent seizures induced progressive cellular/molecular abnormalities and neocortical/hippocampal atrophy. Here, we exploited the same model to verify when, where, and how cell death occurred in neurons and glia during epilepsy course. We analyzed Fluoro Jade (FJ) staining and the activation of c-Jun- and caspase-3-dependent pathways during epilepsy, from few hours post-SE up to six months of spontaneous recurrent seizures. FJ staining revealed that cell injury in MP rats was not temporally restricted to SE, but extended throughout the different epileptic stages. The region-specific pattern of FJ staining changed during epilepsy, and FJ(+) neurons became more prominent in the dorsal and ventral hippocampal CA at chronic epilepsy stages. Phospho-c-Jun- and caspase-3-dependent pathways were selectively activated respectively in neurons and glia, at early but even more conspicuously at late chronic stages. Phospho-c-Jun activation was associated with increased cytochrome-c staining, particularly at chronic stages, and the staining pattern of cytochrome-c was suggestive of its release from the mitochondria. Taken together, these data support the content that at least in the MP rat model the recurrence of seizures can also sustain cell death mechanisms, thus continuously contributing to the pathologic process triggered by the occurrence of SE.

Human axonal survival of motor neuron (a-SMN) protein stimulates axon growth, cell motility, C-C motif ligand 2 (CCL2), and insulin-like growth factor-1 (IGF1) production.

Spinal muscular atrophy is a fatal genetic disease of motoneurons due to loss of full-length survival of motor neuron protein, the main product of the disease gene SMN1. Axonal SMN (a-SMN) is an alternatively spliced isoform of SMN1, generated by retention of intron 3. To study a-SMN function, we generated cellular clones for the expression of the protein in mouse motoneuron-like NSC34 cells. The model was instrumental in providing evidence that a-SMN decreases cell growth and plays an important role in the processes of axon growth and cellular motility. In our conditions, low levels of a-SMN expression were sufficient to trigger the observed biological effects, which were not modified by further increasing the amounts of the expressed protein. Differential transcriptome analysis led to the identification of novel a-SMN-regulated factors, i.e. the transcripts coding for the two chemokines, C-C motif ligands 2 and 7 (CCL2 and CCL7), as well as the neuronal and myotrophic factor, insulin-like growth factor-1 (IGF1). a-SMN-dependent induction of CCL2 and IGF1 mRNAs resulted in increased intracellular levels and secretion of the respective protein products. Induction of CCL2 contributes to the a-SMN effects, mediating part of the action on axon growth and random cell motility, as indicated by chemokine knockdown and re-addition studies. Our results shed new light on a-SMN function and the underlying molecular mechanisms. The data provide a rational framework to understand the role of a-SMN deficiency in the etiopathogenesis of spinal muscular atrophy.

Long-duration epilepsy affects cell morphology and glutamatergic synapses in type IIB focal cortical dysplasia.

To investigate hypothesized effects of severe epilepsy on malformed cortex, we analyzed surgical samples from eight patients with type IIB focal cortical dysplasia (FCD) in comparison with samples from nine non-dysplastic controls. We investigated, using stereological quantification methods, where appropriate, dysplastic neurons, neuronal density, balloon cells, glia, glutamatergic synaptic input, and the expression of N-methyl-D-aspartate (NMDA) receptor subunits and associated membrane-associated guanylate kinase (MAGUK). In all FCD patients, the dysplastic areas giving rise to epileptic discharges were characterized by larger dysmorphic neurons, reduced neuronal density, and increased glutamatergic inputs, compared to adjacent areas with normal cytology. The duration of epilepsy was found to correlate directly (a) with dysmorphic neuron size, (b) reduced neuronal cell density, and (c) extent of reactive gliosis in epileptogenic/dysplastic areas. Consistent with increased glutamatergic input, western blot revealed that NMDA regulatory subunits and related MAGUK proteins were up-regulated in epileptogenic/dysplastic areas of all FCD patients examined. Taken together, these results support the hypothesis that epilepsy itself alters morphology-and probably also function-in the malformed epileptic brain. They also suggest that glutamate/NMDA/MAGUK dysregulation might be the intracellular trigger that modifies brain morphology and induces cell death.

Spinal muscular atrophy pathogenic mutations impair the axonogenic properties of axonal-survival of motor neuron.

The axonal survival of motor neuron (a-SMN) protein is a truncated isoform of SMN1, the spinal muscular atrophy (SMA) disease gene. a-SMN is selectively localized in axons and endowed with remarkable axonogenic properties. At present, the role of a-SMN in SMA is unknown. As a first step to verify a link between a-SMN and SMA, we investigated by means of over-expression experiments in neuroblastoma-spinal cord hybrid cell line (NSC34) whether SMA pathogenic mutations located in the N-terminal part of the protein affected a-SMN function. We demonstrated here that either SMN1 missense mutations or small intragenic re-arrangements located in the Tudor domain consistently altered the a-SMN capability of inducing axonal elongation in vitro. Mutated human a-SMN proteins determined in almost all NSC34 motor neurons the growth of short axons with prominent morphologic abnormalities. Our data indicate that the Tudor domain is critical in dictating a-SMN function possibly because it is an association domain for proteins involved in axon growth. They also indicate that Tudor domain mutations are functionally relevant not only for FL-SMN but also for a-SMN, raising the possibility that also a-SMN loss of function may contribute to the pathogenic steps leading to SMA.

Status epilepticus-induced pathologic plasticity in a rat model of focal cortical dysplasia.

We have generated an experimental 'double-hit' model of chronic epilepsy to recapitulate the co-existence of abnormal cortical structure and frequently recurrent seizures as observed in human focal cortical dysplasia. We induced cortical malformations by exposing rats prenatally to methylazoxymethanol acetate and triggered status epilepticus and recurrent seizures in adult methylazoxymethanol acetate rats with pilocarpine. We studied the course of epilepsy and the long-term morphologic and molecular changes induced by the occurrence of status epilepticus and subsequent chronic epilepsy in the malformed methylazoxymethanol acetate exposed brain. Behavioural and electroencephalographic analyses showed that methylazoxymethanol acetate pilocarpine rats develop more severe epilepsy than naïve rats. Morphologic and molecular analyses demonstrated that status epilepticus and subsequent seizures, but not pilocarpine treatment per se, was capable of affecting both cortical architectural and N-methyl-D-aspartate receptor abnormalities induced by methylazoxymethanol acetate. In particular, cortical thickness was further decreased and N-methyl-D-aspartate regulatory subunits were recruited at the postsynaptic membrane. In addition, methylazoxymethanol acetate pilocarpine rats showed abnormally large cortical pyramidal neurons with neurofilament over-expression. These neurons bear similarities to the hypertrophic/dysmorphic pyramidal neurons observed in acquired human focal cortical dysplasia. These data show that status epilepticus sets in motion a pathological process capable of significantly changing the cellular and molecular features of pre-existing experimental cortical malformations. They suggest that seizure recurrence in human focal cortical dysplasia might be an additional factor in establishing a pathological circuitry that favours chronic neuronal hyperexcitability.

SMA-miRs (miR-181a-5p, -324-5p, and -451a) are overexpressed in spinal muscular atrophy skeletal muscle and serum samples.

Background: Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by the degeneration of the second motor neuron. The phenotype ranges from very severe to very mild forms. All patients have the homozygous loss of the SMN1 gene and a variable number of SMN2 (generally 2-4 copies), inversely related to the severity. The amazing results of the available treatments have made compelling the need of prognostic biomarkers to predict the progression trajectories of patients. Besides the SMN2 products, few other biomarkers have been evaluated so far, including some miRs. Methods: We performed whole miRNome analysis of muscle samples of patients and controls (14 biopsies and 9 cultures). The levels of muscle differentially expressed miRs were evaluated in serum samples (51 patients and 37 controls) and integrated with SMN2 copies, SMN2 full-length transcript levels in blood and age (SMA-score). Results: Over 100 miRs were differentially expressed in SMA muscle; 3 of them (hsa-miR-181a-5p, -324-5p, -451a; SMA-miRs) were significantly upregulated in the serum of patients. The severity predicted by the SMA-score was related to that of the clinical classification at a correlation coefficient of 0.87 (p<10-5). Conclusions: miRNome analyses suggest the primary involvement of skeletal muscle in SMA pathogenesis. The SMA-miRs are likely actively released in the blood flow; their function and target cells require to be elucidated. The accuracy of the SMA-score needs to be verified in replicative studies: if confirmed, its use could be crucial for the routine prognostic assessment, also in presymptomatic patients. Funding: Telethon Italia (grant #GGP12116).

Targeting PSD95-nNOS interaction by Tat-N-dimer peptide during status epilepticus is neuroprotective in MAM-pilocarpine rat model.

Glutamate receptors play a crucial pathogenic role in brain damage induced by status epilepticus (SE). SE may initiate NMDAR-dependent excitotoxicity through the production of oxidative damage mediated by the activation of a ternary complex formed by the NMDA receptor, the post-synaptic density scaffolding protein 95 (PSD95) and the neuronal NO synthase (nNOS). The inhibition of the protein-protein-interaction (PPI) of the NMDAR-PSD95-nNOS complex is one of the most intriguing challenges recently developed to reduce neuronal death in both animal models and in patients with cerebral ischemia. We took advantage of this promising approach to verify whether early administration of a neuroprotective NMDAR-PSD95-nNOS PPI inhibitor preserves the brain from SE-induced damage in a model of acquired cortical dysplasia, the methylazoxymethanol (MAM)/pilocarpine rat. Pilocarpine-induced SE rapidly determined neurodegenerative changes mediated by a NMDAR-downstream neurotoxic pathway in MAM rats. We demonstrated that SE rapidly induces NMDAR activation, nNOS membrane translocation, PSD95-nNOS molecular interaction associated with neuronal and glial peroxynitrite accumulation in the neocortex of MAM-pilocarpine rats. These changes were paralleled by rapid c-fos overexpression and by progressive spectrin proteolysis, suggestive of calpain activity and irreversible cytoskeletal damage. Early administration of a cell-penetrating Tat-N-dimer peptide inhibitor of NMDAR-PSD95-nNOS PPI during SE significantly rescued the MAM-pilocarpine rats from SE-induced mortality, reduced the number of degenerating neurons, decreased neuronal c-fos activation, peroxynitrite formation and cytoskeletal degradation and prevented astrogliosis. Our findings suggest an overall neuroprotective effect of blocking PSD95-nNOS protein-protein-interaction against SE insult.

Axon outgrowth and neuronal differentiation defects after a-SMN and FL-SMN silencing in primary hippocampal cultures.

Spinal Muscular Atrophy (SMA) is a severe autosomal recessive disease characterized by selective motor neuron degeneration, caused by disruptions of the Survival of Motor Neuron 1 (Smn1) gene. The main product of SMN1 is the full-length SMN protein (FL-SMN), that plays an established role in mRNA splicing. FL-SMN is also involved in neurite outgrowth and axonal transport. A shorter SMN isoform, axonal-SMN or a-SMN, displays a more specific axonal localization and has remarkable axonogenic properties in NSC-34. Introduction of known SMA mutations into the a-SMN transcript leads to impairment of axon growth and morphological defects similar to those observed in SMA patients and animal models. Although there is increasing evidence for the relevance of SMN axonal functions in SMA pathogenesis, the specific contributions of FL-SMN and a-SMN are not known yet. This work aimed to analyze the differential roles of FL-SMN and a-SMN in axon outgrowth and in neuronal homeostasis during differentiation of neurons into a mature phenotype. We employed primary cultures of hippocampal neurons as a well-defined model of polarization and differentiation. By analyzing subcellular localization, we showed that a-SMN is preferentially localized in the growing axonal compartment. By specifically silencing FL-SMN or a-SMN proteins, we demonstrated that both proteins play a role in axon growth, as their selective down-regulation reduces axon length without affecting dendritic arborization. a-SMN silencing, and in minor extent FL-SMN silencing, resulted in the growth of multi-neuritic neurons, impaired in the differentiation process of selecting a single axon out of multiple neurites. In these neurons, neurites often display mixed axonal and dendritic markers and abnormal distribution of the axonal initial segment protein Ankirin G, suggesting loss of neuronal polarity. Our results indicate that a-SMN and FL-SMN are needed for neuronal polarization and organization of axonal and dendritic compartments, processes that are fundamental for neuronal function and survival.

Different Stability and Proteasome-Mediated Degradation Rate of SMN Protein Isoforms.

The key pathogenic steps leading to spinal muscular atrophy (SMA), a genetic disease characterized by selective motor neuron degeneration, are not fully clarified. The full-length SMN protein (FL-SMN), the main protein product of the disease gene SMN1, plays an established role in the cytoplasm in snRNP biogenesis ultimately leading to mRNA splicing within the nucleus. It is also involved in the mRNA axonal transport. However, to what extent the impairment of these two SMN functions contributes to SMA pathogenesis remains unknown. A shorter SMN isoform, axonal-SMN or a-SMN, with more specific axonal localization, has been discovered, but whether it might act in concert with FL-SMN in SMA pathogenesis is not known. As a first step in defining common or divergent intracellular roles of FL-SMN vs a-SMN proteins, we here characterized the turn-over of both proteins and investigated which pathway contributed to a-SMN degradation. We performed real time western blot and confocal immunofluorescence analysis in easily controllable in vitro settings. We analyzed co-transfected NSC34 and HeLa cells and cell clones stably expressing both a-SMN and FL-SMN proteins after specific blocking of transcript or protein synthesis and inhibition of known intracellular degradation pathways. Our data indicated that whereas the stability of both FL-SMN and a-SMN transcripts was comparable, the a-SMN protein was characterized by a much shorter half-life than FL-SMN. In addition, as already demonstrated for FL-SMN, the Ub/proteasome pathway played a major role in the a-SMN protein degradation. We hypothesize that the faster degradation rate of a-SMN vs FL-SMN is related to the protection provided by the protein complex in which FL-SMN is assembled. The diverse a-SMN vs FL-SMN C-terminus may dictate different protein interactions and complex formation explaining the different localization and role in the neuronal compartment, and the lower expression and stability of a-SMN.

Progressive brain damage, synaptic reorganization and NMDA activation in a model of epileptogenic cortical dysplasia.

Whether severe epilepsy could be a progressive disorder remains as yet unresolved. We previously demonstrated in a rat model of acquired focal cortical dysplasia, the methylazoxymethanol/pilocarpine - MAM/pilocarpine - rats, that the occurrence of status epilepticus (SE) and subsequent seizures fostered a pathologic process capable of modifying the morphology of cortical pyramidal neurons and NMDA receptor expression/localization. We have here extended our analysis by evaluating neocortical and hippocampal changes in MAM/pilocarpine rats at different epilepsy stages, from few days after onset up to six months of chronic epilepsy. Our findings indicate that the process triggered by SE and subsequent seizures in the malformed brain i) is steadily progressive, deeply altering neocortical and hippocampal morphology, with atrophy of neocortex and CA regions and progressive increase of granule cell layer dispersion; ii) changes dramatically the fine morphology of neurons in neocortex and hippocampus, by increasing cell size and decreasing both dendrite arborization and spine density; iii) induces reorganization of glutamatergic and GABAergic networks in both neocortex and hippocampus, favoring excitatory vs inhibitory input; iv) activates NMDA regulatory subunits. Taken together, our data indicate that, at least in experimental models of brain malformations, severe seizure activity, i.e., SE plus recurrent seizures, may lead to a widespread, steadily progressive architectural, neuronal and synaptic reorganization in the brain. They also suggest the mechanistic relevance of glutamate/NMDA hyper-activation in the seizure-related brain pathologic plasticity.

Selective vulnerability of spinal and cortical motor neuron subpopulations in delta7 SMA mice.

Loss of the survival motor neuron gene (SMN1) is responsible for spinal muscular atrophy (SMA), the most common inherited cause of infant mortality. Even though the SMA phenotype is traditionally considered as related to spinal motor neuron loss, it remains debated whether the specific targeting of motor neurons could represent the best therapeutic option for the disease. We here investigated, using stereological quantification methods, the spinal cord and cerebral motor cortex of ∆7 SMA mice during development, to verify extent and selectivity of motor neuron loss. We found progressive post-natal loss of spinal motor neurons, already at pre-symptomatic stages, and a higher vulnerability of motor neurons innervating proximal and axial muscles. Larger motor neurons decreased in the course of disease, either for selective loss or specific developmental impairment. We also found a selective reduction of layer V pyramidal neurons associated with layer V gliosis in the cerebral motor cortex. Our data indicate that in the ∆7 SMA model SMN loss is critical for the spinal cord, particularly for specific motor neuron pools. Neuronal loss, however, is not selective for lower motor neurons. These data further suggest that SMA pathogenesis is likely more complex than previously anticipated. The better knowledge of SMA models might be instrumental in shaping better therapeutic options for affected patients.

Axonal-SMN (a-SMN), a protein isoform of the survival motor neuron gene, is specifically involved in axonogenesis.

Spinal muscular atrophy (SMA) is an autosomal recessive disease of childhood due to loss of the telomeric survival motor neuron gene, SMN1. The general functions of the main SMN1 protein product, full-length SMN (FL-SMN), do not explain the selective motoneuronal loss of SMA. We identified axonal-SMN (a-SMN), an alternatively spliced SMN form, preferentially encoded by the SMN1 gene in humans. The a-SMN transcript and protein are down-regulated during early development in different tissues. In the spinal cord, the a-SMN protein is selectively expressed in motor neurons and mainly localized in axons. Forced expression of a-SMN stimulates motor neuron axonogenesis in a time-dependent fashion and induces axonal-like growth in non-neuronal cells. Exons 2b and 3 are essential for the axonogenic effects. This discovery indicates an unexpected complexity of the SMN gene system and may help in understanding the pathogenesis of SMA.