J. Neurochem. (2010) 113, 1188-1199. The finding of a secretion pathway and toxicity for mutant superoxide dismutase 1 (SOD1) raised up the possibility of using immunization approaches to reduce or ...neutralize the burden of toxic SOD1 species in the nervous system. Here we tested a passive immunization approach based on intracerebroventricular infusion in G93A-SOD1 mice of monoclonal antibodies specific to misfolded forms of SOD1 (mSOD1). We tested two monoclonal antibodies that bind distinct epitopes in mSOD1 and that do not bind to intact wild-type (WT) SOD1. One antibody succeeded in reducing the level of mSOD1 by 23% in the spinal cord and in prolonging the lifespan of G93A-SOD1 mice in proportion to the duration of treatment. However, another monoclonal antibody binding to a different SOD1 epitope failed to confer protection indicating that not all anti-SOD1 antibodies might be suitable for immunotherapy. Interestingly, the variable Fab fragment of an anti-SOD1 antibody was sufficient to confer some protection in G93A-SOD1 mice. The partial dispensability of Fc region should offer some advantages for development of immunotherapy with antibodies of smaller molecular size and low immunogenicity. From these results, we propose that passive immunization strategies should be considered as potential avenues for treatment of familial amyotrophic lateral sclerosis caused by SOD1 mutations.
Missense mutations (P56S) in Vapb are associated with autosomal dominant motor neuron diseases: amyotrophic lateral sclerosis and lower motor neuron disease. Although transgenic mice overexpressing ...the mutant vesicle-associated membrane protein-associated protein B (VAPB) protein with neuron-specific promoters have provided some insight into the toxic properties of the mutant proteins, their role in pathogenesis remains unclear. To identify pathological defects in animals expressing the P56S mutant VAPB protein at physiological levels in the appropriate tissues, we have generated Vapb knock-in mice replacing wild-type Vapb gene with P56S mutant Vapb gene and analyzed the resulting pathological phenotypes. Heterozygous P56S Vapb knock-in mice show mild age-dependent defects in motor behaviors as characteristic features of the disease. The homozygous P56S Vapb knock-in mice show more severe defects compared with heterozygous mice reflecting the dominant and dose-dependent effects of P56S mutation. Significantly, the knock-in mice demonstrate accumulation of P56S VAPB protein and ubiquitinated proteins in cytoplasmic inclusions, selectively in motor neurons. The mutant mice demonstrate induction of ER stress and autophagic response in motor neurons before obvious onset of behavioral defects, suggesting that these cellular biological defects might contribute to the initiation of the disease. The P56S Vapb knock-in mice could be a valuable tool to gain a better understanding of the mechanisms by which the disease arises.
Mutations in the gene encoding for the neurofilament light subunit (NF-L) are responsible for Charcot–Marie–Tooth (CMT) neuropathy type 2E. To address whether CMT2E disease is potentially reversible, ...we generated a mouse model with conditional doxycycline-responsive gene system that allows repression of mutant hNF-LP22S transgene expression in adult neurons. The hNF-LP22S;tTa transgenic (tg) mice recapitulated key features of CMT2E disease, including aberrant hindlimb posture, motor deficits, hypertrophy of muscle fibres and loss of muscle innervation without neuronal loss. Remarkably, a 3-month treatment of hNF-LP22S;tTa mice with doxycycline after onset of disease efficiently down-regulated expression of hNF-LP22S and it caused reversal of CMT neurological phenotypes with restoration of muscle innervation and of neurofilament protein distribution along the sciatic nerve. These data suggest that therapeutic approaches aimed at abolishing expression or neutralizing hNF-L mutants might not only halt the progress of CMT2E disease, but also revert the disabilities.
Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS MIM 270550) is an early-onset neurodegenerative disorder caused by mutations in the SACS gene. Over 200 SACS mutations have been ...identified. Most mutations lead to a complete loss of a sacsin, a large 520 kD protein, although some missense mutations are associated with low levels of sacsin expression. We previously showed that Sacs knock-out mice demonstrate early-onset ataxic phenotype with neurofilament bundling in many neuronal populations. To determine if the preservation of some mutated sacsin protein resulted in the same cellular and behavioral alterations, we generated mice expressing an R272C missense mutation, a homozygote mutation found in some affected patients. Though Sacs
mice express 21% of wild type brain sacsin and sacsin is found in many neurons, they display similar abnormalities to Sacs knock-out mice, including the development of an ataxic phenotype, reduced Purkinje cell firing rates, and somatodendritic neurofilament bundles in Purkinje cells and other neurons. Together our results support that Sacs missense mutation largely lead to loss of sacsin function.
Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a childhood-onset neurological disease resulting from mutations in the SACS gene encoding sacsin, a 4,579-aa protein of unknown ...function. Originally identified as a founder disease in Québec, ARSACS is now recognized worldwide. Prominent features include pyramidal spasticity and cerebellar ataxia, but the underlying pathology and pathophysiological mechanisms are unknown. We have generated an animal model for ARSACS, sacsin knockout mice, that display agedependent neurodegeneration of cerebellar Purkinje cells. To explore the pathophysiological basis for this observation, we examined the cell biological properties of sacsin. We show that sacsin localizes to mitochondria in non-neuronal cells and primary neurons and that it interacts with dynamin-related protein 1, which participates in mitochondrial fission. Fibroblasto from ARSACS patients show a hyperfused mitochondrial network, consistent with defects in mitochondrial fission. Sacsin knockdown leads to an overly interconnected and functionally impaired mitochondrial network, and mitochondria accumulate in the soma and proximal dendrites of sacsin knockdown neurons. Disruption of mitochondrial transport into dendrites has been shown to lead to abnormal dendritic morphology, and we observe striking alterations in the organization of dendritic fields in the cerebellum of knockout mice that precedes Purkinje cell death. Our data identifies mitochondrial dysfunction/mislocalization as the likely cellular basis for ARSACS and indicates a role for sacsin in regulation of mitochondrial dynamics.
Peripherin, a type III neuronal intermediate filament, is widely expressed in neurons of the peripheral nervous system and in selected central nervous system hindbrain areas with projections towards ...peripheral structures, such as cranial nerves and spinal cord neurons. Peripherin appears to play a role in neurite elongation during development and axonal regeneration, but its exact function is not known. We noticed high peripherin expression in the posterior hypothalamus of mice, and decided to investigate further the exact location of expression and function of peripherin in the mouse posterior hypothalamus.
In situ hybridization indicated expression of peripherin in neurons with a distribution reminiscent of the histaminergic neurons, with little signal in any other part of the forebrain. Immunocytochemical staining for histidine decarboxylase and peripherin revealed extensive colocalization, showing that peripherin is produced by histaminergic neurons in all parts of the tuberomammillary nucleus. We next used histamine immunostaining in peripherin knockout, overexpressing and wild type mice to study if altered peripherin expression affects these neurons, but could not detect any visible difference in the appearance of these neurons or their axons. Peripherin knockout mice and heterozygotic littermates were used for measurement of locomotor activity, feeding, drinking, and energy expenditure. Both genotypes displayed diurnal rhythms with all the parameters higher during the dark period. The respiratory quotient, an indicator of the type of substrate being utilized, also exhibited a significant diurnal rhythm in both genotypes. The diurnal patterns and the average values of all the recorded parameters for 24 h, daytime and night time were not significantly different between the genotypes, however.
In conclusion, we have shown that peripherin is expressed in the tuberomammillary neurons of the mouse hypothalamus. Monitoring of locomotor activity, feeding, drinking, and energy expenditure in mice either lacking or overexpressing peripherin did not reveal any difference, so the significance of peripherin in these neurons remains to be determined. The complete overlap between histidine decarboxylase and peripherin, both the protein and its mRNA, renders peripherin a useful new marker for histaminergic neurons in the hypothalamus.
J. Neurochem. (2010) 115, 1102-1111. ABSTRACT: Recent studies provided evidence that chromogranins can interact with mutant superoxide dismutase 1 (SOD1) and that chromogranin B (CgB) may act as a ...susceptibility gene and modifier of onset in amyotrophic lateral sclerosis (ALS). To further investigate the role of chromogranins in ALS pathogenesis, we generated SOD1G³⁷R mice that over‐express CgA under the control of Thy1 promoter. Here, we report that neuronal over‐expression of CgA in SOD1G³⁷R mice caused acceleration of onset of motor impairment and exacerbation of motor neuron degeneration. The use of monoclonal antibody specific to misfolded mutant SOD1 demonstrated a higher level of misfolded SOD1 species in double transgenic mice compared to SOD1G³⁷R mice, suggesting a stabilization of pathogenic SOD1 species by excess CgA. These results suggest a role of chromogranins as modulators of disease onset in ALS pathogenesis.
Recent studies suggest that increased activity of cyclin-dependent kinase 5 (Cdk5) may contribute to neuronal death and cytoskeletal abnormalities in Alzheimer's disease. We report here such ...deregulation of Cdk5 activity associated with the hyperphosphorylation of tau and neurofilament (NF) proteins in mice expressing a mutant superoxide dismutase (
SOD1
G37R
) linked to amyotrophic lateral sclerosis (ALS). A Cdk5 involvement in motor neuron degeneration is supported by our analysis of three
SOD1
G37R
mouse lines exhibiting perikaryal inclusions of NF proteins. Our results suggest that perikaryal accumulations of NF proteins in motor neurons may alleviate ALS pathogenesis by acting as a phosphorylation sink for Cdk5 activity, thereby reducing the detrimental hyperphosphorylation of tau and other neuronal substrates.
ABSTRACT
Loss of sacsin, a large 520 kDa multidomain protein, causes autosomal recessive spastic ataxia of the Charlevoix‐Saguenay, one of the most common childhood‐onset recessive ataxias. A ...prominent feature is abnormal bundling of neurofilaments in many neuronal populations. This study shows the direct involvement of sacsin domains in regulating intermediate filament assembly and dynamics and identifies important domains for alleviating neurofilament bundles in neurons lacking sacsin. Peptides encoding sacsin internal repeat (SIRPT) 1, J‐domains, and ubiquitin‐like domain modified neurofilament assembly in vivo. The domains with chaperone homology, the SIRPT and the J‐domain, had opposite effects, promoting and preventing filament assembly, respectively. In cultured Sacs−/− motor neurons, both the SIRPT1 and J‐domain resolved preexisting neurofilament bundles. Increasing expression of heat shock proteins also resolved neurofilament bundles, indicating that this endogenous chaperone system can compensate to some extent for sacsin deficiency.—Gentil, B. J., Lai, G.‐T., Menade, M., Larivière, R., Minotti, S., Gehring, K., Chappie, J.‐P., Brais, B., Durham, H. D. Sacsin, mutated in the ataxia ARSACS, regulates intermediate filament assembly and dynamics. FASEB J. 33, 2982–2994 (2019). www.fasebj.org
PDF
