Dominant mutations in superoxide dismutase cause amyotrophic lateral sclerosis (ALS), a progressive paralytic disease characterized by loss of motor neurons. With the use of mice carrying a deletable ...mutant gene, expression within motor neurons was shown to be a primary determinant of disease onset and of an early phase of disease progression. Diminishing the mutant levels in microglia had little effect on the early disease phase but sharply slowed later disease progression. Onset and progression thus represent distinct disease phases defined by mutant action within different cell types to generate non-cell-autonomous killing of motor neurons; these findings validate therapies, including cell replacement, targeted to the non-neuronal cells.
Dominant mutations in superoxide dismutase cause amyotrophic lateral sclerosis (ALS), an adult-onset neurodegenerative disease that is characterized by the loss of motor neurons. Using mice carrying ...a deletable mutant gene, diminished mutant expression in astrocytes did not affect onset, but delayed microglial activation and sharply slowed later disease progression. These findings demonstrate that mutant astrocytes are viable targets for therapies for slowing the progression of non-cell autonomous killing of motor neurons in ALS.
We report here that amyotrophic lateral sclerosis-linked superoxide dismutase 1 (SOD1) mutants with different biochemical characteristics disrupted the blood-spinal cord barrier in mice by reducing ...the levels of the tight junction proteins ZO-1, occludin and claudin-5 between endothelial cells. This resulted in microhemorrhages with release of neurotoxic hemoglobin-derived products, reductions in microcirculation and hypoperfusion. SOD1 mutant-mediated endothelial damage accumulated before motor neuron degeneration and the neurovascular inflammatory response occurred, indicating that it was a central contributor to disease initiation.
Heterozygous loss-of-function mutations of
(
cause familial ALS, yet downstream mechanisms of
mutations remained elusive. TBK1 is a pleiotropic kinase involved in the regulation of selective ...autophagy and inflammation. We show that heterozygous
deletion alone does not lead to signs of motoneuron degeneration or disturbed autophagy in mice during a 200-d observation period. Surprisingly, however, hemizygous deletion of
inversely modulates early and late disease phases in mice additionally overexpressing ALS-linked
, which represents a "second hit" that induces both neuroinflammation and proteostatic dysregulation. At the early stage, heterozygous
deletion impairs autophagy in motoneurons and prepones both the clinical onset and muscular denervation in
mice. At the late disease stage, however, it significantly alleviates microglial neuroinflammation, decelerates disease progression, and extends survival. Our results indicate a profound effect of TBK1 on brain inflammatory cells under pro-inflammatory conditions and point to a complex, two-edged role of TBK1 in
-linked ALS.
ANXA11 mutations have previously been discovered in amyotrophic lateral sclerosis (ALS) motor neuron disease. To confirm the contribution of ANXA11 mutations to ALS, a large exome data set obtained ...from 330 French patients, including 150 familial ALS index cases and 180 sporadic ALS cases, was analyzed, leading to the identification of 3 rare ANXA11 variants in 5 patients. The novel p.L254V variant was associated with early onset sporadic ALS. The novel p.D40Y mutation and the p.G38R variant concerned patients with predominant pyramidal tract involvement and cognitive decline. Neuropathologic findings in a p.G38R carrier associated the presence of ALS typical inclusions within the spinal cord, massive degeneration of the lateral tracts, and type A frontotemporal lobar degeneration. This mutant form of annexin A11 accumulated in various brain regions and in spinal cord motor neurons, although its stability was decreased in patients' lymphoblasts. Because most ANXA11 inclusions were not colocalized with transactive response DNA-binding protein 43 or p62 deposits, ANXA11 aggregation does not seem mandatory to trigger neurodegeneration with additional participants/partner proteins that could intervene.
•Novel ANXA11 mutations are responsible for ALS.•ANXA11 mutations can be associated with early onset ALS and FTD.•Mutant G38 R ANXA11 is unstable in patient lymphoblasts.•Mutant G38 R ANXA11 led to cytoplasmic inclusions in post-mortem tissue.
Dominant mutations in ubiquitously expressed superoxide dismutase (SOD1) cause familial ALS by provoking premature death of adult motor neurons. To test whether mutant damage to cell types beyond ...motor neurons is required for the onset of motor neuron disease, we generated chimeric mice in which all motor neurons and oligodendrocytes expressed mutant SOD1 at a level sufficient to cause fatal, early-onset motor neuron disease when expressed ubiquitously, but did so in a cellular environment containing variable numbers of non-mutant, non-motor neurons. Despite high-level mutant expression within 100% of motor neurons and oligodendrocytes, in most of these chimeras, the presence of WT non-motor neurons substantially delayed onset of motor neuron degeneration, increasing disease-free life by 50%. Disease onset is therefore non-cell autonomous, and mutant SOD1 damage within cell types other than motor neurons and oligodendrocytes is a central contributor to initiation of motor neuron degeneration.
Mutations in UBQLN2 have been associated with rare cases of X-linked juvenile and adult forms of amyotrophic lateral sclerosis (ALS) and ALS linked to frontotemporal dementia (FTD). Here, we report 1 ...known (c.1489C>T, p.Pro497Ser, P497S) and 3 novel (c.1481C>T, p.Pro494Leu, P494L; c.1498C>T, p.Pro500Ser, P500S; and c.1516C>G, p.Pro506Ala, P506A) missense mutations in the PXX domain of UBQLN2 in familial motor neuron diseases including ALS and spastic paraplegia (SP). A novel missense mutation (c.1462G>A, p.Ala488Thr, A488T) adjacent to this hotspot UBQLN2 domain was identified in a sporadic case of ALS. These mutations are conserved in mammals, are absent from ExAC and gnomAD browsers, and are predicted to be deleterious by SIFT in silico analysis. Patient lymphoblasts carrying a UBQLN2 mutation showed absence of ubiquilin-2 accumulation, disrupted binding with HSP70, and impaired autophagic pathway. Our results confirm the role of PXX repeat in ALS pathogenesis, show that UBQLN2-linked disease can manifest like a SP phenotype, evidence a highly reduced disease penetrance in females carrying UBQLN2 mutations, which is important information for genetic counseling, and underline the pivotal role of ubiquilin-2 in proteolysis regulation pathways.
Glutamine synthetase (GS) is a key enzyme that metabolizes glutamate into glutamine. While GS is highly enriched in astrocytes, expression in other glial lineages has been noted. Using a combination ...of reporter mice and cell type‐specific markers, we show that GS is expressed in myelinating oligodendrocytes (OL) but not oligodendrocyte progenitor cells of the mouse and human ventral spinal cord. To investigate the role of GS in mature OL, we used a conditional knockout (cKO) approach to selectively delete GS‐encoding gene (Glul) in OL, which caused a significant decrease in glutamine levels on mouse spinal cord extracts. GS cKO mice (CNP‐cre+:Glulfl/fl) showed no differences in motor neuron numbers, size or axon density; OL differentiation and myelination in the ventral spinal cord was normal up to 6 months of age. Interestingly, GS cKO mice showed a transient and specific decrease in peak force while locomotion and motor coordination remained unaffected. Last, GS expression in OL was increased in chronic pathological conditions in both mouse and humans. We found a disease‐stage dependent increase of OL expressing GS in the ventral spinal cord of SOD1(G93A) mouse model of amyotrophic lateral sclerosis. Moreover, we showed that GLUL transcripts levels were increased in OL in leukocortical tissue from multiple sclerosis but not control patients. These findings provide evidence towards OL‐encoded GS function in spinal cord sensorimotor axis, which is dysregulated in chronic neurological diseases.
Main Points
Glutamine synthetase (GS) is expressed in oligodendrocytes (OL) of the mouse and human spinal cord.
OL‐specific loss of function causes transient decrease in peak force.
GS expression in OL is altered in chronic pathological conditions.
Neurodegeneration in an inherited form of ALS is non-cell-autonomous, with ALS-causing mutant SOD1 damage developed within multiple cell types. Selective inactivation within motor neurons of an ...ubiquitously expressed mutant SOD1 gene has demonstrated that mutant damage within motor neurons is a determinant of disease initiation, whereas mutant synthesis within neighboring astrocytes or microglia accelerates disease progression. We now report the surprising finding that diminished synthesis (by 70%) within Schwann cells of a fully dismutase active ALS-linked mutant (SOD1G³⁷R) significantly accelerates disease progression, accompanied by reduction of insulin-like growth factor 1 (IGF-1) in nerves. Coupled with shorter disease duration in mouse models caused by dismutase inactive versus dismutase active SOD1 mutants, our findings implicate an oxidative cascade during disease progression that is triggered within axon ensheathing Schwann cells and that can be ameliorated by elevated dismutase activity. Thus, therapeutic down-regulation of dismutase active mutant SOD1 in familial forms of ALS should be targeted away from Schwann cells.
The blood-spinal cord barrier (BSCB) considerably limits the delivery and efficacy of treatments for spinal cord diseases. The blood-brain barrier can be safely opened with low-intensity pulsed ...ultrasound when microbubbles are simultaneously administered intravenously. This technique was tested on the BSCB in a rabbit model in this work. Twenty-three segments of spinal cord were sonicated with a 1-MHz unfocused pulsed ultrasound device and compared with non-sonicated segments. BSCB disruption was assessed using Evan's blue dye (EBD) extravasation. Tolerance was assessed by histologic analysis. An increased EBD concentration indicating BSCB disruption was clearly observed in sonicated segments compared with controls (p = 0.004). On one animal, which received 10 sonications, repetitive BSCB disruptions revealed no evidence of cumulative toxicity. BSCB can be disrupted using an unfocused pulsed ultrasound device in combination with microbubbles without neurotoxicity even in case of repeated sonications.
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