Amyotrophic lateral sclerosis (ALS) is a degenerative disorder that is characterized by loss of motor neurons and shows clinical, pathological, and genetic overlap with frontotemporal dementia (FTD). ...Activated microglia are a universal feature of ALS/FTD pathology; however, their role in disease pathogenesis remains incompletely understood. The recent discovery that ORF 72 on chromosome 9 (C9orf72), the gene most commonly mutated in ALS/FTD, has an important role in myeloid cells opened the possibility that altered microglial function plays an active role in disease. This Review highlights the contribution of microglia to ALS/FTD pathogenesis, discusses the connection between autoimmunity and ALS/FTD, and explores the possibility that C9orf72 and other ALS/FTD genes may have a "dual effect" on both neuronal and myeloid cell function that could explain a shared propensity for altered systemic immunity and neurodegeneration.
Inflammation in ALS/FTD pathogenesis McCauley, Madelyn E.; Baloh, Robert H.
Acta neuropathologica,
05/2019, Letnik:
137, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative diseases that overlap in their clinical presentation, pathology and genetics, and likely represent a ...spectrum of one underlying disease. In ALS/FTD patients, neuroinflammation characterized by innate immune responses of tissue-resident glial cells is uniformly present on end-stage pathology, and human imaging studies and rodent models support that neuroinflammation begins early in disease pathogenesis. Additionally, changes in circulating immune cell populations and cytokines are found in ALS/FTD patients, and there is evidence for an autoinflammatory state. However, despite the prominent role of neuro- and systemic inflammation in ALS/FTD, and experimental evidence in rodents that altering microglial function can mitigate pathology, therapeutic approaches to decrease inflammation have thus far failed to alter disease course in humans. Here, we review the characteristics of inflammation in ALS/FTD in both the nervous and peripheral immune systems. We further discuss evidence for direct influence on immune cell function by mutations in ALS/FTD genes including C9orf72, TBK1 and OPTN, and how this could lead to the altered innate immune system “tone” observed in these patients.
Accumulations of aggregated proteins are a key feature of the pathology of all of the major neurodegenerative diseases. Amyotrophic lateral sclerosis (ALS) was brought into this fold quite recently ...with the discovery of TDP‐43 (TAR DNA binding protein, 43 kDa) inclusions in nearly all ALS cases. In part this discovery was fueled by the recognition of the clinical overlap between ALS and frontotemporal lobar degeneration, where ubiquitinated TDP‐43 inclusions were first identified. Later the identification of TDP‐43 mutations in rare familial forms of ALS confirmed that altered TDP‐43 function can be a primary cause of the disease. However, the simple concept that TDP‐43 is an aggregation‐prone protein that forms toxic inclusions capable of promoting neurodegeneration has not been upheld by initial investigations. This review discusses observations from human pathology, cell culture and animal model systems, to highlight our somewhat murky understanding of the relationship between TDP‐43 aggregation and neurodegeneration.
Aggregated proteins are a key pathologic feature of the major neurodegenerative diseases. TDP‐43 aggregates are present in amyotrophic lateral sclerosis (ALS), and mutations in TDP‐43 cause rare familial forms of ALS. This review discusses observations from human pathology, cell culture, and animal model systems, to explore our understanding of the relationship between TDP‐43 aggregation and neurodegeneration.
Noncoding expansions of a hexanucleotide repeat (GGGGCC) in the C9orf72 gene are the most common cause of familial amyotrophic lateral sclerosis and frontotemporal dementia. Here we report transgenic ...mice carrying a bacterial artificial chromosome (BAC) containing the full human C9orf72 gene with either a normal allele (15 repeats) or disease-associated expansion (∼100–1,000 repeats; C9-BACexp). C9-BACexp mice displayed pathologic features seen in C9orf72 expansion patients, including widespread RNA foci and repeat-associated non-ATG (RAN) translated dipeptides, which were suppressed by antisense oligonucleotides targeting human C9orf72. Nucleolin distribution was altered, supporting that either C9orf72 transcripts or RAN dipeptides promote nucleolar dysfunction. Despite early and widespread production of RNA foci and RAN dipeptides in C9-BACexp mice, behavioral abnormalities and neurodegeneration were not observed even at advanced ages, supporting the hypothesis that RNA foci and RAN dipeptides occur presymptomatically and are not sufficient to drive neurodegeneration in mice at levels seen in patients.
•Transgenic mice expressing the C9orf72 repeat expansion were generated•C9-BACexp mice develop widespread RNA foci and RAN peptide pathology•Expanded C9orf72 led to altered nucleolin distribution•RNA foci and RAN peptides can be suppressed by ASOs to human C9orf72
Repeat expansions in C9orf72 are the most common cause of ALS and FTD. O’Rourke et al. generated BAC transgenic mice with expanded human C9orf72 that develop widespread RNA foci and DPR proteins, but lack neurodegeneration.
Introduction/Aims
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative illness with great unmet patient need. We aimed to evaluate whether mesenchymal stem cells induced to secrete high ...levels of neurotrophic factors (MSC‐NTF), a novel autologous cell‐therapy capable of targeting multiple pathways, could safely slow ALS disease progression.
Methods
This randomized, double‐blind, placebo‐controlled study enrolled ALS participants meeting revised El Escorial criteria, revised ALS Functional Rating Scale (ALSFRS‐R) ≥25 (screening) and ≥3 ALSFRS‐R points decline prior to randomization. Participants received three treatments of MSC‐NTF or placebo intrathecally. The primary endpoint evaluated efficacy of MSC‐NTF through a responder analysis and safety. A change in disease progression post‐treatment of ≥1.25 points/mo defines a clinical response. A pre‐specified analysis leveraged baseline ALSFRS‐R of 35 as a subgroup threshold.
Results
Overall, MSC‐NTF treatment was well tolerated; there were no safety concerns. Thirty‐three percent of MSC‐NTF and 28% of placebo participants met clinical response criteria at 28 wk (odds ratio OR = 1.33, P = .45); thus, the primary endpoint was not met. A pre‐specified analysis of participants with baseline ALSFRS‐R ≥ 35 (n = 58) showed a clinical response rate at 28 wk of 35% MSC‐NTF and 16% placebo (OR = 2.6, P = .29). Significant improvements in cerebrospinal biomarkers of neuroinflammation, neurodegeneration, and neurotrophic factor support were observed with MSC‐NTF, with placebo unchanged.
Discussion
The study did not reach statistical significance on the primary endpoint. However, a pre‐specified subgroup suggests that MSC‐NTF participants with less severe disease may have retained more function compared to placebo. Given the unmet patient need, the results of this trial warrant further investigation.
Mitofusins (Mfn1 and Mfn2) are outer mitochondrial membrane proteins involved in regulating mitochondrial dynamics. Mutations in Mfn2 cause Charcot-Marie-Tooth disease (CMT) type 2A, an inherited ...disease characterized by degeneration of long peripheral axons, but the nature of this tissue selectivity remains unknown. Here, we present evidence that Mfn2 is directly involved in and required for axonal mitochondrial transport, distinct from its role in mitochondrial fusion. Live imaging of neurons cultured from Mfn2 knock-out mice or neurons expressing Mfn2 disease mutants shows that axonal mitochondria spend more time paused and undergo slower anterograde and retrograde movements, indicating an alteration in attachment to microtubule-based transport systems. Furthermore, Mfn2 disruption altered mitochondrial movement selectively, leaving transport of other organelles intact. Importantly, both Mfn1 and Mfn2 interact with mammalian Miro (Miro1/Miro2) and Milton (OIP106/GRIF1) proteins, members of the molecular complex that links mitochondria to kinesin motors. Knockdown of Miro2 in cultured neurons produced transport deficits identical to loss of Mfn2, indicating that both proteins must be present at the outer membrane to mediate axonal mitochondrial transport. In contrast, disruption of mitochondrial fusion via knockdown of the inner mitochondrial membrane protein Opa1 had no effect on mitochondrial motility, indicating that loss of fusion does not inherently alter mitochondrial transport. These experiments identify a role for mitofusins in directly regulating mitochondrial transport and offer important insight into the cell type specificity and molecular mechanisms of axonal degeneration in CMT2A and dominant optic atrophy.
Frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative diseases that show considerable clinical and pathologic overlap, with no effective treatments ...available. Mutations in the RNA binding protein TDP-43 were recently identified in patients with familial amyotrophic lateral sclerosis (ALS), and TDP-43 aggregates are found in both ALS and FTLD-U (FTLD with ubiquitin aggregates), suggesting a common underlying mechanism. We report that mice expressing a mutant form of human TDP-43 develop a progressive and fatal neurodegenerative disease reminiscent of both ALS and FTLD-U. Despite universal transgene expression throughout the nervous system, pathologic aggregates of ubiquitinated proteins accumulate only in specific neuronal populations, including layer 5 pyramidal neurons in frontal cortex, as well as spinal motor neurons, recapitulating the phenomenon of selective vulnerability seen in patients with FTLD-U and ALS. Surprisingly, cytoplasmic TDP-43 aggregates are not present, and hence are not required for TDP-43-induced neurodegeneration. These results indicate that the cellular and molecular substrates for selective vulnerability in FTLD-U and ALS are shared between mice and humans, and suggest that altered DNA/RNA-binding protein function, rather than toxic aggregation, is central to TDP-43-related neurodegeneration.
Objective
To define the genetic landscape of amyotrophic lateral sclerosis (ALS) and assess the contribution of possible oligogenic inheritance, we aimed to comprehensively sequence 17 known ALS ...genes in 391 ALS patients from the United States.
Methods
Targeted pooled‐sample sequencing was used to identify variants in 17 ALS genes. Fragment size analysis was used to define ATXN2 and C9ORF72 expansion sizes. Genotype–phenotype correlations were made with individual variants and total burden of variants. Rare variant associations for risk of ALS were investigated at both the single variant and gene level.
Results
A total of 64.3% of familial and 27.8% of sporadic subjects carried potentially pathogenic novel or rare coding variants identified by sequencing or an expanded repeat in C9ORF72 or ATXN2; 3.8% of subjects had variants in >1 ALS gene, and these individuals had disease onset 10 years earlier (p = 0.0046) than subjects with variants in a single gene. The number of potentially pathogenic coding variants did not influence disease duration or site of onset.
Interpretation
Rare and potentially pathogenic variants in known ALS genes are present in >25% of apparently sporadic and 64% of familial patients, significantly higher than previous reports using less comprehensive sequencing approaches. A significant number of subjects carried variants in >1 gene, which influenced the age of symptom onset and supports oligogenic inheritance as relevant to disease pathogenesis. ANN NEUROL 2015;77:100–113
Mitofusins (MFNs) promote fusion-mediated mitochondrial content exchange and subcellular trafficking. Mutations in
cause neurodegenerative Charcot-Marie-Tooth disease type 2A (CMT2A). We showed that ...MFN2 activity can be determined by Met
and His
interactions with Asp
and Leu
and controlled by PINK1 kinase-mediated phosphorylation of adjacent MFN2 Ser
Small-molecule mimics of the peptide-peptide interface of MFN2 disrupted this interaction, allosterically activating MFN2 and promoting mitochondrial fusion. These first-in-class mitofusin agonists overcame dominant mitochondrial defects provoked in cultured neurons by CMT2A mutants MFN2 Arg
→Gln
and MFN2 Thr
→Met
, as demonstrated by amelioration of mitochondrial dysmotility, fragmentation, depolarization, and clumping. A mitofusin agonist normalized axonal mitochondrial trafficking within sciatic nerves of MFN2 Thr
→Met
mice, promising a therapeutic approach for CMT2A and other untreatable diseases of impaired neuronal mitochondrial dynamism and/or trafficking.
Mutations in the mitochondrial fusion protein mitofusin 2 (MFN2) are the most commonly identified cause of Charcot-Marie-Tooth type 2 (CMT2), a dominantly inherited disease characterized by ...degeneration of peripheral sensory and motor axons. However, the mechanism by which mutations in this ubiquitously expressed mitochondrial fusion protein lead to neuropathy has not yet been elucidated. To explore how MFN2 mutations lead to degeneration of peripheral axons, we expressed neuropathy-associated forms of MFN2 in cultured dorsal root ganglion neurons, cells preferentially affected in CMT2. Disease-associated MFN2 mutant proteins induced abnormal clustering of small fragmented mitochondria in both neuronal cell bodies and proximal axons. Interestingly, transport of mitochondria in axons was significantly impaired in neurons expressing disease-mutated forms of MFN2. The diminished axonal mitochondrial transport was not attributable to diminished ATP levels in the neurons, and oxidative respiration was normal in mutant MFN2-expressing cells. Additionally, mitochondrial oxidative enzyme activity was normal in muscle mitochondria from a CMT2 patient with an MFN2 mutation, further supporting that abnormal mitochondrial transport in neurons is independent from an energy production defect. This abnormal mitochondrial trafficking provides a likely explanation for the selective susceptibility of the longest peripheral axons to MFN2 mutations, in which proper localization of mitochondria is critical for axonal and synaptic function.
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