Editing Aberrant astrocytes
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[[Key concepts in ALS]] | [[Key concepts in ALS]] | ||
− | ''ALS is a paradigmatic neurodegenerative disease, characterized by progressive paralysis of skeletal muscles associated with motor neuron degeneration. It is well-established that glial cells play a key role in ALS pathogenesis. In transgenic rodent models for familial ALS reactive astrocytes, microglia and oligodendrocyte precursors accumulate in the degenerating spinal cord and appear to contribute to primary motor neuron death through a non-cell autonomous pathogenic mechanism. Furthermore in rats expressing the ALS-linked SOD1G93A mutation, rapid spread of paralysis coincides with emergence of neurotoxic and proliferating aberrant glia cells with an astrocyte-like phenotype (AbA cells) that are found surrounding damaged motor neurons. AbAs simultaneously express astrocytic markers GFAP, S100β and Connexin-43 along with microglial markers Iba-1, CD11b and CD163. '''Studies with cell cultures have shown that AbAs originate from inflammatory microglial cells that undergo phenotypic transition. Because AbAs appear only after paralysis onset and exponentially increase in parallel with disease progression, they appear to actively contribute to ALS progression.''' While several reviews have been published on the pathogenic role of glial cells in ALS, this review focuses on emergence and pro-inflammatory activity of AbAs as part of an increasingly complex neurodegenerative microenvironment during ALS disease development.''{{#pmid:27473942|Trias2016}} | + | ''Amyotrophic Lateral Sclerosis (ALS) is a paradigmatic neurodegenerative disease, characterized by progressive paralysis of skeletal muscles associated with motor neuron degeneration. It is well-established that glial cells play a key role in ALS pathogenesis. In transgenic rodent models for familial ALS reactive astrocytes, microglia and oligodendrocyte precursors accumulate in the degenerating spinal cord and appear to contribute to primary motor neuron death through a non-cell autonomous pathogenic mechanism. Furthermore in rats expressing the ALS-linked SOD1G93A mutation, rapid spread of paralysis coincides with emergence of neurotoxic and proliferating aberrant glia cells with an astrocyte-like phenotype (AbA cells) that are found surrounding damaged motor neurons. AbAs simultaneously express astrocytic markers GFAP, S100β and Connexin-43 along with microglial markers Iba-1, CD11b and CD163. '''Studies with cell cultures have shown that AbAs originate from inflammatory microglial cells that undergo phenotypic transition. Because AbAs appear only after paralysis onset and exponentially increase in parallel with disease progression, they appear to actively contribute to ALS progression.''' While several reviews have been published on the pathogenic role of glial cells in ALS, this review focuses on emergence and pro-inflammatory activity of AbAs as part of an increasingly complex neurodegenerative microenvironment during ALS disease development.''{{#pmid:27473942|Trias2016}} |
''Astrocytes expressing mutant SOD1 are strongly implicated in the pathogenesis of ALS: we have shown that '''media conditioned by astrocytes carrying mutant SOD1(G93A) contains toxic factor(s) that kill motoneurons by activating voltage-sensitive sodium (Na v ) channels. In contrast, a recent study suggests that astrocytes expressing mutated TDP43 contribute to ALS pathology, but do so via cell-autonomous processes and lack non-cell-autonomous toxicity.''' Here we investigate whether astrocytes that express diverse ALS-causing mutations release toxic factor(s) that induce motoneuron death, and if so, whether they do so via a common pathogenic pathway. We exposed primary cultures of wild-type spinal cord cells to conditioned medium derived from astrocytes (ACM) that express SOD1 (ACM-SOD1(G93A) and ACM-SOD1(G86R)) or TDP43 (ACM-TDP43(A315T)) mutants; we show that such exposure rapidly (within 30-60 min) increases dichlorofluorescein (DCF) fluorescence (indicative of nitroxidative stress) and leads to extensive motoneuron-specific death within a few days. '''Co-application of the diverse ACMs with anti-oxidants Trolox or esculetin (but not with resveratrol) strongly improves motoneuron survival. We also find that co-incubation of the cultures in the ACMs with Na v channel blockers (including mexiletine, spermidine, or riluzole) prevents both intracellular nitroxidative stress and motoneuron death.''' Together, our data document that two completely unrelated ALS models lead to the death of motoneuron via non-cell-autonomous processes, and show that astrocytes expressing mutations in SOD1 and TDP43 trigger such cell death through a common pathogenic pathway that involves nitroxidative stress, induced at least in part by Na v channel activity.''{{#pmid:24570655|Rojas2014}} | ''Astrocytes expressing mutant SOD1 are strongly implicated in the pathogenesis of ALS: we have shown that '''media conditioned by astrocytes carrying mutant SOD1(G93A) contains toxic factor(s) that kill motoneurons by activating voltage-sensitive sodium (Na v ) channels. In contrast, a recent study suggests that astrocytes expressing mutated TDP43 contribute to ALS pathology, but do so via cell-autonomous processes and lack non-cell-autonomous toxicity.''' Here we investigate whether astrocytes that express diverse ALS-causing mutations release toxic factor(s) that induce motoneuron death, and if so, whether they do so via a common pathogenic pathway. We exposed primary cultures of wild-type spinal cord cells to conditioned medium derived from astrocytes (ACM) that express SOD1 (ACM-SOD1(G93A) and ACM-SOD1(G86R)) or TDP43 (ACM-TDP43(A315T)) mutants; we show that such exposure rapidly (within 30-60 min) increases dichlorofluorescein (DCF) fluorescence (indicative of nitroxidative stress) and leads to extensive motoneuron-specific death within a few days. '''Co-application of the diverse ACMs with anti-oxidants Trolox or esculetin (but not with resveratrol) strongly improves motoneuron survival. We also find that co-incubation of the cultures in the ACMs with Na v channel blockers (including mexiletine, spermidine, or riluzole) prevents both intracellular nitroxidative stress and motoneuron death.''' Together, our data document that two completely unrelated ALS models lead to the death of motoneuron via non-cell-autonomous processes, and show that astrocytes expressing mutations in SOD1 and TDP43 trigger such cell death through a common pathogenic pathway that involves nitroxidative stress, induced at least in part by Na v channel activity.''{{#pmid:24570655|Rojas2014}} | ||
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''The interplay between motor neurons and astrocytes is crucial in the outcome of the disease. We show that mutant copper-zinc superoxide dismutase (SOD1) overexpression in primary astrocyte cultures is associated with decreased levels of proteins involved in secretory pathways. This is linked to a general reduction of total secreted proteins, except for specific enrichment in a number of proteins in the media, such as mutant SOD1 and valosin-containing protein (VCP)/p97. Because there was also an increase in exosome release, '''we can deduce that astrocytes expressing mutant SOD1 activate unconventional secretory pathways, possibly as a protective mechanism.''' This may help limit the formation of intracellular aggregates and overcome mutant SOD1 toxicity. '''We also found that astrocyte-derived exosomes efficiently transfer mutant SOD1 to spinal neurons and induce selective motor neuron death.''' We conclude that the expression of mutant SOD1 has a substantial impact on astrocyte protein secretion pathways, contributing to motor neuron pathology and disease spread.''{{#pmid:23592792|Basso2014}} | ''The interplay between motor neurons and astrocytes is crucial in the outcome of the disease. We show that mutant copper-zinc superoxide dismutase (SOD1) overexpression in primary astrocyte cultures is associated with decreased levels of proteins involved in secretory pathways. This is linked to a general reduction of total secreted proteins, except for specific enrichment in a number of proteins in the media, such as mutant SOD1 and valosin-containing protein (VCP)/p97. Because there was also an increase in exosome release, '''we can deduce that astrocytes expressing mutant SOD1 activate unconventional secretory pathways, possibly as a protective mechanism.''' This may help limit the formation of intracellular aggregates and overcome mutant SOD1 toxicity. '''We also found that astrocyte-derived exosomes efficiently transfer mutant SOD1 to spinal neurons and induce selective motor neuron death.''' We conclude that the expression of mutant SOD1 has a substantial impact on astrocyte protein secretion pathways, contributing to motor neuron pathology and disease spread.''{{#pmid:23592792|Basso2014}} | ||
− | ''The evidence for increased oxidative stress and DNA damage in amyotrophic lateral sclerosis (ALS) prompted studies to determine if the expression of poly(ADP-ribose) polymerase (PARP) is increased in ALS. Using Western analyses of postmortem tissue, we demonstrated that PARP-immunoreactivity (PARP-IR) was increased 3-fold in spinal cord tissues of sporadic ALS (sALS) patients compared with non-neurological disease controls. Despite the increased PARP-IR, PARP mRNA expression was not increased significantly. Immunohistochemical analyses revealed PARP-IR was increased in both white and gray matter of sALS spinal cord. | + | ''The evidence for increased oxidative stress and DNA damage in amyotrophic lateral sclerosis (ALS) prompted studies to determine if the expression of poly(ADP-ribose) polymerase (PARP) is increased in ALS. Using Western analyses of postmortem tissue, we demonstrated that PARP-immunoreactivity (PARP-IR) was increased 3-fold in spinal cord tissues of sporadic ALS (sALS) patients compared with non-neurological disease controls. Despite the increased PARP-IR, PARP mRNA expression was not increased significantly. Immunohistochemical analyses revealed PARP-IR was increased in both white and gray matter of sALS spinal cord. While PARP-IR was predominantly seen in astrocytes, large motor neurons displayed reduced staining compared with controls. This result contrasts sharply to the staining of Alzheimer and MPTP-induced Parkinson diseased tissue, where poly(ADP-ribose) (PAR)-IR was seen mostly in neurons, with little astrocytic staining. PARP-IR was increased in the pellet fraction of sALS homogenates compared with control homogenates, representing potential PARP binding to chromatin or membranes and suggesting a possible mechanism of PARP stabilization. The present results demonstrate glial alterations in sALS spinal cord tissue and support the role of glial alterations in sALS pathogenesis. Additionally, these results demonstrate differences in sALS spinal motor neurons and astrocytes compared to brain neurons and astrocytes in Alzheimer disease and MPTP-induced Parkinson disease despite the presence of markers for oxidative stress in all 3 diseases.''{{#pmid:12528821|Kim2003}} |
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==References== | ==References== | ||
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