Difference between revisions of "Aberrant astrocytes"

Revision as of 19:09, 12 February 2017

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.^[1]

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.^[2]

References

1. ↑ Trias et al.: Significance of aberrant glial cell phenotypes in pathophysiology of amyotrophic lateral sclerosis. Neurosci. Lett. 2017;636:27-31. PMID: 27473942. DOI. 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 SOD1(G93A) 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.
2. ↑ Rojas et al.: Astrocytes expressing mutant SOD1 and TDP43 trigger motoneuron death that is mediated via sodium channels and nitroxidative stress. Front Cell Neurosci 2014;8:24. PMID: 24570655. DOI. Amyotrophic lateral sclerosis (ALS) is a fatal paralytic disorder caused by dysfunction and degeneration of motor neurons. Multiple disease-causing mutations, including in the genes for SOD1 and TDP-43, have been identified in ALS. 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.