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Disruption of neuronal autophagy by infected microglia results in neurodegeneration.

Alirezaei M, Kiosses WB, Flynn CT, Brady NR, Fox HS - PLoS ONE (2008)

Bottom Line: We demonstrate here that products of simian immunodeficiency virus (SIV)-infected microglia inhibit neuronal autophagy, resulting in decreased neuronal survival.Two major mediators of HIV-induced neurotoxicity, tumor necrosis factor-alpha and glutamate, had similar effects on reducing autophagy in neurons.Taken together, these results identify that induction of deficits in autophagy is a significant mechanism for neurodegenerative processes that arise from glial, as opposed to neuronal, sources, and that the maintenance of autophagy may have a pivotal role in neuroprotection in the setting of HIV infection.

View Article: PubMed Central - PubMed

Affiliation: Molecular and Integrative Neurosciences Department, The Scripps Research Institute, La Jolla, California, United States of America.

ABSTRACT
There is compelling evidence to support the idea that autophagy has a protective function in neurons and its disruption results in neurodegenerative disorders. Neuronal damage is well-documented in the brains of HIV-infected individuals, and evidence of inflammation, oxidative stress, damage to synaptic and dendritic structures, and neuronal loss are present in the brains of those with HIV-associated dementia. We investigated the role of autophagy in microglia-induced neurotoxicity in primary rodent neurons, primate and human models. We demonstrate here that products of simian immunodeficiency virus (SIV)-infected microglia inhibit neuronal autophagy, resulting in decreased neuronal survival. Quantitative analysis of autophagy vacuole numbers in rat primary neurons revealed a striking loss from the processes. Assessment of multiple biochemical markers of autophagic activity confirmed the inhibition of autophagy in neurons. Importantly, autophagy could be induced in neurons through rapamycin treatment, and such treatment conferred significant protection to neurons. Two major mediators of HIV-induced neurotoxicity, tumor necrosis factor-alpha and glutamate, had similar effects on reducing autophagy in neurons. The mRNA level of p62 was increased in the brain in SIV encephalitis and as well as in brains from individuals with HIV dementia, and abnormal neuronal p62 dot structures immunoreactivity was present and had a similar pattern with abnormal ubiquitinylated proteins. Taken together, these results identify that induction of deficits in autophagy is a significant mechanism for neurodegenerative processes that arise from glial, as opposed to neuronal, sources, and that the maintenance of autophagy may have a pivotal role in neuroprotection in the setting of HIV infection.

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Transcriptional regulation of p62 in SIVE monkey brains, and its presence in human and monkey neurons associated with ubiquitin.(A) Relative values (RV) of p62 mRNA level in frontal lobe of SIVE versus SIV and uninfected (UN) monkeys, n = 7 for SIVE, n = 12 for SIV and n = 9 for UN, P<0.05. (B) RV of p62 mRNA level in frontal cortex of HAD versus non neurological diseased subjects (NNDS), n = 8 for HAD and n = 10 for NNDS, P<0.0001. (C) p62 and ubiquitin immunoreactivity on serial sections in SIVE monkeys, as well as those with HAD in brain sections from hippocampus. p62 has a diffuse immunoreactivity in UN monkeys and in human NNDS and a dot profile structures in SIVE and HAD brain tissues. Higher magnification views are shown in green insets. Black arrows indicate p62- or ubiquitin-immunoreactive structures within the neuronal cell body or proximal processes, and red arrowheads indicate a dot-like immunoreactivity in the neuropil. Scale bar, 20 µm.
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pone-0002906-g007: Transcriptional regulation of p62 in SIVE monkey brains, and its presence in human and monkey neurons associated with ubiquitin.(A) Relative values (RV) of p62 mRNA level in frontal lobe of SIVE versus SIV and uninfected (UN) monkeys, n = 7 for SIVE, n = 12 for SIV and n = 9 for UN, P<0.05. (B) RV of p62 mRNA level in frontal cortex of HAD versus non neurological diseased subjects (NNDS), n = 8 for HAD and n = 10 for NNDS, P<0.0001. (C) p62 and ubiquitin immunoreactivity on serial sections in SIVE monkeys, as well as those with HAD in brain sections from hippocampus. p62 has a diffuse immunoreactivity in UN monkeys and in human NNDS and a dot profile structures in SIVE and HAD brain tissues. Higher magnification views are shown in green insets. Black arrows indicate p62- or ubiquitin-immunoreactive structures within the neuronal cell body or proximal processes, and red arrowheads indicate a dot-like immunoreactivity in the neuropil. Scale bar, 20 µm.

Mentions: It has been shown that the expression of p62 is involved in protein aggregation of different neurodegenerative diseases and its transcript is upregulated in response to pro-apoptotic conditions [35]. Moreover examining changes in p62 expression, at both the mRNA and protein levels, can be used as an index of autophagic activity [36]. To examine p62 expression, we first assessed the level of p62 mRNA in uninfected monkeys compared to those infected with SIV but lacking SIVE, as well as those with SIVE. Quantitative real time PCR analysis revealed a significant increase of the p62 transcript level (Figure 7A), shown here in the frontal lobe, in SIVE compared to both brains from uninfected animals or those infected with SIV but without encephalitis. Assessment of hippocampus, caudate and cerebellum in addition to the frontal lobe indicates an approximate 2-fold increase in p62 mRNA levels in SIVE compared to uninfected monkeys. We next examined the p62 mRNA transcripts levels in human brain specimens affected with HAD and we compared with those with non neurological diseased subjects. We found a significant upregulation of mRNA p62 level in HAD patients (3.2-fold increase) versus non neurological diseased subjects demonstrating the translation of the results from experimental animals to humans (Figures 7A and 7B). We next analyzed p62 immunoreactivity in brains of monkeys with SIVE and humans with HAD. Distinct staining within the neuronal soma and proximal portions of their processes, as well as dot-like structures in the neuropil, were found in both SIVE and HAD brains (Figure 7C). Analysis of ubiquitin antibody labeling in SIVE and HAD brains revealed a similar dot-like structures in neurons and similar abnormal pattern of increased ubiquitin immunoreactivity as was found for p62 (Figure 7C).


Disruption of neuronal autophagy by infected microglia results in neurodegeneration.

Alirezaei M, Kiosses WB, Flynn CT, Brady NR, Fox HS - PLoS ONE (2008)

Transcriptional regulation of p62 in SIVE monkey brains, and its presence in human and monkey neurons associated with ubiquitin.(A) Relative values (RV) of p62 mRNA level in frontal lobe of SIVE versus SIV and uninfected (UN) monkeys, n = 7 for SIVE, n = 12 for SIV and n = 9 for UN, P<0.05. (B) RV of p62 mRNA level in frontal cortex of HAD versus non neurological diseased subjects (NNDS), n = 8 for HAD and n = 10 for NNDS, P<0.0001. (C) p62 and ubiquitin immunoreactivity on serial sections in SIVE monkeys, as well as those with HAD in brain sections from hippocampus. p62 has a diffuse immunoreactivity in UN monkeys and in human NNDS and a dot profile structures in SIVE and HAD brain tissues. Higher magnification views are shown in green insets. Black arrows indicate p62- or ubiquitin-immunoreactive structures within the neuronal cell body or proximal processes, and red arrowheads indicate a dot-like immunoreactivity in the neuropil. Scale bar, 20 µm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2483417&req=5

pone-0002906-g007: Transcriptional regulation of p62 in SIVE monkey brains, and its presence in human and monkey neurons associated with ubiquitin.(A) Relative values (RV) of p62 mRNA level in frontal lobe of SIVE versus SIV and uninfected (UN) monkeys, n = 7 for SIVE, n = 12 for SIV and n = 9 for UN, P<0.05. (B) RV of p62 mRNA level in frontal cortex of HAD versus non neurological diseased subjects (NNDS), n = 8 for HAD and n = 10 for NNDS, P<0.0001. (C) p62 and ubiquitin immunoreactivity on serial sections in SIVE monkeys, as well as those with HAD in brain sections from hippocampus. p62 has a diffuse immunoreactivity in UN monkeys and in human NNDS and a dot profile structures in SIVE and HAD brain tissues. Higher magnification views are shown in green insets. Black arrows indicate p62- or ubiquitin-immunoreactive structures within the neuronal cell body or proximal processes, and red arrowheads indicate a dot-like immunoreactivity in the neuropil. Scale bar, 20 µm.
Mentions: It has been shown that the expression of p62 is involved in protein aggregation of different neurodegenerative diseases and its transcript is upregulated in response to pro-apoptotic conditions [35]. Moreover examining changes in p62 expression, at both the mRNA and protein levels, can be used as an index of autophagic activity [36]. To examine p62 expression, we first assessed the level of p62 mRNA in uninfected monkeys compared to those infected with SIV but lacking SIVE, as well as those with SIVE. Quantitative real time PCR analysis revealed a significant increase of the p62 transcript level (Figure 7A), shown here in the frontal lobe, in SIVE compared to both brains from uninfected animals or those infected with SIV but without encephalitis. Assessment of hippocampus, caudate and cerebellum in addition to the frontal lobe indicates an approximate 2-fold increase in p62 mRNA levels in SIVE compared to uninfected monkeys. We next examined the p62 mRNA transcripts levels in human brain specimens affected with HAD and we compared with those with non neurological diseased subjects. We found a significant upregulation of mRNA p62 level in HAD patients (3.2-fold increase) versus non neurological diseased subjects demonstrating the translation of the results from experimental animals to humans (Figures 7A and 7B). We next analyzed p62 immunoreactivity in brains of monkeys with SIVE and humans with HAD. Distinct staining within the neuronal soma and proximal portions of their processes, as well as dot-like structures in the neuropil, were found in both SIVE and HAD brains (Figure 7C). Analysis of ubiquitin antibody labeling in SIVE and HAD brains revealed a similar dot-like structures in neurons and similar abnormal pattern of increased ubiquitin immunoreactivity as was found for p62 (Figure 7C).

Bottom Line: We demonstrate here that products of simian immunodeficiency virus (SIV)-infected microglia inhibit neuronal autophagy, resulting in decreased neuronal survival.Two major mediators of HIV-induced neurotoxicity, tumor necrosis factor-alpha and glutamate, had similar effects on reducing autophagy in neurons.Taken together, these results identify that induction of deficits in autophagy is a significant mechanism for neurodegenerative processes that arise from glial, as opposed to neuronal, sources, and that the maintenance of autophagy may have a pivotal role in neuroprotection in the setting of HIV infection.

View Article: PubMed Central - PubMed

Affiliation: Molecular and Integrative Neurosciences Department, The Scripps Research Institute, La Jolla, California, United States of America.

ABSTRACT
There is compelling evidence to support the idea that autophagy has a protective function in neurons and its disruption results in neurodegenerative disorders. Neuronal damage is well-documented in the brains of HIV-infected individuals, and evidence of inflammation, oxidative stress, damage to synaptic and dendritic structures, and neuronal loss are present in the brains of those with HIV-associated dementia. We investigated the role of autophagy in microglia-induced neurotoxicity in primary rodent neurons, primate and human models. We demonstrate here that products of simian immunodeficiency virus (SIV)-infected microglia inhibit neuronal autophagy, resulting in decreased neuronal survival. Quantitative analysis of autophagy vacuole numbers in rat primary neurons revealed a striking loss from the processes. Assessment of multiple biochemical markers of autophagic activity confirmed the inhibition of autophagy in neurons. Importantly, autophagy could be induced in neurons through rapamycin treatment, and such treatment conferred significant protection to neurons. Two major mediators of HIV-induced neurotoxicity, tumor necrosis factor-alpha and glutamate, had similar effects on reducing autophagy in neurons. The mRNA level of p62 was increased in the brain in SIV encephalitis and as well as in brains from individuals with HIV dementia, and abnormal neuronal p62 dot structures immunoreactivity was present and had a similar pattern with abnormal ubiquitinylated proteins. Taken together, these results identify that induction of deficits in autophagy is a significant mechanism for neurodegenerative processes that arise from glial, as opposed to neuronal, sources, and that the maintenance of autophagy may have a pivotal role in neuroprotection in the setting of HIV infection.

Show MeSH
Related in: MedlinePlus