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. 2008 Aug 6;3(8):e2906.
doi: 10.1371/journal.pone.0002906.

Disruption of neuronal autophagy by infected microglia results in neurodegeneration

Mehrdad Alirezaei  1 , William B Kiosses, Claudia T Flynn, Nathan R Brady, Howard S Fox
Affiliations

Disruption of neuronal autophagy by infected microglia results in neurodegeneration

Mehrdad Alirezaei et al. PLoS One. .

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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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Confocal imaging and three-dimensional model reconstruction of neuron transfected with GFP-LC3.
(A–J) Confocal images of different z sections (0.2 µm of thickness) of a neuron transfected with GFP-LC3 (A–D) and all sections are flattened (E). Higher magnification images of the area outlined in white are shown in the inserts (A–D). Different sections of images of transfected neuron with GFP-LC3 (green) merged with DAPI (blue). Scale bar, 20 µm. (K–O) Three-dimensional reconstruction from serial sections using IMARIS software, cell body and process (K) and higher magnification of the zoomed area outlined in white (K-I). Reconstructed 3D image of the same neuron using IMARIS, which evaluates AV localization in the reconstructed 3D image (M–O). Enlarged areas of neuron revealed the presence of AV in soma and neurites (N–O).
Figure 2
Figure 2. In vitro analysis of the impact of SIV-infected microglia supernatant on autophagy in primary neurons.
(A) Model of experimental design, as detailed in the Materials and Methods. (B) Total AV counting results show that a significant drop in the number of AV occurs in neurons exposed to SIV-infected microglia supernatant for 3 or 24 hr. Total number of AV are significantly increased after the pretreatment with rapamycin followed by SIV-infected microglia supernatant (Sup) exposure for 24 hr. *** P<0.001, * P<0.05 for n = 6 experiments. All values are mean±SEM. AV counting using 3D model reconstruction for neurons exposed to different treatments. (C) Flattened images of multi-stack confocal optical slices of neurons transfected with GFP-LC3 (green) to label AV, and DAPI (blue) to label the nucleus. The five panels display a typical sample image of a neuron under control conditions as well as 3 hr and 24 hr exposure to SIV-infected microglia supernatant or pretreated with rapamycin prior the exposure to SIV-infected microglia supernatant. The right hand panels show a snap shot of a 3D outline of the neuron with AV marked as green spheres. Scale bar, 20 µm.
Figure 3
Figure 3. Process length and AV distribution in neurons exposed to different treatments.
(A) The number of AV in neurites decreased significantly in neurons exposed to the SIV-infected microglia supernatant for 3 or 24 hr, however; pretreatment with rapamycin blocked this effect. *** P<0.001, for n = 6 experiments. Scale bar, 20 µm. (B) The AV number is unchanged in neuronal soma after exposure to the SIV-infected microglia supernatant for 3 or 24 hr. (C and D) Both the total length of neuronal processes (C) and number of brunch points (D) are decreased after exposure to after SIV-infected microglia supernatant treatment. *** P<0.001, for n = 6 experiments. All values are mean±SEM.
Figure 4
Figure 4. Western blot analysis of autophagy related proteins.
(A) The LC3-II level is reduced after 3 or 24 hr exposure to SIV-infected microglia supernatant and this decrease effect is blocked when is pretreated with rapamycin (2 µM). The protein level of elongation complex Atg12-Atg5 is also reduced, and again the effect is blocked in the presence of rapamycin. The protein level of p62 is increased for similar conditions with SIV-infected microglia supernatant, and the increase is blocked in the presence of rapamycin. GAPDH protein was used in these experiments as the loading control. One representative experiment of n = 4 is shown. (B, C and D) Ratios between LC3-II, Atg12-Atg5, p62, respectively, normalized to GAPDH. Data are reported as mean±SEM (n = 4). *** P<0.001.
Figure 5
Figure 5. AV counting and distribution for neurons exposed to different treatments.
(A) Total AV counting results show that a significant drop occurs in neurons exposed to TNF-α or NMDA for 3 or 24 hr. *** P<0.001, ** P<0.01 for n = 6 experiments. All values are mean±SEM. (B and C) Distribution of AV number in soma and neurites respectively. (B) The number of AV in neurites decreased significantly in neurons exposed to both TNF-α or NMDA for 3 or 24 hr. *** P<0.001, for n = 6 experiments. (C) The AV number in soma is increased in neurons after exposure to TNF-α for 3 or 24 hr, however it remained unaffected in neurons after exposure to NMDA. ** P<0.01 for n = 6 experiments. (D) Flattened images of multi-stack confocal optical slices of neurons transfected with GFP-LC3 (green) to label AV, and DAPI (blue) to label the nucleus. transfected with GFP-LC3 (green) to label AV, and DAPI (blue) to label the nucleus. The four panels display a typical sample image of a neuron under 3 hr and 24 hr exposure to TNF-α or NMDA at 25 ng/ml and 35 µM respectively. Scale bar, 20 µm.
Figure 6
Figure 6. Neuronal survival after exposure to SIV-infected microglia supernatant in the presence of different autophagy related drugs.
(A). Neuronal survival tested by MTT. There are significant decreases of neuronal survival after exposure to SIV-infected microglia supernatant for 3 or 24 hr, which is significantly abrogated in the presence of rapamycin. Rapamycin alone has no effect. MK-801 (100 µM) also prevented the neurotoxicity induced by SIV-infected microglia supernatant. *** P<0.001, for n = 6 experiments. (B) Neuronal survival was examined with MTT in cultures exposed to SIV-infected microglia supernatant for 24 hr and in the presence or absence of different drugs such as 3-MA (1 mM) or Baf (100 nM). There is no significant difference between cells exposed to SIV-infected microglia supernatant and a pretreatment with 3-MA followed by exposure to SIV-infected microglia supernatant. However, there is a significant decrease of neuronal survival exposed to SIV-infected microglia supernatant when cells are pretreated with Baf. The SIV-infected microglia supernatant from no infected monkey (no Sup) doesn't affect neuronal survival and there is no significant difference with control samples. All values are mean±SEM.
Figure 7
Figure 7. 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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References

    1. Komatsu M, Ueno T, Waguri S, Uchiyama Y, Kominami E, et al. Constitutive autophagy: vital role in clearance of unfavorable proteins in neurons. Cell Death Differ. 2007;14:887–894. - PubMed
    1. Levine B, Klionsky DJ. Development by self-digestion: molecular mechanisms and biological functions of autophagy. Dev Cell. 2004;6:463–477. - PubMed
    1. Boland B, Nixon RA. Neuronal macroautophagy: from development to degeneration. Mol Aspects Med. 2006;27:503–519. - PubMed
    1. Rideout HJ, Lang-Rollin I, Stefanis L. Involvement of macroautophagy in the dissolution of neuronal inclusions. Int J Biochem Cell Biol. 2004;36:2551–2562. - PubMed
    1. Rubinsztein DC, Gestwicki JE, Murphy LO, Klionsky DJ. Potential therapeutic applications of autophagy. Nat Rev Drug Discov. 2007;6:304–312. - PubMed

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