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Morphological remodeling of C. elegans neurons during aging is modified by compromised protein homeostasis.

Vayndorf EM, Scerbak C, Hunter S, Neuswanger JR, Toth M, Parker JA, Neri C, Driscoll M, Taylor BE - NPJ Aging Mech Dis (2016)

Bottom Line: Our results show that the expression of misfolded proteins in neurodegenerative disease such as Huntington's disease modifies the morphological remodeling that is normally associated with neuronal aging.Our results also show that morphological remodeling of healthy neurons during aging can be regulated by the UPS and other proteostasis pathways.Collectively, our data highlight a model in which morphological remodeling during neuronal aging is strongly affected by disrupted proteostasis and expression of disease-associated, misfolded proteins such as human polyQ-Htt species.

View Article: PubMed Central - PubMed

Affiliation: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA.

ABSTRACT

Understanding cellular outcomes, such as neuronal remodeling, that are common to both healthy and diseased aging brains is essential to the development of successful brain aging strategies. Here, we used Caenorhabdits elegans to investigate how the expression of proteotoxic triggers, such as polyglutamine (polyQ)-expanded huntingtin and silencing of proteostasis regulators, such as the ubiquitin-proteasome system (UPS) and protein clearance components, may impact the morphological remodeling of individual neurons as animals age. We examined the effects of disrupted proteostasis on the integrity of neuronal cytoarchitecture by imaging a transgenic C. elegans strain in which touch receptor neurons express the first 57 amino acids of the human huntingtin (Htt) gene with expanded polyQs (128Q) and by using neuron-targeted RNA interference in adult wild-type neurons to knockdown genes encoding proteins involved in proteostasis. We found that proteostatic challenges conferred by polyQ-expanded Htt and knockdown of specific genes involved in protein homeostasis can lead to morphological changes that are restricted to specific domains of specific neurons. The age-associated branching of PLM neurons is suppressed by N-ter polyQ-expanded Htt expression, whereas ALM neurons with polyQ-expanded Htt accumulate extended outgrowths and other soma abnormalities. Furthermore, knockdown of genes important for ubiquitin-mediated degradation, lysosomal function, and autophagy modulated these age-related morphological changes in otherwise normal neurons. Our results show that the expression of misfolded proteins in neurodegenerative disease such as Huntington's disease modifies the morphological remodeling that is normally associated with neuronal aging. Our results also show that morphological remodeling of healthy neurons during aging can be regulated by the UPS and other proteostasis pathways. Collectively, our data highlight a model in which morphological remodeling during neuronal aging is strongly affected by disrupted proteostasis and expression of disease-associated, misfolded proteins such as human polyQ-Htt species.

No MeSH data available.


Related in: MedlinePlus

Effects of neuron-targeted RNAi knockdown of proteostasis components on the neuronal morphology of naturally aged touch receptor neurons. Pmec-4GFP animals were treated with RNAi for the corresponding gene starting at the late L4 stage and morphological changes, either branches (a) extended outgrowths (b), kinks (c) or loops (d) were quantified on day 5 of adulthood. Data were analyzed using the Mann–Whitney U-test with Holm–Sidak step-down comparisons. Branches: N = 120, 131, 107, 242 neurons for icd-1, pas-6, lgg-1 and empty vector control, respectively. Branches: P ≤ 0.004 for each gene versus the corresponding control. Extended outgrowths: N = 96, 109, 38, 91, 268 neurons for chn-1, lgg-1, zig-4, phi-32 and empty vector control, respectively. Extended outgrowths: P ≤ 0.011 for each gene versus the corresponding control. Kinks: N = 52, 48, 53, 56 and 172 neurons for gob-1, pas-3, pek-1 (ALM), pek-1(PLM) and empty vector control, respectively. Kinks: P<0.01 for each gene versus the corresponding control. Loops: N = 96, 26, 55 and ⩾ 172 for chn-1(ALM), vha-13(ALM), cup-5(PLM) and empty vector control, respectively. Loops: P<0.04 for each gene versus the corresponding control. GFP, green fluorescent protein; RNAi, RNA interference.
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Figure 4: Effects of neuron-targeted RNAi knockdown of proteostasis components on the neuronal morphology of naturally aged touch receptor neurons. Pmec-4GFP animals were treated with RNAi for the corresponding gene starting at the late L4 stage and morphological changes, either branches (a) extended outgrowths (b), kinks (c) or loops (d) were quantified on day 5 of adulthood. Data were analyzed using the Mann–Whitney U-test with Holm–Sidak step-down comparisons. Branches: N = 120, 131, 107, 242 neurons for icd-1, pas-6, lgg-1 and empty vector control, respectively. Branches: P ≤ 0.004 for each gene versus the corresponding control. Extended outgrowths: N = 96, 109, 38, 91, 268 neurons for chn-1, lgg-1, zig-4, phi-32 and empty vector control, respectively. Extended outgrowths: P ≤ 0.011 for each gene versus the corresponding control. Kinks: N = 52, 48, 53, 56 and 172 neurons for gob-1, pas-3, pek-1 (ALM), pek-1(PLM) and empty vector control, respectively. Kinks: P<0.01 for each gene versus the corresponding control. Loops: N = 96, 26, 55 and ⩾ 172 for chn-1(ALM), vha-13(ALM), cup-5(PLM) and empty vector control, respectively. Loops: P<0.04 for each gene versus the corresponding control. GFP, green fluorescent protein; RNAi, RNA interference.

Mentions: We knocked down four genes that make up subunits of the proteasome: pas-3, an alpha type 4 subunit of the 20S core particle; pas-6, a type 1 alpha subunit of the 20S core particle; rpt-5, a triple A ATPase of the 19S regulatory particle, and aip-1, a negative regulatory particle of the 19S proteasome (aip-1 RNAi activates the proteasome and can be neuroprotective against polyQ128). Disruption of two of the four genes increased aberrant PLM morphology: pas-6 increased branches by 261% from a mean of 0.186 to 0.672 aberrations/cell (Table 1, Figure 4a), pas-3 increased kinks from 0 to 0.458 kinks/cell (Table 2, Figure 4c), and rpt-5 and aip-1 had no significant effect (Supplementary Tables S1 and S2). Our data suggest that the integrity of the core 20S subunit of the proteasome may have an important role in the maintenance of PLM process morphology.


Morphological remodeling of C. elegans neurons during aging is modified by compromised protein homeostasis.

Vayndorf EM, Scerbak C, Hunter S, Neuswanger JR, Toth M, Parker JA, Neri C, Driscoll M, Taylor BE - NPJ Aging Mech Dis (2016)

Effects of neuron-targeted RNAi knockdown of proteostasis components on the neuronal morphology of naturally aged touch receptor neurons. Pmec-4GFP animals were treated with RNAi for the corresponding gene starting at the late L4 stage and morphological changes, either branches (a) extended outgrowths (b), kinks (c) or loops (d) were quantified on day 5 of adulthood. Data were analyzed using the Mann–Whitney U-test with Holm–Sidak step-down comparisons. Branches: N = 120, 131, 107, 242 neurons for icd-1, pas-6, lgg-1 and empty vector control, respectively. Branches: P ≤ 0.004 for each gene versus the corresponding control. Extended outgrowths: N = 96, 109, 38, 91, 268 neurons for chn-1, lgg-1, zig-4, phi-32 and empty vector control, respectively. Extended outgrowths: P ≤ 0.011 for each gene versus the corresponding control. Kinks: N = 52, 48, 53, 56 and 172 neurons for gob-1, pas-3, pek-1 (ALM), pek-1(PLM) and empty vector control, respectively. Kinks: P<0.01 for each gene versus the corresponding control. Loops: N = 96, 26, 55 and ⩾ 172 for chn-1(ALM), vha-13(ALM), cup-5(PLM) and empty vector control, respectively. Loops: P<0.04 for each gene versus the corresponding control. GFP, green fluorescent protein; RNAi, RNA interference.
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Figure 4: Effects of neuron-targeted RNAi knockdown of proteostasis components on the neuronal morphology of naturally aged touch receptor neurons. Pmec-4GFP animals were treated with RNAi for the corresponding gene starting at the late L4 stage and morphological changes, either branches (a) extended outgrowths (b), kinks (c) or loops (d) were quantified on day 5 of adulthood. Data were analyzed using the Mann–Whitney U-test with Holm–Sidak step-down comparisons. Branches: N = 120, 131, 107, 242 neurons for icd-1, pas-6, lgg-1 and empty vector control, respectively. Branches: P ≤ 0.004 for each gene versus the corresponding control. Extended outgrowths: N = 96, 109, 38, 91, 268 neurons for chn-1, lgg-1, zig-4, phi-32 and empty vector control, respectively. Extended outgrowths: P ≤ 0.011 for each gene versus the corresponding control. Kinks: N = 52, 48, 53, 56 and 172 neurons for gob-1, pas-3, pek-1 (ALM), pek-1(PLM) and empty vector control, respectively. Kinks: P<0.01 for each gene versus the corresponding control. Loops: N = 96, 26, 55 and ⩾ 172 for chn-1(ALM), vha-13(ALM), cup-5(PLM) and empty vector control, respectively. Loops: P<0.04 for each gene versus the corresponding control. GFP, green fluorescent protein; RNAi, RNA interference.
Mentions: We knocked down four genes that make up subunits of the proteasome: pas-3, an alpha type 4 subunit of the 20S core particle; pas-6, a type 1 alpha subunit of the 20S core particle; rpt-5, a triple A ATPase of the 19S regulatory particle, and aip-1, a negative regulatory particle of the 19S proteasome (aip-1 RNAi activates the proteasome and can be neuroprotective against polyQ128). Disruption of two of the four genes increased aberrant PLM morphology: pas-6 increased branches by 261% from a mean of 0.186 to 0.672 aberrations/cell (Table 1, Figure 4a), pas-3 increased kinks from 0 to 0.458 kinks/cell (Table 2, Figure 4c), and rpt-5 and aip-1 had no significant effect (Supplementary Tables S1 and S2). Our data suggest that the integrity of the core 20S subunit of the proteasome may have an important role in the maintenance of PLM process morphology.

Bottom Line: Our results show that the expression of misfolded proteins in neurodegenerative disease such as Huntington's disease modifies the morphological remodeling that is normally associated with neuronal aging.Our results also show that morphological remodeling of healthy neurons during aging can be regulated by the UPS and other proteostasis pathways.Collectively, our data highlight a model in which morphological remodeling during neuronal aging is strongly affected by disrupted proteostasis and expression of disease-associated, misfolded proteins such as human polyQ-Htt species.

View Article: PubMed Central - PubMed

Affiliation: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA.

ABSTRACT

Understanding cellular outcomes, such as neuronal remodeling, that are common to both healthy and diseased aging brains is essential to the development of successful brain aging strategies. Here, we used Caenorhabdits elegans to investigate how the expression of proteotoxic triggers, such as polyglutamine (polyQ)-expanded huntingtin and silencing of proteostasis regulators, such as the ubiquitin-proteasome system (UPS) and protein clearance components, may impact the morphological remodeling of individual neurons as animals age. We examined the effects of disrupted proteostasis on the integrity of neuronal cytoarchitecture by imaging a transgenic C. elegans strain in which touch receptor neurons express the first 57 amino acids of the human huntingtin (Htt) gene with expanded polyQs (128Q) and by using neuron-targeted RNA interference in adult wild-type neurons to knockdown genes encoding proteins involved in proteostasis. We found that proteostatic challenges conferred by polyQ-expanded Htt and knockdown of specific genes involved in protein homeostasis can lead to morphological changes that are restricted to specific domains of specific neurons. The age-associated branching of PLM neurons is suppressed by N-ter polyQ-expanded Htt expression, whereas ALM neurons with polyQ-expanded Htt accumulate extended outgrowths and other soma abnormalities. Furthermore, knockdown of genes important for ubiquitin-mediated degradation, lysosomal function, and autophagy modulated these age-related morphological changes in otherwise normal neurons. Our results show that the expression of misfolded proteins in neurodegenerative disease such as Huntington's disease modifies the morphological remodeling that is normally associated with neuronal aging. Our results also show that morphological remodeling of healthy neurons during aging can be regulated by the UPS and other proteostasis pathways. Collectively, our data highlight a model in which morphological remodeling during neuronal aging is strongly affected by disrupted proteostasis and expression of disease-associated, misfolded proteins such as human polyQ-Htt species.

No MeSH data available.


Related in: MedlinePlus