Amyloid β induces hormetic-like effects through major stress pathways in a C. elegans model of Alzheimer's Disease

Abstract

Amyloid β (Aβ) is a peptide known for its characteristic aggregates in Alzheimer's Disease and its ability to induce a wide range of detrimental effects in various model systems. However, Aβ has also been shown to induce some beneficial effects, such as antimicrobial properties against pathogens. In this work, we explore the influence of Aβ in stress resistance in a C. elegans model of Alzheimer's Disease. We found that C. elegans that express human Aβ exhibit increased resistance to heat and anoxia, but not to oxidative stress. This beneficial effect of Aβ was driven from Aβ in neurons, where the level of induction of Aβ expression correlated with stress resistance levels. Transcriptomic analysis revealed that this selective stress resistance was mediated by the Heat Shock Protein (HSPs) family of genes. Furthermore, neuropeptide signaling was necessary for Aβ to induce stress resistance, suggesting neuroendocrine signaling plays a major role in activating organismal stress response pathways. These results highlight the potential beneficial role of Aβ in cellular function, as well as its complex effects on cellular and organismal physiology that must be considered when using C. elegans as a model for Alzheimer's Disease.

Fig 1. Aβ provides selective resistance to severe heat and hypoxic stress, but not paraquat-induced oxidative stress.

(A) Overview of experimental setup. Animals were age-synchronized to L4 larvae and then allowed to grow for another 24 hrs. before exposure to stressors. (B) Survival rate after 24 hrs. exposure to 50mM paraquat stress. (C) Survival rate after 4 hrs. 37 °C heat stress exposure and overnight recovery at 20 °C. (D) Survival rate after 48 hrs. anoxia (< 0.1% O₂) exposure and overnight recovery. WT is wild-type N2 Bristol, Aβ+ is JKM2, Aβ- is JKM3. N = 9 (12 for anoxia stress) replicates per strain. Each dot represents a replicate of approx. 30 worms. Statistical analysis was performed using ANOVA. * is p-value < 0.05, ** is p-value < 0.01, *** is p-value < 0.005.

Fig 2. Aβ-induced heat stress resistance is dependent on Aβ expression levels and neuronal localization.

(A) Overview of experimental setup. Temperature upshift to 25 °C was staggered such that stress exposure occurred at the same time for each condition. (B) Survival rate after 5.5 hr. at 37 °C heat stress exposure and overnight recovery at 20 °C. Time at 25 °C correlates to levels of Aβ in the neurons in nAβ strain. (C) Survival rate after 5.5 hr. 37 °C heat stress exposure and overnight recovery at 20 °C. Time at 25 °C correlates to levels of Aβ in the neurons in nAβ strain and in muscles in mAβ strain. In C, statistical values represent whether each strain is affected by temperature, comparisons between strains are not made. WT is wild-type N2 Bristol, nAβ is CL2355, mAβ is CL4176. N=9 replicates per condition. Each dot represents a replicate of approx. 30 worms. Statistical analysis was performed using two-sample t-test and two-way ANOVA. * is p-value < 0.05, ** is p-value < 0.01, *** is p-value < 0.005.

Fig 3. Heat stress resistance is partially replicated with other neuronally expressed proteins and is not eliminated with NAC treatment.

(A) Survival rate after 4 hr. 37 °C heat stress exposure and overnight 20 °C recovery in pan-neuronal GFP strain. (B) Survival rate after 4 hr. 37 °C heat stress exposure and overnight recovery in worms grown on control and 5 mM NAC plates for 24 hrs. before heat stress exposure. WT is wild-type N2 Bristol, nGFP is OH438, Aβ+ is JKM2, Aβ- is JKM3. N=9 replicates per condition. Each dot represents a replicate of approx. 30 worms. Statistical analysis was performed using two-sample t-test and two-way ANOVA. * is p-value < 0.05, ** is p-value < 0.01, *** is p-value < 0.005.

Fig 4. nCounter expression analysis indicates several resistance genes upregulated in both stressed and unstressed worms and RNAi suppression suggests resistance is communicated through neuropeptide signaling. (A-C) nCounter analysis on unstressed (A), heat stressed (B), and hypoxic stressed (C) worms. Genes are grouped by type and box color indicates expression changes. 3 biological replicates were pooled per sample. (D) Survival rate after 4 hr. 37 °C heat stress exposure in RNAi suppressed worms. RNAi control was HT115 with empty vector. WT is wild-type N2 Bristol, Aβ+ is JKM2, Aβ- is JKM3, rrf-3(-) is RNAi-sensitive strain NL2099, Aβ+rrf-3(-) is ASM35, a cross between JKM2 and NL2099. N=9 replicates per condition. Each dot represents a replicate of approx. 30 worms. Statistical analysis was performed using two-sample t-test and two-way ANOVA. * is p-value < 0.05, ** is p-value < 0.01, *** is p-value < 0.005.