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Published on: June 14, 2020
Basic Science and Pathogenesis
Stefan Wendt1, Ada J Lin1, Sarah N Ebert1
1University of British Columbia, Vancouver, BC, Canada.
Background:
Alzheimer's disease is characterized by the accumulation of Aβ plaques in the brain, but the pathways leading from early Aβ deposits to eventual neurodegeneration are not fully understood. The specific role of microglia in AD is controversial, with microglial activation to be protective or detrimental depending on disease progression. We developed a 3D human iPSC-derived neurosphere model to better characterize how microglia respond to Aβ pathology.
Method:
Neurospheres were grown from iPSC-derived neuronal progenitor cells and cultured for 60 days. iPSC-derived microglia were added separately to assess their functional impact. Continuous synthetic oligomeric Aβ treatment was used to model amyloidosis. Genetically encoded sensors roGFP1 and GCaMP6f allowed to monitor neuronal oxidative stress and calcium activity, respectively. Single nuclei RNA sequencing (snRNA-seq) was performed to examine transcriptomic differences induced by Aβ and microglia.
Result:
Neurospheres grew to consist of a complex network of healthy mature neurons and astrocytes. The added microglia readily infiltrate the 3D tissue. Chronic Aβ treatment resulted in the formation of plaque-like aggregates and subsequently led to severe oxidative stress and loss of neuronal activity. Microglia were able to prevent these neurotoxic effects in neurospheres that received mild 3 weeks Aβ treatment, but failed to do so after severe 5 weeks treatment. snRNA-seq revealed that, after 3 weeks treatment, microglia induced upregulation of genes linked to oxidative regulation in astrocytes. After 5 week treatment, microglia more noticeably drove the expression of many AD-associated genes, such as APOE, CLU, and FTL, in astrocytes and neurons. Microglia also appear to have enhanced ability for Aβ clearance after treatment with anti-Aβ antibodies.
Conclusion:
We developed a human 3D neurosphere model to study microglial responses to Aβ pathology. In this model, microglia acquire a neuroprotective phenotype which may be enhanced by anti-Aβ antibodies. Microglia are essential for driving the transcriptomic profile linked to AD after severe Aβ treatment. By mimicking critical AD pathological features, this model offers a platform to identify therapeutic targets with translational relevance.
Insights
Microglia can protect against early Alzheimer's disease (AD) pathology in a 3D human model, but their effectiveness diminishes with severe amyloid-beta (Aβ) exposure. This model aids in identifying new therapeutic targets for AD.
Area of Science:
- Neuroscience
- Cell Biology
- Genomics
Background:
- Alzheimer's disease (AD) involves amyloid-beta (Aβ) plaques, but the role of microglia in neurodegeneration remains unclear.
- Microglial function in AD can be either protective or detrimental depending on disease stage.
Purpose of the Study:
- To characterize microglial responses to Aβ pathology using a novel 3D human induced pluripotent stem cell (iPSC)-derived neurosphere model.
- To investigate the impact of microglia on neuronal health and gene expression in the context of Aβ-induced amyloidosis.
Main Methods:
- Developed a 60-day 3D neurosphere model using iPSC-derived neurons and microglia.
- Induced amyloidosis with continuous synthetic oligomeric Aβ treatment.
- Monitored neuronal oxidative stress and calcium activity using roGFP1 and GCaMP6f sensors.
- Analyzed transcriptomic changes via single-nuclei RNA sequencing (snRNA-seq).
Main Results:
- Microglia infiltrated neurospheres and prevented neurotoxicity in mild Aβ exposure (3 weeks).
- Microglia failed to prevent neurotoxicity in severe Aβ exposure (5 weeks).
- snRNA-seq revealed microglia modulated oxidative stress genes and AD-associated genes (APOE, CLU, FTL) in astrocytes and neurons.
- Microglia showed enhanced Aβ clearance after anti-Aβ antibody treatment.
Conclusions:
- The 3D neurosphere model effectively mimics key Alzheimer's disease pathological features.
- Microglia exhibit neuroprotective properties in this model, potentially enhanced by antibody treatment.
- Microglia are critical in driving AD-associated transcriptomic changes under severe Aβ insult, highlighting their complex role and therapeutic potential.
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