Proteostasis and Lysosomal Repair Deficits in Transdifferentiated Neurons of Alzheimer’s Disease

Neurology Cell Biology Life Sciences Medicine
Alzheimer’s Disease Transdifferentiated Neurons Proteostasis Lysosomal Repair Ageing Inflammation Cell Death

Academic Background

Alzheimer’s disease (AD) is the most common neurodegenerative disorder among the elderly, characterized by the pathological features of amyloid-beta (Aβ) deposits and hyperphosphorylated tau protein. Although aging is the most prominent risk factor for AD, the cellular mechanisms linking the decline in neuronal proteostasis to the aberrant protein deposits in the brains of AD patients remain unclear. To address this issue, researchers developed a neuronal model derived from the transdifferentiation of human dermal fibroblasts (transdifferentiated neurons, tneurons), which retains aging hallmarks and exhibits AD-linked vulnerabilities.

Source of the Paper

This paper was co-authored by Ching-Chieh Chou, Ryan Vest, Miguel A. Prado, and other scientists from institutions such as Stanford University and Harvard University. It was published in Nature Cell Biology in April 2025, titled “Proteostasis and lysosomal repair deficits in transdifferentiated neurons of Alzheimer’s disease.” The study aims to reveal the early events of lysosomal dysfunction and proteostasis disruption in aging and AD through the tneurons model.

Research Process and Results

1. Establishment of the tneurons Model and Validation of Aging and AD-Related Phenotypes

Researchers used transcription factors (Brn2, Ascl1, Myt1l, and Ngn2) and small molecules to transdifferentiate human dermal fibroblasts into cortical neurons. Fibroblasts were collected from healthy young (average age 25.6 years), healthy aged (average age 70.3 years), and AD patients (average age 70.4 years). Through immunofluorescence and proteomic analyses, researchers found that fibroblasts from aged and AD donors exhibited significant aging characteristics, such as DNA damage and histone modifications (e.g., H3K9me3 and H4K16ac).

In the transdifferentiated tneurons, researchers observed proteostasis deficits under basal conditions in aged and AD tneurons, including the accumulation of ubiquitin-positive (ub+) proteins and the autophagy receptor p62/SQSTM1. Additionally, deposits of Aβ42 and phosphorylated tau (ptau) were significantly increased in AD tneurons, resembling the pathological features observed in the brains of AD patients.

2. Proteomic Analysis Reveals Lysosomal Dysfunction in Aging and AD

Quantitative proteomic analysis was performed to compare the protein expression profiles of young, aged, and AD tneurons. The results showed that aging and AD significantly impacted proteostasis and organelle homeostasis, particularly components of the endosome-lysosome pathway. The expression of lysosome-related proteins (e.g., CLU, CTSC, and TMEM175) was markedly downregulated in AD tneurons, indicating severe lysosomal dysfunction in AD.

3. Defects in Lysosomal Damage and Repair Mechanisms

Transmission electron microscopy (TEM) was used to observe the ultrastructure of lysosomes in tneurons, revealing enlarged lysosomes with abundant electron-dense granules in aged and AD tneurons. Further studies showed that the baseline levels of lysosomal damage markers (e.g., ESCRT-III CHMP2B and galectin-3) were significantly increased in aged and AD tneurons, suggesting constitutive lysosomal damage in these cells.

To assess lysosomal repair kinetics, researchers treated tneurons with the lysosomotropic agent L-leucyl-L-leucine methyl ester (LLOME) and monitored the spatiotemporal changes of the ESCRT-0 component HGS. The results showed that lysosomal repair efficiency was significantly impaired in AD tneurons, with a repair half-life (t1/2) extended to 3.6 hours, compared to 1.1 hours in young tneurons.

4. Interaction Between Lysosomal Damage and Other Proteostasis Pathways

Researchers also found that lysosomal damage affects other proteostasis pathways, such as the localization of the RNA-binding protein TDP-43 and the molecular chaperone HSP70. In AD tneurons, TDP-43 and HSP70 were recruited to damaged lysosomes, indicating that lysosomal damage may exacerbate neuronal pathology by affecting other proteostasis processes.

5. Improvement of AD Pathology Through Lysosomal Function Rescue

To validate the central role of lysosomal dysfunction in AD pathology, researchers used several small molecules to ameliorate lysosomal function. Among them, C381 significantly reduced Aβ42 deposits in AD tneurons and decreased the secretion of inflammatory cytokines (e.g., IL-6 and CCL2). Additionally, C381 restored lysosomal acidification, enhanced lysosomal enzyme activity, and protected neurons from lysosomal damage-induced cell death.

Conclusion and Significance

This study, through the tneurons model, revealed the early events of lysosomal dysfunction and proteostasis disruption in aging and AD, demonstrating that lysosomal repair defects are key drivers of AD pathology. The findings not only provide new insights into the pathogenesis of AD but also suggest potential therapeutic strategies for AD by improving lysosomal function.

Research Highlights

  1. Innovative Model: The tneurons model retains aging hallmarks, offering a unique tool for studying the cellular mechanisms of aging and AD.
  2. Lysosomal Dysfunction: The study systematically revealed, for the first time, the defects in lysosomal damage and repair mechanisms in AD and elucidated their role in proteostasis disruption.
  3. Therapeutic Potential: The study demonstrated that improving lysosomal function through small molecules can effectively reduce Aβ deposits and inflammatory responses, providing a new direction for AD treatment.

Additional Valuable Information

The limitations of this study include the lack of glial cell support in the tneurons model and the short-term culture conditions, which may not fully replicate the complex tissue organization and long-term aging processes in the human brain. Future research could further explore the role of other lysosomal quality control (LQC) pathways in AD and validate these findings in broader AD patient populations.

This study provides important insights into the early cellular biological processes of AD and lays the foundation for developing early intervention strategies for AD.