Scientific Research Report

Background Introduction

For a long time, aging has been considered an irreversible process. However, recent research suggests that aging is a biological process that can be regulated. Various interventions have been shown to delay or even reverse certain characteristics of aging. Partial reprogramming is a method that reverses somatic cells into a state similar to embryonic stem cells by transiently expressing reprogramming transcription factors such as Oct4, Sox2, Klf4, and c-Myc (‘OSKM’). This method has been proven to erase many aging characteristics in vitro. However, in vivo application of complete reprogramming can lead to loss of cell identity and increased risk of tumorigenesis. Therefore, a more promising approach is to achieve “partial reprogramming” by controlling the expression of reprogramming factors. Partial reprogramming has shown improvements in mouse tissue functions in several studies, but its effects on the aging brain are still largely unknown.

Source of the Paper

This study was collaboratively conducted by scientists from Stanford University’s Department of Genetics, Department of Biology, Department of Biomedical Data Science, Wu Tsai Neurosciences Institute, and Glenn Center for the Biology of Aging. The main authors include Lucy Xu, Julliana Ramirez-Matias, Max Hauptschein, Eric D. Sun, Judith C. Lunger, Matthew T. Buckley, and Anne Brunet. The paper was published in the April 2024 issue of Nature Aging (volume 4, 546-567) and can be accessed online at DOI:10.1038/s43587-024-00594-3.

Research Process

Research Subjects and Methods

The study utilized single-cell transcriptomics to systematically investigate how partial reprogramming affects the subventricular zone (SVZ) neurogenic region of the aging mouse brain. Using a genetically engineered mouse model, i.e., the ioskm mouse, where the four reprogramming factors (Oct4, Sox2, Klf4, c-Myc) can be induced and expressed throughout the body.

Aged ioskm mice were divided into two groups for partial reprogramming treatment. The treatment scheme involved providing 2 days of tetracycline drinking water, followed by 5 days without the drug, repeated three times. Subsequently, single-cell RNA sequencing (scRNA-seq) was performed on cells from the SVZ region.

Data Collection and Processing

During the analysis, researchers collected SVZ tissue samples from partially reprogrammed aged mice (one group aged 18-20 months and another aged 24-26 months), untreated aged mice, and untreated young mice. scRNA-seq was performed, and dimensional reduction and clustering methods (such as UMAP and Louvain clustering) identified key cell types including neural stem cells (NSCs), activated NSCs, neural precursor cells (NPCs), and neuroblasts.

Experimental Procedures and Analysis

Various experimental methods including immunostaining and machine learning models were employed to validate the effects of partial reprogramming on the proportions of cells in the SVZ region. The findings indicated that the proportion of neuroblasts and their precursor cells significantly declined with age in aged mice, but partial reprogramming could restore these proportions.

Research Results

1. Partial reprogramming significantly increased the proportion of neuroblasts in the SVZ region of aged mice, restoring it to younger mouse levels.
2. This effect was observed in whole-body aged mice subjected to partial reprogramming and mice specifically reprogrammed in the SVZ region.
3. A machine learning model trained on cell type proportions showed that partial reprogramming could decrease the predicted age by approximately 2.7 months.
4. Further transcriptome analysis revealed that partial reprogramming could reverse several aging-related molecular characteristics, such as RNA processing and cell adhesion pathways, across various cell types.

Research Conclusions

This study demonstrates that partial reprogramming can exert direct and inherent beneficial effects on the SVZ region of aged mice, increasing the proportion of neuroblasts and enhancing neurogenesis capabilities. This could provide new strategies for restoring neurogenic region function and combating brain decline in aging individuals.

Further findings indicate that partial reprogramming does not generate new cell types (such as embryonic stem cells) but enhances the function of existing cells, providing a degree of assurance for its safety in vivo. Additionally, partial reprogramming showed significant autonomous effects in aged NSC experiments in vitro.

Research Highlights

1. Novelty: Utilizing single-cell transcriptomics to systematically reveal the impact of partial reprogramming on the SVZ region of aged mice.
2. Practicality: Partial reprogramming not only increased the proportion of neuroblasts but also improved neurogenesis ability, showing potential application value.
3. Method Innovation: This is the first study to confirm the restorative effects of partial reprogramming on cell proportions and functions in the aged brain SVZ region, proposing a machine learning prediction model for evaluating aging and reprogramming effects.

Research Significance and Prospects

The findings from this study lay the foundation for the application of partial reprogramming in neuroscience, potentially offering new intervention strategies for age-related brain function decline. Future research could explore the durability of reprogramming effects, its impact on other brain regions and cell types, and whether this intervention can improve behavioral functions in aged individuals. These aspects will provide critical references for optimizing reprogramming strategies and developing more effective anti-aging therapies.