Intermittent Clearance of High p21-Expressing Cells Extends Lifespan and Delivers Sustained Health Benefits

Research Background

With the significant extension of human lifespan, the global elderly population is rapidly increasing. Elderly individuals often face decreased functionality and various chronic diseases in their later years, such as cardiovascular diseases and cancer, as well as physical decline and loss of independence. These issues lead to a decline in quality of life and place a significant social, emotional, and economic burden on families and society. Currently, there is a gap of about 9 years between lifespan and “healthspan.” Increasing lifespan does not necessarily mean an extension of healthspan. How to extend healthspan while maintaining good physical function and reducing the occurrence of diseases has long been the goal of aging research.

Research Origin

This study was conducted by researchers Binsheng Wang, Lichao Wang, Nathan S. Gasek, and others from multiple institutions such as the Center on Aging, the Department of Genetics and Genome Sciences, and the Department of Public Health Sciences at the University of Connecticut Health Center, USA. The paper was published in the journal “Cell Metabolism” on August 6, 2024. The corresponding author is Ming Xu, with the email mixu@uchc.edu.

Research Process

Workflow

The core of the research is to extend the lifespan and improve the health status of mice by intermittently clearing high p21-expressing cells. The specific process is as follows:

1. Mouse Model Construction: Using genetic engineering to construct a p21-cre mouse model, which includes a bi-cistronic transcript driven by a p21 promoter, containing a cre fused to a tamoxifen-inducible estrogen receptor (ER) element along with enhanced GFP.
2. Mouse Handling and Tracking: Conducting twice-monthly tamoxifen treatments on 20-month-old p21-cre/+; +/+ (P) mice and p21-cre/+; dta/+ (P/D) mice to clear high p21-expressing cells in P/D mice. Their health and physical functions were tracked and evaluated until natural death.
3. Assessment of Physical Function and Health Status: Monthly evaluation of the physical functions and health status of the mice through methods such as grip strength tests, maximal walking speed tests, and frailty index scoring.

Cellular Treatment and Experimental Methods

1. Cell Clearance Technique: Crossing p21-cre mice with floxed dta mice, utilizing tamoxifen treatment to achieve clearance of high p21-expressing cells.
2. Genomic Sequencing: Conducting single-cell RNA sequencing (scRNA-seq) and bulk RNA sequencing (bulk RNA-seq) on different tissues to comprehensively understand the transcriptomic characteristics of high p21-expressing cells and their response after clearance in aged mice.
3. Physiological Function Testing: Regular grip strength, maximal walking speed, and frailty index testing to assess physical and health status. Echocardiography was used to evaluate cardiac function, glucose tolerance tests and insulin tolerance tests to assess metabolic function, and liver function tests to evaluate liver health.

Research Results

Intervention Effects

1. Extended Lifespan: It was found that regular clearance of high p21-expressing cells significantly extended the median lifespan of P/D mice by 9% (79 days) compared to P mice, with a 27% increase in overall survival and reduced mortality risk.
2. Improved Health Status: After the removal of high p21-expressing cells, P/D mice showed significant improvement in physical and health status, with grip strength and maximal walking speed being significantly better than P mice at various ages.
3. Extended Healthspan: Standardized analysis of the remaining life years showed that P/D mice experienced widespread improvements in physical function throughout the post-treatment survival period, further demonstrating that intermittent clearance of high p21-expressing cells indeed extended the healthspan of mice.
4. Improved Organ Function: There was a significant improvement in cardiac, metabolic, and liver functions in P/D mice, indicating enhancement of organ health.

Cellular and Molecular Mechanisms

1. Cellular Heterogeneity: scRNA-seq analysis revealed heterogeneity in high p21-expressing cells across different tissues, present in a wide range of cell types, especially in aged heart, liver, and adipose tissue.
2. Expression of Inflammation-Related Genes: High p21-expressing cells exhibited a conserved pro-inflammatory gene profile, reflecting their key role in inflammation and aging.
3. Transcriptomic Analysis: Bulk RNA-seq showed that intermittent clearance of high p21-expressing cells reduced the expression of inflammation-related genomes in the liver, adipose, and muscle, and significantly improved metabolic function and cardiac regenerative capacity in aged mice.

Conclusion and Research Significance

This study demonstrated that intermittent clearance of high p21-expressing cells helps extend the lifespan and healthspan of mice. This intermittent clearance significantly reduced inflammation levels and restored aging-related transcriptomic features across multiple organs. The study identifies high p21-expressing cells as potential therapeutic targets in aging and associated health issues, providing new directions for developing anti-aging drugs.

Research Highlights

• Key Findings: The clearance of high p21-expressing cells effectively extended lifespan and improved health status.
• Innovative Methods: Successfully developed a new genetically edited mouse model to accurately monitor and clear high p21-expressing cells.
• Potential Practical Applications: Provides potential therapeutic targets, laying the groundwork for developing therapies that promote healthy aging.

Future Research Directions

Despite the significant achievements of this study, several issues merit further research. For instance, the specific mechanisms remain unclear, necessitating further exploration of the roles of different cell types within high p21-expressing cells in aging and inflammation. Additionally, the potential role of low p21-expressing cells in aging and their mechanisms warrant further study. In-depth research on these issues will aid in comprehensively understanding the complexity of cellular aging and advancing the development of related therapies.