Primary Hallmarks of Aging: Five Damage-Associated Pathways

What Are the Primary Hallmarks of Aging?

The Hallmarks of Aging framework groups age-associated biological processes into primary, antagonistic and integrative categories. In the updated 2023 framework, the five primary hallmarks are genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis and disabled macroautophagy.

These primary hallmarks describe forms of molecular and cellular damage that progressively accumulate with age. They are considered upstream damage-associated processes within the framework, while all of the hallmarks remain interconnected.

The original 2013 Hallmarks of Aging review described four primary hallmarks. The 2023 update expanded the overall framework to 12 hallmarks and recognized disabled macroautophagy as a distinct hallmark.

The Five Primary Hallmarks of Aging

(1) Genomic Instability – Changes & Damage Affecting the Genome

DNA is continually exposed to internal and environmental sources of damage. Aging research examines how accumulated DNA damage, mutations, chromosome abnormalities and changes in DNA-repair processes relate to genomic stability over time.

(2) Telomere Attrition – Changes at Chromosome Ends

Telomeres help protect the ends of chromosomes. Telomere shortening and dysfunction are studied as age-associated processes that can affect cellular replication, genomic stability and cellular senescence.

(3) Epigenetic Alterations – Changes in Gene Regulation

Epigenetic regulation includes DNA methylation, histone modifications and chromatin organization. These regulatory patterns change with age and are studied for their relationships with cellular identity, function and age-associated biology.

(4) Loss of Proteostasis – Declining Protein Quality Control

Proteostasis describes the systems that help proteins fold correctly, remain functional and be removed when damaged. Aging is associated with changes in these quality-control systems and with greater accumulation of damaged or misfolded proteins.

(5) Disabled Macroautophagy – Impaired Cellular Recycling

Macroautophagy is a cellular recycling process that helps remove damaged proteins, macromolecules and organelles. The 2023 Hallmarks of Aging framework recognizes disabled macroautophagy as a distinct hallmark associated with the accumulation of cellular damage during aging.

How Researchers Study the Primary Hallmarks

Researchers investigate the primary hallmarks through experimental models, observational studies and human research examining biological pathways such as:

⚬ Genome maintenance – DNA damage and repair pathways
⚬ Telomere biology – Telomere length, protection and dysfunction
⚬ Epigenetic regulation – DNA methylation, chromatin and gene regulation
⚬ Proteostasis – Protein folding, quality control and degradation
⚬ Macroautophagy – Cellular recycling and removal of damaged components

Experimental interventions can influence some of these pathways, particularly in laboratory and animal models. Changes in a hallmark-related pathway or biomarker do not by themselves establish that an intervention slows human aging or extends human lifespan.

How the Primary Hallmarks Fit into the Aging Framework

The original Hallmarks of Aging framework proposed a hierarchy in which primary hallmarks represent forms of accumulating cellular damage. Antagonistic hallmarks describe responses to damage that may be beneficial in some contexts but become detrimental when excessive or chronic, while integrative hallmarks reflect broader effects on tissue homeostasis and function.

The 2023 framework retains this general hierarchy while expanding the total number of hallmarks to 12. Importantly, mitochondrial dysfunction is grouped among the antagonistic hallmarks rather than the primary hallmarks. Disabled macroautophagy is included in the expanded framework as a distinct damage-associated hallmark.

Because these pathways interact extensively, the framework is best understood as a research model for organizing aging biology rather than as proof that targeting a single pathway will prevent, stop or reverse human aging. Continue with our overview of the antagonistic hallmarks or review the complete 12 Hallmarks of Aging.

Continue Exploring the Primary Hallmarks

The primary hallmarks provide a useful framework for understanding several forms of molecular and cellular damage associated with aging. Continue exploring how these pathways interact with the antagonistic and integrative hallmarks throughout the aging process.