Path 4: Epigenetic Alterations

Rationale: Aging as an epigenetic “drift” or loss of cellular memory. This path views aging as a progressive distortion of the epigenome – the chemical modifications on DNA and histones that regulate gene expression. Over time, cells lose their youthful gene expression patterns, leading to dysfunction. Epigenetic changes are potentially reversible, suggesting we might “reprogram” old cells to a younger state. Breakthroughs in iPSC technology show even very old cells can be reset to an embryonic-like state by Yamanaka factors.

Prerequisites: Genetics and epigenetics (chromatin structure, methylation, histone code), regenerative biology.

Dependencies: Links with Path 1 (evolutionary: epigenetic aging could be the “information theory” concept) and interacts with many other paths (DNA damage can cause epigenetic changes, and vice versa).

Signs of Progress: Safely reprogramming cells in vivo to a younger state without causing cancer. A treatment that restores an old organ’s gene expression to a youthful profile. Slowing the ticking of the epigenetic clock. Partial reprogramming studies (Ocampo 2016 in progeroid mice, Lu 2020 restoring vision in old mice).

BC4.1: Epigenetics Fundamentals

Scope: Build a solid foundation in what epigenetics is: DNA methylation, histone modifications, and chromatin remodeling.

• Allis, C. & Jenuwein, T. Epigenetics (Second Edition). Cold Spring Harbor Press, 2015. – Introductory chapter explains concepts in straightforward language.
• Feinberg, A. “The key role of epigenetics in human disease prevention and mitigation.” N Engl J Med, 2018. – Explains epigenetic mechanisms very clearly for a general audience.
• Jaenisch, R. & Bird, A. “Epigenetic regulation of gene expression.” Nat. Genet., 2003. – Classic review explaining DNA methylation and histone code with minimal jargon.

BC4.2: Epigenetic Drift and Clocks in Aging

Scope: Investigate how the epigenome changes with age. Introduce Horvath’s epigenetic clock.

• Horvath, Steve. “DNA methylation age of human tissues and cell types.” Genome Biol., 2013. – Landmark paper defining the multi-tissue epigenetic clock.
• Johnson, A.A. et al. “DNA methylation biomarkers of aging: paradigm and promises.” Genome Biol., 2017. – Accessible review on epigenetic clocks and using them to test interventions.
• Pal, S. & Tyler, J.K. “Epigenetics and aging.” Sci. Adv., 2016. – Concise overview of known epigenetic changes in aging.

BC4.3: Mechanisms Linking Epigenetics to Cell Function Decline

Scope: How do changes in epigenetic landscape cause aging phenotypes? Cover transposable element derepression, inappropriate embryonic gene expression, and feedback loops with DNA damage.

• López-Otín, C. et al. “Metabolic control of longevity through epigenetic remodeling.” Cell, 2016. – Ties nutrient sensing to epigenetic changes affecting aging.
• Sedivy, J.M. et al. “Epigenetic senescence: aging through chromatin.” Trends Cell Biol., 2008. – Senescent cells have unique chromatin states.
• Sinclair, David & LaPlante, M. Lifespan: Why We Age and Why We Don’t Have To. Atria Books, 2019. – Popular science book explaining the “Information Theory of Aging” in simple terms.

BC4.4: Epigenetic Reprogramming and Age Reversal

Scope: Yamanaka factors (OSKM) to reset epigenetic age. Partial reprogramming. Cover Ocampo 2016 and Lu 2020.

• Ocampo, A. et al. “In Vivo Amelioration of Age-Associated Hallmarks by Partial Reprogramming.” Cell, 2016. – Seminal proof that partial reprogramming can be beneficial in progeroid mice.
• Lu, Y. et al. “Reprogramming to recover youthful epigenetic information and restore vision.” Nature, 2020. – Restored optic nerve regeneration and vision in old mice by expressing OSK.
• Sinha, M. et al. “The programming and reprogramming of cellular age.” Nat. Rev. Mol. Cell Biol., 2022. – Review focused on cutting-edge reprogramming approaches.

Bibliography (Path 4)

• Horvath, Steve. “DNA Methylation Age of Human Tissues and Cell Types.” Genome Biol. 14(10): 3156, 2013. (Unveiled the epigenetic clock)
• Sen, Pranay et al. “Epigenetic Mechanisms of Longevity and Aging.” Cell 184(9): 2684–2704, 2021. (Current review of how epigenetic changes contribute to aging)
• Cox, Lauren S. & Gordon L. Mattison. “Epigenetics in Aging and Development.” Developmental Biology 447(1): 1–16, 2019. (Developmental epigenetic programs become dysregulated with age)
• Ocampo, Alejandro et al. “In Vivo Amelioration of Age-Associated Hallmarks by Partial Reprogramming.” Cell 167(7): 1719–1733, 2016. (Landmark study demonstrating cyclic OSKM in progeroid mice)
• Sinclair, David A. et al. “Epigenetic Reprogramming Reverses Aging in Tissues.” Cell 184(12): 310–312, 2021. (Perspective summarizing recent advances in epigenetic rejuvenation)
• Sen, Pranay et al. “Epigenetic Mechanisms of Longevity and Aging.” Cell 166(4): 822–839, 2016. (Earlier review of epigenetic aging mechanisms)