Many have proposed using the 9 hallmarks of aging as a roadmap for extending healthspan and lifespan. Encouragingly, this is actually happening.
As a reminder, these are the 9 hallmarks [1]:
- Genomic instability
- Telomere attrition
- Epigenetic alterations
- Loss of proteostasis
- Deregulated nutrient sensing
- Mitochondrial dysfunction
- Cellular senescence
- Stem cell exhaustion
- Altered intercellular communication
The hallmarks are believed to be molecular drivers of aging. Thus, these are compelling targets. The hallmarks have held up pretty well since publication nearly 10 years ago now in 2013. You might argue that several of these are more important than others (e.g. loss of proteostasis (#4) seems especially damaging). You can also argue that these are not mutually exclusive or collectively exhaustive. They are deeply interwined. For example, cellular senescence (#7) leads to the senescence-associated secretory phenotype (SASP) which alters intercellular communication (#9). You might also argue that any of genomic instability (#1), epigenetic alterations (#3) or loss of proteostasis (#4) is an upstream cause of senescence. Still, slowing or reversing these hallmarks are likely to slow aging.
Researchers are learning how to reverse these hallmarks, both individually and in combination. For example, we have developed senolytics that remove senescent cells and show extended lifespan in mice [2], and human trials are underway [3]. One exciting recent paper combined partial reprogramming with senolytics in Drosophila (fruit flies) [4]. Each therapy on its own led to increased lifespan. Combining the two led to even larger increased in lifespan and the survival curve. The combined therapies led to improved stem cell proliferation, addressing hallmark 7, as well as reducing cellular senescence, addressing hallmark 7.
Researchers are also developing biomarkers for these hallmarks. A 2020 paper proposes a specific biomarker for each of the hallmarks of aging [5]. If we can measure the molecular basis of aging as it progresses, we can more directly develop therapies for model organisms and humans. These kinds of measurements could become successful consumer products for the longevity nerds of the world, similar to how biological age measurements have had direct-to-consumer commercial success.
One of the reasons I write this blog is to explore how to guide a long-term research program for aging research. Targeting the hallmarks of aging is one reasonable path
References:
[1] Carlos López-Otín, Maria A. Blasco, Linda Partridge, Manuel Serrano, Guido Kroemer. The Hallmarks of Aging. Cell,Volume 153, Issue 6, 2013, pp. 1194-1217, https://doi.org/10.1016/j.cell.2013.05.039
[2] Xu, M., Pirtskhalava, T., Farr, J.N. et al. Senolytics improve physical function and increase lifespan in old age. Nat Med 24, 1246–1256 (2018). https://doi.org/10.1038/s41591-018-0092-9
[3] Search for "senolytics" at ClinicalTrials.gov. U.S. National Library of Medicine. Accessed Nov 13, 2022. URL: https://clinicaltrials.gov/ct2/results?cond=&term=senolytics&cntry=&state=&city=&dist=
[4] Kaur P, Otgonbaatar A, Ramamoorthy A, Chua EHZ, Harmston N, Gruber J, Tolwinski NS. Combining stem cell rejuvenation and senescence targeting to synergistically extend lifespan. Aging (Albany NY). 2022 Oct 25; 14:8270-8291. https://doi.org/10.18632/aging.204347
[5] Guerville, F., De Souto Barreto, P., Ader, I. et al. Revisiting the Hallmarks of Aging to Identify Markers of Biological Age. J Prev Alzheimers Dis 7, 56–64 (2020). https://doi.org/10.14283/jpad.2019.50