A new, emerging paradigm of longevity research focuses on cellular therapies rather than specific metabolic interventions. Cellular epigenetic reprogramming (CER) has been shown to be effective in mouse models of aging damage and injury by regenerating axons in the optic nerve, restoring vision¹. CER relies on the introduction of transcription factors Oct3/4, Sox2, and KLF4 into cells using an adeno-associated viral (AAV) vector, enabling them to revert to youthful epigenetic methylation patterns and promoting cellular regeneration. However, since the viral vector can elicit a deleterious immune response², testing CER in vivo is currently limited to immunologically-isolated tissues and organs. To overcome this constraint of in vivo studies, testing CER therapies in organoids would facilitate their diversification to other tissue types.

Organoids are small, stem cell-derived, three-dimensional tissue cultures capable of simulating organs in vitro. Currently used in high-throughput drug screening assays³, I believe they can be similarly used to test CER therapies. Not only can organoids provide in vitro models of injury or damage in diverse organs and tissues⁴, but they can also model immune function within those tissues⁵. Therefore, organoids can provide an ideal environment to optimize the efficacy of CER therapies and minimize immune response to the therapeutic AAV vector. Using human cell-derived organoids in CER screening assays instead of rodent cell-based organoids could also shorten the timeline to impactful in vivo trials in humans. 

Using organoid-based, high-throughput CER therapy-screening has the potential to surpass the current paradigm of longevity research that targets specific proteins or metabolic interactions using drugs, supplements, or lifestyle interventions. Examples of this current paradigm include rapamycin, a drug that targets the mTOR pathway to simulate the healthspan benefits of calorie-restriction⁶, supplements like nicotinamide riboside, which replaces NAD⁺, a metabolically critical coenzyme whose levels decrease with age⁷, or lifestyle changes like Dean Ornish’s Lifestyle Reversal Program, which has been shown to increase telomere length⁸. While these interventions can extend healthspan, they do not lend themselves to radical increases in maximum lifespan. Even if a particular drug, such as rapamycin, delays the progression of aging-associated pathologies, we cannot expect the benefit to correlate linearly with the dose ad infinitum. Low doses of rapamycin can improve immune system function⁹, but large doses are immunosuppressive¹⁰. Another drawback of such metabolic interventions is that combination studies would need to be repeated at a staggering rate to prevent contraindications as new drugs were approved. It is unlikely that this current drug-centric paradigm of longevity research would achieve significant increases in maximum lifespan on a relevant timeframe.

Currently, companies such as AgeX Therapeutics, Celularity, and Osiris Therapeutics are developing stem-cell based rejuvenation therapies, and only one, Life Biosciences, is exploring CER. However, there does not yet exist a platform for the optimization and expansion of CER therapies to the diversity of organs necessary for robust systemic rejuvenation. As a potential starting point for the development of such a platform, I propose the use of organoid models of myocardial infarction to test CER therapies delivered by modified, immune-resistant vectors. Cardiovascular disease is an especially attractive target, considering that it is the leading cause of death in the United States, claiming over 600,000 lives every year¹¹. Optimizing such a therapy would serve as an ideal proof-of-concept to show the promise of an impactful technology with the potential not only to fix broken hearts but also radically increase lifespan.

Reference List:

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2. Hartman ZC, Appledorn DM, Amalfitano A. Adenovirus vector induced innate immune responses: Impact upon efficacy and toxicity in gene therapy and vaccine applications. Virus Research. 2008;132(1):1-14. doi:10.1016/j.virusres.2007.10.005

3. Mills RJ, Parker BL, Quaife-Ryan GA, et al. Drug Screening in Human PSC-Cardiac Organoids Identifies Pro-proliferative Compounds Acting via the Mevalonate Pathway. Cell Stem Cell. 2019;24(6):895-907.e6. doi:10.1016/j.stem.2019.03.009

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8. Ornish D, Lin J, Chan JM, et al. Effect of comprehensive lifestyle changes on telomerase activity and telomere length in men with biopsy-proven low-risk prostate cancer: 5-year follow-up of a descriptive pilot study. Lancet Oncol. 2013;14(11):1112-1120. doi:10.1016/S1470-2045(13)70366-8

9. Mannick JB, Morris M, Hockey H-UP, et al. TORC1 inhibition enhances immune function and reduces infections in the elderly. Science Translational Medicine. 2018;10(449). doi:10.1126/scitranslmed.aaq1564

10. Baroja-Mazo A, Revilla-Nuin B, Ramírez P, Pons JA. Immunosuppressive potency of mechanistic target of rapamycin inhibitors in solid-organ transplantation. World J Transplant. 2016;6(1):183-192. doi:10.5500/wjt.v6.i1.183

11. CDC. Heart Disease Facts | cdc.gov. Centers for Disease Control and Prevention. Published September 8, 2020. Accessed May 18, 2021. https://www.cdc.gov/heartdisease/facts.htm