#09 - David Sabatini, M.D., Ph.D.: rapamycin and the discovery of mTOR — the nexus of aging and longevity?

Episode Summary

Executive Summary: Peter Attia interviews David Sabatini about his scientific path from MD-PhD student to leading mTOR researcher, recounting the discovery of rapamycin’s target, mTOR, the identification of mTORC1 and mTORC2, and how nutrient sensing links to aging, autophagy, immunity, metabolism, and disease. The discussion emphasizes why intermittent mTOR modulation may be more beneficial than chronic inhibition and why upstream nutrient sensors may enable safer longevity therapies.

Main Topics: Sabatini’s scientific origin story and discovery of mTOR (Priority: 5/5): Sabatini explains how, as a Hopkins MD-PhD student in Solomon Snyder’s lab, he chose rapamycin as a project, purified the target protein, and ultimately cloned and identified mTOR/RAFT1, turning a control compound into a landmark discovery. mTOR complexes and pathway biology (Priority: 5/5): The conversation covers the later discovery of mTORC1 and mTORC2, the role of Raptor and Rictor, and how detergent choice (CHAPS vs Triton) enabled purification of interacting proteins and clarified pathway architecture. mTOR as a nutrient sensor and longevity regulator (Priority: 5/5): Attia and Sabatini discuss mTORC1 as a central integrator of nutrients, growth factors, and cellular state, and why its broad regulatory reach makes it a plausible lever for lifespan extension and healthspan improvement. Rapamycin’s benefits and limitations (Priority: 4/5): They examine rapamycin’s partial inhibition of mTORC1, delayed effects on mTORC2, immune suppression concerns, and why intermittent dosing may preserve benefits while reducing toxicity. Amino acid sensing: leucine, arginine, and methionine/SAM (Priority: 5/5): Sabatini describes his lab’s work identifying nutrient sensors for leucine, arginine, and methionine via SAM, and how these inputs regulate mTORC1 in tissue- and context-specific ways. Autophagy, fasting, and cycling between anabolism and catabolism (Priority: 4/5): The discussion links mTOR inhibition to autophagy and argues that health may depend on periodic switching between growth and recycling states rather than constant activation or suppression. Future directions: tissue-specific and upstream targeting (Priority: 4/5): Sabatini argues that the next step is mapping nutrient signaling across tissues over time and developing upstream modulators that can tune mTORC1 without fully suppressing mTORC2.

Key Arguments: Sabatini’s discovery of mTOR emerged from pursuing rapamycin, initially a control compound in his lab, showing that major breakthroughs can come from overlooked tools. mTORC1 is the main mediator of rapamycin’s known effects on growth, translation, autophagy, and metabolism; mTORC2 is distinct and more tied to PI3K/AKT signaling. mTOR is unusually important because it acts like a cellular “general contractor,” coordinating many subsystems, which makes it a plausible single lever for aging-related interventions. Chronic, complete mTOR inhibition would likely be harmful because mTORC1 is essential for normal cell growth and tissue maintenance; partial/intermittent inhibition is more plausible therapeutically. Rapamycin is not a perfect mTORC1 inhibitor: it blocks only some substrates and can, over time, affect mTORC2, contributing to side effects such as glucose dysregulation. Autophagy is likely one important mechanism behind longevity benefits, but Sabatini stresses that it is probably not the only one. Leucine and arginine are key amino acid inputs to mTORC1 in mammals, while methionine acts indirectly through SAM; these sensors help explain nutrient-dependent control of growth. Methionine restriction may be especially relevant to longevity because methionine and SAM drop strongly during fasting, and the pathway can be bypassed experimentally by SAM. The best future drugs may target upstream nutrient sensors rather than mTOR itself, enabling more selective, tissue-specific modulation of mTORC1. The ideal intervention may be cycling between anabolic and catabolic states, rather than maximizing either one continuously.

Data Points: Year of rapamycin/mTOR discovery paper: 1994 - Sabatini notes his Cell paper identifying the protein was published in 1994. Year rapamycin was FDA-approved as Rapamune: 1999 - Attia references rapamycin’s approval for transplant immunosuppression. Approximate size of mTOR protein: ~300 kDa - Sabatini describes mTOR as a very large protein. Approximate size of associated smaller protein: ~30 kDa - He contrasts the smaller associated protein with mTOR’s size. Full-length cDNA length: 8–9 kilobases - Sabatini describes the unusually large cDNA he cloned. Rapamycin binding complex discovery timing: Early 2000s - He places mTORC1/mTORC2 discovery around 2001–2002. Mouse fasting weight loss: ~25% of body weight - Sabatini notes that a mouse fasted for two days loses about a quarter of its weight. Rapamycin effect on mTORC1: Partial inhibition - He emphasizes rapamycin does not fully inhibit mTORC1 or all substrates. Rapamycin effect on mTORC2: Delayed inhibition with longer exposure - He notes rapamycin can inhibit mTORC2 over time, which may worsen glucose homeostasis. SAM in enzyme usage: Second most common cofactor after ATP - Sabatini highlights SAM’s broad metabolic importance.

Pivotal Quotes: "“mTOR basically has a finger in every major process in the cell.”" — David Sabatini: Explaining why mTOR is such a powerful lever for aging and cellular state. "“The only way you can do all of those things with one button is to go after mTOR.”" — David Sabatini: Describing mTOR as a central integrator of many aging-relevant processes. "“Cycling, anabolism, catabolism might be the single most important thing to do.”" — David Sabatini: Discussing why intermittent modulation may be better than constant suppression or activation.

Implications: The episode frames mTOR as a central aging and metabolism control node, suggesting future longevity therapies will likely require intermittent, tissue-aware modulation or upstream nutrient-sensor targeting rather than blunt chronic inhibition.