Semaglutide Started Late in Life Extends Lifespan and Slows Aging in Female Mice

**Why This Matters** Caloric restriction (CR) reliably slows aging and extends lifespan across species, but sustained adherence is practically impossible for most people. Identifying pharmacological CR mimetics is therefore a major goal of longevity research. Semaglutide, a long-acting GLP-1 receptor agonist already widely prescribed for type 2 diabetes and obesity, has demonstrated pleiotropic benefits — reduced cardiovascular events, kidney protection, lower neurodegeneration risk — whose mechanistic basis remains poorly understood. This study tests the hypothesis that these broad benefits reflect genuine CR-mimicking activity that slows the aging process itself.

**What Was Studied** Feng and colleagues at the University of California Berkeley treated 20-month-old female C57BL/6 mice — equivalent to roughly 60–65 years in humans — with daily subcutaneous semaglutide or vehicle. One cohort was followed for lifespan; a parallel cohort was assessed after 3 months of treatment for physiological, cellular, and molecular endpoints. A matched CR group was included for direct longitudinal comparison. Semaglutide reduced food intake by 24% without altering locomotor activity, respiratory exchange ratio, oxygen consumption, or energy expenditure after body-weight adjustment, indicating that caloric reduction rather than increased expenditure drove the energy deficit.

**Key Results** Median lifespan increased from 742 to 834 days in semaglutide-treated mice. Across behavioral batteries, treated mice showed greater locomotor exploration (open-field and elevated plus maze), improved spatial memory (Barnes maze), better motor coordination (rotarod), and superior muscle endurance (inverted screen and treadmill tests) — improvements in motor and muscle tests that remained significant after ANCOVA adjustment for body weight. Glucose clearance and AKT phosphorylation in metabolic tissues confirmed improved glucose homeostasis and insulin sensitivity.

At the cellular level, semaglutide attenuated five well-established hallmarks of aging simultaneously: (1) Stem cell attrition — HSC numbers normalized, myeloid bias reversed, and hippocampal neurogenesis (BrdU⁺ and DCX⁺ cells) increased in the dentate gyrus. (2) Chronic inflammation — inflammatory cytokine expression, IL-6-high macrophages (CD68⁺), and pro-inflammatory Ly6Chigh monocytes were all reduced. (3) Cellular senescence — p16 and p21 expression and senescence-associated β-galactosidase activity declined. (4) Mitochondrial dysfunction — markers of mitochondrial integrity improved. (5) Loss of proteostasis — autophagic and proteasomal flux were enhanced. Nutrient-sensing pathways (AMPK, mTORC1, sirtuins, insulin–IGF1 signaling) were modulated in directions consistent with CR.

**Comparison With Caloric Restriction** In direct longitudinal comparison to weight-matched CR, semaglutide preserved baseline physiological function while also attenuating age-associated decline, as CR did. However, semaglutide produced superior trajectories over CR in three domains: exploratory drive, spatial memory, and glucose control — suggesting mechanistic contributions beyond reduced calorie intake alone.

**Implications and Caveats** These findings provide the first direct lifespan evidence that pharmacological GLP-1R activation initiated late in life slows aging and extends longevity, offering a mechanistic framework — CR mimicry — that could explain the drug class's broad clinical benefits. The study is limited to female mice of a single inbred strain, so sex-specific and strain-specific effects require further investigation before human translation can be assumed.