Sirtuins are NAD-dependent protein deacetylase linked to aging. Some sirtuins are in nucleus while others are in cytosol and/or in mitochondria.
(Level A) A drug regulating sirtuins has been reported to extend lifespan of fat/obese mice but not lean/normal mice. Provide an explanation why the drug only helps fat/obese mice. Propose an experiment to test whether your explanation is true or not.