In vivo spectrofluorimetry reveals endogenous biomarkers that report healthspan and dietary restriction in Caenorhabditis elegans

Autofluorescent lipofuscin and advanced glycation end-products (age pigments) accumulate with age across phyla, yet little is understood about their formation under physiological conditions and their specific contributions to the aging process. We used in vivo spectrofluorimetry to quantitate autofluorescence in wild-type Caenorhabditis elegans and longevity mutants disrupted for distinct aspects of the aging process. In wild-type animals, age pigments increase into adulthood, accumulating slowly during the reproductive phase and more rapidly during the post-reproductive period. As in humans, insulin signaling influences age pigment accumulation - mutations that lower efficacy of insulin signaling and extend lifespan [daf-2(e1370) insulin receptor and age-1(hx546) PI3-kinase] dramatically lower age pigment accumulation; conversely, elimination of the insulin-inhibited DAF-16/FOXO transcription factor causes a huge increase in age pigment accumulation, supporting that the short-lived daf-16 null mutant is truly progeric. By contrast, mutations that increase mitochondrial reactive oxygen species production do not affect age pigment accumulation, challenging assumptions about the role of oxidative stress in generating these species in vivo. Dietary restriction reduces age pigment levels significantly and is associated with a unique spectral shift that might serve as a rapidly scored reporter of the dietary restricted state. Unexpectedly, genetically identical siblings that age poorly (as judged by decrepit locomotory capacity) have dramatically higher levels of age pigments than their same-aged siblings that appear to have aged more gracefully and move youthfully. Thus, high age pigment levels indicate a physiologically aged state rather than simply marking chronological time, and age pigments are valid reporters of nematode healthspan.