Identification of gradual aging and late-onset aging markers using male African turquoise killifish.

Vertebrates grow and mature with age after birth, deteriorate, and eventually die. However, the long lifespan of most vertebrates makes it challenging to identify markers of these distinct stages. Here, we leverage the short-lived vertebrate African Turquoise killifish (N. furzeri) to isolate molecular markers distinguishing gradual aging from late-onset aging. N. furzeri lifespan was divided into four stages-growth/maturation, young, midlife, and old-based on biological parameters. Cellular and molecular changes continually increasing or decreasing with age from young to midlife to old stages were defined as "gradual aging", and changes specifically between midlife and old stages as "late-onset aging". We discovered hepatic lipid droplets formed at birth and disappeared during the midlife stage. Metabolome and gene expression analyses of the liver where the majority of changes occurred identified several metabolites and genes as gradual aging markers (e.g., methylhistidine, glutarylcarnitine, and γ-butyrobetaine) and late-onset aging markers (e.g., creatine, homocitrulline, pipecolic acid, p21, htra1, and slc13a5 genes) providing insights into alternative mechanisms of gradual aging and late-onset aging that may be conserved. Thus, molecular markers reflecting gradual aging and late-onset aging at the organ levels can be isolated using N. furzeri.