Causes of spermidine-mediated longevity

Aging is a complex, progressive process accompanied by cellular and/or organismal deterioration, causing multiple diseases and ultimately resulting in death. A variety of existing theories posit aging to proceed in an unregulated manner, largely a consequence of damage accumulated through exposure to reactive oxygen species and other toxic elements. However, findings from many groups demonstrate that lifespan can be extended several-fold in a multitude of different model organisms through regimens of caloric restriction, site specific mutations, or the application of certain natural compounds. These observations have prompted the formulation of several alternate theories to explain aging at least in parts, as a regulated process. Recently, our group reported that external application of spermidine, a naturally occurring polyamine whose levels progressively decline during aging, serves to counteract necrotic cell death, induce autophagy and improve the lifespan of yeast, flies, worms, and human immune cells, as well as to decrease oxidative protein damage in aging mice. Despite recent progress in the study of aging, very, little is known regarding the proteomic changes that mediate the effects of spermidine on autophagy and longevity. Herein, we propose a systematic and exhaustive analysis of both the standard proteome and phospho-/acetyl-specific proteomic profiles of spermidine-treated yeast cells, as well as hepatocytes and neuronal cells obtained from aging mice. By using this approach, we expect to identify regulators of aging that are causative to spermidine-induced longevity and induction of autophagy. The most promising results from these analyses will be further functionally characterised using genetic, cell biological and biochemical techniques. Additionally, the potential of the identified proteins or protein modifications to promote cytoprotection and autophagy will be investigated in human cell culture model. Notably, at the time of submission of this proposal, we have preliminary experimental evidence that sporulation- and meiosis-associated gene products act downstream of spermidine, the results of which will also be extensively investigated in this project.

Aging is a complex, progressive process accompanied by cellular and/or organismal deterioration, causing multiple diseases and ultimately resulting in death. Our group previously reported that external application of spermidine, a naturally occurring polyamine whose levels progressively decline during aging, counteracts necrotic cell death, induces autophagy, improves the lifespan of yeast, flies, worms, and human immune cells, and decreases oxidative protein damage in aging mice. However, hitherto little is known about the molecular mechanisms that mediate the effects of spermidine on autophagy and longevity. We herein performed a systematic and exhaustive analysis of the proteome, the metabolome and the transcriptome (i.e. the entirety of proteins, metabolites and transcripts, respectively) of different kind of cells, as well as hepatocytes, neuronal cells and cardiac tissue obtained from aging mice. By using this approach, we identified regulators of aging that are causative to spermidine-induced longevity and induction of autophagy. For instance, we found that spermidine acts as an inhibitor of the acetyltransferase EP300, thereby inducing autophagy. More importantly, spermidine appeared to act longevity-promoting and tumorsuppressive in mammals. Furthermore, we could show that spermidine causes stress resistance against the neurotoxic agent paraquat or mild doses of hydrogen peroxide in fruit flies, as they showed better survival as well as improved locomotor activity upon spermidine treatment. Interestingly, with respect to the stressor, this effect appeared dependent or independent on autophagy. Our fruit fly studies also showed that spermidine counteracts age-associated dementia as well as the consequences of Parkinsons disease. Notably, we had preliminary experimental evidence that sporulation- and meiosis-associated gene products act downstream of spermidine. Accordingly, within this project we were able to identify that spermidine promotes mating and fertilization efficiency. In conclusion, we successfully broadened our knowledge on the molecular basis underlying spermidine-mediated cytoprotection. These results might facilitate the usage of spermidine as a natural anti-aging substance in humans.