18 alpha-Glycyrrhetinic Acid Proteasome Activator Decelerates Aging and Alzheimer's Disease Progression in Caenorhabditis elegans and Neuronal Cultures

Aims: Proteasomes are constituents of the cellular proteolytic networks that maintain protein homeostasis through regulated proteolysis of normal and abnormal (in any way) proteins. Genetically mediated proteasome activation in multicellular organisms has been shown to promote longevity and to exert protein antiaggregation activity. In this study, we investigate whether compound-mediated proteasome activation is feasible in a multicellular organism and we dissect the effects of such approach in aging and Alzheimer's disease (AD) progression. Results: Feeding of wild-type Caenorhabditis elegans with 18 alpha-glycyrrhetinic acid (18 alpha-GA; a previously shown proteasome activator in cell culture) results in enhanced levels of proteasome activities that lead to a skinhead-1- and proteasomeactivation-dependent life span extension. The elevated proteasome function confers lower paralysis rates in various AD nematode models accompanied by decreased A beta deposits, thus ultimately decelerating the progression of AD phenotype. More importantly, similar positive results are also delivered when human and murine cells of nervous origin are subjected to 18 alpha-GA treatment. Innovation: This is the first report of the use of 18 alpha-GA, a diet-derived compound as prolongevity and antiaggregation factor in the context of a multicellular organism. Conclusion: Our results suggest that proteasome activation with downstream positive outcomes on aging and AD, an aggregation-related disease, is feasible in a nongenetic manipulation manner in a multicellular organism. Moreover, they unveil the need for identification of antiaging and antiamyloidogenic compounds among the nutrients found in our normal diet.Peer reviewe

Functional analysis of the proteasome in eukaryotic organisms

Proteasome degradation machinery is responsible for the turnover of a huge variety of normal and abnormal proteins, thus regulating a plethora of cellular processes. Aging is an inevitable biological process that is characterized by reduced proteasome function that leads to proteotoxic stress. Compound-related interventions, that ameliorate proteasome system collapse, retard aging process. In the present thesis, 18α-glycyrrhetinic acid (18α-GA), a natural compound with known proteasome activating properties in cells, was indicated to activate proteasome also in the multicellular organism Caenorhabditis elegans (C. elegans). Evaluation of the antiaging and protein anti-aggregation effects of this bioactive compound indicated that 18α-GA promoted longevity in nematodes through proteasome-and SKN-1-mediated activation and decelerated Alzheimer’sdisease progression and neuropathology both in nematodes and neuronal cells. Additionally, the crosstalk between protein synthesis and proteasome-mediated protein degradation was analyzed in eukaryotic organisms under various cellular conditions. Protein synthesis inhibition was observed to increase proteasome function and assembly in human primary embryonic fibroblasts, with heat shock protein chaperone machinery to contribute to the elevated proteasome assembly. Alternatively, protein synthesis inhibition increased the protein levels of specific proteasome subunits without influencing the proteasome activity in C. elegans. Furthermore, proteasome activation by means which have also pro-longevity effects decreased the protein synthesis rate both in human fibroblast cellsand nematodes. This thesis suggests: 1) that a diet-derived compound could act as a pro-longevity and anti-aggregation agent in the context of amulticellular organism and 2) the existence of a complex interplay between anabolic and catabolic processes under different cellular conditions, across species