Are Planarians Immortal? Markers of Metabolism and Aging in Planarians

Abstract

Tese de mestrado, Biologia Humana e Ambiente , 2024, Universidade de Lisboa, Faculdade de CiênciasCellular aging is a process characterized by the accumulation of physiological changes involving various metabolic pathways and their interactions. Despite the ongoing research on the aging process, the study of simple animals, such as planarians, might be crucial in understanding the physiological pathways involved and their interactions, as well as the compensatory processes that might be used to overcome oxidative stress. The study of Girardia tigrina is of great importance due to its remarkable regenerative capacities, having no aging signs, and often considered an immortal species. This research work aimed to determine a battery of biomarkers to assess the aging process of planarians of the species Girardia tigrina, and to establish the potential interactions between several physiological pathways, focusing on aerobic and anaerobic energy production (ETS and LDH, respectively), enzymatic and non-enzymatic antioxidant capacity (CAT and TG, respectively), detoxification activity (glutathione S-transferase; GST), oxidative stress (LPO), and the neuromuscular activity (ChE). The results obtained make it possible to distinguish four stages, with a state of oxidative stress in planarians aged between 9 and 12 months associated with a decrease in antioxidant capacity and energy production. Additionally, there was a tendency for ChE activity to increase over time, particularly in organisms from 12 months onwards, which suggests a metabolic balance strategy through protein turnover. The observed weight loss in end-of-life organisms results from continued cell death exceeding the cellular components synthesis. In addition, it was possible to observe phenotypic changes such as the formation of neoplasms and profound mutations in organisms between 18 and 24 months, supporting the hypothesis that these show signs of normal aging over time, corroborating the idea of mortality. In summary, this study shows preliminary indications of the aging process in Girardia tigrina, emphasizing the need for further future contributions to explore interactions of aging-related physiological pathways