By Rahul Kumar
Aging is inevitable for every organism including insects. Aging is a complex biological process triggered by numerous factors. One of the hallmark of aging is decline in redox homeostasis of the body and oxidative stress is a major contributing factor associated with aging. Imbalance in levels of Reactive Oxygen Species (ROS) leads to disruption of redox homeostasis causing oxidative stress. ROS consists of highly reactive oxygen containing unstable molecules or free radicals like peroxides, superoxide, hydroxyl radical, singlet oxygen, etc. which have capabilities to damage cellular components by initiating a chain reaction. This leads to dysfunctional cellular metabolism if not regulated. Redox dyshomeostasis results when this regulation fails. The endogenous anti-oxidant system forms the primary system of defense against ROS. The endogenous antioxidant system is a multicomponent system comprising of enzymes, water soluble antioxidants and lipid soluble antioxidants. Superoxide dismutase (SOD) and catalase are the major antioxidant enzymes involved in detoxification of ROS and Hydrogen peroxide (H2O2) in insects. Previously scientists have found a clear association between oxidative stress, antioxidant defenses, and aging in a study conducted in crickets (Gryllodes sigillatus). Early studies have also established a positive relationship between SOD overexpression and longevity.
In a recent study conducted by a group of Indian scientists, it has been found that the lifespan of Drosophila melanogaster reduces when antioxidant enzymes are genetically suppressed. In this study, the effect of genetic repression of antioxidant enzymes SOD and catalase, on longevity of Drosophila was investigated using RNAi (RNA interference) based transgenic flies in which SOD and catalase mRNA was ubiquitously silenced respectively. Antioxidant enzyme activities were studied for SOD and catalase separately using fly homogenate and artificial substrates in vitro. SOD activity was assessed by monitoring inhibition of pyrogallol auto-oxidation and catalase activity was assessed by measuring decrease in levels of H2O2. Further survivability of the flies were studied by recording mortality against non-transgenic controls under male and female groups. From this study it was found that RNAi based repression of SOD (SOD1 expression specifically) and catalase in flies respectively led to drastic reduction in longevity. 77% (male 76.8%, female 77.3%) reduction was found in case of SOD silencing and 83% (male 84.84%, female 81.8%) reduction was found in case of catalase silencing. Therefore, it is evident here that genetic repression of antioxidant enzymes leads to reduction in the life span of Drosophila melanogaster. This work provides experimental evidence in support of the positive role of antioxidant defenses in longevity in insects (as well as other organisms).
Figure: Silencing of genes encoding for antioxidant enzymes leads to accumulation of reactive oxygen species (ROS) which are involved in cellular damage and aging whereas overexpression of these enzymes has opposite effects.
For more details, please refer
Deepashree, S., Shivanandappa, T. & Ramesh, S.R. Genetic repression of the antioxidant enzymes reduces the lifespan in Drosophila melanogaster. Journal of Comparative Physiology B (2021). https://doi.org/10.1007/s00360-021-01412-7
Rahul Kumar is one of the Associate Editors of IE. He is working as Assistant Professor of Zoology at Department of Zoology, Sheodeni Sao College (Magadh University), Kaler-824127, Arwal, Bihar, India. You can contact him at email@example.com.
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