Aging process is influenced by the insulin/insulin-like growth factor-1 signaling (IIS) pathway or IGF-1 signaling pathway. Studies done on the genes of this pathway were found to affect longevity. However, no conclusive results have been drawn.The purpose of this systematic review is to summarize the function of genes involved in the IIS pathway of Caenorhabditis Elegans (C. elegans), a nematode commonly used as a model organism in molecular genetics and developmental biology. A literature search for relevant studies was done through PubMed and Scopus databases using MeSH keywords Caenorhabditis elegans, C. elegans, nematode, genes, RNA, DNA, IIS pathway, IGF pathway, lifespan, and longevity. The search was limited to studies that were published in the last ten years (2008-May 2018). After exclusion of duplicates, review papers, human, in vitro, and other organismal studies, a total of 76 research articles were selected for further assessments. Data relevant to the effects of IIS genes on the lifespan ofC. eleganswas independently extracted. Reduction of daf-2 and age-1 and overexpression of sir-2.1 were reported to promote increment of the lifespan of C. elegans. Furthermore, differentially expressed genes that were involved in the protection against oxidative stress, pathogen attack, and toxicity includeins-18, numr-1/-2, sgk-1, and rgs-1. The knockdown of daf-2, age-1, and overexpression of sir-2.1 genes prolonged the lifespan of C. elegans while knockdown of daf-16, hsf-1, sir-2.1 as well as skn-1 shorten the lifespan of C. elegans.In conclusion, the differential expression of genes in the IIS pathway prolongs the lifespan of C. elegans.
Vitamin E is an established antioxidant. However, the effect of vitamin E on healthspan, which deteriorates during ageing, has not been determined because most related studies have emphasized its effects on lifespan. Therefore, the purpose of this study was to determine the effect of palm tocotrienol-rich fraction (TRF) on the lifespan, locomotion and thermotolerance of Caenorhabditis elegans, which share many common gene sequences with humans. The nematodes were treated with different concentrations of TRF (0 - 200 μg/mL), and the number of surviving nematodes at each concentration (N=30, duplicate) was counted daily under a light microscope to determine the optimal dose of treatment. The nematodes were divided into 3 groups, namely; control, Tween-80 (vehicle) and TRF-treated. Locomotion and thermotolerance were determined on day 4 and 12 of treatment in adult nematodes. ImageJ was used for locomotion analysis, and thermotolerance was determined based on nematode survivals after exposure to 37 °C. TRF-treated C. elegans had significantly longer lifespans compared to controls (P = 0.003). The TRF group (50 μg/mL) had the longest mean lifespan (23.5 days), which was significantly longer compared to controls, (18.5 days; (P = 0.002). However, locomotion was similar between all groups. In the thermotolerance assay, the survival determined on day 4 and day 12 of TRF-treatment was higher compared to controls (P= 0.046). Interestingly, the Tween- 80-treated group showed similar results as the TRF-treated group compared to controls. The findings indicate that TRF prolongs the lifespan and increases the thermotolerance of C. elegans but does not improve the locomotion of the worms as they age.
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