Glucose 6-phosphate dehydrogenase deficiency enhances germ cell apoptosis and causes defective embryogenesis in Caenorhabditis elegans

Yang, H-C; Chen, T-L; Wu, Y-H; Cheng, K-P; Lin, Y-H; Cheng, M-L; Ho, H-Y; Lo, S J; Chiu, D T-Y

susceptible to hydrogen peroxide (H 2 O 2 )-induced senescence. 11 The susceptibility to oxidative stress-induced cytotoxic effect in G6PD-depleted cells is a recurring theme. Recently, G6PD-knockdown HepG2 cells have been shown to be highly susceptible to diamide-induced cytotoxicity with concomitant increased membrane peroxidation and cytoskeletal protein aggregation. 12 Such enhanced susceptibility to diamide-induced oxidative stress has been attributed mainly to impaired glutathione regeneration. These observations suggest that G6PD-deficient cells are predisposed to imbalanced redox status and oxidative stress. As a result, the increased oxidative stress elicits oxidative damage in macromolecules, such as DNA, protein, and lipid. Indeed, elevated DNA oxidative damage is found in G6PD-deficient fibroblasts, 11 and such cumulative genotoxic insult impairs cell growth. 17 The mitogen-activated protein kinase (MAPK) signaling pathway is involved in coordinating the response to oxidative stress, 18 thereby modulating cellular events including proliferation, differentiation, stress adaptation, and apoptosis. Recently, it has been shown that G6PD-knockdown human HepG2 cells are sensitive to oxidant-induced apoptosis due to altered MAPK signaling pathway. 13 Although much progress have been made on understanding the cellular effects of G6PD deficiency in erythrocytes and nucleated cells, the role of G6PD at the level of multicellular organism has not been investigated extensively due to the lack of G6PD-deficient animal model. The free-living soil nematode, Caenorhabditis elegans, is the first multicellular animal with its genome being fully sequenced 19 and the C. elegans G6PD protein shows 56% amino-acid sequence homology with the human counterpart. In addition, the advantages of using C. elegans, including short life span, ease for large-scale culture, transparent body for microscopic examination, and readily frozen for storage as well as tractable genetic system, make it an invaluable animal model for G6PD research as well as other biomedical research. [20] [21] [22] In the present study, we used RNA interference (RNAi) knockdown technique to establish a reproducible G6PDdeficient C. elegans animal model. Such G6PD-knockdown C. elegans displayed defective oogenesis (increased apoptotic germ cells and reduced egg production) with concomitant increase of oxidative stress and DNA oxidative damage. Most importantly, we have found that G6PD-knockdown C. elegans displayed a severe defect in embryogenesis as indicated by a dramatic reduction of hatching of the embryos from these animals. Mechanistically, the reduced egg production and defective hatching induced by G6PD deficiency could be attributed partly to increased oxidative stress and possibly mediated by altered MAPK pathways in C. elegans, respectively.