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. 2021 Nov 19;9:758402. doi: 10.3389/fcell.2021.758402

FIGURE 5.

FIGURE 5

Telomere 8-oxoG hormesis model and the crucial roles of the GO system enzymes in telomere stability. In unstressed conditions of basal ROS, low levels of 8-oxoG (yellow X) may promote telomere maintenance by destabilizing G4s structures (as shown in Figure 4) which block telomerase loading and impair replication, and may thereby facilitate telomere lengthening. Conversely, elevated ROS under oxidative stress inhibits telomere maintenance by producing excess 8-oxoG lesions (yellow X) and repair intermediates that impair telomere replication, and by producing 8-oxodGTP (yellow X) which inhibits telomerase. Thus, under oxidative stress the GO system may play a critical role in telomere preservation through MTH1 hydrolysis and removal of 8-oxodGTP, OGG1 initiated BER of 8-oxoG opposite C, and MUTYH initiated BER removal of A misinserted opposite 8-oxoG in the template strand. Thus, a little telomeric 8-oxoG may be beneficial for telomere maintenance, but too much telomeric 8-oxoG is detrimental for telomere stability.