Human-length Telomeres Limit Regeneration of Liver Epithelial Cells in Mice

BACKGROUND & AIMS: Telomeres, or the ends of linear chromosomes, are critical for maintaining genomic integrity. The commonly used C57BL/6 mouse strain has telomeres about 5 times longer than those present in humans. We recently engineered the C57BL/6 "Telomouse" to enable the study of human length telomeres, which we used here to study the effects of shortened telomeres on liver regeneration. METHODS: We performed partial hepatectomy experiments with Telomice using wild type C57BL/6 mice as controls. Staggered injections of the thymidine analogs 5-chloro-2'-deoxyuridine (CldU) and 5-iodo-2'-deoxyuridine (IdU) were used to analyze their incorporation into nuclear DNA during cells' S-phase to assess proliferation. In a second model, we employed a competitive hepatocyte repopulation assay in fumarylacetoacetate hydrolase (Fah) null mice. RESULTS: We found that human-length telomeres limit the proliferative capacity of cholangiocytes and hepatocytes in short-term liver regeneration. Control mice exhibited significant cholangiocyte proliferation at 36 hours post-partial hepatectomy (PHx), which remained stable at 46 hours post-PHx. In contrast, Telomice exhibited decreased cholangiocyte proliferation at 36 hours post-PHx, which further decreased at 46 hours post-PHx. Both control and Telomice exhibit increased hepatocyte proliferation at 46 hours compared with 36 hours post-PHx. However, Telomice exhibit less proliferation than controls at both time points. Compared with controls, Telomice exhibit an increased DNA damage response in the liver after partial hepatectomy. In a second model, Telomice hepatocytes also exhibited reduced efficacy in a competitive repopulation study using the Fah null mouse model of conditional hepatocyte ablation. CONCLUSIONS: Short telomeres induce DNA damage in the regenerating liver, hampering its ability to accelerate cell proliferation and regenerate the liver.