Longitudinal studies of telomere length in feline blood cells: Implications for hematopoietic stem cell turnover in vivo

Abstract Objective To address questions about stem cell turnover in relation to telomere length dynamics, we analyzed telomere length in serial blood samples from cats. Materials and Methods Lymphocytes and granulocytes from two newborn kittens, a 2-year-old cat, a 10-year-old recipient of a double autologous stem cell transplant, and a 10-year-old control animal were analyzed by fluorescence in situ hybridization and flow cytometry at 2-week intervals over a 1-year period. Results At study onset, long telomeres were found in granulocytes and lymphocytes from the two kittens (mean ± SD: 70.2 ± 3.1 and 72.5 ± 3.1 telomere fluorescence units [TFU], respectively) compared with the 2-year-old cat (55.6 ± 2.5 and 64.1 ± 4.3 TFU, respectively) and the two adult animals (49.6 ± 1.5 and 45.4 ± 0.8 TFU, respectively). The rate of telomere shortening in both granulocytes and lymphocytes was most rapid in the kittens (slope: −16.7 ± 1.4 and −15.6 ± 0.2 TFU/year, respectively). As in humans, telomere shortening with age was more rapid in lymphocytes than in granulocytes. An average rate of telomere attrition of −0.52 ± 0.03 TFU per cell division was calculated for cultured lymphocytes from the two kittens, approximately 5-fold higher than the rate observed in human cells. Conclusions The average telomere length in cats is 5- to 10-fold longer than in humans, but the rate of telomere shortening is much higher both in vivo and in vitro. These observations are compatible with similar stem cell kinetics in both species.