Telomere length in different visceral and subcutaneous adipose tissue depots of overconditioned cows

Abstract Text: Telomeres are short and repetitive sequences of the chromosomes which shorten with every cell-division. Therefore telomere length (TL) is considered as a biological marker for aging and cell proliferation depending on the tissue type. Increasing oxidative stress in response to nutrient surplus, e.g. in overconditioned dairy cows at the onset of lactation, accelerates telomere attrition. Adipose tissue (AT) is mobilized in early lactating cows to cope with the nutrient demands for milk synthesis. The different AT depots are divided into visceral (vc) and subcutaneous (sc) depots which exhibit different metabolic functions and cellular composition. We hypothesized that TL shortening within AT is depot specific in overconditioned cows due to different metabolic activities of sc and vcAT. Herein, we aimed to characterize the TL in seven different fat depots after rapid, diet-induced fat accumulation in cows. Eight German Holstein cows (non-lactating, non-pregnant, age: 4-6 years) were gradually adapted to a high-energy ration by increasing the portion of concentrate in the ration from 0 to 60% of daily dry matter intake within 6 wk. Animals were fed the 60% diets for further 10 wk and were then slaughtered; tissue samples from scAT (sternum, withers and tailhead) and vcAT (pericardial, mesenteric, omental and retroperitoneal) were collected and snap frozen for further analyses. After isolation of genomic DNA, a multiplex quantitative PCR was used to analyze the relative quantity of telomere (qT) products compared with ß-globin products which served as reference gene to estimate TL in AT. Differences between qT in the single AT depots were analyzed using the Student’s t-test (SPSS; mean ± SEM). Mesenteric AT exhibited 1.3-fold lower qT compared to omental (59.1 ± 7.4; P= 0.01) and pericardial (57.7 ± 7.9; P= 0.004) depots and 1.2-fold lower qT than retroperitoneal (53.5 ± 4.9; P= 0.01) AT. In scAT depots, fat from withers displayed 1.3-fold higher qT values than sternum (47.3 ± 3.5; P=0.005) AT and 1.1-fold higher qT compared to tailhead (54.1 ± 8.2; P=0.05) fat. Although vcAT is known to have a higher metabolic activity than scAT in dairy cows, we did not observe any differences in TL when comparing all sc versus all vcAT. Depot specific differences of TL might nevertheless be a hint to depot specific roles

Keywords: Telomere length, adipose tissue, dairy cow