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Telomere length shortening in response to an excessive fat accumulation in subcutaneous adipose tissue of dairy cows
With the onset of lactation, overconditioned cows mobilize more body tissue than thin cows and are prone to develop metabolic disorders. The metabolic stress in cows with higher body condition score (BCS) prior to calving and greater loss of BCS after calving comprises oxidative stress. Increased production of reactive oxygen metabolites may damage cells and accelerate telomere shortening which serves as biological marker for age and stress-related conditions. Herein we aimed to investigate the telomere length (TL) in subcutaneous adipose tissue (AT) during exemplarily induced excessive fat accumulation in cows. We hypothesized that TL is associated with the production of derivates of reactive oxygen metabolites (dROM), as indicator for oxidative stress, in overconditioned cows. Eight non-lactating, non-pregnant German Holstein cows (4 – 6 years) received diets with increasing concentrate feed proportions (0 to 60% of the total daily dry matter intake) during the first 6 weeks of the experiment which was maintained for 9 weeks. The BCS (5-point scale) increased from 2.3 ± 0.12 to 4.57 ± 0.14 and the average body weight (BW) gain was 243 ± 33.3 kg. Blood samples were taken monthly for photometric quantification of dROM in serum using N,N,diethyl-1,4-phenylendiamine as chromogen. Subcutaneous AT from tailhead was collected at the beginning and of the experiment and after 15 weeks. Samples were snap frozen for 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. Data (mean ± SEM) for TL, BCS and BW as well as for dROM were evaluated using repeated measurement ANOVA or non-parametric tests, respectively. Correlations were calculated using the Spearman (r) and Pearson (r) correlation coefficient. Relative qT decreased throughout the experiment (51.8 ± 3.26 to 43.6 ± 1.76; P = 0.01) whereas dROM increased more than 2-fold (P = 0.003). Shorter TL were correlated with BCS (r = -0.586, P = 0.017), BW (r = -0.653, P = 0.008) and dROM (r = -0.596, P = 0.015). Increasing dROM indicating oxidative stress were observed in overconditioned cows. Fat accumulation was accompanied by reduced TL in bovine AT. Shortening of telomeres might indicate fibrosis and would thus result in AT dysfunction which might compromise the adaptive capability of AT to the needs of lactation in overconditioned cows.
Keywords:
Telomere length, adipose tissue, oxidative stress