1435
Differences in mitochondrial DNA copy numbers in various subcutaneous and visceral fat depots of overconditioned cows
In dairy cows, adipose tissue (AT) is mobilized during early lactation to meet the increased energy demands through lactation. Overconditioned cows are more prone to metabolic disorders during this period than lean cows. Just like in other tissues, mitochondria are the main site of energy production within AT. Different energy demands may lead to changes of mitochondrial DNA (mtDNA), which reflects the abundance of mitochondria in a cell. Different bovine AT depots differentiated into visceral (vc) and subcutaneous (sc) regions, might present different mtDNA contents, due to diverse metabolic functions. Therefore, we aimed to compare the number of mtDNA copies per cell between various sc and vcAT depots from overconditioned cows. Eight non-lactating, non-pregnant German Holstein cows (Age: 4 – 6 years) received diets with increasing proportions of concentrate feed during the first 6 weeks of the trial until 60% were reached. This diet was maintained for 10 weeks and cows had an average body weight (BW) gain of 243 ± 33.3 kg within this period. Animals were slaughtered at the end of the experiment and tissue samples from sc (sternum, withers and tailhead) and vc (mesenterial, omental and retroperitoneal) AT were collected and snap frozen for genomic DNA isolation. The number of mtDNA copies/cell was quantified by multiplex quantitative PCR using ß-globin as reference gene. Data (mean ± SEM) were analyzed using Mann-Whitney-U-test and the Spearman (r) correlation coefficient (SPSS). The number of mtDNA copies/cell was 2.6-fold higher in all vc compared to all sc (P< 0.001) AT. Retroperitoneal AT exhibits greatest mtDNA copies/cell (3488 ± 190) compared to all other AT depots. The mtDNA copy number/cell in mesenterial and omental AT were 3058 ± 405 and 2921 ± 235, respectively. In tailhead and sternum AT mtDNA copy number/cell was 3-fold and in withers AT 2-fold lower compared to retroperitoneal. Different amounts of mtDNA copies/cell might reflect individual energy demands and metabolic functions in different sc and vcAT depots. In this study, mtDNA was isolated from whole AT including both adipocytes and the cells belonging to the stromal vascular cell fraction (SVF). Therefore, lower values of mtDNA copies in scAT might be due to an increased SVF, which contains significantly less mtDNA copy numbers. Higher amounts of mtDNA copies per cell in vcAT compared to scAT are in accordance to the higher metabolic activity of vcAT, particularly the retroperitoneal AT depot.
Keywords: Adipose tissue, mtDNA copy number, cows