White Adipose Tissue Depot-Specific Activity of Lipogenic Enzymes in Response to Fasting and Refeeding in Young and Old Rats

Abstract

Background: Although the heterogeneity of white adipose tissue (WAT) in different anatomical sites is a well-known phenomenon, there are scarce data on aging-associated metabolic alterations in various WAT depots. Objective: We used the model of fasting and refeeding to analyze the effect of aging on the activity of key lipogenic enzymes in retroperitoneal (rWAT), epididymal (eWAT), and subcutaneous (sWAT) adipose tissue depots. Methods: 5- and 24-month-old male Wistar rats were fasted for 48 h or were fasted for 2 days and subsequently refed for 2 or 4 days. Control animals had ad libitum access to chow. Samples obtained from three WAT deposits were analyzed for the enzymatic activities of ATP citrate lyase (ACL), fatty acid synthase (FAS), and glucose-6-phosphate dehydrogenase (G6PD). Concentrations of lipids and proteins were measured in the blood serum. Results: Fasting for 2 days decreased the concentration of free fatty acids only in the young rats. The basal activities of ACL and FAS were lower in eWAT than in rWAT and sWAT of the young rats. In the young rats, fasting did not change ACL and FAS activities in any of the studied depots. Refeeding increased these activities more quickly in rWAT than in eWAT, while in sWAT no induction was observed. ACL and FAS activities were manifold lower in all WAT depots of the old than in those of the young rats. In the old animals fasting had no effect on ACL activity in any depot and decreased FAS activity only in sWAT. After 4 days of refeeding, FAS activity increased in rWAT and sWAT, but no change in ACL activity occurred. G6PD activity in the young rats was lower by 40% in eWAT than in rWAT. The induction of the enzyme by refeeding occurred faster in rWAT than in eWAT, while in sWAT no change in G6PD activity was observed. G6PD activity did not change with aging. Fasting of the old rats decreased G6PD activity in rWAT and sWAT. Refeeding failed to induce the enzyme in these depots, whereas in eWAT G6PD activity increased by 76% after 4 days of refeeding. Conclusion: Fasting and refeeding revealed WAT depot-specific, age-related changes of the activities of lipogenic enzymes.