Adipose triglyceride lipase expression and fasting regulation are differently affected by cold exposure in adipose tissues of lean and obese Zucker rats

Adipose triglyceride lipase (ATGL) hydrolyzes triacylglycerols to diacylglycerols in the first step of lipolysis, providing substrates for hormone-sensitive lipase (HSL). Here we studied whether ATGL messenger RNA (mRNA) and protein levels were affected by 24-h cold exposure in different white adipose tissue depots and in interscapular brown adipose tissue of lean and obese Zucker rats submitted to feeding and 14-h fasting conditions. HSL mRNA expression was also studied in selected depots. In both lean and obese rats, as a general trend, cold exposure increased ATGL mRNA and protein levels in the different adipose depots, except in the brown adipose tissue of lean animals, where a decrease was observed. In lean rats, cold exposure strongly improved fasting up-regulation of ATGL expression in all the adipose depots. Moreover, in response to fasting, in cold-exposed lean rats, there was a stronger positive correlation between circulating nonesterified fatty acids (NEFA) and ATGL mRNA levels in the adipose depots and a higher percentage increase of circulating NEFA in comparison with control animals not exposed to cold. In obese rats, fasting-induced up-regulation of ATGL was impaired and was not improved by cold. The effects of obesity and cold exposure on HSL mRNA expression were similar to those observed for ATGL, suggesting common regulatory mechanisms for both proteins. Thus, cold exposure increases ATGL expression and improves its fasting-up-regulation in adipose tissue of lean rats. In obese rats, cold exposure also increases ATGL expression but fails to improve its regulation by fasting, which could contribute to the increased difficulty for mobilizing lipids in these animals.