Fasting-induced increases in aquaporin 7 and adipose triglyceride lipase mRNA expression in adipose tissue are attenuated by peroxisome proliferator-activated receptor a deficiency

Objective: To investigate the impact of peroxisome proliferator-activated receptor alpha deficiency on gene expression of adipose triglyceride lipase and the glycerol transporter aquaglyceroporin 7 in white adipose tissue in the fed and fasted states in relation to glycerol release by isolated adipocytes. Measurements: Studies using wild-type and peroxisome proliferator-activated receptor alpha null mice. Hormone and metabolite concentrations, real-time polymerase chain reaction (PCR), basal and stimulated adipocyte lipolysis, estimated by glycerol release. Results: Peroxisome proliferator-activated receptor alpha deficiency blocked the increase in aquaglyceroporin 7 transcript level and attenuated the increase in adipose triglyceride lipase transcript level in white adipose tissue elicited by fasting. Fasting glycerol levels were lower in peroxisome proliferator-activated receptor alpha null than wild-type mice, despite increased mobilization of adipocyte fat reserves in vivo as indicated by reduced adipose tissue masses (three distinct depots) and a significantly lower epididymal adipocyte diameter. Basal net glycerol release was unchanged but beta-adrenergic-stimulated net glycerol release was higher with isolated adipocytes from fasted peroxisome proliferator-activated receptor alpha null mice compared with those of fasted wild-type mice. Conclusion: Peroxisome proliferator-activated receptor alpha deficiency prevents effects of fasting to increase adipocyte aquaglyceroporin 7 gene expression, and influences the regulation of inter-tissue glycerol flux after fasting via lowered adipocyte aquaglyceroporin 7 expression. Lowered gene expression of adipose triglyceride lipase and aquaglyceroporin 7 in peroxisome proliferator-activated receptor alpha null mice is not limiting for adipose triglyceride breakdown in vivo during fasting.