The increase in obesity and the development of type 2 diabetes in childhood is of great concern. The acute elevation of free fatty acids (FFA) levels, as occurs in obesity, is controlled by the triglyceride/FFA cycle. As much as 60% of the FFA released by the adipose tissue during fasting is re-esterified back to triglyceride within the adipose tissue and liver through a pathway called glyceroneogenesis. We have studied the role of the triglyceride/fatty acid cycle in the development of insulin resistance, using a mouse model with a deletion of the PPAR binding site in the cytosolic form of phosphoenolpyruvate carboxykinase (PEPCK-C) gene promoter (PPARE-/- mice). This mutation results in ablation of expression of the PEPCK-C gene in the white adipose tissue and brown adipose tissue as well as in the mammary gland. In 5-week-old virgin PPARE-/- mice, the mammary gland has fewer terminal end buds (TEB) and less branching compared to wild type mice. The PPARE-/- females are fertile and able to produce milk for their young;however, the triglyceride content of the milk from the PPARE-/- mothers contains 40% less triglyceride than the wild type mice. The reduced triglyceride content in the milk has metabolic consequences. Pups from PPARE-/- mothers exhibit insulin resistance as early as 9-days after birth and this insulin resistance persists into adulthood. We hypothesize that the alteration of the triglyceride/fatty acid cycle through the deletion of the PEPCK-C gene expression in the adipose tissues and mammary gland results in 1)an increase of FFA levels in the blood, which ultimately causes insulin resistance and 2) in alteration of triglyceride content of the milk during lactation patterns the pup for insulin resistance. Using both the PPARE-/- mice and mouse mammary epithelial cell lines we propose to 1) Determine the role the triglyceride/fatty acid cycle through the regulation of the PEPCK-C gene in the patterning of the mouse for the development of insulin resistance, 2) investigate the in vivo functions of the PEPCK-C gene in the mammary gland and 3) determine the action of thiazolidinediones (TZD) in the alteration of the triglyceride/fatty acid cycle in the liver, adipose and mammary gland through regulation of PEPCK-C gene transcription at the PPARE binding site in the promoter of PEPCK-C gene. Understanding the regulation of PEPCK-C and defining its role in the mammary gland is critical to our understanding of the development of glucose homeostasis and diabetes.
