Description:

Our studies focus on the molecular physiology of the muscle glucose transporter as it relates to Type II diabetes. Insufficient glucose sequestration within this tissue is accepted as one clear complication of the disease progression. Measuring glucose transport has previously been complicated and slow. However, the advent of the self-referencing glucose microsensor, developed by the BioCurrents Research Center, has greatly improved our ability to examine the dynamics of transport at the single cell level - the subject of these studies in Dr Harper's laboratory.

Progress:

We determined effects of physiologic UCP3 overexpression on glucose and fatty acid oxidation and on mitochondrial uncoupling and reactive oxygen species (ROS) production in L6 muscle cells. An adenoviral construct caused a 2.2- to 2.5-fold increase in UCP3 protein. Palmitate oxidation was increased in muscle cells incubated under normoglycemic or hyperglycemic conditions, whereas adenoviral green fluorescent protein infection or chronic low doses of the uncoupler dinitrophenol had no effect. Increased UCP3 did not affect glucose oxidation, whereas dinitrophenol and insulin treatments caused increases. Basal oxygen consumption, assessed in situ using self-referencing microelectrodes, was not significantly affected, whereas dinitrophenol caused increases. Mitochondrial membrane potential was decreased by dinitrophenol but was not affected by increased UCP3 expression. Finally, mitochondrial ROS production decreased significantly with increased UCP3 expression. Results are consistent with UCP3 functioning to facilitate fatty acid oxidation and minimize ROS production. As impaired fatty acid metabolism and ROS handling are important precursors in muscular insulin resistance, UCP3 is an important therapeutic target in type 2 diabetes.

From: MacLellan, J. D., Gerrits, M., Gowing, A., Smith, P.J.S., Sivitz, W., Wheeler, M. B., and Harper, M. E. 2005. Physiological increases in uncoupling protein 3 augment fatty acid oxidation and decrease reactive oxygen species production without uncoupling respiration in muscle cells. Diabetes, 54(8): 2343-50.