Submitted on December 19, 2006
Accepted on March 22, 2007
Suppression of PPAR
Attenuates Insulin-Stimulated Glucose Uptake by Affecting Both GLUT1 and GLUT4 in 3T3-L1 Adipocytes
wei liao1, M.T. Audrey Nguyen1, Takeshi Yoshizaki1, Svetlana Favelyukis1, David Patsouris2, Takeshi Imamura1, Inder M Verma3, and Jerrold M. Olefsky4*
1 Medicine, UCSD, La Jolla, California, United States
2 Medicie, UCSD, La Jolla, California, United States
3 Laboratory of Genetics, The Salk Institute, La Jolla, California, United States
4 Department of Medicine (0673), University of California-San Diego, La Jolla, California, United States
* To whom correspondence should be addressed. E-mail: jolefsky{at}ucsd.edu.
PPAR
plays a critical role in regulating insulin sensitivity and glucose homeostasis. In this study, we identified highly efficient siRNA sequences, and used lentiviral shRNA and electroporation of siRNAs to deplete PPAR from 3T3-L1 adipocytes to elucidate its role in adipogenesis and insulin signaling. We show that PPAR knockdown prevented adipocytes differentiation, but was not required for maintenance of the adipocyte differentiation state after the cells had undergone adipogenesis. We further demonstrate that PPAR suppression reduced insulin-stimulated glucose uptake without affecting the early insulin signaling steps in the adipocytes. Using dual siRNA strategies we show that this effect of PPAR deletion was mediated by both GLUT4 and GLUT1. Interestingly, PPAR depleted cells displayed enhanced inflammatory response to TNF
stimulation, consistent with a chronic anti-inflammatory effect of endogenous PPAR. In summary: (1) PPAR is essential for the process of adipocyte differentiation, but is less necessary for maintenance of the differentiated state. (2) PPAR supports normal insulin-stimulated glucose transport, and (3) endogenous PPAR may play a role in suppression of the inflammatory pathway in 3T3-L1 cells.
