Insulin stimulated a maximal dose-related increase in lipoprotein lipase synthetic rate to 300% of control and induced a 2-fold increase in LPL mRNA in isolated rat adipocytes.
Insulin increases the synthetic rate of lipoprotein lipase protein by stimulating an increase in specific LPL mRNA in isolated rat adipocytes.
Effect estimate: 300% of control
Lipoprotein lipase (LPL) is the enzyme responsible for hydrolysis of circulating triglyceride-rich lipoproteins and is important for storage of adipocyte lipid. To study the regulation of LPL synthetic rate in adipose tissue, primary cultures of isolated rat adipocytes were pulse-labeled with 35Smethionine, and LPL was immunoprecipitated with an LPL-specific antibody. A pulse-chase experiment identified the cellular and secreted forms of LPL as a 55-57-kDa protein. In the presence of heparin, there was a large increase in secretion of newly synthesized LPL from the cells, although heparin did not stimulate cellular LPL synthetic rate. When cells were exposed to insulin for 2 h, pulse-labeling revealed that insulin stimulated a maximal dose-related increase in LPL synthetic rate of 300% of control. This increase in LPL synthetic rate was observed after an exposure to insulin for as little as 60 min and was accompanied by only a 10-25% increase in total protein synthesis. In addition, insulin had no effect on the turnover of intracellular LPL. Using a cDNA probe for LPL, insulin induced a 2-fold increase in the LPL mRNA. Thus, insulin stimulated an increase in specific LPL mRNA in isolated rat adipocytes. This increase in LPL mRNA then leads to an increase in the synthetic rate of the LPL protein.
Ong et al. (Thu,) conducted a other in isolated rat adipocytes. Insulin vs. Control was evaluated on Lipoprotein lipase (LPL) synthetic rate and mRNA level (300% of control). Insulin stimulated a maximal dose-related increase in lipoprotein lipase synthetic rate to 300% of control and induced a 2-fold increase in LPL mRNA in isolated rat adipocytes.