Fatty acid induced changes in gene expression in cultured L6 rat muscle cells : An in vitro model on high dietary fat-induced insulin resistance in red gastrocnemius rat muscle in vivo

Abstract

ABSTRACT Type 2 diabetes is a serious cause of morbidity and mortality and the disease is reaching epidemic proportions in the developed world. A core defect in type 2 diabetes is insulin resistance in skeletal muscle. Previous global gene expression experiments conducted at the Garvan Medical Research Institute has shown that 3 weeks high fat feeding induced increased expression of stress related genes in rat muscle. These stress-related genes could be involved in the development of insulin resistance in rat muscle in vivo. However, it is not known whether the observed effect on stress associated gene expression in rat muscle is a direct effect of increased fatty acid availability or if the change in gene expression in rat muscle are a secondary effect of increased dietary fat intake. To investigate the direct action of free fatty acids on gene expression we examined the effect of 24 and 48 h exposure to 1mM linoleate on gene expression on a cultured muscle cell line (cultured L6 myotubes). RT-PCR results showed that linoleate did not upregulate any of the stress-genes measured in L6 rat muscle cells neither after 24 nor 48 hours. This indicates that either free fatty acids have a secondary effect on upregulation of stress-associated genes in rat muscle in vivo or that L6 myotubes may not be an appropriate model for comparison with in vivo effects. To further investigate the impact on gene expression on muscle imposed by exposure to free fatty acids, an AffymetrixÔ global gene expression analysis was conducted on mRNA from 24 hour linoleate treated L6 rat muscle cells and appropriate control cells. This experiment confirmed the previous RT-PCR measurements, but also revealed that there is a substantial difference in gene expression between cultured L6 rat muscle cells and red gastroc rat muscle in vivo.