Liver-specific knockdown of JNK1 up-regulates proliferator-activated receptor gamma coactivator 1 beta and increases plasma triglyceride despite reduced glucose and insulin levels in diet-induced obese mice.

The c-Jun N-terminal kinases (JNKs) have been implicated in the development of insulin resistance, diabetes, and obesity. Genetic disruption of JNK1, but not JNK2, improves insulin sensitivity in diet-induced obese (DIO) mice. We applied RNA interference to investigate the specific role of hepatic JNK1 in contributing to insulin resistance in DIO mice. Adenovirus-mediated delivery of JNK1 short-hairpin RNA (Ad-shJNK1) resulted in almost complete knockdown of hepatic JNK1 protein without affecting JNK1 protein in other tissues. Liver-specific knockdown of JNK1 resulted in significant reductions in circulating insulin and glucose levels, by 57 and 16%, respectively. At the molecular level, JNK1 knockdown mice had sustained and significant increase of hepatic Akt phosphorylation. Furthermore, knockdown of JNK1 enhanced insulin signaling in vitro. Unexpectedly, plasma triglyceride levels were robustly elevated upon hepatic JNK1 knockdown. Concomitantly, expression of proliferator-activated receptor gamma coactivator 1 beta, glucokinase, and microsomal triacylglycerol transfer protein was increased. Further gene expression analysis demonstrated that knockdown of JNK1 up-regulates the hepatic expression of clusters of genes in glycolysis and several genes in triglyceride synthesis pathways. Our results demonstrate that liver-specific knockdown of JNK1 lowers circulating glucose and insulin levels but increases triglyceride levels in DIO mice.

Hepatic knockdown of stearoyl-CoA desaturase 1 via RNA interference in obese mice decreases lipid content and changes fatty acid composition.

Stearoyl-CoA desaturases (SCDs) catalyze the biosynthesis of monounsaturated fatty acids from saturated fatty acids. Four scd genes have been identified in mice and three in human (including one pseudogene). Among the four mouse SCD isoforms, SCD1 is predominantly expressed in liver and adipose tissue. Mice null for the scd1 gene have reduced adiposity, increased energy expenditure and altered lipid profiles. To further evaluate the specific role of hepatic SCD1 and the potential to achieve similar desirable phenotypic changes in adult obese mice, adenovirus-mediated short hairpin interfering RNA (shRNA) was used to acutely knock down hepatic scd1 expression in ob/ob mice. Robust reductions in hepatic SCD1 mRNA and SCD1 enzymatic activity were achieved, sustained up to 2 weeks. Reduced hepatic content of neutral lipids and robust lowering of lipid desaturation indexes, but increased content of liver phosphotidylcholine were observed with SCD1 knockdown. Increased total plasma cholesterol levels were also observed. No significant changes in body weight were observed. Expression levels of several lipogenic and lipid oxidation genes were not significantly altered by short term SCD1 reduction, but UCP2 expression was increased. Our results demonstrate that significant changes to both hepatic and systemic lipid profiles can be achieved through specific knockdown of liver-expressed SCD1 in the ob/ob mouse model. However, hepatic SCD1 knockdown does not result in significant changes in body weight in the short term.