I think if you ever wanted to know what "gene expression" exactly is, look no further than nuclear receptors. You have receptors around your DNA nucleus in your cells that bind different things, this basically causes activation of your DNA to produce difference proteins ( polypeptides is a better word ) , thus expressing different gene's. !!!!
Sustained activation of PPARα by endogenous ligands increases hepatic fatty acid oxidation and prevents obesity in ob/ob mice.
PPARα is nothing other than simply a certain receptor sported on the nucleus of mainly your liver cells. And it binds fatty acids. I havent so far been able to find a comprehensive list of ligands but PPARα is reported to be responsible for the fasting response.
PPARα activation also reverses fatty liver. yay!
In the study above the researchers manipulated some enzyme called Peroxisomal acyl-coenzyme A oxidase 1, basically turning it off, such that PPARα was excessively activated, the result was a lean rodent. ( even though this rodent is genetically predisposed to be fat )
However it seems there was a price to pay, all the extra fat burning in the liver resulted in oxidative stress overload and liver cancer.