Leptin is produced primarily in the adipocytes of white adipose tissue. It also is produced by brown adipose tissue, placenta (syncytiotrophoblasts), ovaries, skeletal muscle, stomach (the lower part of the fundic glands), mammary epithelial cells, bone marrow, gastric chief cells and P/D1 cells.
The fuel filter, in a 2008 Ford fusion, is located inside of the fuel tank. Drain the fuel from the fuel tank. Remove the fuel filter plate. The fuel filter will slide out. Reverse the process to install the new fuel filter. The fuel filter, in a 2008 Ford fusion, is located inside of the fuel tank. Drain the fuel from the fuel tank.
This is a little tougher than replacing an air filter, since finding the thing can be half the battle. It's typically located near the top-center of the engine, close to the air filter, although sometimes, with more modern cars, it's actually built into the fuel tank and is a job best suited to your mechanic.