Biology news 4: Taming Cholesterol

We're back. In this issue, as you munch on festival sweets and cakes, biologists bring you new insights into a scary aspect of diet: cholesterol. You can read the actual article here: http://www.pubmedcentral.gov/articlerender.fcgi?tool=pubmed&pubmedid=16100574.

There's a lot of bad hype about cholesterol: it can cause heart problems, you want to keep your numbers low, and it can lead to a bigger gut (along with its ugly cousin, fat). But cholesterol can be good for you, too.

We all need a little bit of cholesterol to keep our cells working properly. Cholesterol is a small molecule that slips into the outer wall (the cell membrane) of the components of our bodies, our cells. In there, it helps keep the cell membrane fluid and smooth, not rigid and impenetrable. If you have too little cholesterol, your liver will actually start to make it!

The problems start when you have too much. Too much cholesterol can combine with fat to clog up arteries.

So it's important that your liver stops making cholesterol. How does your body know that there's too much cholesterol and to stop making it? That's something scientists have puzzled over, until now.

Recent studies have shown that when you have too much cholesterol, two genes in your DNA get turned on. They make two proteins called the "Insigs." What are insigs and what do they do? The Insig proteins are special in one particular way: they prevent cholesterol from being made by binding to one of the parts of the cholesterol-making machine.

Imagine: you eat a particularly high cholesterol diet (a large fast-food lunch, or several slices of pizza with lots of cheese). You get a lot of cholesterol into your cells. In the meantime, your body has already been making cholesterol! That's cholesterol you don't need. A machine in your cell is chugging away, making cholesterol, with cholesterol-making proteins.

Now, your insigs spring into action. They go over to the cholesterol-making protein (called SREBPs), and they grab on to it. They glom on and trap it inside the cell so that it can't make more cholesterol-making proteins and more cholesterol. Ta da - you stop making cholesterol. Of course, now you have to do something with the cholesterol you already have.

What happens when your insigs stop working? The scientists removed the insig genes from some mice. When those mice ate a lot of cholesterol-rich food (mmm, cheese!), they got fat. Of course. But not only that! They continued to make cholesterol even when their livers would normally stop.

The cool thing about this study is that if you could treat people who normally make too much cholesterol with something that activates their insigs, they would make less. Then you could someday even increase your insigs to prevent from getting fatty!