Mice lacking a key protein involved in cholesterol regulation have low-density lipoprotein, or “bad” cholesterol, levels more than 50 percent lower than normal mice, and researchers suggest that inhibiting the same protein in humans could lead to new cholesterol-lowering drugs.In a study to be published in the Proceedings of the National Academy of Sciences and available online this week, researchers at UT Southwestern Medical Center deleted the Pcsk9 gene in mice. The gene, present in both mice and humans, makes the PCSK9 protein, which normally gets rid of receptors that latch onto LDL cholesterol in the liver. Without this degrading protein, the mice had more LDL receptors and were thus able to take up more LDL cholesterol from their blood.