Cholesterol’s link to heart disease gets clearer - and more complicated
By considering molecular level events on a broader scale, researchers now have a clearer, if more complicated, picture of how one class of immune cells goes wrong when loaded with cholesterol. The findings reported in the February 3rd issue of Cell Metabolism, a Cell Press publication, show that, when it comes to the development of atherosclerosis and heart disease, it’s not about any one bad actor - it’s about a network gone awry.
The new findings also highlight a pretty remarkable thing, Heinecke says: “Despite 30 years of study, we still don’t know how cholesterol causes heart disease.” But, with the new findings, scientists are getting closer.
Earlier studies had shown that heart disease is about more than just high LDL (”bad”) cholesterol. Cells known as macrophages also play a critical role. Macrophages are part of the innate immune system that typically gobble up pathogens and clear away dead cells. But they also take up and degrade cholesterol derivatives. When they get overloaded with those lipoproteins, they take on a foamy appearance under the microscope to become what scientists aptly refer to as foam cells. Those foam cells are the ones that seem to have critical importance in the development of atherosclerosis.
People had typically thought about this problem in terms of linear pathways, Heinecke explained. In essence, macrophages end up with too much cholesterol going in and not enough coming out. The macrophages get overwhelmed and trapped in the artery wall, and somehow plaques form as a result.
But the new results show that it isn’t really about simple paths in and out; rather, there is an integrated network of macrophage proteins involved. When that network gets disrupted, as it does when too much cholesterol comes in, atherosclerosis forms. “It’s definitely a different way to think about what is going on,” Heinecke says.
Heinecke’s group applied sophisticated technologies and statistical tools to get a global view of what happens to macrophage proteins when they turn into foam cells. Their analysis revealed what they call a macrophage sterol responsive network (MSRN), including proteins already known to work together. Most of them are also found in one place, within microvesicles outside the macrophage cells.