For middle and high school students: Cholesterol is essential for cell membranes and steroid hormones, but too much raises the risk of atherosclerosis. Brown and Goldstein discovered that low-density lipoprotein (LDL), the main cholesterol carrier in blood, binds to LDL receptors on the cell surface and is taken into the cell by endocytosis. When this pathway is blocked, blood LDL rises, leading to a genetic disease called familial hypercholesterolemia (FH). Their work established the concept of cholesterol homeostasis and inspired the development of HMG-CoA reductase inhibitors, known as statins. Statins are now widely prescribed to prevent heart attacks and strokes.

Using radiolabeled LDL uptake assays in human fibroblasts, Brown and Goldstein demonstrated that LDL receptor abundance is feedback-regulated by extracellular cholesterol. In fibroblasts from FH patients they defined multiple mutation classes—null synthesis, transport-defective, binding-defective and others—each causing dramatic elevation of serum LDL. They proposed a dual control mechanism in which intracellular cholesterol, once internalized, suppresses transcription of both HMG-CoA reductase and the LDL receptor via the SREBP pathway. This framework became central to lipoprotein metabolism and explained why statins, by inhibiting cholesterol synthesis, up-regulate receptor expression and lower blood LDL. Moreover, the concept of receptor-mediated endocytosis influenced studies of EGF and insulin receptors and is now a core principle of modern cell biology.

Brown and Goldstein used 125I-LDL binding–dissociation kinetics to show that human LDLR displays both high-affinity (Kd≈5×10^−9 M) and low-affinity components and that pH-dependent dissociation in endosomes is essential for receptor recycling. Complementation analysis of FH cell lines delineated five mutation classes, ranging from Class 1 null alleles to Class 4 NPXY motif internalization defects, systematizing LDLR structure–function relationships. They further proposed that cholesterol accumulation induces ER retention of the SREBP-SCAP complex, thereby blocking SRE-dependent transcription of HMGCR and LDLR. Cholesterol homeostasis was thus redefined as a multilayered network integrating receptor cycling, de novo synthesis, esterification, and crosstalk with ergosteroid signals. Their work provided the conceptual foundation for therapeutic targets such as PCSK9-blocking antibodies and remains a benchmark in atherosclerosis research.