Regulation of HMG CoA reductase activity in fibroblasts from a normal subject and from an FH homozygote. A, Monolayers of cells were grown in dishes containing 10% fetal calf serum. On day 6 of cell growth (zero time), the medium was replaced with fresh medium containing 5% human serum from which the lipoproteins had been removed. At the indicated time, extracts were prepared, and HMG CoA reductase activity was measured. B, 24 hours after addition of 5% human lipoprotein-deficient serum, human LDL was added to give the indicated cholesterol concentration. HMG CoA reductase activity was measured in cell free extracts at the indicated time. (Modified from 8).

Sequential steps in the LDL receptor pathway of mammalian cells (already defined in text). (Modified from 58).

Joseph L. Goldstein (left) and Michael S. Brown on the day of announcement of their Nobel Prize in Physiology or Medicine on October 15, 1985.

A 10-year-old girl with homozygous FH. Note the elevated orange-yellow xanthomas lying superficially over the knees, the wrists, and interdigital webs. These xanthomas arise from the deposition of plasma LDL-derived cholesterol into macrophages of the skin. The rate of deposition is proportional to the severity and duration of the elevation in plasma LDL. A similar deposition of LDL-derived cholesterol occurred in the coronary arteries of this girl, producing atheromas of artery wall, which led to her first myocardial infarction at age 8.

Internalization and degradation at 37° C of ¹²⁵I-LDL by fibroblasts from a normal subject (A) and from J.D., a patient with the internalization-defective form of FH (B). Each cell monolayer was allowed to bind ¹²⁵I-LDL (10 μg protein/ml) at 4° C for 2 hours, after which the cells were washed extensively. In one set of dishes, the amount of ¹²⁵I-LDL bound was determined by measuring the amount of ¹²⁵I-LDL that could be released from the surface by treatment with heparin. Replicate dishes then received warm medium and were incubated at 37° C. After the indicated interval, the dishes were rapidly chilled to 4° C, and the amounts of surface-bound (heparin-releasable) ¹²⁵I-LDL, internalized (heparin-resistant) ¹²⁵I-LDL, and degraded (trichloroacetic acid-soluble) ¹²⁵I-LDL were measured. (Modified from 27).

Actions attributable to the LDL receptor in fibroblasts from a normal subject and from a homozygote with the receptor-negative form of FH . Cells were incubated with varying concentrations of ¹²⁵I-LDL or unlabeled LDL at 37° C for 5 hours and assayed as described 58. All data are normalized to 1 mg of total cell protein. The units for each assay are as follows: Binding, μg of ¹²⁵I-LDL bound to cell surface; Internalization, μg of ¹²⁵I-LDL contained within the cell; Hydrolysis of apoprotein B-100, μg of ¹²⁵I-LDL degraded to ¹²⁵I-monoiodotyrosine per hour; Hydrolysis of cholesteryl esters, nmol of [³H]cholesterol formed per hour from the hydrolysis of LDL labeled with [³H]cholesteryl linoleate; Cholesterol synthesis, nmol of [¹⁴C]acetate incorporated into [¹⁴C]cholesterol per hour by intact cells; Cholesterol esterification, nmol of [¹⁴C]oleate incorporated into cholesteryl [¹⁴C]oleate per hour by intact cells. (Modified from 58).