Journal of Lipid Research, Vol 16, 211-223, Copyright © 1975 by Lipid Research, Inc.
Regulation of cholesterol synthesis and storage in fat cells
PT Kovanen, EA Nikkila and TA Miettinen
The fat cells of rat epididymal adipose tissue contain an average of 0.5 mg
of cholesterol per gram of triglyceride. Of this cholesterol, 90% is
nonesterified and 80% is located in the lipid storage compartment. The fat
cell cholesterol content correlated positively with cell size. During
fasting the free cholesterol of the adipocyte decreased in parallel with
triglyceride, whereas the amount of esterified cholesterol did not change.
The fat cell cholesterol content is independent of the amount of dietary
cholesterol. On in vitro incubation of rat fat cells with radiolabeled
acetate, mevalonate, glucose, leucine, or water, labeled cholesterol was
synthesized. The rate of cholesterol synthesis increased with fat cell
size. Fasting suppressed cholesterol synthesis by 90%, whereas refeeding
stimulated the synthesis above values found in normally fed rats.
Stimulation of lipolysis with theophylline or with dibutyryl cyclic AMP
markedly inhibited cholesterol synthesis in fat cells. Insulin increased
the incorporation of glucose and leucine into fat cell cholesterol. The
cholesterol synthesis in fat cells was not suppressed by a high cholesterol
diet. Addition of very low or low density lipoprotein into the incubation
medium suppressed fat cell cholesterol synthesis whereas high density
lipoprotein did not. The lipoprotein-free serum stimulated cholesterol
synthesis compared with serum-free medium. The rate of cholesterol
synthesis in total adipose tissue of rat was estimated to be 4% of that in
the liver. It seems unlikely that the increased body cholesterol turnover
present in obesity is accounted for by the enhanced cholesterol formation
in the enlarged adipose tissue.