A possible role of cholesterol-sphingomyelin/phosphatidylcholine in nuclear matrix during rat liver regeneration.

Background/aims: Phospholipids and cholesterol in chromatin have been previously demonstrated. The lipid fraction changes during cell proliferation in relation to activation of enzymes of phospholipid metabolism. The aim of the present work is to clarify if chromatin lipids may derive or not from nuclear matrix and if they have different roles.
Methods: The subnuclear fractions were isolated from rat hepatocyte nuclei and the lipid fraction was extracted and analysed by chromatography in normal and regenerating liver. The phosphatidylcholine-sphingomyelin metabolism enzymes activity was assayed, by using radioactive substrates.
Results: In nuclear matrix, cholesterol and sphingomyelin are respectively five and three times higher than those present in chromatin; the amount of phosphatidylcholine, which it is enriched in saturated fatty acids, is lower, thus indicating a less fluid structure. The lower content in phosphatidylcholine may be justified by the phosphatidylcholine-dependent phospholipase C activity, which increases during liver regeneration, reaching a peak at the beginning of S-phase, when also cholesterol and sphingomyelin increase.
Conclusions: The nuclear matrix lipids are independent from chromatin lipids; the ratio cholesterol-sphingomyelin/phosphatidylcholine is higher and, as a consequence, nuclear matrix is less fluid in relation to DNA synthesis, suggesting a specific role of nuclear matrix as a structure involved in DNA duplication.