Age-related alteration in hepatic acyl-CoA: cholesterol acyltransferase and its relation to LDL receptor and MAPK.

The aim of this study was to evaluate changes in the regulation of lipid metabolism and mitogen-activated protein kinases (MAPK) in the liver of C57BL/6 mice as they age. This was done by assessing the status of total cholesterol content and its enzyme, acyl-CoA: cholesterol acyltransferase (ACAT), in liver microsomal preparations and the low-density lipoprotein receptor (LDLr) mRNA expression in the livers of 4-24-month-old C57B/6 mice, without exogenous cholesterol feeding. With aging, there was an increase in cholesterol content and ACAT activity in liver microsomes. Northern blot analysis and real-time quantitative polymerase chain reaction data showed that ACAT-2 mRNA increased with age as well. LDLr expression decreased significantly in an age-dependent manner. In addition, we studied the basal and activated forms of MAPK, e.g. extracellular regulatory kinase (ERK-1/2), c-jun NH2-terminal kinase (JNK-1/2) and p38 MAPK. During aging, there was a considerable decrease in phosphorylated ERK-1/2 level while JNK-1/2 and p38 MAPK levels increased with age. Our studies showed an altered LDLr expression and altered phosphorylated MAPK in the liver of C57BL/6 mice during aging. These alterations might contribute to the development of atherosclerosis, hypercholesterolemia and other cholesterol-related conditions.