Contrasting adrenergic effects on lipoprotein lipase gene expression in the brown adipose tissue of intact mice and in cultured brown adipocytes from mice

Abstract

To examine the regulation of lipoprotein lipase (LPL) gene expression, LPL mRNA levels in the brown adipose tissue of intact mice and in mouse brown adipocyte cultures were examined. In intact mice, exposure to cold resulted in a rapid, transient, 5-fold increase in LPL mRNA level. Norepinephrine (NE) injection could fully mimic the effect of acute exposure to cold, and LPL mRNA and enzymatic activity were increased in parallel after NE injection. These results indicated positive adrenergic control of LPL gene expression in the brown adipose tissue of intact mice. In cultured mouse brown adipocytes, the level of spontaneously expressed LPL mRNA decreased in parallel with the progression of brown adipocyte differentiation. NE treatment of undifferentiated cells led to a decrease in LPL mRNA levels. In brown adipocytes that had reached a mature state, NE had a small negative or no effect on LPL mRNA levels, irrespective of whether the experiment was performed in the presence or absence of insulin or of newborn-calf serum. It was concluded that LPL gene expression in brown adipose tissue in intact mice is under adrenergic control but that this gene is not under positive adrenergic control in cultured brown adipocytes from mice, although these cells are otherwise adrenergically sensitive. The presence of additional factors may be necessary to confer adrenergic sensitivity to the LPL gene in the cultured brown adipocytes; alternatively, cells other than the mature brown adipocytes may confer the positive adrenergic sensitivity to the brown adipose tissue depots in situ. © 1997 Elsevier Science B.V. All rights reserved.