EXPRESSION OF HORMONE-SENSITIVE LIPASE MESSENGER-RNA IN MACROPHAGES

Macrophages contain a neutral cholesteryl ester hydrolase that can be activated by cAMP-dependent protein kinase. Immunological studies stro ngly suggest that hormone-sensitive lipase (HSL) is probably responsib le for the cholesteryl ester hydrolase activity in macrophages; howeve r, due to the very low level of expression in macrophages, it has been difficult to determine whether the macrophage cholesteryl ester hydro lase and adipose HSL are, in fact, products of the same gene. We have used the sensitive polymerase chain reaction (PCR) technique to demons trate expression of HSL mRNA in resident and thioglycollate-elicited m ouse peritoneal macrophages, as well as in the P388D1 mouse macrophage cell line. PCR was performed using oligonucleotide primer sequences p resent on adjacent exons of the mouse HSL gene to allow discrimination between products derived from HSL mRNA or genomic DNA sequences; spec ificity of the PCR was demonstrated by the absence of a product in liv er, which does not express HSL mRNA. Northern blot analysis of poly (A )+ RNA from peritoneal macrophages with a mouse adipose HSL cDNA probe demonstrated a low abundance of mRNA of 3.2 kb, identical in size to HSL mRNA in adipose tissue. These findings, together with the results of previous studies demonstrating similarities between HSL and macroph age neutral cholesteryl ester hydrolase, strongly support the conclusi on that both are products of a single gene. The development of a PCR a ssay for HSL mRNA may allow further study of the regulation of neutral cholesteryl ester hydrolase expression in macrophages and foam cells, and its potential role in atherogenesis.