AJP - Cell Physiology, Vol 258, Issue 4 C673-C681, Copyright © 1990 by American Physiological Society
Lipoprotein lipase: cellular origin and functional distribution
L. Camps, M. Reina, M. Llobera, S. Vilaro and T. Olivecrona
Department of Biochemistry and Physiology, University of Barcelona, Spain.
Lipoprotein lipase (LPL, E.C. 3.3.1.34) is the enzyme responsible for
hydrolysis of triacylglycerols in plasma lipoproteins, making the fatty
acids available for use by subjacent tissues. LPL is functional at the
surface of endothelial cells, but it is not clear which cells synthesize
the enzyme and what its distribution is within tissues and vessels. We have
searched for specific cell expression of the LPL gene by in situ
hybridization using a RNA probe and for the corresponding protein
distribution by immunocytochemistry on cryosections of some LPL-producing
tissues of guinea pigs. In white and brown adipose tissues, heart and
skeletal muscle, and lactating mammary gland, there was positive
hybridization for LPL mRNA over all members of the major cell types,
indicating that mature and immature adipocytes, muscle cells, and mammary
epithelial cells are main sources of LPL. In large vessels, LPL expression
was detected in some smooth muscle cells in the media layer. There was no
positive hybridization for LPL mRNA over endothelial cells in any of the
tissues studied, but there was immunoreaction for LPL protein at
endothelial surfaces of all blood vessels. In the kidney, there was strong
immunofluorescence at the vascular endothelium, particularly in the
glomeruli, but little or no LPL mRNA was detected in the surrounding cells.
These observations suggest that in some tissues LPL is synthesized by
parenchymal cells and spreads along the vascular mesh. Transfer to the
vascular endothelium is, however, not the only route taken by LPL. In the
mammary gland most of the enzyme protein appeared to be secreted, partly in
association with milk fat droplets.(ABSTRACT TRUNCATED AT 250 WORDS)
