Journal of Lipid Research, Vol 38, 913-925, Copyright © 1997 by Lipid Research, Inc.
Lipid-depleted diet perturbs membrane composition and intracellular transport in lactating mammary cells
M Ollivier-Bousquet, F Lavialle, P Guesnet, D Rainteau and G Durand
Laboratoire de Biologie Cellulaire et Moleculaire, INRA, Jouy-en-Josas, France.
When rats were fed a control or a lipid-depleted diet for five generations,
reproduction was not disturbed but pup growth was affected. The membrane
organization and the secretory activity of mammary epithelial cells from
these lactating rats were investigated. This diet induced a large decrease
in the level of polyunsaturated fatty acids of membrane phospholipids
(26.6% versus 44.0%). The level of 20:4 (n-6) was strongly decreased,
mainly in phosphatidylethanolamine. Annexin VI, which interacts
preferentially with this phospholipid, accumulated at the periphery of the
cell and was largely associated to the hydrophobic region of the bilayer as
compared to control membranes. Casein synthesis and casein secretion
measured in incubated explants, after pulse-chase metabolic labeling, were
both reduced by about 60% in lipid-deprived cells. The secretory ratio
(radioactive secreted caseins in %) was not modified, suggesting that the
mechanism of basal secretion was not mainly affected. On the contrary, the
secretagogue effect of prolactin disappeared. The intracellular transport
of the hormone was considerably slowed down by the diet and prolactin did
not reach the lumen of the acini after 1 h of chase, in contrast to what
occurred in control cells. Addition of 20:4 (n-6), in vitro, to mammary
fragments from lipid-deprived rats restored the localization of annexin VI,
increased synthesis and secretion of caseins as well as intracellular
transport of PRI. Together, these data underline the importance of the
level of 20:4 (n- 6) in membrane phospholipids for exocytic and endocytic
transport in lactating mammary epithelial cells.