Kinetics of milk lipid droplet transport, growth, and secretion revealed by intravital imaging: lipid droplet release is intermittently stimulated by oxytocin

The lipid droplet (LD) fraction of milk has attracted special attention because it supplies preformed lipids for neonatal development, and the assembled LDs are secreted by a unique apocrine mechanism. Because many aspects of this key process remain uncharacterized, we developed a facile method for...

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Bibliographic Details
Published in:Molecular biology of the cell 2017-04, Vol.28 (7), p.935-946
Main Authors: Masedunskas, Andrius, Chen, Yun, Stussman, Rebecca, Weigert, Roberto, Mather, Ian H
Format: Article
Language:English
Subjects:
Animals
Cell Membrane - metabolism
Epithelial Cells - metabolism
Female
Intravital Microscopy - methods
Kinetics
Lactation - metabolism
Lactation - physiology
Lipid Droplets - metabolism
Lipid Droplets - physiology
Lipid Metabolism
Lipids
Mammary Glands, Animal - metabolism
Mice
Milk
Oxytocin - metabolism
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Summary:The lipid droplet (LD) fraction of milk has attracted special attention because it supplies preformed lipids for neonatal development, and the assembled LDs are secreted by a unique apocrine mechanism. Because many aspects of this key process remain uncharacterized, we developed a facile method for the intravital imaging of mammary cells in transgenic mice that express fluorescently tagged marker proteins. Using these techniques, we describe the first kinetic analysis of LD growth and secretion at peak lactation in real time. LD transit from basal to apical regions was slow (0-2 μm/min) and frequently intermittent. Droplets grew by the fusion of preexisting droplets, with no restriction on the size of fusogenic partners. Most droplet expansion took several hours and occurred in apical nucleation centers, either close to or in association with the apical surface. Droplets even continued to expand as they were emerging from the cell. Contrary to expectations, LDs attached to the apical plasma membrane but still associated with the cytoplasm were released after oxytocin-mediated contraction of the myoepithelium. Thus milk LD secretion is an intermittently regulated process. This novel procedure will have broad application for investigating trafficking events within the mammary epithelium in real time.
ISSN:1059-1524
1939-4586
DOI:10.1091/mbc.E16-11-0776