Lipid Transport Across the Mammary Gland
Mammary secretory cells have evolved robust processes for transporting and secreting nutrients, including lipids, proteins, and sugars, required for neonatal growth and development. The processes responsible for secreting lipids are particularly unique to
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Lipid Transport Across the Mammary Gland James L. McManaman
Abstract Mammary secretory cells have evolved robust processes for transporting and secreting nutrients, including lipids, proteins, and sugars, required for neonatal growth and development. The processes responsible for secreting lipids are particularly unique to mammary secretory cells and represent novel adaptations of apocrine secretion. All eukaryotic cells depend on phospholipid (PL) and fatty acid (FA) transport to maintain membrane structure and organization, and to fuel and regulate cellular functions. The copious milk secretion, including large quantities of lipid in some species, requires adaptation and integration of PL and FA synthesis and transport processes to meet secretion demands. At present, few details exist about how these processes are regulated within the mammary gland. However, recent advances in our understanding of the structural and molecular biology of membrane systems and cellular lipid trafficking provide insights into the mechanisms underlying the regulation and integration of PL and FA transport processes in the secretion of milk lipids. This review discusses the PL and FA transport processes required to maintain the structural integrity and organization of the mammary gland and support its secretory functions within the context of current molecular and cellular models of their regulation. Keywords Biosynthesis, Lactation · Lipids · Mammary gland · Membranes · Transport mechanisms
J. L. McManaman (*) Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, USA e-mail: [email protected] © The American Physiological Society 2020 K. L. Hamilton, D. C. Devor (eds.), Ion Transport Across Epithelial Tissues and Disease, Physiology in Health and Disease, https://doi.org/10.1007/978-3-030-55310-4_7
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J. L. McManaman
The Mammary Secretory Cell
The mammary gland is a mammalian-specific exocrine organ comprised of a network of ducts and acini lined by single layers of cuboidal or columnar epithelial cells that serve barrier, structural, and/or secretory functions. Epithelial cells lining acini (hereafter referred to as mammary secretory cells) undergo functional differentiation during pregnancy and lactation to synthesize and secrete a complex fluid, which contains the diverse array of nutritive and bioactive substances that comprise milk. Epithelial cells lining ducts serve structural and barrier functions forming the conduits that supply milk to nursing young. Unlike ductal epithelial cells of other exocrine organs, such as the salivary gland, ductal epithelial cells of the mammary gland lack recognized synthetic or secretory functions (McManaman et al. 2006), and little is known about their specific transport functions. In contrast, mammary secretory cells require efficient and integrated cellular transport mechanisms to produce molecularly complex milk and meet the robust secretory functions of the mammary gland during lactation (Shennan and Peaker 2000). This chapter f
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