Origin and secretion of milk lipids
Origin and secretion of milk lipids
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DOI：
10.1023/a:1018711410270
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发表时间：
1998-07-01
影响因子：
2.5
通讯作者：
Keenan, TW
中科院分区：
文献类型：
--
作者：
Mather, IH;Keenan, TW
乳的奶油部分包含涂覆有细胞膜的三酰甘油的液滴。在这篇综述中，我们讨论了这些液滴是如何形成和分泌的乳腺上皮细胞在哺乳期。这种分泌系统特别有趣，因为组装的脂滴是从细胞膜包裹的细胞质中分泌的。在其他细胞中，如肝细胞和肠上皮细胞，脂质通过分泌途径的膜结合区室的胞吐作用分泌。乳脂来源于小滴的三酰甘油，在粗面内质网（ER）膜内或表面合成（4）。这些微滴作为微脂滴（MLD）释放到细胞质中，表面有蛋白质和极性脂质的外壳。MLD可以彼此融合以形成更大的细胞质脂滴（CLD）。不同大小的液滴通过未知的机制被运输到顶端细胞质，并从包被有外部双层膜的细胞中分泌。CLD的大小可能在细胞的所有区域中增加，特别是在分泌期间的质膜处。已经提出了两种可能的脂质分泌机制：顶端机制，其中脂滴被顶端质膜包裹，和分泌囊泡机制，其中脂滴被细胞质中的分泌囊泡包围，并通过胞吐作用从细胞质内空泡的表面释放。两种机制的组合是可能的。分泌后，围绕小球的一部分膜可能从液滴脱落，并在脱脂乳相中产生膜碎片。
The cream fraction of milk comprises droplets of triacylglycerol coated with cellular membranes. In this review, we discuss how these droplets are formed and secreted from mammary epithelial cells during lactation. This secretory system is especially interesting because the assembled lipid droplets are secreted from the cytoplasm enveloped by cellular membranes. In other cells, such as hepatocytes and enterocytes, lipid is secreted by exocytosis from membrane-bounded compartments of the secretory pathway. Milk lipids originate as small droplets of triacylglycerol, synthesized in or on the surfaces of rough endoplasmic reticulum (ER)(4) membranes. These droplets are released into the cytoplasm as microlipid droplets (MLDs) with a surface coat of protein and polar lipid. MLDs may fuse with each other to form larger cytoplasmic lipid droplets (CLDs). Droplets of varying size, are transported to the apical cytoplasm by unknown mechanisms and are secreted from the cell coated with an outer bilayer membrane. CLDs may increase in size in all regions of the cell, especially at the plasma membrane during secretion. Two possible mechanisms for lipid secretion have been proposed: an apical mechanism, in which lipid droplets are enveloped with apical plasma membrane, and a secretory-vesicle mechanism, in which fat droplets are surrounded by secretory vesicles in the cytoplasm and are released from the surface by exocytosis from intracytoplasmic vacuoles. A combination of both mechanisms may be possible. Following secretion, a fraction of the membrane surrounding the globules may be shed from the droplets and give rise to membrane fragments in the skim milk phase.