Department of Animal Science, the Robert H. Smith Faculty of Agriculture, Food and Environment, the Hebrew University of Jerusalem, Israel, POB 76100.
J Dairy Sci. 2019 Mar;102(3):2783-2795. doi: 10.3168/jds.2018-15240. Epub 2019 Jan 11.
Milk fat globule (MFG) size ranges over 3 orders of magnitude, from less than 200 nm to over 15 µm. The significance of MFG size derives from its tight association with its lipidome and proteome. More specifically, small MFG have relatively higher content of membrane compared with large globules, and this membrane exerts diverse positive health effects, as reported in human and animal studies. In addition, MFG size has industrial significance, as it affects the physicochemical and sensory characteristics of dairy products. Studies on the size regulation of MFG are scarce, mainly because various confounders indirectly affect MFG size. Because MFG size is determined before and during its secretion from mammary epithelial cells, studies on the size regulation of its precursors, the intracellular lipid droplets (LD), have been used as a proxy for understanding the mechanisms controlling MFG size. In this review, we provide evidence for 2 distinct mechanisms regulating LD size in mammary epithelial cells: co-regulation of fat content and triglyceride-synthesis capacity of the cells, and fusion between LD. The latter is controlled by the membrane's polar lipid composition and involves mitochondrial enzymes. Accordingly, this review also discusses MFG size regulation in the in vivo metabolic context, as MFG morphometric features are often modulated under conditions that involve animals' altered energy status.
乳脂肪球（MFG）的大小范围跨越 3 个数量级，从小于 200nm 到超过 15µm。MFG 大小的重要性源于其与脂质组和蛋白质组的紧密关联。更具体地说，与大的脂肪球相比，小的 MFG 具有相对更高的膜含量，并且如人类和动物研究中所报道的，这种膜具有多种积极的健康影响。此外，MFG 大小具有工业意义，因为它会影响乳制品的物理化学和感官特性。关于 MFG 大小调节的研究很少，主要是因为各种混杂因素间接影响 MFG 大小。由于 MFG 大小在乳腺上皮细胞分泌之前和期间就已确定，因此研究其前体——细胞内脂滴（LD）的大小调节已被用作了解控制 MFG 大小的机制的替代方法。在这篇综述中，我们提供了证据表明有 2 种不同的机制可以调节乳腺上皮细胞中 LD 的大小：细胞脂肪含量和甘油三酯合成能力的共同调节，以及 LD 之间的融合。后者受膜的极性脂质组成和涉及线粒体酶的控制。因此，这篇综述还讨论了在体内代谢背景下 MFG 大小的调节，因为在涉及动物能量状态改变的情况下，MFG 的形态特征经常被调节。
