Department of Biology, Georgia State University, Atlanta, GA 30303, USA.
Department of Obstetrics, Gynecology and Reproductive Science, University of California, San Francisco, CA 94143, USA.
Int J Mol Sci. 2021 Jul 29;22(15):8144. doi: 10.3390/ijms22158144.
Although once perceived as inert structures that merely serve for lipid storage, lipid droplets (LDs) have proven to be the dynamic organelles that hold many cellular functions. The LDs' basic structure of a hydrophobic core consisting of neutral lipids and enclosed in a phospholipid monolayer allows for quick lipid accessibility for intracellular energy and membrane production. Whereas formed at the peripheral and perinuclear endoplasmic reticulum, LDs are degraded either in the cytosol by lipolysis or in the vacuoles/lysosomes by autophagy. Autophagy is a regulated breakdown of dysfunctional, damaged, or surplus cellular components. The selective autophagy of LDs is called lipophagy. Here, we review LDs and their degradation by lipophagy in yeast, which proceeds via the micrometer-scale raft-like lipid domains in the vacuolar membrane. These vacuolar microdomains form during nutrient deprivation and facilitate internalization of LDs via the vacuolar membrane invagination and scission. The resultant intra-vacuolar autophagic bodies with LDs inside are broken down by vacuolar lipases and proteases. This type of lipophagy is called microlipophagy as it resembles microautophagy, the type of autophagy when substrates are sequestered right at the surface of a lytic compartment. Yeast microlipophagy via the raft-like vacuolar microdomains is a great model system to study the role of lipid domains in microautophagic pathways.
虽然曾经被认为是仅作为脂质储存的惰性结构,但脂滴(LDs)已被证明是具有许多细胞功能的动态细胞器。LDs 的基本结构是由中性脂质组成的疏水核心,被一层磷脂单层包围,允许细胞内能量和膜的快速脂质可及性。LDs 虽然是在内质网的外周和核周形成的,但可以在细胞质中通过脂解作用或在液泡/溶酶体中通过自噬作用进行降解。自噬是一种对功能失调、受损或多余的细胞成分进行调节性分解的过程。LDs 的选择性自噬称为脂噬。在这里,我们回顾了酵母中 LDs 及其通过脂噬作用的降解,该过程通过液泡膜上的微米级筏状脂质域进行。这些液泡微域在营养物质缺乏时形成,并通过液泡膜的内陷和分裂促进 LDs 的内化。带有 LDs 的内部的内含体通过液泡脂肪酶和蛋白酶进行分解。这种类型的脂噬作用称为微脂噬,因为它类似于微自噬,即当底物被隔离在溶酶体的表面时发生的自噬类型。酵母通过筏状液泡微域的微脂噬是研究脂质域在微自噬途径中作用的理想模型系统。
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