Lipid Droplets, the Central Hub Integrating Cell Metabolism and the Immune System

Abstract

Lipid droplets (LDs) are commonly found in various biological cells and are organelles related to cell metabolism. LDs, the number and size of which are heterogeneous across cell type, are primarily composed of polar lipids and proteins on the surface with neutral lipids in the core. Neutral lipids stored in LDs can be degraded by lipolysis and lipophagocytosis, which are regulated by various proteins. The process of LD formation can be summarized in four steps. In addition to energy production, LDs play an extremely pivotal role in a variety of physiological and pathological processes, such as endoplasmic reticulum stress, lipid toxicity, storage of fat-soluble vitamins, regulation of oxidative stress, and reprogramming of cell metabolism. Interestingly, LDs, the hub of integration between metabolism and the immune system, are involved in antitumor immunity, anti-infective immunity (viruses, bacteria, parasites, etc.) and some metabolic immune diseases. Herein, we summarize the role of LDs in several major immune cells as elucidated in recent years, including T cells, dendritic cells, macrophages, mast cells, and neutrophils. Additionally, we analyze the role of the interaction between LDs and immune cells in two typical metabolic immune diseases: atherosclerosis and Mycobacterium tuberculosis infection.

Quantitative determination of sn-positional phospholipid isomers in MSn using silver cationization

“…S4a and S4b), similar as shown by differential mobility [31]. Further selection and analysis of individual isomers show that there is a distinct difference in drift time between the silver-containing product ions after the neutral loss of the PC head group in cIMS 2 . Additional fragmentation in cIMS 3 shows that the loss of AgH provides product ions at m/z 575.5034 that have identical drift times.…”

“…1a shows that silver cationization (m/z 866.4822) exceeds all other adduct formations, suggesting that silver adduct formation of PC 34:1 is preferred under these experimental conditions. Fragmentation of the [M + 107 Ag] + precursor ions of PC 16:0/18:1 and PC 18:1/16:0 in MS 2 produces product ions at m/z 807.4091 and m/z 683.4162, which correspond to losses of the choline moiety (NL of C 3 H 9 N) and the full head group (NL of C 5 H 14 NPO 4 ), respectively (Figs. 1b and S1) [37].…”

“…Mass spectrometry of glycerophospholipids enables identification based on their mass-to-charge value (m/z), and further structural elucidation can be provided by the use of tandem mass spectrometry, MS 2 , and MS n [11]. In particular, the head group of glycerophospholipids is readily determined in MS 2 by identifying and/or scanning for the specific head group product ions or neutral losses (NL) [11,12].…”

“…Glycerophospholipids consist of a glycerol backbone to which fatty acyl side chains and a phosphate head group are bound. Glycerophospholipids have several functions in cells including being the major components of cellular membranes, essential in the induction of cell signaling, and important as precursors and storage centers for smaller signaling molecules [ 1 , 2 ]. The phosphate head group is located at the sn -3 position of the glycerol backbone and the two acyl chains in the sn -1 and sn -2 positions.…”

Lipid Metabolism in Glioblastoma: From De Novo Synthesis to Storage

“…The most predominant features of LDs are their heterogeneity and diversity. The number, size, and composition of LDs vary widely between cells or even within the same cell depending on different conditions [ 109 , 112 , 129 , 130 , 131 ]. Only one LD with a diameter often >100 µm is found in most adipocytes, whereas a greater number of LDs are found in non-adipocyte cells and are usually <1 µm in diameter [ 132 , 133 ].…”