Lipid body formation during maturation of human mast cells

Abstract

This article is available online at http://www.jlr.org can be found in almost any type of cell ( 1 ). Currently, the role of lipid droplets in the pathophysiology of obesitydependent metabolic diseases involving insulin resistance is studied intensively ( 2 ). Lipid droplets are also present in various types of infl ammatory cells ( 3-6 ), where they are usually called lipid bodies (LB) and participate in cell signaling and in the generation of biologically active lipid mediators evoked by infl ammatory and infectious conditions ( 7-11 ).Lipid bodies consist of a neutral lipid core that is surrounded by a monolayer of amphipathic lipids (phospholipids and unesterifi ed cholesterol) and by proteins involved in the formation and traffi cking of the LBs and in the turnover of their lipids. Depending on the type and metabolic state of a cell, the protein and lipid compositions of the LBs may vary considerably, refl ecting active metabolism of their lipid components ( 12 ). The main proteins known to regulate the metabolism of the LB lipids are the members of the PAT protein family, mostly studied in adipocytes. This family includes fi ve perilipins: perilipin 1 (PLIN1; formerly perilipin), perilipin 2 (PLIN2; formerly adipose differentiation-related protein), perilipin 3 (PLIN3; formerly tail-interacting protein of 47 kDa), perilipin 4 (PLIN4; formerly S3-12), and perilipin 5 (PLIN5; formerly lipid storage droplet protein 5) ( 13 ). PLIN1 regulates the lipolytic activity of adipose triglyceride lipase (ATGL) during triacylglycerol (TG) mobilization via interacting with its coactivating factor, the comparative gene identifi cation 58 (CGI-58) ( 14 ), whereas overexpression Abstract Lipid droplets, also called lipid bodies (LB) in infl ammatory cells, are important cytoplasmic organelles. However, little is known about the molecular characteristics and functions of LBs in human mast cells (MC). Here, we have analyzed the genesis and components of LBs during differentiation of human peripheral blood-derived CD34+ progenitors into connective tissue-type MCs. In our serumfree culture system, the maturing MCs, derived from 18 different donors, invariably developed triacylglycerol (TG)-rich LBs. Not known heretofore, the MCs transcribe the genes for perilipins (PLIN)1-4, but not PLIN5, and PLIN2 and PLIN3 display different degrees of LB association. Upon MC activation and ensuing degranulation, the LBs were not cosecreted with the cytoplasmic secretory granules. Exogenous arachidonic acid (AA) enhanced LB genesis in Triacsin C-sensitive fashion, and it was found to be preferentially incorporated into the TGs of LBs. The large TG-associated pool of AA in LBs likely is a major precursor for eicosanoid production by MCs. In summary, we demonstrate that cultured human MCs derived from CD34 + progenitors in peripheral blood provide a new tool to study regulatory mechanisms involving LB functions, with particular emphasis on AA metabolism, eicosanoid biosynthesis, and subsequent release of proinfl ammatory lipid mediators from t...

Lipolysis meets inflammation: arachidonic acid mobilization from fat

“…Interestingly, Dichlberger and colleagues have previously shown that a considerable amount of AA is found esterifi ed in the TG pool of human MCs ( 22 ). The current study now provides compelling evidence that ATGL releases AA from LD-associated TGs as a crucial step for eicosanoid biosynthesis in MCs.…”

Phospholipase A2 regulation of lipid droplet formation

“…eicosanoids generated by oxygenation of the cPLA 2 α product free AA [78]. However, when added exogenously, the free fatty acid is able to induce significant LD formation in cells in the presence of cyclooxygenase and lipoxygenase inhibitors [39,40,52,54]. Importantly, this process occurs in a cPLA 2 α-dependent manner because blockade of the enzyme strongly inhibits LD formation [52,54].…”

“…LDs of different cell populations such as eosinophils, macrophages, neutrophils or mast cell avidly incorporate exogenous AA. Lipid analyses of LDs isolated from blood leukocytes have shown that AA is mainly esterified in phospholipids [39], whereas in mast cells and macrophages it is found primarily in neutral lipids [40]. Whether these differences in localization have a physiological consequence or are due to other factors, i.e.…”

Adipose triglyceride lipase regulates eicosanoid production in activated human mast cells

“…Surprisingly, the same effect was even more pronounced for the release of LTC4. Based on the current literature, ATGL is a single-compartmentacting enzyme that exerts its activity on TGs in LDs only, ( 9 ), these stores could serve as a quantitatively major source of AA for eicosanoid biosynthesis. In adipocytes under basal conditions, ATGL mediates the initial step in TG hydrolysis by producing 1,3-DAG, while under hormonal stimulation of lipolysis the enzyme becomes activated by its coactivating factor CGI-58, and the selectivity of ATGL broadens to the sn -1 position leading to the production of 2,3-DAG as well ( 22 ).…”

“…MC LDs were visualized by Oil Red O staining and quantifi ed by fl ow cytometry as described previously ( 9 ). Briefl y, MCs were sedimented (Cytospin, Shandon Instruments) onto glass slides (15 × 10 3 cells/slide) and fi xed with 10% neutral buffered formalin solution (Sigma).…”