A group IIA-secreted phospholipase A2 from snake venom induces lipid body formation in macrophages: the roles of intracellular phospholipases A2 and distinct signaling pathways

Abstract

We investigated the ability of the sPLA(2), known as MT-III, isolated from the viperid snake Bothrops asper, to induce LB formation in macrophages and the major cellular signaling pathways involved in this process. The effects of MT-III on ADRP localization and expression and macrophage ultrastructure were assessed. Our results showed that this sPLA(2) induced a marked increase in LB numbers in macrophages, induced the recruitment of ADRP in macrophages, and up-regulated ADRP expression. Ultrastructural analysis showed the presence of weakly and strongly osmiophilic LBs in sPLA(2)-stimulated cells. Enlargement of the ER and Golgi cisterns was also observed. Pretreatment of cells with H7 or staurosporine (PKC inhibitors), LY294002 or wortmannin (PI3K inhibitors), SB202190 or PD98059 (p38(MAPK) and ERK1/2 inhibitors, respectively), or Pyr-2 or Bel (cPLA(2) and iPLA(2) inhibitors, respectively) significantly reduced sPLA(2)-induced LB formation. Herbimycin (a PTK inhibitor) and indomethacin or etoricoxib (COX inhibitors) failed to alter sPLA(2)-induced effects. In conclusion, our results show for the first time the ability of a venom sPLA(2) to induce the formation of LBs and the expression of ADRP in macrophages. Venom PLA(2)-induced LB formation is dependent on PKC, PI3K, p38(MAPK), ERK1/2, cPLA(2), and iPLA(2) signaling pathways but not on PTK, COX-1, or COX-2 pathways. Activation of the ER and Golgi complex may play an important role in the formation of LBs induced by this sPLA(2) in macrophages.

sPLA2-IIA Augments Oxidized LDL-Induced MCP-1 Expression in Vitro Through Activation of Akt

“…Our data showed the importance of sPLA2-IIA in the pathogenesis of atherosclerosis, with emphasis on its effects in vascular SMCs. Our findings that sPLA2-IIA secreted by LV-GFP-sPLA2-IIA transduced cells failed to increase MCP-1 level is in contrast with a recent study by Leiquez et al [34] that sPLA2-IIA from snake venom induces lipid body (LB) formation in macrophages through which atherosclerosis is facilitated. This might be due to the different localization and function of sPLA2-IIA in different cell types.…”

Phospholipase A2 regulation of lipid droplet formation

“…For example, free fatty acids could directly activate cPLA 2 α to induce LD formation in monocytes [54], and the activation of MAPK-derived signaling, including cPLA 2 α phosphorylation, has been described to lie downstream of iPLA 2 β activation under certain conditions [113]. Coordinate actions of both iPLA 2 β and cPLA 2 α in regulating cellular signaling leading to LD formation have also recently been suggested in macrophages treated with a snake venom PLA 2 [48].…”

“…PLA 2 s may act at several levels, namely (i) as providers of free fatty acids from membrane phospholipids for the synthesis of neutral lipids [46][47][48], (ii) as modifiers of phospholipid-containing particles to facilitate their uptake and internalization by cells [49,50], (iii) as generators of metabolites that may control LD formation [51], and (iv) as direct regulators of the formation of the organelle [52][53][54].…”

Cellular Mechanisms of Action of Snake Phospholipase A2 Toxins

“…Crotoxin increases the basal expression of COX-1 in a process that involves iPLA2 (Moreira et al 2008). Macrophage activation by B. asper myotoxins (both catalytically active and inactive) involves different protein kinases and intracellular phospholipases, COX-2 expression, and prostaglandin production via a NF-kB pathway and leads to the formation of intracellular lipid droplets (Moreira et al 2008;Leiguez et al 2011;Giannotti et al 2013). The accumulation of lipids in cytoplasmic inclusions has been recently associated with inflammatory and metabolic pathologies (atherosclerosis, obesity, diabetes).…”

“…Different human secreted PLA2s are involved in inflammation and atherosclerosis, and some of them share a very high homology with snake venom PLA2s (about 50 % of identity). Human sPLA2 activity is partially independent from the enzymatic activity and presumably involves the interaction with specific receptors (Dennis et al 2011;Leiguez et al 2011).…”