Studies on the mechanisms involved in lipid body formation induced by a snake venom phospholipase A2 in isolated macrophages: participation of lipid homeosthasis factors

Abstract

Bothrops genus snake venoms contain high amounts of secretory phospholipases A2 (sFLA2) with high grade of structural and functional homology with mammalian sFLA2, which are increased in inflammatory diseases, such as atherosclerosis. We have recently shown that MT-III, a group IIA venom sFLA2 is able to directly induce lipid body formation and ADRP expression in macrophages. ADRP is a key protein in neutral lipid storage and lipid body biogenesis, and has been associated with foam cell formation. However, the mechanisms involved in these MT-III-induced effects were not elucidated, mainly those related to up-regulation of ADRP expression and accumulation of lipids into lipid bodies. In this study the knowledge of the mechanisms by which MT-III stimulates LB formation and ADRP expression in macrophages will be extended by focusing on major factors involved in lipid homeostasis. To this purpose, the effects of MT-III will be analyzed in macrophages with regard to: 1) gene and protein expression of the enzymes acyl-CoA:diacylglycerol acyltransferase (DGAT) and Acyl-CoA:cholesterol acyltransferase (ACAT), responsible for triacylglycerol and cholesterol, respectively; 2) levels of triacylglycerol and cholesterol; 3) activation and gene and protein expression of the receptors PPAR-delta and PPAR-beta/delta; 4) gene and protein expression of the CD36 receptor; 5) gene and protein expression of SREBP-2; 6) participation of the signaling proteins PKC, PI3K, PTK, JNK, p38MAPK, ERK1/2 and intracellular phospholipases A2 (cFLA2 and iFLA2) in MT-III- induced ADRP expression. In addition, participation of PPAR-gama, PPAR-beta/delta, CD36, DGAT and ACAT in both lipid body formation and up-regulation of ADRP expression induced by MT-III will be evaluated. This study will contribute to understanding the effects of both MT-III and sPLA2s in processes associated with lipid storage in immunocompetent cells, such as macrophages, as well as to a better knowledge of physiopathology of the local reaction induced by Bothrops venoms. Moreover, new therapeutic targets of lipid disorder-associated diseases may be identified. (AU)