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  • Interestingly anti inflammatory actions for sPLA


    Interestingly, anti-inflammatory actions for sPLA2-V were also described in mice a few years ago in a model of autoimmune complex mediated arthritis [148]. A novel mechanism was delineated, whereby sPLA2-V promotes phagocytosis of immune complexes by macrophages to ameliorate inflammation in autoimmune inflammatory arthritis. This function of sPLA2-V appears to strikingly depend on enzymatic activity [148]. More recent studies have correlated sPLA2-V with alternative macrophage activation (M2) in human and murine macrophages [149,150]. sPLA2-V expression was induced during both human and mouse interleukin-4–mediated activation of macrophages in vitro, and its absence impaired macrophage activation in vivo. The elimination or depletion of sPLA2-V from the macrophages of both species selectively reduces the expression of CCL22/CCL17 that determines effector T cell recruitment and eosinophilic inflammation. Collectively, these findings suggest that sPLA2-V contributes to the Th2-dependent response for polarized activation of macrophages and that this function is conserved across species. Such a role is in intriguing p38 inhibitors with earlier results suggesting that stimuli that polarize macrophages to M1 such as LPS, are also able to significantly up-regulate sPLA2-V in several mouse tissues [151] and the transformed murine macrophage-like cell lines P388D1 [152] and RAW264.7 (J. Rubio and J. Balsinde, unpublished results). As discussed elsewhere [34], it is possible that sPLA2-V may be a bi-faceted enzyme with both pro- and anti-inflammatory (“Th2-prone”) roles depending on conditions, cell types, and species. Apart from its roles in innate immunity, sPLA2-V is also suggested to participate in the progression of atherosclerosis. The enzyme is found in human atherosclerotic lesions, and hydrolyzes low-density-lipoprotein phospholipids in a way that the modified lipoproteins promote foam cell formation. However, there is not always an agreement on whether sPLA2-V affects positively or negatively the cardiovascular process [153,154]. The hydrolysis of PC by sPLA2-V seems to be favored in obesity, where adipocyte-released sPLA2-V hydrolyzes excess PC of low density lipoproteins from animals fed a high fat diet, eventually protecting from hyperlipidemia. This links sPLA2-V with energy metabolism, as seen in obese Pla2g5−/− mice and in human white adipose tissue, where PLA2G5 expression inversely correlates with plasma low density lipoprotein levels [150]. The explanation is that the hydrolysis of low density lipoprotein particles produces unsaturated free fatty acids such as oleic or linoleic acid, which shift M1 to M2 macrophages or prevent palmitic acid-induced M1 macrophage polarization [150].
    Of all members of the sPLA2 family of enzymes, sPLA2-X is the one that shows the highest activity towards PC [155]. The enzyme is long known to release various fatty acids including AA and oleic acid, and increases prostaglandin E2 production when added exogenously to phagocytic cells, suggesting a role for this enzyme in inflammation [156]. Later, its role in inflammatory lung diseases, both mouse and human, was defined [[157], [158], [159], [160], [161]]. More recently, using an inhaled allergen model, Nolin et al. [162] demonstrated that Pla2g10−/− mice are protected from developing allergic airway disease, altering the polarization of macrophages to an M2 state. These results point out to a critical function for sPLA2-X in both the innate and adaptive immune response to inhaled allergens in human and mice. Other studies have described the involvement of sPLA2-X in regulating the formation of cysteinyl leukotrienes in neutrophils by mechanisms involving cross talk with cPLA2α [163,164]. Aside from the ability of sPLA2-X to effect AA mobilization from a variety of cells [143,155,156], some recent studies have also described the ability of the enzyme to liberate DHA and other omega-3 fatty acids [133]. sPLA2-X would effect the release of all omega-3 fatty acids, i.e. DHA, DPA and EPA preferentially over that of AA, placing this enzyme as another possible regulator of anti-inflammatory pro-resolving pathways [36]. In keeping with this notion, other works have attributed anti-inflammatory properties to sPLA2-X in the development of atherosclerosis by limiting Th-1 responses or adipogenesis in murine models of obesity [165,166].