The amelioration of phagocytic ability in microglial cells by curcumin through the inhibition of EMF-induced pro-inflammatory responses

Background: insufficient clearance by microglial cells,prevalent in several neurological conditions and diseases,is intricately intertwined with mfg-e8 expression and inflammatory responses. electromagnetic field (emf) exposure can elicit the pro-inflammatory activation and may also trigger an alteration of the clearance function in microglial cells. curcumin has important roles in the anti-inflammatory and phagocytic process. here,we evaluated the ability of curcumin to ameliorate the phagocytic ability of emf-exposed microglial cells (n9 cells) and documented relative pathways.methods: n9 cells were pretreated with or without recombinant murine mfg-e8 (rmmfg-e8),curcumin and an antibody of toll-like receptor 4 (anti-tlr4),and subsequently treated with emf or a sham exposure. their phagocytic ability was evaluated using phosphatidylserine-containing fluorescent bioparticles. the pro-inflammatory activation of microglia was assessed via cd11b immunoreactivity and the production of tumor necrosis factor-α (tnf-α),interleukin-6 (il-6),interleukin-1β (il-1β) and nitric oxide (no) via the enzyme-linked immunosorbent assay or the griess test. we evaluated the ability of curcumin to ameliorate the phagocytic ability of emf-exposed n9 cells,including checking the expression of mfg-e8,αvβ3 integrin,tlr4,nuclear factor-κb (nf-κb) and signal transducer and activator of transcription 3 (stat3) using western blotting.results: emf exposure dramatically enhanced the expression of cd11b and depressed the phagocytic ability of n9 cells. rmmfg-e8 could clearly ameliorate the phagocytic ability of n9 cells after emf exposure. we also found that emf exposure significantly increased the secretion of pro-inflammatory cytokines (tnf-α,il-6 and il-1β) and the production of no; however,these increases were efficiently chilled by the addition of curcumin to the culture medium. this reduction led to the amelioration of the phagocytic ability of emf-exposed n9 cells. western blot analysis revealed that curcumin and naloxone restored the expression of mfg-e8 but had no effect on tlr4 and cytosolic stat3. moreover,curcumin significantly reduced the expression of nf-κb p65 in nuclei and phospho-stat3 (p-stat3) in cytosols and nuclei.conclusions: this study indicates that curcumin ameliorates the depressed mfg-e8 expression and the attenuated phagocytic ability of emf-exposed n9 cells,which is attributable to the inhibition of the pro-inflammatory response through the nf-κb and stat3 pathways. © 2014 he et al.; licensee biomed central ltd.