Therapeutic targeting of Krüppel-like factor 4 abrogates microglial activation

Background: neuroinflammation occurs as a result of microglial activation in response to invading micro-organisms or other inflammatory stimuli within the central nervous system. according to our earlier findings,krüppel-like factor 4 (klf4),a zinc finger transcription factor,is involved in microglial activation and subsequent release of proinflammatory cytokines,tumor necrosis factor alpha,macrophage chemoattractant protein-1 and interleukin-6 as well as proinflammatory enzymes,inducible nitric oxide synthase and cyclooxygenase-2 in lipopolysaccharide-treated microglial cells. our current study focuses on finding the molecular mechanism of the anti-inflammatory activities of honokiol in lipopolysaccharide-treated microglia with emphasis on the regulation of klf4.methods: for in vitro studies,mouse microglial bv-2 cell lines as well as primary microglia were treated with 500 ng/ml lipopolysaccharide as well as 1 μm and 10 μm of honokiol. we cloned full-length klf4 cdna in pcdna3.1 expression vector and transfected bv-2 cells with this construct using lipofectamine for overexpression studies. for in vivo studies,brain tissues were isolated from balb/c mice treated with 5 mg/kg body weight of lipopolysaccharide either with or without 2.5 or 5 mg/kg body weight of honokiol. expression of klf4,cyclooxygenase-2,inducible nitric oxide synthase and phospho-nuclear factor-kappa b was measured using immunoblotting. we also measured the levels of cytokines,reactive oxygen species and nitric oxide in different conditions.results: our findings suggest that honokiol can substantially downregulate the production of proinflammatory cytokines and inflammatory enzymes in lipopolysaccharide-stimulated microglia. in addition,honokiol downregulates lipopolysaccharide-induced upregulation of both klf4 and phospho-nuclear factor-kappa b in these cells. we also found that overexpression of klf4 in bv-2 cells suppresses the anti-inflammatory action of honokiol.conclusions: honokiol potentially reduces inflammation in activated microglia in a klf4-dependent manner. © 2012 kaushik et al; licensee biomed central ltd.