Peroxisome proliferator-activated receptor gamma agonist rosiglitazone attenuates oxyhemoglobin-induced Toll-like receptor 4 expression in vascular smooth muscle cells

Abstract Inflammation and immune response have been implicated in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH). Recently, increased TLR4 expression has been associated with the development of cerebral vasospasm in a rabbit model of SAH. Peroxisome proliferator-activated receptor gamma (PPARγ) agonists, effective inhibitors of TLR4 activation, may modulate the vasospasm progression via their anti-inflammation effects. We investigate whether the blood component oxyhemoglobin (OxyHb) can induce the expression of Toll-like receptor (TLR) 4 in vascular smooth muscle cells (VSMCs), and evaluate the modulatory effects of PPARγ agonist rosiglitazone on OxyHb-induced inflammation in VSMCs. Cultured VSMCs incubated with or without rosiglitazone were exposed to OxyHb at 10 μM for up to 48 h. Expression of TLR4 was assessed by immunocytochemistry and Western blot analysis. Production of tumor necrosis factor α (TNF-α) in conditioned medium were quantified by ELISA. A marked increase of TLR4 production and TNF-α release was observed at 48 h after cells were treated with OxyHb. Rosiglitazone reduced TLR4 immunocytochemistry staining and protein production significantly in VSMCs. A specific antagonist for PPARγ, GW9662, could reverse the anti-inflammatory effects of rosiglitazone. The results demonstrated that OxyHb exposure could induce TLR4 activation in cultured VSMCs. Rosiglitazone suppressed TLR4 expression and cytokine release via the activation of PPARγ and may have a therapeutic potential for the treatment of vasospasm following SAH.