TGR5 activation attenuates neuroinflammation via Pellino3 inhibition of Caspase-8/NLRP3 after middle cerebral artery occlusion in rats

Abstract Background NLRP3 (nucleotide-binding oligomerization domain-like receptor pyrin domain-containing protein 3) plays an important role in mediating inflammatory responses during ischemic stroke. Bile acid receptor TGR5 has been identified as an important component in regulating inflammatory response in brain. In this study, we investigated the mechanism of TGR5 on alleviating neuroinflammation after middle cerebral artery occlusion (MCAO).Methods—Sprague-Dawley rats were subjected to MCAO and INT777 was administered intranasally 1 hour after MCAO. Small interfering RNA for TGR5 and Pellino3 were administered through intracerebroventricular injection 48 hours before MCAO. Infarct volumes, neurological scores, ELISA,flow cytometry༌ immunofluorescence staining, Western blot and co-immunoprecipitation were evaluated.Results— Endogenous TGR5 and Pellino3 expressions were increased after MCAO.TGR5 activation by INT777 significantly decreased pro-inflammatory cytokines levels, reduced cleaved caspase-8 and NLRP3 expressions, thereby reducing brain infarction, improving both short- and long-term neurobehavioral assessment. Ischemic damage induced interaction of TGR5 with Pellino3. Knockdown of either TGR5 or Pellino3 increased expressions of cleaved caspase-8 and NLRP3, aggravated brain impairments, abolished the anti-inflammatory effects of INT777 after MCAO.Conclusions—TGR5 activation attenuated brain injury by inhibiting neuroinflammation after MCAO, which may be mediated by Pellino3 inhibition of Caspase-8/NLRP3.