The proximal tubular alpha 7 nicotinic acetylcholine receptor attenuates ischemic acute kidney injury through Akt/PKC signaling-mediated HO-1 induction

Abstract

Activation of the alpha 7 nicotinic acetylcholine receptor (alpha 7nAChR) has been shown to attenuate excessive inflammation by inhibiting proinflammatory cytokines during ischemia-reperfusion (IR) injury; however, the underlying kidney-specific molecular mechanisms remain unclear. The protective action of alpha 7nAChR against renal IR injury was investigated using a selective alpha 7nAChR agonist and antagonist. alpha 7nAChR activation reduced plasma creatinine levels and tubular cell damage, whereas alpha 7nAChR inhibition aggravated the IR-induced phenotype. alpha 7nAChR activation decreased neutrophil infiltration and proinflammatory cytokine expression, increased heme oxygenase-1 (HO-1) expression, and reduced proximal tubular apoptosis after IR as shown by terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and caspase-3 cleavage. In this study, we first showed that alpha 7nAChR activation in the proximal tubules induced HO-1 expression through the phosphoinositide 3-kinase (PI3K)/Akt and protein kinase C (PKC) signaling pathway in vivo in renal IR mice and in vitro in proximal tubular cells. Chemical inhibitors of PKC or PI3K/Akt and small interfering RNA-mediated PKC silencing confirmed the signal specificity of alpha 7nAChR-mediated HO-1 induction in the proximal tubular cells. alpha 7nAChR activation inhibited high-mobility group box 1 release by inducing HO-1 expression and reduced proinflammatory cytokine gene expression and apoptotic cell death in tumor necrosis factor alpha-stimulated proximal tubular cells. Taken together, we conclude that alpha 7nAChR activation in proximal tubular cells directly protects cells against renal IR injury by inducing HO-1 expression through PI3K/Akt and PKC signaling.