CKIP-1 acts downstream to Cx43 on the activation of Nrf2 signaling pathway to protect from renal fibrosis in diabetes.

CKIP-1 participates in the activation of Nrf2 signaling pathway by Cx43 and the regulation of diabetic renal fibrosis Under normal conditions, CKIP-1 was combined with Cx43 via Cx43 CT domain on the membrane of GMCs, which induced the interaction between CKIP-1 and Nrf2 and the nuclear accumulation of Nrf2, leading the activation of Nrf2 anti-oxidative stress signaling pathway. When the cells were stimulated by high glucose, the expression of Cx43 was inhibited, following with the down-regulation of CKIP-1 protein level. Moreover, the interaction between CKIP-1 and Nrf2 was weaken whereas the binding of Nrf2 to its inhibitory protein Keap1 was enhanced, as a result of which the activity of Nrf2 signaling pathway was inhibited with the overproduction of intracellular superoxide. Increased oxidative stress further promoted the expression of FN eventually exacerbating diabetic renal fibrosis. • CKIP-1 participated in the activation of Nrf2 signaling pathway by Cx43 and the regulation of diabetic renal fibrosis. • Cx43 interacted with CKIP-1, and the interaction was weakened by high glucose treatment. • Cx43 regulated the expression of CKIP-1 and the interaction of CKIP-1 with Nrf2 via Cx43 carboxyl terminus domain. We previously reported that both Cx43 and CKIP-1 attenuated diabetic renal fibrosis via the activation of Nrf2 signaling pathway. However, whether CKIP-1, a scaffold protein, participates in regulating the activation of Nrf2 signaling pathway by Cx43 remains to be elucidated. In this study, the effect of adenovirus-mediated Cx43 overexpression on renal fibrosis in CKIP-1−/− diabetic mice was investigated. We found that overexpression of Cx43 could significantly alleviate renal fibrosis by activating the Nrf2 pathway in diabetic mice, but have no obvious effect in CKIP-1−/− diabetic mice. Cx43 overexpressed plasmid and CKIP-1 small interfering RNA were simultaneously transfected into glomerular mesangial cells and the result demonstrated that the effect of activation of Nrf2 signaling pathway by Cx43 was blocked by CKIP-1 depletion. The interaction between Cx43 and CKIP-1 was analyzed by immunofluorescence and immunoprecipitation assays. We found that Cx43 interacted with CKIP-1, and the interaction was weakened by high glucose treatment. Moreover, Cx43 regulated the expression of CKIP-1 and the interaction of CKIP-1 with Nrf2 via Cx43 carboxyl terminus (CT) domain, thereby activating Nrf2 signaling pathway. According to the results, we preliminary infer that CKIP-1 acts downstream to CX43 on the activation of Nrf2 signaling pathway to protect from renal fibrosis in diabetes, the mechanism of which might be related to the interaction of CKIP-1 with Nrf2 through Cx43 CT. Our study provides further experimental basis for targeting the Cx43-CKIP-1-Nrf2 axis to resist diabetic renal fibrosis. [ABSTRACT FROM AUTHOR]