Abstract
Interleukin-6 (IL-6) is a multifunctional cytokine that employs IL-6 classic and trans-signalling pathways, and these two signal channels execute different or even opposite effects in certain diseases. As a cardinal event of diabetic kidney disease (DKD), whether the podocyte abnormalities are associated with IL-6 signalling, especially classic or trans-signalling respectively, remains unclear. In this study, we identified that the circulatory IL-6, soluble IL-6R (sIL-6R) and soluble glycoprotein 130 (sgp130) levels are elevated in patients with DKD. The expressions of membrane-bound IL-6R (mIL-6R), sIL-6R and gp130 are enhanced in kidney cortex of diabetic mice accompanying with activated STAT3 by tyrosine 705 residue phosphorylation, while not serine 727. Above data infer both classic signalling and trans-signalling of IL-6 are activated during DKD. In cultured podocyte, high glucose (HG) up-regulates the expression of mIL-6R and gp130, as well as STAT3 tyrosine 705 phosphorylation, in a time-dependent manner. Entirely blocking IL-6 signalling by gp130 shRNA, gp130 or IL-6 neutralizing antibodies attenuates HG-induced podocyte injury. Interestingly, either inhibiting IL-6 classic signalling by mIL-6R shRNA or suppressing its trans-signalling using sgp130 protein dramatically alleviates HG-induced podocyte injury, suggesting both IL-6 classic signalling and trans-signalling play a detrimental role in HG-induced podocyte injury. Additionally, activation of IL-6 classic or trans-signalling aggravates podocyte damage in vitro. In summary, our observations demonstrate that the activation of either IL-6 classic or trans-signalling advances podocyte harming under hyperglycaemia. Thus, suppressing IL-6 classic and trans-signalling simultaneously may be more beneficial in podocyte protection and presents a novel therapeutic target for DKD.