Kaempferol attenuates streptozotocin-induced diabetic nephropathy by downregulating TRAF6 expression: The role of TRAF6 in diabetic nephropathy

Ethnopharmacological relevance: Kaempferia rhizome is a famous traditional herbal medical in tropical and subtropical areas. Kaempferol (KPF) is one of the main bioactive compounds in Kaempferia rhizome, with anti-oxidant/anti-inflammatory effects demonstrated in various disease models, including cancers, obesity and diabetes. Aim of the study: Inflammation plays an important role in the pathogenesis of diabetic nephropathy (DN). TRAF6 functions as a signal transducer in toll-like receptor 4 and NF-kappa B pro-inflammatory signaling pathway. We aimed at investigate whether KPF is able to mitigate inflammatory responses by regulating TRAF6 in DN. Material and methods: C57BL/6 mice were injected with streptozotocin to induce type 1 DN. NRK-52E, a tubular epithelial cell line, was used for in vitro analysis. TRAF6 was knockdown using siRNA in vitro and AAV2/2-shRNA in vivo. The anti-DN and inflammatory effects of KPF or knockdown of TRAF6 were evaluated by investigating renal filtration index, pathological changes of kidney tissue. Proinflammatory cytokine levels were detected using ELISA. NF-kappa B pathway and protein levels of related pathways were detected through Western blot. Results: KPF significantly reduced renal inflammation, fibrosis, and kidney dysfunction in diabetic mice. These effects were associated with a downregulation of TRAF6 in diabetic mouse kidneys, indicating the potential role of TRAF6. Knockdown of TRAF6 in mice through AAV2-shTRAF6 confirmed the importance of TRAF6 in DN. In vitro, treatment of KPF in NRK-52E cells attenuated high glucose (HG)-induced inflammatory and fibrogenic responses, associated with downregulated TRAF6 expression. The conclusion was further confirmed in NRK-52E cells by knocking down the expression and by overexpression of TRAF6. Conclusion: Our findings provide direct evidence that TRAF6 mediates diabetes-induced inflammation leading to renal dysfunction. We also show that KPF is a potential therapeutic agent to reduce inflammatory responses in DN. Also, TRAF6 may represent an interesting target to combat DN.

Automated summary

The study showed that KPF can significantly reduce renal inflammation, fibrosis, and kidney dysfunction in diabetic mice. The downregulation of TRAF6 in diabetic mouse kidneys was associated with these effects, suggesting the potential role of TRAF6. Treatment with KPF in NRK-52E cells attenuated high glucose-induced inflammatory and fibrogenic responses, with downregulated TRAF6 expression.