Effects of Curcumin on High Glucose-Induced Epithelial-to-Mesenchymal Transition in Renal Tubular Epithelial Cells Through the TLR4-NF-κB Signaling Pathway

Abstract

Objective

Diabetic kidney disease (DKD) is a microvascular complication in diabetes mellitus, while tubuloepithelial to mesenchymal transition (EMT) of mature tubular epithelial cells is a key point in the early development and progression of renal interstitial fibrosis. The present study aimed to investigate the protective effects of Curcumin on EMT and fibrosis in cultured normal rat kidney tubular epithelial cell line (NRK-52E).

Methods

By using immunofluorescence staining and Western blot protocols, in vitro experiments were designed to analyze EMT markers, including collagen I and E-cadherin in high glucose (HG) exposed NRK-52E cells and to detect the expression levels of phosphorylated-NF-κB, TLR4 and reactive oxygen species (ROS) after Curcumin pre-treatment. With co-treatment with TAK242, these molecules in the TLR4-NF-κB signaling pathway were further evaluated.

Results

Curcumin decreased the HG-induced EMT levels and ROS production in NRK-52E cells. Furthermore, Curcumin was found to inhibit the TLR4-NF-κB signaling activation in HG-induced EMT of NRK-52E cells.

Conclusion

The present study provides evidence suggesting a novel mechanism that Curcumin exerts the anti-fibrosis effects via inhibiting activation of the TLR4-NF-κB signal pathway and consequently protecting the HG-induced EMT in renal tubular epithelial cells. Thereby, TLR4-NF-κB may be a useful target for therapeutic intervention in DKD.

Keywords:

• diabetic kidney disease
• tubuloepithelial to mesenchymal transition
• toll-like receptor 4
• curcumin
• inflammation

Abbreviations

ACR, albumin to creatinine ratio; cAMP, adenosine 3ʹ, 5ʹ-cyclic monophosphate; CKD, chronic kidney disease; DKD, diabetic kidney disease; DMSO, dimethyl sulfoxide; DN, diabetic nephropathy; ECM, accumulation of extracellular matrix; ECL, enhanced chemiluminescence; EMT, tubuloepithelial to mesenchymal trans-differentiation; ESKD, end-stage kidney disease; FSH, follicle-stimulating hormone; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; HG, high glucose; HO-1, heme oxygenase-1; IDF, international Diabetes Federation; IL-6, interleukin-6; MTT, 3-(4,5-dimethylthiazol-2-yl)-2 and 5-diphenyltetrazolium bromide; Nrf2, NF-E2-related factor 2; PB, phosphate buffer; PI3K, phosphatidylinositol 3-kinase; PVDF, polyvinylidene difluoride; ROS, reactive oxygen species; STZ, Streptozotocin; TGF-β1, Transforming growth factor beta 1; TLRs, toll-like receptor; TNF-α, tumor necrosis factor-alpha.

Author Contributions

All authors contributed to data analysis, drafting or revising the article, have agreed on the journal to which the article will be submitted, gave final approval of the version to be published, and agree to be accountable for all aspects of the work.

Disclosure

All the authors declared no competing interests.

Additional information

Funding

This work was supported by grants from the Natural Science Foundation of China (81670670), Postdoctoral Science Foundation of China (2014MM551144), Shenzhen Key Medical Discipline Construction Fund (SZXK009), and Start grant of China Pharmaceutical University (20180705).