Circ_0008529 Contributes to Renal Tubular Cell Dysfunction in High Glucose Stress via miR-185-5p/SMAD2 Pathway in Diabetic Nephropathy.

Circular RNA (circRNA) is key regulator of diabetic nephropathy (DN) progression. However, the role of circ_0008529 in DN progression remains to be better deciphered. Cell viability, cell cycle, apoptosis and inflammation were measured by MTS assay, flow cytometry and corresponding assay kits. RT-qPCR was used to assess the expression of circ_0008529, miR-185-5p and SMAD family member 2 (SMAD2). Also, western blotting was performed to measure protein expression. Target relationship was validated by RNA pull-down assay, dual-luciferase reporter assay and RNA immunoprecipitation assay. Urinary exosome was isolated using ultracentrifugation method and identified by transmission electron microscopy. Receiver operating characteristic curve was used to analyze the diagnostic value of circ_0008529 in DN patients. Circ_0008529 and SMAD2 were upregulated, while miR-185-5p was downregulated in high glucose (HG)-induced renal tubular HK-2 cells. Under HG treatment, cell viability and cell cycle process were suppressed, while apoptosis, inflammation and extracellular matrix accumulation were enhanced. However, interfering circ_0008529 could attenuate HG-induced effects, and this protection was abated by miR-185 inhibition or SMAD2 re-expression. Mechanically, circ_0008529 and SMAD2 were competing endogenous RNAs for miR-185-5p via target binding, and circ_0008529 regulated SMAD2 expression via miR-185-5p. Notably, circ_0008529 expression was upregulated in urinary exosomes of DN patients, and showed diagnostic value (Sensitivity: 70.21%; Specificity: 86.67%). Circ_0008529 might be a potential target for DN, which regulated DN progression via miR-185-5p/SMAD2 pathway.