miR⁃21⁃5p targets the SKP2/p27 pathway to modulate TGF-β1⁃induced fibrosis in human renal tubular epithelial cells

ObjectiveTo investigate the mechanism by which microRNA‑21‑5p （miR‑21‑5p） targets the S‑phase kinase‑associated protein 2 （SKP2）/p27 pathway to participate in transforming growth factor‑β1 （TGF‑β1）‑induced fibrosis of human renal tubular epithelial cells.MethodsHuman renal proximal tubular epithelial cells （HK‑2） were randomized into six groups： control， model （TGF‑β1 induction）， miR‑NC， miR‑21‑5p mimic， miR‑21‑5p mimic + pcDNA‑NC， and miR‑21‑5p mimic + SKP2 overexpression （miR‑21‑5p mimic + pcDNA‑SKP2）. Cell viability was measured by cell counting kit-8 （CCK-8） assay. Levels of tumor necrosis factor‑α （TNF‑α） and interleukin‑1β （IL‑1β） in culture supernatants were measured by enzyme-linked immunosorbent assay （ELISA）. Expression of miR‑21‑5p and mRNAs of SKP2 and p27 were quantified by real-time quantitative polymerase chain reaction （RT‑qPCR）. Protein levels of SKP2， p27， and fibrosis markers α‑smooth muscle actin （α‑SMA）， fibronectin （Fn）， and collagen I were assessed by Western blot. A dual‑luciferase reporter assay was used to validate direct targeting between miR‑21‑5p and SKP2.ResultsCompared with the control group， TGF‑β1 treatment （model） significantly reduced HK‑2 cell viability at 48 h ［control （98.42±3.69）% vs model （67.49±6.21）%］ and 72 h ［（101.35±4.20）% vs （62.78±6.48）%］ （P