miR-337-3p targets IRS1 and Nox4 in tendinopathy. (A) Schematic representation of the rno-IRS1 and rno-Nox4 3′UTR indicating the binding sites of rno-miR-337-3p. WT, wild-type; MT, mutant. (B) HEK293T cells were transfected with psiCHECK™-2 Vector containing a fragment of rno-IRS1, rno-Nox4 3′UTR harboring binding sites for rno-miR-337-3p, or the corresponding mutant constructs. The effect of rno-miR-337 mimics on the corresponding vector luciferase activity was tested. (C) Protein levels of IRS1, p-IRS1, and Nox4 in rTDSCs treated with miR-337 mimics or negative control siRNAs (NC) for 3 days. The densitometric analysis of each protein expression was normalized to GAPDH. Three independent experiments were analyzed for the bar graph on the right. (D) Real-time PCR analysis of miR-337-3p, IRS1, and Nox4 expression in normal tendon tissues obtained from four osteoarthritis patients and calcified tendon tissues from five tendinopathy patients. (E) Immunocytochemistry staining of Runx2, Sox9, IRS1, and Nox4 in diseased tendon of tendinopathy patients and normal tendon samples. The densitometric analysis of the proteins was normalized to GAPDH. Error bars, SEM (n = 3). *P < 0.05; **P < 0.01. Scale bar, 50 μm.