circCDR1as/miR-671-5p Axis Modulates Chondrocyte Ferroptosis and Macrophage Reprogramming via Targeting NCOA4 and TLR4 in Legg-Calvé-Perthes Disease.

Legg-Calvé-Perthes disease (LCPD) causes malformations of femoral head in children, which presents as a treatment challenge due to its unclear pathogenesis. This study aimed to investigate the influence of circCDR1as on LCPD and its related mechanisms. An in vivo LCPD model was established in spontaneously hypertensive rats (SHRs) and HMGB1-stimulated chondrocytes were used to mimic LCPD in vitro. We found that circCDR1as was up-regulated, while miR-671-5p was down-regulated in LCPD patients, which exhibited a negative correlation. Depletion of circCDR1as restored the proliferation and inhibited -ferroptosis of HMGB1-exposed chondrocytes, Mechanistically, circCDR1as silencing increased miR-671-5p expression that targeted NCOA4 mRNA to disrupt the NCOA4-FTH1 interaction-mediated ferritinophagy. Moreover, treatment with conditioned medium (CM) of circCDR1as-silenced chondrocytes repressed M1 macrophage polarization via enhancing miR-671-5p expression that subsequently targeted TLR4 mRNA to inactivate TLR4/NF-κB pathway. FUS was responsible for circCDR1as biogenesis via the direct binding to pre-CDR1as mRNA. Collectively, chondrocyte ferroptosis was triggered by FUS-activated circCDR1as via sponging miR-671-5p to enhance NCOA4-FTH1 interaction-mediated ferritinophagy, which resulted in M1 macrophage reprogramming via activating the TLR4/NF-κB pathway, thus promoting LCPD development.