miR-122/SIRT1 axis regulates chondrocyte extracellular matrix degradation in osteoarthritis

Abstract

Background/aims: MicroRNAs (miRNAs) are involved in the pathogenesis of osteoarthritis (OA). The present study aimed to investigate the potential function of miR-122 in the development of OA and its potential molecular mechanisms.

Methods: The expression of miR-122, silent information regulator 1 (SIRT1), collagen II, aggrecan, matrix metalloproteinase (MMP) 13 (MMP13) and ADAMTS4 in OA cartilage was detected by RT-qPCR. Target gene prediction and screening, luciferase reporter assay were used to verify downstream target genes of miR-122.

Results: Compared with osteonecrosis, the expression of miR-122 was significantly increased in OA cartilage, while the expression of SIRT1 was significantly decreased. Overexpression of miR-122 increased the expression of extracellular matrix (ECM) catabolic factors, for example disintegrins, MMPs and metalloproteinases with platelet reaction protein motifs, and inhibited the expression of synthetic metabolic genes such as collagen II and aggregating proteoglycan. Inhibition of miR-122 expression had the opposite effect. Furthermore, SIRT1 was identified as a direct target of miR-122. SIRT1 was significantly inhibited by miR-122 overexpression. Knockdown of SIRT1 reversed the degradation of chondrocyte ECM by miR-122 inhibitors.

Conclusion: The miR-122/SIRT1 axis can regulate the degradation of ECM in OA, thus providing new insights into the treatment of OA.

Keywords: ECM; SIRT1; chondrocytes; miR-122; osteoarthritis.

Figure 1. MiR-122 and SIRT1 expression levels in OA cartilage

(A) miR-122 level in human OA. (B) SIRT1 level in human OA. (C) Correlation between SIRT1 mRNA expression and miR-122 expression in cartilage samples. Data represent mean ± SD. Compared with the con group, ***P<0.001. con means control.

Figure 2. Effect of miR-122 on EMT degradation of SIRT1 and chondrocytes

(A–F) The expression of miR-122, SIRT1, collagen II, aggrecan, MMP13 and ADAMTS4. (G) SIRT1, collagen II, aggrecan, MMP13 and ADAMTS4 protein expression were assessed by Western blot. Data represent mean ± SD. Compared with the con group. **P<0.01. con means control.

Figure 3. SIRT1 was a direct target of miR-122

(A) Schematic representation of the predicted binding site of miR-122 in the 3′-UTR of SIRT1. (B) Luciferase activity. Data represent mean ± SD. Compared with the con group, **P<0.01. con means control.

Figure 4. miR-122 induced chondrocyte ECM degradation by modulating SIRT1

(A) The mRNA and protein expression levels of SIRT1. Data represent mean ± SD. **P<0.01 compared with si-con. (B–E) Expression of collagen II, aggrecan, MMP13 and ADAMTS4. (F) Expression of collagen II, aggrecan, MMP13 and ADAMTS4 proteins. Data represented mean ± SD. Compared with the con group, **P<0.01, compared with the si-SIRT1 group. ^##P<0.01, compared with the miR-122 inhibitor group. con means control.