Asiatic acid attenuates hypertrophic and fibrotic differentiation of articular chondrocytes via AMPK/PI3K/AKT signaling pathway

Na Liu,Xin Wang,Liu Yang,Junjun Yang,Pingju Liu,Zhenlan Fu,Jiajia Chen,Dejie Fu,Xiaoyuan Gong,Rui Li,Cheng Chen,Xiongbo Song

doi:10.1186/s13075-020-02193-0

Abstract

BackgroundOsteoarthritis (OA), the most common joint disorder, is characterized by a progressive degradation of articular cartilage. Increasing evidence suggests that OA is closely associated with cartilage pathologies including chondrocyte hypertrophy and fibrosis.MethodsIn this study, we showed that asiatic acid (AA) treatment reduced chondrocyte hypertrophy and fibrosis. First, the cytotoxicity of AA (0, 5, 10, and 20 μM) to chondrocytes was evaluated, and 5 μM was selected for subsequent experiments. Then, we detected the gene and protein level of chondrocyte hypertrophic markers including type X collagen (COL-X), matrix metalloproteinase-13 (MMP-13), alkaline phosphatase (ALP), and runt-related transcription factor 2 (Runx2); chondrocyte fibrosis markers including type I collagen (COL-Ι) and alpha-smooth muscle actin (α-SMA); and chondrogenic markers including SRY-related HMG box 9 (SOX9), type II collagen (COL-II), and aggrecan (ACAN). Further, we tested the mechanism of AA on inhibiting chondrocyte hypertrophy and fibrosis. Finally, we verified the results in an anterior cruciate ligament transection (ACLT) rat OA model.ResultsWe found that AA treatment inhibited the hypertrophic and fibrotic phenotype of chondrocytes, without affecting the chondrogenic phenotype. Moreover, we found that AA treatment activated AMP-activated protein kinase (AMPK) and inhibited phosphoinositide-3 kinase/protein kinase B (PI3K/AKT) signaling pathway in vitro. The results in an ACLT rat OA model also indicated that AA significantly attenuated chondrocyte hypertrophy and fibrosis.ConclusionAA treatment could reduce hypertrophic and fibrotic differentiation and maintain the chondrogenic phenotype of articular chondrocytes by targeting the AMPK/PI3K/AKT signaling pathway. Our study suggested that AA might be a prospective drug component that targets hypertrophic and fibrotic chondrocytes for OA treatment.

Highlights

Chondrocyte hypertrophy plays an essential role in endochondral ossification during bone formation and growth [1]
In early stages of OA, articular chondrocytes respond to the degenerative events by decreasing the production of type II collagen (COL-II) and increasing the synthesis of type X collagen (COL-X), which is an indication of chondrocyte hypertrophy [5]
Chondrocytes treated with 5 μM asiatic acid (AA) showed comparable staining with untreated control, while 10 μM and 20 μM AA treatment induced more dead chondrocytes

Summary

Introduction

Chondrocyte hypertrophy plays an essential role in endochondral ossification during bone formation and growth [1]. Ectopic hypertrophy of articular chondrocytes has been recognized as an osteoarthritis (OA)-promoting factor [2,3,4]. A significantly increased expression of alkaline phosphatase (ALP) and runt-related transcription factor 2 (Runx2) is identified in osteoarthritic chondrocytes [7, 8]. Kamekura et al investigated the functional involvement of Runx in chondrocyte hypertrophy and OA development and found that compared with wildtype mice, Runx2-deficient mice had no hypertrophic chondrocytes and showed a decrease in cartilage destruction, along with a reduction in COL-X and MMP-13 expression [9]. Chondrocyte hypertrophy is closely related to OA pathogenesis. Increasing evidence suggests that OA is closely associated with cartilage pathologies including chondrocyte hypertrophy and fibrosis

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Results

Discussion

Conclusion