m ⁶A-mediated upregulation of AC008 promotes osteoarthritis progression through the miR-328-3p‒AQP1/ANKH axis

Abstract

Long noncoding RNAs (lncRNAs) have emerged as important regulators of osteoarthritis (OA), but the biological roles and clinical significance of most lncRNAs in OA are not fully understood. Microarray analysis was performed to identify differentially expressed lncRNAs, mRNAs, and miRNAs between normal and osteoarthritic cartilage. We found that AC008440.5 (abbreviated AC008), as well as AQP1 and ANKH, were highly expressed in osteoarthritic cartilage, whereas miR-328-3p was expressed at a low level in osteoarthritic cartilage. Functional assays showed that ectopic expression of AC008, AQP1, and ANKH significantly decreased chondrocyte viability and promoted chondrocyte apoptosis and extracellular matrix (ECM) degradation, whereas knockdown of AC008, AQP1, and ANKH resulted in the opposite effects. Moreover, miR-328-3p overexpression increased chondrocyte viability and attenuated chondrocyte apoptosis and ECM degradation, whereas inhibition of miR-328-3p resulted in the opposite effects. Bioinformatics analysis, RNA immunoprecipitation (RIP), and luciferase assays revealed that AC008 functioned as a competing endogenous RNA (ceRNA) to regulate miR-328-3p, which specifically targeted the AQP1 and ANKH genes. In addition, miR-328-3p significantly ameliorated MIA-induced OA, whereas AC008 accelerated OA progression in vivo. Furthermore, fat mass and obesity-associated (FTO)-mediated N6-methyladenosine demethylation downregulated AC008 transcription, while lower FTO expression led to upregulation of AC008 transcription in OA. In conclusion, our data reveal that AC008 plays a critical role in OA pathogenesis via the miR-328-3p ‒AQP1/ANKH pathway, suggesting that AC008 may be a potential therapeutic target for OA.

Osteoarthritis: a pathway for protecting cartilage

A search for genes involved in the joint disease osteoarthritis reveals a non-coding RNA that regulates molecular pathways responsible for maintaining healthy cartilage. The genome encodes many such RNAs, which control the activity of protein-coding genes via diverse mechanisms. Researchers led by Changyan Ma and Yucui Jin at Nanjing Medical University in China recently determined that one such short RNA, known as AC008, is notably over-expressed in osteoarthritic cartilage compared with healthy tissue. They showed that AC008 impairs the survival of cartilage-forming chondrocytes and leads to degradation of the extracellular matrix surrounding them. The researchers also identified two proteins regulated by AC008 that directly contribute to this process of chondrocyte loss, and uncovered the mechanism by which this regulation occurs. This pathway could thus offer potentially useful new targets for osteoarthritis drug development.