Osteoporosis is characterized by reduced bone mass and microstructural damage that is resulted from the injury of the process during osteogenic differentiation and bone remodeling[11]. However, the pathogenesis of OP is incompletely understood. A better understanding of its pathogenesis contributes to developing novel and efficient therapeutic approaches to OP. Here in this study, according to bioinformatics prediction and in vitro experiments, we speculate that the RNA-binding protein ZFP36 may regulate the development of OP by targeting JUN.
We integrated multiple OP microarray datasets to identify DEGs in the progression of OP and found that ZFP36, an RNA-binding protein, is a potential target of OP. Previous studies have shown that ALP staining, Alizarin Red Staining, and the expression of RUNX2, OCN and ALP are well-established markers of osteogenic differentiation[12, 13]. Here, the results showed that overexpressing of ZFP36 could result in enhanced ALP activity and increased mineralized nodule content along with expression of osteogenic differentiation markers, which were all reduced by silencing of ZFP36. Therefore, ZFP36 may have the potential to serve as a therapeutic target against OP.
RNA-binding proteins are a class of targeted binding to specific RNAs, playing important roles in RNA stability and RNA translation of post-translational regulatory processes[14, 15]. The targeting function of RNA binding proteins is based on adenylate and uridylate rich elements (AREs) in the 3'-UTR of mRNA[16, 17]. The relationship between RNA-binding proteins and transcription factors of BMSCs in the progress of OP has not been fully explored[18, 19]. The ZFP36 family is a group of highly conserved RNA binding proteins with CCCH-type RNA binding domains, including ZFP36, ZFP36 ring finger protein-like 1 (ZFP36L1), ZFP36 ring finger protein-like 2 (ZFP36L2), and ZFP36 ring finger protein-like protein 3 (ZFP36L3) found in rodent placental tissue[20, 21]. The most important biological function of ZFP36 protein is post-transcriptional regulation. Through the tandem zinc finger structure and the ARE of the 3'-UTR of the target mRNA, ZFP36 promotes the deadenylation of target mRNAs to remove the polyadenylate tail structure, thereby degrading the target mRNA and regulating the expression of inflammatory factors and transcription factors. ZFP36 protein is involved in numerous biological processes, such as cell cycle transition, cell differentiation and anti-inflammation[22–24].
Mechanismly, the present study confirmed that ZFP36 can bind to the 3’UTR of JUN mRNA and inhibit its translation. In vitro study also found that the role of ZFP36 in inducing osteogenic differentiation was reversed by T-5224, the inhibitor of JUN. A previous study has elucidated that JUN promote the osteogenic differentiation of osteoblasts. Taken together, this study firstly represents the post-transcriptional regulation of JUN by ZFP36 in hBMSCs and may have importance in regulating the progression of OP.
In conclusion, ZFP36 facilitated osteogenic differentiation via binding to the 3’UTR of JUN to inhibit its expression. This study helps us to deepen the understanding of RNA-binding protein ZFP36 in the pathogenesis of OP. These findings suggest a novel therapeutic target for this disease and further clinical trials are needed for the development of ZFP36-based therapeutic agents.