Background

The periodontal ligament has stem cells that have the ability to regenerate lost periodontal tissues [1,2,3]. Orthodontic tooth movement progresses by a combination of periodontal ligament tissue and alveolar bone remodeling processes [4, 5]. Periodontitis is the most common types of diseases that cause bone destruction [6]. Periodontitis, tooth replantation, and repair of bone defects around implants all require periodontal tissue bone regeneration [7].

Periodontal ligament stem cells (PDLSCs) a new population of mesenchymal stem cells (MSCs), exhibited the ability to repair alveolar bone defects in periodontitis [8]. Also, there is need to understand molecular mechanism involved in PDLSCs osteogenic differentiation [9].

MicroRNAs (miRNAs) belong to a class of non-coding RNAs. Mechanically, miRNAs bind to complementary sites on the 3′-untranslated region (3′-UTR) of mRNAs and cause mRNA degradation or translational suppression, thereby inhibiting the expression of target genes [10,1: S1).

ATF1 3′UTR sequence contained the binding sites for miR-589-3p (Fig. 6A), implying that ATF1 might be a downstream target of miR-589-3p.

Fig. 6
figure 6

miR-589-3p directly target to ATF1 3′UTR. A Putative binding sites between miR-589-3p and ATF1; B Luciferase reporter assay showed that miR-589-3p mimic transfection suppressed the relative luciferase activity of the ATF1-Wt reporter in PGLSCs; C Relative ATF1 expression in inhibitor NC, miR-589-3p inhibitor, mimic NC and miR-589-3p mimic groups. *P < 0.05

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The luciferase activity assay revealed the miR-589-3p mimic suppressed ATF1 3′-UTR wild-type (WT) luciferase activity, whereas it had no effect on ATF1 3′-UTR mutant (Mut) luciferase activity compared with control in PDLSCs (Fig. 6B).

In contrast to miR-589-3p expression, Similar to BM-MSCs, the expression of ATF1 during the process of osteogenic differentiation of PDLSCs was reduced in a time-dependent manner (Fig. 6C).

Overexpression ATF1 reversed the effects of miR-589-3p on proliferation and osteogenic differentiation of PDLSCs

In order to validate whether miR-589-3p promoted osteogenic differentiation of PDLSCs by inhibiting ATF1, the rescue experiments were performed by co-transfection with miR-589-3p mimic and ATF1.

Compared with control group, better ALP activity and mineralized nodule formation was found in miR-589-3p group, but partially reversed by co-transfection with ATF1 overexpression plasmid. Meanwhile, ATF1 overexpression alone could also delay the osteogenic differentiation process (Fig. 7A). Real-time PCR and western blot assays further confirmed that the upregulation of RUNX2, OPN and OCN induced by miR-589-3p could be partially blockaded by overexpression of ATF1. Moreover, overexpression of ATF1 could also decrease the RUNX2, OPN and OCN expression (Fig. 7B, C).

Fig. 7
figure 7

Overexpression ATF1 partially reversed the effects of miR-589-3p-overexpression on PDLSCs. A Images of ALP and Alizarin Red S staining in control, miR-589-3p mimic, miR-589-3p mimic + ATF1 and ATF1 groups; B Relative RUNX2, OPN and OCN mRNA expression in control, miR-589-3p mimic, miR-589-3p mimic + ATF1 and ATF1 groups; C Relative RUNX2, OPN and OCN protein expression in control, miR-589-3p mimic, miR-589-3p mimic + ATF1 and ATF1 groups. *P < 0.05.

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Discussion

In this study, we firstly identified the differentially expressed miRNAs between osteogenic induction and non-osteogenic induction PDLSCs through bioinformatic analysis. miR-153-3p mimic or ATF1 suppression promoted the osteogenic differentiation of PDLSCs, as demonstrated by increases in ALP activity and matrix mineralization. Further studies revealed that miR-589-3p promoted osteogenic differentiation of PDLSCs by sponging ATF1.

Among these altered miRNAs, miR-589-3p was chosen for further study for two reasons. First, miR-589-3p showed a significant fold change among the upregulated miRNAs. Also, this is the first report of altered miR-589-3p expression in osteogenic differentiation of PDLSCs. miR-589-3p upregulation promoted the osteogenic differentiation of PDLSCs, as demonstrated by increases in ALP activity, matrix mineralization, and ALP, Runx2, and OPN expression.

MicroRNA (miRNA) has been reported to become novel therapeutic targets for skeletal related diseases.

Some miRNAs are differentially expressed in stem cells, and have significant effects on the osteogenic differentiation of stem cells. Lu et al. [20] identified the role of miR-589-3p in human lumbar disc degeneration and its potential mechanism. They found that miR-589-3p was significantly upregulated in lumbar disc degeneration patients. Following dual-luciferase reporter assay, Smad was demonstrated to be a target gene for miR-589-3p.

Furthermore, ATF1, which is a target gene of miR-589-3p, decreased osteogenic differentiation of PDLSCs; however, these effects were partially reversed by miR-589-3p mimic.

ATF1 has been shown to play an important role in cell proliferation, differentiation and apoptosis [27]. ATF1, as a regulator, also promoting sexual differentiation and entry into the stationary phase in S. pombe [28]. AtfA and Atf1 are quite highly conserved and that they are involved in multiple cellular processes [28]. In this study, we found that overexpression of ATF1 partially reversed the promotion effects of miR-589-3p on osteogenic differentiation of PDLSCs. Moreover, luciferase activity verified that miR-589-3p could significantly inhibited the luciferase activity of wild-type ATF1, but it failed to suppress luciferase activity of mutated one.

Limitation of this study can be listed as follows: (1) in vivo study was lack and thus should be further study in future studies; (2) following signaling pathway should be further explored the mechanism of miR-589-3p.

Conclusion

In conclusion, this study suggested that miR-589-3p promotes osteogenic differentiation of PDLSCs by targeting ATF1. The results of the present study demonstrated that the miR-589-3p/ATF1 interaction network may serve as a potential regulatory mechanism underlying PDLSCs osteogenesis.