Archives

  • 2018-07
  • 2018-10
  • 2018-11
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-06
  • 2023-07
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • To unveil the underlying molecular mechanisms by which miR p

    2018-10-24

    To unveil the underlying molecular mechanisms by which miR-375 promotes hASC osteogenesis, we conducted a microarray analysis 7 days after osteoinduction. According to the microarray profiles, the osteogenesis-associated genes RUNX2 (ratio = 1.6431) and ALP (ratio = 1.6367) were upregulated, and DEPTOR expression was decreased. As an mTOR-interacting protein, DEPTOR endogenously inhibits the activity of mTOR (Peterson et al., 2009). Furthermore, DEPTOR plays a key role in maintaining the pluripotency of embryonic stem purchase GDC-0994 (ESCs) (Agrawal et al., 2014). Recent studies demonstrated that DEPTOR was a crucial regulator of adipogenic differentiation, and that its overexpression and suppression promote and block adipogenesis, respectively (Caron et al., 2016; Laplante et al., 2012). Here, we showed that DEPTOR is downregulated during the osteogenic differentiation of hASCs and that its knockdown resulted in enhanced mineralization activity of hASCs and elevated expression of osteogenesis-associated markers. Promotion effects of miR-375 on the osteogenic differentiation of hASCs might be attributed to repression of DEPTOR, which leads to loss of stem cell pluripotency. The Hippo pathway is now being recognized as an integrator of mechanical and cellular-contact-dependent sensory signals with the intracellular components that regulate cell fate (Yang et al., 2014). Active Hippo signaling inhibits the transcriptional activity of YAP1 and TAZ by phosphorylating and sequestering them in the cytoplasm (Meng et al., 2016). Although YAP1 and TAZ are often considered functionally analogous orthologs of Drosophila Yorkie (Yki), their functions in osteogenic differentiation remains distinct. TAZ was identified as a fate-determination factor that binds to and activates RUNX2, a transcriptional regulator of the osteoblast lineage, while YAP1 was downregulated during the osteogenic differentiation of MSCs and suppressed their osteogenesis by binding to β-catenin to inhibit WNT signaling (Hong et al., 2005; Seo et al., 2013). Several studies have shown that YAP1 contains an miR-375 target site in its 3′ UTR and represses tumorigenesis in carcinomas (Liu et al., 2010; Selth et al., 2016). In our study, miR-375 directly targeted the predicted binding site of YAP1, resulting in its downregulation during the osteogenic differentiation of hASCs. YAP1 maintains the pluripotency of ESCs by binding to a number of “stemness” genes, including Nanog, OCT4, and SOX2 (Lian et al., 2010), and often acts as a transcriptional co-activator (Hong and Guan, 2012). In some instances, YAP1 also functions as a transcriptional co-repressor (Kim et al., 2015). Moreover, studies focused on miRNA biogenesis reveal that activation of YAP1 is responsible for the widespread miRNA repression. The mechanism might lie in DEAD box helicase 17 (DDX17), a microprocessor component. Knockdown of YAP1 facilitates DDX17 association with microprocessor and binding to a specific sequence motif in pri-miRNA (Mori et al., 2014). However, YAP1 conversely induces the biogenesis of some miRNAs, such as miR-16, -21, and -23, by increasing Dicer through the Let-7 family (Chaulk et al., 2014). In our study, we show that knockdown of YAP1 in hASCs increased miR-375 expression by binding to its promoter. The upregulation of miR-375 during the osteogenic differentiation of hASCs was modulated, at least in part, by the decrease in YAP1 expression. As a nutrient sensor, mTOR responds to PI3K-mediated growth factor signaling to regulate cell growth in mammals (Dibble and Cantley, 2015). The PI3K/AKT/mTOR pathway is involved in osteogenic differentiation and osteoporosis (Martin et al., 2010; Xi et al., 2015). Here, we demonstrated that miR-375 overexpression activated S6K via mTORC1, leading to a negative feedback inhibition of IRS1-PI3K-AKT in hASCs, resulting in a decrease in the phosphorylated AKT level. Moreover, YAP1 inhibits the transcription of PTEN and then activates PI3K/AKT/mTOR signaling by inducing miR-29 (Tumaneng et al., 2012). As a key downstream effector of the Hippo pathway, YAP1 plays a crucial role in regulating cell proliferation and organ size (Hansen et al., 2015a). Our research indicated that knockdown of YAP1 induced the transcription of miR-375, thus activating AKT signaling by directly targeting DEPTOR. The link from YAP1 to miR-375 to DEPTOR and AKT suggests their collaboration in cell growth control, and illustrates that signaling networks function in a coordinated manner to fine-tune the osteogenic differentiation of MSCs.