AP2a enhanced the osteogenic differentiation of mesenchymal stem cells by inhibiting the formation of YAP/RUNX2 complex and BARX1 transcription

Abstract

Objectives: Bone regeneration by bone tissue engineering is a therapeutic option for bone defects. Improving the osteogenic differentiation of mesenchymal stem cells (MSCs) is essential for successful bone regeneration. We previously showed that AP2a enhances the osteogenic differentiation in MSCs. The present study investigated the mechanism of how AP2a regulates the direct differentiation. Materials and methods:Co-immunoprecipitation and ChIP assays were carried out to investigate the underlying mechanism in MSCs differentiation. The osteogenic differentiation potential was determined by mineralization ability and the expression of osteogenic marker in vitro and the in vivo bone-like tissue generation in nude mice. Results:We show that AP2a can compete with RUNX2, a key transcription factor in osteogenic differentiation, to recruit YAP and release the inhibition of RUNX2 activity from YAP by forming YAP-AP2a protein complex. YAP-AP2a protein complex also interacts with the BARX1 promoter through AP2a, inhibit the transcription of BARX1. Moreover, BARX1 inhibits osteogenic differentiation of MSCs.Conclusions: Our discoveries revealed that AP2a may regulate the osteogenic differentiation in an indirect way through competing with RUNX2 to relieve the RUNX2 activity which inhibited by YAP, and also in a direct way via targeting the BARX1 and directly repressed its transcription. Thus, our discoveries shed new light on the mechanism of direct differentiation of MSCs and provide candidate targets for improving the osteogenic differentiation and enhancing bone tissue regeneration.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Role of YAP/TAZ in Cell Lineage Fate Determination and Related Signaling Pathways

“…The findings of Lin et al (2019) may shed some light on the ambiguous role of YAP in regulating osteogenesis. They found that YAP binds to and inhibits the upstream pro-osteogenic transcription factor RUNX2 in human bone marrow and dental-derived MSCs, and that this inhibition is released by competitive binding of AP2a (activator protein 2a) to YAP ( Lin et al, 2019 ). Thus, YAP binding and inhibition of RUNX2 may serve as a negative feedback mechanism to YAP activation of RUNX transcription through TEAD, and AP2a may provide a release from this negative feedback mechanism.…”

“…As described earlier, an intracellular protein that binds directly with YAP is AP2a, with formation of the YAP-AP2a protein complex releasing YAP binding and inhibition of RUNX2 activity (Lin et al, 2019). Additionally, the YAP-AP2a protein complex blocks transcription of BARX1, which inhibits osteogenesis (Lin et al, 2019). Snail and Slug are zinc-finger transcription factors that interact directly with both YAP and TAZ, thereby promoting osteogenesis via activation of RUNX2 transcription (Panciera et al, 2016;Tang et al, 2016).…”

“…Other adult stem cells in which YAP plays an integral role in self-renewal and maintenance of the "stemness" phenotype include neural stem cells (Han et al, 2015;Bao et al, 2017), muscle satellite cells (Judson et al, 2012), and intestinal stem cells (Imajo et al, 2015;Kim H. B. et al, 2017). These will be discussed in greater detail in sections "Role of YAP/TAZ in Neurogenesis and Neuroregeneration, " "Role of YAP/TAZ in Myogenic Differentiation and Skeletal Muscle Regeneration, " and (Hong et al, 2005;Suh et al, 2012Suh et al, , 2014Yang et al, 2013;, the role of YAP in osteogenic differentiation is controversial (Seo et al, 2013;Sen et al, 2015;Pan et al, 2018;Zhu W. Q. et al, 2018;Bai et al, 2019;Lin et al, 2019;Wei et al, 2019). The role of TAZ in the osteogenesis of MSCs was first reported by Hong et al (2005), who found that TAZ co-activates gene transcription by RUNX2, an upstream regulator of osteogenesis, while at the same time repressing gene transcription by PPARγ that directs murine bone marrow MSCs into the adipocyte lineage.…”

“…There is abundant evidence for key roles of YAP/TAZ in the osteogenic differentiation pathway of primary osteoblasts and various types of adult stem cells, especially bone marrow-derived MSCs. While TAZ activation is consistently associated with osteogenesis ( Hong et al, 2005 ; Suh et al, 2012 , 2014 ; Yang et al, 2013 ; Zhu Y. et al, 2018 ), the role of YAP in osteogenic differentiation is controversial ( Seo et al, 2013 ; Sen et al, 2015 ; Pan et al, 2018 ; Zhu W. Q. et al, 2018 ; Bai et al, 2019 ; Lin et al, 2019 ; Wei et al, 2019 ).…”

“…It is precisely this delicate balance of nuclear to cytoplasmic ratio of unphosphorylated and phosphorylated YAP/TAZ respectively, which plays such a crucial role in cell lineage fate determination ( Figure 3 ); and in the activation and mobilization of endogenous stem/progenitor cells during the regeneration process following tissue/organ disease or injury ( Figure 4 ). Nevertheless, it must be noted that there are additional layers of complex mechanisms that modulate the effects of YAP/TAZ signaling via (i) factors that modulate YAP/TAZ binding to TEAD, such as P38 MAPK4 ( Lin et al, 2017a ) and VGLL4 ( Zhang et al, 2014 ; Lin et al, 2016 ; Deng and Fang, 2018 ); (ii) methylation and phosphorylation of YAP/TAZ via SET7 ( Oudhoff et al, 2013 ) and PTPN14 ( Liu et al, 2013 ) respectively; and (iii) YAP/TAZ binding and modulation of various non-TEAD transcription factors, such as Smad2/3 ( Grannas et al, 2015 ), Runx2 ( Brusgard et al, 2015 ; Lin et al, 2019 ), p63 ( Tomlinson et al, 2010 ), p73 ( Roperch et al, 2008 ), PRDM4 ( Liu et al, 2018 ), OCT4 and SOX2 ( Bora-Singhal et al, 2015 ).…”