Cytoplasmic Interactions between the Glucocorticoid Receptor and HDAC2 Regulate Osteocalcin Expression in VPA-Treated MSCs

Abstract

Epigenetic regulation has been considered an important mechanism for influencing stem cell differentiation. In particular, histone deacetylases (HDACs) have been shown to play a role in the osteoblast differentiation of mesenchymal stem cells (MSCs). In this study, the effect of the HDAC inhibitor, valproic acid (VPA), on bone formation in vivo by MSCs was determined. Surprisingly, VPA treatment, unlike other HDAC inhibitors, produced a well-organized lamellar bone tissue when MSCs–collagen sponge constructs were implanted subcutaneously into nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice, although a decrease of osteocalcin (OC) expression was observed. Consequently, we decided to investigate the molecular mechanisms by which VPA exerts such effects on MSCs. We identified the glucocorticoid receptor (GR) as being responsible for that downregulation, and suggested a correlation between GR and HDAC2 inhibition after VPA treatment, as evidenced by HDAC2 knockdown. Furthermore, using co-immunoprecipitation analysis, we showed for the first time in the cytoplasm, binding between GR and HDAC2. Additionally, chromatin immunoprecipitation (ChIP) assays confirmed the role of GR in OC downregulation, showing recruitment of GR to the nGRE element in the OC promoter. In conclusion, our results highlight the existence of a cross-talk between GR and HDAC2, providing a mechanistic explanation for the influence of the HDAC inhibitor (namely VPA) on osteogenic differentiation in MSCs. Our findings open new directions in targeted therapies, and offer new insights into the regulation of MSC fate determination.

Epigenetic Regulation of Dental Pulp Stem Cell Fate

“…Several studies have reported that glucocorticoid receptor (GR) is critical for this regulation. HDAC2 binds to GR and inhibits its translocation into the nucleus, but when HDAC2 is inhibited by VPA, GR can enter the nucleus and thus affect the expression of the OC [ 141 , 142 ]. Suberoylanilide hydroxamic acid (SAHA), a pan inhibitor of HDACs, increases the expression of DSPP via the activation of Nfic and enhances odontogenic differentiation in DPSCs [ 143 ].…”

New Frontiers in Stem Cell Research and Translational Approaches

“…Additionally, chromatin immunoprecipitation (ChIP) assays confirmed the role of GR in OC downregulation, showing recruitment of GR to the nGRE element in the OC promoter. These results open new directions in targeted therapies and offer new insights into the regulation of MSCs fate determination [12].…”

“…The second young researcher of this session was Dr. Marcella La Noce (University of Campania, Napoli, Italy) who spoke about adult stem cells isolated from the dental pulp which is an interesting source of postnatal progenitor cells and stem cells [12]. The aim of this study was to evaluate the osteogenic differentiation of dental pulp stem cells (DPSCs) treated with the following different histone deacetylase inhibitors (HDACi): Valproic acid (VPA), entinostat (MS275), trichostatin A (TSA), and vorinostat (SAHA).…”

The chondrogenic differentiation potential of dental pulp stem cells

“…In particular, their osteogenic and odontoblastic differentiation potential for intramembranous bone TE and dentistry applications is the most extensively studied (Anitua et al, 2018;Gronthos et al, 2000;La Noce et al, 2019;Morad et al, 2013;Nuti et al, 2016;Paino et al, 2017). In contrast, the chondrogenic potential of DPSCs for TE applications remains underexplored as most studies investigating DPSCs have only addressed their chondrogenesis as part of their multilineage differentiation potential for human (Hilkens et al, 2013;Koyama et al, 2009;Mokry et al, 2010;Takebe et al, 2017;Zhang et al, 2006), murine (Grottkau et al, 2010) and porcine cells (Iohara et al, 2006).…”