Effects of TAZ on human dental pulp stem cell proliferation and migration

Emerging Roles of YAP/TAZ in Tooth and Surrounding: from Development to Regeneration

Yes associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are ubiquitous transcriptional co-activators that control organ development, homeostasis, and tissue regeneration. Current in vivo evidence suggests that YAP/TAZ regulates enamel knot formation during murine tooth development, and is indispensable for dental progenitor cell renewal to support constant incisor growth. Being a critical sensor for cellular mechano-transduction, YAP/TAZ lays at the center of the complex molecular network that integrates mechanical cues from the dental pulp chamber and surrounding periodontal tissue into biochemical signals, dictating in vitro cell proliferation, differentiation, stemness maintenance, and migration of dental stem cells. Moreover, YAP/TAZ-mediated cell-microenvironment interactions also display essential regulatory roles during biomaterial-guided dental tissue repair and engineering in some animal models. Here, we review recent advances in YAP/TAZ functions in tooth development, dental pulp, and periodontal physiology, as well as dental tissue regeneration. We also highlight several promising strategies that harness YAP/TAZ activation for promoting dental tissue regeneration.

RNA-sequencing analysis reveals the potential molecular mechanism of RAD54B in the proliferation of inflamed human dental pulp cells

AIM

To investigate the role of RAD54B in the proliferation of inflamed human dental pulp cells (hDPCs) induced by lipopolysaccharide (LPS).

METHODOLOGY

Normal, carious and pulpitic human dental pulp tissues were collected. Total RNA was subjected to RNA-sequencing (seq) and gene expression profiles were studied by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Differentially expressed genes (DEGs) in homologous recombination repair (HRR) were validated with qRT-PCR. The expression of RAD54B and TNF-α in human dental pulp tissues was detected using immunohistochemistry. HDPCs were cultured and RAD54B level in hDPCs was detected after LPS stimulation using western blot. CCK-8 was used to investigate the proliferation of hDPCs transfected with negative control (Nc) small interfering RNA (siRNA), RAD54B siRNA, P53 siRNA or both siRNAs with or without LPS stimulation. Flow cytometry was used to detect the cell cycle distribution, and western blot and immunofluorescence were used to analyse the expression of RAD54B, P53 and P21 under the above treatments. One-way and two-way anova followed by least significant difference posttest were used for statistical analysis.

RESULTS

RNA-seq results identified DEGs amongst the three groups. KEGG pathway analysis revealed enrichment of DEGs in the replication and repair pathway. HRR and non-homologous end joining (NHEJ) components were further verified and qRT-PCR results were basically consistent with the sequencing data. RAD54B, an HRR accessory factor highly expressed in carious and pulpitic tissues as compared to that in normal pulps, was chosen as our gene of interest. High RAD54B expression was confirmed in inflamed human dental pulp tissues and LPS-stimulated hDPCs. Upon RAD54B knockdown, P53 and P21 expressions in hDPCs were upregulated whereas the proliferation was significantly downregulated, accompanied by increased G2/M phase arrest. After inhibiting P53 expression in RAD54B-knockdown hDPCs, P21 expression and cell proliferation were reversed.

CONCLUSIONS

Gene expression profiles of normal, carious and pulpitic human dental pulp tissues were revealed. HRR components were elucidated to function in dental pulp inflammation. Amongst the DEGs in HRR, RAD54B regulated the proliferation of inflamed hDPCs via P53/P21 signalling. This research deepens our understanding of dental pulp inflammation and provides new insight to clarify the underlying mechanisms.

Focusing on Hippo Pathway in Stem Cells of Oral Origin, Enamel Formation and Periodontium Regeneration

Hippo pathway is a cellular regulatory pathway composed of core molecules such as MST1/2, LATS1/2, SAV1, MOB1A/B and downstream YAP/TAZ. Fully involved in regulating cell proliferation, differentiation, migration and apoptosis, the Hippo pathway is critical in regulating stem cells of oral origin, for instance, DPSCs and PDLSCs, enamel formation and periodontium regeneration. Here, we summarized the Hippo pathway involved in these progresses and concluded crosstalks of the Hippo pathway with BCL-2, ERK1/2, ROCK, TGF-β/BMP and Wnt/β-catenin pathways, hoping to provide foundation for further clinical therapy.

Knockdown of microRNA-584 promotes dental pulp stem cells proliferation by targeting TAZ

Proliferation of dental pulp stem cells (DPSCs) is crucial in tooth development and damage repairing, also includes its therapy application for tissue engineering. MicroRNAs (miRNAs) are key players in biological processes of DPSCs, and transcriptional co-activator with PDZ-binding motif (TAZ) also plays important roles in cell proliferation and differentiation, however, the roles of miR-584 and TAZ in DPSCs are not known. We found up-regulated miR-584 expression and down-regulated TAZ expression levels in aging dental pulp tissue compare to those in young dental pulp tissue. In proliferating DPSCs we demonstrated the decreased miR-584 expression and increased TAZ expression. miR-584 mimics suppressed DPSCs proliferation and migration, and significantly reduced TAZ production, whereas miR-584 inhibition exerted the converse effects. Knocking down of the TAZ in DPSCs had a similar effect as overexpression of miR-584. Furthermore, luciferase reporter assay demonstrated that miR-584 could directly bind to the TAZ mRNA 3'UTR to repress its translation. Overexpression of TAZ can partly rescue miR-584 mimic-mediated the inhibition of proliferation. Additionally, miR-584 inhibited cell proliferation and downregulated expression of cell cycle proteins by AKT signaling pathway. Together, we identified that miR-584 may be a key regulator in the proliferation of DPSCs by regulating TAZ expression via AKT signaling pathway. It would be a promising biomarker and therapeutic target for pulp disease.

Metabolism as an early predictor of DPSCs aging

Tissue resident adult stem cells are known to participate in tissue regeneration and repair that follows cell turnover, or injury. It has been well established that aging impedes the regeneration capabilities at the cellular level, but it is not clear if the different onset of stem cell aging between individuals can be predicted or prevented at an earlier stage. Here we studied the dental pulp stem cells (DPSCs), a population of adult stem cells that is known to participate in the repair of an injured tooth, and its properties can be affected by aging. The dental pulp from third molars of a diverse patient group were surgically extracted, generating cells that had a high percentage of mesenchymal stem cell markers CD29, CD44, CD146 and Stro1 and had the ability to differentiate into osteo/odontogenic and adipogenic lineages. Through RNA seq and qPCR analysis we identified homeobox protein, Barx1, as a marker for DPSCs. Furthermore, using high throughput transcriptomic and proteomic analysis we identified markers for DPSC populations with accelerated replicative senescence. In particular, we show that the transforming growth factor-beta (TGF-β) pathway and the cytoskeletal proteins are upregulated in rapid aging DPSCs, indicating a loss of stem cell characteristics and spontaneous initiation of terminal differentiation. Importantly, using metabolic flux analysis, we identified a metabolic signature for the rapid aging DPSCs, prior to manifestation of senescence phenotypes. This metabolic signature therefore can be used to predict the onset of replicative senescence. Hence, the present study identifies Barx1 as a DPSCs marker and dissects the first predictive metabolic signature for DPSCs aging.