Sympathetic nerves inhibit dental pulp stem cell differentiation and tertiary dentine formation via α1B-adrenergic receptor.

Aim: The dental pulp is extensively innervated. Our previous study showed that the α1B-adrenergic receptor ADRA1B is the primary sympathetic neurotransmitter receptor in human dental pulp stem cells (hDPSCs) and its expression was enhanced in inflamed pulp tissues. The sympathetic nerve system (SNS) negatively impacts the proliferation and migration capacities of hDPSCs via ADRA1B. In this study, we aimed to explore the role of the SNS in odontoblast differentiation of hDPSCs and tertiary dentine formation during dentine-pulp injury repair.

Methodology: We investigated in vitro function of ADRA1B activity in regulating odontoblast differentiation of hDPSCs by evaluating protein and RNA expression levels of DSPP and DMP1, alkaline phosphatase (ALP) activity and alizarin red S (ARS) staining in control, ADRA1B-overexpression and ADRA1B-knockdown groups. The underlying mechanisms were further examined by assessing the oxygen consumption rate (OCR), glucose consumption and mitochondrial morphology. In vivo, a rat model with superior cervical ganglionectomy (SCGx) followed by direct pulp capping was established to assess the effects of the SNS on tertiary dentinogenesis. Additionally, Adra1b^flox/flox, Prx1-cre mice, combined with a severe dentine exposure model, were used to explore the effects of the SNS on mesenchymal cells via ADRA1B during tertiary dentine formation. Tertiary dentine was determined by histological staining.

Results: Adrenergic signalling through ADRA1B was a crucial signal that inhibits the odontoblast differentiation ability of hDPSCs in vitro by suppressing mitochondrial metabolism via PGC-1α. Sympathectomy enhanced dentine formation in the direct pulp capping rat model. Furthermore, the ablation of Adra1b in mesenchymal cells led to increased odontoblast differentiation and tertiary dentine formation in a mouse model with severe dentine exposure.

Conclusion: Here, we show a new link between the SNS and the odontoblast differentiation capacity of hDPSCs through the adrenergic receptor ADRA1B. Our findings indicate that the SNS impedes the odontoblast differentiation capacity of hDPSCs by suppressing mitochondrial metabolism, which further hampers tertiary dentine formation via ADRA1B.