The role of neurovascular formation in dental pulp regeneration

Abstract

The dental pulp is a highly vascularized and innervated connective tissue located within the root canal space, encased by impermeable root canal walls. These walls restrict blood supply via a single apical opening. In cases where pulp infection or inflammation arises due to caries, dental trauma, or operative procedures, it could develop into irreversible pulpitis or pulp necrosis. Traditionally, damaged pulp is removed and replaced with synthetic materials. Recently, regenerative endodontic procedures (REPs) have been implemented clinically with a high success rate. However, histological assessments reveal that the newly formed tissue primarily comprises cellular cementum, osseous-like, and periodontal-like tissues rather than actual dentin/pulp complex. Pursuing innovative regenerative strategies to reproduce natural functional pulp-like tissue is crucial in endodontic research. Recognizing that neurovascular niches can incite mesenchymal stem cell (MSC) proliferation and differentiation and encourage their involvement in pulp tissue repair and regeneration, integrating angiogenesis/vasculogenesis and neurogenesis is advantageous for dental pulp regeneration. Stem cells from the apical papilla (SCAPs) are recognized for their multipotency and ability to differentiate into neuronal, endothelial, and smooth muscle cells. These attributes make them a potential singular source of cells for pulp angiogenesis and neurogenesis. Therefore, the objectives of this project are to: (1) optimize methods for neuronal cell differentiation from SCAPs; (2) evaluate the neuroregenerative potential of neuronally induced SCAP (iSCAP) spheroids under various microenvironments in a pulp-on-chip system; (3) explore iSCAP spheres, human umbilical vascular endothelial cells (HUVECs), and SCAPs interactions on neurogenesis and vasculogenesis.

Three studies, accompanied by a scoping review, have been concluded. The initial study assessed whether forming 3D spheres could enhance SCAP neurogenic potential. The subsequent research used a pulp-on-chip system to explore the neuroregenerative potential of SCAP-derived neuronal cell spheroids under various microenvironments. The final study investigated the interactions between neuronally induced SCAP (iSCAP) spheres, SCAPs, and HUVECs, focusing on vasculogenesis and neurogenesis.

From the scoping review, several conclusions were drawn: dental spheres possess great potential in neural regeneration; using multiple assays and associated characterizations provides a better understanding of the mechanism of sphere enhancement on dental stem cell neural differentiation; in vivo, studies are essential for validating the treatment for neurodegenerative diseases. Our in vitro studies concluded that the formation of 3D spheres enhances the neurogenic potential of SCAPs, illustrating the benefits of using 3D SCAP spheres for treating neural diseases. Furthermore, local microenvironments play a critical role in regulating the neuroregenerative potential of SCAP-derived neuronal spheroids. Lastly, spheres formed by iSCAP interact with SCAPs and HUVECs, facilitating vasculogenesis and neurogenesis.

In conclusion, SCAPs are a valuable source for neural regeneration. SCAP neural potentials could be enhanced by sphere formation and are meticulously regulated by the surrounding local microenvironments. Co-culturing iSCAP spheres with SCAPs and HUVECs could promote vasculogenesis and neurogenesis, which holds a promising potential for advancements in regenerative endodontics.