Periodic Reporting for period 4 - STEMMING-FROM-NERVE (Targeted Cell Recruitment During Organogenesis And Regeneration: Glia Makes The Tooth)
Reporting period: 2020-02-01 to 2020-09-30
Our results responded to the overall objectives and addressed how, when and to what extent peripheral glial cells residing in the dental nerves are recruited to produce cells of pulp and odontoblast lineages in the tooth, which might also manifest in additional tooth-inducing properties. For this, we had to describe the existing cell heterogeneity and describe the transitions between cell types (this part is now published in Krivanek et al., Nature Communications 2020). Most recently, we discovered and analyzed the transition of glial cells into dental mesenchymal populatioins at gene expression level (still unpublished data). In parallel, we also demonstrated how the neural crest cells give rise to cranial mesenchymal populations, including those giving rise to teeth, and how such mesenchymal population might be connected lineage-wise with developing glial cells (we published this part in Soldatov et al., Science 2019). Finally, the profiling of immune cells showed the presence of previously unknown macrophage subtypes and their site-specific spatial distribution conserved also in human teeth. The interactomics mapping suggested that CSF1 secreted by specific pulp cells is a key for hosting dental macrophages. The conditional knockout of Csf1 gene in the neural crest-derived pulp resulted not only in a loss of dental macrophages, but also in a failure of correct incisor development and shaping. Taken together, the unbiased analysis of dental cell types combined with predictions of communications between the cell populations resulted in new discoveries that proved catalyzing power of dental cell type atlas.
The conclusion of the action
Taken together, in this study, for the sake of understanding the plasticity of glial and other populations, we generated the unbiased atlas of cell types and subtypes building the human and mouse growing and non-growing teeth, with the special focus on progenitors and glial cells and including continuously self-renewing mouse incisor as the major model system for addressing the mechanisms of growth. We generated polygenic signatures delineating the known and new subtypes, which resulted in new markers and molecular tools for manipulating these populations in the future. Using this dataset, as a proof of principle, we identified and validated previously unknown cell subtypes in epithelial, mesenchymal and immune system compartments. We predicted and validated new stem cell and progenitor populations (including glial) and described differentiation trajectories for ameloblasts, odontoblasts and other terminally differentiated cell types in the tooth, which will become an essential tool for the future regenerative medicine application and in vitro derivation of these cell types. We demonstrated how the denervation influences the conversion of nerve-associated Schwann cells into mesenchymal populations in the tooth by changing differentiation dynamics. To provide functional predictions of cell type integration within dental tissues, we generated the interactomics maps that visualize potential ligand-receptor mediated interactions between all identified populations. Functional validation of one of such predictions showed that Csf1-Csfr1 interaction is essential for previously unanticipated morphogenetic function of macrophages both in epithelial and mesenchymal compartments of the tooth. Finally, the interactomics maps and the cluster structure of all identified populations are available for further exploration and deep data mining online via the intuitive interface Atlas project webpage: http://pklab.med.harvard.edu/ruslan/dental.atlas.html
1. We generated the complete and unbiased atlas of dental cell types for mouse and human, and growing and non-growing teeth (see Figure graphical abstract)
2. Thanks to the atlas work, we discovered the new stem and progenitor cell types important for tooth growth and maintenance
3. We profiled the transition from glial cells into mesenchymal populations within the tooth (see Figures 1-2), and described the transitory moments, trauma condition and potential signals influencing plasticity of glia
4. We discovered the importance of dental macrophages for the maintenance of stem cell niches (see Figures 3-4) and overall dental integrity
5. We revealed the potential origins of glial plasticity and its similarity to embryonic multipotent neural crest cells
6. We investigated the tooth-inducing potential of glial cells and did not manage to obtain the proof of this phenomena in vivo.
The results were published in multiple top journals (Science, Nature, Nature Communications) and disseminated via professional academic and non-academic communities (see Publications and Dissemination sections)
Address (URL) of the project's public website