Single-cell census of human tooth development enables generation of human enamel.

Tooth enamel secreted by ameloblasts (AMs) is the hardest material in the human body, acting as a shield to protect the teeth. However, the enamel is gradually damaged or partially lost in over 90% of adults and cannot be regenerated due to a lack of ameloblasts in erupted teeth. Here, we use single-cell combinatorial indexing RNA sequencing (sci-RNA-seq) to establish a spatiotemporal single-cell census for the developing human tooth and identify regulatory mechanisms controlling the differentiation process of human ameloblasts. We identify key signaling pathways involved between the support cells and ameloblasts during fetal development and recapitulate those findings in human ameloblast in vitro differentiation from induced pluripotent stem cells (iPSCs). We furthermore develop a disease model of amelogenesis imperfecta in a three-dimensional (3D) organoid system and show AM maturation to mineralized structure in vivo. These studies pave the way for future regenerative dentistry.

Epigenetic metabolites license stem cell states.

It has become clear during recent years that stem cells undergo metabolic remodeling during their activation process. While these metabolic switches take place in pluripotency as well as adult stem cell populations, the rules that govern the switch are not clear. In this review, we summarize some of the transitions in adult and pluripotent cell types and will propose that the key function in this process is the generation of epigenetic metabolites that govern critical epigenetic modifications, and therefore stem cell states.

Wnt5a Supports Osteogenic Lineage Decisions in Embryonic Stem Cells.

The specification of pluripotent stem cells into the bone-forming osteoblasts has been explored in a number of studies. However, the current body of literature has yet to adequately address the role of Wnt glycoproteins in the differentiation of pluripotent stem cells along the osteogenic lineage. During mouse embryonic stem cell (ESC) in vitro osteogenesis, the noncanonical WNT5a is expressed early on. Cells either sorted by their positive WNT5a expression or when supplemented with recombinant WNT5a (rWNT5a) during a 2-day window showed significantly enhanced osteogenic yield. Mechanistically, rWNT5a supplementation upregulated protein kinase C (PKC), calcium/calmodulin-dependent kinase II (CamKII) and c-Jun N-terminal kinase (JNK) activity while antagonizing the key effector of canonical Wnt signaling: ß-catenin. Conversely, when recombinant WNT3a (rWNT3a) or other positive regulators of ß-catenin were employed during this same time window there was a decrease in osteogenic marker expression. However, if rWNT3a was supplemented during a time window following rWNT5a treatment, osteogenic differentiation was enhanced both in murine and human ESCs. Elucidating the role of these WNT ligands in directing the early stages of osteogenesis has the potential to considerably improve tissue engineering protocols and applications for regenerative medicine.

Stem cells for osteodegenerative diseases: current studies and future outlook.

As the worldwide population grows and life expectancies continue to increase, degenerative diseases of the bones, muscles, and connective tissue are a growing problem for society. Current therapies for osteodegenerative disorders such as hormone replacement therapies, calcium/vitamin D supplements and oral bisphosphonates are often inadequate to stop degeneration and/or have serious negative side effects. Thus, there is an urgent need in the medical community for more effective and safer treatments. Stem cell therapies for osteodegenerative disorders have been rigorously explored over the last decade and are yielding some promising results in animal models and clinical trials. Although much work still needs to be done to ensure the safety and efficacy of these therapies, stem cells represent a new frontier of exciting possibilities for bone and cartilage regeneration.