Notum balances Wnt signaling during tracheal cartilage development

BMP and WNT signaling are involved in tracheal cartilage development in chicken embryos

The respiratory system consists of the tracheal tube which extends from the back of the mouth, down the neck and branches into the bronchial tubes of the lungs, which are the major sites of respiration. Cartilaginous rings are present along the length of the trachea and are essential for keeping the airways open. Understanding trachea and cartilage development is crucial to better understanding respiratory disorders and diseases. We analyzed cartilage development across different chicken embryonic stages using a combination of cellular and molecular biology tools. We found that chondrogenic condensations are barely visible histologically from HH35 (E8.5) while differentiated cartilage rings are distinct by HH36 (E10). In situ hybridisation data shows that Bmp2 is expressed in a ring-like pattern along the length of the tracheal tube from HH36. We further show that BMP2, but not BMP4, colocalises with COL2A1. qPCR data shows that genes such as COL2A1, and WNT are substantially upregulated between HH34 to HH37, while other genes (e.g. SHH, TBX4/5) are downregulated. Within this three to four day period, we detected a reduction in SHH and WNT during cartilage condensation formation and an upregulation of COL2A1 and WNT during overt cartilage differentiation. We next used a known Bmp2 type 1 receptor inhibitor (DMH1) to attempt to disrupt tracheal cartilage development. Following inhibition, we observed a widening and lengthening of the tracheal cartilage rings with some narrowing of the spaces between the rings. Our gene expression analysis reveals significant increases in COL2A1, WNT, and BMP4 following BMP receptor blocking compared to sham controls and indicates that these genes are important for the molecular response that results in patterning the tracheal cartilage ring morphology. This study provides a framework to further understand development of these important airway cartilages in the avian model.

NOTUM plays a bidirectionally modulatory role in the odontoblastic differentiation of human stem cells from the apical papilla through the WNT/β-catenin signaling pathway

OBJECTIVE

Notum is a secreted deacylase, which is crucial for tooth dentin development in mice. This study aimed to investigate the effect of NOTUM on the odontoblastic differentiation of human stem cells from the apical papilla (hSCAPs), to reveal the potential value of NOTUM in pulp-dentin complex regeneration.

DESIGN

The expression pattern of NOTUM in human tooth germs and during in vitro odontoblastic differentiation of hSCAPs was evaluated by immunohistochemical staining, and quantitative polymerase chain reaction, respectively. To manipulate the extracellular NOTUM level, ABC99 or small interfering RNA was used to down-regulate it, while recombinant NOTUM protein was added to up-regulate it. The effects of changing NOTUM level on the odontoblastic differentiation of hSCAPs and its interaction with the WNT/β-catenin signaling pathway were studied using alkaline phosphatase staining, alizarin red staining, quantitative polymerase chain reaction, and western blot.

RESULTS

NOTUM was observed in the apical papilla of human tooth germs. During in vitro odontoblastic differentiation of hSCAPs, NOTUM expression initially increased, while the WNT/β-catenin pathway was activated. Downregulation of NOTUM hindered odontoblastic differentiation. Recombinant NOTUM protein had varying effects on odontoblastic differentiation depending on exposure duration. Continuous addition of the protein inhibited both odontoblastic differentiation and the WNT/β-catenin pathway. However, applying the protein solely in the first 3 days enhanced odontoblastic differentiation and up-regulated the WNT/β-catenin pathway.

CONCLUSION

NOTUM demonstrated a bidirectional impact on in vitro odontoblastic differentiation of hSCAPs, potentially mediated by the WNT/β-catenin pathway. These findings suggest its promising potential for pulp-dentin complex regeneration.

Notum Deletion From Late-Stage Skeletal Cells Increases Cortical Bone Formation and Potentiates Skeletal Effects of Sclerostin Inhibition

Wnt signaling plays a vital role in the cell biology of skeletal patterning, differentiation, and maintenance. Notum is a secreted member of the α/β-hydrolase superfamily that hydrolyzes the palmitoleoylate modification on Wnt proteins, thereby disrupting Wnt signaling. As a secreted inhibitor of Wnt, Notum presents an attractive molecular target for improving skeletal health. To determine the cell type of action for Notum's effect on the skeleton, we generated mice with Notum deficiency globally (Notum-/- ) and selectively (Notumf/f ) in limb bud mesenchyme (Prx1-Cre) and late osteoblasts/osteocytes (Dmp1-Cre). Late-stage deletion induced increased cortical bone properties, similar to global mutants. Notum expression was enhanced in response to sclerostin inhibition, so dual inhibition (Notum/sclerostin) was also investigated using a combined genetic and pharmacologic approach. Co-suppression increased cortical properties beyond either factor alone. Notum suppressed Wnt signaling in cell reporter assays, but surprisingly also enhanced Shh signaling independent of effects on Wnt. Notum is an osteocyte-active suppressor of cortical bone formation that is likely involved in multiple signaling pathways important for bone homeostasis © 2021 American Society for Bone and Mineral Research (ASBMR).