What can we learn from comparing Giants with Miniatures – The role of NOTCH4 signalling in the canine growth plate and chondrogenic differentiation of canine bone marrow derived mesenchymal stromal cells.

Abstract

At this moment there are many challenges in the regeneration of large bone defects. An interesting alternative to the current treatment standards could be the use of mesenchymal stem cells (MSCs). These cells produce bone by endochondral bone formation, thereby overcoming the limitations that arise with the use of bone grafts. In this project, we used next generation sequencing to study differences in the gene expression profile of the growth plate of Great Danes (GD), a large breed dog, and Miniature Poodles (MP), a small breed dog, in order to find new targets that could enhance the pace of endochondral bone formation. We found that NOTCH4 was highly upregulated (FC: 490) in the proliferative zone of the GD growth plate compared to the MP, although absolute transcript counts were low (7 counts (GD) vs 0 counts (MP)). Using immunohistochemistry to validate the difference in NOTCH4 expression at the protein level, we found significantly more NOTCH4 protein in the proliferative and reserve zone of GD growth plate compared to the MP growth plate. Interestingly, NOTCH4 expression was mainly found in the chondrocytes surrounding the blood vessels. The next step of the project was to induce expression of NOTCH4 in bone marrow derived MSCs in order to investigate the role of NOTCH4 during endochondral bone formation. Unfortunately, none of the used growth factors or small molecules were able to induce NOTCH4 expression. These findings suggests that although NOTCH4 might play an interesting role in the canine growth plate, further research is necessary.