Cartilage tumors are the most common and terminal primary neoplasms in bone. Physiologically, bones formed through endochondral ossification are regulated by the Hedgehog pathway and Parathyroid hormone-like hormone feedback loop. The upregulation of the infamous Hedgehog pathway has been demonstrated in several non-cartilaginous neoplasms. Recently, frequent mutational events of isocitrate dehydrogenase1 (IDH1) were identified in cartilage tumors. In other neoplasms, IDH mutations produces an oncometabolite that can promote HIF1a activation, contributing to tumorigenesis. Currently, the role of IDH1 mutations in cartilage tumors remain unknown. Investigating the physiological aspect of IDH1proves useful in identifying novel therapeutic targets for cartilage tumors. IDH1 deficient and wild-type littermates, were harvested for forelimbs and hindlimbs at various developmental stages for phenotypic analysis via hematoxylin and eosin staining. Histological analysis demonstrated IDH1 homozygous deficient mice at embryonic stages exhibited dwarfism and an elongated layer of hypertrophic chondrocytes. This was verified via immunohistochemistry Type 10 Collagen staining and Quantitative PCR (qPCR) using the chondrocyte terminal differentiation marker Col10a1. Whole skeletons of IDH1 deficient mice were subjected to skeletal double staining which demonstrated delayed mineralization of underdeveloped IDH1 deficient mice contrasted with wild-type littermates. qPCR was performed to examine the status of chondrocyte differentiation through the Hedgehog pathway in cultured primarymouse growth plate chondrocytes. Interestingly, IDH1 deficient non-neoplastic cells revealed significant upregulation of Hedgehog target molecules in IDH1 deficient chondrocytes. As a result, the loss-offunction of IDH1 was identified as a potential impairment of chondrocyte differentiation and a factor towards chondrocyte tumorgenisis.
