During the process of endochondral bone formation, Indian Hedgehog (Ihh), a member of the hedgehog (Hh) family of secreted morphogens, and parathyroid hormone-related peptide (PTHrP) play key roles in the regulation of cartilage cell (chondrocyte) differentiation. Previous studies have established that Ihh coordinates chondrocyte differentiation indirectly by activating PTHrP expression, which in turn delays their transition to the terminal hypertrophic state. In the present study, using an in vitro system of cultured CFK-2 chondrocytic cells, we have explored the possibility that Ihh may also influence chondrocytic differentiation directly and investigated how this process is modulated by PTHrP, Engrailed-1 (En-1), and heparan sulfate glycosaminoglycans (HS-GAG). We show that Ihh signaling enhances, rather than inhibits, expression of markers of chondrocytic differentiation and that an inactivating missense mutation mapping to its NH2-terminal domain (N-IhhW160G) abolishes this capacity. Moreover, activation of protein kinase A (PKA) by PTHrP-signaling also perturbs Ihh-mediated differentiation. Indicative of a novel regulatory mechanism, Ihh in turn downregulates PKA activity downstream of the PTH/PTHrP-receptor (PTH1R). En-1, detected in prehypertrophic growth plate chondrocytes in situ, influences chondrocytic differentiation and impedes Hh-signaling in vitro, suggesting a novel role for this protein in cartilage development. Finally, we show that HS-GAGS are required for proper mediation of Hh-signaling and thus also participate in modulating chondrocytic differentiation. Taken together, this study provides experimental evidence that Ihh harbors the capacity to directly induce rather than impede chondrogenic differentiation, and that this function is modulated by the cellular actions of PTHrP, En-1, and HS-GAG.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.84454 |
| Date | January 2002 |
| Creators | Deckelbaum, Ron Avi |
| Contributors | Karaplis, Andrew C. (advisor), Goltzman, David (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001975081, proquestno: AAINQ88696, Theses scanned by UMI/ProQuest. |
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