Primary Cilia Organization Orchestrating Cell Polarity in the Growth Plate and Its Loss in Osteochondroma
CE de Andrea, M Wiweger, JVMG Bovee, S Romeo, PCW Hogendoorn. Leiden University Medical Center, Leiden, Netherlands; Treviso Regional Hospital, Treviso, Italy
Background: The growth plate is a cartilaginous template needed for the elongation of long bones. In its regulation, heparan sulphate proteoglycan (HSPG) and primary cilia play a role. Impaired HSPG biosynthesis is associated with osteochondroma formation. Primary cilia function as cell's antennas that receive and transduce mechanical and chemical signals from the surrounding cells and the extracellular matrix.
Design: We evaluated the organization of primary cilia in the growth plate (n=5) and osteochondroma (n=5) and its relation with cell polarity. The cilium was immunolabed with acetylated α-tubulin antibody and its organization was studied by confocal microscopy. The centrioles were stained with γ-tubulin. The ciliary assembly was analyzed by electron microscopy and by the immunolocalization of KIF3A motor protein.
Results: The primary cilia organization in the growth plate reflected that chondrocytes non-polarized (resting chondrocytes) became polarized (proliferating and hypertrophic chondrocytes) orienting the cilium parallel to the longitudinal axis of the bone. The primary cilia alignment formed one virtual axis which crossed the center of column of chondrocytes. The centrioles organization also confirmed the presence of the virtual axis. The ciliary axes showed the polarity axis of the growth plate. In osteochondroma, primary cilia were randomly located in the central or in the lateral-medial region of the cells related to the growth axis of the tumor. Interestingly, the virtual axis was also found in the osteochondroma cells focally arranged into column. The primary cilia organization in osteochondroma reflected loss of cell polarity. The ciliary assembly, as judged by electron microscopy and the immunolocalization of KIF3A motor protein, was similar in both. We also demonstrated the dynamicity of primary cilia, whose presence/absence was correlated with the cell cycle.
Conclusions: We showed that the organization of primary cilia in the growth plate reflects cell polarity. The achievement and maintenance of individual and collective polarity in the growth plate is essential for its normal regulation. The loss of cell polarity in osteochondroma seems to be a key event and might be related with its formation and indicate abnormal transduction of signaling molecules or impaired cell-matrix interaction.
Category: Bone & Soft Tissue
Tuesday, March 23, 2010 9:30 AM
Poster Session III # 28, Tuesday Morning