Chondrocytes in the resting zone of the growth plate are maintained in a Wnt-inhibitory environment
Shawn A. Hallett, Yuki Matsushita, Wanida Ono, Naoko Sakagami, Koji Mizuhashi, Nicha Tokavanich, Mizuki Nagata, Annabelle Zhou, Takao Hirai, Henry M. Kronenberg, Noriaki Ono
Abstract
Chondrocytes in the resting zone of the postnatal growth plate are characterized by slow cell cycle progression, and encompass a population of parathyroid hormone-related protein (PTHrP)-expressing skeletal stem cells that contribute to the formation of columnar chondrocytes. However, how these chondrocytes are maintained in the resting zone remains undefined. We undertook a genetic pulse-chase approach to isolate slow cycling, label-retaining chondrocytes (LRCs) using a chondrocyte-specific doxycycline-controllable Tet-Off system regulating expression of histone 2B-linked GFP. Comparative RNA-seq analysis identified significant enrichment of inhibitors and activators for Wnt signaling in LRCs and non-LRCs, respectively. Activation of Wnt/β-catenin signaling in PTHrP + resting chondrocytes using Pthlh-creER and Apc -floxed allele impaired their ability to form columnar chondrocytes. Therefore, slow-cycling chondrocytes are maintained in a Wnt-inhibitory environment within the resting zone, unraveling a novel mechanism regulating maintenance and differentiation of PTHrP + skeletal stem cells of the postnatal growth plate.