Indian hedgehog stimulates periarticular chondrocyte differentiation to regulate growth plate length independently of PTHrP
Tatsuya Kobayashi, … , Andrew P. McMahon, Henry M. Kronenberg
Tatsuya Kobayashi, … , Andrew P. McMahon, Henry M. Kronenberg
Published July 1, 2005
Citation Information: J Clin Invest. 2005;115(7):1734-1742. https://doi.org/10.1172/JCI24397.
View: Text | PDF
Research Article Bone biology

Indian hedgehog stimulates periarticular chondrocyte differentiation to regulate growth plate length independently of PTHrP

Abstract

In the developing growth plate, periarticular chondrocytes proliferate, differentiate into columnar chondrocytes, and then further differentiate into postmitotic hypertrophic chondrocytes. Parathyroid hormone–related (PTH-related) protein (PTHrP), regulated by Indian hedgehog (Ihh), prevents premature hypertrophic differentiation, thereby maintaining the length of columns. Ihh regulates cartilage development through PTHrP-independent pathways as well. Here we show that Ihh stimulates differentiation of periarticular to columnar chondrocytes (periarticular chondrocyte differentiation) and thereby regulates the length of columns independently of PTHrP. Mosaic ablation of the PTH/PTHrP receptor in the growth plate caused upregulation of Ihh action, PTHrP upregulation, acceleration of periarticular chondrocyte differentiation, and elongation of the columnar region. Decreasing Ihh action in these mice reduced elongation of columns, whereas decreasing PTHrP showed only a modest effect on column length. Overexpression of Ihh caused PTHrP upregulation, elongation of columns, and acceleration of periarticular chondrocyte differentiation. PTHrP heterozygosity in this model had a minimal effect on the elongation of columns. Moreover, the elongation of columns and stimulation of periarticular chondrocyte differentiation in these models were still observed when PTHrP signaling was maintained so that it remained constant. These results demonstrate that Ihh acts on periarticular chondrocytes to stimulate their differentiation, thereby regulating the columnar cell mass independently of PTHrP.

Authors

Tatsuya Kobayashi, Desi W. Soegiarto, Yingzi Yang, Beate Lanske, Ernestina Schipani, Andrew P. McMahon, Henry M. Kronenberg

×

Figure 5

Options: View larger image (or click on image) Download as PowerPoint
Hedgehog overactivation in periarticular chondrocytes stimulates differe...
Hedgehog overactivation in periarticular chondrocytes stimulates differentiation into columnar chondrocytes. (A) Bapx1 is expressed predominantly in columnar chondrocytes. H&E staining and in situ hybridization for Bapx1 were performed on sections of the proximal tibial growth plate of an E16.5 wild-type mouse embryo. (B) Overexpression of Ihh in PTHrP-expressing cartilage induces Bapx1-expressing cells. In contrast, the PTHrP-Tg tibia, comprising almost exclusively periarticular chondrocytes, lacks the Bapx1 domain. In situ hybridization was performed on distal tibiae of E16.5 embryos. Dotted lines indicate bone contours. (C) Induction of Bapx1 after Shh treatment. Chondrocytes were isolated from E18.5 PTHrP-Tg tibiae, comprising almost exclusively periarticular chondrocytes, dispersed, and cultured in vitro with or without stimulation with 1 mg/ml recombinant Shh for indicated periods. The expression of Bapx1 mRNA and Gapdh mRNA was assessed by quantitative RT-PCR. The expression of Bapx1 mRNA, a marker for columnar chondrocytes, was significantly increased after stimulation with recombinant Shh, whereas Gapdh mRNA was unchanged. The expression level of Bapx1 mRNA was normalized to that of Gapdh mRNA. Expression levels are shown as relative to mean values of control (100%). White bars and gray bars represent control and Shh-treated cells, respectively. Standard deviations are shown. n = 3 in each group; *P < 0.01.