Cartilage-specific ablation of XBP1 signaling in mouse results in a chondrodysplasia characterized by reduced chondrocyte proliferation and delayed cartilage maturation and mineralization

Summary Objective To investigate the in vivo role of the IRE1/XBP1 unfolded protein response (UPR) signaling pathway in cartilage. Design Xbp1 flox/flox. Col2a1 - Cre mice ( Xbp1 CartΔEx2 ), in which XBP1 activity is ablated specifically from cartilage, were analyzed histomorphometrically by Alizari...

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Published in:Osteoarthritis and cartilage 2015-04, Vol.23 (4), p.661-670
Main Authors: Cameron, T.L, Gresshoff, I.L, Bell, K.M, Piróg, K.A, Sampurno, L, Hartley, C.L, Sanford, E.M, Wilson, R, Ermann, J, Boot-Handford, R.P, Glimcher, L.H, Briggs, M.D, Bateman, J.F
Format: Article
Language:English
Subjects:
Animals
Apoptosis - physiology
Calcification, Physiologic - physiology
Cartilage, Articular - pathology
Cartilage, Articular - physiopathology
Cell Proliferation - physiology
Chondrocytes - pathology
Chondrodysplasia
Disease Models, Animal
DNA-Binding Proteins - genetics
DNA-Binding Proteins - physiology
Endochondral ossification
Endoplasmic Reticulum Stress - physiology
ER stress
Gene Deletion
Growth plate
Growth Plate - pathology
Growth Plate - physiopathology
Membrane Proteins - genetics
Membrane Proteins - physiology
Mice
Mice, Transgenic
Osteochondrodysplasias - pathology
Osteochondrodysplasias - physiopathology
Protein-Serine-Threonine Kinases - genetics
Protein-Serine-Threonine Kinases - physiology
Regulatory Factor X Transcription Factors
Rheumatology
Signal Transduction - genetics
Signal Transduction - physiology
Transcription Factors - genetics
Transcription Factors - physiology
X-Box Binding Protein 1
XBP1
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Summary:Summary Objective To investigate the in vivo role of the IRE1/XBP1 unfolded protein response (UPR) signaling pathway in cartilage. Design Xbp1 flox/flox. Col2a1 - Cre mice ( Xbp1 CartΔEx2 ), in which XBP1 activity is ablated specifically from cartilage, were analyzed histomorphometrically by Alizarin red/Alcian blue skeletal preparations and X-rays to examine overall bone growth, histological stains to measure growth plate zone length, chondrocyte organization, and mineralization, and immunofluorescence for collagen II, collagen X, and IHH. Bromodeoxyuridine (BrdU) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) analyses were used to measure chondrocyte proliferation and cell death, respectively. Chondrocyte cultures and microdissected growth plate zones were analyzed for expression profiling of chondrocyte proliferation or endoplasmic reticulum (ER) stress markers by Quantitative PCR (qPCR), and of Xbp1 mRNA splicing by RT-PCR to monitor IRE1 activation. Results Xbp1 CartΔEx2 displayed a chondrodysplasia involving dysregulated chondrocyte proliferation, growth plate hypertrophic zone shortening, and IRE1 hyperactivation in chondrocytes. Deposition of collagens II and X in the Xbp1 CartΔEx2 growth plate cartilage indicated that XBP1 is not required for matrix protein deposition or chondrocyte hypertrophy. Analyses of mid-gestation long bones revealed delayed ossification in Xbp1 CartΔEx2 embryos. The rate of chondrocyte cell death was not significantly altered, and only minimal alterations in the expression of key markers of chondrocyte proliferation were observed in the Xbp1 CartΔEx2 growth plate. IRE1 hyperactivation occurred in Xbp1 CartΔEx2 chondrocytes but was not sufficient to induce regulated IRE1-dependent decay (RIDD) or a classical UPR. Conclusion Our work suggests roles for XBP1 in regulating chondrocyte proliferation and the timing of mineralization during endochondral ossification, findings which have implications for both skeletal development and disease.
ISSN:1063-4584
1522-9653
DOI:10.1016/j.joca.2015.01.001