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Site-specific Wnt signalling explains regional differences in bone physiology – Evidence from a cross-species RNA-Seq study comparing osteocyte transcriptomes in the tibia and skull

ABSTRACT: Local site-specific differences between bones in different regions of the skeleton account for their different properties and functions. To identify mechanisms behind these differences, we have performed a cross-species study comparing RNA transcriptomes of cranial and tibial osteocytes, from bones with very different primary functions and physiological responses, collected from the same individual mouse, rat and rhesus macaque. Bioinformatic analysis was performed to identify 32 genes changed in the same direction between sites and shared across all three species. Several well-established key genes in bone growth and remodelling were upregulated in the tibias of all three species (BMP7, DKK1, FGF1, FRZB, SOST). Many of them associate or crosstalk with the canonical Wnt signalling pathway. These results suggest Wnt signalling-related candidates for different control of regulatory mechanisms in bone homeostasis in the skull and tibia and indicate a different balance between genetically determined structure and feedback mechanisms to strains induced by mechanical loading at the different sites.

ORGANISM(S): Mus musculus Rattus norvegicus Macaca mulatta

PROVIDER: GSE151971 | GEO | 2020/07/08

REPOSITORIES: GEO

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Project description:WNT signaling is critical in most aspects of skeletal development and homeostasis, and antagonists of WNT signaling are emergning as key regulatory proteins with great promise as therapeutic agents for bone disorders. Until recently Sost and its paralog Sostdc1 have been described as growth factors with highly restricted expression in the adult where Sost was assumed 'osteocyte-' and Sostdc1 'kidney-' specific. Here we show that these two proteins emerged throgh ancestral genome duplication and their expression patterns have diverged to span complimentary domains in most organ systems including musculoskeletal, cardiovascular, nervous, digestive, reproductive and respiratory. In the developing limb, Sost and Sostdc1 display dynamic expression patterns with Sost being restricted to the distal ectoderm and Sostdc1 to the proximal ectoderm and the mesenchyme. While Sostdc1-/- mice lack any obvious limb and skeletal defects, Sost-/- mice recapitulate the hand defects described for sclerosteosis patients. However, elevated WNT signaling in Sost-/-; Sostdc1-/- mice causes misregulation of SHH signaling, ectopic activation of Sox9 in the digit 1 field and ultimately preaxial polydactyly. In addition, we show that the syndactyly documented in Sclerosteosis is present in both Sost-/- and Sost-/-; Sostdc1-/- mice, and is driven by misregulation of Fgf8 in the AER, a region lacking Sost and Sostdc1 expression. This study highlights the complexity of WNT signaling in skeletal biology and disease and emphasizes how redundant mechanisms and non-cell autonomous effects can synergize to unveil new intricate phenotypes caused by elevated WNT signaling. Five arrays were analyzed, consisting of two total embryonic fore-limb RNA (experimental) and three total embryonic forelimb RNA (reference) samples at E11.5 DPC mouse (C57Bl6 strain). Embryos were not pooled to generate samples. Each time point has 3 to 5 biological replicates for limb bud samples, duplicates for whole embryos. Comparisons were made between limb bud samples and whole embryo at the same stage, fore-limb samples of different stages, hind-limb samples of different stages, and fore-limb samples compared to hind-limb samples at the same or the next stage.

Project description:Objective : To study molecular changes in the articular cartilage and subchondral bone of the tibial plateau from mice deficient in frizzled related protein (Frzb) compared to wild-type mice by transcriptome analysis. Methods : Gene-expression analysis of the articular cartilage and subchondral bone of 3 wild-type and 3 Frzb-/- mice was performed by microarray. Pathway analysis of differentially expressed genes between 3 wild-type and 2 Frzb-/- samples was explored with PANTHER, DAVID and GSEA bioinformatics tools. Activation of the WNT pathway was analyzed using western blot. The effects of Frzb gain and loss of function on chondrogenesis and cell proliferation was examined using ATDC5 micromasses and mouse ribcage chondrocytes. Results : Extracellular matrix-associated integrin and cadherin pathways, as well as WNT pathway genes were upregulated in Frzb-/- samples. Several WNT receptors, target genes, and other antagonists were upregulated, but no difference in active β-catenin was found. Analysis of ATDC5 cell micromasses overexpressing FRZB indicated an upregulation of aggrecan and Col2a1, and downregulation of molecules related to damage and repair in cartilage, Col3a1 and Col5a1. Silencing of Frzb resulted in downregulation of aggrecan and Col2a1. Pathways associated with cell cycle were downregulated. Ribcage chondrocytes derived from Frzb-/- mice showed decreased proliferation compared to wild-type cells. Conclusions : Our analysis provides evidence for tight regulation of WNT signaling, shifts in extracellular matrix components and effects on cell proliferation and differentiation in the articular cartilage - subchondral bone unit in Frzb-/- mice. These data further support an important role for FRZB in joint homeostasis and highlight the complex biology of WNT signaling in the joint. Gene-expression analysis of the articular cartilage and subchondral bone of 3 wild-type and 3 Frzb-/- mice was performed by microarray. Pathway analysis of differentially expressed genes between 3 wild-type and 2 Frzb-/- samples was explored with PANTHER, DAVID and GSEA bioinformatics tools.

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Site-specific Wnt signalling explains regional differences in bone physiology – Evidence from a cross-species RNA-Seq study comparing osteocyte transcriptomes in the tibia and skull

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