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Updated: Feb 6, 2026
Quantifying Agonist Activity at G Protein-coupled Receptors
Published on: December 26, 2011
R-spondin-2 is a Wnt agonist that regulates osteoblast activity and bone mass
M Noelle Knight1, Kannan Karuppaiah2, Michele Lowe2
11Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, USA.
Abstract:
The R-spondin family of proteins are Wnt agonists, and the complete embryonic disruption of Rspo2 results in skeletal developmental defects that recapitulate the phenotype observed with Lrp5/6 deficiency. Previous work has shown that R-spondin-2 (Rspo2, RSPO2) is both highly expressed in Wnt-stimulated pre-osteoblasts and its overexpression induces osteoblast differentiation in the same cells, supporting its putative role as a positive autocrine regulator of osteoblastogenesis. However, the role of Rspo2 in regulating osteoblastogenesis and bone formation in postnatal bone has not been explored. Here we show that limb-bud progenitor cells from Rspo2 knockout mice undergo reduced mineralization during osteoblastogenesis in vitro and have a corresponding alteration in their osteogenic gene expression profile. We also generated the first Rspo2 conditional knockout (Rspo2floxed) mouse and disrupted Rspo2 expression in osteoblast-lineage cells by crossing to the Osteocalcin-Cre mouse line (Ocn-Cre + Rspo2f/f). Ocn-Cre + Rspo2f/f male and female mice at 1, 3, and 6 months were examined. Ocn-Cre + Rspo2f/f mice are decreased in overall body size compared to their control littermates and have decreased bone mass. Histomorphometric analysis of 1-month-old mice revealed a similar number of osteoblasts and mineralizing surface per bone surface with a simultaneous decrease in mineral apposition and bone formation rates. Consistent with this observation, serum osteocalcin in 3-month-old Ocn-Cre + Rspo2f/f was reduced, and bone marrow-mesenchymal stem cells from Ocn-Cre + Rspo2f/f mice undergo less mineralization in vitro. Finally, gene expression analysis and immunohistochemistry of mature bone shows reduced beta-catenin signaling in Ocn-Cre + Rspo2f/f. Overall, RSPO2 reduces osteoblastogenesis and mineralization, leading to reduced bone mass.
Insights
R-spondin-2 (RSPO2) is crucial for bone formation. Disrupting RSPO2 in osteoblasts reduces bone mass and impairs mineralization, highlighting its role in postnatal bone development.
Area of Science:
- Bone Biology
- Skeletal Development
- Cell Signaling
Background:
- R-spondin proteins are Wnt agonists involved in skeletal development.
- R-spondin-2 (RSPO2) is expressed in osteoblasts and promotes osteoblast differentiation.
- The role of RSPO2 in postnatal bone formation remains unexplored.
Purpose of the Study:
- To investigate the role of RSPO2 in postnatal osteoblastogenesis and bone formation.
- To determine the impact of RSPO2 deficiency on bone mass and skeletal development.
Main Methods:
- In vitro studies using limb-bud progenitor cells from Rspo2 knockout mice.
- Generation of Rspo2 conditional knockout mice (Ocn-Cre+Rspo2floxed).
- Histomorphometric analysis, serum osteocalcin measurements, and gene expression analysis.
Main Results:
- Rspo2 knockout progenitor cells show reduced mineralization and altered osteogenic gene expression.
- Ocn-Cre+Rspo2floxed mice exhibit decreased body size and bone mass.
- Reduced mineral apposition and bone formation rates, decreased serum osteocalcin, and impaired beta-catenin signaling were observed.
Conclusions:
- RSPO2 is essential for regulating osteoblastogenesis and mineralization in postnatal bone.
- RSPO2 deficiency leads to reduced bone mass and impaired skeletal development.
- RSPO2 plays a critical role in maintaining bone homeostasis through beta-catenin signaling.
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