Disruption of c-Kit Signaling in Kit(W-sh/W-sh) Growing Mice Increases Bone Turnover.

Sutada Lotinun,Nateetip Krishnamra

doi:10.1038/srep31515

Abstract

c-Kit tyrosine kinase receptor has been identified as a regulator of bone homeostasis. The c-Kit loss-of-function mutations in WBB6F1/J-KitW/W-v mice result in low bone mass. However, these mice are sterile and it is unclear whether the observed skeletal phenotype is secondary to a sex hormone deficiency. In contrast, C57BL/6J-KitW-sh/W-sh (Wsh/Wsh) mice, which carry an inversion mutation affecting the transcriptional regulatory elements of the c-Kit gene, are fertile. Here, we showed that Wsh/Wsh mice exhibited osteopenia with elevated bone resorption and bone formation at 6- and 9-week-old. The c-Kit Wsh mutation increased osteoclast differentiation, the number of committed osteoprogenitors, alkaline phosphatase activity and mineralization. c-Kit was expressed in both osteoclasts and osteoblasts, and c-Kit expression was decreased in Wsh/Wshosteoclasts, but not osteoblasts, suggesting an indirect effect of c-Kit on bone formation. Furthermore, the osteoclast-derived coupling factor Wnt10b mRNA was increased in Wsh/Wsh osteoclasts. Conditioned medium from Wsh/Wsh osteoclasts had elevated Wnt10b protein levels and induced increased alkaline phosphatase activity and mineralization in osteoblast cultures. Antagonizing Wnt10b signaling with DKK1 or Wnt10b antibody inhibited these effects. Our data suggest that c-Kit negatively regulates bone turnover, and disrupted c-Kit signaling couples increased bone resorption with bone formation through osteoclast-derived Wnt 10 b.

Highlights

Sutada Lotinun1,2 & Nateetip Krishnamra[3] c-Kit tyrosine kinase receptor has been identified as a regulator of bone homeostasis
The c-Kit Wsh mutation increased osteoclast differentiation, the number of committed osteoprogenitors, alkaline phosphatase activity and mineralization. c-Kit was expressed in both osteoclasts and osteoblasts, and c-Kit expression was decreased in Wsh/Wsh osteoclasts, but not osteoblasts, suggesting an indirect effect of c-Kit on bone formation
Quantitative real-time PCR indicated that c-Kit expression was decreased in Wsh/Wsh bone marrow macrophage (BMM) and osteoclasts but not osteoblasts, suggesting that increased bone formation in Wsh/Wsh mice was not an osteoblasts intrinsic effect

Summary

Introduction

Sutada Lotinun1,2 & Nateetip Krishnamra[3] c-Kit tyrosine kinase receptor has been identified as a regulator of bone homeostasis. The c-Kit loss-offunction mutations in WBB6F1/J-KitW/W-v mice result in low bone mass These mice are sterile and it is unclear whether the observed skeletal phenotype is secondary to a sex hormone deficiency. Were infertile due to a lack of germ cells in the ovary and had reduced estrogen and progesterone levels, leading to increased FSH level[19] It is unclear whether the observed skeletal phenotype in W/Wv mice resulted from cell-autonomous effects in osteoclasts or was a consequence of changes in sex hormone levels. We focused on the skeletal phenotype of C57BL/6J-KitW-sh/W-sh (Wsh/Wsh) mice that were fully fertile and determined the mechanism by which altered c-Kit signaling affected bone turnover. These findings demonstrate that c-Kit regulates bone turnover by suppressing osteoblast and osteoclast differentiation. C-Kit mutation increased bone formation by increasing the generation of osteoclast-derived coupling factor Wnt10b

Methods

Results

Conclusion