VWC2 Increases Bone Formation Through Inhibiting Activin Signaling

Calcif Tissue Int. 2018 Dec;103(6):663-674. doi: 10.1007/s00223-018-0462-9. Epub 2018 Aug 3.

Abstract

By a bioinformatics approach, we have identified a novel cysteine knot protein member, VWC2 (von Willebrand factor C domain containing 2) previously known as Brorin. Since Brorin has been proposed to function as a bone morphogenetic protein (BMP) antagonist, we investigated the binding of Brorin/VWC2 to several BMPs; however, none of the BMPs tested were bound to VWC2. Instead, the βA subunit of activin was found as a binding partner among transforming growth factor (TGF)-β superfamily members. Here, we show that Vwc2 gene expression is temporally upregulated early in osteoblast differentiation, VWC2 protein is present in bone matrix, and localized at osteoblasts/osteocytes. Activin A-induced Smad2 phosphorylation was inhibited in the presence of exogenous VWC2 in MC3T3-E1 osteoblast cell line and primary osteoblasts. The effect of VWC2 on ex vivo cranial bone organ cultures treated with activin A was investigated, and bone morphometric parameters decreased by activin A were restored with VWC2. When we further investigated the biological mechanism how VWC2 inhibited the effects of activin A on bone formation, we found that the effects of activin A on osteoblast cell growth, differentiation, and mineralization were reversed by VWC2. Taken together, a novel secretory protein, VWC2 promotes bone formation by inhibiting Activin-Smad2 signaling pathway.

Keywords: Activin A; Bone formation; Calvaria; Osteoblasts; Von Willebrand factor C domain containing 2 (VWC2).

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Cell Differentiation / physiology
  • Extracellular Matrix Proteins / metabolism*
  • HEK293 Cells
  • Humans
  • Inhibin-beta Subunits / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Nerve Tissue Proteins / metabolism*
  • Osteoblasts / metabolism
  • Osteogenesis / physiology*
  • Signal Transduction / physiology

Substances

  • Extracellular Matrix Proteins
  • Nerve Tissue Proteins
  • Vwc2 protein, mouse
  • inhibin beta A subunit
  • Inhibin-beta Subunits