Title

The Wnt antagonist secreted frizzled-related protein-1 controls osteoblast and osteocyte apoptosis

UMMS Affiliation

Department of Cell Biology

Date

12-9-2005

Document Type

Article

Medical Subject Headings

Animals; Annexin A5; Apoptosis; Cell Differentiation; Cells, Cultured; Dinoprostone; Gene Expression Regulation; Humans; In Situ Hybridization; Mice; Osteoblasts; Osteocytes; Proteins; RNA, Messenger; Rats; Recombinant Fusion Proteins; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Transforming Growth Factor beta; Transforming Growth Factor beta1; Wnt Proteins

Disciplines

Cell Biology

Abstract

Mechanisms controlling human bone formation remain to be fully elucidated. We have used differential display-polymerase chain reaction analysis to characterize osteogenic pathways in conditionally immortalized human osteoblasts (HOBs) representing distinct stages of differentiation. We identified 82 differentially expressed messages and found that the Wnt antagonist secreted frizzled-related protein (sFRP)-1 was the most highly regulated of these. Transient transfection of HOBs with sFRP-1 suppressed canonical Wnt signaling by 70% confirming its antagonistic function in these cells. Basal sFRP-1 mRNA levels increased 24-fold during HOB differentiation from pre-osteoblasts to pre-osteocytes, and then declined in mature osteocytes. This expression pattern correlated with levels of cellular viability such that the pre-osteocytes, which had the highest levels of sFRP-1 mRNA, also had the highest rate of cell death. Basal sFRP-1 mRNA levels also increased 29-fold when primary human mesenchymal stem cells were differentiated to osteoblasts supporting the developmental regulation of the gene. Expression of sFRP-1 mRNA was induced 38-fold following prostaglandin E2 (PGE2) treatment of pre-osteoblasts and mature osteoblasts that had low basal message levels. In contrast, sFRP-1 expression was down-regulated by as much as 80% following transforming growth factor (TGF)-beta1 treatment of pre-osteocytes that had high basal mRNA levels. Consistent with this, treatment of pre-osteoblasts and mature osteoblasts with PGE(2) increased apoptosis threefold, while treatment of pre-osteocytes with TGF-beta1 decreased cell death by 50%. Likewise, over-expression of sFRP-1 in HOBs accelerated the rate of cell death threefold. These results establish sFRP-1 as an important negative regulator of human osteoblast and osteocyte survival.

Rights and Permissions

Citation: J Cell Biochem. 2005 Dec 15;96(6):1212-30. Link to article on publisher's site

Related Resources

Link to Article in PubMed

PubMed ID

16149051