Differential gene expression in cultured osteoblasts and bone marrow stromal cells from patients with Paget's disease of bone.
Paget's disease is a focal condition of bone. To study changes in cells within pagetic lesions, we cultured osteoblasts and stromal cells from 22 patients and compared gene expression in these cells to cells from healthy bone. We identified several differentially regulated genes, and we suggest that these changes could lead to the formation of the lesions.


BACKGROUND
Paget's disease is a focal condition of bone of unknown cause. Although it is regarded as primarily an osteoclast disorder, the tight coupling of the activity of osteoclasts and osteoblasts suggests that the osteoblast could play a key role in its pathogenesis. The aim of the study was to identify possible changes in pagetic osteoblasts and stromal cells that might contribute to the development of pagetic lesions.


METHODS
Candidate genes were identified based on known bone cell regulators, supplemented with microarray analysis. Gene expression was determined by real-time PCR in primary cultures of osteoblasts and bone marrow stromal cells from pagetic patients and control subjects. Concentrations of secreted proteins were determined by ELISA.


RESULTS
Dickkopf1 mRNA and protein levels were increased in both pagetic osteoblast and stromal cell cultures, and interleukin (IL)-1 and IL-6 were overexpressed in pagetic osteoblasts. These changes parallel recent findings in myeloma bone disease, which shares some clinical similarities with Paget's disease. Alkaline phosphatase was overexpressed, and bone sialoprotein and osteocalcin were underexpressed in pagetic osteoblasts, consistent with their circulating levels in pagetic patients. It is hypothesized that overexpression of Dickkopf1, IL-1, and IL-6 would result in stimulation of osteoclast proliferation and inhibition of osteoblast growth, leading to the development of the characteristic lytic bone lesions. By stimulating osteoblast differentiation, Dickkopf1 and IL-6 may also promote mineralization, leading to the conversion of lytic lesions to sclerotic.


CONCLUSIONS
These findings suggest that dysregulated gene expression in pagetic osteoblasts could cause the changes in bone cell number and function characteristic of Paget's disease.
Naot
Dorit
D
Department of Medicine, University of Auckland, New Zealand. d.naot@auckland.ac.nz
Bava
Usha
U
Matthews
Brya
B
Callon
Karen E
KE
Gamble
Gregory D
GD
Black
Michael
M
Song
Sarah
S
Pitto
Rocco P
RP
Cundy
Tim
T
Cornish
Jill
J
Reid
Ian R
IR
D000368:Aged; D000369:Aged, 80 and over; D001854:Bone Marrow Cells / Q000378:metabolism*; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D008297:Male; D020411:Oligonucleotide Array Sequence Analysis; D010001:Osteitis Deformans / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D010006:Osteoblasts / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D017154:Stromal Cells / Q000378:metabolism*
C501126:DKK1 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D012333:RNA, Messenger