Rescue of the osteopetrotic defect in op/op mice by osteoblast-specific targeting of soluble colony-stimulating factor-1.
Soluble colony-stimulating factor-1 (sCSF-1) and membrane bound CSF-1 are synthesized by osteoblasts and stromal cells. However, the precise role of each form in osteoclastogenesis is unclear. In the op/op mouse, absence of osteoblast-derived CSF-1 leads to decreased osteoclasts and osteopetrosis. To determine whether sCSF-1 gene replacement can cure the osteopetrotic defect, we took advantage of the osteoblast specificity of the osteocalcin promoter to selectively express sCSF-1 in the bone of op/op mice. Transgenic mice harboring the human sCSF-1 cDNA under the control of the osteocalcin promoter were generated and cross-bred with heterozygous op/wt mice to establish op/op mutants expressing the transgene (op/opT). The op/op genotype and transgene expression were confirmed by PCR and Southern blot analysis, respectively. High levels of human sCSF-1 protein were selectively expressed in bone. At 2(1/2) wk, op/opT mice showed normal growth and tooth eruption. Femurs removed at 5 and 14 wk were analyzed by peripheral quantitative computed tomography and histomorphometry. The abnormal bone mineral density, cancellous bone volume, and growth plate width observed in op/op mice was completely reversed in op/opT mice by 5 wk, and this effect persisted at 14 wk, with measurements comparable with wt/wt mice at each time point. Correction of the skeletal abnormalities in the 5-wk-old op/opT mice correlated with a marked increase in the total osteoclast number, and their number per millimeter of bone surface compared with that of op/op mutants. Osteoclast number was maintained at 14 wk in op/opT mice and morphologically resembled wt/wt osteoclasts. These results indicate that sCSF-1 is sufficient to drive normal osteoclast development and that the osteocalcin promoter provides an efficient tool for delivery of exogenous genes to the bone. Moreover, targeting sCSF-1 to osteoblasts in the bone microenvironment may be a potentially useful therapeutic modality for treating bone disorders.
Abboud
S L
SL
Department of Pathology, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78284, USA. abbouds@uthscsa.edu
Woodruff
K
K
Liu
C
C
Shen
V
V
Ghosh-Choudhury
N
N
D000135:Acid Phosphatase; D000818:Animals; D001835:Body Weight / Q000502:physiology; D015519:Bone Density; D005269:Femur / Q000473:pathology; D015316:Genetic Therapy; D006801:Humans; D007527:Isoenzymes; D016173:Macrophage Colony-Stimulating Factor / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D010006:Osteoblasts / Q000473:pathology* / Q000502:physiology; D015675:Osteocalcin / Q000235:genetics; D010022:Osteopetrosis / Q000235:genetics* / Q000473:pathology / Q000517:prevention & control*; D011401:Promoter Regions, Genetic / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000071681:Tartrate-Resistant Acid Phosphatase; D014057:Tomography, X-Ray Computed; D019076:Transgenes
D007527:Isoenzymes; D015675:Osteocalcin; D016173:Macrophage Colony-Stimulating Factor; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase