Murine spinal fusion induced by engineered mesenchymal stem cells that conditionally express bone morphogenetic protein-2.
OBJECTIVE
The authors hypothesized that spinal fusion can be achieved and monitored by using cell-mediated gene therapy. Mesenchymal stem cells (MSCs) genetically engineered to express recombinant human bone morphogenetic protein-2 (rhBMP-2) conditionally, were implanted into the paraspinal muscles of mice to establish spinal fusion. The goal was to demonstrate an MSC-based gene therapy platform in which controlled gene expression is used to obtain spinal fusion in a murine model.


METHODS
Mesenchymal stem cells expressing the rhBMP-2 gene were injected into the paravertebral muscle in mice. Bone formation in the paraspinal region was longitudinally followed by performing micro-computerized tomography scanning, histological studies, and an analysis of osteocalcin expression to demonstrate the presence of engrafted engineered MSCs. The minimal period of rhBMP-2 expression by the engineered MSCs required to induce fusion was determined. The results of this study demonstrate that genetically engineered MSCs induce bone formation in areas adjacent to and touching the posterior elements of the spine. This newly formed bone fuses the spine, as demonstrated by radiological and histological studies. The authors demonstrate that injected cells induce active osteogenesis at the site of implantation for up to 4 weeks postinjection. They found that a 7-day induction of rhBMP-2 expression in genetically engineered MSCs was sufficient to form new bone tissue, although the quantity of this bone increased as longer expression periods were implemented.


CONCLUSIONS
After their injection genetically engineered MSCs can efficiently form new bone in the paraspinal muscle of the mouse to obtain spinal fusion. The extent and quantity of this newly formed bone can be monitored by controlling the duration of rhBMP-2 gene expression.
Hasharoni
Amir
A
Department of Orthopedic Surgery, Hadassah Medical Center, Skeletal Biotech Laboratory, Hebrew University-Hadassah Medical Center, Ein-Kerem, Jerusalem, Israel.
Zilberman
Yoram
Y
Turgeman
Gadi
G
Helm
Gregory A
GA
Liebergall
Meir
M
Gazit
Dan
D
D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000502:physiology*; D005240:Feasibility Studies; D005260:Female; D005818:Genetic Engineering; D045164:Mesenchymal Stem Cell Transplantation; D059630:Mesenchymal Stem Cells / Q000502:physiology*; D051379:Mice; D008809:Mice, Inbred C3H; D023421:Models, Animal; D010012:Osteogenesis / Q000502:physiology*; D013123:Spinal Fusion / Q000379:methods*; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000502:physiology*
C525718:BMP2 protein, human; C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D016212:Transforming Growth Factor beta