Murine spinal fusion induced by engineered mesenchymal stem cells that conditionally express bone morphogenetic protein—2

Abstract

<jats:p content-type="fine-print"><jats:italic>Object.</jats:italic> 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.</jats:p> <jats:p content-type="fine-print"><jats:italic>Methods.</jats:italic> Mesenchymal stem cells expressing the <jats:italic>rhBMP-2</jats:italic> 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 <jats:italic>osteocalcin</jats:italic> 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.</jats:p> <jats:p content-type="fine-print">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.</jats:p> <jats:p content-type="fine-print"><jats:italic>Conclusions.</jats:italic> 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 <jats:italic>rhBMP-2</jats:italic> gene expression.</jats:p>

Genetically Modified Mesenchymal Stem Cells Induce Mechanically Stable Posterior Spine Fusion

“…20,28 Cell culture Cells were cultured in 140-mm culture plates in a complete growth medium (Dulbecco's modified Eagle's medium containing 10% fetal bovine serum, 2 mM L-glutamine, 100 U/ mL penicillin, and 100 U/mL streptomycin; Biological Industries, Beit Haemek, Israel) in a 5% CO 2 /95% air atmosphere at 378C. DOX (1 mg/mL) was added to the medium to prevent cell differentiation before implantation.…”

“…We have explored structural, 20,21 nanomechanical, and nanostructural properties of bone tissue induced by engineered MSCs, and showed that intrinsic biomechanical properties may depend on the injection site. 26,27 However, to date, no one has reported whether the bone mass generated by engineered MSCs can indeed lead to mechanical stabilization, which is the prime goal of spine fusion.…”

“…[16][17][18][19] We previously demonstrated that MSCs overexpressing a BMP gene could be effectively used to induce spine fusion in a mouse model. 20,21 The BMP gene can be introduced into a cell in a variety of ways, including viral 22,23 and nonviral methods. 21,24 MSCs can be isolated from various adult tissues, such as bone marrow and adipose tissue, 25 following common procedures such as liposuction.…”

Genetically Engineered Mesenchymal Stem Cells: The Ongoing Research for Bone Tissue Engineering

“…BMP-2, approved by Food and Drug Administration (FDA) for clinical practice, is the most potent member in promoting bone and cartilage development and therefore wins a popular choice for MSCs-based BTE (Lieberman et al, 1998;Lieberman et al, 1999;Lou et al, 1999;Turgeman et al, 2001;Olmsted-Davis et al, 2002;Blum et al, 2003;Gugala et al, 2003;Park et al, 2003;Riew et al, 2003;Tsuda et al, 2003;Kumar et al, 2004;Hasharoni et al, 2005;Egermann et al, 2006;Feeley et al, 2006). The BMP-2-modified MSCs are proven to increase the alkaline phosphatase (ALP) activity, mineralization, and cell proliferation in vitro and induce ectopic bone formation, heal critical size bone defect, repair fracture, and trigger spinal fusion in vivo (Lou et al, 1999;Moutsatsos et al, 2001;Turgeman et al, 2001;Blum et al, 2003;Park et al, 2003;Riew et al, 2003;Tsuda et al, 2003;Hasharoni et al, 2005;Egermann et al, 2006;Feeley et al, 2006). BMP-7 plays a key role in osteoblast differentiation, and there is only one study in which MSCs are engineered with BMP-7.…”

“…When engineered MSCs are implanted to thigh muscles (Lou et al, 1999;Dayoub et al, 2003;Li et al, 2003) or paraspinal muscles (Dumont et al, 2002;Hasharoni et al, 2005), ectopic bone formation is observed. Indeed, skeletal muscle injection is an optimal method in testing the viability and function of genetically engineered MSCs in vivo.…”