Aims. Gene therapy research in the field of orthopaedics and traumatology have evolved during the last decade, leading to possible applications for the treatment of pathological conditions, such as bone fractures and cartilage defects. In particular, several gene transfer techniques have been employed so far for inducing bone formation in animal models of bone defects. Cell-based approaches, using in vitro and ex vivo genetically modified cells to be implanted in the animal, produced promising results as they enable the production of physiologic doses of an osteoinductive gene product into selected anatomical sites. In this study we used autologous skin fibroblasts, which are very simple to harvest and propagate in culture, transduced ex vivo with the new osteo-genic factor Lim Mineralization Factor-3 (Ad-LMP-3). These engineered cells produced successful bone healing when implanted by the use of a scaffold in rats, validating the in vivo osteoinductive properties of hLMP-3.
Methods. Primary dermal fibroblasts cultures were established using a 1cm2 biopsy of shaved skin obtained from the abdomen of each rat after anesthesia. Semi-confluent primary fibroblasts were infected with either AdBMP-2 or AdhLMP-3 or both, using a overall multiplicity of infection (MOI) of 100 viral particles per cell. Cells transduced with Ad-eGFP at the same MOI were used as a viral infection control, while untreated cells served as a negative control. The transduced cells were harvested 24 hours after viral infection, resuspended in sterile PBS, let adsorbed on a Hydroxyapatite/Collagen scaffold and then implanted in a bone defect surgically performed in the mandible of immunocompetent rats. The animals were divided in 4 groups: 9 rats were treated with cells infected with AdLMP-3, 9 rats with cells infected with AdBMP-2 (positive controls), 9 rats with cells transduced with Ad-eGFP and 9 rats with untreated cells (controls). 3 Rats from each group were sacrified at 1, 2 and 3 months after the treatment and studied by x-rays, Micro-CT and histology (Von kossa and Alizarin staining).
Results. All the animals treated with LMP-3 showed healing of the bone defect after 3 months, as confirmed his-tologically and radiographically. On the contrary none of the controls showed bone formation at latest time point.
Conclusions. Recently, Lim Mineralization Proteins (LMP), coded by three different splice variants (LMP-1, LMP-2, LMP-3) of the same gene, have been identified as regulators of the osteoblast differentiation program. We have previously demonstrated that human LMP-3 (hLMP-3) contributes actively to bone formation, acting at least in part, through the BMP-2 signaling pathway, being capable of inducing differentiation of cells of mes-enchymal derivation towards the osteoblastic lineage, through the up-regulation of bone-specific genes, along with ectopic bone formation in vivo and mineralization in vitro. In this study we have analyzed the efficacy of an ex-vivo approach using autologous dermal fibroblasts infected with AdLMP-3. Engineered cells produced bone healing when implanted by the use of a scaffold in a rodent model, validating the in vivo osteoinductive properties of hLMP-3.
