Lim mineralisation protein (LMP) is a new positive regulator of the osteoblast differentiation programme. In humans three “splice variants” of LMP have been identified: LMP-1, LMP-2 and LMP-3. Recent studies demostrated that LMP-1 gene acts as a transcriptional factor inside the cells and is able to induce expression of specific bone genes, like the bone morphogenetic proteins (BMPs), to improve bone formation in vitro and ectopic bone formation in vivo and seems to induce spinal fusion in several animal models.

In order to evaluate the osteoinductive properties of the shorter variant of LMP, plasmidic and adeno-viral vectors expressing the optimised sequence of human LMP-3 have been generated. The osteogenic activity of LMP-3 was evaluated in vitro with experiments of transfection and infection of mesenchymal stem cells, fibroblasts and pre-osteoblasts; in vivo we investigated whether direct gene transfer of LMP-3 in the triceps muscles of immunocompetent mice was able to induce ectopic bone formation. All the animals were studied by histology and X-rays at different time points. In all the experiments BMP-2 was used as positive control.

These experiments demonstrated that the “gene transfer” of LMP-3 in fibroblasts and pre-osteoblasts stimulates production of specific bone proteins, such as osteocalcin, osteopontin and bone sialoprotein, and induces bone mineralisation in vitro. It was also demonstrated that LMP-3 is able to induce, in a dose-dependent manner, bone mineralisation and expression of specific bone genes (BMP-2, OSX, RunX2, alkaline phosphatase) in mesenchymal stem cells. Finally, the experiments showed that direct gene transfer of LMP-3 in the triceps muscle of mice induces ectopic bone formation in all the animals treated more efficiently than BMP-2.

These data demonstrate that gene transfer of LMP-3 could be used, more efficiently than BMP-2, in inducing bone formation in several cell lines and in vivo, establishing the osteoinductive ability of LMP-3. Thus, LMP-3 could represent, in the near future, a therapeutic alternative in several clinical conditions.