Recombinant DNA cloning of the active region of the receptor activator of NF-κB ligand (RANKL) gene and its role in osteoclastogenesis

Osteopetrosis belongs to a group of rare genetic diseases typically treated with bone marrow transplantation. This approach is not effective in a recently identified form of the disease caused by mutations in the receptor activator of NF-κB ligand (RANKL) gene. In these patients, replacement therapy and RANKL delivery may be a more valid approach than transplantation. Here, we describe the construction of a recombinant gene encoding regions of RANKL (rRANKL), including the biologically active regional loop sequence. We present detailed methods for the cloning, expression, and purification of the recombinant protein. The activity of rRANKL including the active region was assessed in vitro and mature osteoclast generation was evaluated in vivo using a mouse model. We provide a proof of concept for the therapeutic potential of full-length and selected active regions of rRANKL in the treatment of osteopetrosis, warranting clinical assessment.