Paget's disease of bone (PDB) is characterized by abnormal osteoclasts with unique characteristics that include increased sensitivity of osteoclast progenitors to 1,25(OH)2 D3 , receptor activator of NF-κB ligand (RANKL), and TNF-α; increased osteoclast numbers; and increased expression of IL-6 and several transcription factors.
The purpose of this study was to evaluate whether functionally active polymorphisms of the interleukin-1α (IL-1α), interleukin-1β (IL-β), interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α) genes would modify the occurrence and the clinical features of PDB.
We also observed specific expression of IL-6 mRNA in a proportion of osteoclasts, suggesting that an autocrine/paracrine loop may contribute to osteoclastogenesis in vivo in FD, as in some other bone diseases, including Paget's disease.
There are abnormalities in the stages of osteoclast development, and studies in Paget's disease have suggested a major role for IL-6 in human osteoclast activity.
In Paget's disease, IL-6 is produced by the osteoclasts, the osteoclasts express IL-6 receptors and IL-6 mRNA, and increased levels of IL-6 are present in the marrow plasma and serum of these patients.
Osteoclasts in both osteoarthritic and pagetic bone express IL-6R mRNA and NF-IL-6, but only pagetic osteoclasts expressed IL-6, suggesting that in Paget's diseaseIL-6 can act as an autocrine factor on osteoclasts.
Further investigations have proposed that the bony abnormalities seen in Paget's disease are due to the effects of the virus on osteoclastic interleukin-6 and c-FOS production, possibly via the transcription factor NF-kappa B.