Soluble receptor activator of nuclear factor-κB ligand (sRANKL)/osteoprotegerin balance in ageing and age-associated diseases

Recently, novel members of the TNF/TNF receptor superfamily, receptor activator of nuclear factor-kappaB ligand (RANKL), its receptor RANK, and the decoy receptor osteoprotegerin (OPG), have been identified as paracrine mediators of both the immune system and bone functions. The balance of RANK/RANK-L and OPG is critical for osteoclastogenesis modulation and physiological bone remodeling. In order to evaluate whether RANKL/OPG balance is modified by ageing, we analyzed, by imunoassay, systemic levels of OPG and sRANKL in healthy elderly subjects (age range from 70 to over 90 years) and in patients affected by two age-related diseases, osteoarthritis (OA) and polymyalgia rheumatica (PMR), characterized by bone metabolism alteration and involvement of the immune system. We demonstrated that (a) plasma concentrations of OPG increased significantly with age; (b) conversely, sRANKL significantly declined in the group of subjects aged between 81 and 90 years, being similar to the young controls in the other age groups; (c) in OA and PMR, circulating OPG did not differ from plasma levels found in age-matched control groups, while sRANKL concentration was significantly increased compared to controls. Hence, in ageing, the sRANKL/OPG system appears to be modified, with prominent changes in circulating OPG levels; in OA and PMR, the sRANKL/OPG balance alteration was shown to be mainly due to the increase of plasma sRANKL concentration.